145 research outputs found
Relativistic dissipative hydrodynamics with spontaneous symmetry breaking
In this paper we consider dissipative hydrodynamic equations for systems with
continuous broken symmetries. We first present the case of superfluidity, in
which the symmetry U(1) is broken and then generalize to the chiral symmetry
. The corresponding new transport coefficients are
introduced.Comment: 5 pages, RevTeX Minor changes, version accepted for publicatio
A consistent approximation scheme beyond RPA for bosons
In this paper, we develop a consistent extension of RPA for bosonic systems.
In order to illustrate the method, we consider the case of the anharmonic
oscillator. We compare our results with those obtained in mean-field and
standard RPA approaches, with the exact ones and show that they are very close
to the exact ones.Comment: 19 pages, Latex, 1 figure, accepted version in EPJ
Hydrodynamics with spontaneous symmetry breaking: application to relativistic heavy ion collisions
In this paper we apply hydrodynamics for systems with continuous broken
symmetries to heavy ion collisions in the framework of (1+1) dimensional
Bjorken model. The temperature profile with respect to proper time determined
in that context exhibits no differences with the ideal fluid. On the contrary,
it is shown that the profile obtained when M\"{u}ller-Israel-Stewart second
order theory of dissipation is included on top of standard hydrodynamics
indicates a slower cooling of the system.Comment: 5 pages, 2 figures, version accepted for publication as a Brief
Report in Physical Review
Extended Skyrme Equation of State in asymmetric nuclear matter
We present a new equation of state for infinite systems (symmetric,
asymmetric and neutron matter) based on an extended Skyrme functional
constrained by microscopic Brueckner-Bethe-Goldstone results. The resulting
equation of state reproduces with very good accuracy the main features of
microscopic calculations and it is compatible with recent measurements of two
times Solar-mass neutron stars. We provide all necessary analytical expressions
to facilitate a quick numerical implementation of quantities of astrophysical
interest
Spurious finite-size instabilities in nuclear energy density functionals: spin channel
It has been recently shown, that some Skyrme functionals can lead to
non-converging results in the calculation of some properties of atomic nuclei.
A previous study has pointed out a possible link between these convergence
problems and the appearance of finite-size instabilities in symmetric nuclear
matter (SNM) around saturation density.
We show that the finite-size instabilities not only affect the ground state
properties of atomic nuclei, but they can also influence the calculations of
vibrational excited states in finite nuclei. We perform systematic fully-self
consistent Random Phase Approximation (RPA) calculations in spherical
doubly-magic nuclei. We employ several Skyrme functionals and vary the
isoscalar and isovector coupling constants of the time-odd term
. We determine critical values of these
coupling constants beyond which the RPA calculations do not converge because
RPA the stability matrix becomes non-positive.By comparing the RPA calculations
of atomic nuclei with those performed for SNM we establish a correspondence
between the critical densities in the infinite system and the critical coupling
constants for which the RPA calculations do not converge. We find a
quantitative stability criterion to detect finite-size instabilities related to
the spin term of a functional. This
criterion could be easily implemented into the standard fitting protocols to
fix the coupling constants of the Skyrme functional
Collective modes of trapped Fermi gases with in-medium interaction
Due to Pauli blocking of intermediate states, the scattering matrix (or
matrix) of two fermionic atoms in a Fermi gas becomes different from that of
two atoms in free space. This effect becomes particularly important near a
Feshbach resonance, where the interaction in free space is very strong but
becomes effectively suppressed in the medium. We calculate the in-medium
matrix in ladder approximation and study its effects on the properties of
collective modes of a trapped gas in the normal-fluid phase. We introduce the
in-medium interaction on both sides of the Boltzmann equation, namely in the
calculation of the mean field and in the calculation of the collision rate.
This allows us to explain the observed upward shift of the frequency of the
quadrupole mode in the collisionless regime. By including the mean field, we
also improve considerably the agreement with the measured temperature
dependence of frequency and damping rate of the scissors mode, whereas the use
of the in-medium cross section deteriorates the description, in agreement with
previous work.Comment: 17 page
Random Phase Approximation and Extensions Applied to a Bosonic Field Theory
An application of a self-consistent version of RPA to quantum field theory
with broken symmetry is presented. Although our approach can be applied to any
bosonic field theory, we specifically study the theory in 1+1
dimensions. We show that standard RPA approach leads to an instability which
can be removed when going to a superior version,i.e. the renormalized RPA. We
present a method based on the so-called charging formula of the many electron
problem to calculate the correlation energy and the RPA effective potential.Comment: 30 pages, LaTeX file, 10 figures included, final version accepted in
EPJ
Linear response in infinite nuclear matter as a tool to reveal finite size instabilities
Nuclear effective interactions are often modelled by simple analytical
expressions such as the Skyrme zero-range force. This effective interaction
depends on a limited number of parameters that are usually fitted using
experimental data obtained from doubly magic nuclei. It was recently shown that
many Skyrme functionals lead to the appearance of instabilities, in particular
when symmetries are broken, for example unphysical polarization of odd-even or
rotating nuclei. In this article, we show how the formalism of the linear
response in infinite nuclear matter can be used to predict and avoid the
regions of parameters that are responsible for these unphysical instabilities.Comment: Based on talk presented at 18th Nuclear Physics Workshop "Maria and
Pierre Curie", 2011, Kazimierz, Polan
How to preserve symmetries with cut-off regularized integrals?
We present a prescription to calculate the quadratic and logarithmic
divergent parts of several integrals employing a cutoff in a coherent way, i.e.
in total agreement with symmetry requirements. As examples we consider one-loop
Ward identities for QED and a phenomenological chiral model.Comment: 11 pages, 3 graph
Fitting Skyrme functionals using linear response theory
Recently, it has been recently shown that the linear response theory in
symmetric nuclear matter can be used as a tool to detect finite size
instabilities for different Skyrme functionals. In particular it has been shown
that there is a correlation between the density at which instabilities occur in
infinite matter and the instabilities in finite nuclei. In this article we
present a new fitting protocol that uses this correlation to add new additional
constraint in Symmetric Infinite Nuclear Matter in order to ensure the
stability of finite nuclei against matter fluctuation in all spin and isospin
channels. As an application, we give the parameters set for a new Skyrme
functional which includes central and spin-orbit parts and which is free from
instabilities by construction.Comment: Proceeding of 19th Nuclear Physics Workshop "Marie & Pierre Curie"
Kazimierz 201
- …