Kavli Affiliate: Gordan Krnjaic
| First 5 Authors: David I. Dunsky, Gordan Krnjaic, Elena Pinetti, ,
| Summary:
Since dark matter is only known to have gravitational interactions, it may
plausibly decay to gravitons on cosmological timescales. Although such a
scenario can be easily realized, there are currently no known limits on this
possibility based on indirect detection searches. We find that the gravitons
produced in dark matter decays can convert to photons in large-scale magnetic
fields along the line of sight to an observer. These conversions primarily
occur within cosmological filaments which occupy a large (order unity) volume
fraction and contain $sim 10-100$ nG fields with $sim$ Mpc coherence lengths.
Thus, dark matter decays to gravitons predict an irreducible population of
extragalactic $textit{photons}$, which we constrain using the extragalactic
gamma-ray background measured by the $textit{Fermi}$-LAT telescope. Using this
conservative method, we place the first limits on the dark matter lifetime in
the $0.1 {rm GeV} – 10^8$ GeV mass range, assuming only decays to gravitons.
We also make projections for the Advanced Particle-astrophysics Telescope,
which can improve sensitivity to this DM decay channel by an order of magnitude
beyond those we set using $textit{Fermi}$-LAT data.
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