Spectra of neutrinos from dark matter annihilations

TL;DR

This work provides a comprehensive framework for predicting neutrino fluxes from dark matter annihilations in the Sun and Earth, covering all neutrino flavors across major annihilation channels and incorporating realistic propagation effects. It combines detailed production spectra (via PYTHIA with medium-energy losses) with a density-matrix treatment of oscillations, NC/CC scatterings, and $\nu_\tau$ regeneration to deliver energy- and flavor-resolved spectra for Earth- and Sun-origin DM neutrinos. The study shows that while the overall flux is subject to large astrophysical uncertainties, spectral shapes and flavor content primarily reflect the DM mass $m_{\rm DM}$ and annihilation BRs, enabling reconstruction of DM properties from multiple detector topologies (through-going muons, fully contained muons, showers). It identifies a heavy-DM limit where the exit spectrum becomes largely independent of initial channels due to repeated interactions, and discusses the implications for current and future neutrino telescopes in constraining or identifying DM scenarios. The results guide experimental analyses by clarifying which observables (flavor spectra, energy distributions, and event topologies) are most informative for DM parameter inference.

Abstract

We study the fluxes of neutrinos from annihilations of dark matter particles in the Sun and the Earth. We give the spectra of all neutrino flavors for the main known annihilation channels: nu-antinu, b-bbar, tau-taubar, c-cbar, light quarks, ZZ, W^+W^-. We present the appropriate formalism for computing the combined effect of oscillations, absorptions, nu_tau-regeneration. Total rates are modified by an O(0.1--10) factor, comparable to astrophysical uncertainties, that instead negligibly affect the spectra. We then calculate different signal topologies in neutrino telescopes: through-going muons, contained muons, showers, and study their capabilities to discriminate a dark matter signal from backgrounds. We finally discuss how measuring the neutrino spectra can allow to reconstruct the fundamental properties of the dark matter: its mass and its annihilation branching ratios.

Figures (11)

• Figure 1: The left plot illustrates how oscillations and CC absorption separately affect a flux of neutrinos produced in the center of the Sun. The right plot shows the oscillation probabilities from the center of the Earth. The continuous line applies to $\nu$ for $\theta_{13}=0$ and to $\bar{\nu}$ for any allowed $\theta_{13}$, since matter effects suppress their mixing. The dotted line applies to $\nu$ for $\theta_{13}=0.1$ rad. The average over the production point has been performed as appropriate for $m_{\rm DM}=100\,{\rm GeV}$. It is responsible for the damping effect visible at $E_{\nu}\,\hbox{$<$$\sim$}\,10\,{\rm GeV}$.
• Figure 2: Neutrino spectra at production. Upper half: the fluxes of electron and muon neutrinos, for the seven main annihilation channels and for different masses of the parent DM particle (different colors). The solid lines apply to the case of the Sun, the dotted of the Earth. In all cases, the spectra of antineutrinos are the same as those of neutrinos. Lower half: the same for $\raisebox{1ex}{\tiny(}\overline\nu\raisebox{1ex}{\tiny)}\space_\tau$.
• Figure 3: Energy distributions of $\nu$ (red) and $\bar{\nu}$ (blue) produced with energy $E'_\nu$ by one NC DIS interaction of a $\raisebox{1ex}{\tiny(}\overline\nu\raisebox{1ex}{\tiny)}\space$ with energy $E_\nu$. The energy is plotted in units of $E_\nu$. Continuous line: in normal matter, where $N_p \approx N_n$. Dotted line: around the center of the Sun, where $N_p\approx 2 N_n$.
• Figure 4: Energy distributions of neutrinos regenerated by CC scatterings of a $\raisebox{1ex}{\tiny(}\overline\nu\raisebox{1ex}{\tiny)}\space_\tau$ of given energy $E_{\nu_\tau}$, produced by one $\raisebox{1ex}{\tiny(}\overline\nu\raisebox{1ex}{\tiny)}\space_\tau$/nucleon scattering. The blue upper curves are $f_{\tau\to\tau}(E_{\nu_\tau},E'_\nu)$, and the red lower curves are $f_{\tau\to e,\mu}(E_{\nu_\tau},E'_\nu)$, plotted for several values of the incident $\nu_\tau$ energy $E_{\nu_\tau}$.
• Figure 5: Neutrino spectra generated by one DM annihilation around the center of Earth. The plots show the spectra of the three neutrino flavors (the three rows) and assume different DM masses (the three columns). Each plot shows the open annihilation channels ${\rm DM~DM}\to$$b\bar{b}$, $\tau^+\tau^-$, $c \bar{c}$, $t\bar{t}$, $W^+ W^-$, $ZZ$. The ${\rm DM~DM}\to\nu\bar{\nu}$ channel (not shown) would produce a line at $E_\nu = m_{\rm DM}$. The dotted lines show the spectra without oscillations while solid lines are the final results after oscillations. The dashed lines in the upper-left panel have been computed with $\theta_{13}=0.1$ rad for illustration (see text); all the other results assume $\theta_{13}=0$. Neutrino and anti-neutrino spectra are roughly equal: we here show $(2\Phi_\nu + \Phi_{\bar{\nu}})/3$, in view of $\sigma(\nu N) \sim 2 \sigma(\bar{\nu} N)$. The shaded region is the atmospheric background, normalized relative to DM$\nu$ as assumed in eq. (\ref{['eq:EarthNorm']}).