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High Energy Physics - Phenomenology, hep-ph, Astrophysics, Solar and Stellar Astrophysics, astro-ph.SR
Abstract:
Neutrino-neutrino refraction in dense media can cause self-induced flavor
conversion triggered by collective run-away modes of the interacting flavor
oscillators. The growth rates were usually found to be of order a typical
vacuum oscillation frequency $\Delta m^2/2E$. However, even in the simple case
of a $\nu_e$ beam interacting with an opposite-moving $\bar\nu_e$ beam, and
allowing for spatial inhomogeneities, the growth rate of the fastest-growing
Fourier mode is of order $\mu=\sqrt{2} G_{\rm F} n_{\nu}$, a typical
$\nu$--$\nu$ interaction energy. This growth rate is much larger than the
vacuum oscillation frequency and gives rise to flavor conversion on a much
shorter time scale. This phenomenon of "fast flavor conversion" occurs even for
vanishing $\Delta m^2/2E$ and thus does not depend on energy, but only on the
angle distributions. Moreover, it does not require neutrinos to mix or to have
masses, except perhaps for providing seed disturbances. We also construct a
simple homogeneous example consisting of intersecting beams and study a
schematic supernova model proposed by Ray Sawyer, where $\nu_e$ and $\bar\nu_e$
emerge with different zenith-angle distributions, the key ingredient for fast
flavor conversion. What happens in realistic astrophysical scenarios remains to
be understood.
