Gamma-Ray Constraints on Neutralino Dark Matter Clumps in the Galactic Halo

TL;DR

This work investigates whether gamma rays from neutralino annihilation in dark matter clumps within the Galactic halo could be detected and used to constrain neutralino properties. It models clumps with SIS, Moore, and NFW density profiles under two limiting distribution scenarios (type I and II) and computes the line-of-sight γ-ray flux, emphasizing π^0-dominated emission. The results show that in the highly concentrated type I scenario, γ-ray fluxes from clumps can exceed the smooth-halo contribution and place strong constraints on $⟨σv⟩$ and $mχ$ (especially for SIS and Moore profiles), while the more conservative type II scenario yields fluxes largely below detectability except for SIS. The findings highlight the critical role of clump survival and concentration in predicting diffuse γ-ray signals and suggest potential detection channels for future γ-ray and Cherenkov-telescope observations.

Abstract

According to high resolution cold dark matter (CDM) simulations, large virialized halos are formed through the constant merging of smaller halos formed at earlier times. In particular, the halo of our Galaxy may have hundreds of dark matter clumps. The annihilation of dark matter particles such as the neutralino in these clumps generates $γ$-ray fluxes that can potentially be detected by future experiments such as GLAST. We find that, depending on the parameters of the clump density profile and on the distribution of clumps in the Galactic halo, the contribution to the diffuse $γ$-ray background from clumps can constrain the properties of neutralinos such as the mass and annihilation cross section. We model the density profile of clumps by three representative dark matter profiles: singular isothermal spheres (SIS), Moore profiles, and Navarro, Frenk and White (NFW) density profiles and calculate the spectrum and angular distribution in the sky of the $γ$-ray flux due to neutralino annihilation in the clumpy halo of the Galaxy. The calculations are carried out in the context of two different scenarios for the distribution of clumps in the Galaxy and their concentrations, which result in very different conclusions.

Figures (7)

• Figure 1: Concentration parameter for dark matter clumps, as a function of the clump mass.
• Figure 2: Stripping radius of clumps as a function of the clump mass, for NFW and Moore density profiles.
• Figure 3: Type I scenario. Flux of gamma-rays in units of (GeV cm$^2$ s sr)$^{-1}$ arriving on Earth averaged in all directions for $m_{\chi}=$ 100 GeV, $\langle \sigma v \rangle=3\times 10^{-27}$ cm$^3$/s and $M_{c,min}=10^5$$M_{\odot}$. SIS density profile (dotted line), Moore et al. density profile (dashed line) and NFW density profile (continuous line). Also shown is the EGRET data on extragalactic diffuse gamma-ray background (Sreekumar 1998)
• Figure 4: Type II scenario. Flux of gamma-rays in units of (GeV cm$^2$ s sr)$^{-1}$ arriving on Earth averaged in all directions for $m_{\chi}=$ 100 GeV, $\langle \sigma v \rangle=3\times 10^{-27}$ cm$^3$/s and $M_{c,min}=10^5$$M_{\odot}$. SIS density profile (dotted line), Moore et al. density profile (dashed line) and NFW density profile (continuous line). The solid line is the EGRET bound on extragalactic diffuse gamma-ray background (Sreekumar 1998).
• Figure 5: Neutralino cross section times velocity (thermally averaged) versus neutralino mass. Crosses are neutralino models from Tasitsiomi and Olinto (2002). Shaded regions are allowed regions of neutralino parameters for type I scenarios for clumps with the labeled dark matter profiles (NFW, Moore, SIS). Models with parameters above the shaded regions are ruled out by the EGRET diffuse flux in type I scenarios.