Phenomenological implications of neutrinos in extra dimensions

Abstract

Standard Model singlet neutrinos propagating in extra dimensions induce small Dirac neutrino masses. While it seems rather unlikely that their Kaluza-Klein excitations directly participate in the observed neutrino oscillations, their virtual exchange may lead to detectable signatures in future neutrino experiments and in rare charged lepton processes. We show how these effects can be described by specific dimension-six effective operators and discuss their experimental signals.

LeptonicCPviolation

“…In other words, in this scenario the effective dimension-five operator responsible for the suppression of neutrino masses can be somehow decoupled from the dimension-six one, allowing at the same time not too small NU effects so that interesting new phenomenology may appear (Deppisch et al, 2006;Deppisch and Valle, 2005;Dev and Mohapatra, 2010;Malinsky et al, 2009a,b). Similar effects arise in other models with large light-heavy neutrino mixing (Nardi et al, 1995;Tommasini et al, 1995), and in scenarios with extra dimensions where the mixing of Kaluza-Klein modes with the light neutrinos may induce NU effects (Bhattacharya et al, 2009;Branco et al, 2003b;De Gouvea et al, 2002). Another possible source of nonunitarity arises from loop corrections to the charged-lepton or neutrino self-energies (Bellazzini et al, 2011) which modify the corresponding kinetic terms, thus inducing NU effects.…”

Probing the nonunitarity of the leptonic mixing matrix at the CEPC

“…Canonically normalising the kinetic terms in general involves a transformation of the neutrino fields by a non-unitary matrix and leads to a non-unitary (effective) leptonic mixing matrix (see, e.g., references 1,3,4 ). The coefficient matrix in the definition of δL d=5 , (cf.…”

Flavor physics of leptons and dipole moments

“…Perhaps some of the neglected operators give relevant constraints on New Physics. For instance, bounds from lepton universality on the (H ') @ (H ') operator [191] are relevant to extra-dimensional scenarios [192].…”