M. Angeles Perez-Garcia

Dark Matter, Neutron Stars, and Strange Quark Matter

We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.

Gamma-Light: High-Energy Astrophysics above 10 MeV

The energy range between 10 and 50 MeV is an experimentally very difficult range and remained uncovered since the time of COMPTEL. Here we propose a possible mission to cover this energy range.

Strangelets and the TeV-PeV cosmic-ray anisotropies

Abstract Several experiments (e.g., Milagro and IceCube) have reported the presence in the sky of regions with significant excess in the arrival direction distributions of Galactic cosmic rays in the TeV-to-PeV energy range. Here we study the possibility that these hotspots are a manifestation of the peculiar nature of these cosmic rays, and of the presence of molecular clouds near the sources. We propose that stable quark matter lumps or so-called strangelets can be emitted in the course of the transition of a neutron star to a more compact astrophysical object. A fraction of these massive particles would lose their charge by spallation or electron capture in molecular clouds located in the immediate neighborhood of their source, and propagate rectilinearly without decaying further, hence inducing anisotropies of the order of the cloud size. With reasonable astrophysical assumptions regarding the neutron star transition rate, strangelet injection and neutralization rates, we can reproduce successfully the observed hotspot characteristics and their distribution in the sky.

Dark matter seeding and the kinematics and rotation of neutron stars

Abstract Self-annihilation of dark matter accreted from the galactic halo in the inner regions of neutron stars may significantly affect their kinematical properties, namely velocity kicks and rotation patterns. We find that if a stable long-lived single or multiple strangelet off-center seed forms leading to an asymmetric ejection of matter and radiation, there is a significant modification in linear and angular momentum observables of the star.

Neutron Fermi liquids under the presence of a strong magnetic field with effective nuclear forces

Landaus Fermi liquid parameters are calculated for non-superfluid pure neutron matter in the presence of a strong magnetic field at zero temperature. The particle-hole interactions in the system, where a net magnetization may be present, are characterized by these parameters in the framework of a multipolar formalism. We use either zero- or finite-range effective nuclear forces to describe the nuclear interaction. Using the obtained Fermi liquid parameters, the contribution of a strong magnetic field on some bulk magnitudes such as isothermal compressibility and spin susceptibility is also investigated.

Magnetization of a neutron plasma with Skyrme and Gogny forces in the presence of a strong magnetic field

Some thermodynamical magnitudes of interest in a pure neutron plasma are studied within the framework of the nonrelativistic Hartree-Fock approximation at finite density and temperature. We use Skyrme and Gogny forces to describe such a neutron plasma and study the main differences that arise in these two effective parametrizations of the nuclear interaction when a strong magnetic field induces a permanent magnetization in the gas. The existence of a nonzero permanent spin polarization in a neutron plasma is explored in the density-temperature parameter space. We find that for moderate temperatures and in the low-density range up to densities {approx_equal}0.5{rho}{sub 0} both parametrizations predict that as density decreases an increasingly strong magnetization is allowed. In the range 0.5{rho}{sub 0} < or. approx. {rho} < or approx. 3{rho}{sub 0} there is an approximately constant polarization that can be as big as {approx_equal}12% for the maximum allowed interior magnetic field B{approx_equal}10{sup 18} G. For higher densities there is a dramatic difference in the polarization trend followed by Skyrme an Gogny forces. Although the former predict a ferromagnetic phase transition, the Gogny forces prevent it keeping the magnetization below 5%.

Constraining decaying dark matter with neutron stars

Abstract The amount of decaying dark matter, accumulated in the central regions in neutron stars together with the energy deposition rate from decays, may set a limit on the neutron star survival rate against transitions to more compact objects provided nuclear matter is not the ultimate stable state of matter and that dark matter indeed is unstable. More generally, this limit sets constraints on the dark matter particle decay time, τ χ . We find that in the range of uncertainties intrinsic to such a scenario, masses ( m χ / TeV ) ≳ 9 × 10 − 4 or ( m χ / TeV ) ≳ 5 × 10 − 2 and lifetimes τ χ ≲ 10 55 s and τ χ ≲ 10 53 s can be excluded in the bosonic or fermionic decay cases, respectively, in an optimistic estimate, while more conservatively, it decreases τ χ by a factor ≳ 10 20 . We discuss the validity under which these results may improve with other current constraints.

Short Gamma-Ray Bursts and Dark Matter Seeding in Neutron Stars

We present a mechanism based on internal self-annihilation of dark matter accreted from the galactic halo in the inner regions of neutron stars that may trigger full or partial conversion into a quark star. We explain how this effect may induce a gamma-ray burst (GRB) that could be classified as short, according to the usual definition based on time duration of the prompt gamma-ray emission. This mechanism differs in many aspects from the most discussed scenario associating short GRBs with compact object binary mergers. We list possible observational signatures that should help distinguish between these two possible classes of progenitors.

Anisotropy in cosmic rays from internal transitions in neutron stars

Abstract We discuss the possibility that some recently measured anisotropic cosmic ray components in the TeV–PeV energy range may be an indication of the ejection of a peculiar type of matter. We present a model where a neutron star internal transition with nuclear deconfinement of the quark content takes place. This catastrophic event may cause a mass ejection process seeding the insterstelar medium with droplets of quark matter, so called nuclearites. Neutralization of these droplets in molecular clouds may drive the anisotropy since quasi-rectilinear trajectories are allowed. Complementary information from current experimental settings on earth or magnetic spectrometers on the ISS may shed light on this exotic form of matter.

Pulsar scintillation patterns and strangelets

Abstract We propose that interstellar extreme scattering events, usually observed as pulsar scintillations, may be caused by a coherent agent rather than the usually assumed turbulence of H 2 clouds. We find that the penetration of a flux of ionizing, positively charged strangelets or quark nuggets into a dense interstellar hydrogen cloud may produce ionization trails. Depending on the specific nature and energy of the incoming droplets, diffusive propagation or even capture in the cloud are possible. As a result, enhanced electron densities may form and constitute a lens-like scattering screen for radio pulsars and possibly for quasars.