1,105 research outputs found
Sarma phase in relativistic and non-relativistic systems
We investigate the stability of the Sarma phase in two-component fermion
systems in three spatial dimensions. For this purpose we compare
strongly-correlated systems with either relativistic or non-relativistic
dispersion relation: relativistic quarks and mesons at finite isospin density
and spin-imbalanced ultracold Fermi gases. Using a Functional Renormalization
Group approach, we resolve fluctuation effects onto the corresponding phase
diagrams beyond the mean-field approximation. We find that fluctuations induce
a second order phase transition at zero temperature, and thus a Sarma phase, in
the relativistic setup for large isospin chemical potential. This motivates the
investigation of the cold atoms setup with comparable mean-field phase
structure, where the Sarma phase could then be realized in experiment. However,
for the non-relativistic system we find the stability region of the Sarma phase
to be smaller than the one predicted from mean-field theory. It is limited to
the BEC side of the phase diagram, and the unitary Fermi gas does not support a
Sarma phase at zero temperature. Finally, we propose an ultracold quantum gas
with four fermion species that has a good chance to realize a zero-temperature
Sarma phase.Comment: version published in Phys.Lett.B; 10 pages, 5 figure
Automating embedded analysis capabilities and managing software complexity in multiphysics simulation part II: application to partial differential equations
A template-based generic programming approach was presented in a previous
paper that separates the development effort of programming a physical model
from that of computing additional quantities, such as derivatives, needed for
embedded analysis algorithms. In this paper, we describe the implementation
details for using the template-based generic programming approach for
simulation and analysis of partial differential equations (PDEs). We detail
several of the hurdles that we have encountered, and some of the software
infrastructure developed to overcome them. We end with a demonstration where we
present shape optimization and uncertainty quantification results for a 3D PDE
application
Standard Model with Cosmologically Broken Quantum Scale Invariance
We argue that scale invariance is not anomalous in quantum field theory,
provided it is broken cosmologically. We consider a locally scale invariant
extension of the Standard Model of particle physics and argue that it fits both
the particle and cosmological observations. The model is scale invariant both
classically and quantum mechanically. The scale invariance is broken
cosmologically producing all the dimensionful parameters. The cosmological
constant or dark energy is a prediction of the theory and can be calculated
systematically order by order in perturbation theory. It is expected to be
finite at all orders. The model does not suffer from the hierarchy problem due
to absence of scalar particles, including the Higgs, from the physical
spectrum.Comment: 13 pages, no figures significant revisions, no change in results or
conclusion
A Comment on the Path Integral Approach to Cosmological Perturbation Theory
It is pointed out that the exact renormalization group approach to
cosmological perturbation theory, proposed in Matarrese and Pietroni, JCAP 0706
(2007) 026, arXiv:astro-ph/0703563 and arXiv:astro-ph/0702653, constitutes a
misnomer. Rather, having instructively cast this classical problem into path
integral form, the evolution equation then derived comes about as a special
case of considering how the generating functional responds to variations of the
primordial power spectrum.Comment: 2 pages, v2: refs added, published in JCA
Renormalization flow of Yang-Mills propagators
We study Landau-gauge Yang-Mills theory by means of a nonperturbative vertex
expansion of the quantum effective action. Using an exact renormalization group
equation, we compute the fully dressed gluon and ghost propagators to lowest
nontrivial order in the vertex expansion. In the mid-momentum regime,
, we probe the propagator flow with various
{\em ans\"atze} for the three- and four-point correlations. We analyze the
potential of these truncation schemes to generate a nonperturbative scale. We
find universal infrared behavior of the propagators, if the gluon dressing
function has developed a mass-like structure at mid-momentum. The resulting
power laws in the infrared support the Kugo-Ojima confinement scenario.Comment: 28 pages, 5 figures. V2: Typos corrected and reference adde
2PI nonequilibrium versus transport equations for an ultracold Bose gas
The far-from-equilibrium dynamics of an ultracold, one-dimensional Bose gas
is studied. The focus is set on the comparison between the solutions of fully
dynamical evolution equations derived from the 2PI effective action and their
corresponding kinetic approximation in the form of Boltzmann-type transport
equations. It is shown that during the time evolution of the gas a kinetic
description which includes non-Markovian memory effects in a gradient expansion
becomes valid. The time scale at which this occurs is shown to exceed
significantly the time scale at which the system's evolution enters a
near-equilibrium drift period where a fluctuation dissipation relation is found
to hold and which would seem to be predestined for the kinetic approximation.Comment: 24 pages, 7 figures. References adde
Quasi--local angular momentum of non--symmetric isolated and dynamical horizons from the conformal decomposition of the metric
A new definition of quasi--local angular momentum of non--axisymmetric
marginally outer trapped surfaces is proposed. It is based on conformal
decomposition of the two--dimensional metric and the action of the group of
conformal symmetries. The definition is completely general and agrees with the
standard one in axi--symmetric surfaces.Comment: Final version to appear in Classical and Quantum Gravity. One
reference adde
Prediction of preterm birth with and without preeclampsia using mid-pregnancy immune and growth-related molecular factors and maternal characteristics.
OBJECTIVE:To evaluate if mid-pregnancy immune and growth-related molecular factors predict preterm birth (PTB) with and without (±) preeclampsia. STUDY DESIGN:Included were 400 women with singleton deliveries in California in 2009-2010 (200 PTB and 200 term) divided into training and testing samples at a 2:1 ratio. Sixty-three markers were tested in 15-20 serum samples using multiplex technology. Linear discriminate analysis was used to create a discriminate function. Model performance was assessed using area under the receiver operating characteristic curve (AUC). RESULTS:Twenty-five serum biomarkers along with maternal age <34 years and poverty status identified >80% of women with PTBâ±âpreeclampsia with best performance in women with preterm preeclampsia (AUCâ=â0.889, 95% confidence interval (0.822-0.959) training; 0.883 (0.804-0.963) testing). CONCLUSION:Together with maternal age and poverty status, mid-pregnancy immune and growth factors reliably identified most women who went on to have a PTBâ±âpreeclampsia
Quantum geometry and the Schwarzschild singularity
In homogeneous cosmologies, quantum geometry effects lead to a resolution of
the classical singularity without having to invoke special boundary conditions
at the singularity or introduce ad-hoc elements such as unphysical matter. The
same effects are shown to lead to a resolution of the Schwarzschild
singularity. The resulting quantum extension of space-time is likely to have
significant implications to the black hole evaporation process. Similarities
and differences with the situation in quantum geometrodynamics are pointed out.Comment: 31 pages, 1 figur
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