A Markov Chain Monte Carlo Study on Dark Matter Property Related to the Cosmic e$^{\pm}$ Excesses

TL;DR

This study employs Markov Chain Monte Carlo methods to analyze dark matter properties related to cosmic ray electron/positron excesses, considering annihilation and decay scenarios, and constrains dark matter profiles using gamma-ray observations.

Contribution

It introduces a MCMC code that self-consistently incorporates gamma-ray constraints to study dark matter properties from cosmic ray data, considering both annihilation and decay channels.

Findings

Favored dark matter mass around 0.7 TeV (annihilation) or 1.4 TeV (decay) for Data set I.

Favored dark matter mass around 2 TeV (annihilation) or 4 TeV (decay) for Data set II.

NFW profile excluded at >5σ for annihilating dark matter based on gamma-ray constraints.

Abstract

In this paper we develop a Markov Chain Monte Carlo code to study the dark matter properties in interpreting the recent observations of cosmic ray electron/positron excesses. We assume that the dark matter particles couple dominantly to leptons and consider two cases separately with annihilating or decaying into lepton pairs. The constraint on the central density profile from diffuse $\gamma$-rays around the Galactic center is also included in the Markov Chain Monte Carlo code self-consistently. In the numerical study, 7 parameters are introduced. We fit two data sets independently and find that for the Data set I (PAMELA+ATIC), dark matter with $m_{\chi}\approx0.7$ TeV for annihilation (or 1.4 TeV for decay) and pure $e^+e^-$ channel is favored, while for the Data set II (PAMELA+Fermi-LAT+H.E.S.S.) $m_{\chi}\approx 2$ TeV for annihilation (or 4 TeV for decay) and the combination of $\mu^+\mu^-$ and $\tau^+\tau^-$ final states can best fit the data. The H.E.S.S. observation of the Galactic center $\gamma$-rays puts a strong constraint on the central density profile of the dark matter halo for the annihilation dark matter scenario. In this case the NFW profile which is regarded as the typical predication from the cold dark matter scenario, is excluded with a high significance ($>5\sigma$). For the decaying dark matter scenario, the constraint is much weaker.