Exclusion of canonical WIMPs by the joint analysis of Milky Way dwarfs with Fermi (1108.2914v2)

Abstract: Dwarf spheroidal galaxies are known to be excellent targets for the detection of annihilating dark matter. We present new limits on the annihilation cross section of Weakly Interacting Massive Particles (WIMPs) based on the joint analysis of seven Milky Way dwarfs using a frequentist Neyman construction and Pass 7 data from the Fermi Gamma-ray Space Telescope. We exclude generic WIMP candidates annihilating into b-bbar with mass less than 40 GeV that reproduce the observed relic abundance. To within 95% systematic errors on the dark matter distribution within the dwarfs, the mass lower limit can be as low as 19 GeV or as high as 240 GeV. For annihilation into tau+tau- these limits become 19 GeV, 13 GeV, and 80 GeV respectively.

• The paper constrains canonical WIMP properties by analyzing gamma-ray emissions from seven Milky Way dwarf galaxies using a frequentist Neyman construction.
• It sets exclusion bounds for WIMPs with masses below 40 GeV for the b-bbar channel and below 19 GeV for the tau+tau- channel, narrowing the dark matter parameter space.
• A data-driven background estimation method minimizes theoretical biases, ensuring the robustness of the derived annihilation cross-section limits.

Exclusion of Canonical WIMPs by Joint Analysis of Milky Way Dwarfs and Fermi Gamma-ray Data

This paper presents an analysis aiming to constrain the parameter space for Weakly Interacting Massive Particles (WIMPs), a leading dark matter candidate, through gamma-ray data obtained from the Fermi Gamma-ray Space Telescope. The researchers undertake a comprehensive examination involving seven Milky Way dwarf spheroidal galaxies, known for their potential as prime candidates in the search for dark matter signatures owing to their high dark matter-to-luminous matter ratio and minimal astrophysical background.

Using a frequentist Neyman construction, the authors establish limits on the annihilation cross section of WIMPs. This analysis is performed under the canonical assumption that WIMPs constitute the entirety of dark matter and primarily undergo annihilation into standard model particles such as $b\bar{b}$ and $\tau^+\tau^-$. The results of the paper are significant in that they exclude WIMP candidates with masses less than 40 GeV for annihilation into $b\bar{b}$ and masses less than 19 GeV for annihilation into $\tau^+\tau^-$, based on central estimates of systematic uncertainties. These exclusions leverage observational data from the Fermi Gamma-ray Telescope, specifically the Pass 7 dataset, targeting regions of interest centered on the chosen dwarf galaxies.

A key aspect of the analysis is its empirical treatment of background estimation. Rather than relying on detailed theoretical models of the gamma-ray background, the paper derives the background probability mass function (PMF) from the observed counts surrounding each dwarf galaxy. This data-driven approach sidesteps potential biases inherent in model-based estimations by using nearby sky regions to characterize the background processes. Further, the confidence intervals are determined for the parameter quantities using a validated Neyman construction, ensuring statistical robustness.

The implications of these findings are multifaceted. On a theoretical level, they challenge the viability of lower-mass WIMP scenarios under the thermal relic assumption, which postulates that the present-day WIMP density results from a weak-scale annihilation cross-section. These limitations thus provide critical bounds that any viable dark matter candidate must satisfy, tightening the constraints on theoretical models for WIMP particles. Practically, this analysis delineates areas within the parameter space that do not warrant further experimental pursuit, allowing resources to be focused on regions more likely to yield positive results.

Future research directions could benefit from enhanced characterization of the dark matter density profile within dwarf galaxies. The current limitations are significantly influenced by uncertainties surrounding the $J$ factors, which quantify the projected dark matter distribution. Improving these estimates, possibly through advanced stellar kinematics analyses or through novel observational techniques, would refine the constraints on the WIMP annihilation cross-section. In addition, as gamma-ray instrumentation and sensitivity continue to progress, extending such analyses could further test the boundaries of the canonical WIMP hypothesis.

Overall, this paper provides a thorough examination of WIMP parameter space and contributes to the ongoing efforts to identify or constrain viable dark matter candidates using astrophysical observations.