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2003-08-19
|
Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors
|
We describe a theory of Mn local-moment magnetization relaxation due to p-d
kinetic-exchange coupling with the itinerant-spin subsystem in the
ferromagnetic semiconductor (Ga,Mn)As alloy. The theoretical Gilbert damping
coefficient implied by this mechanism is calculated as a function of Mn moment
density, hole concentration, and quasiparticle lifetime. Comparison with
experimental ferromagnetic resonance data suggests that in annealed strongly
metallic samples, p-d coupling contributes significantly to the damping rate of
the magnetization precession at low temperatures. By combining the theoretical
Gilbert coefficient with the values of the magnetic anisotropy energy, we
estimate that the typical critical current for spin-transfer magnetization
switching in all-semiconductor trilayer devices can be as low as $\sim 10^{5}
{\rm A cm}^{-2}$.
|
0308386v3
|
2003-09-18
|
Memory-function approach to the normal-state optical properties of the Bechgaard salt (TMTSF)_2PF_6
|
The gauge invariant, two-component optical conductivity model, with a
correlation gap structure related to the umklapp scattering processes, is
applied to the quasi-one-dimensional electronic systems and compared to the
recent measurements on the Bechgaard salt (TMTSF)_2PF_6. The optical response
of both the insulating and metallic state is found for the half-filled
conduction band, depending on the ratio between the correlation energy scale 2
\Delta^0_2 and the transfer integral in the direction perpendicular to the
conducting chains, t_{{\rm b}'}. The estimated value 2 \Delta^0_2/t_{{\rm b}'}
agrees reasonably well with the previous experimental and theoretical
conclusions. Parallel to the chains the thermally activated conduction
electrons in the insulating state are found to exhibit an universal behaviour,
accounting for the observed single-particle optical conductivity of the ordered
ground state of charge-density-wave systems. The band parameters and the
related damping energies suitable to the normal metallic state of (TMTSF)_2PF_6
are estimated from the measured spectra. Not only the spectral weights but also
the damping energies clearly indicate an opening of the correlation gap in the
charge excitation spectrum
|
0309419v1
|
2003-10-03
|
Effects of electrostatic fields and Casimir force on cantilever vibrations
|
The effect of an external bias voltage and fluctuating electromagnetic fields
on both the fundamental frequency and damping of cantilever vibrations is
considered. An external voltage induces surface charges causing
cantilever-sample electrostatic attraction. A similar effect arises from
charged defects in dielectrics that cause spatial fluctuations of electrostatic
fields. The cantilever motion results in charge displacements giving rise to
Joule losses and damping. It is shown that the dissipation increases with
decreasing conductivity and thickness of the substrate, a result that is
potentially useful for sample diagnostics. Fluctuating electromagnetic fields
between the two surfaces also induce attractive (Casimir) forces. It is shown
that the shift in the cantilever fundamental frequency due to the Casimir force
is close to the shift observed in recent experiments of Stipe et al. Both the
electrostatic and Casimir forces have a strong effect on the cantilever
eigenfrequencies, and both effects depend on the geometry of the cantilever
tip. We consider cylindrical, spherical, and ellipsoidal tips moving parallel
to a flat sample surface. The dependence of the cantilever effective mass and
vibrational frequencies on the geometry of the tip is studied both numerically
and analytically.
|
0310081v1
|
2003-10-07
|
Precessional switching of thin nanomagnets: analytical study
|
We study analytically the precessional switching of the magnetization of a
thin macrospin. We analyze its response when subjected to an external field
along its in-plane hard axis. We derive the exact trajectories of the
magnetization. The switching versus non switching behavior is delimited by a
bifurcation trajectory, for applied fields equal to half of the effective
anisotropy field. A magnetization going through this bifurcation trajectory
passes exactly along the hard axis and exhibits a vanishing characteristic
frequency at that unstable point, which makes the trajectory noise sensitive.
Attempting to approach the related minimal cost in applied field makes the
magnetization final state unpredictable. We add finite damping in the model as
a perturbative, energy dissipation factor. For a large applied field, the
system switches several times back and forth. Several trajectories can be gone
through before the system has dissipated enough energy to converge to one
attracting equilibrium state. For some moderate fields, the system switches
only once by a relaxation dominated precessional switching. We show that the
associated switching field increases linearly with the damping parameter. The
slope scales with the square root of the effective anisotropy. Our simple
concluding expressions are useful to assess the potential application of
precessional switching in magnetic random access memories.
|
0310147v1
|
2003-11-27
|
Temperature dependent Bogoliubov approximation in the classical fields approach to weakly interacting Bose gas
|
A classical fields approximation to the finite temperature microcanonical
thermodynamics of weakly interacting Bose gas is applied to the idealized case
of atoms confined in a box with periodic boundary conditions. We analyze in
some detail the microcanonical temperature in the model. We also analyze the
spectral properties of classical amplitudes of the plane waves -- the
eigenmodes of the time averaged one--particle density matrix. Looking at the
zero momentum component -- the order parameter of the condensate, we obtain the
nonperturbative results for the chemical potential. Analogous analysis of the
other modes yields nonperturbative temperature dependent Bogoliubov frequencies
and their damping rates. Damping rates are linear functions of momenta in the
phonon range and show more complex behavior for the particle sector. Where
available, we make comparison with the analytic estimates of these quantities.
|
0311622v1
|
2003-12-29
|
Plasmon attenuation and optical conductivity of a two-dimensional electron gas
|
In a ballistic two-dimensional electron gas, the Landau damping does not lead
to plasmon attenuation in a broad interval of wave vectors q << k_F. Similarly,
it does not contribute to the optical conductivity \sigma (\omega, q) in a wide
domain of its arguments, E_F > \omega > qv_F, where E_F, k_F and v_F are,
respectively, the Fermi energy, wavevector and velocity of the electrons. We
identify processes that result in the plasmon attenuation in the absence of
Landau damping. These processes are: the excitation of two electron-hole pairs,
phonon-assisted excitation of one pair, and a direct plasmon-phonon conversion.
We evaluate the corresponding contributions to the plasmon linewidth and to the
optical conductivity.
|
0312684v3
|
2004-02-03
|
First-principles study of magnetization relaxation enhancement and spin-transfer in thin magnetic films
|
The interface-induced magnetization damping of thin ferromagnetic films in
contact with normal-metal layers is calculated from first principles for clean
and disordered Fe/Au and Co/Cu interfaces. Interference effects arising from
coherent scattering turn out to be very small, consistent with a very small
magnetic coherence length. Because the mixing conductances which govern the
spin transfer are to a good approximation real valued, the spin pumping can be
described by an increased Gilbert damping factor but an unmodified gyromagnetic
ratio. The results also confirm that the spin-current induced magnetization
torque is an interface effect.
|
0402088v2
|
2004-03-05
|
Mode-coupling theory and molecular dynamics simulation for heat conduction in a chain with transverse motions
|
We study heat conduction in a one-dimensional chain of particles with
longitudinal as well as transverse motions. The particles are connected by
two-dimensional harmonic springs together with bending angle interactions. The
problem is analyzed by mode-coupling theory and compared with molecular
dynamics. We find very good, quantitative agreement for the damping of modes
between a full mode-coupling theory and molecular dynamics result, and a
simplified mode-coupling theory gives qualitative description of the damping.
The theories predict generically that thermal conductance diverges as N^{1/3}
as the size N increases for systems terminated with heat baths at the ends. The
N^{2/5} dependence is also observed in molecular dynamics which we attribute to
crossover effect.
|
0403162v1
|
2004-03-21
|
Evidence for Superfluidity in a Resonantly Interacting Fermi Gas
|
We observe collective oscillations of a trapped, degenerate Fermi gas of
$^6$Li atoms at a magnetic field just above a Feshbach resonance, where the
two-body physics does not support a bound state. The gas exhibits a radial
breathing mode at a frequency of 2837(05) Hz, in excellent agreement with the
frequency of $\nu_H\equiv\sqrt{10\nu_x\nu_y/3}=2830(20)$ Hz predicted for a
{\em hydrodynamic} Fermi gas with unitarity limited interactions. The measured
damping times and frequencies are inconsistent with predictions for both the
collisionless mean field regime and for collisional hydrodynamics. These
observations provide the first evidence for superfluid hydrodynamics in a
resonantly interacting Fermi gas.
|
0403540v2
|
2004-03-22
|
Parametric Driving of Dark Solitons in Atomic Bose-Einstein Condensates
|
A dark soliton oscillating in an elongated harmonically-confined atomic
Bose-Einstein condensate continuously exchanges energy with the sound field.
Periodic optical `paddles' are employed to controllably enhance the sound
density and transfer energy to the soliton, analogous to parametric driving. In
the absence of damping, the amplitude of the soliton oscillations can be
dramatically reduced, whereas with damping, a driven soliton equilibrates as a
stable dark soliton with lower energy, thereby extending the soliton lifetime
up to the lifetime of the condensate.
|
0403566v2
|
2004-04-09
|
Network-Induced Oscillatory Behavior in Material Flow Networks
|
Network theory is rapidly changing our understanding of complex systems, but
the relevance of topological features for the dynamic behavior of metabolic
networks, food webs, production systems, information networks, or cascade
failures of power grids remains to be explored. Based on a simple model of
supply networks, we offer an interpretation of instabilities and oscillations
observed in biological, ecological, economic, and engineering systems. We find
that most supply networks display damped oscillations, even when their units -
and linear chains of these units - behave in a non-oscillatory way. Moreover,
networks of damped oscillators tend to produce growing oscillations. This
surprising behavior offers, for example, a new interpretation of business
cycles and of oscillating or pulsating processes. The network structure of
material flows itself turns out to be a source of instability, and cyclical
variations are an inherent feature of decentralized adjustments.
|
0404226v1
|
2004-04-28
|
Dynamics of the Electro-Reflective Response of TaS3
|
We have observed a large (~1%) change in infrared reflectance of the
charge-density-wave (CDW) conductor, orthorhombic TaS3, when its CDW is
depinned. The change is concentrated near one current contact. Assuming that
the change in reflectance is proportional to the degree of CDW polarization, we
have studied the dynamics of CDW repolarization through position dependent
measurements of the variation of the electro-reflectance with the frequency of
square wave voltages applied to the sample, and have found that the response
could be characterized as a damped harmonic oscillator with a distribution of
relaxation (i.e. damping) times. The average relaxation time, which increases
away from the contacts, varies with applied voltage as t0 ~ 1/V^p with p ~ 3/2,
but the distribution of times broadens as the voltage approaches the depinning
threshold. Very low resonant frequencies (~ 1 kHz) indicate a surprisingly
large amount of inertia, which is observable in the time dependence of the
change in reflectance as a polarity dependent delay of ~ 100 microsec.
|
0404690v1
|
2004-05-06
|
Damping of the de Haas-van Alphen oscillations in the superconducting state of MgB_2
|
The de Haas-van Alphen (dHvA) signal arising from orbits on the $\pi$ Fermi
surface sheet of the two-gap superconductor MgB$_2$ has been observed in the
vortex state below $H_{c2}$. An extra attenuation of the dHvA signal, beyond
those effects described in the conventional Lifshitz-Kosevich expression, is
seen due to the opening of the superconducting gap. Our data show that the
$\pi$ band gap is still present up to $H_{c2}$. The data are compared to
current theories of dHvA oscillations in the superconducting state which allow
us to extract estimates for the evolution of the $\pi$ band gap with magnetic
field. Contrary to results for other materials, we find that the most recent
theories dramatically underestimate the damping in MgB$_2$.
|
0405120v1
|
2004-05-26
|
Magnetic droplets in a metal close to a ferromagnetic quantum critical point
|
Using analytical and path integral Monte Carlo methods, we study the
susceptibility $\chi_{dc}(T)$ of a spin-S impurity with XY rotational symmetry
embedded in a metal. Close to a ferromagnetic quantum critical point, the
impurity polarizes conduction electrons in its vicinity and forms a large
magnetic droplet with moment M>>S. At not too low temperatures, the strongly
damping paramagnon modes of the conduction electrons suppress large quantum
fluctuations (or spin flips) of this droplet. We show that the susceptibility
follows the law $\chi_{dc}(T)=(M^{2}/T)[1-(\pi g)^{-1}\ln(gE_{0}/T)]$, where
the parameter g>>1 describes the strong damping by conduction electrons, and
E_0 is the bandwidth of paramagnon modes. At exponentially low temperatures T
<< T_{*} ~ E_{0}\exp(-\pi g/2) we show that spin flips cannot be ignored. In
this regime we find that $\chi_{dc}(T) \approx \chi_{dc}(0)
[1-(2/3)(T/T_{*})^2]$, where $\chi_{dc}(0)\sim M^{2}/T_{*}$ is finite and
exponentially large in g. We also discuss these effects in the context of the
multi-channel Kondo impurity model.
|
0405618v2
|
2004-06-29
|
Pairing gaps in atomic gases at the BCS-BEC crossover
|
Strong evidence for pairing and superfluidity has recently been found in
atomic Fermi gases at the BCS-BEC crossover both in collective modes and RF
excitation energies. It is argued that the scale for the effective pairing gaps
measured in RF experiments is set by the lowest quasiparticle in-gap excitation
energies. These are calculated at the BCS-BEC crossover from semiclassical
solutions to the Bogoliubov-deGennes equations. The strong damping of the
radial breathing mode observed in the BCS limit occur when the lowest
quasiparticle excitation energies coincide with the radial frequency, which
indicates that a coupling between them take place.
|
0406714v3
|
2004-08-26
|
Decoherence of Rabi oscillations in a single quantum dot
|
We develop a realistic model of Rabi oscillations in a quantum-dot
photodiode. Based in a multi-exciton density matrix formulation we show that
for short pulses the two-level models fails and higher levels should be taken
into account. This affects some of the experimental conclusions, such as the
inferred efficiency of the state rotation (population inversion) and the
deduced value of the dipole interaction. We also show that the damping observed
cannot be explained using \emph{constant} rates with fixed pulse duration. We
demonstrate that the damping observed is in fact induced by an off-resonant
excitation to or from the continuum of wetting layer states. Our model
describes the nonlinear decoherence behavior observed in recent experiments.
|
0408570v2
|
2004-08-28
|
Breakdown of Hydrodynamics in the Radial Breathing Mode of a Strongly-Interacting Fermi Gas
|
We measure the magnetic field dependence of the frequency and damping time
for the radial breathing mode of an optically trapped, Fermi gas of $^6$Li
atoms near a Feshbach resonance. The measurements address the apparent
discrepancy between the results of Kinast et al., [Phys. Rev. Lett. {\bf 92},
150402 (2004)] and those of Bartenstein et al., [Phys. Rev. Lett. {\bf 92},
203201 (2004)]. Over the range of magnetic field from 770 G to 910 G, the
measurements confirm the results of Kinast et al. Close to resonance, the
measured frequencies are in excellent agreement with predictions for a unitary
hydrodynamic gas. At a field of 925 G, the measured frequency begins to
decrease below predictions. For fields near 1080 G, we observe a breakdown of
hydrodynamic behavior, which is manifested by a sharp increase in frequency and
damping rate. The observed breakdown is in qualitative agreement with the sharp
transition observed by Bartenstein et al., at 910 G.
|
0408634v2
|
2004-10-01
|
Magnetic Properties of Cuprate Perovskites
|
The magnetic susceptibility of underdoped yttrium and lanthanum cuprates is
interpreted based on the self-consistent solution of the t-J model of a Cu-O
plane. The calculations reproduce correctly the frequency dependencies of the
susceptibility in YBa2Cu3O_{7-y} and La_{2-x}Sr_xCuO4 attributing their
dissimilarity to the difference in the damping of spin excitations. In
YBa2Cu3O_{7-y} these excitations are well defined at the antiferromagnetic wave
vector Q=(\pi,\pi) even in the normal state which manifests itself in a
pronounced maximum -- the resonance peak -- in the susceptibility. In
La_{2-x}Sr_xCuO4 the spin excitations are overdamped which leads to a broad
low-frequency feature in the susceptibility. The low-frequency
incommensurability in the magnetic response is attributed to a dip in the
magnon damping at Q. The calculated concentration and temperature dependencies
of the incommensurability parameter conform with experimental observations.
Generally the incommensurate magnetic response is not accompanied with an
inhomogeneity of the carrier density.
|
0410009v1
|
2004-11-12
|
Microwave induced resistance oscillations on a high-mobility 2DEG: absorption/reflection and temperature damping experiments
|
In this work we address experimentally a number of unresolved issues related
to microwave induced resistance oscillations (MIRO) and the zero-resistance
states observed recently on very high-mobility 2D electron gases in GaAs/AlGaAs
heterostructures. In particular, we examine electrodynamic effects via
reflection/absorption experiments and study the exact waveform of MIRO and
their damping due to temperature. It is shown that electrodynamic effects due
to metallic-like reflection and plasmons are important producing a wide
cyclotron resonance line and a number of oscillations which do not coincide
with the MIRO. To describe the MIRO waveform a simple model was employed
involving radiation-induced scattering with displacement. A very good
correlation was found between the temperature dependencies of the quantum
lifetime from MIRO and the transport scattering time from the electron
mobility. The results are compared with measurements of Shubnikov-de Haas
oscillations down to 30 mK on the same sample.
|
0411338v1
|
2004-11-17
|
Path integral derivation of Bloch-Redfield equations for a qubit weakly coupled to a heat bath: Application to nonadiabatic transitions
|
Quantum information processing has greatly increased interest in the
phenomenon of environmentally-induced decoherence. The spin boson model is
widely used to study the interaction between a spin-modelling a quantum
particle moving in a double well potential-and its environment-modelled by a
heat bath of harmonic oscillators. This paper extends a previous analysis of
the static spin boson study to the driven spin boson case, with the derivation
of an exact integro-differential equation for the time evolution of the
propagator of the reduced spin density matrix. This is the first main result.
By specializing to weak damping we then obtain the next result, a set of
Bloch-Redfield equations for the equilibrium fixed spin initial condition.
Finally we show that these equations can be used to solve the classic
dissipative Landau-Zener problem and illustrate these solutions for the weak
damping case. The effect of dissipation is seen to be minimised as the speed of
passage is increased, implying that qubits need to be switched as fast as
possible.
|
0411443v1
|
2004-11-24
|
Josephson tunnel junctions with nonlinear damping for RSFQ-qubit circuit applications
|
We demonstrate that shunting of Superconductor-Insulator-Superconductor
Josephson junctions by Superconductor-Insulator-Normal metal (S-I-N) structures
having pronounced non-linear I-V characteristics can remarkably modify the
Josephson dynamics. In the regime of Josephson generation the phase behaves as
an overdamped coordinate, while in the superconducting state the damping and
current noise are strikingly small, that is vitally important for application
of such junctions for readout and control of Josephson qubits. Superconducting
Nb/AlO${_x}$/Nb junction shunted by Nb/AlO${_x}$/AuPd junction of S-I-N type
was fabricated and, in agreement with our model, exhibited non-hysteretic I-V
characteristics at temperatures down to at least 1.4 K.
|
0411607v1
|
2004-12-01
|
Reply to Millis et al. on "A Tale of Two Theories: Quantum Griffiths Effects in Metallic Systems"
|
In a recent paper (cond-mat/0411197) we showed the equivalence of two
seemingly contradictory theories on Griffiths-McCoy singularities (GMS) in
metallic antiferromagnets close to a quantum critical point (QCP). In a recent
comment, Millis {\it et al.} (cond-mat/0411738) argue that in heavy-fermion
materials the electronic damping is large leading to the freezing of locally
magnetically ordered droplets at high temperatures. In this reply we show that
this erroneous conclusion is based on a treatment of the problem of disorder
close to a QCP which is not self-consistent. We argue that a self-consistent
treatment of the ordered droplets must lead to weak damping and to a large
region of GMS behavior, in agreement with the our ealier results.
|
0412020v2
|
2005-01-04
|
On continuum modeling of sputter erosion under normal incidence: interplay between nonlocality and nonlinearity
|
Under specific experimental circumstances, sputter erosion on semiconductor
materials exhibits highly ordered hexagonal dot-like nanostructures. In a
recent attempt to theoretically understand this pattern forming process, Facsko
et al. [Phys. Rev. B 69, 153412 (2004)] suggested a nonlocal, damped
Kuramoto-Sivashinsky equation as a potential candidate for an adequate
continuum model of this self-organizing process. In this study we theoretically
investigate this proposal by (i) formally deriving such a nonlocal equation as
minimal model from balance considerations, (ii) showing that it can be exactly
mapped to a local, damped Kuramoto-Sivashinsky equation, and (iii) inspecting
the consequences of the resulting non-stationary erosion dynamics.
|
0501049v2
|
2005-01-18
|
Incommensurate spin dynamics in underdoped cuprate perovskites
|
The incommensurate magnetic response observed in normal-state cuprate
perovskites is interpreted based on the projection operator formalism and the
t-J model of Cu-O planes. In agreement with experiment the calculated
dispersion of maxima in the susceptibility has the shape of two parabolas with
upward and downward branches which converge at the antiferromagnetic wave
vector. The maxima are located at the momenta $({1/2},{1/2}\pm\delta)$,
$({1/2}\pm\delta,{1/2})$ and at $({1/2}\pm\delta,{1/2}\pm\delta)$,
$({1/2}\pm\delta,{1/2}\mp\delta)$ in the lower and upper parabolas,
respectively. The upper parabola reflects the dispersion of magnetic
excitations of the localized Cu spins, while the lower parabola arises due to a
dip in the spin-excitation damping at the antiferromagnetic wave vector. For
moderate doping this dip stems from the weakness of the interaction between the
spin excitations and holes near the hot spots. The frequency dependence of the
susceptibility is shown to depend strongly on the hole bandwidth and damping
and varies from the shape observed in YBa$_2$Cu$_3$O$_{7-y}$ to that inherent
in La$_{2-x}$Sr$_x$CuO$_4$.
|
0501418v1
|
2005-02-21
|
Velocity dependence of atomic-scale friction: a comparative study of the one- and two-dimensional Tomlinson model
|
We present a comparative analysis of the velocity dependence of atomic-scale
friction for the Tomlinson model, at zero and finite temperatures, in 1D and
2D, and for different values of the damping. Combining analytical arguments
with numerical simulations, we show that an appreciable velocity dependence of
the kinetic friction force $F_{fric}$, for small scanning velocities $v_s$
(from 1 nm/s to 2 $\mu$m/s), is inherent in the Tomlinson model. In the absence
of thermal fluctuations in the stick-slip regime, it has the form of a
power-law, $F_{fric}-F_0\propto v_s^{\beta}$ with $\beta=2/3$, irrespective of
dimensionality and value of the damping. Since thermal fluctuations enhance the
velocity dependence of friction, we provide guidelines to establish when
thermal effects are important and to which extent the surface corrugation
affects the velocity dependence.
|
0502496v1
|
2005-02-28
|
Magnetization dynamics of two interacting spins in an external magnetic field
|
The longitudinal relaxation time of the magnetization of a system of two
exchange coupled spins subjected to a strong magnetic field is calculated
exactly by averaging the stochastic Gilbert-Landau-Lifshitz equation for the
magnetization, i.e., the Langevin equation of the process, over its
realizations so reducing the problem to a system of linear
differential-recurrence relations for the statistical moments (averaged
spherical harmonics). The system is solved in the frequency domain by matrix
continued fractions yielding the complete solution of the two-spin problem in
external fields for all values of the damping and barrier height parameters.
The magnetization relaxation time extracted from the exact solution is compared
with the inverse relaxation rate from Langer's theory of the decay of
metastable states, which yields in the high barrier and intermediate-to-high
damping limits the asymptotic behaviour of the greatest relaxation time.
|
0502661v2
|
2005-03-12
|
Collective Oscillations of Strongly Correlated One-Dimensional Bosons on a Lattice
|
We study the dipole oscillations of strongly correlated 1D bosons, in the
hard-core limit, on a lattice, by an exact numerical approach. We show that far
from the regime where a Mott insulator appears in the system, damping is always
present and increases for larger initial displacements of the trap, causing
dramatic changes in the momentum distribution, $n_k$. When a Mott insulator
sets in the middle of the trap, the center of mass barely moves after an
initial displacement, and $n_k$ remains very similar to the one in the ground
state. We also study changes introduced by the damping in the natural orbital
occupations, and the revival of the center of mass oscillations after long
times.
|
0503302v2
|
2005-04-28
|
Coherence properties of bulk matter
|
We prove a theorem, using the density functional approach and relying on a
classical result by Lieb and Simon on Thomas-Fermi model, showing that in the
thermodynamic limit bulk matter is at most semiclassical and coherence
preserving. The connection between quantum fluid dynamics and density
functional theory in the formulation due to Kohn and Sham play a significant
role leading to a Vlasov-Poisson system of equations for the Wigner function.
Coherence stability is achieved by noting that small oscillations in bulk
matter are damped by Landau damping. In some conditions the initial Wigner
function could generate an opposite effect and coherence stability can be lost
involving higher order quantum effects for a macroscopic body.
|
0504768v3
|
2005-05-19
|
Harmonic Content of Strain-induced Potential Modulation in Unidirectional Lateral Superlattices
|
Detailed analysis of the commensurability oscillation (CO) has been performed
on unidirectional lateral superlattices with periods ranging from a=92 to 184
nm. Fourier analysis reveals the second (and the third) harmonics along with
the fundamental oscillation for a>=138 nm (184 nm) at low-enough temperature,
evincing the presence of corresponding harmonics in the profile of the
potential modulation. The harmonics manifest themselves in CO with demagnified
amplitude due to the low-pass filtering action of the thermal damping factor;
with a suitable consideration of the damping effect, the harmonics of the
modulation potential are found to have the amplitudes V_2 and V_3 up to roughly
30% of that of the fundamental component V_1, despite the small ratio of the
period a to the depth d = 99 nm of the two-dimensional electron gas (2DEG) from
the surface. The dependence of V_n on a indicates that the fundamental
component originates at the surface, while the higher harmonics arise from the
effect of the strain that penetrates down into subsurface. The manipulation of
high harmonics thus provides a useful technique to introduce small length-scale
modulation into high-mobility 2DEGs located deep inside the wafer.
|
0505479v1
|
2005-06-14
|
Lifetime of the first and second collective excitations in metallic nanoparticles
|
We determine the lifetime of the surface plasmon in metallic nanoparticles
under various conditions, concentrating on the Landau damping, which is the
dominant mechanism for intermediate-size particles. Besides the main
contribution to the lifetime, which smoothly increases with the size of the
particle, our semiclassical evaluation yields an additional oscillating
component. For the case of noble metal particles embedded in a dielectric
medium, it is crucial to consider the details of the electronic confinement; we
show that in this case the lifetime is determined by the shape of the
self-consistent potential near the surface. Strong enough perturbations may
lead to the second collective excitation of the electronic system. We study its
lifetime, which is limited by two decay channels: Landau damping and
ionization. We determine the size dependence of both contributions and show
that the second collective excitation remains as a well defined resonance.
|
0506320v2
|
2005-07-27
|
Dynamics of a nanomechanical resonator coupled to a superconducting single-electron transistor
|
We present an analysis of the dynamics of a nanomechanical resonator coupled
to a superconducting single electron transistor (SSET) in the vicinity of the
Josephson quasiparticle (JQP) and double Josephson quasiparticle (DJQP)
resonances. For weak coupling and wide separation of dynamical timescales, we
find that for either superconducting resonance the dynamics of the resonator is
given by a Fokker-Planck equation, i.e., the SSET behaves effectively as an
equilibrium heat bath, characterised by an effective temperature, which also
damps the resonator and renormalizes its frequency. Depending on the gate and
drain-source voltage bias points with respect to the superconducting resonance,
the SSET can also give rise to an instability in the mechanical resonator
marked by negative damping and temperature within the appropriate Fokker-Planck
equation. Furthermore, sufficiently close to a resonance, we find that the
Fokker-Planck description breaks down. We also point out that there is a close
analogy between coupling a nanomechanical resonator to a SSET in the vicinity
of the JQP resonance and Doppler cooling of atoms by means of lasers.
|
0507645v1
|
2005-08-01
|
Unexpected Effect of Internal Degrees of Freedom on Transverse Phonons in Supercooled Liquids
|
We show experimentally that in a supercooled liquid composed of molecules
with internal degrees of freedom the internal modes contribute to the frequency
dependent shear viscosity and damping of transverse phonons, which results in
an additional broadening of the transverse Brillouin lines. Earlier, only the
effect of internal modes on the frequency dependent bulk viscosity and damping
of longitudinal phonons was observed and explained theoretically in the limit
of weak coupling of internal degrees of freedom to translational motion. A new
theory is needed to describe this new effect. We also demonstrate, that the
contributions of structural relaxation and internal processes to the width of
the Brillouin lines can be separated by measurements under high pressure.
|
0508046v1
|
2005-08-05
|
Damping of vortex waves in a superfluid
|
The damping of vortex cyclotron modes is investigated within a generalized
quantum theory of vortex waves. Similarly to the case of Kelvin modes, the
friction coefficient turns out to be essentially unchanged under such
oscillations, but it is shown to be affected by appreciable memory corrections.
On the other hand, the nonequilibrium energetics of the vortex, which is
investigated within the framework of linear response theory, shows that its
memory corrections are negligible. The vortex response is found to be of the
Debye type, with a relaxation frequency whose dependence on temperature and
impurity concentration reflects the complexity of the heat bath and its
interaction with the vortex.
|
0508167v1
|
2005-08-08
|
Collective excitations of low density fermion-boson quantum-liquid mixtures
|
We investigate the collective excitations of a low temperature dilute gas
mixture that consists of a Bose-Einstein condensate and a Fermi-gas that is a
normal (i.e. non-superfluid) Fermi-liquid. We find that the BEC-mediated
fermion-fermion interactions, as a consequence of retardation, can become
repulsive and support a zero-sound mode that is essentially undamped. In
addition, we find a damped zero-sound mode that can be described as a BEC-sound
mode modified by fermion mediated boson-boson interactions, and we derive its
decay-rate caused by Landau damping. We study the mode structure of these
excitations and find avoided crossing behavior as well as a termination point.
The collective mode dynamics also reveals that phase separation sets in when
the fermion-mediated boson-boson interaction destroys the stability of the
homogeneous BEC. We estimate the time and length scales of the onset of the
phase separation, and we discuss the feasibility of experimentally probing
these consequences of mediated interactions.
|
0508207v1
|
2005-09-02
|
Inhomogeneous soliton ratchets under two ac forces
|
We extend our previous work on soliton ratchet devices [L. Morales-Molina et
al., Eur. Phys. J. B 37, 79 (2004)] to consider the joint effect of two ac
forces including non-harmonic drivings, as proposed for particle ratchets by
Savele'v et al. [Europhys. Lett. 67}, 179 (2004); Phys. Rev. E {\bf 70} 066109
(2004)]. Current reversals due to the interplay between the phases, frequencies
and amplitudes of the harmonics are obtained. An analysis of the effect of the
damping coefficient on the dynamics is presented. We show that solitons give
rise to non-trivial differences in the phenomenology reported for particle
systems that arise from their extended character. A comparison with soliton
ratchets in homogeneous systems with biharmonic forces is also presented. This
ratchet device may be an ideal candidate for Josephson junction ratchets with
intrinsic large damping.
|
0509051v1
|
2005-10-27
|
Acoustic damping in Li$_2$O-2B$_2$O$_3$ glass observed by inelastic x-ray and optical Brillouin scattering
|
The dynamic structure factor of lithium-diborate glass has been measured at
several values of the momentum transfer $Q$ using high resolution inelastic
x-ray scattering. Much attention has been devoted to the low $Q$-range, below
the observed Ioffe-Regel crossover \qco{}$\simeq$ 2.1 nm$^{-1}$. We find that
below \qco{}, the linewidth of longitudinal acoustic waves increases with a
high power of either $Q$, or of the frequency $\Omega$, up to the crossover
frequency \OMco{} $\simeq$ 9 meV that nearly coincides with the center of the
boson peak. This new finding strongly supports the view that resonance and
hybridization of acoustic waves with a distribution of rather local low
frequency modes forming the boson peak is responsible for the end of acoustic
branches in strong glasses. Further, we present high resolution Brillouin
light-scattering data obtained at much lower frequencies on the same sample.
These clearly rule out a simple $\Omega^2$-dependence of the acoustic damping
over the entire frequency range.
|
0510714v1
|
2005-12-07
|
Acoustic attenuation probe for fermion superfluidity in ultracold atom gases
|
Dilute gas Bose-Einstein condensates (BEC's), currently used to cool
fermionic atoms in atom traps, can also probe the superfluidity of these
fermions. The damping rate of BEC-acoustic excitations (phonon modes), measured
in the middle of the trap as a function of the phonon momentum, yields an
unambiguous signature of BCS-like superfluidity, provides a measurement of the
superfluid gap parameter and gives an estimate of the size of the Cooper-pairs
in the BEC-BCS crossover regime. We also predict kinks in the momentum
dependence of the damping rate which can reveal detailed information about the
fermion quasi-particle dispersion relation.
|
0512134v4
|
2005-12-29
|
Current-induced magnetization dynamics in disordered itinerant ferromagnets
|
Current-driven magnetization dynamics in ferromagnetic metals are studied in
a self-consistent adiabatic local-density approximation in the presence of
spin-conserving and spin-dephasing impurity scattering. Based on a quantum
kinetic equation, we derive Gilbert damping and spin-transfer torques entering
the Landau-Lifshitz equation to linear order in frequency and wave vector.
Gilbert damping and a current-driven dissipative torque scale identically and
compete, with the result that a steady current-driven domain-wall motion is
insensitive to spin dephasing in the limit of weak ferromagnetism. A uniform
magnetization is found to be much more stable against spin torques in the
itinerant than in the \textit{s}-\textit{d} model for ferromagnetism. A dynamic
spin-transfer torque reminiscent of the spin pumping in multilayers is
identified and shown to govern the current-induced domain-wall distortion.
|
0512715v4
|
2006-01-11
|
Apparent phonon side band modes in pi-conjugated systems: polymers, oligomers and crystals
|
The emission spectra of many pi-conjugated polymers and oligomers contain
side-band replicas with apparent frequencies that do not match the Raman active
mode frequencies. Using a time dependent model we show that in such many mode
systems, the increased damping of the time dependent transition dipole moment
correlation function results in an effective elimination of the vibrational
modes from the emission spectrum; subsequently causing the appearance of a
regularly spaced progression at a new apparent frequency. We use this damping
dependent vibrational reshaping to quantitatively account for the vibronic
structure in the emission spectra of pi-conjugated systems in the form of
films, dilute solutions and single crystals. In particular, we show that by
using the experimentally measured Raman spectrum we can account in detail for
the apparent progression frequencies and their relative intensities in the
emission spectrum.
|
0601218v1
|
2006-03-01
|
Renormalization of the electron-spin-fluctuation interaction in the t-t'-U Hubbard model
|
We study the renormalization of the electron-spin-fluctuation (el-sp) vertex
in a two-dimensional Hubbard model with nearest-neighbor (t) and
next-nearest-neighbor (t') hopping by a Quantum-Monte-Carlo calculation. Our
results show that for t'=0, the renormalized el-sp vertex decreases quite
generally with decreasing temperature at all spin-fluctuation momentum
transfers. The suppression of the el-sp vertex results in a substantial
reduction of the effective pairing interaction mediated by antiferromagnetic
spin fluctuations in both the intermediate- and strong-correlation regimes. The
inclusion of a finite t'/t<0, increases the Landau damping rate of spin
fluctuations, especially in the overdoped region. The increased damping rate
leads to smaller vertex corrections, in agreement with earlier diagrammatic
calculations. Still, the vertex correction reduces the spin-fermion vertex, as
at t'=0.
|
0603014v3
|
2006-07-18
|
Equilibrium and non-equilibrium dynamics of the sub-ohmic spin-boson model
|
Employing the non-perturbative numerical renormalization group method, we
study the dynamics of the spin-boson model, which describes a two-level system
coupled to a bosonic bath with spectral density J(omega) propto omega^s. We
show that, in contrast to the case of ohmic damping, the delocalized phase of
the sub-ohmic model cannot be characterized by a single energy scale only, due
to the presence of a non-trivial quantum phase transition. In the strongly
sub-ohmic regime, s<<1, weakly damped coherent oscillations on short time
scales are possible even in the localized phase - this is of crucial relevance,
e.g., for qubits subject to electromagnetic noise.
|
0607443v2
|
2006-09-29
|
Quantum master equation for electron transport through quantum dots and single molecules
|
A quantum master equation (QME) is derived for the many-body density matrix
of an open current-carrying system weakly coupled to two metal leads. The
dynamics and the steady-state properties of the system for arbitrary bias are
studied using projection operator techniques, which keep track of number of
electrons in the system. We show that coherences between system states with
different number of electrons, n, (Fock space coherences) do not contribute to
the transport to second order in system-lead coupling.
However, coherences between states with the same n may effect transport
properties when the damping rate is of the order or faster then the system Bohr
frequencies.
For large bias, when all the system many-body states lie between the chemical
potentials of the two leads, we recover previous results. In the rotating wave
approximation (when the damping is slow compared to the Bohr frequencies of the
system), the dynamics of populations and the coherences in the system
eigenbasis are decoupled. The QME then reduces to a birth and death master
equation for populations.
|
0610004v1
|
2006-10-25
|
Pulse and hold strategy for switching current measurements
|
We investigate by theory and experiment, the Josephson junction switching
current detector in an environment with frequency dependent damping. Analysis
of the circuit's phase space show that a favorable topology for switching can
be obtained with overdamped dynamics at high frequencies. A pulse-and-hold
method is described, where a fast switch pulse brings the circuit close to an
unstable point in the phase space when biased at the hold level. Experiments
are performed on Cooper pair transistors and Quantronium circuits, which are
overdamped at high frequencies with an on-chip RC shunt. For 20 us switch
pulses the switching process is well described by thermal equilibrium escape,
based on a generalization of Kramers formula to the case of frequency dependent
damping. A capacitor bias method is used to create very rapid, 25 ns switch
pulses, where it is observed that the switching process is not governed by
thermal equilibrium noise.
|
0610704v2
|
2006-10-29
|
Experimental Studies of Low-field Landau Quantization in Two-dimensional Electron Systems in GaAs/AlGaAs Heterostructures
|
By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional
electron systems, we study the low-field Landau quantization when the thermal
damping is reduced with decreasing the temperature. Magneto-oscillations
following Shubnikov-de Haas (SdH) formula are observed even when their
amplitudes are so large that the deviation to such a formula is expected. Our
experimental results show the importance of the positive magneto-resistance to
the extension of SdH formula under the damping induced by the disorder.
|
0610805v1
|
2007-01-12
|
Electron spin quantum beats in positively charged quantum dots: nuclear field effects
|
We have studied the electron spin coherence in an ensemble of positively
charged InAs/GaAs quantum dots. In a transverse magnetic field, we show that
two main contributions must be taken into account to explain the damping of the
circular polarization oscillations. The first one is due to the nuclear field
fluctuations from dot to dot experienced by the electron spin. The second one
is due to the dispersion of the transverse electron Lande g-factor, due to the
inherent inhomogeneity of the system, and leads to a field dependent
contribution to the damping. We have developed a model taking into account both
contributions, which is in good agreement with the experimental data. This
enables us to extract the pure contribution to dephasing due to the nuclei.
|
0701284v2
|
2007-02-05
|
Verification of stable operation of rapid single flux quantum devices with selective dissipation
|
It has been suggested that Rapid Single Flux Quantum (RSFQ) devices could be
used as the classical interface of superconducting qubit systems. One problem
is that the interface acts as a dissipative environment for a qubit. Recently
ways to modify the RSFQ damping to reduce the dissipation have been introduced.
One of the solutions is to damp the Josephson junctions by a
frequency-dependent linear circuit instead of the plain resistor. The approach
has previously been experimentally tested with a simple SFQ comparator. In this
paper we perform experiments with a full RSFQ circuit, and thus conclude that
in terms of stable operation the approach is applicable for scalable RSFQ
circuits. Realisation and optimisation issues are also discussed.
|
0702104v1
|
2007-02-21
|
RPAE versus RPA for the Tomonaga model with quadratic energy dispersion
|
Recently the damping of the collective charge (and spin) modes of interacting
fermions in one spatial dimension was studied. It results from the nonlinear
correction to the energy dispersion in the vicinity of the Fermi points. To
investigate the damping one has to replace the random phase approximation (RPA)
bare bubble by a sum of more complicated diagrams. It is shown here that a
better starting point than the bare RPA is to use the (conserving) linearized
time dependent Hartree-Fock equations, i.e. to perform a random phase
approximation (with) exchange
(RPAE) calculation. It is shown that the RPAE equation can be solved
analytically for the special form of the two-body interaction often used in the
Luttinger liquid framework. While (bare) RPA and RPAE agree for the case of a
strictly linear disperson there are qualitative differences for the case of the
usual nonrelativistic quadratic dispersion.
|
0702488v2
|
2007-03-01
|
Spin dynamics across the superfluid-insulator transition of spinful bosons
|
Bosons with non-zero spin exhibit a rich variety of superfluid and insulating
phases. Most phases support coherent spin oscillations, which have been the
focus of numerous recent experiments. These spin oscillations are Rabi
oscillations between discrete levels deep in the insulator, while deep in the
superfluid they can be oscillations in the orientation of a spinful condensate.
We describe the evolution of spin oscillations across the superfluid-insulator
quantum phase transition. For transitions with an order parameter carrying
spin, the damping of such oscillations is determined by the scaling dimension
of the composite spin operator. For transitions with a spinless order parameter
and gapped spin excitations, we demonstrate that the damping is determined by
an associated quantum impurity problem of a localized spin excitation
interacting with the bulk critical modes. We present a renormalization group
analysis of the quantum impurity problem, and discuss the relationship of our
results to experiments on ultracold atoms in optical lattices.
|
0703011v2
|
2007-03-21
|
Edge magnetoplasmons in a partially screened two-dimensional electron gas on a helium surface
|
We report a study of edge magnetoplasmons in a partially-screened system of
electrons on a helium surface. We compare experimental results with theories of
the frequency, damping, and penetration-depth dependence on magnetic field,
temperature-dependent damping, and the dependence of the frequency on
screening. We show explicitly the dependence of frequency on the edge density
profile. The frequency and screening are in qualitative agreement with the
theory of Fetter at small fields, and the frequencies agree with theory in the
limit of zero magnetic field. The frequency and linewidths in intermediate and
large fields exhibit the features of the qualitative predictions of Volkov and
Mikhailov, but differ numerically. Deviations from theory for a finite sample
occur at smaller fields. The dependence of frequency on the density profile is
stronger than predicted by these authors, and the penetration-depth variation
with field confirms their prediction for small fields.
|
0703558v1
|
1997-02-12
|
On the problem of semiinfinite beam oscillation with internal damping
|
We study the Cauchy problem for the equation of the form $$ \ddot{u}(t) +
(\aa A + B)\dot{u}(t) + (A+G)u(t) = 0,\tag* $$ where $A$, $B$, and $G$ are \o s
in a Hilbert space $\Cal H$ with $A$ selfadjoint, $\sigma(A)=[0,\infty)$,
$B\ge0$ bounded, and $G$ symmetric and $A$-subordinate in a certain sense.
Spectral properties of the correspondent operator pencil
$L(\lambda) := \lambda^2I + \lambda (\alpha A + B) + A + G$ are studied, and
existence and uniqueness of generalized and classical solutions of the Cauchy
problem are proved. Equations of the type (*) include, e.g., an abstract model
for the problem of semiinfinite beam oscillations with internal damping.
|
9702007v1
|
1994-04-14
|
Decoherence, Correlation, and Unstable Quantum States in Semiclassical Cosmology
|
It is demonstrated that almost any S-matrix of quantum field theory in curved
spaces posses an infinite set of complex poles (or branch cuts). These poles
can be transformed into complex eigenvalues, the corresponding eigenvectors
being Gamow vectors. All this formalism, which is heuristic in ordinary Hilbert
space, becomes a rigorous one within the framework of a properly chosen rigged
Hilbert space. Then complex eigenvalues produce damping or growing factors. It
is known that the growth of entropy, decoherence, and the appearance of
correlations, occur in the universe evolution, but only under a restricted set
of initial conditions. It is proved that the damping factors allow to enlarge
this set up to almost any initial conditions.
|
9404028v1
|
1994-09-27
|
Effects of weak self-interactions in a relativistic plasma on cosmological perturbations
|
The exact solutions for linear cosmological perturbations which have been
obtained for collisionless relativistic matter within thermal field theory are
extended to a self-interacting case. The two-loop contributions of scalar
$\lambda\phi^4$ theory to the thermal graviton self-energy are evaluated, which
give the $O(\lambda)$ corrections in the perturbation equations. The changes
are found to be perturbative on scales comparable to or larger than the Hubble
horizon, but the determination of the large-time damping behavior of subhorizon
perturbations requires a resummation of thermally induced masses.
|
9409055v2
|
1995-03-07
|
ON THE OSCILLATION SPECTRA OF ULTRA COMPACT STARS
|
Quasinormal modes of ultra compact stars with uniform energy density have
been calculated. For less compact stars, there is only one very slowly damped
polar mode (corresponding to the Kelvin f-mode) for each spherical harmonic
index $l$. Further long-lived modes become possible for a sufficiently compact
star (roughly when $M/R \ge 1/3$). We compare the characteristic frequencies of
these resonant polar modes to the axial modes first found by Chandrasekhar and
Ferrari [{\em Proc. Roy. Soc. London A} {\bf 434} 449 (1991)]. We find that the
two spectra approach each other as the star is made more compact. The
oscillation frequencies of the corresponding polar and axial modes agree to
within a percent for stars more compact than $M/R = 0.42$. At the same time,
the damping times are slightly different. The results illustrate that there is
no real difference between the origin of these axial and polar modes: They are
essentially spacetime modes.
|
9503012v1
|
1998-02-13
|
Radiation Damping in FRW Space-times with Different Topologies
|
We study the role played by the compactness and the degree of connectedness
in the time evolution of the energy of a radiating system in the
Friedmann-Robertson-Walker (FRW) space-times whose $t=const $ spacelike
sections are the Euclidean 3-manifold ${\cal R}^3$ and six topologically
non-equivalent flat orientable compact multiply connected Riemannian
3-manifolds. An exponential damping of the energy $E(t)$ is present in the
${\cal R}^3$ case, whereas for the six compact flat 3-spaces it is found
basically the same pattern for the evolution of the energy, namely relative
minima and maxima occurring at different times (depending on the degree of
connectedness) followed by a growth of $E(t)$. Likely reasons for this
divergent behavior of $E(t)$ in these compact flat 3-manifolds are discussed
and further developments are indicated. A misinterpretation of Wolf's results
regarding one of the six orientable compact flat 3-manifolds is also indicated
and rectified.
|
9802031v1
|
1998-05-06
|
Damping of Gravitational Waves and Density Perturbations in the Early Universe
|
Since the discovery of the large angular scale anisotropies in the microwave
background radiation, the behaviour of cosmological perturbations (especially,
density perturbations and gravitational waves) has been of great interest. In
this study, after a detailed and rigorous treatment of the behaviour of
gravitational waves in viscous cosmic media, we conclude that the damping of
cosmological gravitational waves of long wavelengths is negligible for most
cases of physical interest. A preliminary analysis suggests that similar
results hold for density perturbations in the long wavelength limit. Therefore,
long wavelength cosmological perturbations have not been practically affected
by viscous processes,and are good probes of the very early Universe.
|
9805016v1
|
1998-11-11
|
Late-Time Evolution of Realistic Rotating Collapse and The No-Hair Theorem
|
We study analytically the asymptotic late-time evolution of realistic
rotating collapse. This is done by considering the asymptotic late-time
solutions of Teukolsky's master equation, which governs the evolution of
gravitational, electromagnetic, neutrino and scalar perturbations fields on
Kerr spacetimes. In accordance with the no-hair conjecture for rotating
black-holes we show that the asymptotic solutions develop inverse power-law
tails at the asymptotic regions of timelike infinity, null infinity and along
the black-hole outer horizon (where the power-law behaviour is multiplied by an
oscillatory term caused by the dragging of reference frames). The damping
exponents characterizing the asymptotic solutions at timelike infinity and
along the black-hole outer horizon are independent of the spin parameter of the
fields. However, the damping exponents at future null infinity are spin
dependent. The late-time tails at all the three asymptotic regions are
spatially dependent on the spin parameter of the field. The rotational dragging
of reference frames, caused by the rotation of the black-hole (or star) leads
to an active coupling of different multipoles.
|
9811032v2
|
1999-09-22
|
Vorticity affects the stability of neutron stars
|
The spin rate \Omega of neutron stars at a given temperature T is constrained
by the interplay between gravitational-radiation instabilities and viscous
damping. Navier-Stokes theory has been used to calculate the viscous damping
timescales and produce a stability curve for r-modes in the (\Omega,T) plane.
In Navier-Stokes theory, viscosity is independent of vorticity, but kinetic
theory predicts a coupling of vorticity to the shear viscosity. We calculate
this coupling and show that it can in principle significantly modify the
stability diagram at lower temperatures. As a result, colder stars can remain
stable at higher spin rates.
|
9909073v2
|
2000-02-02
|
Active controls in interferometric detectors of gravitational waves: inertial damping of the VIRGO superattenuator
|
The operation of an interferometer for gravitational waves detection requires
sophisticated feedback controls in many parts of the apparatus. The aim of this
lecture is to introduce the types of problems to be faced in this line of
research. The attention is focused on the "inertial damping" of the test mass
suspension of the VIRGO interferometer (the superattenuator): it is a
multidimensional local control aimed to reduce the residual motion of the
suspended mirror associated to the normal modes of the suspension. Its
performance is very important for the locking of the interferometer.
|
0002006v2
|
2000-08-09
|
Gravitational Wave Damping of Neutron Star Wobble
|
We calculate the effect of gravitational wave (gw) back-reaction on realistic
neutron stars (NS's) undergoing torque-free precession. By `realistic' we mean
that the NS is treated as a mostly-fluid body with an elastic crust, as opposed
to a rigid body. We find that gw's damp NS wobble on a timescale tau_{theta}
approx 2 x 10^5 yr [10^{-7}/(DId/I_0)]^2 (kHz/ nu_s)^4, where nu_s is the spin
frequency and DId is the piece of the NS's inertia tensor that "follows" the
crust's principal axis (as opposed to its spin axis). We give two different
derivations of this result: one based solely on energy and angular momentum
balance, and another obtained by adding the Burke-Thorne radiation reaction
force to the Newtonian equations of motion. This problem was treated long ago
by Bertotti and Anile (1973), but their claimed result is wrong. When we
convert from their notation to ours, we find that their tau_{theta} is too
short by a factor of order 10^5 for typical cases of interest, and even has the
wrong sign for DId negative. We show where their calculation went astray.
|
0008021v1
|
2000-11-30
|
Tests of strong-field gravity and gravitational radiation damping in binary-pulsar systems
|
This talk reviews the constraints imposed by binary-pulsar data on gravity
theories, and notably on "scalar-tensor" theories which are the most natural
alternatives to general relativity. Because neutron stars have a strong
gravitational binding energy, binary-pulsar tests are qualitatively different
from solar-system experiments: They have the capability of probing models which
are indistinguishable from general relativity in weak gravitational field
conditions. Besides the two most precise binary-pulsar experiments, in the
systems B1913+16 and B1534+12, we also present the results of the various
"null" tests of general relativity provided by several neutron star-white dwarf
binaries, notably those of gravitational radiation damping. [The main interest
of this very short paper is its figure, which also takes into account the
"strong equivalence principle" tests.]
|
0011114v1
|
2001-07-17
|
Properties of r modes in rotating magnetic neutron stars. I. Kinematic Secular Effects and Magnetic Evolution Equations
|
The instability of r-mode oscillations in rapidly rotating neutron stars has
attracted attention as a potential mechanism for producing high frequency,
almost periodic gravitational waves. The analyses carried so far have shown the
existence of these modes and have considered damping by shear and bulk
viscosity. However, the magnetohydrodynamic coupling of the modes with a
stellar magnetic field and its role in the damping of the instability has not
been fully investigated yet. Following our introductory paper (Rezzolla, Lamb
and Shapiro 2000), we here discuss in more detail the existence of secular
higher-order kinematical effects which will produce toroidal fluid drifts. We
also define the sets of equations that account for the time evolution of the
magnetic fields produced by these secular velocity fields and show that the
magnetic fields produced can reach equipartition in less than a year. The full
numerical calculations as well as the evaluation of the impact of strong
magnetic fields on the onset and evolution of the r-mode instability will be
presented in a companion paper.
|
0107061v1
|
2006-12-07
|
Improved calculation of relic gravitational waves
|
In this paper, we improve the calculation of the relic gravitational waves
(RGW) in two aspects: First, we investigate the transfer function after
considering the redshift-suppression effect, the accelerating expansion effect,
the damping effect of free-streaming relativistic particles, and the damping
effect of cosmic phase transition, and give a simple approximate analytic
expression, which clearly illustrates the dependent relations on the
cosmological parameters. Second, we develop a numerical method to calculate the
primordial power spectrum of RGW at a very wide frequency range, where the
observed constraints on $n_s$ (the scalar spectral index) and $P_S(k_0)$ (the
amplitude of primordial scalar spectrum) and the Hamilton-Jacobi equation are
used. This method is applied to two kinds of inflationary models, which all
satisfy the current constraints on $n_s$, $\alpha$ (the running of $n_s$) and
$r$ (the tensor-scalar ratio). We plot them in the $r-\Omega_g$ diagram, where
$\Omega_g$ is the strength of RGW, and study their detection by the CMB
experiments and laser interferometers.
|
0612041v3
|
2007-01-16
|
Influence of Lorentz violation on Dirac quasinormal modes in the Schwarzschild black hole spacetime
|
Using the third-order WKB approximation and monodromy methods, we investigate
the influence of Lorentz violating coefficient $b$ (associated with a special
axial-vector $b_{\mu}$ field) on Dirac quasinormal modes in the Schwarzschild
black hole spacetime. At fundamental overtone, the real part decreases linearly
as the parameter $b$ increases. But the variation of the imaginary part with
$b$ becomes more complex. For the larger multiple moment $k$, the magnitude of
imaginary part increases with the increase of $b$, which means that presence of
Lorentz violation makes Dirac field damps more rapidly. At high overtones, it
is found that the real part of high-damped quasinormal frequency does not tend
to zero, which is quite a different from the symptotic Dirac quasinormal modes
without Lorentz violation.
|
0701089v1
|
2007-03-29
|
Constraint Damping in First-Order Evolution Systems for Numerical Relativity
|
A new constraint suppressing formulation of the Einstein evolution equations
is presented, generalizing the five-parameter first-order system due to Kidder,
Scheel and Teukolsky (KST). The auxiliary fields, introduced to make the KST
system first-order, are given modified evolution equations designed to drive
constraint violations toward zero. The algebraic structure of the new system is
investigated, showing that the modifications preserve the hyperbolicity of the
fundamental and constraint evolution equations. The evolution of the
constraints for pertubations of flat spacetime is completely analyzed, and all
finite-wavelength constraint modes are shown to decay exponentially when
certain adjustable parameters satisfy appropriate inequalities. Numerical
simulations of a single Schwarzschild black hole are presented, demonstrating
the effectiveness of the new constraint-damping modifications.
|
0703145v1
|
1994-01-21
|
Transport Properties of Quark and Gluon Plasmas
|
The kinetic properties of relativistic quark-gluon and electron-photon
plasmas are described in the weak coupling limit. The troublesome Rutherford
divergence at small scattering angles is screened by Debye screening for the
longitudinal or electric part of the interactions. The transverse or magnetic
part of the interactions is effectively screened by Landau damping of the
virtual photons and gluons transferred in the QED and QCD interactions
respectively. Including screening a number of transport coefficients for QCD
and QED plasmas can be calculated to leading order in the interaction strength,
including rates of momentum and thermal relaxation, electrical conductivity,
viscosities, flavor and spin diffusion of both high temperature and degenerate
plasmas. Damping of quarks and gluons as well as color diffusion in quark-gluon
plasmas is, however, shown not to be sufficiently screened and the rates
depends on an infrared cut-off of order the ``magnetic mass", $m_{\rm mag}\sim
g^2 T$.
|
9401300v1
|
1994-04-20
|
Electroweak Baryogenesis and Standard Model CP Violation
|
We analyze the mechanism of electroweak baryogenesis proposed by Farrar and
Shaposhnikov in which the phase of the CKM mixing matrix is the only source of
$CP$ violation. This mechanism is based on a phase separation of baryons via
the scattering of quasiparticles by the wall of an expanding bubble produced at
the electroweak phase transition. In agreement with the recent work of Gavela,
Hern\'andez, Orloff and P\`ene, we conclude that QCD damping effects reduce the
asymmetry produced to a negligible amount. We interpret the damping as quantum
decoherence. We compute the asymmetry analytically. Our analysis reflects the
observation that only a thin, outer layer of the bubble contributes to the
coherent scattering of the quasiparticles. The generality of our arguments
rules out any mechanism of electroweak baryogenesis that does not make use of a
new source of $CP$ violation.
|
9404302v1
|
1994-06-11
|
Standard Model CP-violation and Baryon asymmetry Part II: Finite Temperature
|
We consider the scattering of quasi-particles off the boundary created during
a first order electroweak phase transition. Spatial coherence is lost due to
the quasi-quark damping rate, and we show that reflection on the boundary is
suppressed, even at tree-level. Simply on CP considerations, we argue against
electroweak baryogenesis in the Standard Model via the charge transport
mechanism. A CP asymmetry is produced in the reflection properties of quarks
and antiquarks hitting the phase boundary. An effect is present at order
$\alpha_W^2$ in rate and a regular GIM behaviour is found, which can be
expressed in terms of two unitarity triangles. A crucial role is played by the
damping rate of quasi-particles in a hot plasma, which is a relevant scale
together with $M_W$ and the temperature. The effect is many orders of magnitude
below what observation requires.
|
9406289v2
|
1995-12-12
|
Bubble Collisions and Defect Formation in a Damping Environment
|
Within the context of a first-order phase transition in the early Universe,
we study the collision process for vacuum bubbles expanding in a plasma. The
effects of the plasma are simulated by introducing a damping term in the
equations of motion for a $U(1)$ global field. We find that Lorentz-contracted
spherically symmetric domain walls adequately describe the overdamped motion of
the bubbles in the thin wall approximation, and study the process of collision
and phase equilibration both numerically and analytically. With an analytical
model for the phase propagation in 1+1 dimensions, we prove that the phase
waves generated in the bubble merging are reflected by the walls of the true
vacuum cavity, giving rise to a long-lived oscillating state that delays the
phase equilibration. The existence of such a state in the 3+1 dimensional model
is then confirmed by numerical simulations, and the consequences for the
formation of vortices in three-bubble collisions are considered.
|
9512290v1
|
1996-09-02
|
The quasiparticle structure of hot gauge theories
|
The study of the ultrarelativistic plasmas in perturbation theory is plagued
with infrared divergences which are not eliminated by the screening
corrections. They affect, in particular, the computation of the lifetime of the
elementary excitations, thus casting doubt on the validity of the quasiparticle
picture. We show that, for Abelian plasmas at least, the infrared problem of
the damping rate can be solved by a non-perturbative treatment based on the
Bloch-Nordsieck approximation. The resulting expression of the fermion
propagator is free of divergences, and exhibits a {\it non-exponential} damping
at large times: $S_R(t)\sim \exp\{-\alpha T t \ln\omega_pt\}$, where
$\omega_p=gT/3$ is the plasma frequency and $\alpha=g^2/4\pi$.
|
9609225v1
|
1996-10-18
|
Finiteness of Hot Classical Scalar Field Theory and the Plasmon Damping Rate
|
We investigate the renormalizability of the classical $\phi^4$ theory at
finite temperature. We calculate the time-dependent two point function to two
loop order and show that it can be rendered finite by the counterterms of the
classical static theory. As an application the classical plasmon damping rate
is found to be $\gamma = \lambda^2 T^2/1536 \pi m$. When we use the high
temperature expression for $m$ given by dimensional reduction, the rate is
found to agree with the quantum mechanical result.
|
9610415v2
|
1996-12-30
|
Defect Formation in First Order Phase Transitions with Damping
|
Within the context of first order phase transitions in the early universe, we
study the influence of a coupling between the (global U(1)) scalar driving the
transition and the rest of the matter content of the theory. The effect of the
coupling on the scalar is simulated by introducing a damping term in its
equations of motion, as suggested by recent results in the electroweak phase
transition. After a preceeding paper, in which we studied the influence that
this coupling has in the dynamics of bubble collisions and topological defect
formation, we proceed in this paper to quantify the impact of this new effects
on the probability of defect creation per nucleating bubble.
|
9612487v1
|
1997-07-28
|
Plasmon properties in classical lattice gauge theory
|
In order to investigate the features of the classical approximation at high
temperatures for real time correlation functions, the plasmon frequencies and
damping rates were recently computed numerically in the SU(2)+Higgs model and
in the pure SU(2) theory. We compare the lattice results with leading order
hard thermal loop resummed perturbation theory. In the broken phase of the
SU(2)+Higgs model, we show that the lattice results can be reproduced and that
the lattices used are too coarse to observe some important plasmon effects. In
the symmetric phase, the main qualitative features of the lattice results can
also be understood. In the pure SU(2) theory, on the other hand, there are
discrepancies which might point to larger Landau and plasmon damping effects
than indicated by perturbation theory.
|
9707489v2
|
1998-09-11
|
Dynamical renormalization group resummation of finite temperature infrared divergences
|
We introduce the method of dynamical renormalization group to study
relaxation and damping out of equilibrium directly in real time and applied it
to the study of infrared divergences in scalar QED. This method allows a
consistent resummation of infrared effects associated with the exchange of
quasistatic transverse photons and leads to anomalous logarithmic relaxation of
the form $e^{-\alpha T t \ln[t/t_0]}$ which prevents a quasiparticle
interpretation of charged collective excitations at finite temperature. The
hard thermal loop resummation program is incorporated consistently into the
dynamical renormalization group yielding a picture of relaxation and damping
phenomena in a plasma in real time that trascends the conceptual limitations of
the quasiparticle picture and other type of resummation schemes. We derive a
simple criterion for establishing the validity of the quasiparticle picture to
lowest order.
|
9809346v2
|
1999-02-12
|
Beyond HTL: The Classical Kinetic Theory of Landau Damping for Selfinteracting Scalar Fields in the Broken Phase
|
The effective theory of low frequency fluctuations of selfinteracting scalar
fields is constructed in the broken symmetry phase. The theory resulting from
integrating fluctuations with frequencies much above the spontanously generated
mass scale $(p_0>>M)$ is found to be local. Non-local dynamics, especially
Landau damping emerges under the effect of fluctuations in the $p_0 \sim M$
region. A kinetic theory of relativistic scalar gas particles interacting via
their locally variable mass with the low frequency scalar field is shown to be
equivalent to this effective field theory for scales below the characteristic
mass, that is beyond the accuracy of the Hard Thermal Loop (HTL) approximation.
|
9902331v1
|
2000-04-05
|
A consistent nonperturbative approach to thermal damping-rates
|
We propose a nonperturbative scheme for the calculation of thermal
damping-rates using exact renormalization group (RG)-equations. Special
emphasis is put on the thermal RG where first results for the rate were given
in M. Pietroni, Phys. Rev. Lett. 81 (1998), 2424. We point out that in order to
obtain a complete result that also reproduces the known perturbative behaviour
one has to take into account effects that were neglected in the work cited
above. We propose a well-defined way of doing the calculations that reproduces
perturbation theory in lowest order but goes considerably beyond perturbative
results and should be applicable also at second order phase-transitions.
|
0004039v2
|
2000-07-07
|
Finite pion width effects on the rho--meson
|
We study the influence of the finite damping width of pions on the in-medium
properties of the rho-meson in an interacting meson gas model at finite
temperature. Using vector dominance also implications on the resulting dilepton
spectra from the decay of the rho-meson are presented. A set of coupled Dyson
equations with self energies up to the sunset diagram level is solved self
consistently. Following a Phi-derivable scheme the self energies are
dynamically determined by the self consistent propagators. Some problems
concerning the self consistent treatment of vector or gauge bosons on the
propagator level, in particular, if coupled to currents arising from particles
with a sizable damping width, are discussed.
|
0007070v3
|
2000-08-31
|
New Regime for Dense String Networks
|
We uncover a new transient regime that reconciles the apparent inconsistency
of the Martins Shellard one scale damped string evolution model with the
initial conditions predicted by the Kibble mechanism for string formation in a
second order phase transition. This regime carries (in a short cosmic time
$\sim .1 t_c$) the dense string network created by the Kibble {\it{mechanism}}
to the (dilute) Kibble {\it{regime}} in which friction dominated strings remain
till times $t_* \sim (M_P/T_c)^2 t_c$. This is possible beacause the cosmic
time at the phase transition ($t_c$) is much larger than the damping time scale
$l_f\sim T_c^2/T^3$. Our result has drastic implications for various non-GUT
scale string mediated mechanisms.}
|
0008330v1
|
2001-01-25
|
The Fermion Boson Interaction Within the Linear Sigma Model at Finite Temperature
|
We reinvestigate the interaction of massless fermions with massless bosons at
finite temperature. Specifically, we calculate the self-energy of massless
fermions due the interaction with massless bosons at high temperature, which is
the region where thermal effects are maximal. The calculations are concentrated
in the limit of vanishing fermion three momentum and after considering the
effective fermion and boson dressed masses, we obtain the damping rate of the
fermion up to order $g^3$. It is shown that in the limit $k_0 \ll T$ the
fermion acquire a thermal mass of order $gT$ and the leading term of the
fermion damping rate is of order $g^2T+g^3T$.
|
0101283v3
|
2001-11-02
|
Quark Number Susceptibility in Hard Thermal Loop Approximation
|
We calculate the quark number susceptibility in the deconfined phase of QCD
using the hard thermal loop (HTL) approximation for the quark propagator. This
improved perturbation theory takes into account important medium effects such
as thermal quark masses and Landau damping in the quark-gluon plasma. We
explicitly show that the Landau damping part in the quark propagator for
spacelike quark momenta does not contribute to the quark number susceptibility
due to the quark number conservation. We find that the quark number
susceptibility only due to the collective quark modes deviates from that of
free one around the critical temperature but approaches free results at
infinite temperature limit. The results are in conformity with recent lattice
calculations.
|
0111022v4
|
2001-12-29
|
Damped $\sin(β-α)$ of Higgs couplings and the lightest Higgs production at $γγ$ colliders in MSSM
|
In the decoupling limit, $M^2_{A^0} \gg M^2_Z$, the heavy CP-even, CP-odd and
charged Higgs boson masses are nearly degenerate, $\sin(\beta-\alpha)$
approaches 1, and the lightest CP-even Higgs boson almost displays the same
properties as the Standard Model Higgs boson. But the stop and sbottom sector
can change this pattern through radiative corrections. We find that there are
parameter regions at small, moderate and large $\tan\beta$ in MSSM under
experimental constraints of $(g-2)_{\mu}$ and $b\to s\gamma$, where
$\sin^2(\beta-\alpha)$ is damped (say below 0.8), which has a significant
effect on Higgs couplings $g_{h^0VV} (V=W^\pm,Z^0)$ and $g_{h^0\gamma\gamma}$.
We discuss its impact on the lightest CP-even Higgs production at
$\gamma\gamma$ colliders.
|
0112356v1
|
2004-05-31
|
Gauge dependence of the fermion quasiparticle poles in hot gauge theories
|
The gauge dependence of the complex fermion quasiparticle poles corresponding
to soft collective excitations is studied in hot gauge theories at one-loop
order and next-to-leading order in the high-temperature expansion, with a view
towards going beyond the leading order hard thermal loops and resummations
thereof. We find that for collective excitations of momenta k ~ eT the
dispersion relations are gauge independent, but the corresponding damping rates
are gauge dependent. For k<<eT and in k \to 0 limit, both the dispersion
relations and the damping rates are found to be gauge dependent. The gauge
dependence of the position of the complex quasiparticle poles signals the need
for resummation. Possible cancellation of the leading gauge dependence at
two-loop order in the case of QED is briefly discussed.
|
0406002v2
|
2004-11-09
|
Numerical investigation of friction in inflaton equations of motion
|
The equation of motion for the expectation value of a scalar quantum field
does not have the local form that is commonly assumed in studies of
inflationary cosmology. We have recently argued that the true, temporally
non-local equation of motion does not possess a time-derivative expansion and
that the conversion of inflaton energy into particles is not, in principle,
described by the friction term estimated from linear response theory. Here, we
use numerical methods to investigate whether this obstacle to deriving a local
equation of motion is purely formal, or of some quantitative importance. Using
a simple scalar-field model, we find that, although the non-equilibrium
evolution can exhibit significant damping, this damping is not well described
by the local equation of motion obtained from linear response theory. It is
possible that linear response theory does not apply to the situation we study
only because thermalization turns out to be slow, but we argue that that the
large discrepancies we observe indicate a failure of the local approximation at
a more fundamental level.
|
0411130v1
|
2006-03-03
|
Damping of supernova neutrino transitions in stochastic shock-wave density profiles
|
Supernova neutrino flavor transitions during the shock wave propagation are
known to encode relevant information not only about the matter density profile
but also about unknown neutrino properties, such as the mass hierarchy (normal
or inverted) and the mixing angle theta_13. While previous studies have
focussed on "deterministic" density profiles, we investigate the effect of
possible stochastic matter density fluctuations in the wake of supernova shock
waves. In particular, we study the impact of small-scale fluctuations on the
electron (anti)neutrino survival probability, and on the observable spectra of
inverse-beta-decay events in future water-Cherenkov detectors. We find that
such fluctuations, even with relatively small amplitudes, can have significant
damping effects on the flavor transition pattern, and can partly erase the
shock-wave imprint on the observable time spectra, especially for
sin^2(theta_13) > O(10^-3).
|
0603033v2
|
2006-08-11
|
Constraining SuperWIMPy and Warm Subhalos with Future Submillilensing
|
We propose to observe QSO-galaxy strong lens systems to give a new constraint
on the damping scale of the initial fluctuations. We find that the future
observation of submilliarc scale astrometric shifts of the multiple lensed
images of QSOs would find \sim 10^{(3-9)} M_{\odot} subhalos inside the
macrolens halo. The superweakly interacting massive particles (superWIMPs)
produced from a WIMP decay and the warm dark matter (WDM) particles that
predict a comoving damping scale larger than \sim 2 kpc can be constrained if
\sim 10^3 M_{\odot} subhalos are detected.
|
0608126v2
|
2006-11-15
|
Time-to-Space Conversion in Neutrino Oscillations
|
We study the neutrino oscillation problem in the framework of the wave packet
formalism. The neutrino state is described by a packet located initially in a
region S (source) and detected in another region D at a distance R from S. We
examine how the oscillation probability as a function of variable R can be
derived from he oscillation probability as a function of time t, the latter
being found by using the Schrodinger equation. We justify the known
prescription "t --> R/c" without referring to a specific form of the neutrino
wave packet and only assuming the finiteness of its support. The effect of the
oscillation damping at large R is revealed. For an illustration, an explicit
expression for the damping factor is obtained using Gaussian packet.
|
0611202v1
|
1991-09-26
|
The Damping of Energetic Gluons and Quarks in High-Temperature QCD
|
When a gluon or a quark is sent through the hot QCD plasma it can be absorbed
into the ambient heat bath and so can acquire an effective lifetime. At high
temperatures and for weak couplings the inverse lifetime, or damping rate, for
energetic quarks and transverse gluons, (those whose momenta satisfy $|\p| \gg
gT$) is given by $\gamma(\p) = c\; g^2 \log\left({1\over g}\right)\; T +
O(g^2T)$. We show that very simple arguments suffice both to fix the numerical
coefficient, $c$, in this expression and to show that the $O(g^2T)$
contribution is incalculable in perturbation theory without further
assumptions. For QCD with $N_c$ colours we find (expressed in terms of the
casimir invariants $C_a=N_c$ and $C_f=(N_c^2-1)/(2N_c)$): $c_g=+{C_a\over
4\pi}$ for gluons and $c_q=+{C_f\over 4\pi}$ for quarks. These numbers agree
with the more detailed calculations of Pisarski \etal\ but disagree with those
of Lebedev and Smilga. The simplicity of the calculation also permits a direct
verification of the gauge-invariance and physical sign of the result.
|
9109051v1
|
1998-09-11
|
Damping and reaction rates and wave function renormalization of fermions in hot gauge theories
|
We examine the relation between the damping rate of a chiral fermion mode
propagating in a hot plasma and the rate at which the mode approaches
equilibrium. We show how these two quantities, obtained from the imaginary part
of the fermion self-energy, are equal when the reaction rate is defined using
the appropriate wave function of the mode in the medium. As an application, we
compute the production rate of hard axions by Compton-like scattering processes
in a hot QED plasma starting from both, the axion self-energy and the electron
self-energy. We show that the latter rate coincides with the former only when
this is computed using the corresponding medium spinor modes.
|
9809083v2
|
2003-12-28
|
A mechanism of the large-scale damping in the CMB anisotropy
|
We present a mechanism through which a certain class of short-distance cutoff
affects the CMB anisotropies at large angular scales. Our analysis is performed
in two steps. The first is given in an intuitive way, using the property of the
inflationary universe that quantum fluctuations of an inflaton field become
classical after crossing the Hubble horizon. We give a condition for a cutoff
to yield a damping on large scales, and show that the holographic cutoff
introduced in the preceding paper (hep-th/0307029) does satisfy the condition.
The second analysis is carried out by setting an initial condition such that
each mode of inflaton starts as the vacuum fluctuation of the Hamiltonian when
being released from the constraint of cutoff. The first intuitive discussion is
then shown to be correct qualitatively.
|
0312298v7
|
2005-03-03
|
Scalar field perturbations of the Schwarzschild black hole in the Gödel Universe
|
We investigate the scalar field perturbations of the 4+1-dimensional
Schwarzschild black hole immersed in a G\"{o}del Universe, described by the
Gimon-Hashimoto solution.This may model the influence of the possible rotation
of the Universe upon the radiative processes near a black hole. In the regime
when the scale parameter $j$ of the G\"{o}del background is small, the
oscillation frequency is linearly decreasing with $j$, while the damping time
is increasing. The quasinormal modes are damping, implying stability of the
Schwarzschild-G\"{o}del space-time against scalar field perturbations. The
approximate analytical formula for large multipole numbers is found.
|
0503029v2
|
2005-08-25
|
The Dynamics of Small Instanton Phase Transitions
|
The small instanton transition of a five-brane colliding with one end of the
S1/Z2 interval in heterotic M-theory is discussed, with emphasis on the
transition moduli, their potential function and the associated non-perturbative
superpotential. Using numerical methods, the equations of motion of these
moduli coupled to an expanding Friedmann-Robertson-Walker spacetime are solved
including non-perturbative interactions. It is shown that the five-brane
collides with the end of the interval at a small instanton. However, the moduli
then continue to evolve to an isolated minimum of the potential, where they are
trapped by gravitational damping. The torsion free sheaf at the small instanton
is ``smoothed out'' into a vector bundle at the isolated minimum, thus
dynamically completing the small instanton phase transition. Radiative damping
at the origin of moduli space is discussed and shown to be insufficient to trap
the moduli at the small instanton point.
|
0508190v2
|
2006-11-21
|
Renormalization group study of damping in nonequilibrium field theory
|
In this paper we shall study whether dissipation in a $\lambda\phi^{4}$ may
be described, in the long wavelength, low frequency limit, with a simple Ohmic
term $\kappa\dot{\phi}$, as it is usually done, for example, in studies of
defect formation in nonequilibrium phase transitions. We shall obtain an
effective theory for the long wavelength modes through the coarse graining of
shorter wavelengths. We shall implement this coarse graining by iterating a
Wilsonian renormalization group transformation, where infinitesimal momentum
shells are coarse-grained one at a time, on the influence action describing the
dissipative dynamics of the long wavelength modes. To the best of our
knowledge, this is the first application of the nonequilibrium renormalization
group to the calculation of a damping coefficient in quantum field theory.
|
0611222v1
|
2006-02-16
|
Exit from a basin of attraction for stochastic weakly damped nonlinear Schrödinger equations
|
We consider weakly damped nonlinear Schr\"odinger equations perturbed by a
noise of small amplitude. The small noise is either complex and of additive
type or real and of multiplicative type. It is white in time and colored in
space. Zero is an asymptotically stable equilibrium point of the deterministic
equations. We study the exit from a neighborhood of zero, invariant by the flow
of the deterministic equation, in $\xLtwo$ or in $\xHone$. Due to noise, large
fluctuations off zero occur. Thus, on a sufficiently large time scale, exit
from these domains of attraction occur. A formal characterization of the small
noise asymptotic of both the first exit times and the exit points is given.
|
0602350v1
|
2006-06-30
|
Uniform attractors for non-autonomous wave equations with nonlinear damping
|
We consider dynamical behavior of non-autonomous wave-type evolutionary
equations with nonlinear damping, critical nonlinearity, and time-dependent
external forcing which is translation bounded but not translation compact
(i.e., external forcing is not necessarily time-periodic, quasi-periodic or
almost periodic). A sufficient and necessary condition for the existence of
uniform attractors is established using the concept of uniform asymptotic
compactness. The required compactness for the existence of uniform attractors
is then fulfilled by some new a priori estimates for concrete wave type
equations arising from applications. The structure of uniform attractors is
obtained by constructing a skew product flow on the extended phase space for
the norm-to-weak continuous process.
|
0606776v1
|
2001-04-17
|
Scattering and radiation damping in gyroscopic Lorentz electrodynamic
|
Relativistic massive Lorentz electrodynamics (LED) is studied in a
``gyroscopic setup'' where the electromagnetic fields and the particle spin are
the only dynamical degrees of freedom.
A rigorous proof of the global existence and uniqueness of the dynamics is
given for essentially the whole range of field strengths reasonable for a
classical theory.
For a class of rotation-reflection symmetric field data it is shown that the
dynamics also satisfies the world-line equations for a non-moving Lorentz
electron, thus furnishing rigorous solutions of the full system of nonlinear
equations of LED.
The previously proven soliton dynamics of the Lorentz electron is further
illucidated by showing that rotation-reflection symmetric deviations from the
soliton state of the renormalized particle die out exponentially fast through
radiation damping if the electrostatic mass is smaller than the bare rest mass.
|
0104023v2
|
2002-06-18
|
Hamiltonian and Linear-Space Structure for Damped Oscillators: I. General Theory
|
The phase space of $N$ damped linear oscillators is endowed with a bilinear
map under which the evolution operator is symmetric. This analog of
self-adjointness allows properties familiar from conservative systems to be
recovered, e.g., eigenvectors are "orthogonal" under the bilinear map and obey
sum rules, initial-value problems are readily solved and perturbation theory
applies to the_complex_ eigenvalues. These concepts are conveniently
represented in a biorthogonal basis.
|
0206026v2
|
2002-06-17
|
Hamiltonian and Linear-Space Structure for Damped Oscillators: II. Critical Points
|
The eigenvector expansion developed in the preceding paper for a system of
damped linear oscillators is extended to critical points, where eigenvectors
merge and the time-evolution operator $H$ assumes a Jordan-block structure. The
representation of the bilinear map is obtained in this basis. Perturbations
$\epsilon\Delta H$ around an $M$-th order critical point generically lead to
eigenvalue shifts $\sim\epsilon^{1/M}$ dependent on only_one_ matrix element,
with the $M$ eigenvalues splitting in equiangular directions in the complex
plane. Small denominators near criticality are shown to cancel.
|
0206027v2
|
2004-02-24
|
Classical harmonic oscillator with Dirac-like parameters and possible applications
|
We obtain a class of parametric oscillation modes that we call K-modes with
damping and absorption that are connected to the classical harmonic oscillator
modes through the "supersymmetric" one-dimensional matrix procedure similar to
relationships of the same type between Dirac and Schroedinger equations in
particle physics. When a single coupling parameter, denoted by K, is used, it
characterizes both the damping and the dissipative features of these modes.
Generalizations to several K parameters are also possible and lead to
analytical results. If the problem is passed to the physical optics (and/or
acoustics) context by switching from the oscillator equation to the
corresponding Helmholtz equation, one may hope to detect the K-modes as
waveguide modes of specially designed waveguides and/or cavities
|
0402065v2
|
2000-02-22
|
Front motion for phase transitions in systems with memory
|
We consider the Allen-Cahn equations with memory (a partial
integro-differential convolution equation). The prototype kernels are
exponentially decreasing functions of time and they reduce the
integrodifferential equation to a hyperbolic one, the damped Klein-Gordon
equation. By means of a formal asymptotic analysis we show that to the leading
order and under suitable assumptions on the kernels, the integro-differential
equation behave like a hyperbolic partial differential equation obtained by
considering prototype kernels: the evolution of fronts is governed by the
extended, damped Born-Infeld equation. We also apply our method to a system of
partial integro-differential equations which generalize the classical phase
field equations with a non-conserved order parameter and describe the process
of phase transitions where memory effects are present.
|
0002039v1
|
2002-03-01
|
Excitation of travelling multibreathers in anharmonic chains
|
We study the dynamics of the "externally" forced and damped Fermi-Pasta-Ulam
(FPU) 1D lattice. The forcing has the spatial symmetry of the Fourier mode with
wavenumber p and oscillates sinusoidally in time with the frequency omega. When
omega is in the phonon band, the p-mode becomes modulationally unstable above a
critical forcing, which we determine analytically in terms of the parameters of
the system. For omega above the phonon band, the instability of the p-mode
leads to the formation of a travelling multibreather, that, in the
low-amplitude limit could be described in terms of soliton solutions of a
suitable driven-damped nonlinear Schroedinger (NLS) equation. Similar
mechanisms of instability could show up in easy-axis magnetic structures, that
are governed by such NLS equations.
|
0203002v1
|
2003-01-15
|
Resonant triad dynamics in weakly damped Faraday waves with two-frequency forcing
|
Many of the interesting patterns seen in recent multi-frequency Faraday
experiments can be understood on the basis of three-wave interactions (resonant
triads). In this paper we consider two-frequency forcing and focus on a
resonant triad that occurs near the bicritical point where two pattern-forming
modes with distinct wavenumbers emerge simultaneously. This triad has been
observed directly (in the form of rhomboids) and has also been implicated in
the formation of quasipatterns and superlattices. We show how the symmetries of
the undamped unforced problem (time translation, time reversal, and Hamiltonian
structure) can be used, when the damping is weak, to obtain general scaling
laws and additional qualitative properties of the normal form coefficients
governing the pattern selection process near onset; such features help to
explain why this particular triad is seen only for certain "low" forcing
ratios, and predict the existence of drifting solutions and heteroclinic
cycles. We confirm the anticipated parameter dependence of the coefficients and
investigate its dynamical consequences using coefficients derived numerically
from a quasipotential formulation of the Faraday problem due to Zhang and
Vinals.
|
0301015v1
|
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