Spin-flavor Oscillations Research Articles

Spin-flavor oscillations of relic neutrinos in primordial magnetic field

The neutrino magnetic moment operator clasps a tiny but nonzero value within the standard model (SM) of particle physics and rather enhanced values in various new physics models. This generation of the magnetic moment (μν) is through quantum loop corrections which can exhibit spin-flavor oscillations in the presence of an external magnetic field. Also, several studies predict the existence of a primordial magnetic field (PMF) in the early Universe, extending back to the era of Big Bang nucleosynthesis (BBN) and before. The recent North American Nanohertz Observatory for Gravitational Waves measurement can be considered as a strong indication of the presence of these PMFs. In this work, we consider the effect of the PMF on the flux of relic neutrinos. For Dirac neutrinos, we show that half of the active relic neutrinos can become sterile due to spin-flavor oscillations well before becoming nonrelativistic owing to the expansion of the Universe and also before the timeline of the formation of galaxies and hence intergalactic fields, subject to the constraints on the combined value of μν and the cosmic magnetic field at the time of neutrino decoupling. For the upper limit of PMF allowed by the BBN, this can be true even if the experimental bounds on μν approach a few times its SM value. Published by the American Physical Society 2024

Cosmic neutrino flux and spin flavor oscillations in intergalactic medium

The ultra high energy (UHE) cosmic neutrinos are expected to play a pivotal role in the disquisition of physics beyond the standard model of particle physics as well as serve as an ideal cosmic messengers. This epitomizes the selling point of several currently running or planned neutrino telescopes. The UHE cosmic neutrinos usually perambulate gargantuan scales in the extragalactic universe having a magnetic field. If neutrinos have a finite magnetic moment (μν) owing to quantum loop corrections, this may result in spin-flavor oscillations, which can affect the cosmic neutrino flux. Using the current limit and assuming neutrinos to be Dirac particles, we show that the flux of cosmic neutrinos will reduce by half if they traverse few Mpcs through the intergalactic magnetic field, in the range of μG to nG. Moreover, one can safely neglect the effect of μν if the current upper bound is improved by a few orders of magnitude even if the neutrinos travel through the size of the visible universe.

Dirac and Majorana neutrino oscillations in magnetized moving and polarized matter

In the present paper we develop the quantum theory of neutrino spin and spin-flavour oscillations in moving magnetized matter with a special focus on the effects of matter polarization. We derive an effective neutrino evolution Hamiltonian and corresponding expressions for the neutrino oscillation probabilities. Both the case of Dirac and Majorana neutrinos are considered. From the comparison of the neutrino spin oscillation probabilities in the transversally moving matter for the Dirac and Majorana neutrinos it follows that the oscillation patterns is different for theses two cases. In particular, the conditions for the resonances in these two cases are realized at different densities of matter.

Spin and spin-flavor oscillations due to neutrino charge radii interaction with an external environment

We derive the effective neutrino evolution Hamiltonian and corresponding expressions for the neutrino flavour and spin-flavour oscillation probabilities accounting for the neutrino interactions with an external electric current though the neutrino charge radius and anapole moment. The obtained results are of interest for neutrino astrophysical applications.

Coherence and mixedness of neutrino oscillations in a magnetic field

The radical departure from classical physics implies quantum coherence, i.e., coherent superposition of eigenstates of Hermitian operators. In resource theory, quantum coherence is a resource for quantum operations. Typically the stochastic phenomenon induces decoherence effects. However, in the present work, we prove that nonunitary evolution leads to the generation of quantum coherence in some cases. Specifically, we consider the neutrino propagation in the dissipative environment, namely in a magnetic field with a stochastic component, and focus on neutrino flavour, spin and spin-flavour oscillations. We present exact analytical results for quantum coherence in neutrino oscillations quantified in terms of the relative entropy. Starting from an initial zero coherence state, we observe persistent oscillations of coherence during the dissipative evolution of an ultra-high energy neutrino in a random interstellar magnetic field. We found that after dissipative evolution, the initial spin-polarized state entirely “thermalizes”, and in the final steady state, the spin-up/down states have the same probabilities. On the other hand, neutrino flavour states also “thermalize”, but the populations of two flavour states do not equate to each other. The initial flavour still dominates in the final steady state.

Neutrino spin-flavor oscillations in solar environment

We study the phenomenon of neutrino spin-flavor oscillations due to solar magnetic fields. This allows us to examine how significantly the electron neutrinos produced in the solar interior undergo a resonant spin-flavor conversion. We construct analytical models for the solar magnetic field in all the three regions of the Sun. Neutrino spin-flavor oscillations in this magnetic field are examined by studying the level crossing phenomenon and comparing the two cases of zero and non-zero vacuum mixing respectively. Results from the Borexino experiment are used to place an upper limit on the magnetic field in the solar core. Related phenomena such as effects of matter on neutrino spin transitions and differences between Dirac and Majorana transitions in the solar magnetic fields are also discussed.

Electromagnetic neutrinos: New constraints and new effects in oscillations

A short overview of neutrino electromagnetic properties with focus on existed experimental constraints and future prospects is presented. The related new effect in neutrino flavour and spin-flavour oscillations in the transversal matter currents is introduced.

Electromagnetic interactions of massive neutrinos and neutrino oscillations

An interplay between electromagnetic properties of massive neutrinos and neutrino oscillation phenomena is discussed. The role of neutrino oscillations in the search of neutrino magnetic moments in experiments on low-energy elastic neutrino-electron scattering is emphasized. A general treatment of neutrino spin-flavor oscillations in a magnetic field is presented. An impact of neutrino electromagnetic interactions on Majorana neutrino fluxes from supernovae is pointed out.

Spin-flavor oscillations of Dirac neutrinos in matter under the influence of a plane electromagnetic wave

We study oscillations of Dirac neutrinos in background matter and a plane electromagnetic wave. First, we find the new exact solution of the Dirac-Pauli equation for a massive neutrino with the anomalous magnetic moment electroweakly interacting with matter under the influence of a plane electromagnetic wave with the circular polarization. We use this result to describe neutrino spin oscillations in the external fields in question. Then we consider several neutrino flavors and study neutrino spin-flavor oscillations in this system. For this purpose we formulate the initial condition problem and solve it accounting for the considered external fields. We derive the analytical expressions for the transition probabilities of spin-flavor oscillations for different types of neutrino magnetic moments. These analytical expressions are compared with the numerical solutions of the effective Schr\"odinger equation and with the findings of other authors. In particular, we reveal that a resonance in neutrino spin-flavor oscillations in the considered external fields cannot happen contrary to the previous claims. Finally, we briefly discuss some possible astrophysical applications.

Neutrino spin and spin-flavor oscillations in transversal matter currents with standard and nonstandard interactions

After a brief history of two known types of neutrino mixing and oscillations, including neutrino spin and spin-flavour oscillations in the transversal magnetic field, we perform systematic study of a new phenomenon of neutrino spin and spin-flavour oscillations engendered by the transversal matter currents on the bases of the developed quantum treatment of the phenomenon. Possibilities for the resonance amplification of these new types of oscillations by the longitudinal matter currents and longitudinal magnetic fields are analyzed. Neutrino spin-flavour oscillations engendered by the transversal matter currents in the case of non-standard interactions of neutrinos with background matter are also considered

Spin-flavor oscillations of Dirac neutrinos in a plane electromagnetic wave

We study spin and spin-flavor oscillations of Dirac neutrinos in a plane electromagnetic wave with circular polarization. The evolution of massive neutrinos with nonzero magnetic moments in the field of an electromagnetic wave is based on the exact solution of the Dirac-Pauli equation. We formulate the initial condition problem to describe spin-flavor oscillations in an electromagnetic wave. The transition probabilities for spin and spin-flavor oscillations are obtained. In case of spin-flavor oscillations, we analyze the transition and survival probabilities for different neutrino magnetic moments and various channels of neutrino oscillations. As an application of the obtained results, we study the possibility of existence of $\nu_{e\mathrm{L}}\to\nu_{\mu\mathrm{R}}$ oscillations in an electromagnetic wave emitted by a highly magnetized neutron star. Our results are compared with findings of other authors.

Neutrino flavour, spin and spin-flavour oscillations and consistent account for a constant magnetic field

Neutrino flavour, spin and spin-flavour oscillations and consistent account for a constant magnetic field

Spin-flavor oscillations of ultrahigh-energy cosmic neutrinos in interstellar space: The role of neutrino magnetic moments

A theoretical analysis of possible influence of neutrino magnetic moments on the propagation of ultrahigh-energy cosmic neutrinos in the interstellar space is carried out under the assumption of two-neutrino mixing. The exact solution of the effective equation for neutrino evolution in the presence of a magnetic field and matter is obtained, which accounts for four neutrino species corresponding to two different flavor states with positive and negative helicities. Using most stringent astrophysical bounds on the putative neutrino magnetic moment, probabilities of neutrino flavor and spin oscillations are calculated on the basis of the obtained exact solution. Specific patterns of spin-flavor oscillations are determined for neutrino-energy values characteristic of, respectively, the cosmogenic neutrinos, the Greisen-Zatsepin-Kuz'min (GZK) cutoff, and well above the cutoff.

Neutrino spin and spin-flavour oscillations in transversally moving or polarized matter

Studies of an interesting effect of neutrino spin and spin-flavour oscillations engenders by neutrino weak interactions with the transversally moving or polarized matter are reviewed.

Neutrino spin-flavor oscillations derived from the mass basis

We reconsider the standard scheme for description of neutrino spin-flavor oscillations aiming at a rigorous derivation of evolution equation for the mixed flavor neutrino states in magnetic field. For this purpose we obtain the evolution equation in the physical basis of massive neutrinos and then trace its transformation into the flavor basis. The effective Hamiltonian of the resulting equation relevant to interaction with the magnetic field differs from the standard one by several entries. The approach leads to interesting relations of the neutrino magnetic moments defined in the two neutrino bases and to some additional subtle properties of the formalism.

Electromagnetic properties of neutrinos: three new phenomena in neutrino spin oscillations

In studies of neutrino electromagnetic properties we discuss three very inter- esting aspects related to neutrino spin oscillations. First we consider neutrino mixing and oscillations in the mass and flavour bases under the influence of a constant magnetic field with nonzero transversal and longitudinal components. Then we discuss the effect of neutrino spin oscillations induced by electroweak interactions of neutrino with mov- ing matter in case there is matter transversal current or polarization. In the final part of the paper we discuss recently developed approach to description of neutrino spin and spin-flavour oscillations in a constant magnetic field that is based on the use of the exact neutrino stationary states in the magnetic field.

Spin-flavor oscillations of Dirac neutrinos described by relativistic quantum mechanics

Spin-flavor oscillations of Dirac neutrinos in matter and a magnetic field are studied using the method of relativistic quantum mechanics. Using the exact solution of the wave equation for a massive neutrino, taking into account external fields, the effective Hamiltonian governing neutrino spin-flavor oscillations is derived. Then the The consistency of our approach with the commonly used quantum mechanical method is demonstrated. The obtained correction to the usual effective Hamiltonian results in the appearance of the new resonance in neutrino oscillations. Applications to spin-flavor neutrino oscillations in an expanding envelope of a supernova are discussed. In particular, transitions between right-polarized electron neutrinos and additional sterile neutrinos are studied for realistic background matter and magnetic field distributions. The influence of other factors such as the longitudinal magnetic field, the matter polarization, and the non-standard contributions to the neutrino effective potential, is also analyzed.

Evolution of a dense neutrino gas in matter and electromagnetic field

We describe the system of massive Weyl fields propagating in a background matter and interacting with an external electromagnetic field. The interaction with an electromagnetic field is due to the presence of anomalous magnetic moments. To canonically quantize this system first we develop the classical field theory treatment of Weyl spinors in frames of the Hamilton formalism which accounts for the external fields. Then, on the basis of the exact solution of the wave equation for a massive Weyl field in a background matter we obtain the effective Hamiltonian for the description of spin–flavor oscillations of Majorana neutrinos in matter and a magnetic field. Finally, we incorporate in our analysis the neutrino self-interaction which is essential when the neutrino density is sufficiently high. We also discuss the applicability of our results for the studies of collective effects in spin–flavor oscillations of supernova neutrinos in a dense matter and a strong magnetic field.

Mimicking diffuse supernova antineutrinos with the sun as a source

Measuring the \( \bar \nu _e \) component of the cosmic diffuse supernova neutrino background (DSNB) is the next ambitious goal for low-energy neutrino astronomy. The largest flux is expected in the lowest accessible energy bin. However, for E ≲ 15 MeV a possible signal can be mimicked by a solar \( \bar \nu _e \) flux that originates from the usual 8B neutrinos by spin-flavor oscillations. We show that such an interpretation is possible within the allowed range of neutrino electromagnetic transition moments and solar turbulent field strengths and distributions. Therefore, an unambiguous detection of the DSNB requires a significant number of events at E ≳ 15 MeV.

Oscillations of Dirac and Majorana neutrinos in matter and a magnetic field

We study the evolution of massive mixed Dirac and Majorana neutrinos in matter under the influence of a transversal magnetic field. The analysis is based on relativistic quantum mechanics. We solve exactly the evolution equation for relativistic neutrinos, find the neutrino wave functions, and calculate the transition probability for spin-flavor oscillations. We analyze the dependence of the transition probability on the external fields and compare the cases of Dirac and Majorana neutrinos. The evolution of Majorana particles in vacuum is also studied and correction terms to the standard oscillation formula are derived and discussed. As a possible application of our results we discuss the spin-flavor transitions in supernovae.