Constraints on the primordial power spectrum of small scales using the neutrino signals from the dark matter decay

TL;DR

This paper investigates how neutrino signals from dark matter decay in ultracompact minihalos can constrain the primordial power spectrum on small scales, providing new limits beyond previous gamma-ray based studies.

Contribution

It introduces a novel method using neutrino flux from dark matter decay in UCMHs to set constraints on small-scale primordial power spectrum, improving upon prior gamma-ray based limits.

Findings

Neutrino flux from UCMHs can be used to constrain small-scale primordial power spectrum.

The derived constraints are more stringent than previous limits from primordial black holes.

Neutrino signals provide a complementary probe to gamma-ray observations for dark matter decay.

Abstract

Many inflation theories predict that the primordial power spectrum is scale invariant. The amplitude of the power spectrum can be constrained by different observations such as the cosmic microwave background (CMB), Lyman-$\alpha$, large-scale structures and primordial black holes (PBHs). Although the constraints from the CMB are robust, the corresponding scales are very large ($10^{-4}<k<1 \mathrm{Mpc^{-1}}$). For small scales ($k > 1 \mathrm{Mpc^{-1}}$), the research on the PBHs provides much weaker limits. Recently, ultracompact dark matter minihalos (UCMHs) was proposed and it was found that they could be used to constraint the small-scale primordial power spectrum. The limits obtained by the research on the UCMHs are much better than that of PBHs. Most of previous works focus on the dark matter annihilation within the UCMHs, but if the dark matter particles do not annihilate the decay is another important issue. In previous work~\cite{EPL}, we investigated the gamma-ray flux from the UCMHs due to the dark matter decay. In addition to these flux, the neutrinos are usually produced going with the gamma-ray photons especially for the lepton channels. In this work, we studied the neutrino flux from the UCMHs due to the dark matter decay. Finally, we got the constraints on the amplitude of primordial power spectrum of small scales.