Signatures of quasi-Dirac neutrinos in diffuse high-energy astrophysical neutrino data (2503.19960v1)

Abstract: We search for signatures of extremely long-baseline oscillations between left- and right-handed neutrinos using the high-energy astrophysical neutrino spectra measured by IceCube. We assume the astrophysical neutrino sources to be distributed in redshift following the star formation rate and use the IceCube all-sky flux measurements from TeV to PeV energies. We find, for the first time, that $\delta m^2$ in the range $2\times 10^{-19}$ to $3 \times 10^{-18}\textrm{eV}^2$ is disfavored at the $3\sigma$ confidence level, while there exists a preference for a $\delta m^2$ of $1.9 \times 10^{-19}\textrm{eV}^2$ at $2.8\sigma$. This preference for quasi-Dirac neutrinos is driven by the tension between cascade and track measurements below $30~\textrm{TeV}$.

Overview of Signatures of Quasi-Dirac Neutrinos in Diffuse High-Energy Astrophysical Neutrino Data

The scholarly work by Carloni et al. explores the potential existence and implications of quasi-Dirac (QDino) neutrinos, using high-energy astrophysical neutrino data sourced from the IceCube observatory. The authors address the theoretical gap regarding the nature of neutrino masses, which remains uncertain in distinguishing between Dirac and Majorana characteristics. The paper targets the ultra-long baseline oscillations of neutrinos across cosmological scales as potential indicators of QDino behavior, driven by exceptionally small mass-squared differences, which are inaccessible in current terrestrial experiments.

Core Hypothesis and Methodology

The fundamental premise of the paper is that, due to new oscillation components attributed to quasi-Dirac neutrinos' hyperfine mass-squared differences, detectable deviations may exist within IceCube's diffuse astrophysical neutrino spectra. The methodology involves assuming that high-energy astrophysical neutrinos, potentially emanating from a cosmologically distributed array of astrophysical sources, experience these quasi-Dirac oscillations. This assumption is scrutinized with IceCube's all-sky data spanning from TeV to PeV energy ranges.

The authors employ a statistical framework to analyze the reported IceCube cosmic neutrino fluxes, CasCADE and ESTES samples, which represent independent neutrino detection strategies. The analysis involves contrasting the traditional Standard Model neutrino oscillation scenario against one allowing for mass-squared differences indicative of QDinos.

Key Results

One striking outcome is the disfavoring of $\delta m^2$ values between $2\times 10^{-19}$ to $3 \times 10^{-18}\, \text{eV}^2$ at a $3\sigma$ confidence level with the presence of a preference for a $\delta m^2$ of approximately $1.9 \times 10^{-19}\, \text{eV}^2$ at $2.8\sigma$. The preference emerges from reconciliation effects between constraints stemming from cascade and track measurements below $30\text{ TeV}$.

Theoretical and Experimental Implications

The exploration in this paper opens significant theoretical implications for understanding the nature of neutrino masses. Neutrino oscillations remained sensitive to small mass differences, pointing to potential mass hierarchies or new physics beyond the Standard Model, specifically suggesting a minimal yet non-zero lepton number violation. Practically, the paper provokes fresh synthetic routes in designing neutrino experiments, especially for future IceCube-spectrum surveys and searches by other neutrino observatories like KM3NeT.

Future Directions and Conclusions

The findings bolster the necessity for continued astrophysical observations of neutrino sources, pushing the envelope from solar neutrinos to cosmic scales. Upcoming technological advancements may both confirm and refine constraints on QDinos and their role in lepton number parity violations. Such confirmations will not only enrich the understanding of fundamental particle physics but could also link broader cosmic phenomenologies, including the baryon asymmetry dilemma. This work lays a scientific framework applicable for future astronomical surveys aimed at understanding the balanced functionalities of neutrinos as either Dirac or Majorana particles, or in hybrid scenarios like quasi-Dirac neutrinos addressed herein.