Searching for Dark Matter with Future Cosmic Positron Experiments

TL;DR

The paper investigates the potential of cosmic positron measurements to reveal dark matter annihilation in the Galactic halo, focusing on PAMELA and AMS-02. It models positron production and propagation with a diffusion-loss framework and computes spectra for neutralino (bino, higgsino, wino) and Kaluza-Klein DM across parameter space, comparing to HEAT data and assessing detectability. It shows characteristic spectral features at $E \approx m_X/2$ and $E \approx m_X$, analyzes the impact of halo profiles and boost factors on flux, and maps the 95% CL reach of PAMELA and AMS-02 for various channels, including leptophilic KKDM and AMSB scenarios. The work demonstrates that future precision positron measurements can probe a broad range of DM models, with AMS-02 extending reach to multi-TeV scales and leptophilic scenarios, making cosmic positrons a valuable indirect probe of particle dark matter.

Abstract

Dark matter particles annihilating in the Galactic halo can provide a flux of positrons potentially observable in upcoming experiments, such as PAMELA and AMS-02. We discuss the spectral features which may be associated with dark matter annihilation in the positron spectrum and assess the prospects for observing such features in future experiments. Although we focus on some specific dark matter candidates, neutralinos and Kaluza-Klein states, we carry out our study in a model independent fashion. We also revisit the positron spectrum observed by HEAT.

Figures (33)

• Figure 1: The positron spectrum from dark matter annihilations prior to propagation for several annihilation channels. Dotted and dashed lines represent the positron spectrum, per annihilation, for annihilations to $b \bar{b}$ and gauge boson pairs, respectively. The dot-dashed and solid lines represent annihilations to $\tau^+ \tau^-$ and $\mu^+ \mu^-$, respectively, which produce considerably harder spectra. The spectrum for annihilations to $e^+ e^-$ is not shown, but is simply a delta function at the energy equal to the WIMP mass. For all cases shown, a WIMP mass of 300 GeV was used. This figure originally appeared in Ref. [17].
• Figure 2: The spectrum of positrons, including the effects of propagation, from dark matter annihilations to b quark pairs. WIMP masses of 50, 100, 300 and 600 GeV were considered. A dark matter distribution with $BF=5$ (see section \ref{['cps']}), $\rho(\rm{local})=0.43 \,\rm{GeV/cm^3}$ and an annihilation cross section of $\sigma v = 10^{-25} \, \rm{cm}^3/\rm{s}$ was used. The effects of solar modulation are not included.
• Figure 3: The spectrum of positrons, including the effects of propagation, from dark matter annihilations to $ZZ$ and $W^+ W^-$ pairs. WIMP masses of 100, 300 and 600 GeV were considered. Note the enhancement near $m_X/2$ as compared to the case of annihilations to b quarks. A dark matter distribution with $BF=5$ (see section \ref{['cps']}), $\rho(\rm{local})=0.43 \,\rm{GeV/cm^3}$ and an annihilation cross section of $\sigma v = 10^{-25} \, \rm{cm}^3/\rm{s}$ was used. The effects of solar modulation are not included.
• Figure 4: The spectrum of positrons, including the effects of propagation, from dark matter annihilations to $e^+ e^-$ pairs. WIMP masses of 50, 100, 300 and 600 GeV were considered. A dark matter distribution with $BF=5$ (see section \ref{['cps']}), $\rho(\rm{local})=0.43 \,\rm{GeV/cm^3}$ and an annihilation cross section of $\sigma v = 10^{-26} \, \rm{cm}^3/\rm{s}$ was used. The effects of solar modulation are not included.
• Figure 5: The spectrum of positrons, including the effects of propagation, from dark matter annihilations to $\tau^+ \tau^-$ pairs. WIMP masses of 50, 100, 300 and 600 GeV were considered. A dark matter distribution with $BF=5$ (see section \ref{['cps']}), $\rho(\rm{local})=0.43 \,\rm{GeV/cm^3}$ and an annihilation cross section of $\sigma v = 10^{-25} \, \rm{cm}^3/\rm{s}$ was used. The effects of solar modulation are not included.