The Neutrino Mass Spectrum in the Supersymmetric Flipped SU(5)xU(1) GUT Model

In the context of the supersymmetric flipped $SU(5)\otimes U(1)$ GUT model, we have studied in detail the neutrino mass spectrum, obtaining an approximate formula for the corresponding effective three-generation mass matrix. It is found that at least two neutrinos are expected to have extremely small masses of no particular interest. The third neutrino, on the other hand, may eventually get a mass of order $10^{-3}$ eV, of relevance for the solution of the solar neutrino problem with the MSW mechanism, as a consequence of vacuum-expectation-values at the GUT mass scale for some of the scalar partners of the right-handed neutrinos.Comment: 11 pages UAB-FT-32

Phase transitions in neutron star and magnetars and their connection with high energetic bursts in astrophysics

The phase transition from normal hadronic matter to quark matter in neutron stars (NS) could give rise to several interesting phenomena. Compact stars can have such exotic states up to their surface (called strange stars (SS)) or they can have quark core surrounded by hadronic matter, known as hybrid stars (HS). As the state of matter of the resultant SS/HS is different from the initial hadronic matter, their masses also differ. Therefore, such conversion leads to huge energy release, sometimes of the order of $10^{53}$ ergs. In the present work we study the qualitative energy released by such conversion. Recent observations reveal huge surface magnetic field in certain stars, termed magnetars. Such huge magnetic fields can modify the equations of state (EOS) of the matter describing the star. Therefore, the mass of magnetars are different from normal NS. The energy released during the conversion process from neutron magnetar (NM) to strange magnetar/hybrid magnetar (SS/HS) is different from normal NS to SS/HS conversion. In this work we calculate the energy release during the phase transition in magnetars. The energy released during NS to SS/HS conversion exceeds the energy released during NM to SM/HM conversion. The energy released during the conversion of NS to SS is always of the order of $10^{53}$ ergs. The amount of energy released during such conversion can only be compared to the energy observed during the gamma ray bursts (GRB). The energy liberated during NM to HM conversion is few times lesser, and is not likely to power GRB at cosmological distances. However, the magnetars are more likely to lose their energy from the magnetic poles and can produce giant flares, which are usually associated with magnetars.Comment: 14 pages, 4 figures, 4 table

Strengthening Ukraine: Policy Recommendations for the New Administration

This project comprises four sections exploring how to strengthen Ukrainian institutions, the Ukrainian military, the Ukrainian economy, and how to assist the Ukrainians in countering Russian propaganda. Within each section we will present background on the topic and make recommendations for how the United States government can work with Ukraine

Comparison of Parametric and Semi-Parametric Binary Response Models

A Bayesian semi-parametric estimation of the binary response model using Markov Chain Monte Carlo algorithms is proposed. The performances of the parametric and semi-parametric models are presented. The mean squared errors, receiver operating characteristic curve, and the marginal effect are used as the model selection criteria. Simulated data and Monte Carlo experiments show that unless the binary data is extremely unbalanced the semi-parametric and parametric models perform equally well. However, if the data is extremely unbalanced the maximum likelihood estimation does not converge whereas the Bayesian algorithms do. An application is also presented