Rate of dark photon emission from electron positron annihilation in massive stars

We calculate the rate of production of dark photons from electron-positron pair annihilation in hot and dense matter characteristic of supernova progenitors. Given the non-linear dependence of the emission rate on the dark photon mass and current astrophysical constraints on the dark photon parameter space, we focus on the mass range of 1--10 MeV. For the conditions under consideration both mixing with the in-medium photon and plasma effects on the electron dispersion relation are non-negligible and are explored in detail. We perform our calculations to the leading order in the fine-structure constant. Transverse and longitudinal photon modes are treated separately given their different dispersion relations. We consider the implications for the evolution of massive stars when dark photons decay either into particles of the standard model or of the dark sector.Comment: 6 pages, 4 figure

A life course perspective on social protection among the working poor of Egypt

This paper employs a generational comparison to examine how increasing labor market informality has affected how poor households in Egypt gain access to and rely on social protection schemes. The results indicate that among the generation of Egyptians approaching retirement, the expansion of public employment and a policy allowing easy access to survivors’ benefits among female dependents served as important means of increasing social insurance coverage. However, many young households do not have even one member enrolled in the public pension system. Labor market instability and informality have also lowered the perceived value of social protection among this generation. The paper discusses five common points of vulnerability across the groups studied, all of which may create significant barriers to social protection access among poor households, and must be addressed if coverage rates are to be extended, or even maintained, in the future