60 research outputs found
Neutrino Capture Cross Sections for Ar-40 and beta-decay of Ti-40
Shell-model calculations of solar neutrino absorption cross sections for
Ar, the proposed component of the ICARUS detector, are presented. It is
found that low-lying Gamow-Teller transitions lead to a significant enhancement
of the absorption rate over that expected from the Fermi transition between the
isobaric analog states, leading to an overall absorption rate of 6.7 SNU. We
also note that the pertinent Gamow-Teller transitions in ^{\sss 40}Ar are
experimentally accessible from the -decay of the mirror nucleus ^{\sss
40}Ti. Predictions for the branching ratios to states in ^{\sss 40}Sc are
presented, and the theoretical halflife of 53~ms is found to be in good
agreement with the experimental value of ~ms.Comment: 12 pages including references and table. NTGMI-94-
Rho meson properties in the Nambu-Jona-Lasinio model
Some properties of the rho vector meson are calculated within the
Nambu-Jona-Lasinio model, including processes that go beyond the random phase
approximation. To classify the higher order contributions, we adopt as
expansion parameter. In particular, we evaluate the leading order contributions
to the decay width, obtaining the value MeV, and to the shift of the rho mass which turns out to be lowered by 64
MeV with respect to its RPA value. A set of model parameters is determined
accordingly.Comment: 21 pages Latex, 4 figures, to be published in Z. Phys.
Properties and observability of glitches and anti-glitches in accreting pulsars
Several glitches have been observed in young, isolated radio pulsars, while a
clear detection in accretion-powered X-ray pulsars is still lacking. We use the
Pizzochero snowplow model for pulsar glitches as well as starquake models to
determine for the first time the expected properties of glitches in accreting
pulsars and their observability. Since some accreting pulsars show
accretion-induced long-term spin-up, we also investigate the possibility that
anti-glitches occur in these stars. We find that glitches caused by quakes in a
slow accreting neutron star are very rare and their detection extremely
unlikely. On the contrary, glitches and anti-glitches caused by a transfer of
angular momentum between the superfluid neutron vortices and the non-superfluid
component may take place in accreting pulsars more often. We calculate the
maximum jump in angular velocity of an anti-glitch and we find that it is
expected to be about 1E-5 - 1E-4 rad/s. We also note that since accreting
pulsars usually have rotational angular velocities lower than those of isolated
glitching pulsars, both glitches and anti-glitches are expected to have long
rise and recovery timescales compared to isolated glitching pulsars, with
glitches and anti-glitches appearing as a simple step in angular velocity.
Among accreting pulsars, we find that GX 1+4 is the best candidate for the
detection of glitches with currently operating X-ray instruments and future
missions such as the proposed Large Observatory for X-ray Timing (LOFT).Comment: Accepted for publication in Astronomy & Astrophysics. 6 pages. Minor
changes to match the final A&A versio
Microscopic calculation of the pinning energy of a vortex in the inner crust of a neutron star
The structure of a vortex in the inner crust of a pulsar is calculated
microscopically in the Wigner-Seitz cell approximation, simulating the
conditions of the inner crust of a cold, non-accreting neutron star, in which a
lattice of nuclei coexists with a sea of superfluid neutrons. The calculation
is based on the axially deformed Hartree-Fock-Bogolyubov framework, using
effective interactions. The present work extends and improves previous studies
in four ways: i) it allows for the axial deformation of protons induced by the
large deformation of neutrons due to the appearance of vortices; ii) it
includes the effect of Coulomb exchange; iii) considers the possible effects of
the screening of the pairing interaction; and iv) it improves the numerical
treatment. We also demonstrate that the binding energy of the nucleus-vortex
system can be used as a proxy to the pinning energy of a vortex and discuss in
which conditions this applies. From our results, we can estimate the mesoscopic
pinning forces per unit length acting on vortices. We obtain values ranging
between to dyn/cm, consistent with previous findings.Comment: Paper submitted for publicatio
Microscopic structure of a vortex line in superfluid neutron star matter
The microscopic structure of an isolated vortex line in superfluid neutron
star matter is studied by solving the Bogoliubov-de Gennes equations. Our
calculation, which is the starting point for a microscopic calculation of
pinning forces in neutron stars, shows that the size of the vortex core varies
differently with density, and is in general smaller than assumed in some
earlier calculations of vortex pinning in neutron star crusts. The implications
of this result are discussedComment: 5 pages, 2 figure
The effect of realistic equations of state and general relativity on the "snowplow" model for pulsar glitches
Many pulsars are observed to "glitch", i.e. show sudden jumps in their
rotational frequency , some of which can be as large as in a subset of pulsars known as giant
glitchers. Recently Pizzochero (2011) has shown that an analytic model based on
realistic values for the pinning forces in the crust and for the angular
momentum transfer in the star can describe the average properties of giant
glitches, such as the inter-glitch waiting time, the step in frequency and that
in frequency derivative. In this paper we extend the model (originally
developed in Newtonian gravity and for a polytropic equation of state) to
realistic backgrounds obtained by integrating the relativistic equations of
stellar structure and using physically motivated equations of state to describe
matter in the neutron star. We find that this more detailed treatment still
reproduces the main features of giant glitches in the Vela pulsar and allows us
to set constraints on the equation of state. In particular we find that stiffer
equations of state are favoured and that it is unlikely that the Vela pulsar
has a high mass (larger than ).Comment: 15 pages, 8 figures, submitted to MNRA
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