Neutrino Capture Cross Sections for Ar-40 and beta-decay of Ti-40

Shell-model calculations of solar neutrino absorption cross sections for $^{40}$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 $\beta$-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 $56^{+18}_{-12}$~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 $1/N_c$ as expansion parameter. In particular, we evaluate the leading order contributions to the $\rho \rightarrow \pi \pi$ decay width, obtaining the value $\Gamma = 118$ 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 $10^{14}$ to $10^{16}$ 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 $\nu$, some of which can be as large as $\Delta \nu/\nu\approx 10^{-6}-10^{-5}$ 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 $M\approx 1.5 M_\odot$).Comment: 15 pages, 8 figures, submitted to MNRA