Tuesdays 10:30 - 11:30 | Fridays 11:30 - 12:30
Showing votes from 2021-04-20 11:30 to 2021-04-23 12:30 | Next meeting is Friday Sep 12th, 11:30 am.
Scalar modes are considered for the propagation of gravitational waves in cosmological background taking into account of thermal radiation and near cosmological singularities. In particular, we point out that the contribution of thermal radiation can heavily affect the dynamics of gravitational waves giving enhancement or dissipation effects both at quantum and classical level. These effects are considered both in General Relativity and in modified theories like $F(R)$ gravity. The possible detection and the disentanglement of the various gravitational modes on the stochastic background are also discussed.
We use the amplitude soft bootstrap method to explore the space of effective field theories (EFT) of massless vectors and scalars. It is known that demanding vanishing soft limits fixes uniquely a special class of EFTs: non-linear sigma model, scalar Galileon and Born-Infeld theories. Based on the amplitudes analysis, we conjecture no-go theorems for higher-derivative vector theories and theories with coupled vectors and scalars. We then allow for more general soft theorems where the non-trivial part of the soft limit of the (n+1)-pt amplitude is equal to a linear combination of n-pt amplitudes. We derive the form of these soft theorems for general power-counting and spins of particles and use it as an input into the soft bootstrap method in the case of Galileon power-counting and coupled scalar-vector theories. We show that this unifies the description of existing Galileon theories and leads us to the discovery of a new exceptional theory: Special scalar-vector Galileon.