28,784 research outputs found

### Comment on "Off-diagonal Long-range Order in Bose Liquids: Irrotational Flow and Quantization of Circulation"

In the context of an application to superfluidity, it is elaborated how to do
quantum mechanics of a system with a rotational velocity. Especially, in both
the laboratory frame and the non-inertial co-rotating frame, the canonical
momentum, which corresponds to the quantum mechanical momentum operator,
contains a part due to the rotational velocity.Comment: 2 page, comment on cond-mat/010435

### A heuristic approach to the weakly interacting Bose gas

Some thermodynamic properties of weakly interacting Bose systems are derived
from dimensional and heuristic arguments and thermodynamic relations, without
resorting to statistical mechanics

### Nonlinear Landau-Zener Tunnelling in Coupled Waveguide Arrays

The possibility of direct observation of Nonlinear Landau-Zener tunnelling
effect with a device consisting of two waveguide arrays connected with a tilted
reduced refractive index barrier is discussed. Numerical simulations on this
realistic setup are interpreted via simplified double well system and different
asymmetric tunnelling scenarios were predicted just varying injected beam
intensity.Comment: 5 pages, 6 figure

### Generalized Emission Functions for Photon Emission from Quark-Gluon Plasma

The Landau-Pomeranchuk-Migdal effects on photon emission from the quark gluon
plasma have been studied as a function of photon mass, at a fixed temperature
of the plasma. The integral equations for the transverse vector function (${\bf
\tilde{f}(\tilde{p}_\perp)}$) and the longitudinal function ($\tilde{g}({\bf
\tilde{p}_\perp})$) consisting of multiple scattering effects are solved by the
self consistent iterations method and also by the variational method for the
variable set \{$p_0,q_0,Q^2$\}, considering the bremsstrahlung and the $\bf
aws$ processes. We define four new dynamical scaling variables,
$x^b_T$,$x^a_T$,$x^b_L$,$x^a_L$ for bremsstrahlung and {\bf aws} processes and
analyse the transverse and longitudinal components as a function of
\{$p_0,q_0,Q^2$\}. We generalize the concept of photon emission function and we
define four new emission functions for massive photon emission represented by
$g^b_T$, $g^a_T$, $g^b_L$, $g^a_L$. These have been constructed using the exact
numerical solutions of the integral equations. These four emission functions
have been parameterized by suitable simple empirical fits. In terms of these
empirical emission functions, the virtual photon emission from quark gluon
plasma reduces to one dimensional integrals that involve folding over the
empirical $g^{b,a}_{T,L}$ functions with appropriate quark distribution
functions and the kinematic factors. Using this empirical emission functions,
we calculated the imaginary part of the photon polarization tensor as a
function of photon mass and energy.Comment: In nuclear physics journals and arxiv listings, my name used to
appear as S.V.S. Sastry. Hereafter, my name will appear as, S.V.
Suryanarayan

### The bound on viscosity and the generalized second law of thermodynamics

We describe a new paradox for ideal fluids. It arises in the accretion of an
\textit{ideal} fluid onto a black hole, where, under suitable boundary
conditions, the flow can violate the generalized second law of thermodynamics.
The paradox indicates that there is in fact a lower bound to the correlation
length of any \textit{real} fluid, the value of which is determined by the
thermodynamic properties of that fluid. We observe that the universal bound on
entropy, itself suggested by the generalized second law, puts a lower bound on
the correlation length of any fluid in terms of its specific entropy. With the
help of a new, efficient estimate for the viscosity of liquids, we argue that
this also means that viscosity is bounded from below in a way reminiscent of
the conjectured Kovtun-Son-Starinets lower bound on the ratio of viscosity to
entropy density. We conclude that much light may be shed on the
Kovtun-Son-Starinets bound by suitable arguments based on the generalized
second law.Comment: 11 pages, 1 figure, published versio

### Dynamic Structure Factor of Normal Fermi Gas from Collisionless to Hydrodynamic Regime

The dynamic structure factor of a normal Fermi gas is investigated by using
the moment method for the Boltzmann equation. We determine the spectral
function at finite temperatures over the full range of crossover from the
collisionless regime to the hydrodynamic regime. We find that the Brillouin
peak in the dynamic structure factor exhibits a smooth crossover from zero to
first sound as functions of temperature and interaction strength. The dynamic
structure factor obtained using the moment method also exhibits a definite
Rayleigh peak ($/omega /sim 0$), which is a characteristic of the hydrodynamic
regime. We compare the dynamic structure factor obtained by the moment method
with that obtained from the hydrodynamic equations.Comment: 19 pages, 9 figure

### Tunable pinning of a superconducting vortex a by a magnetic vortex

The interaction between a straight vortex line in a superconducting film and
a soft magnetic nanodisk in the magnetic vortex state in the presence of a
magnetic field applied parallel to the film surfaces is studied theoretically.
The superconductor is described by London theory and the nanodisk by the
Landau-Lifshitz continuum theory of magnetism, using the approximation known as
the rigid vortex model. Pinning of the vortex line by the nanodisk is found to
result, predominantly, from the interaction between the vortex line and the
changes in the nanodisk magnetization induced by the magnetic field of the
vortex line and applied field. In the context of the rigid vortex model, these
changes result from the displacement of the magnetic vortex. This displacement
is calculated analytically by minimizing the energy, and the pinning potential
is obtained. The applied field can tune the pinning potential by controlling
the displacement of the magnetic vortex. The nanodisk magnetization curve is
predicted to change in the presence of the vortex lineComment: 9 pages, 8 figures. Submitted to Phys. Rev.

### Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates

We study the behavior of a Bose-Einstein condensate in which atoms are weakly
coupled to a highly excited Rydberg state. Since the latter have very strong
van der Waals interactions, this coupling induces effective, nonlocal
interactions between the dressed ground state atoms, which, opposed to dipolar
interactions, are isotropically repulsive. Yet, one finds partial attraction in
momentum space, giving rise to a roton-maxon excitation spectrum and a
transition to a supersolid state in three-dimensional condensates. A detailed
analysis of decoherence and loss mechanisms suggests that these phenomena are
observable with current experimental capabilities.Comment: 4 pages, 5 figure

### 3+1D hydrodynamic simulation of relativistic heavy-ion collisions

We present MUSIC, an implementation of the Kurganov-Tadmor algorithm for
relativistic 3+1 dimensional fluid dynamics in heavy-ion collision scenarios.
This Riemann-solver-free, second-order, high-resolution scheme is characterized
by a very small numerical viscosity and its ability to treat shocks and
discontinuities very well. We also incorporate a sophisticated algorithm for
the determination of the freeze-out surface using a three dimensional
triangulation of the hyper-surface. Implementing a recent lattice based
equation of state, we compute p_T-spectra and pseudorapidity distributions for
Au+Au collisions at root s = 200 GeV and present results for the anisotropic
flow coefficients v_2 and v_4 as a function of both p_T and pseudorapidity. We
were able to determine v_4 with high numerical precision, finding that it does
not strongly depend on the choice of initial condition or equation of state.Comment: 16 pages, 11 figures, version accepted for publication in PRC,
references added, minor typos corrected, more detailed discussion of
freeze-out routine adde

### Modified Friedman scenario from the Wheeler-DeWitt equation

We consider the possible modification of the Friedman equation due to
operator ordering parameter entering the Wheeler-DeWitt equation.Comment: 2 pages, 1 figur

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