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

Understand

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.