37 research outputs found
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
Implications of observed neutrinoless double beta decay
Recently a positive indication of the neutrinoless double beta decay has been
announced. We study the implications of this result taking into consideration
earlier results on atmospheric neutrinos and solar neutrinos. We also include
in our discussions the recent results from SNO and K2K. We point out that on
the confidence level given for the double beta signal, the neutrino mass
matrices are now highly constrained. All models predicting Dirac masses are
ruled out and leptogenesis becomes a natural choice. Only the degenerate and
the inverted hierarchical solutions are allowed for the three generation
Majorana neutrinos. In both these cases we find that the radiative corrections
destabilize the solutions and the LOW, VO and Just So solutions of the solar
neutrinos are ruled out. For the four generation case only the inverted
hierarchical scenario is allowed.Comment: 16 pages, 2 postscript 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
Wave-Particle duality at the Planck scale: Freezing of neutrino oscillations
A gravitationally-induced modification to de Broglie wave-particle duality is
presented. At Planck scale, the gravitationally-modified matter wavelength
saturates to a few times the Planck length in a momentum independent manner. In
certain frameworks, this circumstance freezes neutrino oscillations in the
Planck realm. This effect is apart, and beyond, the gravitational red-shift. A
conclusion is drawn that in a complete theory of quantum gravity the notions of
``quantum'' and ``gravity'' shall carry new meanings -- meanings, that are yet
to be deciphered from theory and observations in their entirety.Comment: Published versio
Probing Quantum Aspects of Gravity
We emphasize that a specific aspect of quantum gravity is the absence of a
super-selection rule that prevents a linear superposition of different
gravitational charges. As an immediate consequence, we obtain a tiny, but
observable, violation of the equivalence principle, provided, inertial and
gravitational masses are not assumed to be operationally identical objects. In
this framework, the cosmic gravitational environment affects local experiments.
A range of terrestrial experiments, from neutron interferometry to neutrino
oscillations, can serve as possible probes to study the emergent quantum
aspects of gravity.Comment: Phys. Lett. B (in press). S. Sarkar's name was inadvertently missed
from the list of authors for "Nature 393 (1998) 763-765." This has been now
correcte
Do Mirrors for Gravitational Waves Exist?
Thin superconducting films are predicted to be highly reflective mirrors for
gravitational waves at microwave frequencies. The quantum mechanical
non-localizability of the negatively charged Cooper pairs, which is protected
from the localizing effect of decoherence by an energy gap, causes the pairs to
undergo non-picturable, non-geodesic motion in the presence of a gravitational
wave. This non-geodesic motion, which is accelerated motion through space,
leads to the existence of mass and charge supercurrents inside the
superconducting film. On the other hand, the decoherence-induced localizability
of the positively charged ions in the lattice causes them to undergo
picturable, geodesic motion as they are carried along with space in the
presence of the same gravitational wave. The resulting separation of charges
leads to a virtual plasma excitation within the film that enormously enhances
its interaction with the wave, relative to that of a neutral superfluid or any
normal matter. The existence of strong mass supercurrents within a
superconducting film in the presence of a gravitational wave, dubbed the
"Heisenberg-Coulomb effect," implies the specular reflection of a gravitational
microwave from a film whose thickness is much less than the London penetration
depth of the material, in close analogy with the electromagnetic case. The
argument is developed by allowing classical gravitational fields, which obey
Maxwell-like equations, to interact with quantum matter, which is described
using the BCS and Ginzburg-Landau theories of superconductivity, as well as a
collisionless plasma model. Several possible experimental tests of these ideas,
including mesoscopic ones, are presented alongside comments on the broader
theoretical implications of the central hypothesis.Comment: 59 pages, 2 figure