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Possible Evidence For Axino Dark Matter In The Galactic Bulge

Dan Hooper, Lian-Tao Wang

TL;DR

The paper tackles the INTEGRAL-observed 511 keV line from the galactic bulge, which is hard to reconcile with standard astrophysical sources. It proposes decaying dark matter in the form of a light axino ($m_{ ilde{a}}\in 1-300\, ext{MeV}$) in R-parity violating SUSY, realized in either KSVZ or DFSZ axion models, with decays producing positrons via channels like $\tilde{a} \rightarrow \nu e^+ e^-$. By modeling the galactic halo with a cusped density profile, the authors derive that the required lifetime is $\tau_{\rm dm} \sim 4\times 10^{26}\, ext{s}/m_{ m dm}(\text{MeV})$ and show that axino lifetimes estimated from $f_a$ and RPV couplings can reach this range for plausible parameters, making the scenario viable. The work links the 511 keV emission to supersymmetric axion physics and suggests potential SUSY/RPV signals at the LHC, while acknowledging the need for future observations to confirm or refute this decaying DM explanation.

Abstract

Recently, the SPI spectrometer on the INTEGRAL satellite observed strong 511 keV line emission from the galactic bulge. Although the angular distribution (spherically symmetric with width of \sim 9 degree) of this emission is difficult to account for with traditional astrophysical scenarios, light dark matter particles could account for the observation. In this letter, we consider the possibility that decaying axinos in an R-parity violating model of supersymmetry may be the source of this emission. We find that \sim 1-300 MeV axinos with R-parity violating couplings can naturally produce the observed emission.

Possible Evidence For Axino Dark Matter In The Galactic Bulge

TL;DR

The paper tackles the INTEGRAL-observed 511 keV line from the galactic bulge, which is hard to reconcile with standard astrophysical sources. It proposes decaying dark matter in the form of a light axino () in R-parity violating SUSY, realized in either KSVZ or DFSZ axion models, with decays producing positrons via channels like . By modeling the galactic halo with a cusped density profile, the authors derive that the required lifetime is and show that axino lifetimes estimated from and RPV couplings can reach this range for plausible parameters, making the scenario viable. The work links the 511 keV emission to supersymmetric axion physics and suggests potential SUSY/RPV signals at the LHC, while acknowledging the need for future observations to confirm or refute this decaying DM explanation.

Abstract

Recently, the SPI spectrometer on the INTEGRAL satellite observed strong 511 keV line emission from the galactic bulge. Although the angular distribution (spherically symmetric with width of \sim 9 degree) of this emission is difficult to account for with traditional astrophysical scenarios, light dark matter particles could account for the observation. In this letter, we consider the possibility that decaying axinos in an R-parity violating model of supersymmetry may be the source of this emission. We find that \sim 1-300 MeV axinos with R-parity violating couplings can naturally produce the observed emission.

Paper Structure

This paper contains 4 sections, 9 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Decaying Dark Matter
  3. Axino Decay
  4. Discussion and Conclusions

Figures (1)

  • Figure 1: The angular distribution of 511 keV $\gamma$-rays from decaying dark matter averaged over the $2^{\circ}$ angular resolution of the SPI spectrometer on INTEGRAL for several halo profiles. SPI's observation indicates a full width half maximum of $9^{\circ}$ with a $6^{\circ}-18^{\circ}$ 2$\sigma$ confidence interval. Shown as vertical dashed and dotted lines are the central value and 2$\sigma$ limits of the angular widths found by SPI. To agree with this data, a cusped halo model with $\gamma \sim$ 0.8-1.5 is favored.