Anisotropic thermal emission from magnetized neutron stars

The thermal emission from isolated neutron stars is not well understood. The X-ray spectrum is very close to a blackbody but there is a systematic optical excess flux with respect to the extrapolation to low energy of the best blackbody fit. This fact, in combination with the observed pulsations in the X-ray flux, can be explained by anisotropies in the surface temperature distribution.We study the thermal emission from neutron stars with strong magnetic fields in order to explain the origin of the anisotropy. We find (numerically) stationary solutions in axial symmetry of the heat transportequations in the neutron star crust and the condensed envelope. The anisotropy in the conductivity tensor is included consistently. The presence of magnetic fields of the expected strength leads to anisotropy in the surface temperature. Models with toroidal components similar to or larger than the poloidal field reproduce qualitatively the observed spectral properties and variability of isolated neutron stars. Our models also predict spectral features at energies between 0.2 and 0.6 keV.Comment: 18 pages, 19 figures, version accepted for publication in A&

Magnetic collapse of a neutron gas: Can magnetars indeed be formed

A relativistic degenerate neutron gas in equilibrium with a background of electrons and protons in a magnetic field exerts its pressure anisotropically, having a smaller value perpendicular than along the magnetic field. For critical fields the magnetic pressure may produce the vanishing of the equatorial pressure of the neutron gas. Taking it as a model for neutron stars, the outcome could be a transverse collapse of the star. This fixes a limit to the fields to be observable in stable neutron star pulsars as a function of their density. The final structure left over after the implosion might be a mixed phase of nucleons and meson condensate, a strange star, or a highly distorted black hole or black "cigar", but no any magnetar, if viewed as a super strongly magnetized neutron star. However, we do not exclude the possibility of a supersotrong magnetic fields arising in supernova explosions which lead directly to strange stars. In other words, if any magnetars exist, they cannot be neutron stars.Comment: 15 pages, 3 figures. European Physical Journal C in pres

Background and principle applications of remote sensing in Mexico

Remote sensing, or the collection of information from objectives at a distance, crystallizes the interest in implementing techniques which assist in the search for solutions to the problems raised by the detection, exploitation, and conservation of the natural resources of the earth. An attempt is made to present an overview of the studies and achievements which have been obtained with remote sensing in Mexico

Neutrino Masses and GUT Baryogenesis

We reconsider the GUT-baryogenesis mechanism for generating the baryon asymmetry of the Universe. The baryon asymmetry is produced by the out of equilibrium decay of coloured Higgs bosons at the GUT scale, conserving B-L. If neutrinos are Majorana particles, lepton number violating interactions erase the lepton number excess, but part of the baryon asymmetry may be preserved, provided those interactions are not in thermal equilibrium when the sphaleron processes become effective, at $T \sim 10^{12}~ GeV$. We analyse whether this mechanism for baryogenesis is feasible in a variety of GUT models of fermion masses proposed in the literature, based on horizontal symmetries.Comment: Talk presented at AHEP2003, Valencia, Spain, October 200

Revising the Solution of the Neutrino Oscillation Parameter Degeneracies at Neutrino Factories

In the context of neutrino factories, we review the solution of the degeneracies in the neutrino oscillation parameters. In particular, we have set limits to $\sin^2 2\theta_{13}$ in order to accomplish the unambiguous determination of $\theta_{23}$ and $\delta$. We have performed two different analysis. In the first, at a baseline of 3000 km, we simulate a measurement of the channels $\nu_e\to\nu_\mu$, $\nu_e\to\nu_\tau$ and $\bar{\nu}_\mu\to\bar{\nu}_\mu$, combined with their respective conjugate ones, with a muon energy of 50 GeV and a running time of five years. In the second, we merge the simulated data obtained at L=3000 km with the measurement of $\nu_e\to\nu_\mu$ channel at 7250 km, the so called 'magic baseline'. In both cases, we have studied the impact of varying the $\nu_\tau$ detector efficiency-mass product, $(\epsilon_{\nu_\tau}\times M_\tau)$, at 3000 km, keeping unchanged the $\nu_\mu$ detector mass and its efficiency. At L=3000 km, we found the existance of degenerate zones, that corresponds to values of $\theta_{13}$, which are equal or almost equal to the true ones. These zones are extremely difficult to discard, even when we increase the number of events. However, in the second scenario, this difficulty is overcomed, demostrating the relevance of the 'magic baseline'. From this scenario, the best limits of $\sin^2 2\theta_{13}$, reached at $3\sigma$, for $\sin^2 2\theta_{23}=0.95$, 0.975 and 0.99 are: 0.008, 0.015 and 0.045, respectively, obtained at $\delta=0$, and considering $(\epsilon_{\nu_\tau}\times M_\tau) \approx 125$, which is five times the initial efficiency-mass combination.Comment: 40 pages, 18 figures; added references, corrected typos, updated Eq (15c

Effective actions, relative cohomology and Chern Simons forms

The explicit expression of all the WZW effective actions for a simple group G broken down to a subgroup H is established in a simple and direct way, and the formal similarity of these actions to the Chern-Simons forms is explained. Applications are also discussed.Comment: 11 pages. Latex2e file. Published versio