High energy neutrinos from neutralino annihilations in the Sun

TL;DR

This paper analyzes high-energy neutrinos from neutralino annihilations in the Sun within the FP region of mSUGRA, where a bino–higgsino LSP leads to large annihilation rates and a Sun capture rate dominated by spin-dependent interactions. It provides a comprehensive treatment of neutrino production from real and virtual $WW$, $ZZ$, $Zh$, and $t\bar t$ channels, including full spin dependence, and propagates the neutrinos through the Sun with oscillations, MSW effects, NC/CC absorption, and $\nu_\tau$ regeneration, then to Earth with flavor mixing. The authors predict observable muon fluxes at IceCube and KM3 for neutralino masses below roughly 400 GeV, with sensitivity peaking around $m_{\chi^0_1}\sim 110$ GeV, while acknowledging model and detection uncertainties. They emphasize that the spin-dependent capture enhances the signal and that the muon energy distribution can inform the neutralino mass and local dark matter properties, offering a complementary probe to direct detection and colliders.

Abstract

Neutralino annihilations in the Sun to weak boson and top quark pairs lead to high-energy neutrinos that can be detected by the IceCube and KM3 experiments in the search for neutralino dark matter. We calculate the neutrino signals from real and virtual WW, ZZ, Zh, and $t \bar t$ production and decays, accounting for the spin-dependences of the matrix elements, which can have important influences on the neutrino energy spectra. We take into account neutrino propagation including neutrino oscillations, matter-resonance, absorption, and nu_tau regeneration effects in the Sun and evaluate the neutrino flux at the Earth. We concentrate on the compelling Focus Point (FP) region of the supergravity model that reproduces the observed dark matter relic density. For the FP region, the lightest neutralino has a large bino-higgsino mixture that leads to a high neutrino flux and the spin-dependent neutralino capture rate in the Sun is enhanced by 10^3 over the spin-independent rate. For the standard estimate of neutralino captures, the muon signal rates in IceCube are identifiable over the atmospheric neutrino background for neutralino masses above M_Z up to 400 GeV.

Figures (15)

• Figure 1: The central FP region in $\mu$ and $M_1$ (left panel) with $m_t=174.3$ GeV and $\tan \beta = 50$ as given in Baer:2005ky. As the mass of the lightest neutralino increases, it becomes largely higgsino shown by the solid, black curve (right panel). However, the higgsino asymmetry, an important quantity for the $Z\chi^0_1\chi^0_1$ coupling, decreases as shown by the red, dashed curve.
• Figure 5: The annihilation cross section of the lightest neutralino to neutrinos via the $WW,ZZ,Zh$ and $t\bar{t}$ channels in the FP region with $\tan \beta = 50$. Note that when the top quark threshold is crossed, the cross section for $t\bar{t}$ production abruptly increases, and the cross sections of all other modes correspondingly decrease in order to give the same $\sigma_{tot}$, as is required to maintain the observed relic density.
• Figure 6: Neutrino energy spectra for $\chi^0_1\chi^0_1\to WW^*$ and $WW$ where at least one $W$ decays leptonically for $m_{\chi^0_1} =$ 110 and 200 GeV. Analytic results are given by the dashed curves.
• Figure 7: Neutrino energy spectra for $\chi^0_1\chi^0_1\to Zh$ where the Z decays to neutrinos for $m_{\chi^0_1} =$ 110, 200, and 400 GeV. Analytic results are given by the dashed curves.
• Figure 8: (a) MC result for off-shell $t \bar{t}$ channel, where $M_{\chi^0_1}=\text{ 170 GeV}$. (b) Neutrino energy distributions for various values of $m_\chi$.