Neutrino ‘decoherence’ Revealed: Magnetic Fields Limit Particle Travel Distance

Scientists are increasingly investigating neutrino oscillations within magnetic fields to better understand these elusive particles. Artem Popov, Alexander Studenikin, and Alexander Tcvirov, all from Moscow State University, present a novel wave packet description of Majorana neutrino oscillations in such environments. Their work analytically solves the modified Dirac equation for neutrinos possessing transition magnetic moments, revealing how magnetic fields impact oscillation probabilities and introduce decoherence effects at significant distances. This research is significant because it demonstrates that decoherence during propagation in a supernova’s magnetic field may be observable, potentially offering a new avenue for probing both neutrino properties and astrophysical phenomena.

This work presents analytical solutions to the modified Dirac equation for neutrinos possessing non-zero transition magnetic moments as they propagate through a magnetic field, specifically within a two-flavour framework.

Derived expressions for oscillation probabilities incorporate the decoherence effect, a phenomenon that emerges when propagation distances exceed the coherence length, offering a more realistic depiction of neutrino behaviour. Investigations reveal that, for neutrinos traversing a magnetic field, the coherence length aligns with that of vacuum oscillations when the vacuum frequency significantly exceeds the magnetic frequency (ωvac ωB), but scales proportionally to the cube of the average neutrino momentum when (ωvac The research demonstrates that decoherence may become significant during neutrino propagation within the intense magnetic fields found in supernovae, potentially altering observed neutrino signals.
By employing the wave packet approach, the study extends previous analyses of vacuum neutrino oscillations, oscillations in matter, and collective oscillations during supernova explosions to encompass the complexities introduced by magnetic fields. The modified Dirac equation, crucial to this analysis, accounts for the interaction between Majorana neutrinos and the magnetic field, utilising an effective Lagrangian that describes the transition magnetic moments.

Researchers constructed one-particle wave functions by convolving plane wave states with a wave packet shape function, enabling a detailed examination of how neutrinos evolve in the presence of both mass and magnetic interactions. Analytical solutions to the resulting system of equations were obtained for the two-flavour case, allowing for the calculation of oscillation probabilities that explicitly include decoherence effects.

The study highlights that the coherence length, a critical parameter governing oscillation patterns, is dependent on the relationship between the vacuum and magnetic oscillation frequencies, and the average neutrino momentum. Furthermore, the analysis considers ultra-relativistic neutrinos and assumes that neutrino masses are significantly larger than the magnetic interaction strength, simplifying the dispersion relation and facilitating analytical progress.

These approximations allow for a clearer understanding of the dominant physical effects governing neutrino propagation in strong magnetic fields, providing insights into potential observational consequences in astrophysical environments like supernovae, where magnetic fields can reach extreme intensities. The findings contribute to a more complete picture of neutrino behaviour and may aid in interpreting future neutrino detection experiments.

Analytical derivation of oscillation probabilities and coherence lengths in magnetic fields is crucial for understanding neutrino propagation

Neutrino oscillations in a magnetic field were investigated using the wave packet formalism to model neutrino propagation. The study analytically solved the modified Dirac equation for neutrinos possessing non-zero transition magnetic moments, specifically within a two-flavour framework. This allowed for the derivation of oscillation probabilities that account for decoherence effects arising at distances exceeding the coherence length.

Researchers demonstrated that, for neutrinos traversing a magnetic field, the coherence length aligns with that of vacuum oscillations when the vacuum frequency significantly exceeds the magnetic frequency (ωB ≫ ωvac). Conversely, when the magnetic frequency dominates (ωB ≪ ωvac), the coherence length becomes proportional to the cube of the average neutrino momentum.

The work explored the potential for decoherence during neutrino propagation within the magnetic field of a supernova. Coherence and oscillation lengths were calculated for Majorana neutrino oscillations as functions of neutrino energy, assuming a magnetic moment of μ = 10−12μB, a value consistent with current experimental upper bounds and predictions from supersymmetric models.

Numerical estimations were performed for magnetic field strengths of B = 1012 Gauss and B = 1011 Gauss, alongside an assumed transverse spread of σx = 10−12cm. For supernova neutrinos with energies around 10 MeV, the calculated coherence lengths ranged from approximately 10 to 100 kilometers, comparable to the size of the supernova region exhibiting strong magnetic fields.

This analysis revealed that the decoherence regime ωB ≫ ωvac is realised for the chosen parameters, resulting in coherence lengths that scale with the cube of neutrino energy, a distinctive signature for Majorana neutrinos in magnetic fields. The study employed analytical expressions for oscillation probabilities and coherence length, derived for the two-flavour case, to quantify the impact of wave packet separation on neutrino oscillations. Future research will incorporate neutrino interactions with matter and a more realistic supernova magnetic field model to refine these findings.

Neutrino oscillation decoherence and coherence length variation in magnetic fields represent significant challenges to precise neutrino measurements

Researchers investigated neutrino oscillations within magnetic fields using the wave packet formalism to analytically solve the modified Dirac equation for neutrinos possessing non-zero transition magnetic moments. The study focused on the two-flavour case, deriving expressions for oscillation probabilities while accounting for decoherence effects occurring at distances exceeding the coherence length.

Results demonstrate that when the vacuum frequency is significantly greater than the magnetic frequency, the coherence length for neutrinos propagating in a magnetic field aligns with that observed for neutrino oscillations in a vacuum. Conversely, the coherence length is found to be proportional to the cube of the average neutrino momentum when the magnetic frequency exceeds the vacuum frequency.

Analysis reveals that decoherence effects can emerge during neutrino propagation within the magnetic fields present in supernovae. Specifically, the work establishes a relationship between the coherence length and both the vacuum and magnetic frequencies, providing a quantitative understanding of decoherence onset.

These findings are pertinent to understanding neutrino behaviour in extreme astrophysical environments. The derived expressions for oscillation probabilities, incorporating decoherence, offer a refined model for predicting neutrino fluxes from supernovae. This improved modelling could enhance the precision of supernova neutrino detection and subsequent astrophysical inferences. Further research builds upon this foundation, exploring the implications of Majorana CP-violating phases and majoron interactions on neutrino oscillations in magnetic fields and matter.

Neutrino decoherence and coherence length scaling in strong magnetic fields are crucial for astrophysical observations

Scientists have investigated neutrino oscillations within strong magnetic fields, such as those found during supernova explosions, incorporating the effects of wave packet separation and resulting decoherence. Analytical expressions describing oscillation probabilities and coherence length were derived for a two-flavour neutrino model, extending previous treatments by explicitly accounting for decoherence arising from the finite size of neutrino wave packets.

The research demonstrates that the coherence length, the distance over which neutrino oscillations are observable, depends on the relationship between the magnetic field frequency and the vacuum oscillation frequency. When the magnetic field frequency significantly exceeds the vacuum frequency, the coherence length scales with the cube of the neutrino energy and the magnetic field strength.

This work establishes that decoherence effects can indeed occur during neutrino propagation through the intense magnetic fields of astrophysical objects like supernovae. Specifically, the study reveals that when the vacuum frequency is much greater than the magnetic frequency, the coherence length mirrors that of vacuum oscillations, whereas it becomes proportional to the cube of the average neutrino momentum when the opposite is true.

Numerical estimations suggest that wave packet separation can lead to observable decoherence in these environments. The authors acknowledge that a more comprehensive analysis would necessitate incorporating neutrino interactions with matter and employing a realistic model of the magnetic field distribution, outlining these as areas for future investigation.