Speaker
Description
The expansion rate of the Universe is modified when the total energy density receives a substantial contribution from a new scalar field, along with the standard radiation energy. This results in a few crucial changes in the set of Boltzmann equations for leptogenesis, governing the evolution of abundance of decaying particle and the lepton asymmetry. Thus the analytical solution of Boltzmann equations (derived assuming radiation dominated cosmology), already available in literature are no longer applicable in the present scenario. Hence we solve the set of modified Boltzmann equations in order to find the expression of the so called efficiency factor for leptogenesis in non-standard cosmological scenario. The asymmetry generated (at an early epoch) due to the CP violating out of equilibrium decay of heavy Right handed neutrino (RHN) suffers from washout effect due to inverse decay. This washout process is mainly controlled by the decay parameter which can be lowered considerably by incorporating the idea of faster expansion of Universe. Therefore in the non-standard cosmological scenario a larger fraction of the asymmetry (produced at high temperature) survives down to the present day temperature. Thus, without altering the underlying particle physics model (Standard Model + three RHNs) we will end up with a larger final asymmetry compared to the standard cosmology. It is a clear hint towards the possible relaxation of the stringent lower bound on the lightest RHN mass required to produce adequate asymmetry in agreement with current experimental data.
| Session | Neutrino Physics |
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