Spin Effects for Neutrinos and Electrons Moving in Dense Matter

We give a review on a recently developed powerful method for investigation of different phenomena that can appear when neutrinos and electrons move in background matter with special focus on the spin phenomena. This paper is devoted to the problem of neutrino and electron motion in a dense matter with special focus on the spin phenomena. It has been proven in recent oscillation experiments that neutrino has nonzero mass. Therefore, the Dirac neutrino should have nontrivial electromagnetic properties, in particular, nonzero magnetic moment. It is also well known [1] that in the minimally extended Standard Model with SU(2)-singlet right-handed neutrino the one-loop radiative correction generates neutrino magnetic moment which is proportional to the neutrino mass μν = 3 8 √ 2π2 eGFmν = 3× 10μ0 ( mν 1eV ) , where μ0 = e/2m is the Bohr magneton, mν and m are the neutrino and electron masses. There are also models (see [2]) in which much large values for magnetic moment of neutrino are predicted. The LEP data require that the number of light neutrinos coupling to Z boson is exactly three, whereas any additional neutrino, if this particle exist, must be heavy. In light of this opportunity we considered the neutrino magnetic moment for various ratios of particles masses. We have obtained [3] values of the neutrino magnetic moment for light (for this particular case see also [1, 4]), intermediate and heavy massive neutrino: 1) μν = eGF 4π2 √ 2 mν 3(2−7a+6a2−2a2 ln a−a3) 4(1−a)3 , for mν ≪ ml ≪ MW , 2) μν = 3eGF 8π2 √ 2 mν { 1 + 5 18 b } , for ml ≪ mν ≪ MW , 3) μ = eGF 8π22mν , for ml ≪ MW ≪ mν , where a = ( ml MW ) and b = ( mν MW ). It should be also mentioned that the neutrino magnetic moment can be affected by the external environment. In particular, the value of the neutrino magnetic moment can be significantly shifted by the presence of strong external magnetic fields [5] (see also [6, 7]). So far, solar neutrino experiments set a limit on the neutrino magnetic moment on the level of μνe ≤ 1.5 × 10−10[8]. More stringent constraint μνe ≤ 5.8 × 10−11 has been provided by the GEMMA accelerator experiment [9]. The constraint from astrophysical considerations (the red giants cooling) is μνe ≤ 3× 10−12 [10]. Developing of the theory of neutrino spin properties in an external environment we have evaluated the Loretz invariant approach to the neutrino spin evolution that was based on the proposed generalized Bargmann-Michel-Telegdi equation [11]. Within the developed Lorentz invariant approach it is also possible to find the solution for the neutrino spin evolution problem for a general case when the neutrino is subjected to general types