Speaker
Description
The Weakly Interacting Massive Particle (WIMP) thermal
decoupling scenario can be used to probe modified Cosmologies. We
apply this idea to the specific example of dilatonic Einstein
Gauss-Bonnet (dEGB) gravity, where the Gauss–Bonnet term is
non–minimally coupled to a scalar field with vanishing potential. We
show that when the WIMP relic density is constrained to match the
observed DM abundance in the Universe the ensuing modified
cosmological scenario can drive the required WIMP annihilation cross
section to Standard Model particles beyond the present bounds from DM
indirect detection searches, allowing to constrain the model
parameters. Moreover, at temperatures much higher than those relevant
for WIMP decoupling, dEGB exhibits only very few asymptotic
behaviors, characterized by a few values of the equation of state
w. We provide a transparent explanation of this peculiar behaviour in
terms of only three attractors (stable critical points) of the set of
autonomous differential equations that describe the evolution of the
Friedmann equations. Compared to standard Cosmology dEGB can show a
strong enhancement of the expected Gravitational Wave stochastic
background produced by the primordial plasma of relativistic particles
of the Standard Model. This is due to the very peculiar fact that dEGB
allows to have an epoch when the energy density of the relativistic
plasma dominates the energy of the Universe while at the same time the
rate of dilution with the temperature of the total energy density is
slower than what usually expected during radiation dominance. The
ensuing bounds are complementary to late-time constraints from compact
binary mergers.
