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Register a new userFast neutrino flavor conversion: roles of dense matter and spectrum crossing
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The flavor conversion of a neutrino usually occurs at densities $lesssim G_F^{-1} omega$, whether in the ordinary matter or the neutrino medium, and on time/distance scales of order $omega^{-1}$, where $G_F$ is the Fermi weak coupling constant and $omega$ is the vacuum oscillation frequency of the neutrino. In 2005 Sawyer and more recently both he and other groups have shown that neutrino flavor
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The flavor transformation in a dense neutrino gas can have a significant impact on the physical and chemical evolution of its surroundings. In this work we demonstrate that a dynamic, fast flavor oscillation wave can develop spontaneously in a one-dimensional (1D) neutrino gas when the angular distributions of the electron neutrino and antineutrino cross each other. Unlike the 2D stationary models which are plagued with small-scale flavor structures, the fast flavor oscillation waves remain coherent in the dynamic 1D model in both the position and momentum spaces of the neutrino. The electron lepton number is redistributed and transported in space as the flavor oscillation wave propagates, although the total lepton number remains constant. This result may have interesting implications in the neutrino emission in and the evolution of the compact objects such as core-collapse supernovae.
We investigate the impact of the nonzero neutrino splitting and elastic neutrino-nucleon collisions on fast neutrino oscillations. Our calculations confirm that a small neutrino mass splitting and the neutrino mass hierarchy have very little effect on fast oscillation waves. We also demonstrate explicitly that fast oscillations remain largely unaffected for the time/distance scales that are much smaller than the neutrino mean free path but are damped on larger scales. This damping originates from both the direct modification of the dispersion relation of the oscillation waves in the neutrino medium and the flattening of the neutrino angular distributions over time. Our work suggests that fast neutrino oscillation waves produced near the neutrino sphere can propagate essentially unimpeded which may have ramifications in various aspects of the supernova physics.
We investigate the importance of going beyond the mean-field approximation in the dynamics of collective neutrino oscillations. To expand our understanding of the coherent neutrino oscillation problem, we apply concepts from many-body physics and quantum information theory. Specifically, we use measures of nontrivial correlations (otherwise known as entanglement) between the constituent neutrinos of the many-body system, such as the entanglement entropy and the Bloch vector of the reduced density matrix. The relevance of going beyond the mean field is demonstrated by comparisons between the evolution of the neutrino state in the many-body picture vs the mean-field limit, for different initial conditions.
Effects of neutrino charge radius and magnetic moment, as well as the medium modifications of the weak and electromagnetic nucleon form factors of the constituents of matter on the neutrino electroweak interaction with dense nuclear matter, are estimated. A relativistic mean-field and quark-meson coupling models are adopted for the in-medium effective nucleon mass and nucleon form factors. We find that the neutrino scattering cross section increases in the cold nuclear medium when neutrino form factors and the in-medium modifications of the nucleon weak and electromagnetic form factors are simultaneously taken into account relative to that without neutrino form factors. The increase of the cross section results in the decrease of the neutrino mean free path, particularly at larger neutrino magnetic moment and charge radius. The quenching of the neutrino mean free path is estimated to be about 12-58% for the values of $mu_ u = 3 times 10^{-12} mu_B$ and $R_ u = 3.5 times 10^{-5}~textrm{MeV}^{-1}$, obtained from the constraints of the astrophysical observations, compared to that of $mu_ u =0$ and $R_ u =0$. The decrease of the neutrino mean free path is expected to decelerate the cooling of neutron stars. Each contribution of the neutrino form factors to the neutrino mean free path is discussed.
Mounting evidence indicates that neutrinos likely undergo fast flavor conversion (FFC) in at least some core-collapse supernovae. Outcomes of FFC, however, remain highly uncertain. Here we study the cascade of flavor-field power from large angular scales in momentum space down to small ones, showing that FFC enhances this process and thereby hastens relaxation. Cascade also poses a computational challenge, which is present even if the flavor field is stable: When power reaches the smallest angular scale of the calculation, error from truncating the angular-moment expansion propagates back to larger scales, to disastrous effect on the overall evolution. Essentially the same issue has prompted extensive work in the context of plasma kinetics. This link suggests new approaches to averting spurious evolution, a problem that presently puts severe limitations on the feasibility of realistic oscillation calculations.
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