Current Dark Matter Annihilation Constraints from CMB and Low-Redshift Data (1310.3815v2)

Abstract: Updated constraints on dark matter cross section and mass are presented combining CMB power spectrum measurements from Planck, WMAP9, ACT, and SPT as well as several low-redshift datasets (BAO, HST, supernovae). For the CMB datasets, we combine WMAP9 temperature and polarization data for l <= 431 with Planck temperature data for 432 < l < 2500, ACT and SPT data for l > 2500, and Planck CMB four-point lensing measurements. We allow for redshift-dependent energy deposition from dark matter annihilation by using a `universal' energy absorption curve. We also include an updated treatment of the excitation, heating, and ionization energy fractions, and provide updated deposition efficiency factors (f_eff) for 41 different dark matter models. Assuming perfect energy deposition (f_eff = 1) and a thermal cross section, dark matter masses below 26 GeV are excluded at the 2-sigma level. Assuming a more generic efficiency of f_eff = 0.2, thermal dark matter masses below 5 GeV are disfavored at the 2-sigma level. These limits are a factor of ~2 improvement over those from WMAP9 data alone. These current constraints probe, but do not exclude, dark matter as an explanation for reported anomalous indirect detection observations from AMS-02/PAMELA and the Fermi Gamma-ray Inner Galaxy data. They also probe relevant models that would explain anomalous direct detection events from CDMS, CRESST, CoGeNT, and DAMA, as originating from a generic thermal WIMP. Projected constraints from the full Planck release should improve the current limits by another factor of ~2, but will not definitely probe these signals. The proposed CMB Stage IV experiment will more decisively explore the relevant regions and improve upon the Planck constraints by another factor of ~2.

Analysis of Dark Matter Annihilation Constraints from CMB and Low-Redshift Data

The paper "Current Dark Matter Annihilation Constraints from CMB and Low-Redshift Data" provides a comprehensive evaluation of constraints on dark matter properties using a combination of cosmic microwave background (CMB) observations and low-redshift datasets. This work is instrumental in refining our understanding of dark matter's annihilation cross section and mass, critical parameters for elucidating its particle nature and its role in cosmology.

Utilizing CMB power spectrum data from the Planck satellite, WMAP9, ACT, and SPT, as well as additional low-redshift observations such as BAO, HST, and supernovae, the authors present updated constraints on the dark matter annihilation cross-section. The paper expands upon previous analyses by incorporating redshift-dependent energy deposition from dark matter annihilation, deploying a universal energy absorption curve. The constraints are further refined by updating the treatment of energy deposition via excitation, heating, and ionization energy fractions across 41 distinct dark matter models.

The numerical results are noteworthy. Under the assumption of perfect energy deposition (an efficiency factor $f_\text{eff}=1$) and a thermal cross-section, dark matter masses below 26 GeV are excluded at the $2\sigma$ level. With a more conservative efficiency estimate ($f_\text{eff}=0.2$), thermal dark matter masses below 5 GeV are disfavored at the same confidence level. This improvement, roughly by a factor of two over constraints from WMAP9 alone, underscores the importance of leveraging comprehensive datasets for enhancing model constraints.

The implications of these results are significant, as the constraints are finely tuned to probe possible dark matter explanations for anomalous signals observed in other indirect and direct detection experiments. Notably, the constraints set by current CMB data do not rule out dark matter interpretations of positron excesses reported by AMS-02/PAMELA and gamma-ray observations by Fermi, nor do they categorically exclude models explaining certain anomalies observed in direct detection experiments like CDMS and DAMA. Nevertheless, this work serves as a pivotal step in the continual effort to refine theoretical models against empirical evidence.

Looking forward, the paper posits that upcoming full Planck CMB data releases could improve current limits by an additional factor of approximately 2, with future CMB projects (e.g., the proposed CMB Stage IV experiment) providing even more decisive capabilities to explore relevant dark matter parameter spaces thoroughly.

From a theoretical standpoint, the research demonstrates the efficacy of combining various cosmological datasets to test dark matter models. The methodological advancements, notably the development of the 'universal' energy absorption curve, offer a valuable toolset for future explorations.

In summary, this paper represents an important analytical milestone in blending observational data with theoretical modeling to constrain dark matter characteristics. The findings highlight existing observational capabilities and anticipate future advancements that promise more definitive explorations of dark matter's role in our Universe.