Neutrino radiative decay in external field and medium
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utrino Radiative Decay in External Field and Medium A. I. Ternova, * and P. A. Eminovb a
Moscow Institute of Physics and Technology, Dolgoprudnyii, 141700 Russia National Research University, High School of Economics, Moscow, 109028 Russia *email: [email protected]
b
Abstract—The current state of the theory of massive neutrino radiative decay is reviewed. By extending our previous studies, we thoroughly analyze the process of radiative decay of a massive Dirac neutrino in the 2 3
strong external magnetic field H H 0 = m e c /e = 4.41 × 1013 G in the presence of medium (degenerate electron gas), and calculate its probability. It is shown that, in the presence of dense medium, the latter quan tity becomes much larger than that in the magnetic field in the case of both relativistic and nonrelativistic neutrinos. Possible astrophysical applications of the obtained results are considered. DOI: 10.1134/S1063779614020051
1. INTRODUCTION The most important discovery in modern neutrino physics was the experimental detection of neutrino oscillations predicted by B. Pontecorvo back in 1950s [1, 2]. Those oscillations were observed in a number of experiments (see, e.g., [3, 4]), thereby providing solid confirmation of the existence of both neutrino mass and mixing in the neutrino sector of the electroweak theory. According to the idea of mixing the neutrino states with definite flavors (i.e., νe, νμ, ντ) are linear superpo sitions of those with definite masses (ν1, ν2, ν3): να =
∑U
restrictions imposed on the latter. Therefore, many modern theoretical models, which study manifesta tions of the “new physics” beyond Standard Model, predict the existence of sterile neutrinos with masses ranging from light to very heavy ones that are nearly beyond experimental capabilities to observe them [12, 13]. Under mixing a heavy massive neutrino can decay producing a lighter one [14, 15]. Depending on the mass of initial neutrino, this decay may proceed through different channels. The most intensively dis cussed channels are the following decays of massive neutrinos:
αi ν i ,
a) νi → νj + e+ + e–,
i
where Uαi is the unitary neutrino mixing matrix (Pon tecorvo–Maki–Nakagawa–Sakata matrix, see [5]). Therefore, the Standard Model of electroweak inter actions with neutrino mixing assumes the existence of three types of active neutrinos that take part in the weak interactions: electron, muon, and τ neutrinos. This is consistent with the known result obtained in the high precision experiments, carried out at the SLC and LEP electron–positron colliders, which analyze “invisible” Z boson decays [6]. From those experi ments it follows that the number of flavors of light active neutrinos is Nν = 2.9840 ± 0.0082, i.e., does not exceed three. Nevertheless, this result does still not restrict the possible number of sterile neutrinos. The latter are neutral leptons that do not directly participate in the weak interactions [7–9]. However, they can mix with ordinary active neutrinos and, because of this, take part in the oscillations [1
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