1,178 research outputs found
Hadron-quark continuity induced by the axial anomaly in dense QCD
We investigate the interplay between the chiral and diquark condensates on
the basis of the Ginzburg-Landau potential with QCD symmetry. We demonstrate
that the axial anomaly drives a new critical point at low temperature in the
QCD phase diagram and leads to a smooth crossover between the hadronic and
color superconducting phases.Comment: 4 pages, 5 figures, to appear in the Proceedings of Quark Matter 2006
held in Shangha
Aspect ratio analysis for ground states of bosons in anisotropic traps
Characteristics of the initial condensate in the recent experiment on
Bose-Einstein condensation (BEC) of Rb atoms in an anisotropic
magnetic trap is discussed. Given the aspect ratio , the quality of BEC is
estimated. A simple analytical Ansatz for the initial condensate wave function
is proposed as a function of the aspect ratio which, in contrast to the
Baym-Pethick trial wave function, reproduces both the weak and the strong
intaraction limits and which is in better agreement with numerical results than
the latter.Comment: 12 pages, latex, 3 figures added, minor corrections; to appear in J.
Res. Nat. Inst. of Standards and Technolog
Photon scattering from strongly driven atomic ensembles
The second order correlation function for light emitted from a strongly and
near-resonantly driven dilute cloud of atoms is discussed. Because of the
strong driving, the fluorescence spectrum separates into distinct peaks, for
which the spectral properties can be defined individually. It is shown that the
second-order correlations for various combinations of photons from different
spectral lines exhibit bunching together with super- or sub-Poissonian photon
statistics, tunable by the choice of the detector positions. Additionally, a
Cauchy-Schwarz inequality is violated for photons emitted from particular
spectral bands. The emitted light intensity is proportional to the square of
the number of particles, and thus can potentially be intense. Three different
averaging procedures to model ensemble disorder are compared.Comment: 7 pages, 4 figure
Conserving Gapless Mean-Field Theory for Bose-Einstein Condensates
We formulate a conserving gapless mean-field theory for Bose-Einstein
condensates on the basis of a Luttinger-Ward thermodynamic functional. It is
applied to a weakly interacting uniform gas with density and s-wave
scattering length to clarify its fundamental thermodynamic properties. It
is found that the condensation here occurs as a first-order transition. The
shift of the transition temperature from the ideal-gas result
is positive and given to the leading order by , in agreement with a couple of previous estimates. The theory is
expected to form a new theoretical basis for trapped Bose-Einstein condensates
at finite temperatures.Comment: Minor errors remove
Fragmentation of Bose-Einstein Condensates
We present the theory of bosonic systems with multiple condensates, unifying
disparate models which are found in the literature, and discuss how
degeneracies, interactions, and symmetries conspire to give rise to this
unusual behavior. We show that as degeneracies multiply, so do the types of
fragmentation, eventually leading to strongly correlated states with no trace
of condensation.Comment: 16 pages, 1 figure, revtex
Renormalization in Self-Consistent Approximations schemes at Finite Temperature I: Theory
Within finite temperature field theory, we show that truncated
non-perturbative self-consistent Dyson resummation schemes can be renormalized
with local counter-terms defined at the vacuum level. The requirements are that
the underlying theory is renormalizable and that the self-consistent scheme
follows Baym''s -derivable concept. The scheme generates both, the
renormalized self-consistent equations of motion and the closed equations for
the infinite set of counter terms. At the same time the corresponding
2PI-generating functional and the thermodynamical potential can be
renormalized, in consistency with the equations of motion. This guarantees the
standard -derivable properties like thermodynamic consistency and exact
conservation laws also for the renormalized approximation schemes to hold. The
proof uses the techniques of BPHZ-renormalization to cope with the explicit and
the hidden overlapping vacuum divergences.Comment: 22 Pages 1 figure, uses RevTeX4. The Revision concerns the correction
of some minor typos, a clarification concerning the real-time contour
structure of renormalization parts and some comments concerning symmetries in
the conclusions and outloo
A planar extrapolation of the correlation problem that permits pairing
It was observed previously that an SU(N) extension of the Hubbard model is
dominated, at large N, by planar diagrams in the sense of 't Hooft, but the
possibility of superconducting pairing got lost in this extrapolation. To allow
for this possibility, we replace SU(N) by U(N,q), the unitary group in a vector
space of quaternions. At the level of the free energy, the difference between
the SU(N)and U(N,q) extrapolations appears only to first nonleading order in N.Comment: 8 pages, 2 figure
Bose-Einstein transition temperature in a dilute repulsive gas
We discuss certain specific features of the calculation of the critical
temperature of a dilute repulsive Bose gas. Interactions modify the critical
temperature in two different ways. First, for gases in traps, temperature
shifts are introduced by a change of the density profile, arising itself from a
modification of the equation of state of the gas (reduced compressibility);
these shifts can be calculated simply within mean field theory. Second, even in
the absence of a trapping potential (homogeneous gas in a box), temperature
shifts are introduced by the interactions; they arise from the correlations
introduced in the gas, and thus lie inherently beyond mean field theory - in
fact, their evaluation requires more elaborate, non-perturbative, calculations.
One illustration of this non-perturbative character is provided by the solution
of self-consistent equations, which relate together non-linearly the various
energy shifts of the single particle levels k. These equations predict that
repulsive interactions shift the critical temperature (at constant density) by
an amount which is positive, and simply proportional to the scattering length
a; nevertheless, the numerical coefficient is difficult to compute. Physically,
the increase of the temperature can be interpreted in terms of the reduced
density fluctuations introduced by the repulsive interactions, which facilitate
the propagation of large exchange cycles across the sample.Comment: two minor corrections, two refs adde
Expansion, Thermalization and Entropy Production in High-Energy Nuclear Collisions
The thermalization process is studied in an expanding parton gas using the
Boltzmann equation with two types of collision terms. In the relaxation time
approximation we determine the criteria under which a time-dependent relaxation
time leads to thermalization of the partons. We calculate the entropy
production due to collisions for the general time-dependent relaxation time. In
a perturbative QCD approach on the other hand, we can estimate the parton
collision time and its dependence on expansion time. The effective `out of
equilibrium' collision time differs from the standard transport relaxation
time, , by a weak time
dependence. It is in both cases Debye screening and Landau damping that
regulate the singular forward scattering processes. We find that the parton gas
does thermalize eventually but only after having undergone a phase of free
streaming and gradual equilibration where considerable entropy is produced
(``after-burning"). The final entropy and thus particle density depends on the
collision time as well as the initial conditions (a ``memory effect"). Results
for entropy production are presented based upon various model estimates of
early parton production.Comment: 15 pages revtex + 4 figures. Figures can be obtained by supplying
address to: [email protected]
Bose Metals and Insulators on Multi-Leg Ladders with Ring Exchange
We establish compelling evidence for the existence of new
quasi-one-dimensional descendants of the d-wave Bose liquid (DBL), an exotic
two-dimensional quantum phase of uncondensed itinerant bosons characterized by
surfaces of gapless excitations in momentum space [O. I. Motrunich and M. P. A.
Fisher, Phys. Rev. B {\bf 75}, 235116 (2007)]. In particular, motivated by a
strong-coupling analysis of the gauge theory for the DBL, we study a model of
hard-core bosons moving on the -leg square ladder with frustrating four-site
ring exchange. Here, we focus on four- and three-leg systems where we have
identified two novel phases: a compressible gapless Bose metal on the four-leg
ladder and an incompressible gapless Mott insulator on the three-leg ladder.
The former is conducting along the ladder and has five gapless modes, one more
than the number of legs. This represents a significant step forward in
establishing the potential stability of the DBL in two dimensions. The latter,
on the other hand, is a fundamentally quasi-one-dimensional phase that is
insulating along the ladder but has two gapless modes and incommensurate power
law transverse density-density correlations. In both cases, we can understand
the nature of the phase using slave-particle-inspired variational wave
functions consisting of a product of two distinct Slater determinants, the
properties of which compare impressively well to a density matrix
renormalization group solution of the model Hamiltonian. Stability arguments
are made in favor of both quantum phases by accessing the universal low-energy
physics with a bosonization analysis of the appropriate quasi-1D gauge theory.
We will briefly discuss the potential relevance of these findings to
high-temperature superconductors, cold atomic gases, and frustrated quantum
magnets.Comment: 33 pages, 16 figures; this is the print version, only very minor
changes from v
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