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

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, $1\lesssim k\lesssim {10}^7{\mathrm{Mpc}}^{-1}$. 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 $k\sim {10}^8{\mathrm{Mpc}}^{-1}$ compared with previous results.

Figure 1

Tau neutrino flux from the UCMH due to dark matter annihilation for the ${\tau }^{+}{\tau }^{-}$ channel. We have set the dark matter mass $m_{\mathrm{DM}}=0.1$ (blue short-dashed line) and 1 TeV (purple dot line), and the thermally averaged cross section $⟨\sigma v⟩=3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. In this plot, we have considered the UCMH formed during the phase transition named $e^{+}{e}^{-}$ annihilation. The distance of the UCMH is $d_{\mathrm{UCMH}}=0.1\mathrm{kpc}$. For comparison, in addition to the ${\nu }_{\tau }$ background flux (red solid line) the ${\nu }_{\mu }$ background flux is also shown (green long-dashed line).

Figure 2

Upper limits (95% C.L.) on the mass fraction of UCMHs for the downward-going tau neutrino flux for IceCube (red solid line) and ANTARES (green dashed line). Here we have set the dark matter mass $m_{\mathrm{DM}}=1\mathrm{TeV}$ and the thermally averaged cross section $⟨\sigma v⟩=3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$. The annihilation channel is ${\tau }^{+}{\tau }^{-}$.

Figure 3

Upper limits (95% C.L.) on the amplitude of the primordial curvature perturbations, ${\mathcal{P}}_{\mathcal{R}}(k)$, for scales $3\lesssim k\lesssim 4\times {10}^8{\mathrm{Mpc}}^{-1}$, for IceCube (red solid line) and ANTARES (green dashed line). The parameters of the dark matter particle are the same as Fig. 2.

Figure 4

Constraints on the mass fraction of UCMHs (left) and the amplitude of primordial curvature perturbations for the different center density profile (right), $r_{\min }/R_{\mathrm{UCMH}}={10}^{-5}$ (green long-dashed line), ${10}^{-6}$ (blue short-dashed line), and ${10}^{-7}$ (blue solid line). The parameters of the dark matter particle are the same as Fig. 2. Here we show the results for IceCube.

Figure 5

Constraints on the mass fraction of UCMHs (left) and the amplitude of primordial curvature perturbations for different annihilation channels (right), $b\overline{b}$ (red solid line), $W^{+}{W}^{-}$ (green long-dashed line), ${\tau }^{+}{\tau }^{-}$ (blue short-dashed line), and ${\mu }^{+}{\mu }^{-}$ (purple dotted line). The parameters of the dark matter particle are the same as Fig. 2. For simplicity, we show the results for IceCube.