Neutrino Masses from Non-minimal Gravitational Interactions of Massive Neutral Fermions

A new mechanism is proposed for generating neutrino masses radiatively through a non-minimal coupling to gravity of fermionic bilinears involving massive neutral fermions. Such coupling terms can arise in theories where the gravity sector is augmented by a scalar field. They necessarily violate the principle of equivalence, but such violations are not ruled out by present experiments. It is shown that the proposed mechanism is realised most convincingly in theories of the RandallSundrum type, realised most convincingly in theories of the RandallSundrum type, where gravity couples strongly in the TeV range. The mechanism has the potential for solving both the solar and atmospheric neutrino problems. The smallness of neutrino masses in this scenario is due to the fact that the interaction of the massive neutral fermions arises entirely from higher-dimensional operators in the effective Lagrangian. Introduction It is well known that non-zero neutrino masses can result in neutrino oscillations. There seems to be strong experimental evidence for neutrino oscillations [1]. Several models have been proposed to generate the neutrino mass matrix [2]. Most of these models modify the particle content of the Standard Model (SM) and introduce new fields and/or new interactions. Possibility of generating neutrino masses in theories with extra dimensions have also been considered [3]. In all these scenarios gravity couples universally to matter, preserving the Equivalence Principle (EP). The EP has been tested on macroscopic scales. This does not rule out possible deviations from this principle at very short distances. The possibility of violation of the Equivalence Principle (VEP) as a source of neutrino oscillations has been explored in the literature [4]. These studies assume non-universal coupling of gravity to different neutrino flavours, inducing possible oscillations in massless/massive neutrinos through E–mail : [email protected] E–mail : [email protected], [email protected] E–mail : [email protected]