We continue our discussions [1-3] of neutrino electromagnetic properties and give a short introduction to the derivation of the general structure of the electromagnetic form factors of Dirac and Majorana neutrinos. Then we consider experimental constraints on neutrino magnetic and electric dipole moments, electric millicharge, charge radii and anapole moments from the terrestrial laboratory experiments (the bounds obtained by the reactor MUNU, TEXONO and GEMMA experiments and the solar Super-Kamiokande and the recent Borexino experiments). A special credit is done to the recent and most severe constraints on neutrino magnetic moments, millicharge and charge radii [4-8]. The world best reactor [4] and solar [5] neutrino and astrophysical [9,10] bounds on neutrino magnetic moments, as well as bounds on millicharge from the reactor [6] neutrinos fluxes are included in the recent issues of the Review of Particle Physics (see the latest Review: M. Tanabashi et al. (Particle Data Group), Phys. Rev. D 98 (2018) 030001). The best astrophysical bound on neutrino millicharge was obtained in [11].
The main manifestation of neutrino electromagnetic interactions, such as: 1) the radiative decay in vacuum, in matter and in a magnetic field, 2) the neutrino Cherenkov radiation, 3) the plasmon decay to neutrino-antineutrino pair, 4) the neutrino spin light in matter, and 5) the neutrino spin and spin-flavour precession are discussed. Phenomenological consequences of neutrino electromagnetic interactions (including the spin light of neutrino [12]) in astrophysical environments are also reviewed.
We present results of the recent detailed study [13] of the electromagnetic interactions of massive neutrinos in the theoretical formulation of low-energy elastic neutrino-electron scattering. The formalism of neutrino charge, magnetic, electric, and anapole form factors defined as matrices in the mass basis with account for three-neutrino mixing is presented. Using the derived new expression for a neutrino electromagnetic scattering cross section [13], we further developed studies of neutrino electromagnetic properties using the COHERENT data [7] and obtained [8] new bounds on the neutrino charge radii from the COHERENT experiment. Worthy of note, our paper [8] has been included by the Editors Suggestion to the Phys. Rev. D “Highlights of 2018”.
The concluding part of the proposed talk is dedicated to results of our recently performed detailed studies of new effects in neutrino spin, spin-flavour and flavor oscillations under the influence of the transversal matter currents [14] and a constant magnetic field [15, 16]. The discussed two new effects can be summarized as follows:
1) it is shown [14] that neutrino spin and spin-flavor oscillations can be engendered by weak interactions of neutrinos with the medium in the case when there are the transversal matter currents; different possibilities for the resonance amplification of oscillations are discussed, the neutrino Standard Model and non-standard interactions are accounted for;
2) within a new treatment [15] of the neutrino flavor, spin and spin-flavour oscillations in the presence of a constant magnetic field, that is based on the use of the exact neutrino stationary states in the magnetic field, it is shown that there is an interplay of neutrino oscillations on different frequencies; in particular: a) the amplitude of the flavour oscillations νLe↔ νLμ at the vacuum frequency is modulated by the magnetic field frequency μB , and b) the neutrino spin oscillation probability (without change of the neutrino flavour) exhibits the dependence on the neutrino energy and mass square difference Δm2 . The discovered new phenomena in neutrino oscillations should be accounted for reinterpretation of results of already performed experiments on detection of astrophysical neutrino fluxes produced in astrophysical environments with strong magnetic fields and dense matter. These new neutrino oscillation phenomena are also of interest in view of future experiments on observations of supernova neutrino fluxes with large liquid-scintillator detectors like JUNO, for instance.
The best world experimental bounds on neutrino electromagnetic properties are confronted with the predictions of theories beyond the Standard Model. It is shown that studies of neutrino electromagnetic properties provide a powerful tool to probe physics beyond the Standard Model.
References:
[1] C. Guinti and A. Studenikin, “Neutrino electromagnetic interactions: A window to new physics”, Rev. Mod. Phys. 87 (2015) 531-591.
[2] C. Giunti, K. Kouzakov, Y. F. Li, A. Lokhov, A. Studenikin, S. Zhou, Electromagnetic neutrinos in laboratory experiments and astrophysics, Annalen Phys. 528 (2016) 198.
[3] A.Studenikin, “Neutrino electromagnetic interactions: A window to new physics - II”,
PoS EPS-HEP2017 (2017) 137.
[4] A. Beda, V. Brudanin, V. Egorov et al., “The results of search for the neutrino magnetic
moment in GEMMA experiment”, Adv. High Energy Phys. 2012 (2012) 350150.
[5] M. Agostini et al (Borexino coll.), “Limiting neutrino magnetic moments with Borexino Phase-II solar neutrino data”, Phys. Rev. D 96 (2017) 091103.
[6] A. Studenikin, “New bounds on neutrino electric millicharge from limits on neutrino magnetic moment”, Europhys. Lett. 107 (2014) 21001.
[7] D. Papoulias, T. Kosmas, “COHERENT constraints to conventional and exotic neutrino physics”, Phys. Rev. D 97 (2018) 033003.
[8] M. Cadeddu, C. Giunti, K. Kouzakov, Y.F. Li, A. Studenikin, Y.Y. Zhang, “Neutrino charge radii from COHERENT elastic neutrino-nucleus scattering”, Phys. Rev. D 98 (2018) 113010.
[9] N. Viaux, M. Catelan, P. B. Stetson, G. G. Raffelt et al., “Particle-physics constraints from the globular cluster M5: neutrino dipole moments”, Astron. & Astrophys. 558 (2013) A12.
[10] S. Arceo-Díaz, K.-P. Schröder, K. Zuber and D. Jack, “Constraint on the magnetic dipole moment of neutrinos by the tip-RGB luminosity in ω-Centauri”, Astropart. Phys. 70 (2015) 1.
[11] A. Studenikin, I. Tokarev, “Millicharged neutrino with anomalous magnetic moment in rotating magnetized matter”, Nucl. Phys. B 884 (2014) 396-407.
[12] A. Grigoriev, A. Lokhov, A. Studenikin, A. Ternov, “Spin light of neutrino in astrophysical environments”, JCAP 1711 (2017) 024 (23 p.).
[13] K. Kouzakov, A. Studenikin, “Electromagnetic properties of massive neutrinos in low-energy
elastic neutrino-electron scattering”, Phys. Rev. D 95 (2017) 055013.
[14] P. Pustoshny, A. Studenikin, "Neutrino spin and spin-flavour oscillations in transversal
matter currents with standard and non-standard interactions", Phys. Rev. D98 (2018) no.11, 113009.
[15] A. Popov, A. Studenikin, "Neutrino eigenstates and flavour, spin and spin-flavour oscillations in a constant magnetic field ", Eur.Phys.J. C79 (2019) no.2, 144.
[16] P. Kurashvili, K. Kouzakov, L. Chotorlishvili, A. Studenikin, “Spin-flavor oscillations of ultrahigh-energy cosmic neutrinos in interstellar space: The role of neutrino magnetic moments”, Phys. Rev. D 96 (2017) 103017.