Loop neutrino masses from d = 7 operator

Neutrino masses from operator mixing

We show that in theories that reduce, at the Fermi scale, to an extension of the standard model with two doublets, there can be additional dimension five operators giving rise to neutrino masses. In particular there exists a singlet operator which can not generate neutrino masses at tree level but generates them through operator mixing. Under the assumption that only this operator appears at tr...

Two-loop neutrino masses and the solar neutrino problem.

The addition of m singlet right-handed neutrinos to the Standard Model leads to radiatively generated mass corrections for the SU(2)L doublet neutrinos. For those neutrinos which are massless at the tree level after this addition, this implies a small mass generated at the two-loop level via W exchange. We calculate these mass corrections exactly by obtaining an analytic form for the general ca...

D-Instanton Generated Dirac Neutrino Masses

We present a stringy mechanism to generate Dirac neutrino masses by D-instantons in an experimentally relevant mass scale without fine-tuning. Within type IIA string theory with intersecting D6-branes, we spell out specific conditions for the emergence of such couplings and provide a class of supersymmetric local SU(5) grand unified models, based on the Z2 × Z'2 orientifold compactification, wh...

Neutrino Masses from Cosmological Probes

There is a renewed interest in constraining the sum of the masses of the three neutrino flavours by using cosmological measurements. Solar, atmospheric, and reactor neutrino experiments have confirmed neutrino oscillations, implying that neutrinos have non-zero mass, but without pinning down their absolute masses. While it is established that the effect of light neutrinos on the evolution of co...

Two-loop-induced neutrino masses: A model-independent perspective