Fast neutrino flavor conversion: Roles of dense matter and spectrum crossing
The flavor conversion of a neutrino usually occurs at densities $${\lesssim}{G}_{\mathrm{F}}^{{-}1}{\omega}$$, whether in ordinary matter or a dense neutrino medium, and on time/distance scales of order $${{\omega}}^{{-}1}$$, where $${G}_{\mathrm{F}}$$ is the Fermi weak coupling constant and $${\omega}$$ is the typical vacuum oscillation frequency of the neutrino. In contrast, fast neutrino flavor conversions or fast neutrino oscillations can occur on scales much shorter than $${{\omega}}^{{-}1}$$ in a very dense, anisotropic neutrino gas such as that in a core-collapse supernova or a binary neutron star merger. The origin of fast neutrino oscillations still seems elusive except that it is a mathematical solution to the equation of motion. It has been suggested that the fast oscillations in stationary neutrino gases require a crossing in the electron lepton number angular distribution of the neutrino and that they are suppressed at large matter densities as normal oscillations are. By inspecting a simple four-beam neutrino model we illustrate how the multi-angle effects that were once found to suppress collective neutrino oscillations now give rise to fast flavor conversions. As a result, a large matter density can induce fast oscillations in certain astrophysical scenarios such as at the early epoch of a core-collapse supernova. We also provide an explicit proof of the necessity of a crossed neutrino angular distribution for fast oscillations to occur in an outward flowing, axially symmetric neutrino flux such as in the multi-bulb supernova model. However, fast oscillations can occur without a crossed angular distribution when both inward and outward flowing neutrino fluxes are present in a stationary neutrino gas.
- Research Organization:
- Univ. of New Mexico, Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Nuclear Physics (NP)
- Grant/Contract Number:
- SC0017803; SC0008142
- OSTI ID:
- 1464852
- Alternate ID(s):
- OSTI ID: 1498890
- Journal Information:
- Physical Review D, Journal Name: Physical Review D Vol. 98 Journal Issue: 4; ISSN 2470-0010
- Publisher:
- American Physical SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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