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Register a new userFlavor Transition Mechanisms of Propagating Astrophysical Neutrinos -A Model Independent Parametrization
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One of the important goals for future neutrino telescopes is to identify the flavors of astrophysical neutrinos and therefore determine the flavor ratio. The flavor ratio of astrophysical neutrinos observed on the Earth depends on both the initial flavor ratio at the source and flavor transitions taking place during propagations of these neutrinos. We propose a model independent parametrization for describing the above flavor transitions. A few flavor transition models are employed to test our parametrization. The observational test for flavor transition mechanisms through our parametrization is discussed.
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We give a very brief overview of collective effects in neutrino oscillations in core collapse supernovae where refractive effects of neutrinos on themselves can considerably modify flavor oscillations, with possible repercussions for future supernova neutrino detection. We discuss synchronized and bipolar oscillations, the role of energy and angular neutrino modes, as well as three-flavor effects. We close with a short summary and some open questions.
A lingering mystery in core-collapse supernova theory is how collective neutrino oscillations affect the dynamics. All previously identified flavor instabilities, some of which might make the effects considerable, are essentially collisionless phenomena. Here it is shown that collisional instabilities exist as well. They are associated with asymmetries between the neutrino and antineutrino interaction rates, are possibly prevalent deep inside supernovae, and pose an unusual instance of decoherent interactions with a thermal environment causing the sustained growth of quantum coherence.
Flavor-dependent neutrino emission is critical to the evolution of a supernova and its neutrino signal. In the dense anisotropic interior of the star, neutrino-neutrino forward-scattering can lead to fast collective neutrino oscillations, which has striking consequences. We present a theory of fast flavor depolarization, explaining how neutrino flavor differences become smaller, i.e., depolarize, due to diffusion to smaller angular scales. We show that transverse relaxation determines the epoch of this irreversible depolarization. We give a method to compute the depolarized fluxes, presenting an explicit formula for simple initial conditions, which can be a crucial input for supernova theory and neutrino phenomenology.
We discuss flavor-mixing probabilities and flavor ratios of high energy astrophysical neutrinos. In the first part of this paper, we expand the neutrino flavor-fluxes in terms of the small parameters U_{e3} and pi/4 - theta_{23}, and show that there are universal first and second order corrections. The second order term can exceed the first order term, and so should be included in any analytic study. We also investigate the probabilities and ratios after a further expansion around the tribimaximal value of sin^2 theta_{12} = 1/3. In the second part of the paper, we discuss implications of deviations of initial flavor ratios from the usually assumed, idealized flavor compositions for pion, muon-damped, and neutron beam sources, viz., (1 : 2 : 0), (0 : 1 : 0), and (1 : 0 : 0), respectively. We show that even small deviations have significant consequences for the observed flavor ratios at Earth. If initial flavor deviations are not taken into account in analyses, then false inferences for the values in the PMNS matrix elements (angles and phase) may result.
We discuss the transition radiation process $ u to u gamma$ at an interface of two media. The medium fulfills the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation. The transition radiation occurs when at least one of those quantities have different values in different media. We present a result for the probability of the transition radiation which is both accurate and analytic. For $E_ u =1$MeV neutrino crossing polyethylene-vacuum interface the transition radiation probability is about $10^{-39}$ and the energy intensity (deposition) is about $10^{-34}$eV. At the surface of the neutron stars the transition radiation probability may be $sim 10^{-20}$. Our result on three orders of magnitude is larger than the results of previous calculations.}
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