Abstract
With the advent of new and more sensitive direct detection experiments, scope for a thermal WIMP explanation of dark matter (DM) has become extremely constricted. The non-observation of thermal WIMP in these experiments has put a strong upper bound on WIMP-nucleon scattering cross section and within a few years it is likely to overlap with the coherent neutrino-nucleon cross section. Hence in all probability, DM may have some non-thermal origin. In this work we explore in detail this possibility of a non-thermal sterile neutrino DM within the framework of U(1)B−L model. The U(1)B−L model on the other hand is a well-motivated and minimal way of extending the standard model so that it can explain the neutrino masses via Type-I see-saw mechanism. We have shown, besides explaining the neutrino mass, it can also accommodate a non-thermal sterile neutrino DM with correct relic density. In contrast with the existing literature, we have found that W± decay can also be a dominant production mode of the sterile neutrino DM . To obtain the comoving number density of dark matter, we have solved here a coupled set of Boltzmann equations considering all possible decay as well as annihilation production modes of the sterile neutrino dark matter. The framework developed here though has been done for a U(1)B−L model, can be applied quite generally for any models with an extra neutral gauge boson and a fermionic non-thermal dark matter.
Highlights
The existence of Dark Matter (DM) in the Universe is an acceptable reality
If we wish to move beyond this thermal Weakly Interacting Massive Particle (WIMP) scenario, there is another class of dark matter candidates which are produced through nonthermal processes at an early stage of the Universe
For an O (MeV) sterile neutrino dark matter we have a dominant decay mode to e± and ν with a very large life time which in turn helps us to propose a possible indirect detection signal of the 511 keV line observed by INTEGRAL/SPI [50] of ESA
Summary
The existence of Dark Matter (DM) in the Universe is an acceptable reality. There are various satellite borne experiments, namely WMAP [1] and Planck [2] who have already measured the current mass density (relic density) of DM in the Universe with an extremely good accuracy. U(1)B−L extension of SM is a very well motivated BSM theory as it provides the explanation of nonzero neutrino mass through Type-I sea-saw mechanism In this model besides the usual SM gauge (SU(3)c × SU(2)L × U(1)Y) symmetry, an additional local U(1)B−L symmetry invariance is imposed on the Lagrangian where B and L respectively represent the baryon and lepton number of a particle. Several other models have successfully discussed non-thermal sterile neutrino dark matter They include some Supersymmetric models [40], models using warped extra-dimensions [41] and decay from charged [42] and neutral scalars [43, 44] or from extra gauge bosons [45, 46]. In terms of our chosen independent set of model parameters, the other parameters appearing in Eq (3) can be written as μ21
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