258 research outputs found
Phase Transitions in Neutron Stars and Maximum Masses
Using the most recent realistic effective interactions for nuclear matter
with a smooth extrapolation to high densities including causality, we constrain
the equation of state and calculate maximum masses of rotating neutron stars.
First and second order phase transitions to, e.g., quark matter at high
densities are included. If neutron star masses of from
quasi-periodic oscillations in low mass X-ray binaries are confirmed, a soft
equation of state as well as strong phase transitions can be excluded in
neutron star cores.Comment: Replaced with revised version, 7 pages, 3 figs. To appear in Ap. J.
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Influence of Induced Interactions on the Superfluid Transition in Dilute Fermi Gases
We calculate the effects of induced interactions on the transition
temperature to the BCS state in dilute Fermi gases. For a pure Fermi system
with 2 species having equal densities, the transition temperature is suppressed
by a factor , and for fermion species, the
transition temperature is increased by a factor . For mixtures of fermions and bosons the exchange of boson density
fluctuations gives rise to an effective interaction, and we estimate the
increase of the transition temperature due to this effect.Comment: 4 pages, 3 figure
Sound modes at the BCS-BEC crossover
First and second sound speeds are calculated for a uniform superfluid gas of
fermi atoms as a function of temperature, density and interaction strength. The
second sound speed is of particular interest as it is a clear signal of a
superfluid component and it determines the critical temperature. The sound
modes and their dependence on density, scattering length and temperature are
calculated in the BCS, molecular BEC and unitarity limits and a smooth
crossover is extrapolated. It is found that first and second sound undergo
avoided crossing on the BEC side due to mixing. Consequently, they are
detectable at crossover both as density and thermal waves in traps.Comment: To appear in Phys. Rev.
Emotion: The commander of the remote control? A psychophysiological approach to predict decline in TV ratings
How to identify a Strange Star
Contrary to young neutron stars, young strange stars are not subject to the
r-mode instability which slows rapidly rotating, hot neutron stars to rotation
periods near 10 ms via gravitational wave emission. Young millisecond pulsars
are therefore likely to be strange stars rather than neutron stars, or at least
to contain significant quantities of quark matter in the interior.Comment: 4 pages, 1 figur
Inhomogeneous freeze-out in relativistic heavy-ion collisions
A QCD phase transition may reflect in a inhomogeneous decoupling surface of
hadrons produced in relativistic heavy-ion collisions. We show that due to the
non-linear dependence of the particle densities on the temperature and
baryon-chemical potential such inhomogeneities should be visible even in the
integrated, inclusive abundances. We analyze experimental data from Pb+Pb
collisions at CERN-SPS and Au+Au collisions at BNL-RHIC to determine the
amplitude of inhomogeneities.Comment: 8 pages, 5 figure
Viscosities of Quark-Gluon Plasmas
The quark and gluon viscosities are calculated in quark-gluon plasmas to
leading orders in the coupling constant by including screening. For weakly
interaction QCD and QED plasmas dynamical screening of transverse interactions
and Debye screening of longitudinal interactions controls the infrared
divergences. For strongly interacting plasmas other screening mechanisms taken
from lattice calculations are employed. By solving the Boltzmann equation for
quarks and gluons including screening the viscosity is calculated to leading
orders in the coupling constant. The leading logarithmic order is calculated
exactly by a full variational treatment. The next to leading orders are found
to be very important for sizable coupling constants as those relevant for the
transport properties relevant for quark-gluon plasmas created in relativistic
heavy ion collisions and the early universe.Comment: 12 pages + 6 figures, report LBL-3492
Phase Transitions in Rotating Neutron Stars
As rotating neutron stars slow down, the pressure and the density in the core
region increase due to the decreasing centrifugal forces and phase transitions
may occur in the center. We extract the analytic behavior near the critical
angular velocity , where the phase transitions occur in the center of
a neutron star, and calculate the moment of inertia, angular velocity, rate of
slow down, braking index, etc. For a first order phase transition these
quantities have a characteristic behavior, e.g., the braking index diverges as
. Observational consequences for first, second
and other phase transitions are discussed.Comment: 5 pages, one figure included, revtex latex styl
Fermi systems with long scattering lengths
Ground state energies and superfluid gaps are calculated for degenerate Fermi
systems interacting via long attractive scattering lengths such as cold atomic
gases, neutron and nuclear matter. In the intermediate region of densities,
where the interparticle spacing is longer than the range of the
interaction but shorter than the scattering length, the superfluid gaps and the
energy per particle are found to be proportional to the Fermi energy and thus
differs from the dilute and high density limits. The attractive potential
increase linearly with the spin-isospin or hyperspin statistical factor such
that, e.g., symmetric nuclear matter undergoes spinodal decomposition and
collapses whereas neutron matter and Fermionic atomic gases with two hyperspin
states are mechanically stable in the intermediate density region. The regions
of spinodal instabilities in the resulting phase diagram are reduced and do not
prevent a superfluid transition.Comment: extended and revised version, 7 pages including new phase diagra
Anisotropic suppression in nuclear collisions
The nuclear overlap zone in non-central relativistic heavy ion collisions is
azimuthally very asymmetric. By varying the angle between the axes of
deformation and the transverse direction of the pair momenta, the suppression
of and will oscillate in a characteristic way. Whereas the
average suppression is mostly sensitive to the early and high density stages of
the collision, the amplitude is more sensitive to the late stages. This effect
provides additional information on the suppression mechanisms such as
direct absorption on participating nucleons, comover absorption or formation of
a quark-gluon plasma. The behavior of the average suppression and its
amplitude with centrality of the collisions is discussed for SPS, RHIC and LHC
energies with and without a phase transition.Comment: Revised and extended version, new figure
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