86,801 research outputs found
Demixing can occur in binary hard-sphere mixtures with negative non-additivity
A binary fluid mixture of non-additive hard spheres characterized by a size
ratio and a non-additivity parameter
is considered in infinitely many
dimensions. From the equation of state in the second virial approximation
(which is exact in the limit ) a demixing transition with a
critical consolute point at a packing fraction scaling as
is found, even for slightly negative non-additivity, if
. Arguments concerning the stability of the
demixing with respect to freezing are provided.Comment: 4 pages, 2 figures; title changed; final paragraph added; to be
published in PRE as a Rapid Communicatio
Computer simulation of uniformly heated granular fluids
Direct Monte Carlo simulations of the Enskog-Boltzmann equation for a
spatially uniform system of smooth inelastic spheres are performed. In order to
reach a steady state, the particles are assumed to be under the action of an
external driving force which does work to compensate for the collisional loss
of energy. Three different types of external driving are considered: (a) a
stochastic force, (b) a deterministic force proportional to the particle
velocity and (c) a deterministic force parallel to the particle velocity but
constant in magnitude. The Enskog-Boltzmann equation in case (b) is fully
equivalent to that of the homogeneous cooling state (where the thermal velocity
monotonically decreases with time) when expressed in terms of the particle
velocity relative to the thermal velocity. Comparison of the simulation results
for the fourth cumulant and the high energy tail with theoretical predictions
derived in cases (a) and (b) [T. P. C. van Noije and M. H. Ernst, Gran. Matt.
1, 57 (1998)] shows a good agreement. In contrast to these two cases, the
deviation from the Maxwell-Boltzmann distribution is not well represented by
Sonine polynomials in case (c), even for low dissipation. In addition, the high
energy tail exhibits an underpopulation effect in this case.Comment: 18 pages (LaTex), 10 figures (eps); to be published in Granular
Matte
Phenomenological Comparison of Models with Extended Higgs Sectors
Beyond the Standard Model (SM) extensions usually include extended Higgs
sectors. Models with singlet or doublet fields are the simplest ones that are
compatible with the parameter constraint. The discovery of new non-SM
Higgs bosons and the identification of the underlying model requires dedicated
Higgs properties analyses. In this paper, we compare several Higgs sectors
featuring 3 CP-even neutral Higgs bosons that are also motivated by their
simplicity and their capability to solve some of the flaws of the SM. They are:
the SM extended by a complex singlet field (CxSM), the singlet extension of the
2-Higgs-Doublet Model (N2HDM), and the Next-to-Minimal Supersymmetric SM
extension (NMSSM). In addition, we analyse the CP-violating 2-Higgs-Doublet
Model (C2HDM), which provides 3 neutral Higgs bosons with a pseudoscalar
admixture. This allows us to compare the effects of singlet and pseudoscalar
admixtures. Through dedicated scans of the allowed parameter space of the
models, we analyse the phenomenologically viable scenarios from the view point
of the SM-like Higgs boson and of the signal rates of the non-SM-like Higgs
bosons to be found. In particular, we analyse the effect of
singlet/pseudoscalar admixture, and the potential to differentiate these models
in the near future. This is supported by a study of couplings sums of the Higgs
bosons to massive gauge bosons and to fermions, where we identify features that
allow us to distinguish the models, in particular when only part of the Higgs
spectrum is discovered. Our results can be taken as guidelines for future LHC
data analyses, by the ATLAS and CMS experiments, to identify specific benchmark
points aimed at revealing the underlying model.Comment: Matches journal version; figures for NMSSM changed; conclusions
unchange
Non-equilibrium tube length fluctuations of entangled polymers
We investigate the nonequilibrium tube length fluctuations during the
relaxation of an initially stretched, entangled polymer chain. The
time-dependent variance of the tube length follows in the early-time
regime a simple universal power law originating in the
diffusive motion of the polymer segments. The amplitude is calculated
analytically both from standard reptation theory and from an exactly solvable
lattice gas model for reptation and its dependence on the initial and
equilibrium tube length respectively is discussed. The non-universality
suggests the measurement of the fluctuations (e.g. using flourescence
microscopy) as a test for reptation models.Comment: 12 pages, 2 figures. Minor typos correcte
Loading of a Bose-Einstein condensate in the boson-accumulation regime
We study the optical loading of a trapped Bose-Einstein condensate by
spontaneous emission of atoms in excited electronic state in the
Boson-Accumulation Regime. We generalize the previous simplified analysis of
ref. [Phys. Rev. A 53, 2466 (1996)], to a 3D case in which more than one trap
level of the excited state trap is considered. By solving the corresponding
quantum many-body master equation, we demonstrate that also for this general
situation the photon reabsorption can help to increase the condensate fraction.
Such effect could be employed to realize a continuous atom laser, and to
overcome condensate losses.Comment: 7 pages, 5 eps figures, uses epl.st
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