93 research outputs found
Nonlocal chiral quark models with Polyakov loop at finite temperature and chemical potential
We analyze the chiral restoration and deconfinement transitions in the
framework of a non-local chiral quark model which includes terms leading to the
quark wave function renormalization, and takes care of the effect of gauge
interactions by coupling the quarks with the Polyakov loop. Non-local
interactions are described by considering both a set of exponential form
factors, and a set of form factors obtained from a fit to the mass and
renormalization functions obtained in lattice calculations.Comment: 8 pages, 2 figures; prepared for IV International Workshop on
Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, 4-8 Oct 200
Quark-hybrid matter in the cores of massive neutron stars
Using a nonlocal extension of the SU(3) Nambu-Jona Lasinio model, which
reproduces several of the key features of Quantum Chromodynamics, we show that
mixed phases of deconfined quarks and confined hadrons (quark-hybrid matter)
may exist in the cores of neutron stars as massive as around 2.1 M_Sun. The
radii of these objects are found to be in the canonical range of
km. According to our study, the transition to pure quark matter does not occur
in stable neutron stars, but is shifted to neutron stars which are unstable
against radial oscillations. The implications of our study for the recently
discovered, massive neutron star PSR J1614-2230, whose gravitational mass is
, are that this neutron star may contain an extended
region of quark-hybrid matter at it center, but no pure quark matter.Comment: 13 pages, 3 figure
Quark deconfinement in high-mass neutron stars
In this paper, we explore whether or not quark deconfinement may occur in
high-mass neutron stars such as J1614-2230 (1.97 \pm 0.04 M_Sun) and J0348+0432
(2.01 \pm 0.04 M_Sun). Our study is based on a non-local extension of the SU(3)
Nambu Jona-Lasinio (n3NJL) model with repulsive vector interactions among the
quarks. This model goes beyond the frequently used local version of the Nambu
Jona-Lasinio (NJL) model by accounting for several key features of QCD which
are not part of the local model. Confined hadronic matter is treated in the
framework of non-linear relativistic mean field theory. We find that both the
local as well as the non-local NJL model predict the existence of extended
regions of mixed quark-hadron (quark-hybrid) matter in high-mass neutron stars
with masses of 2.1 to 2.4 M_Sun. Pure quark matter in the cores of neutron
stars is obtained for certain parametrizations of the hadronic lagrangian and
choices of the vector repulsion among quarks. The radii of high-mass neutron
stars with quark-hybrid matter and/or pure quark matter cores in their centers
are found to lie in the canonical range of 12 to 13 km.Comment: 31 pages, 17 figures, PRC accepted versio
Thermal evolution of hybrid stars within the framework of a nonlocal Nambu--Jona-Lasinio model
We study the thermal evolution of neutron stars containing deconfined quark
matter in their core. Such objects are generally referred to as quark-hybrid
stars. The confined hadronic matter in their core is described in the framework
of non-linear relativistic nuclear field theory. For the quark phase we use a
non-local extension of the SU(3) Nambu Jona-Lasinio model with vector
interactions. The Gibbs condition is used to model phase equilibrium between
confined hadronic matter and deconfined quark matter. Our study indicates that
high-mass neutron stars may contain between 35 and 40 % deconfined quark-hybrid
matter in their cores. Neutron stars with canonical masses of around would not contain deconfined quark matter. The central proton
fractions of the stars are found to be high, enabling them to cool rapidly.
Very good agreement with the temperature evolution established for the neutron
star in Cassiopeia A (Cas A) is obtained for one of our models (based on the
popular NL3 nuclear parametrization), if the protons in the core of our stellar
models are strongly paired, the repulsion among the quarks is mildly repulsive,
and the mass of Cas A has a canonical value of .Comment: 10 pages, 7 figure
Nonlocal Polyakov-Nambu-Jona-Lasinio model with wavefunction renormalization at finite temperature and chemical potential
We study the phase diagram of strongly interacting matter in the framework of
a non-local SU(2) chiral quark model which includes wave function
renormalization and coupling to the Polyakov loop. Both non-local interactions
based on the frequently used exponential form factor, and on fits to the quark
mass and renormalization functions obtained in lattice calculations are
considered. Special attention is paid to the determination of the critical
points, both in the chiral limit and at finite quark mass. In particular, we
study the position of the Critical End Point as well as the value of the
associated critical exponents for different model parameterizations.Comment: v.2_August 2010, 26 pp, 8 fi
Neutrino emissivity in the quark-hadron mixed phase of neutron stars
Numerous theoretical studies using various equation of state models have
shown that quark matter may exist at the extreme densities in the cores of
high-mass neutron stars. It has also been shown that a phase transition from
hadronic matter to quark matter would result in an extended mixed phase region
that would segregate phases by net charge to minimize the total energy of the
phase, leading to the formation of a crystalline lattice. The existence of
quark matter in the core of a neutron star may have significant consequences
for its thermal evolution, which for thousands of years is facilitated
primarily by neutrino emission. In this work we investigate the effect a
crystalline quark-hadron mixed phase can have on the neutrino emissivity from
the core. To this end we calculate the equation of state using the relativistic
mean-field approximation to model hadronic matter and a nonlocal extension of
the three-flavor Nambu-Jona-Lasinio model for quark matter. Next we determine
the extent of the quark-hadron mixed phase and its crystalline structure using
the Glendenning construction, allowing for the formation of spherical blob,
rod, and slab rare phase geometries. Finally we calculate the neutrino
emissivity due to electron-lattice interactions utilizing the formalism
developed for the analogous process in neutron star crusts. We find that the
contribution to the neutrino emissivity due to the presence of a crystalline
quark-hadron mixed phase is substantial compared to other mechanisms at fairly
low temperatures ( K) and quark fractions (), and
that contributions due to lattice vibrations are insignificant compared to
static-lattice contributions.Comment: 12 pages, 10 figures; accepted for publication in the European
Physical Journal A - "Hadrons and Nuclei.
Hybrid stars with sequential phase transitions: the emergence of the g mode
Neutron stars are the densest objects in the Universe, with and km, and the equation of state associated to their
internal composition is still unknown. The extreme conditions to which matter
is subjected inside neutron stars could lead to a phase transition in their
inner cores, giving rise to a hybrid compact object. The observation of
binary pulsars (PSR~J1614-2230, PSR~J03430432 and
PSR~J07406620) strongly constraints theoretical models of the equation of
state. Moreover, the detection of gravitational waves emitted during the binary
neutron star merger, GW170817, and its electromagnetic counterpart, GRB170817A,
impose additional constraints on the tidal deformability. In this work, we
investigate hybrid stars with sequential phase transitions hadron-quark-quark
in their cores. We assume that both phase transitions are sharp and analyse the
rapid and slow phase conversion scenarios. For the outer core, we use modern
hadronic equations of state. For the inner core we employ the constant speed of
sound parametrization for quark matter. We analyze more than 3000 hybrid
equations of state, taking into account the recent observational constraints
from neutron stars. The effects of hadron-quark-quark phase transitions on the
normal oscillation modes and , are studied under the Cowling
relativistic approximation. Our results show that, in the slow conversion
regime, a second quark-quark phase transition gives rise to a new ~mode.
We discuss the observational implications of our results associated to the
gravitational waves detection and the possibility of detecting hints of
sequential phase transitions and the associated ~mode.Comment: 24 pages, 9 figure
- …