The next cosmology seminars take place on Friday 28th of March, room E349 at 2:00pm. We have the pleasure to listen to our new members, Chiara Animali and Eemeli Tomberg.
At 2pm, room E349, Chiara Animali, will be talking about
Large perturbations from inflation: recent results and open challenges in the stochastic delta N formalism
During inflation, quantum vacuum fluctuations are stretched beyond the Hubble radius, modifying the large-scale dynamics of the universe. Although typically negligible in the perturbative regime, this backreaction can become significant in regimes leading to primordial black hole (PBH) formation, where large density fluctuations arise. The combination of stochastic inflation and delta N formalisms provides an efficient non-perturbative framework to track these large fluctuations. In this context, I will explore recent results and ongoing challenges, particularly in describing backward quantities, which requires a deeper understanding of the relationship between field values and physical distances, as well as how this information is encoded within the recursive geometry of a stochastically inflating universe, thereby enabling the consistent inclusion of volume-weighting effects. The implications for primordial black holes (as their abundance and clustering properties) will also be discussed.
Around 3pm, same place, Eemeli Tomberg will talk about
New developments in stochastic inflation
Stochastic inflation lets us compute the statistics of inflationary perturbations non-perturbatively. I discuss new developments in these computations. First, I talk about the choice of the stochastic scheme, Itô or Stratonovich, and show that the distinction results from the Markovian approximation. If this approximation is dropped, the different schemes become equivalent. Then, using stochastic tools, I discuss eternal inflation in models that produce primordial black holes. I argue that eternal inflation is common in these models and may jeopardize their CMB predictions.