Neutrino spin oscillations in polarized matter

Abstract

We study the neutrino spin oscillations, i.e., neutrino spin precession caused by the neutrino interaction with matter polarized by external magnetic field (or, equivalently, by the interaction of the induced magnetic moment (IMM) of a neutrino with the magnetic field). In the analysis, we consider realistic conditions inside supernovae and discuss both the Dirac and Majorana cases. We show that due to the interaction with the polarized matter a neutrino flux from a supernova suffers additional attenuation at low neutrino energies. Another possible effect is that when taken together the effects of conventional magnetic moment and polarized matter can cancel each other so that under certain condition the oscillations disappear. We note that this can lead to the appearance of a characteristic maximum in the spectrum of electron neutrinos from supernovae. Accounting for neutrino mixing (in the two-flavor approximation) can significantly increase (almost twice) the effective value of the IMM of the electron neutrino. As a result, electron neutrinos with twice as high energy will be able to participate in the processes of spin conversion. Various feedback mechanisms accompanying the considered phenomena are also discussed.

Effects of nonstandard neutrino self-interactions and magnetic moment on collective Majorana neutrino oscillations

“…In the absence of NSSIs, these blocks vanish, so nothing is able to catalyze the helicity-mixing effect introduced by a small magnetic moment, analogously to the Majorana case [25]. Next, we have tested Majorana neutrinos with scalar/pseudoscalar interactions for instabilities initiated by the so-called induced magnetic moment [42], which physically is a helicitydependent Wolfenstein potential in a magnetized medium, and found no new instabilities. Among other possible reasons, this is definitely related to the fact that at least for a nonmoving background medium, the induced magnetic moment term in the Hamiltonian does not flip the neutrino helicity.…”

Geometric and Majorana phases in neutrino oscillations

“…Strategies for making this discovery are sought, most prominently including neutrinoless double beta decay experiments [1]. Other ideas involve helicity-flavor oscillations [2][3][4][5][6][7][8] and neutrino decay [9,10].…”

Neutrino spin operator and dispersion in moving matter

“…Matter polarization occurs due to the interaction with external magnetic field (see, for example, [15]) and in this connection it is often assumed that equation (1) describes scattering of neutrinos on medium particles polarized by an external field. Note that there is another physical interpretation of this phenomenon, according to which a direct interaction of the neutrino induced magnetic moment (IMM) with an external magnetic field takes place [16]. Both approaches are equivalent and lead to the same results.…”

“…The theory of the phenomenon was further developed in [8], where it was considered on the quantum level by calculating the amplitudes that enter the effective neutrino evolution equation. Neutrino spin oscillations in a supernova environment associated with the presence of IMM were considered in [16], see also [25,26].…”