Solar Gamma Rays Powered by Secluded Dark Matter

Abstract

Secluded dark matter models, in which WIMPs annihilate first into metastable mediators, can present novel indirect detection signatures in the form of gamma rays and fluxes of charged particles arriving from directions correlated with the centers of large astrophysical bodies within the solar system, such as the Sun and larger planets. This naturally occurs if the mean free path of the mediator is in excess of the solar (or planetary) radius. We show that existing constraints from water Cerenkov detectors already provide a novel probe of the parameter space of these models, complementary to other sources, with significant scope for future improvement from high angular resolution gamma-ray telescopes such as Fermi-LAT. Fluxes of charged particles produced in mediator decays are also capable of contributing a significant solar system component to the spectrum of energetic electrons and positrons, a possibility which can be tested with the directional and timing information of PAMELA and Fermi.

Figures (3)

• Figure 1: A schematic illustration of the new indirect detection signature of secluded WIMPs captured in the solar core, annihilating to metastable mediators and leading to an electromagnetic flux: $\gamma, e^{\pm},\mu^{\pm},\cdots$. Sensitivity to conventional WIMPs arises only through annihilation to neutrinos.
• Figure 2: Angular and spectral distributions of the photon flux generated by two-photon decays of the mediators with $\gamma v\tau=0.5 R_\odot$ and $\gamma=1000$. (a) The normalized angular distribution $\frac{\textrm{d} \Phi(\theta)}{\textrm{d}\Omega}/(C_\odot \textrm{Br}_V \textrm{Br}_\gamma \cdot 10^{-21}\textrm{cm}^{-2})$; and (b) the fully differential flux $\frac{\textrm{d}^2\Phi(p, \theta)}{\textrm{d} p\,\textrm{d}\Omega}/ (C_\odot \textrm{Br}_V \textrm{Br}_\gamma m_\chi^{-1} \cdot 10^{-21}\textrm{cm}^{-2})$ in the direction $\theta=0$, averaged over a Gaussian profile that mimics an angular resolution of $\Delta\theta=0.1 \theta_\odot$; (c) The same for $\theta = 0.1 \theta\odot$.
• Figure 3: Contours (in blue) of the local $\gamma$-ray flux $\Phi$ in units of cm$^{2}$s$^{-1}$ in the plane of dark matter mass $m_\chi$ and a normalized injection cross-section assuming spin-dependent scattering. The decay distance in the detector frame has been fixed to $R_\odot$. The red line indicates a figure of merit for the sensitivity of Milagro (see the text for more details).