Calculation of Momentum Distribution Function of a Non-thermal Fermionic Dark Matter (Via Skype)

The most widely studied scenario in dark matter phenomenology is the thermal WIMP (Weakly Interacting Massive Particle) scenario. Inspite of numerous efforts to detect WIMP, till now we have no direct evidence for it. A possible explanation for this non-observation of dark matter could be because of its very feeble interaction strength and hence, failing to thermalise with the rest of the cosmic soup. In other words, the dark matter might be of non-thermal origin where the relic density is obtained by the so called freeze-in mechanism. Furthermore, if this non-thermal dark matter is itself produced substantially from the decay of another non-thermal mother particle, then their distribution function may differ in both size and shape from the usual equilibrium distribution. In this talk I will discuss about such a non-thermal (fermionic) dark matter scenario in the light of a new type of U(1)B-L model.  The model is interesting, since, besides being anomaly free, it can give rise to neutrino mass by Type II see-saw mechanism. Moreover, we will see, that it can accommodate a non-thermal fermionic dark matter as well. Starting from
the collision terms, I will briefly outline the calculation of momentum distribution function for the dark matter by solving a coupled system of Boltzmann equations and compare the result with that obtained by using the conventional procedure.