1,089 research outputs found
Is \lq\lq Heavy Quark Damping Rate Puzzle'' in Hot QCD Really the Puzzle?
Within the framework of perturbative resummation scheme of Pisarski and
Braaten, the decay- or damping-rate of a moving heavy quark (muon) to leading
order in weak coupling in hot QCD (QED) is examined. Although, as is well
known, the conventionally-defined damping rate diverges logarithmically at the
infrared limit, shown is that no such divergence appears in the physically
measurable decay rate. The cancellation occurs between the contribution from
the \lq\lq real'' decay diagram and the contribution from the diagrams with
\lq\lq thermal radiative correction''.Comment: 13pages, OCU-PHYS-15
Finite-temperature reaction-rate formula: Finite volume system, detailed balance, limit, and cutting rules
A complete derivation, from first principles, of the reaction-rate formula
for a generic process taking place in a heat bath of finite volume is given. It
is shown that the formula involves no finite-volume correction. Through
perturbative diagrammatic analysis of the resultant formula, the
detailed-balance formula is derived. The zero-temperature limit of the formula
is discussed. Thermal cutting rules, which are introduced in previous work, are
compared with those introduced by other authors.Comment: 35pages (text) plus 4pages (figures
Exploring the Kondo model in and out of equilibrium with alkaline-earth atoms
We propose a scheme to realize the Kondo model with tunable anisotropy using
alkaline-earth atoms in an optical lattice. The new feature of our setup is
Floquet engineering of interactions using time-dependent Zeeman shifts, that
can be realized either using state-dependent optical Stark shifts or magnetic
fields. The properties of the resulting Kondo model strongly depend on the
anisotropy of the ferromagnetic interactions. In particular, easy-plane
couplings give rise to Kondo singlet formation even though microscopic
interactions are all ferromagnetic. We discuss both equilibrium and dynamical
properties of the system that can be measured with ultracold atoms, including
the impurity spin susceptibility, the impurity spin relaxation rate, as well as
the equilibrium and dynamical spin correlations between the impurity and the
ferromagnetic bath atoms. We analyze the non-equilibrium time evolution of the
system using a variational non-Gaussian approach, which allows us to explore
coherent dynamics over both short and long timescales, as set by the bandwidth
and the Kondo singlet formation, respectively. In the quench-type experiments,
when the Kondo interaction is suddenly switched on, we find that real-time
dynamics shows crossovers reminiscent of poor man's renormalization group flow
used to describe equilibrium systems. For bare easy-plane ferromagnetic
couplings, this allows us to follow the formation of the Kondo screening cloud
as the dynamics crosses over from ferromagnetic to antiferromagnetic behavior.
On the other side of the phase diagram, our scheme makes it possible to measure
quantum corrections to the well-known Korringa law describing the temperature
dependence of the impurity spin relaxation rate. Theoretical results discussed
in our paper can be measured using currently available experimental techniques.Comment: 22 pages, 12 figure
Energy and pressure densities of a hot quark-gluon plasma
We calculate the energy and hydrostatic pressure densities of a hot
quark-gluon plasma in thermal equilibrium through diagrammatic analyses of the
statistical average, , of the
energy-momentum-tensor operator . To leading order at high
temperature, the energy density of the long wave length modes is consistently
extracted by applying the hard-thermal-loop resummation scheme to the
operator-inserted no-leg thermal amplitudes .
We find that, for the long wave length gluons, the energy density, being
positive, is tremendously enhanced as compared to the noninteracting case,
while, for the quarks, no noticeable deviation from the noninteracting case is
found.Comment: 33 pages. Figures are not include
Analytical Formulation of the Local Density of States around a Vortex Core in Unconventional Superconductors
On the basis of the quasiclassical theory of superconductivity, we obtain a
formula for the local density of states (LDOS) around a vortex core of
superconductors with anisotropic pair-potential and Fermi surface in arbitrary
directions of magnetic fields. Earlier results on the LDOS of d-wave
superconductors and NbSe are naturally interpreted within our theory
geometrically; the region with high intensity of the LDOS observed in numerical
calculations turns out to the enveloping curve of the trajectory of Andreev
bound states. We discuss experimental results on YNiBC within the
quasiclassical theory of superconductivity.Comment: 13 pages, 16 figure
Ultrafast optical nonlinearity in quasi-one-dimensional Mott-insulator
We report strong instantaneous photoinduced absorption (PA) in the
quasi-one-dimensional Mott insulator in the IR spectral
region. The observed PA is to an even-parity two-photon state that occurs
immediately above the absorption edge. Theoretical calculations based on a
two-band extended Hubbard model explains the experimental features and
indicates that the strong two-photon absorption is due to a very large
dipole-coupling between nearly degenerate one- and two-photon states. Room
temperature picosecond recovery of the optical transparency suggests the strong
potential of for all-optical switching.Comment: 10 pages, 4 figure
Bogoliubov - de Gennes versus Quasiclassical Description of Josephson Structures
The applicability of the quasiclassical theory of superconductivity in
Josephson multi-layer structures is analyzed. The quasiclassical approach is
compared with the exact theory based on the Bogoliubov - de Gennes equation.
The angle and energy resolved (coarse-grain) currents are calculated using both
techniques. It is shown that the two approaches agree in geometries
after the coarse-grain averaging. A quantitative discrepancy, which exceeds the
quasiclassical accuracy, is observed when three or more interfaces are present.
The invalidity of the quasiclassical theory is attributed to the presence of
closed trajectories formed by sequential reflections on the interfaces.Comment: revtex4,12 pages, 12 figure
High frequency sound in superfluid 3He-B
We present measurements of the absolute phase velocity of transverse and
longitudinal sound in superfluid 3He-B at low temperature, extending from the
imaginary squashing mode to near pair-breaking. Changes in the transverse phase
velocity near pair-breaking have been explained in terms of an order parameter
collective mode that arises from f-wave pairing interactions, the so-called
J=4- mode. Using these measurements, we establish lower bounds on the energy
gap in the B-phase. Measurement of attenuation of longitudinal sound at low
temperature and energies far above the pair-breaking threshold, are in
agreement with the lower bounds set on pair-breaking. Finally, we discuss our
estimations for the strength of the f-wave pairing interactions and the Fermi
liquid parameter, F4s.Comment: 15 pages, 8 figures, accepted to J. Low Temp. Phy
Andreev Bound States and Self-Consistent Gap Functions for SNS and SNSNS Systems
Andreev bound states in clean, ballistic SNS and SNSNS junctions are
calculated exactly and by using the Andreev approximation (AA). The AA appears
to break down for junctions with transverse dimensions chosen such that the
motion in the longitudinal direction is very slow. The doubly degenerate states
typical for the traveling waves found in the AA are replaced by two standing
waves in the exact treatment and the degeneracy is lifted.
A multiple-scattering Green's function formalism is used, from which the
states are found through the local density of states. The scattering by the
interfaces in any layered system of ballistic normal metals and clean
superconducting materials is taken into account exactly. The formalism allows,
in addition, for a self-consistent determination of the gap function. In the
numerical calculations the pairing coupling constant for aluminum is used.
Various features of the proximity effect are shown
Absorption of Electro-magnetic Waves in a Magnetized Medium
In continuation to our earlier work, in which the structure of the vacuum
polarisation tensor in a medium was analysed in presence of a background
electro-magnetic field, we discuss the absorptive part of the vacuum
polarization tensor. Using the real time formalism of finite temperature field
theory we calculate the absorptive part of 1-loop vacuum polarisation tensor in
the weak field limit (). Estimates of the absorption probability are
also made for different physical conditions of the background medium.Comment: 9 Pages. One figure. LaTe
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