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arxiv_dataset-1300906.3449 | Recent developments in the theory of multimode random lasers
physics.optics cond-mat.mes-hall
We review recent extensions of semiclassical multimode laser theory to open
systems with overlapping resonances and inhomogeneous refractive index. An
essential ingredient of the theory are biorthogonal quasimodes that describe
field decay in an open passive system and are used as a basis for lasing modes.
We discuss applications of the semiclassical theory, as well as other
experimental and numerical results related to random lasing with mode
competition.
| arxiv topic:physics.optics cond-mat.mes-hall |
arxiv_dataset-1301906.3549 | Are Black Holes Elementary Particles?
gr-qc astro-ph.HE hep-ph hep-th
Quantum black holes are the smallest and heaviest conceivable elementary
particles. They have a microscopic size but a macroscopic mass. Several
fundamental types have been constructed with some remarkable properties.
Quantum black holes in the neighborhood of the Galaxy could resolve the paradox
of ultra-high energy cosmic rays detected in Earth's atmosphere. They may also
play a role as dark matter in cosmology.
| arxiv topic:gr-qc astro-ph.HE hep-ph hep-th |
arxiv_dataset-1302906.3649 | Asymptotic non-equilibrium steady state operators
cond-mat.stat-mech cond-mat.mes-hall
We present a method for the calculation of asymptotic operators for
nonequilibrium steady-state quantum systems. The asymptotic steady-state
operator is obtained by averaging the corresponding operator in Heisenberg
representation over infinitely long time. Several examples are considered to
demonstrate the utility of our method. The results obtained within our approach
are compared to those obtained within the Schwinger-Keldysh nonequilibrium
Green's functions.
| arxiv topic:cond-mat.stat-mech cond-mat.mes-hall |
arxiv_dataset-1303906.3749 | The Busy Beaver Competition: a historical survey
math.LO
Tibor Rado defined the Busy Beaver Competition in 1962. He used Turing
machines to give explicit definitions for some functions that are not
computable and grow faster than any computable function. He put forward the
problem of computing the values of these functions on numbers 1, 2, 3, ... More
and more powerful computers have made possible the computation of lower bounds
for these values. In 1988, Brady extended the definitions to functions on two
variables. We give a historical survey of these works. The successive record
holders in the Busy Beaver Competition are displayed, with their discoverers,
the date they were found, and, for some of them, an analysis of their behavior.
| arxiv topic:math.LO |
arxiv_dataset-1304906.3849 | Squeezing the Arimoto-Blahut algorithm for faster convergence
cs.IT math.IT stat.CO
The Arimoto--Blahut algorithm for computing the capacity of a discrete
memoryless channel is revisited. A so-called ``squeezing'' strategy is used to
design algorithms that preserve its simplicity and monotonic convergence
properties, but have provably better rates of convergence.
| arxiv topic:cs.IT math.IT stat.CO |
arxiv_dataset-1305906.3949 | The knee in the cosmic ray energy spectrum
hep-ph astro-ph.HE
An update of the status of the knee in the cosmic ray energy spectrum at 3-4
PeV is presented. We argue that the evidence in favour of the presence of a
'single source' is even stronger than before.
| arxiv topic:hep-ph astro-ph.HE |
arxiv_dataset-1306906.4049 | Cosmological and Astrophysical Implications of Sterile Neutrinos
hep-ph
The discovery of neutrino masses implies the existence of new particles, the
sterile neutrinos. These particles can have important implications for
cosmology and astrophysics. A sterile neutrino with mass of a few keV can
account for the dark matter of the universe. Its relic abundance can be
produced via different mechanisms. A minimal extension of the Higgs sector of
the Standard Model, with a gauge-singlet boson coupled to sterile neutrinos,
can provide a consistent framework for the theory of neutrino masses, and can
produce relic keV sterile neutrinos via decays of the singlet Higgs. This
mechanism operates around the electroweak scale, and has interesting
consequences for the electroweak phase transition. The resulting dark matter is
"colder" than the one produced via oscillations. This property changes the
small-scale structure formation limits. Heavier sterile neutrinos can be
produced in supernova cores and affect the thermal evolution of the star. Being
short-lived, they decay inside the envelope and facilitate the energy transport
from the core to the vicinity of the supernova shock. This enhances the
probability for a successful explosion.
| arxiv topic:hep-ph |
arxiv_dataset-1307906.4149 | Adaptive Process Management in Highly Dynamic and Pervasive Scenarios
cs.SE
Process Management Systems (PMSs) are currently more and more used as a
supporting tool for cooperative processes in pervasive and highly dynamic
situations, such as emergency situations, pervasive healthcare or domotics/home
automation. But in all such situations, designed processes can be easily
invalidated since the execution environment may change continuously due to
frequent unforeseeable events. This paper aims at illustrating the theoretical
framework and the concrete implementation of SmartPM, a PMS that features a set
of sound and complete techniques to automatically cope with unplanned
exceptions. PMS SmartPM is based on a general framework which adopts the
Situation Calculus and Indigolog.
| arxiv topic:cs.SE |
arxiv_dataset-1308906.4249 | Tree based functional expansions for Feynman--Kac particle models
math.PR
We design exact polynomial expansions of a class of Feynman--Kac particle
distributions. These expansions are finite and are parametrized by coalescent
trees and other related combinatorial quantities. The accuracy of the
expansions at any order is related naturally to the number of coalescences of
the trees. Our results include an extension of the Wick product formula to
interacting particle systems. They also provide refined nonasymptotic
propagation of chaos-type properties, as well as sharp $\mathbb{L}_p$-mean
error bounds, and laws of large numbers for $U$-statistics.
| arxiv topic:math.PR |
arxiv_dataset-1309906.4349 | Edge states interferometry and spin rotations in zigzag graphene
nanoribbons
cond-mat.mes-hall
An interesting property of zigzag graphene nanoribbons is the presence of
edge states which are extended along its borders but localized in the
transverse direction. We show that because of this property, electron transport
through an externally induced potential well displays two-paths-interference
oscillations when subject either to a magnetic or a transverse electric field.
This effect does not require the existence of an actual `hole' in the
nanoribbon's geometry. Moreover, since edge states are spin polarized, having
opposite polarization on opposite sides, such interference effect can be used
to rotate the spin of the incident carriers in a controlled way.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-1310906.4449 | Heuristic theory for many-faced d-dimensional Poisson-Voronoi cells
cond-mat.stat-mech
We consider the d-dimensional Poisson-Voronoi tessellation and investigate
the applicability of heuristic methods developed recently for two dimensions.
Let p_n(d) be the probability that a cell have n neighbors (be `n-faced') and
m_n(d) the average facedness of a cell adjacent to an n-faced cell. We obtain
the leading order terms of the asymptotic large-n expansions for p_n(d) and
m_n(3). It appears that, just as in dimension two, the Poisson-Voronoi
tessellation violates Aboav's `linear law' also in dimension three. A
confrontation of this statement with existing Monte Carlo work remains
inconclusive. However, simulations upgraded to the level of present-day
computer capacity will in principle be able to confirm (or invalidate) our
theory.
| arxiv topic:cond-mat.stat-mech |
arxiv_dataset-1311906.4549 | Mean-field theory of a plastic network of integrate-and-fire neurons
q-bio.NC cond-mat.dis-nn
We consider a noise driven network of integrate-and-fire neurons. The network
evolves as result of the activities of the neurons following
spike-timing-dependent plasticity rules. We apply a self-consistent mean-field
theory to the system to obtain the mean activity level for the system as a
function of the mean synaptic weight, which predicts a first-order transition
and hysteresis between a noise-dominated regime and a regime of persistent
neural activity. Assuming Poisson firing statistics for the neurons, the
plasticity dynamics of a synapse under the influence of the mean-field
environment can be mapped to the dynamics of an asymmetric random walk in
synaptic-weight space. Using a master-equation for small steps, we predict a
narrow distribution of synaptic weights that scales with the square root of the
plasticity rate for the stationary state of the system given plausible
physiological parameter values describing neural transmission and plasticity.
The dependence of the distribution on the synaptic weight of the mean-field
environment allows us to determine the mean synaptic weight self-consistently.
The effect of fluctuations in the total synaptic conductance and plasticity
step sizes are also considered. Such fluctuations result in a smoothing of the
first-order transition for low number of afferent synapses per neuron and a
broadening of the synaptic weight distribution, respectively.
| arxiv topic:q-bio.NC cond-mat.dis-nn |
arxiv_dataset-1312906.4649 | On the lengths of quotients of ideals and depths of fiber cones
math.AC
Let $(R,\mathfrak{m})$ be a Cohen-Macaulay local ring, $I$ an
$\mathfrak{m}$-primary ideal of $R$ and $J$ its minimal reduction. We study the
depths of $F(I)$ under certain depth assumptions on $G(I)$ and length condition
on quotients of powers of $I$ and $J$, namely
$\sum_{n\geq0}\lambda(\mathfrak{m}I^{n+1}/\mathfrak{m}JI^n)$ and
$\sum_{n\geq0}\lambda(\mathfrak{m}I^{n+1} \cap J/\mathfrak{m}JI^n)$.
| arxiv topic:math.AC |
arxiv_dataset-1313906.4749 | On the Siegel-Weil Theorem for Loop Groups (II)
math.RT math.QA
We formulate and prove the Siegel-Weil formula for loop groups.
| arxiv topic:math.RT math.QA |
arxiv_dataset-1314906.4849 | Difference Principle and Black-hole Thermodynamics
physics.pop-ph
The heuristic principle that constructive dynamics may arise wherever there
exists a difference, or gradient, is discussed. Consideration of black-hole
entropy appears to provide a clue for setting a lower bound on any extensive
measure of such collective system difference, or potential to give rise to
constructive dynamics. It is seen that the second-power dependence of
black-hole entropy on mass is consistent with the difference principle, while
consideration of Hawking radiation forces one to beware of implicit
figure-ground distinctions in the application of the difference principle.
| arxiv topic:physics.pop-ph |
arxiv_dataset-1315906.4949 | Quantum Many-Body Dynamics of Dark Solitons in Optical Lattices
cond-mat.quant-gas cond-mat.mes-hall nlin.PS
We present a fully quantum many-body treatment of dark solitons formed by
ultracold bosonic atoms in one-dimensional optical lattices. Using
time-evolving block decimation to simulate the single-band Bose-Hubbard
Hamiltonian, we consider the quantum dynamics of density and phase engineered
dark solitons as well as the quantum evolution of mean-field dark solitons
injected into the quantum model. The former approach directly models how one
may create quantum entangled dark solitons in experiment. While we have already
presented results regarding the latter approach elsewhere [Phys. Rev. Lett.
{\bf 103}, 140403 (2009)], we expand upon those results in this work. In both
cases, quantum fluctuations cause the dark soliton to fill in and may induce an
inelasticity in soliton-soliton collisions. Comparisons are made to the
Bogoliubov theory which predicts depletion into an anomalous mode that fills in
the soliton. Our many-body treatment allows us to go beyond the Bogoliubov
approximation and calculate explicitly the dynamics of the system's natural
orbitals.
| arxiv topic:cond-mat.quant-gas cond-mat.mes-hall nlin.PS |
arxiv_dataset-1316906.5049 | Rigorous results for tight-binding networks: particle trapping and
scattering
quant-ph cond-mat.str-el
We investigate the particle trapping and scattering properties in a
tight-binding network which consists of several subgraphs. The particle
trapping condition is proved under which particles can be trapped in a subgraph
without leaking. Based on exact solutions for the configuration of a
$\pi$-shaped lattice, it is argued that the bound states in a specified
subgraph are of two types, resonant and evanescent. It is also shown that, when
such a subgraph is embedded in a one-dimensional chain as the waveguide, an
incident wave experiences total reflection if its energy matches the resonant
bound state energy.
| arxiv topic:quant-ph cond-mat.str-el |
arxiv_dataset-1317906.5149 | The new screening characteristics of strongly non-ideal and dusty
plasmas. Part 2: Two-Component Systems
physics.plasm-ph
A new model method for describing of the electrostatic screening in
two-component systems (electron-ion plasmas, dusty plasmas, electrolytes, etc)
is developed. The method is applicable to the systems of higher non-ideality
degree. The expressions for all the screening parameters introduced in the
previous paper (Part 1) of this work, as well as for an additional parameter
characteristic for multi-component systems, are obtained. All these parameters
are presented in a simple analytic form suitable for operative laboratory
usage, especially for theoretical interpretation of experimental data.
| arxiv topic:physics.plasm-ph |
arxiv_dataset-1318906.5249 | Universal Correlations and Power-Law Tails in Financial Covariance
Matrices
q-fin.ST cond-mat.stat-mech physics.data-an
Signatures of universality are detected by comparing individual eigenvalue
distributions and level spacings from financial covariance matrices to random
matrix predictions. A chopping procedure is devised in order to produce a
statistical ensemble of asset-price covariances from a single instance of
financial data sets. Local results for the smallest eigenvalue and individual
spacings are very stable upon reshuffling the time windows and assets. They are
in good agreement with the universal Tracy-Widom distribution and Wigner
surmise, respectively. This suggests a strong degree of robustness especially
in the low-lying sector of the spectra, most relevant for portfolio selections.
Conversely, the global spectral density of a single covariance matrix as well
as the average over all unfolded nearest-neighbour spacing distributions
deviate from standard Gaussian random matrix predictions. The data are in fair
agreement with a recently introduced generalised random matrix model, with
correlations showing a power-law decay.
| arxiv topic:q-fin.ST cond-mat.stat-mech physics.data-an |
arxiv_dataset-1319906.5349 | Empirical Estimate of Lyman-alpha Escape Fraction in a Statistical
Sample of Lyman-alpha Emitters
astro-ph.CO
The Lyman-alpha (Lya) recombination line is a fundamental tool for galaxy
evolution studies and modern observational cosmology. However, subsequent
interpretations are still prone to a number of uncertainties. Besides numerical
efforts, empirical data are urgently needed for a better understanding of Lya
escape process. We empirically estimate the Lyman-alpha escape fraction
fesc(Lya) in a statistically significant sample of z ~ 0 - 0.3 galaxies in
order to calibrate high-redshift Lyman-alpha observations. An optical
spectroscopic follow-up of a sub-sample of 24 Lyman-alpha emitters (LAEs)
detected by GALEX at z ~ 0.2-0.3, combined with a UV-optical sample of local
starbursts, both with matched apertures, allow us to quantify the dust
extinction through Balmer lines, and to estimate the Lyman-alpha escape
fraction from the Halpha flux corrected for extinction in the framework of the
recombination theory. The global escape fraction of Lyman-alpha radiation spans
nearly the entire range of values, from 0.5 to 100 %, and fesc(Lya) clearly
decreases with increasing nebular dust extinction E(B-V). Several objects show
fesc(Lya) greater than fesc(continuum) which may be an observational evidence
for clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture
size effects may still prevail between z ~ 0.2-0.3 LAEs and local starbursts,
which may explain the difference observed for fesc(Lya).
| arxiv topic:astro-ph.CO |
arxiv_dataset-1320906.5449 | New extended atomic data in cool star model atmospheres - Using Kurucz's
new iron data in MAFAGS-OS models
astro-ph.SR
Context. Cool star model atmospheres are a common tool for the investigation
of stellar masses, ages and elemental abundance composition. Theoretical
atmospheric models strongly depend on the atomic data used when calculating
them. Aims. We present the changes in flux and temperature stratification when
changing from iron data computed by R.L. Kurucz in the mid 90s to the Kurucz
2009 iron computations. Methods. MAFAGS-OS opacity sampling atmospheres were
recomputed with Kurucz 2009 iron atomic data as implemented in the VALD
database by Ryabchikova. Temperature stratification and emergent flux
distribution of the new version, called MAFAGS-OS9, is compared to the former
version and to solar flux measurements. Results. Using the Kurucz line lists
converted into the VALD format and new bound-free opacities for Mg i and Al i
leads to changes in the solar temperature stratification by not more than 28 K.
At the same time, the calculated solar flux distribution shows significantly
better agreement between observations and theoretical solar models. These
changes in the temperature stratification of the corresponding models are
small, but nevertheless of a magnitude that affects stellar parameter
determinations and abundance analysis.
| arxiv topic:astro-ph.SR |
arxiv_dataset-1321906.5549 | Classification of commutative algebras and tube realizations of
hyperquadrics
math.CV math.RA
In this paper we classify up to affine equivalence all local tube
realizations of real hyperquadrics in C^n. We show that this problem can be
reduced to the classification, up to isomorphism, of commutative nilpotent real
and complex algebras. We also develop some structure theory for commutative
nilpotent algebras over arbitrary fields of characteristic zero.
| arxiv topic:math.CV math.RA |
arxiv_dataset-1322907.0035 | Deconfinement of neutron star matter within the Nambu-Jona-Lasinio model
astro-ph.HE hep-ph nucl-th
We study the deconfinement transition of hadronic matter into quark matter
under neutron star conditions assuming color and flavor conservation during the
transition. We use a two-phase description. For the hadronic phase we use
different parameterizations of a non-linear Walecka model which includes the
whole baryon octet. For the quark matter phase we use an SU(3)_f
Nambu-Jona-Lasinio effective model including color superconductivity.
Deconfinement is considered to be a first order phase transition that conserves
color and flavor. It gives a short-lived transitory colorless-quark-phase that
is not in beta-equilibrium, and decays to a stable configuration in tau ~
tau_{weak} ~ 10^{-8} s. However, in spite of being very short lived, the
transition to this intermediate phase determines the onset of the transition
inside neutron stars. We find the transition free-energy density for
temperatures typical of neutron star interiors. We also find the critical mass
above which compact stars should contain a quark core and below which they are
safe with respect to a sudden transition to quark matter. Rather independently
on the stiffness of the hadronic equation of state (EOS) we find that the
critical mass of hadronic stars (without trapped neutrinos) is in the range of
~ 1.5 - 1.8 solar masses. This is in coincidence with previous results obtained
within the MIT Bag model.
| arxiv topic:astro-ph.HE hep-ph nucl-th |
arxiv_dataset-1323907.0135 | Crepant Resolutions, Quivers and GW/NCDT Duality
math.AG math-ph math.MP
We propose a conjecture that relates some local Gromov-Witten invariants of
some crepant resolutions of Calabi-Yau 3-folds with isolated singularities with
some Donaldson-Thomas type invariants of the moduli spaces of representations
of some quivers with potentials.
| arxiv topic:math.AG math-ph math.MP |
arxiv_dataset-1324907.0235 | Sommerfeld enhancement from Goldstone pseudo-scalar exchange
hep-ph astro-ph.HE nucl-th
We point out that the exchange of a Goldstone pseudo-scalar can provide an
enhancement in the dark matter annihilation rate capable of explaining the
excess flux seen in high energy cosmic ray data. The mechanism of enhancement
involves the coupling of s and d waves through the tensor force that is very
strong and, in fact, singular at short distances. The results indicate that
large enhancements require some amount of fine tuning. We also discuss the
enhancement due to other singular attractive potentials, such as WIMP models
with a permanent electric dipole.
| arxiv topic:hep-ph astro-ph.HE nucl-th |
arxiv_dataset-1325907.0335 | Population dynamics on random networks: simulations and analytical
models
q-bio.PE cond-mat.stat-mech nlin.AO physics.bio-ph
We study the phase diagram of the standard pair approximation equations for
two different models in population dynamics, the
susceptible-infective-recovered-susceptible model of infection spread and a
predator-prey interaction model, on a network of homogeneous degree $k$. These
models have similar phase diagrams and represent two classes of systems for
which noisy oscillations, still largely unexplained, are observed in nature. We
show that for a certain range of the parameter $k$ both models exhibit an
oscillatory phase in a region of parameter space that corresponds to weak
driving. This oscillatory phase, however, disappears when $k$ is large. For
$k=3, 4$, we compare the phase diagram of the standard pair approximation
equations of both models with the results of simulations on regular random
graphs of the same degree. We show that for parameter values in the oscillatory
phase, and even for large system sizes, the simulations either die out or
exhibit damped oscillations, depending on the initial conditions. We discuss
this failure of the standard pair approximation model to capture even the
qualitative behavior of the simulations on large regular random graphs and the
relevance of the oscillatory phase in the pair approximation diagrams to
explain the cycling behavior found in real populations.
| arxiv topic:q-bio.PE cond-mat.stat-mech nlin.AO physics.bio-ph |
arxiv_dataset-1326907.0435 | NIR spectroscopy of SDSS J0303-0019: a low luminosity, high Eddington
ratio quasar at z~6
astro-ph.CO
We present sensitive near--infrared VLT ISAAC spectroscopic observations of
the z=6.08 quasar SDSS J030331.40-001912.9. This QSO is more than a magnitude
fainter than other QSOs at z~6 for which NIR spectroscopy has been obtained to
date and is therefore presumably more representative of the QSO population at
the end of Cosmic Reionization. Combining rest--frame UV continuum luminosity
with the width measurements of the Mg II and C IV lines, we derive a black hole
mass of 2(+1.0/-0.5) x 10^8 solar masses, the lowest mass observed for z~6 QSOs
to date, and derive an Eddington ratio of 1.6(+0.4/-0.6), amongst the highest
value derived for QSOs at any redshift. The Spitzer 24 micron non--detection of
this QSO does not leave space for a significant hot dust component in its
optical/near--infrared SED, in common with one other faint QSO at z=6, but in
contrast to more than twenty more z=6 QSOs and all known lower redshift QSOs
with sufficiently deep multi-wavelength photometry. We conclude that we have
found evidence for differences in the intrinsic properties of at least one z~6
QSO as compared to the lower--redshift population.
| arxiv topic:astro-ph.CO |
arxiv_dataset-1327907.0535 | Relating the generating functionals in field/antifield formulation
through finite field dependent BRST transformation
hep-th
We study the field/antifield formulation of pure Yang Mills theory in the
framework of finite field dependent BRST transformation. We show that the
generating functionals corresponding to different solutions of quantum master
equation are connected through the finite field dependent BRST transformations.
We establish this result with the help of several explicit examples.
| arxiv topic:hep-th |
arxiv_dataset-1328907.0635 | Hydrogen Stark broadened Brackett lines
astro-ph.SR
Stark broadened lines of the hydrogen Brackett series are computed for the
conditions of stellar atmospheres and circumstellar envelopes. The computation
is performed within the Model Microfield Method, which includes the ion dynamic
effects and makes the bridge between the impact limit at low density and the
static limit at high density and in the line wings. The computation gives the
area normalized line shape, from the line core up to the static line wings.
| arxiv topic:astro-ph.SR |
arxiv_dataset-1329907.0735 | Probing the Epoch of Reionization with the Lyman Alpha Forest at z~4-5
astro-ph.CO astro-ph.GA
The inhomogeneous cosmological reionization process leaves tangible imprints
in the intergalactic medium down to z=4-5. The Lyman-alpha forest flux power
spectrum provides a potentially powerful probe of the epoch of reionization.
With the existing SDSS I/II quasar sample we show that two cosmological
reionization scenarios, one completing reionization at z=6 and the other at
z=9, can be distinguished at ~7 sigma level by utilizing Lyman alpha forest
absorption spectra at z=4.5+-0.5, in the absence of other physical processes
that may also affect the Lyman alpha flux power spectrum. The redshift range
z=4-5 may provide the best window, because there is still enough transmitted
flux and quasars to measure precise statistics of the flux fluctuations, and
the IGM still retains a significant amount of memory of reionization.
| arxiv topic:astro-ph.CO astro-ph.GA |
arxiv_dataset-1330907.0835 | New nonlinear coherent states associated to inverse bosonic and
$f$-deformed ladder operators
quant-ph
Using the {\it nonlinear coherent states method}, a formalism for the
construction of the coherent states associated to {\it "inverse bosonic
operators"} and their dual family has been proposed. Generalizing the approach,
the "inverse of $f$-deformed ladder operators" corresponding to the nonlinear
coherent states in the context of quantum optics and the associated coherent
states have been introduced. Finally, after applying the proposal to a few
known physical systems, particular nonclassical features as sub-Poissonian
statistics and the squeezing of the quadratures of the radiation field
corresponding to the introduced states have been investigated.
| arxiv topic:quant-ph |
arxiv_dataset-1331907.0935 | Testing the Realistic Seesaw Model with Two Heavy Majorana Neutrinos at
the CERN Large Hadron Collider
hep-ph
In the conventional type-(I+II) seesaw model, the effective mass matrix of
three known light neutrinos is given by M_nu = M_L - M_D M^{-1}_R M^T_D in the
leading-order approximation. We propose an intriguing scenario, in which the
structural cancellation condition M_D M^{-1}_R M^T_D = 0 is guaranteed by the
A_4 x Z_2 flavor symmetry. As a consequence, neutrino masses are mainly
generated by the Higgs triplet M_nu = M_L, while the neutrino mixing matrix is
non-unitary and takes on the nearly tri-bimaximal pattern. A discriminating
feature of this scenario from the pure type-II seesaw model is that the
lepton-number-violating signatures induced by the heavy Majorana neutrinos can
be discovered at the CERN Large Hadron Collider. We calculate the total cross
section of the same-sign dilepton events pp to l^+(-)_alpha N_i to l^+(-)_alpha
l^+(-)_beta jj (for i=1, 2 and alpha, beta = e, mu, tau), and emphasize the
significant interference of the contributions from two different heavy Majorana
neutrinos. The background from the standard model and the kinematic cuts used
to reduce it have been considered. The possible way to distinguish between the
signals from heavy Majorana neutrinos and those from doubly-charged Higgs
bosons is briefly discussed.
| arxiv topic:hep-ph |
arxiv_dataset-1332907.1035 | Search for single sources of ultra high energy cosmic rays on the sky
astro-ph.HE
In this paper, we suggest a new way to identify single bright sources of
Ultra High Energy Cosmic Rays (UHECR) on the sky, on top of background. We look
for doublets of events at the highest energies, E > 6 x 10^19 eV, and identify
low energy tails, which are deflected by the Galactic Magnetic Field (GMF). For
the sources which are detected, we can recover their angular positions on the
sky within one degree from the real ones in 68% of cases. The reconstruction of
the deflection power of the regular GMF is strongly affected by the value of
the turbulent GMF. For typical values of 4 microG near the Earth, one can
reconstruct the deflection power with 25% precision in 68% of cases.
| arxiv topic:astro-ph.HE |
arxiv_dataset-1333907.1135 | Electro-spinon in one-dimensional Mott insulator
cond-mat.str-el cond-mat.mtrl-sci
The low-energy dynamical optical response of dimerized and undimerized spin
liquid states in a one-dimensional charge transfer Mott insulator is
theoretically studied. An exact analysis is given for the low-energy asymptotic
behavior using conformal field theory for the undimerized state. In the
dimerized state, the infrared absorption due to the bound state of two
solitons, i.e, the breather mode, is predicted with an accurate estimate for
its oscillator strength, offering a way to detect experimentally the excited
singlet state. Effects of external magnetic fields are also discussed.
| arxiv topic:cond-mat.str-el cond-mat.mtrl-sci |
arxiv_dataset-1334907.1235 | Global Bifurcation of Positive Equilibria in Nonlinear Population Models
math.AP math.FA
Existence of nontrivial nonnegative equilibrium solutions for age structured
population models with nonlinear diffusion is investigated. Introducing a
parameter measuring the intensity of the fertility, global bifurcation is shown
of a branch of positive equilibrium solutions emanating from the trivial
equilibrium. Moreover, for the parameter-independent model we establish
existence of positive equilibria by means of a fixed point theorem for conical
shells.
| arxiv topic:math.AP math.FA |
arxiv_dataset-1335907.1335 | Strong exciton-plasmon coupling in semiconducting carbon nanotubes
cond-mat.mes-hall
We study theoretically the interactions of excitonic states with surface
electromagnetic modes of small-diameter (~1 nm) semiconducting single-walled
carbon nanotubes. We show that these interactions can result in strong
exciton-surface-plasmon coupling. The exciton absorption line shape exhibits
Rabi splitting ~0.1 eV as the exciton energy is tuned to the nearest interband
surface plasmon resonance of the nanotube. We also show that the quantum
confined Stark effect may be used as a tool to control the exciton binding
energy and the nanotube band gap in carbon nanotubes in order, e.g., to bring
the exciton total energy in resonance with the nearest interband plasmon mode.
The exciton-plasmon Rabi splitting we predict here for an individual carbon
nanotube is close in its magnitude to that previously reported for hybrid
plasmonic nanostructures artificially fabricated of organic semiconductors on
metallic films. We expect this effect to open up paths to new tunable
optoelectronic device applications of semiconducting carbon nanotubes.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-1336907.1435 | Repulsive Casimir Force in Chiral Metamaterials
cond-mat.mtrl-sci
We demonstrate theoretically that one can obtain repulsive Casimir forces and
stable nanolevitations by using chiral metamaterials. By extending the Lifshitz
theory to treat chiral metamaterials, we find that a repulsive force and a
minimum of the interaction energy exist for strong chirality, under realistic
frequency dependencies and correct limiting values (for zero and infinite
frequencies) of the permittivity, permeability, and chiral coefficients.
| arxiv topic:cond-mat.mtrl-sci |
arxiv_dataset-1337907.1535 | Anomalies, U(1)' and the MSSM
hep-ph hep-th
This Thesis reviews an extension of the MSSM by the addition of an anomalous
abelian vector multiplet and contains some original results concerning the
phenomenology of an anomalous $Z'$. The review part covers an introduction of
the MSSM focusing on its main features, a discussion on the chiral anomalies
and how to cancel them in the Standard Model and by the Green-Schwarz
mechanism. Then, the original results are presented. We build the Lagrangian
for the Minimal Anomalous $U(1)'$ Extension of the MSSM where the anomalies are
cancelled by the Green-Schwarz mechanism and the addition of Chern-Simons
terms, stressing the main differences between our model and the MSSM. The
advantage of this choice over the standard one is that it allows for arbitrary
values of the quantum numbers of the extra U(1). As a first step towards the
study of hadron annihilations producing four leptons in the final state (a
clean signal which might be studied at LHC) we then compute the decays $Z'\to
Z_0 \g$ and $Z'\to Z_0 Z_0$. We find that the largest values of the decay rate
are $\sim 10^{-4}$ GeV, while the expected number of events per year at LHC is
at most of the order of 10. Then we compute the relic density predicted by our
model with a new dark matter candidate, the axino, which is the LSP of the
theory. We find agreement with experimental data admitting a bino-higgsino NLSP
or a wino-like NLSP, almost degenerate in mass to the axino.
| arxiv topic:hep-ph hep-th |
arxiv_dataset-1338907.1635 | Implementation of Fault-tolerant Quantum Logic Gates via Optimal Control
quant-ph
The implementation of fault-tolerant quantum gates on encoded logic qubits is
considered. It is shown that transversal implementation of logic gates based on
simple geometric control ideas is problematic for realistic physical systems
suffering from imperfections such as qubit inhomogeneity or uncontrollable
interactions between qubits. However, this problem can be overcome by
formulating the task as an optimal control problem and designing efficient
algorithms to solve it. In particular, we can find solutions that implement all
of the elementary logic gates in a fixed amount of time with limited control
resources for the five-qubit stabilizer code. Most importantly, logic gates
that are extremely difficult to implement using conventional techniques even
for ideal systems, such as the T-gate for the five-qubit stabilizer code, do
not appear to pose a problem for optimal control.
| arxiv topic:quant-ph |
arxiv_dataset-1339907.1735 | Seismic vulnerability analysis of moderate seismicity areas using in
situ experimental techniques: from the building to the city scale ?
Application to Grenoble and Pointe-\`a-Pitre (France)
physics.geo-ph physics.class-ph
Seismic vulnerability analysis of existing buildings requires basic
information on their structural behaviour. The ambient vibrations of buildings
and the modal parameters (frequencies, damping ration and modal shapes) that
can be extracted from them naturally include the geometry and quality of
material in the linear elastic part of their behaviour. The aim of this work is
to use this modal information to help the vulnerability assessment. A linear
dynamic modal model based on experimental modal parameters is proposed and the
fragility curve corresponding to the damage state ?Slight? is built using this
model and a simple formula is proposed. This curve is particularly interesting
in moderate seismic areas. This methodology is applied to the Grenoble City
where ambient vibrations have been recorded in 61 buildings of various types
and to the Pointe-\`a-Pitre City with 7 study-buildings. The fragility curves
are developed using the aforementioned methodology. The seismic risk of the
study-buildings is discussed by performing seismic scenarios.
| arxiv topic:physics.geo-ph physics.class-ph |
arxiv_dataset-1340907.1835 | Information geometry for testing pseudorandom number generators
stat.CO
The information geometry of the 2-manifold of gamma probability density
functions provides a framework in which pseudorandom number generators may be
evaluated using a neighbourhood of the curve of exponential density functions.
The process is illustrated using the pseudorandom number generator in
Mathematica. This methodology may be useful to add to the current family of
test procedures in real applications to finite sampling data.
| arxiv topic:stat.CO |
arxiv_dataset-1341907.1935 | Near-Infrared Counterparts to Chandra X-ray Sources toward the Galactic
Center. I. Statistics and a Catalog of Candidates
astro-ph.GA
We present a catalog of 5184 candidate infrared counterparts to X-ray sources
detected towards the Galactic center. The X-ray sample contains 9017 point
sources detected in this region by the Chandra X-ray Observatory, including
data from a recent deep survey of the central 2 x 0.8 deg of the Galactic
plane. A total of 6760 of these sources have hard X-ray colors, and the
majority of them lie near the Galactic center, while most of the remaining 2257
soft X-ray sources lie in the foreground. We cross-correlated the X-ray source
positions with the 2MASS and SIRIUS near-infrared catalogs, which collectively
contain stars with a 10-sigma limiting flux of K_s<=15.6 mag. In order to
distinguish absorbed infrared sources near the Galactic center from those in
the foreground, we defined red and blue sources as those which have H-K_s>=0.9
and <=0.9 mag, respectively. We find that 5.8(1.5)% of the hard X-ray sources
have real infrared counterparts, of which 228(99) are red and 166(27) are blue.
The red counterparts are probably comprised of WR/O stars, HMXBs, and
symbiotics near the Galactic center. We also find that 39.4(1.0)% of the soft
X-ray sources have blue infrared counterparts; most of these are probably
coronally active dwarfs in the foreground. There is a noteworthy collection of
~20 red counterparts to hard X-ray sources near the Sagittarius-B H II region,
which are probably massive binaries that have formed within the last several
Myr. For each of the infrared matches to X-ray sources in our catalog we
derived the probability that the association is real, based on the results of
the cross-correlation analysis. The catalog will serve spectroscopic surveys to
identify infrared counterparts to X-ray sources near the Galactic center.
| arxiv topic:astro-ph.GA |
arxiv_dataset-1342907.2035 | Numerical scheme for backward doubly stochastic differential equations
math.PR
We study a discrete-time approximation for solutions of systems of decoupled
forward-backward doubly stochastic differential equations (FBDSDEs). Assuming
that the coefficients are Lipschitz-continuous, we prove the convergence of the
scheme when the step of time discretization, $|\pi|$ goes to zero. The rate of
convergence is exactly equal to $|\pi|^{1/2}$. The proof is based on a
generalization of a remarkable result on the $^{2}$-regularity of the solution
of the backward equation derived by J. Zhang
| arxiv topic:math.PR |
arxiv_dataset-1343907.2135 | Shrinkage regression for multivariate inference with missing data, and
an application to portfolio balancing
stat.ME stat.AP
Portfolio balancing requires estimates of covariance between asset returns.
Returns data have histories which greatly vary in length, since assets begin
public trading at different times. This can lead to a huge amount of missing
data--too much for the conventional imputation-based approach. Fortunately, a
well-known factorization of the MVN likelihood under the prevailing historical
missingness pattern leads to a simple algorithm of OLS regressions that is much
more reliable. When there are more assets than returns, however, OLS becomes
unstable. Gramacy, et al. (2008), showed how classical shrinkage regression may
be used instead, thus extending the state of the art to much bigger asset
collections, with further accuracy and interpretation advantages. In this
paper, we detail a fully Bayesian hierarchical formulation that extends the
framework further by allowing for heavy-tailed errors, relaxing the historical
missingness assumption, and accounting for estimation risk. We illustrate how
this approach compares favorably to the classical one using synthetic data and
an investment exercise with real returns. An accompanying R package is on CRAN.
| arxiv topic:stat.ME stat.AP |
arxiv_dataset-1344907.2235 | Sizes of Lyman-Alpha-Emitting Galaxies and Their Rest-Frame Ultraviolet
Components at z=3.1
astro-ph.CO astro-ph.GA
We present a rest-frame ultraviolet analysis of ~120 z~3.1 Lyman Alpha
Emitters (LAEs) in the Extended Chandra Deep Field South (ECDF-S). Using Hubble
Space Telescope (HST) images taken as part of the Galaxy Evolution From
Morphology and SEDS (GEMS) survey, Great Observatories Origins Deep Survey
(GOODS), and Hubble Ultradeep Field (HUDF) surveys, we analyze the sizes of
LAEs, as well as the spatial distribution of their components, which are
defined as distinct clumps of UV-continuum emission. We set an upper limit of
~1 kpc (~0.1") on the rms offset between the centroids of the continuum and
Lyman-alpha emission. The star formation rates of LAE components inferred from
the rest-frame ultraviolet continuum range from ~0.1 M_{sun}/yr to ~5$
M_{sun}/yr. A subsample of LAEs with coverage in multiple surveys (at different
imaging depths) suggests that one needs a signal-to-noise ratio, S/N>~30, in
order to make a robust estimate of the half-light radius of an LAE system. The
majority of LAEs have observed half-light radii <~2 kpc, and LAE components
typically have observed half-light radii <~1.5 kpc (<~ 0.2"). Although only
~50% of the detected LAE components are resolved at GOODS depth, the brightest
(V<~26.3) are all resolved in both GOODS and GEMS. Since we find little
evidence for a correlation between the rest-UV sizes and magnitudes of LAEs,
the majority should be resolved in a deeper survey at the ~0.05" angular
resolution of HST. Most of the multi-component LAEs identified in shallow
frames become connected in deeper images, suggesting that the majority of the
rest-UV "clumps" are individual star-forming regions within a single system.
| arxiv topic:astro-ph.CO astro-ph.GA |
arxiv_dataset-1345907.2335 | Self-inverse Sheffer sequences and Riordan involutions
math.CO
In this short note we focus on self-inverse Sheffer sequences and involutions
in the Riordan group. We translate the results of Brown and Kuczma on
self-inverse sequences of Sheffer polynomials to describe all involutions in
the Riordan group.
| arxiv topic:math.CO |
arxiv_dataset-1346907.2435 | Sequential Posted Pricing and Multi-parameter Mechanism Design
cs.GT
We consider the classical mathematical economics problem of {\em Bayesian
optimal mechanism design} where a principal aims to optimize expected revenue
when allocating resources to self-interested agents with preferences drawn from
a known distribution. In single-parameter settings (i.e., where each agent's
preference is given by a single private value for being served and zero for not
being served) this problem is solved [Myerson '81]. Unfortunately, these single
parameter optimal mechanisms are impractical and rarely employed [Ausubel and
Milgrom '06], and furthermore the underlying economic theory fails to
generalize to the important, relevant, and unsolved multi-dimensional setting
(i.e., where each agent's preference is given by multiple values for each of
the multiple services available) [Manelli and Vincent '07]. In contrast to the
theory of optimal mechanisms we develop a theory of sequential posted price
mechanisms, where agents in sequence are offered take-it-or-leave-it prices.
These mechanisms are approximately optimal in single-dimensional settings, and
avoid many of the properties that make optimal mechanisms impractical.
Furthermore, these mechanisms generalize naturally to give the first known
approximations to the elusive optimal multi-dimensional mechanism design
problem. In particular, we solve multi-dimensional multi-unit auction problems
and generalizations to matroid feasibility constraints. The constant
approximations we obtain range from 1.5 to 8. For all but one case, our posted
price sequences can be computed in polynomial time.
| arxiv topic:cs.GT |
arxiv_dataset-1347907.2535 | Proximity induced interface bound states in superconductor-graphene
junctions
cond-mat.mes-hall cond-mat.supr-con
We show that interface bound states are formed at isolated
graphene-superconductor junctions. These states arise due to the interplay of
virtual Andreev and normal reflections taking place at these interfaces. Simple
analytical expressions for their dispersion are obtained considering interfaces
formed along armchair or zig-zag edges. It is shown that the states are
sensitive to a supercurrent flowing on the superconducting electrode. The
states provide long range superconducting correlations on the graphene layer
which may be exploited for the detection of crossed Andreev processes.
| arxiv topic:cond-mat.mes-hall cond-mat.supr-con |
arxiv_dataset-1348907.2635 | Detection of charge motion in a non-metallic silicon isolated double
quantum dot
cond-mat.mes-hall cond-mat.other
As semiconductor device dimensions are reduced to the nanometer scale,
effects of high defect density surfaces on the transport properties become
important to the extent that the metallic character that prevails in large and
highly doped structures is lost and the use of quantum dots for charge sensing
becomes complex. Here we have investigated the mechanism behind the detection
of electron motion inside an electrically isolated double quantum dot that is
capacitively coupled to a single electron transistor, both fabricated from
highly phosphorous doped silicon wafers. Despite, the absence of a direct
charge transfer between the detector and the double dot structure, an efficient
detection is obtained. In particular, unusually large Coulomb peak shifts in
gate voltage are observed. Results are explained in terms of charge
rearrangement and the presence of inelastic cotunneling via states at the
periphery of the single electron transistor dot.
| arxiv topic:cond-mat.mes-hall cond-mat.other |
arxiv_dataset-1349907.2735 | Delayed Seasonal Cycle and African Monsoon in a Warmer Climate
physics.ao-ph
Increasing greenhouse gases will change many aspects of the Earth's climate,
from its annual mean to the frequency of extremes such as heat waves and
droughts. Here we report that the current generation of climate models predicts
a delay in the seasonal cycle of global rainfall and ocean temperature in
response to increasing greenhouse gases, with important implications for the
regional monsoons. In particular, the rainy season of the semi-arid African
Sahel is projected to start later and become shorter: an undesirable change for
local rainfed agriculture and pastoralism. Previous work has highlighted the
uncertainty in this region's response to anthropogenic global warming: summer
rainfall is predicted either to decrease or increase by up to 30% depending
which model is used. The robust agreement across models on the seasonal
distribution of rainfall changes signifies that the onset date and length of
the rainy season should be more predictable than annual mean anomalies.
| arxiv topic:physics.ao-ph |
arxiv_dataset-1350907.2835 | Form factors in RQM approaches: constraints from space-time
translations, extension to constituents with spin-1/2 and unequal masses
nucl-th hep-ph
Constraints related to transformations of currents under space-time
translations have been considered for the relativistic quantum mechanics
calculation of form factors of J=0 systems composed of scalar constituents with
equal masses. Accounting for these constraints amounts to take into account
many-body currents that restore the equality of the momentum transferred
separately to the system and to the constituents, which holds in field-theory
approaches but is not generally fulfilled in relativistic quantum mechanics
ones. When this was done, discrepancies between results from different
approaches could be found to vanish. The results are extended here to systems
composed of spin-1/2 constituents with unequal masses. Moreover, as far as the
equivalence of different approaches is concerned, some intermediate step could
be skipped and the presentation of these results therefore slightly differs
from the previous one. Due to the technical aspect of present results, this
work is not aimed to be published but it could be useful for some applications
like the form factors of the pion or kaon particles.
| arxiv topic:nucl-th hep-ph |
arxiv_dataset-1351907.2935 | Positive expansiveness versus network dimension in symbolic dynamical
systems
math.DS
A `symbolic dynamical system' is a continuous transformation F:X-->X of a
closed perfect subset X of A^V, where A is a finite set and V is countable.
(Examples include subshifts, odometers, cellular automata, and automaton
networks.) The function F induces a directed graph structure on V, whose
geometry reveals information about the dynamical system (X,F). The `dimension'
dim(V) is an exponent describing the growth rate of balls in the digraph as a
function of their radius. We show: if X has positive entropy and dim(V)>1, and
the system (A^V,X,F) satisfies minimal symmetry and mixing conditions, then
(X,F) cannot be positively expansive; this generalizes a well-known result of
Shereshevsky about multidimensional cellular automata. We also construct a
counterexample to a version of this result without the symmetry condition.
Finally, we show that network dimension is invariant under topological
conjugacies which are Holder-continuous.
| arxiv topic:math.DS |
arxiv_dataset-1352907.3035 | Modified proof of a local analogue of the Grothendieck conjecture
math.NT
A local analogue of the Grothendieck Conjecture is an equivalence of the
category of complete discrete valuation fields $K$ with finite residue fields
of characteristic $p\ne 0$ and the category of absolute Galois groups of fields
$K$ together with their ramification filtrations. The case of characteristic 0
fields $K$ was considered by Mochizuki several years ago. Then the author
proved it by different method if $p>2$ (but $\operatorname{char}K=0$ or $p$).
This paper represents a modified approach: it covers the case $p=2$, contains
considerable technical simplifications and replaces the Galois group of $K$ by
its maximal pro-$p$-quotient. Special attention is paid to the procedure of
recovering field isomorphisms coming from isomorphisms of Galois groups, which
are compatible with the corresponding ramification filtrations.
| arxiv topic:math.NT |
arxiv_dataset-1353907.3135 | Fast Searching in Packed Strings
cs.DS
Given strings $P$ and $Q$ the (exact) string matching problem is to find all
positions of substrings in $Q$ matching $P$. The classical Knuth-Morris-Pratt
algorithm [SIAM J. Comput., 1977] solves the string matching problem in linear
time which is optimal if we can only read one character at the time. However,
most strings are stored in a computer in a packed representation with several
characters in a single word, giving us the opportunity to read multiple
characters simultaneously. In this paper we study the worst-case complexity of
string matching on strings given in packed representation. Let $m \leq n$ be
the lengths $P$ and $Q$, respectively, and let $\sigma$ denote the size of the
alphabet. On a standard unit-cost word-RAM with logarithmic word size we
present an algorithm using time $$ O\left(\frac{n}{\log_\sigma n} + m +
\occ\right). $$ Here $\occ$ is the number of occurrences of $P$ in $Q$. For $m
= o(n)$ this improves the $O(n)$ bound of the Knuth-Morris-Pratt algorithm.
Furthermore, if $m = O(n/\log_\sigma n)$ our algorithm is optimal since any
algorithm must spend at least $\Omega(\frac{(n+m)\log
\sigma}{\log n} + \occ) = \Omega(\frac{n}{\log_\sigma n} + \occ)$ time to
read the input and report all occurrences. The result is obtained by a novel
automaton construction based on the Knuth-Morris-Pratt algorithm combined with
a new compact representation of subautomata allowing an optimal
tabulation-based simulation.
| arxiv topic:cs.DS |
arxiv_dataset-1354907.3235 | Dark energy, integrated Sachs-Wolfe effect and large-scale magnetic
fields
astro-ph.CO gr-qc hep-ph hep-th
The impact of large-scale magnetic fields on the interplay between the
ordinary and integrated Sachs-Wolfe effects is investigated in the presence of
a fluctuating dark energy component. The modified initial conditions of the
Einstein-Boltzmann hierarchy allow for the simultaneous inclusion of dark
energy perturbations and of large-scale magnetic fields. The temperature and
polarization angular power spectra are compared with the results obtained in
the magnetized version of the (minimal) concordance model. Purported
compensation effects arising at large scales are specifically investigated. The
fluctuating dark energy component modifies, in a computable manner, the shapes
of the 1- and 2-$\sigma$ contours in the parameter space of the magnetized
background. The allowed spectral indices and magnetic field intensities turn
out to be slightly larger than those determined in the framework of the
magnetized concordance model where the dark energy fluctuations are absent.
| arxiv topic:astro-ph.CO gr-qc hep-ph hep-th |
arxiv_dataset-1355907.3335 | Hopf algebras, tetramodules, and n-fold monoidal categories
math.CT math.QA
The abelian category of tetramodules over an associative bialgebra $A$ is
related with the Gerstenhaber-Schack (GS) cohomology as
$Ext_\Tetra(A,A)=H_\GS(A)$. We construct a 2-fold monoidal structure on the
category of tetramodules of a bialgebra.
Suppose $C$ is an abelian $n$-fold monoidal category with the unit object
$A$. We prove, provided some condition (*), that $Ext_C(A,A)$ is an
$(n+1)$-algebra. In the case of bialgebras this condition (*) is satisfied when
$A$ is a Hopf algebra. Finally, the GS cohomology of a Hopf algebra is a
3-algebra.
As well, we consider this kind of questions of (bi)algebras over integers.
Let $A$ be an associative algebra over $Z$ flat over $Z$. We prove that the
operad acting on its Hochschild cohomology is the operad of stable homotopy
groups of the little discs operad.
| arxiv topic:math.CT math.QA |
arxiv_dataset-1356907.3435 | Hochschild cohomology and support varieties for tame Hecke algebras
math.RT math.KT
We give a basis for the Hochschild cohomology ring of tame Hecke algebras. We
then show that the Hochschild cohomology ring modulo nilpotence is a finitely
generated algebra of Krull dimension 2, and describe the support varieties of
modules for these algebras. As a consequence we obtain the result that the
Hochschild cohomology ring modulo nilpotence of a Hecke algebra has Krull
dimension 1 if the algebra is of finite type and has Krull dimension 2 if the
algebra is of tame type.
| arxiv topic:math.RT math.KT |
arxiv_dataset-1357907.3535 | Niveau and coniveau filtrations on cohomology groups and Chow groups
math.AG
The Bloch-Beilinson-Murre conjectures predict the existence of a descending
filtration on Chow groups of smooth projective varieties which is functorial
with respect to the action of correspondences and whose graded parts depend
solely on the topology -- i.e. the cohomology -- of $X$. In this paper, we wish
to explore, at the cost of having to assume general conjectures about algebraic
cycles, how the coniveau filtration on the cohomology of $X$ has an incidence
on the Chow groups of $X$. However, by keeping such assumptions minimal, we are
able to prove some of these conjectures either in low-dimensional cases or when
a variety is known to have small Chow groups. For instance, we give a new
example of a fourfold of general type with trivial Chow group of zero-cycles
and we prove Murre's conjectures for threefolds dominated by a product of
curves, for threefolds rationally dominated by the product of three curves, for
rationally connected fourfolds and for complete intersections of low degree.
The BBM conjectures are closely related to Kimura-O'Sullivan's notion of
finite-dimensionality. Assuming the standard conjectures on algebraic cycles
the former is known to imply the latter. We show that the missing ingredient
for finite-dimensionality to imply the BBM conjectures is the coincidence of a
certain niveau filtration with the coniveau filtration on Chow groups.
| arxiv topic:math.AG |
arxiv_dataset-1358907.3635 | Delensing Gravitational Wave Standard Sirens with Shear and Flexion Maps
astro-ph.CO
Supermassive black hole binary systems (SMBHB) are standard sirens -- the
gravitational wave analogue of standard candles -- and if discovered by
gravitational wave detectors, they could be used as precise distance
indicators. Unfortunately, gravitational lensing will randomly magnify SMBHB
signals, seriously degrading any distance measurements. Using a weak lensing
map of the SMBHB line of sight, we can estimate its magnification and thereby
remove some uncertainty in its distance, a procedure we call "delensing." We
find that delensing is significantly improved when galaxy shears are combined
with flexion measurements, which reduce small-scale noise in reconstructed
magnification maps. Under a Gaussian approximation, we estimate that delensing
with a 2D mosaic image from an Extremely Large Telescope (ELT) could reduce
distance errors by about 30-40% for a SMBHB at z=2. Including an additional
wide shear map from a space survey telescope could reduce distance errors by
50%. Such improvement would make SMBHBs considerably more valuable as
cosmological distance probes or as a fully independent check on existing
probes.
| arxiv topic:astro-ph.CO |
arxiv_dataset-1359907.3735 | Talk on Anomalies in Quantum Field Theory and Cohomologies of
Configuration Spaces
math-ph hep-th math.MP
This is a review of the paper "Anomalies in Quantum Field Theory and
Cohomologies of Configuration Spaces" (arXiv:0903.0187).
| arxiv topic:math-ph hep-th math.MP |
arxiv_dataset-1360907.3835 | Supersonic Evershed flow outside Sunspots
astro-ph.SR
We report on the discovery of mostly horizontal field channels just outside
sunspot penumbrae (in the so-called `moat' region) that are seen to sustain
supersonic flows (line-of-sight component of 6 km s{-1}). The spectral
signature of these supersonic flows corresponds to circular polarization
profiles with an additional, satellite, third lobe of the same sign as the
parent sunspot' Stokes V blue lobe, for both downflows and upflows. This is
consistent with an outward directed flow that we interpret as the continuation
of the magnetized Evershed flow outside sunspots at supersonic speeds. In
Stokes Q and U, a clear signature of a transverse field connecting the two flow
streams is observed. Such an easily detectable spectral signature should allow
for a clear identification of these horizontal field channels in other
spectropolarimetric sunspot data. For the spot analyzed in this paper, a total
of 5 channels with this spectral signature have been unambiguously found.
| arxiv topic:astro-ph.SR |
arxiv_dataset-1361907.3935 | Dileptons and Direct Photons at SPS
hep-ex
The study of dilepton and direct photon emission was one of the main topics
of the experimental program at the SPS devoted to the search of signals for QGP
formation. Three generations of experiments, Helios-3, NA38/NA50, CERES and
NA60 measured e+e- or mu+mu- production in various colliding systems and at
different energies. While lepton pair production in p-A collisions was found to
be reasonably well described by the expected sources, all experiments observed
in nuclear collisions an excess of the yield above the extrapolation from p-A.
As a result of this joint experimental effort we have currently a large amount
of information characterizing this excess: its mass spectrum over the full
range from 0.2 GeV/c^2 up to the J/psi, its transverse momentum spectra
including their mass dependence, its angular distributions, its dependence on
collision centrality over the complete range etc. Putting together all this
information leads to the conclusion that what we observe is the long-sought
thermal radiation from the fireball.
| arxiv topic:hep-ex |
arxiv_dataset-1362907.4035 | Hard Core entropy: lower bounds
math.PR math-ph math.MP
We establish lower bounds for the entropy of the Hard Core Model on a few 2d
lattices $\scriptstyle {\rm {\bf L}}.$ In this model the allowed configurations
inside $\scriptstyle \{0,1\}^{{\rm {\bf L}}}$ are the one's in which the
nearest neighbor $\scriptstyle 1$'s are forbidden. Our method which is based on
a sequential fill-in scheme is unbiassed and thereby yields in principle
arbitrarily good estimates for the topological entropy. The procedure also
gives some detailed information on the support of the measure of maximal
entropy.
| arxiv topic:math.PR math-ph math.MP |
arxiv_dataset-1363907.4135 | A note on positive energy of topologically massive gravity
gr-qc hep-th
I review how "classical SUGRA" embeddability establishes positive energy E
for D=3 topologically massive gravity (TMG), with or without a cosmological
term, a procedure familiar from D=4 Einstein gravity (GR). It also provides
explicit expressions for E. In contrast to GR, E is not manifestly positive,
due to the peculiar two-term nature of TMG.
| arxiv topic:gr-qc hep-th |
arxiv_dataset-1364907.4235 | Cation composition effects on oxide conductivity in the
Zr_2Y_2O_7-Y_3NbO_7 system
physics.chem-ph physics.comp-ph
Realistic, first-principles-based interatomic potentials have been used in
molecular dynamics simulations to study the effect of cation composition on the
ionic conductivity in the Zr2Y2O7-Y3NbO7 system and to link the dynamical
properties to the degree of lattice disorder. Across the composition range,
this system retains a disordered fluorite crystal structure and the vacancy
concentration is constant. The observed trends of decreasing conductivity and
increasing disorder with increasing Nb5+ content were reproduced in simulations
with the cations randomly assigned to positions on the cation sublattice. The
trends were traced to the influences of the cation charges and relative sizes
and their effect on vacancy ordering by carrying out additional calculations in
which, for example, the charges of the cations were equalised. The simulations
did not, however, reproduce all the observed properties, particularly for
Y3NbO7. Its conductivity was significantly overestimated and prominent diffuse
scattering features observed in small area electron diffraction studies were
not always reproduced. Consideration of these deficiencies led to a preliminary
attempt to characterise the consequence of partially ordering the cations on
their lattice, which significantly affects the propensity for vacancy ordering.
The extent and consequences of cation ordering seem to be much less pronounced
on the Zr2Y2O7 side of the composition range.
| arxiv topic:physics.chem-ph physics.comp-ph |
arxiv_dataset-1365907.4335 | From Entropic Dynamics to Quantum Theory
quant-ph cond-mat.stat-mech gr-qc
Non-relativistic quantum theory is derived from information codified into an
appropriate statistical model. The basic assumption is that there is an
irreducible uncertainty in the location of particles: positions constitute a
configuration space and the corresponding probability distributions constitute
a statistical manifold. The dynamics follows from a principle of inference, the
method of Maximum Entropy. The concept of time is introduced as a convenient
way to keep track of change. A welcome feature is that the entropic dynamics
notion of time incorporates a natural distinction between past and future. The
statistical manifold is assumed to be a dynamical entity: its curved and
evolving geometry determines the evolution of the particles which, in their
turn, react back and determine the evolution of the geometry. Imposing that the
dynamics conserve energy leads to the Schroedinger equation and to a natural
explanation of its linearity, its unitarity, and of the role of complex
numbers. The phase of the wave function is explained as a feature of purely
statistical origin. There is a quantum analogue to the gravitational
equivalence principle.
| arxiv topic:quant-ph cond-mat.stat-mech gr-qc |
arxiv_dataset-1366907.4435 | Signals of the QCD Critical Point in Hydrodynamic Evolutions
nucl-th
The presence of a critical point in the QCD phase diagram can deform the
trajectories describing the evolution of the expanding fireball in the QCD
phase diagram. The deformation of the hydrodynamic trajectories will change the
transverse velocity dependence of the proton-antiproton ratio when the fireball
passes in the vicinity of the critical point. An unusual transverse velocity
dependence of the anti-proton/proton ratio in a narrow beam energy window would
thus signal the presence of the critical point.
| arxiv topic:nucl-th |
arxiv_dataset-1367907.4535 | Effects of multiple pairs on visibility measurements of entangled
photons generated by spontaneous parametric processes
quant-ph
Entangled photon-pair sources based on spontaneous parametric processes are
widely used in photonic quantum information experiments. In this paper, we
clarify the relationship between average photon-pair number and the visibility
of two-photon interference (TPI) using those entanglement sources. We consider
sources that generate distinguishable and indistinguishable entangled photon
pairs, assuming coincidence measurements that use threshold detectors. We
present formulas for the TPI visibility of a polarization entanglement that
take account of all the high-order multi-pair emission events. Moreover, we
show that the formulas can be approximated with simple functions of the average
pair number when the photon collection efficiency is small. As a result, we
reveal that an indistinguishable entangled pair provides better visibility than
a distinguishable one.
| arxiv topic:quant-ph |
arxiv_dataset-1368907.4635 | A kinematic study of the irregular dwarf galaxy NGC 4861 using HI and
Halpha observations
astro-ph.CO
Context. Outflows powered by the injection of kinetic energy from massive
stars can strongly affect the chemical evolution of galaxies, in particular of
dwarf galaxies, as their lower gravitational potentials enhance the chance of a
galactic wind.
Aims. We therefore performed a detailed kinematic analysis of the neutral and
ionised gas components in the nearby star-forming irregular dwarf galaxy NGC
4861. Similar to a recently published study of NGC 2366, we want to make
predictions about the fate of the gas and to discuss some general issues about
this galaxy.
Methods. Fabry-Perot interferometric data centred on the Halpha line were
obtained with the 1.93m telescope at the Observatoire de Haute-Provence. They
were complemented by HI synthesis data from the VLA. We performed a Gaussian
decomposition of both the Halpha and the HI emission lines in order to search
for multiple components indicating outflowing gas. The expansion velocities of
the detected outflows were compared to the escape velocity of NGC 4861, which
was modelled with a pseudo-isothermal halo.
Results. Both in Halpha and HI the galaxy shows several outflows, three
directly connected to the disc and probably forming the edges of a supergiant
shell, and one at kpc-distance from the disc. We measured velocity offsets of
20 to 30 km/s, which are low in comparison to the escape velocity of the galaxy
and therefore minimise the chance of a galactic wind.
| arxiv topic:astro-ph.CO |
arxiv_dataset-1369907.4735 | Temperature dependence of resistivity and Hall-coefficient in a strongly
disordered metal: NbN
cond-mat.dis-nn cond-mat.str-el cond-mat.supr-con
We report the temperature dependence of resistivity (rho) and Hall
coefficient (R_H) in the normal state of homogeneously disordered epitaxial NbN
thin films with kFl~3.27-10.12. The superconducting transition temperature (Tc)
of these films varies from 8.13K to 16.8K. While our least disordered film
displays usual metallic behavior, for all the films with kFl<8.13, both and are
negative up to 300K. We observe that R_H(T) varies linearly with rho(T) for all
the films. Measurements performed on a 2nm thick Be film shows similar behavior
>. This behavior is inconsistent with existing theories of localization and e-e
interactions in a disordered metal.
| arxiv topic:cond-mat.dis-nn cond-mat.str-el cond-mat.supr-con |
arxiv_dataset-1370907.4835 | Universal magnetic structure of the half-magnetization phase in Cr-based
spinels
cond-mat.mtrl-sci cond-mat.str-el
Using an elastic neutron scattering technique under a pulsed magnetic field
up to 30 T, we determined the magnetic structure in the half-magnetization
plateau phase in the spinel CdCr$_2$O$_4$. The magnetic structure has a cubic
$P4_3$32 symmetry, which is the same as that observed in HgCr$_2$O$_4$. This
suggests that there is a universal field induced spin-lattice coupling
mechanism at work in the Cr-based spinels.
| arxiv topic:cond-mat.mtrl-sci cond-mat.str-el |
arxiv_dataset-1371907.4935 | Asymmetry in the presence of migration stabilizes multistrain disease
outbreaks
q-bio.PE q-bio.QM
We study the effect of migration between coupled populations, or patches, on
the stability properties of multistrain disease dynamics. The epidemic model
used in this work displays a Hopf bifurcation to oscillations in a single well
mixed population. It is shown numerically that migration between two
non-identical patches stabilizes the endemic steady state, delaying the onset
of large amplitude outbreaks and reducing the total number of infections. This
result is motivated by analyzing generic Hopf bifurcations with different
frequencies and with diffusive coupling between them. Stabilization of the
steady state is again seen, indicating that our observation in the full
multistrain model is based on qualitative characteristics of the dynamics
rather than on details of the disease model.
| arxiv topic:q-bio.PE q-bio.QM |
arxiv_dataset-1372907.5035 | An Analogue of the L\'Evy-Cram\'Er Theorem for Multi-Dimensional
Rayleigh Distributions
math.PR
In the present paper we prove that every k-dimensional Cartesian product of
Kingman convolutions can be embedded into a k-dimensional symmetric convolution
(k=1, 2, ...) and obtain an analogue of the Cram\'er-L\'evy theorem for
multi-dimensional Rayleigh distributions.
| arxiv topic:math.PR |
arxiv_dataset-1373907.5135 | The Two Higgs Doublet of Type II facing flavour physics data
hep-ph
We discuss tests of the charged Higgs sector of the Two Higgs Doublet Model
(2HDM) of Type II in the light of recent flavour physics data. Particular
attention is paid to recent measurement of purely leptonic decays of
heavy-light mesons, which depart more or less significantly from the Standard
Model (SM) predictions. We derive constraints on the parameters of the 2HDM
type II from leptonic and semileptonic $\Delta F=1$ decays as well as loop
processes ($b \to s \gamma$, $B\bar{B}$ mixing or $Z\to\bar{b}b$) sensitive to
charged Higgs contributions.
The outcome of this work is that while 2HDM Type II can fit individual
observable through fine-tuning schemes, in a combined analysis it does not
perform better than the SM by favouring a decoupling solution. Assuming that
2HDM Type II is realized in Nature, constraints on its parameters ($m_{H^+}$
and $\tan \beta$) are derived. A limit on the charged Higgs mass $m_{H^+} > 316
\; {\rm GeV}$ at $95\%$~CL is obtained irrespective of the value of $\tan
\beta$. This limit is dominated by the $b\rightarrow s \gamma$ branching ratio
measurement.
All results have been obtained with the \ckmfitter\ analysis package,
featuring the frequentist statistical approach \rfit\ to handle theoretical
uncertainties.
| arxiv topic:hep-ph |
arxiv_dataset-1374907.5235 | Time variations in the deep underground muon flux
hep-ex
More than 35 million high-energy muons collected with the MACRO detector at
the underground Gran Sasso Laboratory have been used to search for flux
variations of different nature. Two kinds of studies were carried out: a search
for the occurrence of clusters of events and a search for periodic variations.
Different analysis methods, including the Scan Statistics test and the
Lomb-Scargle spectral analysis have been applied to the data.
| arxiv topic:hep-ex |
arxiv_dataset-1375907.5335 | Self-Collapse and Sliding of Nanotubes in a Bundle
cond-mat.mtrl-sci cond-mat.mes-hall
We have discovered that the influence of the surrounding nanotubes in a
bundle is similar to that of a liquid having surface tension equal to the
surface energy of the nanotubes. This surprising behaviour is confirmed by the
calculation of the self-collapse diameters of nanotubes in a bundle. Other
systems, such as peapods, fullerites, are similarly treated, including the
effect of the presence of a solvent. Finally, we have evaluated the strength
and toughness of the nanotube bundle, with or without collapsed nanotubes,
assuming a sliding failure.
| arxiv topic:cond-mat.mtrl-sci cond-mat.mes-hall |
arxiv_dataset-1376907.5435 | The VERITAS Survey of the Cygnus Region of the Galactic Plane
astro-ph.HE astro-ph.GA
The Cygnus region of the Galactic plane contains many known supernova
remnants, pulsars, X-ray and GeV gamma-ray emitters which make it a prime
candidate for a Very High Energy (VHE) gamma-ray survey in the Northern
Hemisphere. The VERITAS observatory, an array of four atmospheric Cherenkov
telescopes located at the base of Mt. Hopkins in southern Arizona, USA, has
carried out an extensive survey of the Cygnus region between 67 and 82 degrees
in galactic longitude and between -1 and 4 degrees in galactic latitude. The
survey, comprising more than 140 hours of observations, reaches an average VHE
flux sensitivity of better than 4% of the Crab Nebula at energies above 200
GeV. Here we report on the preliminary results from this survey.
| arxiv topic:astro-ph.HE astro-ph.GA |
arxiv_dataset-1377907.5535 | Dissipative dynamics of a qubit coupled to a nonlinear oscillator
quant-ph
We consider the dissipative dynamics of a qubit coupled to a nonlinear
oscillator (NO) embedded in an Ohmic environment. By treating the nonlinearity
up to first order and applying Van Vleck perturbation theory up to second order
in the qubit-NO coupling, we derive an analytical expression for the
eigenstates and eigenfunctions of the coupled qubit-NO system beyond the
rotating wave approximation. In the regime of weak coupling to the thermal
bath, analytical expressions for the time evolution of the qubit's populations
are derived: they describe a multiplicity of damped oscillations superposed to
a complex relaxation part toward thermal equilibrium. The long time dynamics is
characterized by a single relaxation rate, which is maximal when the qubit is
tuned to one of the resonances with the nonlinear oscillator.
| arxiv topic:quant-ph |
arxiv_dataset-1378908.0029 | Minimal period estimates for brake orbits of nonlinear symmetric
Hamiltonian systems
math.DS math.CA
In this paper, we consider the minimal period estimates for brake orbits of
nonlinear symmetric Hamiltonian systems. We prove that if the Hamiltonian
function $H\in C^2(\Bbb R^{2n}, \Bbb R)$ is super-quadratic and convex, for
every number $\tau>0$, there exists at least one $\tau$-periodic brake orbit
$(\tau,x)$ with minimal period $\tau$ or $\tau/2$ provided $H(Nx)=H(x)$.
| arxiv topic:math.DS math.CA |
arxiv_dataset-1379908.0129 | A stochastic min-driven coalescence process and its hydrodynamical limit
math.PR
A stochastic system of particles is considered in which the sizes of the
particles increase by successive binary mergers with the constraint that each
coagulation event involves a particle with minimal size. Convergence of a
suitably renormalised version of this process to a deterministic hydrodynamical
limit is shown and the time evolution of the minimal size is studied for both
deterministic and stochastic models.
| arxiv topic:math.PR |
arxiv_dataset-1380908.0229 | Bidirectional Single-Electron Counting and the Fluctuation Theorem
cond-mat.mes-hall cond-mat.stat-mech
We investigate theoretically and experimentally the full counting statistics
of bidirectional single-electron tunneling through a double quantum dot in a
GaAs/GaAlAs heterostructure and compare with predictions of the fluctuation
theorem (FT) for Markovian stochastic processes. We observe that the quantum
point contact electrometer used to study the transport induces nonequilibrium
shot noise and dot-level fluctuations and strongly modifies the tunneling
statistics. As a result, the FT appears to be violated. We show that it is
satisfied if the back-action of the electrometer is taken into account, and we
provide a quantitative estimate of this effect.
| arxiv topic:cond-mat.mes-hall cond-mat.stat-mech |
arxiv_dataset-1381908.0329 | On an Expansion Method for Black Hole Quasinormal Modes and Regge Poles
gr-qc
We present a new method for determining the frequencies and wavefunctions of
black hole quasinormal modes (QNMs) and Regge poles. The key idea is a novel
ansatz for the wavefunction, which relates the high-$l$ wavefunctions to null
geodesics which start at infinity and end in perpetual orbit on the photon
sphere. Our ansatz leads naturally to the expansion of QNMs in inverse powers
of angular momentum $L = l + 1/2$ (in 4D), and to the expansion of Regge poles
in inverse powers of frequency. The expansions can be taken to high orders. We
begin by applying the method to the Schwarzschild spacetime, and validate our
results against existing numerical and WKB methods. Next, we generalise the
method to treat static spherically-symmetric spacetimes of arbitrary spatial
dimension. We confirm that, at lowest order, the real and imaginary components
of the QNM frequency are related to the orbital frequency and the Lyapunov
exponent for geodesics at the unstable orbit. We apply the method to five
spacetimes of current interest, and conclude with a discussion of the
advantages and limitations of the new approach, and its practical applications.
| arxiv topic:gr-qc |
arxiv_dataset-1382908.0429 | The early evolution of the H-free process
math.CO
The H-free process, for some fixed graph H, is the random graph process
defined by starting with an empty graph on n vertices and then adding edges one
at a time, chosen uniformly at random subject to the constraint that no H
subgraph is formed. Let G be the random maximal H-free graph obtained at the
end of the process. When H is strictly 2-balanced, we show that for some c>0,
with high probability as $n \to \infty$, the minimum degree in G is at least
$cn^{1-(v_H-2)/(e_H-1)}(\log n)^{1/(e_H-1)}$. This gives new lower bounds for
the Tur\'an numbers of certain bipartite graphs, such as the complete bipartite
graphs $K_{r,r}$ with $r \ge 5$. When H is a complete graph $K_s$ with $s \ge
5$ we show that for some C>0, with high probability the independence number of
G is at most $Cn^{2/(s+1)}(\log n)^{1-1/(e_H-1)}$. This gives new lower bounds
for Ramsey numbers R(s,t) for fixed $s \ge 5$ and t large. We also obtain new
bounds for the independence number of G for other graphs H, including the case
when H is a cycle. Our proofs use the differential equations method for random
graph processes to analyse the evolution of the process, and give further
information about the structure of the graphs obtained, including asymptotic
formulae for a broad class of subgraph extension variables.
| arxiv topic:math.CO |
arxiv_dataset-1383908.0529 | Sub-Saturn Planet MOA-2008-BLG-310Lb: Likely To Be In The Galactic Bulge
astro-ph.EP astro-ph.GA
We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and
argue that it is the strongest candidate yet for a bulge planet. Deviations
from the single-lens fit are smoothed out by finite-source effects and so are
not immediately apparent from the light curve. Nevertheless, we find that a
model in which the primary has a planetary companion is favored over the
single-lens model by \Delta\chi^2 ~ 880 for an additional three degrees of
freedom. Detailed analysis yields a planet/star mass ratio
q=(3.3+/-0.3)x10^{-4} and an angular separation between the planet and star
within 10% of the angular Einstein radius. The small angular Einstein radius,
\theta_E=0.155+/-0.011 mas, constrains the distance to the lens to be D_L>6.0
kpc if it is a star (M_L>0.08 M_sun). This is the only microlensing exoplanet
host discovered so far that must be in the bulge if it is a star. By analyzing
VLT NACO adaptive optics images taken near the baseline of the event, we detect
additional blended light that is aligned to within 130 mas of the lensed
source. This light is plausibly from the lens, but could also be due to a
companion to lens or source, or possibly an unassociated star. If the blended
light is indeed due to the lens, we can estimate the mass of the lens,
M_L=0.67+/-0.14 M_sun, planet mass m=74+/-17 M_Earth, and projected separation
between the planet and host, 1.25+/-0.10 AU, putting it right on the "snow
line". If not, then the planet has lower mass, is closer to its host and is
colder. To distinguish among these possibilities on reasonable timescales would
require obtaining Hubble Space Telescope images almost immediately, before the
source-lens relative motion of \mu=5 mas yr^{-1} causes them to separate
substantially.
| arxiv topic:astro-ph.EP astro-ph.GA |
arxiv_dataset-1384908.0629 | Constraints on background torsion from birefringence of CMB polarization
astro-ph.CO gr-qc
We show that a non-minimal coupling of electromagnetism with background
torsion can produce birefringence of the electromagnetic waves. This
birefringence gives rise to a B-mode polarization of the CMB. From the bounds
on B-mode from WMAP and BOOMERanG data, one can put limits on the background
torsion at $\xi_{1}T_{1}=(-3.35 \pm 2.65) \times 10^{-22} GeV^{-1}$.
| arxiv topic:astro-ph.CO gr-qc |
arxiv_dataset-1385908.0729 | Confluent operator algebras and the closability property
math.FA math.OA
Certain operator algebras A on a Hilbert space have the property that every
densely defined linear transformation commuting with A is closable. Such
algebras are said to have the closability property. They are important in the
study of the transitive algebra problem. More precisely, if A is a
two-transitive algebra with the closability property, then A is dense in the
algebra of all bounded operators, in the weak operator topology. In this paper
we focus on algebras generated by a completely nonunitary contraction, and
produce several new classes of algebras with the closability property. We show
that this property follows from a certain strict cyclicity property, and we
give very detailed information on the class of completely nonunitary
contractions satisfying this property, as well as a stronger property which we
call confluence.
| arxiv topic:math.FA math.OA |
arxiv_dataset-1386908.0829 | Revival-collapse phenomenon in the fluctuations of quadrature field
components of the multiphoton Jaynes-Cummings model
quant-ph
In this paper we consider a system consisting of a two-level atom, initially
prepared in a coherent superposition of upper and lower levels, interacting
with a radiation field prepared in generalized quantum states in the framework
of multiphoton Jaynes-Cummings model. For this system we show that there is a
class of states for which the fluctuation factors can exhibit revival-collapse
phenomenon (RCP) similar to that exhibited in the corresponding atomic
inversion. This is shown not only for normal fluctuations but also for
amplitude-squared fluctuations. Furthermore, apart from this class of states we
generally demonstrate that the fluctuation factors associated with three-photon
transition can provide RCP similar to that occurring in the atomic inversion of
the one-photon transition. These are novel results and their consequence is
that RCP occurred in the atomic inversion can be measured via a homodyne
detector. Furthermore, we discuss the influence of the atomic relative phases
on such phenomenon.
| arxiv topic:quant-ph |
arxiv_dataset-1387908.0929 | Homomorphisms between Kaehler groups
math.AG math.DG
This is partly a survey and partly a research article. Some known results and
open problems about Kaehler groups (fundamental groups of compact Kaehler
manifolds) are discussed. A new notion of Kaehler homomorphism is introduced.
This is a homomorphism induced by a holomorphic map between these types of
manifolds. Some obstructions for a homomorphism to be Kaehler are discussed.
Among these is the main result on the vanishing of a certain cohomology class
associated to such map. This is reduced to the decomposition theorem for
perverse sheaves suitably extended to Kaehler orbifolds.
| arxiv topic:math.AG math.DG |
arxiv_dataset-1388908.1029 | Non-linear pulsations in Wolf-Rayet stars
astro-ph.SR
Numerical simulations of the evolution of strange-mode instabilities into the
non-linear regime have been performed for a wide range of stellar parameters
for Wolf-Rayet stars. It has been shown that the Wolf-Rayet models reach radial
velocities which amount to up to 30% of their escape velocity. The acoustic
luminosities suggest a connection to the observed mass loss. Most of the models
show a jump in the mean effective temperature after reaching the non-linear
regime. This jump is related to the run of the opacity.
| arxiv topic:astro-ph.SR |
arxiv_dataset-1389908.1129 | Finite-time Lagrangian transport analysis: Stable and unstable manifolds
of hyperbolic trajectories and finite-time Lyapunov exponents
nlin.CD physics.ao-ph physics.flu-dyn
We consider issues associated with the Lagrangian characterisation of flow
structures arising in aperiodically time-dependent vector fields that are only
known on a finite time interval. A major motivation for the consideration of
this problem arises from the desire to study transport and mixing problems in
geophysical flows where the flow is obtained from a numerical solution, on a
finite space-time grid, of an appropriate partial differential equation model
for the velocity field. Of particular interest is the characterisation,
location, and evolution of "transport barriers" in the flow, i.e. material
curves and surfaces. We argue that a general theory of Lagrangian transport has
to account for the effects of transient flow phenomena which are not captured
by the infinite-time notions of hyperbolicity even for flows defined for all
time. Notions of finite-time hyperbolic trajectories, their finite time stable
and unstable manifolds, as well as finite-time Lyapunov exponent (FTLE) fields
and associated Lagrangian coherent structures have been the main tools for
characterizing transport barriers in the time-aperiodic situation. In this
paper we consider a variety of examples, some with explicit solutions, that
illustrate, in a concrete manner, the issues and phenomena that arise in the
setting of finite-time dynamical systems. Of particular significance for
geophysical applications is the notion of "flow transition" which occurs when
finite-time hyperbolicity is lost, or gained. The phenomena discovered and
analysed in our examples point the way to a variety of directions for rigorous
mathematical research in this rapidly developing, and important, new area of
dynamical systems theory.
| arxiv topic:nlin.CD physics.ao-ph physics.flu-dyn |
arxiv_dataset-1390908.1229 | On Batalin-Vilkovisky Formalism of Non-Commutative Field Theories
hep-th
We apply the BV formalism to non-commutative field theories, introduce BRST
symmetry, and gauge-fix the models. Interestingly, we find that treating the
full gauge symmetry in non-commutative models can lead to reducible gauge
algebras. As one example we apply the formalism to the Connes-Lott two-point
model. Finally, we offer a derivation of a superversion of the
Harish-Chandra-Itzykson-Zuber integral.
| arxiv topic:hep-th |
arxiv_dataset-1391908.1329 | Charged impurity scattering in bilayer graphene
cond-mat.mes-hall
We have examined the impact of charged impurity scattering on charge carrier
transport in bilayer graphene (BLG) by deposition of potassium in ultra-high
vacuum at low temperature. Charged impurity scattering gives a conductivity
which is supra-linear in carrier density, with a magnitude similar to
single-layer graphene for the measured range of carrier densities of 2-4 x
10^12 cm^-2. Upon addition of charged impurities of concentration n_imp, the
minimum conductivity Sigma_min decreases proportional to n_imp^-1/2, while the
electron and hole puddle carrier density increases proportional to n_imp^1/2.
These results for the intentional deposition of potassium on BLG are in good
agreement with theoretical predictions for charged impurity scattering.
However, our results also suggest that charged impurity scattering alone cannot
explain the observed transport properties of pristine BLG on SiO2 before
potassium doping.
| arxiv topic:cond-mat.mes-hall |
arxiv_dataset-1392908.1429 | Dark Matter as a Possible New Energy Source for Future Rocket Technology
astro-ph.CO hep-ph
Current rocket technology can not send the spaceship very far, because the
amount of the chemical fuel it can take is limited. We try to use dark matter
(DM) as fuel to solve this problem. In this work, we give an example of DM
engine using dark matter annihilation products as propulsion. The acceleration
is proportional to the velocity, which makes the velocity increase
exponentially with time in non-relativistic region. The important points for
the acceleration are how dense is the DM density and how large is the
saturation region. The parameters of the spaceship may also have great
influence on the results. We show that the (sub)halos can accelerate the
spaceship to velocity $ 10^{- 5} c \sim 10^{- 3} c$. Moreover, in case there is
a central black hole in the halo, like the galactic center, the radius of the
dense spike can be large enough to accelerate the spaceship close to the speed
of light.
| arxiv topic:astro-ph.CO hep-ph |
arxiv_dataset-1393908.1529 | The GammeV suite of experimental searches for axion-like particles
hep-ex physics.ins-det
We report on the design and results of the GammeV search for axion-like
particles and for chameleon particles. We also discuss plans for an improved
experiment to search for chameleon particles, one which is sensitive to both
cosmological and power-law chameleon models. Plans for an improved axion-like
particle search using coupled resonant cavities are also presented. This
experiment will be more sensitive to axion-like particles than stellar
astrophysical models or current helioscope experiments.
| arxiv topic:hep-ex physics.ins-det |
arxiv_dataset-1394908.1629 | MMTF: The Maryland-Magellan Tunable Filter
astro-ph.IM
This paper describes the Maryland-Magellan Tunable Filter (MMTF) on the
Magellan-Baade 6.5-meter telescope. MMTF is based on a 150-mm clear aperture
Fabry-Perot (FP) etalon that operates in low orders and provides transmission
bandpass and central wavelength adjustable from ~5 to ~15 A and from ~5000 to
over ~9200 A, respectively. It is installed in the Inamori Magellan Areal
Camera and Spectrograph (IMACS) and delivers an image quality of ~0.5" over a
field of view of 27' in diameter (monochromatic over ~10'). This versatile and
easy-to-operate instrument has been used over the past three years for a wide
variety of projects. This paper first reviews the basic principles of FP
tunable filters, then provides a detailed description of the hardware and
software associated with MMTF and the techniques developed to observe with this
instrument and reduce the data. The main lessons learned in the course of the
commissioning and implementation of MMTF are highlighted next, before
concluding with a brief outlook on the future of MMTF and of similar facilities
which are soon coming on line.
| arxiv topic:astro-ph.IM |
arxiv_dataset-1395908.1729 | Neptune migration model with one extra planet
astro-ph.EP
We explore conventional Neptune migration model with one additional planet of
mass at 0.1-2.0 Me. This planet inhabited in the 3:2 mean motion resonance with
Neptune during planet migration epoch, and then escaped from the Kuiper belt
when Jovian planets parked near the present orbits. Adding this extra planet
and assuming the primordial disk truncated at about 45 AU in the conventional
Neptune migration model, it is able to explain the complex structure of the
observed Kuiper belt better than the usual Neptune migration model did in
several respects. However, numerical experiments imply that this model is a
low-probability event. In addition to the low probability, two features
produced by this model may be inconsistent with the observations. They are
small number of low-inclination particles in the classical belt, and the
production of a remnant population with near-circular and low-inclination orbit
within a = 50-52 AU. According to our present study, including one extra planet
in the conventional Neptune migration model as the scenario we explored here
may be unsuitable because of the low probability, and the two drawbacks
mentioned above, although this model can explain better several features which
is hard to produce by the conventional Neptune migration model. The issues of
low-probability event and the lack of low-inclination KBOs in the classical
belt are interesting and may be studied further under a more realistic
consideration.
| arxiv topic:astro-ph.EP |
arxiv_dataset-1396908.1829 | Single photon interference between two modes originated from a single
quantum dot
cond-mat.mes-hall cond-mat.mtrl-sci
Interference of a single photon generated from a single quantum dot is
observed between two photon polarization modes. Each emitted single photon has
two orthogonal polarization modes associated with the solid-state single photon
source, in which two non-degenerate neutral exciton states are involved. The
interference between the two modes takes place only under the condition that
the emitted photon is free from which-mode information.
| arxiv topic:cond-mat.mes-hall cond-mat.mtrl-sci |
arxiv_dataset-1397908.1929 | All speed scheme for the low mach number limit of the Isentropic Euler
equation
math-ph math.MP
An all speed scheme for the Isentropic Euler equation is presented in this
paper. When the Mach number tends to zero, the compressible Euler equation
converges to its incompressible counterpart, in which the density becomes a
constant. Increasing approximation errors and severe stability constraints are
the main difficulty in the low Mach regime. The key idea of our all speed
scheme is the special semi-implicit time discretization, in which the low Mach
number stiff term is divided into two parts, one being treated explicitly and
the other one implicitly. Moreover, the flux of the density equation is also
treated implicitly and an elliptic type equation is derived to obtain the
density. In this way, the correct limit can be captured without requesting the
mesh size and time step to be smaller than the Mach number. Compared with
previous semi-implicit methods, nonphysical oscillations can be suppressed. We
develop this semi-implicit time discretization in the framework of a first
order local Lax-Friedrich (LLF) scheme and numerical tests are displayed to
demonstrate its performances.
| arxiv topic:math-ph math.MP |
arxiv_dataset-1398908.2029 | Yet another proof from the Book: the Gauss theorem on regular polygons
math.HO math.AC
This note is purely expository. The statement of the Gauss theorem on the
constructibility of regular polygons by means of compass and ruler is simple
and well-known. However, its proofs given in most textbooks rely upon much
unmotivated material and are far from being economic. In this note a short
elementary proof of the Gauss theorem is presented. The note is accessible for
students familiar with polynomials and complex numbers, and could be an
interesting easy reading for professional mathematicians.
| arxiv topic:math.HO math.AC |
arxiv_dataset-1399908.2129 | On the role of the magnetic field on jet emission in X-ray binaries
astro-ph.HE
Radio and X-ray fluxes of accreting black holes in their hard state are known
to correlate over several orders of magnitude. This correlation however shows a
large scatter: black hole candidates with very similar X-ray luminosity,
spectral energy distribution and variability, show rather different radio
luminosities. This challenges theoretical models that aim at describing both
the radio and the X-ray fluxes in terms of radiative emission from a
relativistic jet. More generally, it opens important questions on how similar
accretion flows can produce substantially different outflows. Here we present a
possible explanation for this phenomenon, based on the strong dependency of the
jet spectral energy distribution on the magnetic field strength, and on the
idea that the strength of the jet magnetic field varies from source to source.
Because of the effect of radiative losses, sources with stronger jet magnetic
field values would have lower radio emission. We discuss the implications of
this scenario, the main one being that the radio flux does not necessarily
provide a direct measure of the jet power. We further discuss how a variable
jet magnetic field, reaching a critical value, can qualitatively explain the
observed spectral transition out of the hard state.
| arxiv topic:astro-ph.HE |
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