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 Randall- Sundrum 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.Comment: 7 page Latex 2e file, axodraw needed. Discussion and references added. Version to appear in MPL

The effect of very low energy solar neutrinos on the MSW mechanism

We study some implications on standard matter oscillations of solar neutrinos induced by a background of extremely low energy thermal neutrinos trapped inside the Sun by means of coherent refractive interactions. Possible experimental tests are envisaged and current data on solar neutrinos detected at Earth are briefly discussed.Comment: RevTex4, 4 pages, no figure

On a generalized gravitational Aharonov-Bohm effect

A massless spinor particle is considered in the background gravitational field due to a rotating body. In the weak field approximation it is shown that the solution of the Weyl equations depend on the angular momentum of the rotating body, which does not affect the curvature in this approximation. This result may be looked upon as a generalization of the gravitational Aharonov-Bohm effect.Comment: 10 pages, LATEX fil

Planck-scale deformation of Lorentz symmetry as a solution to the UHECR and the TeV-γ\gamma paradoxes

One of the most puzzling current experimental physics paradoxes is the arrival on Earth of Ultra High Energy Cosmic Rays with energies above the GZK threshold. The recent observation of 20TeV photons from Mk 501 is another somewhat similar paradox. Several models have been proposed for the UHECR paradox. No solution has yet been proposed for the TeV-$\gamma$ paradox. Remarkably, the drastic assumption of a violation of ordinary Lorentz invariance would resolve both paradoxes. We present a formalism for the description of the type of Lorentz-invariance deformation (LID) that could be induced by non-trivial short-distance structure of space-time, and we show that this formalism is well suited for comparison of experimental data with LID predictions. We use the UHECR and TeV-$\gamma$ data, as well as bounds on time-of-flight differences between photons of different energies, to constrain the LID parameter space. A model with only two parameters, an energy scale and a dimensionless parameter characterizing the functional dependence on the energy scale, is shown to be sufficient to solve both the UHECR and the TeV-$\gamma$ threshold anomalies while satisfying the time-of-flight bounds. The allowed region of the two-parameter space is relatively small, but, remarkably, it fits perfectly the expectations of the quantum-gravity-motivated space-time models known to support such deformations of Lorentz invariance: integer value of the dimensionless parameter and characteristic energy scale constrained to a narrow interval in the neighborhood of the Planck scale.Comment: LaTex (epsfig), 20 pages, 3 figure