3,783 research outputs found

### Condensate density and superfluid mass density of a dilute Bose gas near the condensation transition

We derive, through analysis of the structure of diagrammatic perturbation
theory, the scaling behavior of the condensate and superfluid mass density of a
dilute Bose gas just below the condensation transition. Sufficiently below the
critical temperature, $T_c$, the system is governed by the mean field
(Bogoliubov) description of the particle excitations. Close to $T_c$, however,
mean field breaks down and the system undergoes a second order phase
transition, rather than the first order transition predicted in Bogoliubov
theory. Both condensation and superfluidity occur at the same critical
temperature, $T_c$ and have similar scaling functions below $T_c$, but
different finite size scaling at $T_c$ to leading order in the system size.
Through a simple self-consistent two loop calculation we derive the critical
exponent for the condensate fraction, $2\beta\simeq 0.66$.Comment: 4 page

### Event-by-Event Fluctuations in Ultrarelativistic Heavy-Ion Collisions

Motivated by forthcoming experiments at RHIC and LHC, we study event-by-event
fluctuations in ultrarelativistic heavy-ion collisions in participant nucleon
as well as thermal models. The calculated physical observables, including
multiplicity, kaon to pion ratios, and transverse momenta agree well with
recent NA49 data at the SPS, and indicate that such studies do not yet reveal
the presence of new physics. Finally, we present a simple model of how a first
order phase transition can be signaled by very large fluctuations.Comment: final version, 4 pages, to appear in Phys. Lett.

### RHIC: From dreams to beams in two decades

This talk traces the history of RHIC over the last two decades, reviewing the
scientific motivations underlying its design, and the challenges and
opportunities the machine presents.Comment: To be published in Proceedings of Quark Matter '01. 10 pages, 1
figur

### Neutron stars and quark matter

Recent observations of neutron star masses close to the maximum predicted by
nucleonic equations of state begin to challenge our understanding of dense
matter in neutron stars, and constrain the possible presence of quark matter in
their deep interiors.Comment: To be published in the proceedings of Quark Confinement and the
Hadron Spectrum VII, Sept. 2006, Ponta Delgada, Azores. 7 pages, 3 figures,
aipro

### Vortex lattices in rapidly rotating Bose-Einstein condensates: modes and correlation functions

After delineating the physical regimes which vortex lattices encounter in
rotating Bose-Einstein condensates as the rotation rate, $\Omega$, increases,
we derive the normal modes of the vortex lattice in two dimensions at zero
temperature. Taking into account effects of the finite compressibility, we find
an inertial mode of frequency $\ge 2\Omega$, and a primarily transverse
Tkachenko mode, whose frequency goes from being linear in the wave vector in
the slowly rotating regime, where $\Omega$ is small compared with the lowest
compressional mode frequency, to quadratic in the wave vector in the opposite
limit. We calculate the correlation functions of vortex displacements and
phase, density and superfluid velocities, and find that the zero-point
excitations of the soft quadratic Tkachenko modes lead in a large system to a
loss of long range phase correlations, growing logarithmically with distance,
and hence lead to a fragmented state at zero temperature. The vortex positional
ordering is preserved at zero temperature, but the thermally excited Tkachenko
modes cause the relative positional fluctuations to grow logarithmically with
separation at finite temperature. The superfluid density, defined in terms of
the transverse velocity autocorrelation function, vanishes at all temperatures.
Finally we construct the long wavelength single particle Green's function in
the rotating system and calculate the condensate depletion as a function of
temperature.Comment: 11 pages Latex, no figure

### Renormalization of interactions of ultracold atoms in simulated Rashba gauge fields

Interactions of ultracold atoms with Rashba spin-orbit coupling, currently
being studied with simulated (artificial) gauge fields, have nontrivial
ultraviolet and infrared behavior. Examining the ultraviolet structure of the
Bethe-Salpeter equation, we show that the linear ultraviolet divergence in the
bare interaction can be renormalized as usual in terms of low-energy scattering
lengths, and that for both bosons and fermions ultraviolet logarithmic
divergences are absent. Calculating the leading order effective interaction
with full dependence on the spin-orbit coupling strength and the center-of-mass
momentum of the colliding pair, we elucidate the relation between mean-field
interactions and physical three-dimensional scattering lengths. As a
consequence of infrared logarithmic divergences in the two-particle propagator,
the effective interaction vanishes as the center-of-mass momentum approaches
zero.Comment: 4 pages, 2 figures, published versio

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