1,721,223 research outputs found
MSW Effect in Loop Quantum Gravity and Constraints on Parameters from Neutrino-Antineutrino Asymmetry
No full textThe MSW effect is studied in the context of loop quantum gravity. In this theory the dispersion relation of fermion depends on the helicity of particles. Bounds on parameters related to helicity-terms, which violate the Lorentz invariance, are derived in the framework of spin-flip conversion of neutrino flavors
Thermal Leptogenesis in f(R) cosmology
No full textThe cosmological consequences of f(R) gravity are reviewed in the framework of thermal leptogenesis. In f(R) cosmology the expansion laws of the Universe are modified with respect to the standard cosmology, which also changes the thermal history of particles. In these cosmological scenarios it turns out that the condition for the out-of-equilibrium decay of the lightest heavy neutrino gives rise to a modulated upper bound on the lightest light neutrino mass, i.e. m_1= 10^−3 A(T=M_1) eV, where A is the ratio
between the expansion rates of the Universe evaluated in f(R) cosmology and in standard cosmology, and M1 is the lightest heavy neutrino mass. This factor can be parametrized in terms of the temperature T as A=(T/T*)^p, where T* is the transition temperature at which the expansion law in f(R) cosmology deviates from the standard one, and p is related to the parameters characterizing the f(R) model under consideration. Results imply that if A > 1 then the thermal leptogenesis scenario can accommodate the
case of a degenerate mass spectrum of the light neutrinos (for a low enough transition temperature), which is otherwise impossible with standard cosmology. In our analysis we consider f(R) models of the form
f(R)= R + α R^n
Pulsar Kicks Induced by Spin Flavor Oscillations of Neutrinos in Gravitational Fields
No full textThe origin of pulsar kicks is reviewed in the framework of the spin-flip conversion of neutrinos propagating in the gravitational field of a magnetized protoneutron star. We find that for a mass in rotation with angular velocity omega, the spin connections entering in the Dirac equation give rise to the coupling term omega (.) p, where p is the neutrino momentum. Such a coupling can be responsible for pulsar kicks owing to the neutrino emission asymmetry generated by the relative orientation of p with respect to omega. For our estimations, the large non-standard neutrino magnetic momentum, mu(v) less than or similar to 10(-11) mu(B), is considered
Cerenkov's Effect and Neutrino Oscillations in Loop QuantumGravity
No full textBounds on the scale parameter L arising in loop quantum gravity theory are derived in the framework of Cerenkov's effect and neutrino oscillations. Assuming that L is an universal constant, we infer L ≲ 10-18 eV-1, a bound compatible with those inferred in different physical context
Effects of CPT and Lorentz Invariance Violation on Pulsar Kicks
No full textThe breakdown of Lorentz and CPT invariance, as described by the extension of the standard model, gives rise to a modification of the dispersion relation of particles. Consequences of such a modification are reviewed in the framework of pulsar kicks induced by neutrino oscillations (active-sterile conversion). A peculiar feature of the modified energy-momentum relations is the occurrence of terms of the form delta Pi, (p) over cap, where delta Pi accounts for the difference of spatial components of flavor depending coefficients which lead to the departure of the Lorentz symmetry, and (p) over cap = p/p, being p the neutrino momentum. Owing to the relative orientation of p with respect to delta Pi, the coupling delta Pi.(p) over cap may induce the mechanism to generate the observed pulsar velocities. Topics related to the velocity distribution of pulsars; are also discussed
Emission of Cerenkov Radiation by Charged Particles in Stationary Geometries
No full textThe emission of the Cerenkov radiation by charged particles is analyzed for stationary metrics. Results are applied to the Kerr geometry and the scalar-tensor theories of gravity. Particular emphasis is given to Brans-Dicke theory of gravity where the Cerenkov effect turns out to be kinematically allowed. It is related to the Brans-Dicke parameter ε, and vanishes in the limit in which general relativity is recovered (ε → ∞)
Neutrino Oscillations and Lorentz Invariance Breakdown
No full textThe breakdown of Lorentz's and CPT invariance gives rise to the occurrence of helicity terms in the dispersion relation of fermions. Consequences of these terms are reviewed in the framework of spin flavor oscillations of neutrinos, and resonance effects are discussed. Bounds on the 0-component of the pseudo-vector potential bμ are derived for solar and atmospheric neutrinos
Neutrino Oscillations in Non-Inertial Frames and the Violation of the Equivalence Principle
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