3,939 research outputs found
Energy and structure of dilute hard- and soft-sphere gases
The energy and structure of dilute hard- and soft-sphere Bose gases are
systematically studied in the framework of several many-body approaches, as the
variational correlated theory, the Bogoliubov model and the uniform limit
approximation, valid in the weak interaction regime. When possible, the results
are compared with the exact diffusion Monte Carlo ones. A Jastrow type
correlation provides a good description of the systems, both hard- and
soft-spheres, if the hypernetted chain energy functional is freely minimized
and the resulting Euler equation is solved. The study of the soft-spheres
potentials confirms the appearance of a dependence of the energy on the shape
of the potential at gas paremeter values of . For quantities
other than the energy, such as the radial distribution functions and the
momentum distributions, the dependence appears at any value of . The
occurrence of a maximum in the radial distribution function, in the momentum
distribution and in the excitation spectrum is a natural effect of the
correlations when increases. The asymptotic behaviors of the functions
characterizing the structure of the systems are also investigated. The uniform
limit approach results very easy to implement and provides a good description
of the soft-sphere gas. Its reliability improves when the interaction weakens.Comment: Accepted in Phys. Rev.
The confining trailing string
We extend the holographic trailing string picture of a heavy quark to the
case of a bulk geometry dual to a confining gauge theory. We compute the
classical trailing confining string solution for a static as well as a
uniformly moving quark. The trailing string is infinitely extended and
approaches a confining horizon, situated at a critical value of the radial
coordinate, along one of the space-time directions, breaking boundary
rotational invariance. We compute the equations for the fluctuations around the
classical solutions, which are used to obtain boundary force correlators
controlling the Langevin dynamics of the quark. The imaginary part of the
correlators has a non-trivial low-frequency limit, which gives rise to a
viscous friction coefficient induced by the confining vacuum. The vacuum
correlators are used to define finite-temperature dressed Langevin correlators
with an appropriate high-frequency behavior.Comment: 63 pages plus appendices, 19 figures; version accepted for
publication in JHE
Ground state properties and excitation spectrum of a two dimensional gas of bosonic dipoles
We present a quantum Monte Carlo study of two-dimensional dipolar Bose gases
in the limit of zero temperature. The analysis is mainly focused on the
anisotropy effects induced in the homogeneous gas when the polarization angle
with respect to the plane is changed. We restrict our study to the regime where
the dipolar interaction is strictly repulsive, although the strength of the
pair repulsion depends on the vector interparticle distance. Our results show
that the effect of the anisotropy in the energy per particle scales with the
gas parameter at low densities as expected, and that this scaling is preserved
for all polarization angles even at the largest densities considered here. We
also evaluate the excitation spectrum of the dipolar Bose gas in the context of
the Feynman approximation and compare the results obtained with the Bogoliubov
ones. As expected, we find that these two approximations agree at very low
densities, while they start to deviate from each other as the density
increases. For the largest densities studied, we observe a significant
influence of the anisotropy of the dipole-dipole interaction in the excitation
spectrum.Comment: 6 pages, 6 figure
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