Angular momentum non-conserving decays in isotropic media

Various processes that are forbidden in the vacuum due to angular momentum conservation can occur in a medium that is isotropic and does not carry any angular momentum. We illustrate this by considering explicitly two examples. The first one is the decay of a spin-0 particle into a photon and another spin-0 particle, using a model involving the Yukawa interactions of the scalar particles with a charged fermion field. The second one involves the decay of a neutrino into another neutrino and a graviton, in the standard model of particle interactions augmented with the linearized gravitational couplings.Comment: 22 pages, Latex, uses axodraw.sty. 3 figures embedded in the tex file. This paper contains the same material as that presented in two earlier papers, arXiv:0901.2981 and arXiv:0901.2982, written by us. This version supersedes those two paper

Remarks on the Coulomb and Covariant Gauges in Finite Temperature QED

We compare the use of the Coulomb gauge in finite temperature QED with a recently proposed prescription for covariant gauges, in which only the transverse photon degrees of freedom are thermalized. Using the Landau rule as a guide, we clarify the relation between the retarded electron self-energy and the elements of the self-energy matrix in the real-time formulation of . The general results are illustrated by means of the one-loop expressions for the electron self-energy in a QED plasma.Comment: LaTeX, 10 pages, no figures; to be published in Phys. Lett.

Did PROGRESA send drop-outs back to school?

This paper analyzes the effect of PROGRESA education grants on school enrollment. It looks at its effect on total school enrollment and in particular on school enrollment of drop-outs, i.e. those children who face a re-enrollment decision since they were not enrolled in school the year prior to the implementation of the PROGRESA program. Estimates of the impact of PROGRESA education grants on drop-outs and non-drop-outs are obtained applying difference estimation and maximum likelihood estimation of a reduced form equation for schooling decision. Differences in results between both groups of children are discussed looking at the distribution of marginal effects. PROGRESA did send drop-outs back to school. It had a larger effect on drop-outs than on non-drop-outs. However, for the particular group of girls who dropped out of school just before attending secondary school PROGRESA grants only had a minor effect. This last finding highlights the fact that determinants of the schooling decision are different for young girls and that PROGRESA grants do not provide a strong enough incentive to send them back to school

Behind the Lines

This creative writing thesis contains fiction by Idalis Nieves

Renormalization of the 1S0 One-Pion-Exchange NN Interaction in Presence of Derivative Contact Interactions

We use standard distorted wave theory techniques and dimensional regularization to find out solutions of the nucleon-nucleon Lippman--Schwinger equation with a kernel determined by the Weinberg's next-to-leading potential, which consists of one--pion exchange and additional contact terms with derivatives. Though for simplicity, we restrict the discussion to the $^1S_0$ channel and to contact terms containing up to two derivatives, the generalization to higher waves and/or number of derivatives is straightforward. The undetermined low energy constants emerging out of the renormalization procedure are fitted to data.Comment: 7 pages, revtex4, Phys. Lett. B in prin