Cosmic ray $e^{+} e^{-}$ spectrum excess and peak feature observed by the DAMPE experiment from dark matter

TL;DR

The DAMPE experiment observed an excess and potential peak in cosmic ray electrons and positrons, which may be explained by dark matter annihilation or decay, but the required conditions are highly improbable.

Contribution

This paper analyzes DAMPE data to interpret the excess and peak as signals of dark matter processes, exploring the feasibility of nearby subhalos as sources.

Findings

Dark matter annihilation can fit the broad excess with high cross-section.

A nearby subhalo could produce a narrow peak if within 0.53 kpc.

The probability of such a subhalo existing is very low.

Abstract

The Chinese satellite Wukong, also known as the DArk Matter Particle Explorer (DAMPE), has released its observation data of the cosmic ray (CR) electrons and positrons. The data shows an excess in the energy spectrum up to TeV energy, and possibly a peak-like fine structure at $\sim 1.4 \TeV$. We investigate the scenario that the source of the excess comes from dark matter annihilation or decay. We find that the annihilation or decay of diffuse dark matter particles in the Galactic halo can give excellent ($W^+W^-$ channel) or at least good (double $\tau^+\tau^-$ channel) fits to the broad excess. However, the annihilation cross-section is $10^{-23}\cm^3s^{-1}$, larger than required for getting the correct relic abundance. We then study whether the narrow peak at $\sim 1.4\TeV$ could be explained by a nearby subhalo, which thanks to the smaller distance, could supply $e^+e^-$ within a narrow energy range. We find that in order to produce a peak width less than the energy bin width (0.2 TeV), the source must be located within $r\lsim 0.53~\kpc$. Our global fit models do not produce the peak-like feature, instead at 1.4 TeV the spectrum show either a slope or a cliff-like feature. However, if less than optimal fit is allowed, the peak-like feature could be generated. Furthermore, an excellent fit with peak could be obtained with model B if the background is rescaled. If the dark matter decay and annihilation rates are determined using the broad excess, the required subhalo mass $\sim10^{5}~M_\odot$ for decay model, or $\sim10^{4.5}\Msun$ for annihilation model and a shallower density profile slope $\alpha=1.2$, or $\sim10^{2.5}\Msun$ for the steep density profile $\alpha=1.7$. However, the probability for the existence of a such nearby subhalo as massive as given above is very low.