Speaker
Dr
Jesus Zavala Franco
(Department of Physics and Astronomy, University of Waterloo (CITA National Fellow))
Description
The extragalactic background light (EBL) observed at multiple wavelengths is a
promising tool to probe the nature of dark matter since it might contain a significant
contribution from gamma-rays produced promptly by dark matter annihilation.
Additionally, the electrons and positrons produced in the annihilation give energy to
the CMB photons to populate the EBL with X-rays and gamma-rays. We have created
full-sky maps of the radiation from both of these contributions using the high-
resolution Millennium-II simulation. We use upper limits on the contributions of
unknown sources to the EBL to constrain the intrinsic properties of dark matter
using a model-independent approach that can be employed as a template to test
different particle physics models (including those with a Sommerfeld enhancement).
These upper limits are based on observations spanning eight orders of magnitude in
energy (from soft X-rays measured by CHANDRA to gamma-rays measured by
Fermi), and on expectations for the contributions from blazars and star forming
galaxies. To exemplify this approach, we analyze a set of benchmark Sommerfeld-
enhanced models that give the correct dark matter abundance, satisfy CMB
constraints, and fit the cosmic ray spectra measured by PAMELA and Fermi without
any contribution from local subhalos. We find that these models are in conflict with
the EBL constraints unless the contribution of unresolved subhalos is small and the
annihilation signal dominates the EBL. We conclude that provided the collisionless
cold dark matter paradigm is accurate, even for conservative estimates of the
contribution from unresolved subhalos and astrophysical backgrounds, the EBL is at
least as sensitive a probe of these types of scenarios as the CMB. Our results disfavor
an explanation of the positron excess measured by PAMELA based only on dark
matter annihilation in the smooth Galactic halo.
Primary author
Dr
Jesus Zavala Franco
(Department of Physics and Astronomy, University of Waterloo (CITA National Fellow))
Co-authors
Dr
Abraham Loeb
(Harvard-Smithsonian Center for Astrophysics)
Dr
Mark Vogelsberger
(Harvard-Smithsonian Center for Astrophysics)
Dr
Tracy Slatyer
(School of Natural Sciences, Institute for Advanced Study)
Dr
Volker Springel
(Heidelberg Institute for Theoretical Studie)
