Consistent explanation for the cosmic-ray positron excess in p-wave Breit–Wigner enhanced dark matter annihilation

Abstract

Dark matter (DM) annihilation in the galactic halo can be enhanced relative to that in the early Universe due to the Breit–Wigner enhancement, if the DM particles annihilate through a narrow resonance. Although the s-wave Breit–Wigner enhancement can provide a consistent explanation for both the observed cosmic-ray (CR) positron excess and the DM thermal relic density, it is severely constrained by the observations of gamma rays from dwarf spheroidal satellite galaxies (dSphs) and the cosmic microwave background (CMB), which have relatively lower allowed DM annihilation cross section and typical DM velocities than that in the galactic halo. Furthermore, in the s-wave Breit–Wigner enhancement, the case where the resonance mass is below a threshold (twice the DM mass) is ruled out due to the monotonically increasing annihilation cross section with decreasing DM velocity. In this work, we consider Breit–Wigner enhanced p-wave DM annihilation. We explore the parameter regions which can simultaneously account for the CR positron excess and DM thermal relic density without violating the constraints from dSphs gamma rays and CMB. We show that the velocity-dependent cross section in this scenario can peak around the typical DM velocity in the galactic halo for the resonance mass both above and below the threshold. Moreover, the highly suppressed annihilation cross section at extremely low DM velocity can evade the constraints from dSphs gamma rays and CMB easily, which results in larger allowed parameter regions than that in the s-wave case.

Enhanced cosmic-ray antihelium production from dark matter annihilation through light mediators

“…becomes velocity dependent due to the Sommerfeld and resonant enhancements [12,13], and must be treated individually for each DM halo. This effect is not significant in this work, as the Sommerfeld effect saturates to be velocity independent when the typical DM velocity v 0 /c m φ /m χ .…”

“…[5][6][7][8] for discussions related to the recent AMS-02 data) which is, however, subject to stringent constraints from the observations of γ-rays from dwarf galaxies (dSphs) [9], the Galactic center [10], and the measurement of the anisotropy in the cosmological microwave background (CMB) [11]. A consistent DM explanation including the DM thermal relic abundance may require complicated temperature dependence of DM annihilation, such as that with p-wave Sommerfeld and resonant enhancements [12,13]. Another important observable is the CR antiproton which is the lightest CR antinucleus and has been measured by a number of experiments such as PAMELA [14], BESS-polar II [15] and AMS-02 [16].…”

Light thermal dark matter beyond p-wave annihilation in minimal Higgs portal model

“…Overall, CMB serves as a distinct and complementary probe for understanding thermal DM, crucial for low-mass DM and models with non-velocity-suppressed s-wave annihilation [27,[33][34][35][36][37][38]. Beyond s-wave annihilation, several mechanisms can simultaneously meet CMB constraints and yield the correct relic abundance, such as p-wave DM annihilation [39][40][41][42][43][44][45], forbidden DM mechanisms [46][47][48][49][50], self-interaction DM [51][52][53][54], and other alternatives [55][56][57][58][59][60][61][62].…”