594 research outputs found
Color Superconductivity in Compact Stars and Gamma Ray Bursts
We study the effects of color superconductivity on the structure and
formation of compact stars. We show that it is possible to satisfy most of
recent observational boundaries on masses and radii if a diquark condensate
forms in a hybrid or a quark star. Moreover, we find that a huge amount of
energy, of the order of erg, can be released in the conversion from a
(metastable) hadronic star into a (stable) hybrid or quark star, if the
presence of a color superconducting phase is taken into account. Accordingly to
the scenario proposed in Astrophys.J.586(2003)1250, the energy released in this
conversion can power a Gamma Ray Burst. This mechanism can explain the recent
observations indicating a delay, of the order of days or years, between a few
Supernova explosions and the subsequent Gamma Ray Burst.Comment: 15 pages, 4 figures, 1 tabl
Conditions for Phase Equilibrium in Supernovae, Proto-Neutron and Neutron Stars
We investigate the qualitative properties of phase transitions in a general
way, if not the single particle numbers of the system but only some particular
charges like e.g. baryon number are conserved. In addition to globally
conserved charges we analyze the implications of locally conserved charge
fractions, like e.g. local electric charge neutrality or locally fixed proton
or lepton fractions. The conditions for phase equilibrium are derived and it is
shown, that the properties of the phase transition do not depend on the locally
conserved fractions. Finally, the general formalism is applied to the
liquid-gas phase transition and the hadron-quark phase transition for typical
astrophysical environments like in supernovae, proto-neutron or a neutron
stars. We demonstrate that the Maxwell construction known from
cold-deleptonized neutron star matter with two locally charge neutral phases
requires modifications and further assumptions concerning the applicability for
hot lepton-rich matter. All possible combinations of local and global
conservation laws are analyzed, and the physical meaningful cases are
identified. Several new kinds of mixed phases are presented, as e.g. a locally
charge neutral mixed phase in proto-neutron stars which will disappear during
the cooling and deleptonization of the proto-neutron star.Comment: 18 page
Formation of Quark Phases in compact stars and their connection to Gamma-Ray-Bursts
We analyse the occurrence of quiescent times in the temporal structure of the
Gamma-Ray-Bursts (GRBs) light curves. We show that if a long quiescent time is
present, it is possible to divide the total duration of GRBs into three
periods: the pre-quiescence emission, the quiescent time and the
post-quiescence emission. We then discuss a model of the GRBs inner engine
based on the formation of quark phases during the life of an hadronic star.
Within this model the pre-quiescence emission is interpreted as due to the
deconfinement of quark inside an hadronic star and the formation of 2SC quark
matter. The post-quiescence emission is due to the conversion of 2SC into the
Color-Flavor-Locking (CFL) phase. The temporal delay between these two
processes is connected with the nucleation time of the CFL phase in the 2SC
phase and it can be associated with the observed quiescent times in the GRBs
light curves. The stability of CFL cores in compact stars is also discussed.Comment: 6 pages, 3 figures, to appear in the proceedings of 3th International
Conference on Nuclear Physics in Astrophysics (NPAIII), 26 - 31 March 2007
Dresden, German
Propagator poles and an emergent stable state below threshold: general discussion and the E(38) state
In the framework of a simple quantum field theory describing the decay of a
scalar state into two (pseudo)scalar ones we study the pole(s) motion(s) of its
propagator: besides the expected pole on the second Riemann sheet, we find --
for a large enough coupling constant -- a second, additional pole on the first
Riemann sheet below threshold, which corresponds to a stable state. We then
perform a numerical study for a hadronic system in which a scalar particle
couples to pions. We investigate under which conditions a stable state below
the two-pion threshold can emerge. In particular, we study the case in which
this stable state has a mass of 38 MeV, which corresponds to the recently
claimed novel scalar state E(38). Moreover, we also show that the resonance
and the stable state E(38) could be two different manifestation of
the same `object'. Finally, we also estimate the order of magnitude of its
coupling to photons.Comment: 9 pages, 4 figure
Focusing inversion techniques applied to electrical resistance tomography in an experimental tank
We present an algorithm for focusing inversion of electrical resistivity
tomography (ERT) data. ERT is a typical example of ill-posed problem.
Regularization is the most common way to face this kind of problems; it
basically consists in using a priori information about targets to reduce the
ambiguity and the instability of the solution. By using the minimum gradient
support (MGS) stabilizing functional, we introduce the following geometrical
prior information in the reconstruction process: anomalies have sharp
boundaries. The presented work is embedded in a project (L.A.R.A.) which aims
at the estimation of hydrogeological properties from geophysical
investigations. L.A.R.A. facilities include a simulation tank (4 m x 8 m x 1.35
m); 160 electrodes are located all around the tank and used for 3-D ERT.
Because of the large number of electrodes and their dimensions, it is important
to model their effect in order to correctly evaluate the electrical system
response. The forward modelling in the presented algorithm is based on the
so-called complete electrode model that takes into account the presence of the
electrodes and their contact impedances. In this paper, we compare the results
obtained with different regularizing functionals applied on a synthetic model.Comment: 4 pages, 7 figures, to appear in the Proceedings of Int. Assoc. for
Mathematical Geology XI International Congres
A new possible quark-hadron mixed phase in protoneutron stars
The phase transition from hadronic matter to quark matter at high density
might be a strong first order phase transition in presence of a large surface
tension between the two phases. While this implies a constant-pressure mixed
phase for cold and catalyzed matter this is not the case for the hot and lepton
rich matter formed in a protoneutron star. We show that it is possible to
obtain a mixed phase with non-constant pressure by considering the global
conservation of lepton number during the stage of neutrino trapping. In turn,
it allows for the appearance of a new kind of mixed phase as long as neutrinos
are trapped and its gradual disappearance during deleptonization. This new
mixed phase, being composed by two electric neutral phases, does not develop a
Coulomb lattice and it is formed only by spherical structures, drops and
bubbles, which can have macroscopic sizes. The disappearance of the mixed phase
at the end of deleptonization might lead to a delayed collapse of the star into
a more compact configuration containing a core of pure quark phase. In this
scenario, a significant emission of neutrinos and, possibly, gravitational
waves are expected.Comment: 4 pages, 4 figure
Focusing inversion techniques applied to electrical resistance tomography in an experimental tank
We present an algorithm for focusing inversion of electrical resistivity
tomography (ERT) data. ERT is a typical example of ill-posed problem. Regularization is the
most common way to face this kind of problems; it basically consists in using a priori
information about targets to reduce the ambiguity and the instability of the solution. By using
the minimum gradient support (MGS) stabilizing functional, we introduce the following
geometrical prior information in the reconstruction process: anomalies have sharp boundaries.
The presented work is embedded in a project (L.A.R.A.) which aims at the estimation of
hydrogeological properties from geophysical investigations. L.A.R.A. facilities include a
simulation tank (4 m x 8 m x 1.35 m); 160 electrodes are located all around the tank and used
for 3-D ERT. Because of the large number of electrodes and their dimensions, it is important
to model their effect in order to correctly evaluate the electrical system response. The forward
modelling in the presented algorithm is based on the so-called complete electrode model that
takes into account the presence of the electrodes and their contact impedances.
In this paper, we compare the results obtained with different regularizing functionals applied
on a synthetic model
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