Generating cosmological perturbations in non-singular Horndeski Bounce

• Pavel Petrov

Room: B438 We construct a concrete model of Horndeski bounce with strong gravity in the past. Within this model we show that the correct spectra of cosmological perturbations may be generated at early contracting epoch, with mild fine-tuning ensuring that the scalar spectral tilt n𝑆 and tensor-to-scalar ratio r are consistent with observations. The smallness of r is governed by the smallness of the scalar sound speed. Arbitrarily small values of r are forbidden in our setup because of the strong coupling in the past. Nevertheless, we show that it is possible to generate perturbations in a controllable way, i.e. in the regime where the background evolution and perturbations are legitimately described within classical field theory and weakly coupled quantum theory. Journal Ref. e-Print: 2207.04071 [hep-th] https://link.springer.com/article/10.1007/JHEP01(2023)026

Constraining majoron by Big Bang Nucleosynthesis

• Sougata Ganguly

Room: B438 In this talk, we will discuss the Big Bang nucleosynthesis (BBN) constraint on the majoron in the mass range between $1\,{\rm MeV}$ to $10\,{\rm GeV}$ which dominantly decays into the standard model neutrinos. When the majoron lifetime is shorter than $1\,{\rm sec}$, the injected neutrinos mainly heat up background plasma, which alters the relation between photon temperature and background neutrino temperature. For a lifetime longer than $1\,{\rm sec}$, most of the injected neutrinos directly contribute to the protons-to-neutron conversion. In both cases, deuterium and helium abundances are enhanced, while the constraint from the deuterium is stronger than that from the helium. 7Li abundance gets decreased as a consequence of additional neutrons, but the parameter range that fits the observed 7Li abundance is excluded by the deuterium constraint. We also estimate other cosmological constraints and compare them with the BBN bound.

Tea Time with light meal Room: B438