269 research outputs found
Dressed Feshbach molecules in the BEC-BCS crossover
We present the RPA theory of the BEC-BCS crossover in an atomic Fermi gas
near a Feshbach resonance that includes the relevant two-body atomic physics
exactly. This allows us to determine the probability for the dressed
molecules in the Bose-Einstein condensate to be in the closed channel of the
Feshbach resonance and to compare with the recent experiments of Partridge {\it
et al.} [cond-mat/0505353] with Li. We determine for this extremely broad
resonance also the condensate density of the dressed molecules throughout the
BEC-BCS crossover.Comment: 4 pages, 3 figure
Sarma Phase in Trapped Unbalanced Fermi Gases
We consider a trapped unbalanced Fermi gas at nonzero temperatures where the
superfluid Sarma phase is stable. We determine in particular the phase
boundaries between the superfluid, normal, and phase separated regions of the
trapped unbalanced Fermi mixture. We show that the physics of the Sarma phase
is sufficient to understand the recent observations of Zwierlein et al.
[Science 311, 492 (2006); Nature 442, 54 (2006)] and indicate how the apparent
contradictions between this experiment and the experiment of Partridge et al.
[Science 311, 503 (2006)] may be resolved.Comment: Replaced with published version; 4 pages, 3 figure
Quantum phase transition in an atomic Bose gas with a Feshbach resonance
We show that in an atomic Bose gas near a Feshbach resonance a quantum phase
transition occurs between a phase with only a molecular Bose-Einstein
condensate and a phase with both an atomic and a molecular Bose-Einstein
condensate. We show that the transition is characterized by an Ising order
parameter. We also determine the phase diagram of the gas as a function of
magnetic field and temperature: the quantum critical point extends into a line
of finite temperature Ising transitions.Comment: 4 pages, 2 figure
Bogoliubov theory of Feshbach molecules in the BEC-BCS crossover
We present the Bogoliubov theory for the Bose-Einstein condensation of
Feshbach molecules in a balanced Fermi mixture. Because the Bogoliubov theory
includes (Gaussian) fluctuations, we can in this manner accurately incorporate
both the two-body and many-body aspects of the BEC-BCS crossover that occurs
near a Feshbach resonance. We apply the theory in particular to the very broad
Feshbach resonance in atomic Li-6 at a magnetic field of B_0 = 834 G and find
good agreement with experiments in that case. The BEC-BCS crossover for more
narrow Feshbach resonances is also discussed.Comment: 13 pages of RevTex and 12 Figures. Submitted for publication in
Physical review
Phase Transitions and Critical Behavior for Charged Black Holes
We investigate the thermodynamics of a four-dimensional charged black hole in
a finite cavity in asymptotically flat and asymptotically de Sitter space. In
each case, we find a Hawking-Page-like phase transition between a black hole
and a thermal gas very much like the known transition in asymptotically anti-de
Sitter space. For a ``supercooled'' black hole--a thermodynamically unstable
black hole below the critical temperature for the Hawking-Page phase
transition--the phase diagram has a line of first-order phase transitions that
terminates in a second order point. For the asymptotically flat case, we
calculate the critical exponents at the second order phase transition and find
that they exactly match the known results for a charged black hole in anti-de
Sitter space. We find strong evidence for similar phase transitions for the de
Sitter black hole as well. Thus many of the thermodynamic features of charged
anti-de Sitter black holes do not really depend on asymptotically anti-de
Sitter boundary conditions; the thermodynamics of charged black holes is
surprisingly universal.Comment: LaTeX, 14 pages, 9 eps figures; higher resolution figures available
on reques
Regularisation, the BV method, and the antibracket cohomology
We review the Lagrangian Batalin--Vilkovisky method for gauge theories. This
includes gauge fixing, quantisation and regularisation. We emphasize the role
of cohomology of the antibracket operation. Our main example is gravity,
for which we also discuss the solutions for the cohomology in the space of
local integrals. This leads to the most general form for the action, for
anomalies and for background charges.Comment: 12 pages, LaTeX, Preprint-KUL-TF-94/2
Cosmological Multi-Black Hole Solutions
We present simple, analytic solutions to the Einstein-Maxwell equation, which
describe an arbitrary number of charged black holes in a spacetime with
positive cosmological constant . In the limit , these
solutions reduce to the well known Majumdar-Papapetrou (MP) solutions. Like the
MP solutions, each black hole in a solution has charge equal
to its mass , up to a possible overall sign. Unlike the limit,
however, solutions with are highly dynamical. The black holes move
with respect to one another, following natural trajectories in the background
deSitter spacetime. Black holes moving apart eventually go out of causal
contact. Black holes on approaching trajectories ultimately merge. To our
knowledge, these solutions give the first analytic description of coalescing
black holes. Likewise, the thermodynamics of the solutions is
quite interesting. Taken individually, a black hole is in thermal
equilibrium with the background deSitter Hawking radiation. With more than one
black hole, because the solutions are not static, no global equilibrium
temperature can be defined. In appropriate limits, however, when the black
holes are either close together or far apart, approximate equilibrium states
are established.Comment: 15 pages (phyzzx), UMHEP-380 (minor referencing error corrected
Supersymmetry of Black Strings in D=5 Gauged Supergravities
Supersymmetry of five dimensional string solutions is examined in the context
of gauged D=5, N=2 supergravity coupled to abelian vector multiplets. We find
magnetic black strings preserving one quarter of supersymmetry and approaching
the half-supersymmetric product space AdS_3\times H^2 near the event horizon.
The solutions thus exhibit the phenomenon of supersymmetry enhancement near the
horizon, like in the cases of ungauged supergravity theories, where the near
horizon limit is fully supersymmetric. Finally, product space compactifications
are studied in detail, and it is shown that only for negative curvature
(hyperbolic) internal spaces, some amount of supersymmetry can be preserved.
Among other solutions, we find that the extremal rotating BTZ black hole
tensored by H^2 preserves one quarter of supersymmetry.Comment: 19 pages, LaTeX, no figures, published versio
The structure of the extreme Schwarzschild-de Sitter space-time
The extreme Schwarzschild-de Sitter space-time is a spherically symmetric
solution of Einstein's equations with a cosmological constant Lambda and mass
parameter m>0 which is characterized by the condition that 9 Lambda m^2=1. The
global structure of this space-time is here analyzed in detail. Conformal and
embedding diagrams are constructed, and synchronous coordinates which are
suitable for a discussion of the cosmic no-hair conjecture are presented. The
permitted geodesic motions are also analyzed. By a careful investigation of the
geodesics and the equations of geodesic deviation, it is shown that specific
families of observers escape from falling into the singularity and approach
nonsingular asymptotic regions which are represented by special "points" in the
complete conformal diagram. The redshift of signals emitted by particles which
fall into the singularity, as detected by those observers which escape, is also
calculated.Comment: 19 pages, 10 figures, LaTeX, to appear in Gen. Rel. Gra
Supersymmetric String Waves
We present plane-wave-type solutions of the lowest order superstring
effective action which have unbroken space-time supersymmetries. They describe
dilaton, axion and gauge fields in a stringy generalization of the Brinkmann
metric. Some conspiracy between the metric and the axion field is required. We
show that there exists a special class of these solutions, for which
stringy corrections to the effective on-shell action, to the
equations of motion (and therefore to the solutions themselves), and to the
supersymmetry transformations vanish. We call these solutions supersymmetric
string waves (SSW).Comment: 19 pages, LaTeX, SU-ITP-92-30 and UG-10/9
- …