## Implications of the Fermi-LAT gamma ray observation on minimal $U(1)_{B-L}$ model    [PDF]

Tanushree Basak, Tanmoy Mondal
The recent observation of Fermi-LAT signal of monochromatic gamma ray has drawn much attention. One of the possible explanations for this observation can be due to the annihilation of the dark matter particles into two photons. In our article we adopt a $B-L$ extended Standard Model which contains a singlet scalar and three right-handed neutrinos. The vacuum expectation value of the singlet scalar breaks the $U(1)_{B-L}$ symmetry. We have imposed a $Z_2$ symmetry in such a way that the 3rd generation right-handed neutrino is qualified as the dark matter candidate. This right-handed neutrino, having mass 130 GeV, annihilates into two photons through a resonance channel via a heavy scalar. We constrain the scalar mixing angle, $\cos\alpha \geq 0.986$ by demanding the desired cross-section $\langle\sigma v\rangle_{\gamma \gamma}$ for the Fermi-line. We have also checked that this mixing angle allows vacuum stability of this model up to $10^5$ GeV. This might hints that this $U(1)_{B-L}$ extended model that can explain Fermi-LAT signal of monochromatic gamma ray line must be a part of larger symmetry group at some high scale.
View original: http://arxiv.org/abs/1308.0023