7,896 research outputs found
Dynamical density functional theory for dense atomic liquids
Starting from Newton's equations of motion, we derive a dynamical density
functional theory (DDFT) applicable to atomic liquids. The theory has the
feature that it requires as input the Helmholtz free energy functional from
equilibrium density functional theory. This means that, given a reliable
equilibrium free energy functional, the correct equilibrium fluid density
profile is guaranteed. We show that when the isothermal compressibility is
small, the DDFT generates the correct value for the speed of sound in a dense
liquid. We also interpret the theory as a dynamical equation for a coarse
grained fluid density and show that the theory can be used (making further
approximations) to derive the standard mode coupling theory that is used to
describe the glass transition. The present theory should provide a useful
starting point for describing the dynamics of inhomogeneous atomic fluids.Comment: 14 pages, accepted for publication in J. Phys.: Condens. Matte
Cosmological Constraints on Late-time Entropy Production
We investigate cosmological effects concerning the late-time entropy
production due to the decay of non-relativistic massive particles. The
thermalization process of neutrinos after the entropy production is properly
solved by using the Boltzmann equation. If a large entropy production takes
place at late time t 1 sec, it is found that a large fraction of
neutrinos cannot be thermalized. This fact loosens the tight constraint on the
reheating temperature T_R from the big bang nucleosynthesis and T_R could be as
low as 0.5 MeV. The influence on the large scale structure formation and cosmic
microwave background anisotropies is also discussed.Comment: 4 pages, using RevTeX and five postscript figures, comments added, to
appear in Phys. Rev. Let
Critical behavior of self-assembled rigid rods on triangular and honeycomb lattices
Using Monte Carlo simulations and finite-size scaling analysis, the critical
behavior of self-assembled rigid rods on triangular and honeycomb lattices at
intermediate density has been studied. The system is composed of monomers with
two attractive (sticky) poles that, by decreasing temperature or increasing
density, polymerize reversibly into chains with three allowed directions and,
at the same time, undergo a continuous isotropic-nematic (IN) transition. The
determination of the critical exponents, along with the behavior of Binder
cumulants, indicate that the IN transition belongs to the q=1 Potts
universality class.Comment: 6 pages, 5 figure
Thermal Conductivity and Chiral Critical Point in Heavy Ion Collisions
Background: Quantum Chromodynamics is expected to have a phase transition in
the same static universality class as the 3D Ising model and the liquid-gas
phase transition. The properties of the equation of state, the transport
coefficients, and especially the location of the critical point are under
intense theoretical investigation. Some experiments are underway, and many more
are planned, at high energy heavy ion accelerators. Purpose: Develop a model of
the thermal conductivity, which diverges at the critical point, and use it to
study the impact of hydrodynamic fluctuations on observables in high energy
heavy ion collisions. Methods: We apply mode coupling theory, together with a
previously developed model of the free energy that incorporates the critical
exponents and amplitudes, to construct a model of the thermal conductivity in
the vicinity of the critical point. The effect of the thermal conductivity on
correlation functions in heavy ion collisions is studied in a boost invariant
hydrodynamic model via fluctuations, or noise. Results: We find that the closer
a thermodynamic trajectory comes to the critical point the greater is the
magnitude of the fluctuations in thermodynamic variables and in the 2-particle
correlation functions in momentum space. Conclusions: It may be possible to
discern the existence of a critical point, its location, and thermodynamic and
transport properties near to it in heavy ion collisions using the methods
developed here.Comment: 36 pages, 8 figures. Version published in Phys.Rev.C86, 054911
(2012). It contains some minor improvements with respect to v1: further
clarifications, small changes on figures and two extra reference
Long Time Tail of the Velocity Autocorrelation Function in a Two-Dimensional Moderately Dense Hard Disk Fluid
Alder and Wainwright discovered the slow power decay
(:dimension) of the velocity autocorrelation function in moderately dense
hard sphere fluids using the event-driven molecular dynamics simulations. In
the two-dimensional case, the diffusion coefficient derived using the time
correlation expression in linear response theory shows logarithmic divergence,
which is called the ``2D long-time-tail problem''. We revisited this problem to
perform a large-scale, long-time simulation with one million hard disks using a
modern efficient algorithm and found that the decay of the long tail in
moderately dense fluids is slightly faster than the power decay ().
We also compared our numerical data with the prediction of the self-consistent
mode-coupling theory in the long time limit ().Comment: 5 pages, 5 figures, to appear in Phys. Rev.
Coexistence of Superconductivity and Antiferromagnetism in Heavy-Fermion Superconductor CeCu_{2}(Si_{1-x}Ge_{x})_{2} Probed by Cu-NQR --A Test Case for the SO(5) Theory--
We report on the basis of Cu-NQR measurements that superconductivity (SC) and
antiferromagnetism (AF) coexist on a microscopic level in
CeCu_{2}(Si_{1-x}Ge_{x})_{2}, once a tiny amount of 1%Ge (x = 0.01) is
substituted for Si. This coexistence arises because Ge substitution expands the
unit-cell volume in nearly homogeneous CeCu2Si2 where the SC coexists with
slowly fluctuating magnetic waves. We propose that the underlying exotic phases
of SC and AF in either nearly homogeneous or slightly Ge substituted CeCu2Si2
are accountable based on the SO(5) theory that unifies the SC and AF. We
suggest that the mechanism of the SC and AF is common in CeCu2Si2.Comment: 7 pages with 6 figures embedded in the text. To be published in J.
Phys. Condens. Matter, 200
Curvaton Scenario with Affleck-Dine Baryogenesis
We discuss the curvaton scenario with the Affleck-Dine baryogenesis. In this
scenario, non-vanishing baryonic entropy fluctuation may be generated even
without primordial fluctuation of the Affleck-Dine field. Too large entropy
fluctuation is inconsistent with the observations and hence constraints on the
curvaton scenario with the Affleck-Dine baryogenesis are obtained. We calculate
the baryonic entropy fluctuation (as well as other cosmological density
fluctuations) in this case and derive constraints. Implications to some of the
models of the curvaton are also discussed.Comment: 16 pages,2 figure
Frequency Dependent Viscosity Near the Critical Point: The Scale to Two Loop Order
The recent accurate measurements of Berg, Moldover and Zimmerli of the
viscoelastic effect near the critical point of xenon has shown that the scale
factor involved in the frequency scaling is about twice the scale factor
obtained theoretically. We show that this discrepancy is a consequence of using
first order perturbation theory. Including two loop contribution goes a long
way towards removing the discrepancy.Comment: No of pages:7,Submitted to PR-E(Rapid Communication),No of EPS
files:
Superheavy Dark Matter and Thermal Inflation
The thermal inflation is the most plausible mechanism that solves the
cosmological moduli problem naturally. We discuss relic abundance of superheavy
particle in the presence of the thermal inflation assuming that its
lifetime is longer than the age of the universe, and show that the long-lived
particle of mass -- GeV may form a part of the dark
matter in the present universe in a wide region of parameter space of the
thermal inflation model. The superheavy dark matter of mass GeV
may be interesting in particular, since its decay may account for the observed
ultra high-energy cosmic rays if the lifetime of the particle is
sufficiently long.Comment: 13 pages (RevTex file) including 8 figures, revised version to be
published in Physical Review
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