Current Dark Matter Annihilation Constraints from CMB and Low-Redshift Data

TL;DR

This paper updates constraints on dark matter annihilation using combined CMB and low-redshift data, improving previous limits and assessing implications for various dark matter models and signals.

Contribution

It provides the most comprehensive dark matter annihilation constraints to date by combining multiple datasets and updating energy deposition modeling.

Findings

Dark matter masses below 26 GeV are excluded at 2-sigma assuming perfect energy deposition.

For f_eff=0.2, dark matter masses below 5 GeV are disfavored at 2-sigma.

Future Planck and CMB Stage IV data will further tighten these constraints.

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.