Tau neutrinos from ultracompact dark matter minihalos and constraints on the primordial curvature perturbations

TL;DR

This paper investigates tau neutrinos from ultracompact dark matter minihalos (UCMHs) to constrain primordial density perturbations, extending previous limits and offering a new indirect method to study dark matter and early universe conditions.

Contribution

It introduces the analysis of downward-going tau neutrinos from UCMHs due to dark matter annihilation to set new constraints on primordial curvature perturbations at smaller scales.

Findings

Constraints on the mass fraction of UCMHs.

Extended limits on primordial curvature perturbations to smaller scales.

Potential for tau neutrino observations to probe dark matter structures.

Abstract

The observations and research on the neutrinos provide a kind of indirect way of revealing the properties of dark matter particles. For the detection of muon neutrinos, the main issue is the large atmospheric background, which is caused by the interactions between the cosmic rays and atoms within the atmosphere. Compared with muon neutrinos, tau neutrinos have a smaller atmospheric background especially for the downward-going direction. Except for the classical neutrino sources, dark matter particles can also annihilate into the neutrinos and are the potential high energy astrophysical sources. The annihilation rate of dark matter particles is proportional to the square of number density; therefore, the annihilation rate is large near the center of dark matter halos especially for the new kind of dark matter structures named ultracompact dark matter minihalos (UCMHs). In previous works, we have investigated the potential muon neutrino flux from UCMHs due to dark matter annihilation. Moreover, since the formation of UCMHs is related to the primordial density perturbations of small scales, we get the constraints on the amplitude of the primordial curvature perturbations of small scales, $1 \lesssim k \lesssim 10^{7} ~\rm Mpc^{-1}$. In this work, we focus on the downward-going tau neutrinos from UCMHs due to dark matter annihilation. Compared with the background of tau neutrino flux we get the constraints on the mass fraction of UCMHs. Then using the limits on the mass fraction of UCMHs we got the constraints on the amplitude of the primordial curvature perturbations which are extended to the scale $k \sim 10^{8} ~ \rm Mpc^{-1}$ compared with previous results.