1,989 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

### 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

### Density profiles of polarized Fermi gases confined in harmonic traps

On the basis of the phase diagram of the uniform system we calculate the
density profiles of a trapped polarized Fermi gas at zero temperature using the
local density approximation. By varying the overall polarization and the
interaction strength we analyze the appearance of a discontinuity in the
profile, signalling a first order phase transition from a superfluid inner core
to a normal outer shell. The local population imbalance between the two
components and the size of the various regions of the cloud corresponding to
different phases are also discussed. The calculated profiles are quantitatively
compared with the ones recently measured by Shin {\it et al.}, Phys. Rev. Lett.
{\bf 101}, 070404 (2008).Comment: 6 pages, 4 figures. We added references and modified the figure

### Strong Interaction Dynamics from Spontaneous Symmetry Breaking of Scale Invariance

Using the mechanism of spontaneous symmetry breaking of scale invariance
obtained from the dynamics of maximal rank field strengths, it is possible to
spontaneously generate confining behavior. Introducing a dilaton field, the
study of non trivial confining and de-confining transitions appears possible.
This is manifest in two ways at least: One can consider bags which contain an
unconfined phase in the internal region and a confined phase outside and also
one obtains a simple model for deconfinement at high Temperature from the
finite Temperature dynamics of the dilaton field.Comment: Latex, 5 pages, references added, few typos corrected and more
consistent notation introduced. Final version to appear in Mod. Phys. Lett.

### Color, Spin and Flavor Diffusion in Quark-Gluon Plasmas

In weakly interacting quark-gluon plasmas diffusion of color is found to be
much slower than the diffusion of spin and flavor because color is easily
exchanged by the gluons in the very singular forward scattering processes. If
the infrared divergence is cut off by a magnetic mass, $m_{mag}\sim \alpha_sT$,
the color diffusion is $D_{color}\sim (\alpha_s\ln(1/\alpha_s)T)^{-1}$, a
factor $\alpha_s$ smaller than spin and flavor diffusion. A similar effect is
expected in electroweak plasmas above $M_W$ due to $W^\pm$ exchanges. The color
conductivity in quark-gluon plasmas and the electrical conductivity in
electroweak plasmas are correspondingly small in relativistic heavy ion
collisions and the very early universe.Comment: 5 pages, no figure

### 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

### Low Energy Dynamics in Ultradegenerate QCD Matter

We study the low energy behavior of QCD Green functions in the limit that the
baryon chemical potential is much larger than the QCD scale parameter
$\Lambda_QCD$. We show that there is a systematic low energy expansion in
powers of $(\omega/m)^{1/3}$, where $\omega$ is the energy and $m$ is the
screening scale. This expansion is valid even if the effective quark-gluon
coupling $g$ is not small. The expansion is purely perturbative in the magnetic
regime $|\vec{k}| \gg k_0$. If the external momenta and energies satisfy $k_0
\sim |\vec{k}|$, planar, abelian ladder diagrams involving the full quark
propagator have to be resummed but the corresponding Dyson-Schwinger equations
are closed.Comment: 4 pages, published versio

### Spin-correlation functions in ultracold paired atomic-fermion systems: sum rules, self-consistent approximations, and mean fields

The spin response functions measured in multi-component fermion gases by
means of rf transitions between hyperfine states are strongly constrained by
the symmetry of the interatomic interactions. Such constraints are reflected in
the spin f-sum rule that the response functions must obey. In particular, only
if the effective interactions are not fully invariant in SU(2) spin space, are
the response functions sensitive to mean field and pairing effects. We
demonstrate, via a self-consistent calculation of the spin-spin correlation
function within the framework of Hartree-Fock-BCS theory, how one can derive a
correlation function explicitly obeying the f-sum rule. By contrast, simple
one-loop approximations to the spin response functions do not satisfy the sum
rule. As we show, the emergence of a second peak at higher frequency in the rf
spectrum, as observed in a recent experiment in trapped $^6\text{Li}$, can be
understood as the contribution from the paired fermions, with a shift of the
peak from the normal particle response proportional to the square of the BCS
pairing gap.Comment: 7 pages, 1 figure, content adde

### Peierls substitution in the energy dispersion of a hexagonal lattice

The method of the Peierls substitution in studying the magnetic subband
structure of a hexagonal lattice is re-examined. Several errors in the
formalism of a couple of recent papers are pointed out and rectified so as to
describe the effect of the magnetic field pertinently.Comment: 3 pages (two-columns), 2 EPS figures, submitted to J. Phys.: Condens.
Matte

### Tkachenko modes of vortex lattices in rapidly rotating Bose-Einstein condensates

We calculate the in-plane modes of the vortex lattice in a rotating Bose
condensate from the Thomas-Fermi to the mean-field quantum Hall regimes. The
Tkachenko mode frequency goes from linear in the wavevector, $k$, for lattice
rotational velocities, $\Omega$, much smaller than the lowest sound wave
frequency in a finite system, to quadratic in $k$ in the opposite limit. The
system also supports an inertial mode of frequency $\ge 2\Omega$. The
calculated frequencies are in good agreement with recent observations of
Tkachenko modes at JILA, and provide evidence for the decrease in the shear
modulus of the vortex lattice at rapid rotation.Comment: 4 pages, 2 figure

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