Solving the Nose-Hoover thermostat for Nuclear Pasta

In this work we present a calculation of the hamiltonian variables solving the molecular dynamics equations of motion for a system of nuclear matter relevant to the description of nuclear pasta. The temperature is kept fixed by using the Nos\'{e}-Hoover Thermostat and the interaction is modelled via a semiclassical potential depending on both positions and momenta.Comment: 7 pages, 3 figures. Journal of Mathematical Chemistry, in pres

Constraining decaying dark matter with neutron stars

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, $\tau_{\chi}$. We find that in the range of uncertainties intrinsic to such a scenario, masses $(m_{\chi}/ \rm TeV) \gtrsim 9 \times 10^{-4}$ or $(m_{\chi}/ \rm TeV) \gtrsim 5 \times 10^{-2}$ and lifetimes ${\tau_{\chi}}\lesssim 10^{55}$ s and ${\tau_{\chi}}\lesssim 10^{53}$ s can be excluded in the bosonic or fermionic decay cases, respectively, in an optimistic estimate, while more conservatively, it decreases $\tau_{\chi}$ by a factor $\gtrsim10^{20}$. We discuss the validity under which these results may improve with other current constraints.Comment: 6 pages, 1 figure, matches published versio

Can Dark Matter explain the Braking Index of Neutron Stars?

We explore a new mechanism of slowing down the rotation of neutron stars via accretion of millicharged dark matter. We find that this mechanism yields pulsar braking indices that can be substantially smaller than the standard $n\sim 3$ of the magnetic dipole radiation model for millicharged dark matter particles that are not excluded by existing experimental constraints thus accommodating existing observations.Comment: 5 page

The continuous star formation history of a giant HII region in M101

We present results about the star formation process in the giant HII region NGC 5471 in the outskirts of M101. From resolved HST/WPFC2 photometry we find that star formation has been going for the last 70 Myr. We further compare previous results from integrated infrared-optical photometry with the stellar resolved CMD and we discuss the star formation properties of this region and its individual knots, as well as characterizing the different stellar content. This result has very important consequences in our understanding of the burst versus continuous star formation activity in spiral galaxies.Comment: 2 pages, 2 figures. Proceeding of the conference From Stars to Galaxies: Building the pieces to build up the Universe (Venice, Italy

Strangelets and the TeV-PeV cosmic-ray anisotropies

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.Comment: 5 pages, 1 figure, submitted to PR

Pulsar scintillation patterns and strangelets

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 $\rm H_2$ 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.Comment: 5 pages, 2 figure