Constraints on Dark Matter Protohalos in Effective Theories and Neutrinophilic Dark Matter

TL;DR

The paper investigates how constraints on DM interactions with leptons translate into the minimal DM structure scale, the protohalo mass, using an effective field theory framework. It analyzes three DM lepton operators and derives their annihilation and scattering cross sections, then maps experimental bounds from LEP, Fermi-LAT, direct detection, IceCube, Super-K, and Planck to limits on the protohalo mass via kinetic decoupling. The main result is that charged lepton couplings are insufficient to explain the missing satellites problem, motivating neutrinophilic DM which can yield much larger protohalos but requires sub-GeV DM with enhanced annihilation cross sections, subject to Planck and neutrino telescope constraints. The study highlights the role of kinetic decoupling and emphasizes the need to explore light mediators and future neutrino-based probes to fully assess the neutrinophilic DM scenario.

Abstract

The mass of primordial dark matter (DM) protohalos remains unknown. However, the missing satellites problem may be an indication that they are quite large. In this paper, we use effective field theory to map constraints on dark matter-SM interactions into limits on the mass of DM protohalos. Given that leptons remain in the thermal bath until late times, we focus on their interactions with DM. To illustrate the method, we use the null results of LEP missing energy searches along with Fermi-LAT searches for DM annihilation in nearby dwarf galaxies, to derive limits on the protohalo mass, $\lesssim (10^{-6}-10^{-1}) M_{\odot}$, with the range depending on the DM mass and the operator. Thus, if DM is to remain thermally coupled until late times and account for the missing satellites, charged lepton interactions are insufficient. This motivates neutrinophilic DM, which can have protohalo masses orders of magnitude larger, with constraints arising from Planck, IceCube and unpublished Super-K data. We show that effective neutrinophilic models offer a solution to the missing satellites problem for sub-GeV DM masses with larger than WIMP-sized annihilation cross sections.

Figures (2)

• Figure 1: LEP limits (yellow) apply to the electron-type coupling and are based on monophoton + MET searches Fox:2011fx. The Fermi-LAT limit (dark red) obtained from the joint likelihood analysis of 10 dwarf galaxies for DM annihilating to $\overline{\tau}\tau$Ackermann:2011wa. For comparison we show the thermal symmetric WIMP (dashed blue line) for $\overline{X}X \rightarrow \ell^{+} \ell^{-}$ comprising the total annihilation cross section. Thermal symmetric models lie within the blue region, whereas thermal asymmetric models lie above. We have highlighted in pink the region, $\Lambda > m_{X}/2\pi$, where the assumption of EFT is no longer valid.
• Figure 2: Constraints on the protohalo mass for neutrinophilic DM. Experimental upper bounds come from IceCube's galactic halo analysis Abbasi:2011eq which restricts DM annihilation into neutrinos (green, solid) and Super-K which has a similar but unpublished preliminary search SKGalactic that extends to lower masses (dashed dark orange). The CMB constraint comes the Planck limit on $N_{\rm eff}$ as analyzed in Boehm:2013jpa.