Nonlinear neutrino oscillations in the expanding Universe

Abstract

We derive the equations that govern neutrino and antineutrino behavior in the early Universe. Results are presented from numerical simulations incorporating nonlinear effects of the neutrinoantineutrino background as well as the leading CP-symmetric and CP-asymmetric terms arising from the interactions with electrons and positrons. A broad spectrum of neutrino and antineutrino behavior is observed, ranging from vacuumlike to smooth. Oscillations exhibiting self-maintained coherence also appear. We identify a variety of neutrino properties arising as a consequence of the nonlinear neutrino self-interactions. The nonlinear effects tend to suppress any CP asymmetry relative to the linear case.An analytical approximation scheme reproducing bulk neutrino behavior is described. We discuss some physical implications of our results. PACS number(s): 95.30. Cq, 12.15.Ff, 14.60.Pq

Self-induced decoherence in dense neutrino gases

“…(58) is traced back to the negative sign in the term (1 − v q · v p ) in Eq. (5). Therefore, the instability of the near-isotropic neutrino gas, for the normal hierarchy, is not just caused by different angular modes experiencing different neutrino-neutrino effects.…”

“…Therefore, if the energy spectrum is broad, the energy dependence of the oscillation frequency quickly leads to kinematical decoherence, i.e., along a neutrino beam the overall flavor content quickly approaches an average value. The situation changes radically when neutrinos themselves provide a significant refractive effect, leading to collective oscillation modes [1,2,3,4,5,6,7,8,9,10,11,12] that can be of practical interest in the early universe [13,14,15,16] or in core-collapse supernovae [17,18,19,20,21,22,23,24,25,26]. Defining the parameter…”

Analysis of collective neutrino flavor transformation in supernovae

“…Because of the neutrino-neutrino forward scattering potential [4][5][6], neutrino flavor transformation in the early universe and near the supernova core can be very different from that in the vacuum or in an ordinary matter background only [7][8][9][10][11][12][13][14][15][16][17]. Recent analytical and numerical studies have revealed a new paradigm for neutrino flavor transformation in supernovae [18][19][20][21][22][23][24][25][26], one which is completely different from vacuum oscillations or the conventional Mikheyev-Smirnov-Wolfenstein (MSW) mechanism [27][28][29].…”

Generational mass splitting of neutrinos in high temperature SU(2) ⊗ U(1) gauge theory

“…The gauge boson diagrams that contribute to the one loop neutrino self-energy are the W -lepton diagram, Σ (1) , and the Z-neutrino diagram, Σ (2) , and they are given by…”

“…In other words, the degeneracy among the massless neutrinos is removed through the interactions with the charged leptons. This can be of immediate interest since even a slight generational asymmetry among the neutrinos can lead to resonant neutrino oscillations [2] and change the evolution of the early universe.…”