Neutrino Dispersion Research Articles

Neutrino Self-Energy and Index of Refraction in Strong Magnetic Field: A New Approach

The Ritus Ep eigenfunction method is extended to the case of spin-1 charged particles in a constant electromagnetic field and used to calculate the one-loop neutrino self-energy in the presence of a strong magnetic field. From the obtained self-energy, the neutrino dispersion relation and index of refraction in the magnetized vacuum are determined within the field range m2e⪡eB⪡M2W. The propagation of neutrinos in the magnetized vacuum is anisotropic due to the dependence of the index of refraction on the angle between the directions of the neutrino momentum and the external field. Possible cosmological implications of the results are discussed.

Momentum-dependent contributions to the gravitational coupling of neutrinos in a medium

When neutrinos travel through a normal matter medium, the electron neutrinos couple differently to gravity compared to the other neutrinos, due to the presence of electrons in the medium and the absence of the other charged leptons. We calculate the momentum-dependent part of the matter-induced gravitational couplings of the neutrinos under such conditions, which arise at order $g^2/M^4_W$, and determine their contribution to the neutrino dispersion relation in the presence of a gravitational potential $\phi^{\mathrm{ext}}$. These new contributions vanish for the muon and tau neutrinos. For electron neutrinos with momentum $K$, they are of the order of the usual Wolfenstein term times the factor $(K^2/M^2_W)\phi^{\mathrm{ext}}$, for high energy neutrinos. In environments where the gravitational potential is substantial, such as those in the vicinity of Active Galactic Nuclei, they could be the dominant term in the neutrino dispersion relation. They must also be taken into account in the analysis of possible violations of the Equivalence Principle in the neutrino sector, in experimental settings involving high energy neutrinos traveling through a matter background.

Neutrino dispersion in a minimal SUSY standard model with explicitly brokenRparity at finite temperature and density

We study the refraction of a light neutrino through a medium. In this connection, we extend a (vacuum) field theory supersymmetric standard model with explicitly broken $R$ parity to a finite temperature and density, where sfermions coupled to fermions give rise to chirality conserving as well as chirality violating corrections to neutrino transitions. The refractive index of the neutrino undergoing such transitions in a heat bath of finite density is then calculated in this framework. Some of the implications of these results to the solar neutrino problem, supernovas, and in the early universe are discussed and compared with earlier works.

NEUTRINO SELF-ENERGY AND DISPERSION EQUATION IN DENSE MATTER

General expressions for the neutrino self-energy and dispersion equations are found in a medium at finite temperature and density. The neutrino self-energy is calculated in the one-loop approximation and using the unitary gauge. The singularities and the absorption mechanisms are discussed. The low momentum (as compared with the vector boson masses) limit of the self-energy is obtained and from it, the dispersion equations for the quasiparticles are found. These solutions exhibit a group velocity smaller than unity which decreases with increasing density and an energy gap leading to a superfluid-type spectrum. In the particle–antiparticle asymmetric case, a negative effective mass is found for neutrinos.

Neutrino dispersion in magnetized media and spin oscillations in the early Universe

We derive general expressions for the neutrino dispersion relation in a magnetized plasma with a wide range of temperatures, chemical potentials, and magnetic field strengths. If the electron and proton chemical potentials vanish, as in the early Universe, there is no magnetization contribution to the neutrino refractive index to leading order in the Fermi coupling constant, contrary to claims in the recent literature. Therefore, as long as the magnetic field satisfies B ≲ T 2, the neutrino refractive index in the early Universe is dominated by the standard “non-local term”. If neutrinos are Dirac particles with magnetic moment μ, then their right-handed components are thermally populated before the nucleosynthesis epoch by magnetically induced spin oscillations if μB 0 > 10 −6 μ B G, where μ B = e/2, e is the Bohr magneton and B 0 is a large-scale primordial magnetic field at T 0 ≈ 1 MeV For a typically expected random field distribution, even smaller values for μB 0 would suffice to thermalize the right-handed Dirac components.

Neutrino physics in hot and dense media.

Neutrino dispersion in hot and dense media is calculated for ranges of temperature and chemical potential T,μ << T QCD (200 MeV) for energies q 2 << M Z 2 , where the electroweak vector bosons Z 0 , W ± are still not liberated. The refractive index of neutrinos and their electric and magnetic form factors are evaluated at temperatures and densities in the above region. Some applications of these results to astrophysics and cosmology are also mentioned