CTPU Joint Tea Time

Asia/Seoul
B438

B438

Description

The purpose of these monthly events is for the two groups to exchange research and socialize.
We will have 30-minute presentations by one person from each research group in the CTPU seminar room at 10:30 am, followed by a 15 minute discussion, and then a light meal in the discussion area in front of the seminar room at 12:00 pm. We invite everyone to join us.

    • 10:30 AM 11:00 AM
      Generating cosmological perturbations in non-singular Horndeski Bounce 30m

      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

      Speaker: Dr Pavel Petrov
    • 11:00 AM 11:15 AM
      Discussion 15m
    • 11:15 AM 11:45 AM
      Constraining majoron by Big Bang Nucleosynthesis 30m

      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.

      Speaker: Dr Sougata Ganguly
    • 11:45 AM 12:00 PM
      Discussion 15m
    • 12:00 PM 1:30 PM
      Tea Time with light meal 1h 30m