IA/U.Lisboa Seminar - Cosmic Transients, Einstein's Equivalence Principle and Dark Matter Halos - 22 janeiro 2018

Cosmic transients, such as gamma-ray bursts and fast radio bursts, have been used to constrain the Einstein's Equivalence Principle (EEP) trough the parametrized-post-Newtonian (PPN) formalism. In this approach, the time delay of photons with different energies from these cosmic transients are used to obtain upper bounds on the difference of the PPN gamma parameter. Assuming that an important contribution to the time delay is due to the dark matter halo of the Milky Way and considering the dark matter mass distribution given by the NavarroFrenkWhite profile, the upper limit on the difference of the PPN parameter gamma for the polarized gamma-ray emission of GRB 110721A is Delta gamma < 1.06 x 10^-28, the most stringent limit to date on the EEP. In addition, a very similar upper bound is obtained if, instead of having a dark matter component, a visible matter density profile and a non-minimal gravitational coupling between curvature and matter are present.