Prof Subir Sarkar

Abstract:

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an SU(2)R gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that mN≳1016 GeV if mN>mWR, and mWRR≳2× 105 GeV(mN/102 GeV)3//4 if mNmwR. We show also that the mN>mwR option is excluded in a supersymmetric theory with gravitinos. © 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract:

Recent observational and theoretical developments concerning the primordial synthesis of the light elements are reviewed, and the implications for dark matter mentioned.

Abstract:

We discuss possible signatures of quantum gravity for the propagation of light, including an energy-dependent velocity (refractive index), dispersion in velocity at a given energy, and birefringence. We also compare the sensitivities of different astrophysical observations, including BATSE data on GRB 920229, BeppoSAX data on GRB 980425, the possible HEGRA observation of GRB 920925c, and Whipple observations of the active galaxy Mrk 421. Finally, we discuss the prospective sensitivities of AMS and GLAST.