Gamma rays and positrons from a decaying hidden gauge boson

TL;DR

The paper proposes a decaying hidden U(1)' gauge boson $A'$ as the dominant dark matter component, with decay governed by a tiny kinetic mixing with hypercharge. It computes the resulting continuous gamma‑ray and positron spectra using hadronization (via PYTHIA) and a diffusion framework, predicting no gamma‑ray line and a sharp peak in the positron spectrum at $E \sim m_{A'}/2$, which can explain the EGRET and HEAT anomalies. The authors show that for $m_{A'}$ around $100$–$300$ GeV and a lifetime $\tau_{A'} \sim 10^{26}$ s, the predicted fluxes fit existing data and yield distinctive signatures for FGST and PAMELA, offering a testable alternative to gravitino scenarios. They also discuss model‑building aspects that generate tiny $ε$ and potential cosmological issues, with several proposed resolutions.

Abstract

We study a scenario that a hidden gauge boson constitutes the dominant component of dark matter and decays into the standard model particles through a gauge kinetic mixing. Interestingly, gamma rays and positrons produced from the decay of hidden gauge boson can explain both the EGRET excess of diffuse gamma rays and the HEAT anomaly in the positron fraction. The spectra of the gamma rays and the positrons have distinctive features; the absence of line emission of the gamma ray and a sharp peak in the positron fraction. Such features may be observed by the GLAST and PAMELA satellites.

Figures (4)

• Figure 1: Decay branching ratios and lifetime of $A^{\prime}$, as a function of $m_{A'}$.
• Figure 2: Energy spectra of $\gamma$ and $e^{+}$ generated from the decay of $A'$.
• Figure 3: $\gamma$ ray flux predicted from decay of $A'$, shown together with the EGRET data Strong:2004ry.
• Figure 4: Fraction of $e^{+}$ flux from $A'$ decay, shown together with experimental data Barwick:1997igGrimani:2002yzAguilar:2007yfAdriani:2008zr.