Cosmic neutrino cascades from secret neutrino interactions

TL;DR

The paper investigates secret neutrino interactions (νSI) by leveraging high-energy astrophysical neutrinos traversing the Cosmic Neutrino Background. It develops a Boltzmann-type propagation framework that includes attenuation and regeneration via a Breit-Wigner cross section, enabling spectral distortions such as dips, bumps, or cutoffs in IceCube-like spectra. By analyzing both line and continuum emission scenarios and introducing benchmark νSI models, the authors show that IceCube can probe a parameter space not excluded by SN 1987A, BBN, CMB, or Z decays, and potentially account for features in the observed spectrum. The study highlights the need for more data and extended modeling, and points to cosmogenic neutrinos as a future platform to further test νSI and inform particle-physics model-building.

Abstract

The first detection of high-energy astrophysical neutrinos by IceCube provides new opportunities for tests of neutrino properties. The long baseline through the Cosmic Neutrino Background (C$ν$B) is particularly useful for directly testing secret neutrino interactions ($ν$SI) that would cause neutrino-neutrino elastic scattering at a larger rate than the usual weak interactions. We show that IceCube can provide competitive sensitivity to $ν$SI compared to other astrophysical and cosmological probes, which are complementary to laboratory tests. We study the spectral distortions caused by $ν$SI with a large s-channel contribution, which can lead to a dip, bump, or cutoff on an initially smooth spectrum. Consequently, $ν$SI may be an exotic solution for features seen in the IceCube energy spectrum. More conservatively, IceCube neutrino data could be used to set model-independent limits on $ν$SI. Our phenomenological estimates provide guidance for more detailed calculations, comparisons to data, and model building.

Figures (7)

• Figure 1: Present constraints and future sensitivity to $\nu$SI in terms of neutrino coupling, $g$, and mediator mass, $M$, with diagonal dotted contours shown for values of the dimensionful coupling $G$. The blue shaded regions are excluded by astrophysical and cosmological considerations based on SN 1987A Kolb:1987qy, BBN Ahlgren:2013wba, and the CMB Cyr-Racine:2013juaArchidiacono:2013dua. The pink dashed lines indicate flavor-dependent limits based on laboratory measurements of meson and lepton decays Lessa:2007up; we consider only the weakest limit, for $\nu_\tau$, to be robustly excluded for all flavors, and it is shaded. The red shaded region is excluded based on measurement of Z-boson decay Bilenky:1999dn. The gray shaded region indicates the non-perturbative regime. The orange lines are contours of unit optical depth for different initial neutrino energies (Eq. \ref{['eq:opticaldepth']}), indicating the approximate boundary of the parameter space above which IceCube is sensitive to $\nu$SI. The squares represent the example parameters (given in Table \ref{['tab:table1']}) used in our calculations.
• Figure 2: The effects of $\nu$SI on an emitted line spectrum at 1 PeV with SFR evolution, for different assumed resonance energies, as labeled. The solid lines are for free-streaming neutrinos, the dotted lines are for $\nu$SI with regeneration of two neutrinos (the beam and target), and the dashed lines are for $\nu$SI with no regeneration.
• Figure 3: The effects of $\nu$SI on an emitted continuum spectrum that is consistent with IceCube data. The solid line indicates the free-streaming case ($\gamma = 2$ and $E_{\rm cut} = 10^{7}\,{\rm GeV}$), while the other lines are for four models of $\nu$SI, with the parameters defined in Table \ref{['tab:table1']}.
• Figure 4: Same as Fig. \ref{['fig:astro1']}, but with different values of $E_{\rm cut}$ for the emitted spectrum. The solid lines are the free streaming case ($\gamma = 2$ and values of $E_{\rm cut}$ as labeled), and the dashed lines are for Model A $\nu$SI.
• Figure 5: Same as Fig. \ref{['fig:astro1']}, but with different values of the spectral index. The solid lines are for the free-streaming cases (values of $\gamma$ as labeled and $E_{\rm cut} = 10^{7}\,{\rm GeV}$), and the dashed lines are for Model B $\nu$SI.