Kohtaroh Miura, Yoshimasa Hidaka, Daisuke Satow, Teiji Kunihiro
Motivated by the scenario of the resonant leptogenesis in which the lepton number creation in the electroweak scale is relevant, we investigate spectral properties and possible collective nature of the standard-model neutrinos at electroweak scale temperature (T). We adopt the R_xi gauge fixing, which includes the unitary gauge as a limiting case, and allows us to study the broken as well as the restored phases of the gauge symmetry in a unified way. We show that the spectral density of the neutrino gets to have a three-peak structure in the low-momentum region due to the scattering with the thermally excited particles (i.e., Landau damping) when T becomes comparable to the weak boson masses in the plasma. The three peaks are identified with a novel ultrasoft mode, the usual quasiparticle, and antiplasmino modes. Varying the gauge-fixing parameter, we show that the three-peak structure appears independently of the gauge fixing and thus has a physical significance. We discuss possible implications of the neutrino spectral density obtained in the present work on particle cosmology, in particular in the context of the resonant leptogenesis.
View original:
http://arxiv.org/abs/1306.1701
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