Gravity Seminars

Upcoming seminars

All Gravity seminars are held on Tuesdays at 13:00, in Auditorium A, Blegdamsvej 17.

The NBIA Gravity seminars bring together three areas of research at the NBIA tied together by gravity:

  • Black hole and gravitational wave astrophysics
  • Strong gravity
  • Gravity from particle amplitudes

The seminars are intended to be accessible to researchers and students spanning the range of topics above.

Date Speaker
May 7, 2024

Sofie Koksbang, Southern University of Denmark (SDU)

Title: Observational effects of cosmic backreaction with concrete abstract cosmology and machine learning

Abstract: Cosmic backreaction is a concept from inhomogeneous cosmology which originally gained attention because the phenomenon can lead to apparent accelerated expansion of the universe without dark energy. However, it is at this point unclear to what extent cosmic backreaction is relevant for our universe. One of the methods for revealing its importance (or lack thereof) is using observational tests that can either reveal a deviation from FLRW behavior or directly reveal effects of cosmic backreaction.

 In this talk, I will give a brief review of cosmic backreaction. I will then introduce "concrete abstract cosmology" and discuss the observational signatures of backreaction that have been uncovered with this approach and what possibilities the approach gives when combined with machine learning.

May 14, 2024

Ira Rothstein, Carnegie Mellon University

Title:
Environmental Effects on Binary Inspirals

Abstract:
The problem of predicting the gravitational wave signal from a binary inspirals involves solving a complicated set of non-linear differential equations. There has been great progress made in making such predictions analytically in Post-Newtonian limit (small relative velocities) using techniques originally developed for quantum field theory. In this talk I will discuss how one can extend these ideas to include the effects of an inviscid fluid environment by utilizing field theoretic techniques developed to study non-equilibtrium systems. I will begin by building a point particle action for a compact object moving in an perfect fluid. By doing so we effectively trade a set of boundary conditions for a coefficient in the action, which greatly simplifies the problem. I will then demonstrate how this approximation can reproduce the full answer at distances large compared to the radius of the object. This will lead naturally to a discussion of "Dalamberts’ paradox'' which states that an object moving at constant velocity through fluid with no viscosity feels no drag force. I will then show how to introduce viscosity using the closed-time path integral formulation of field theory. By covariantizing this theory I will show how one can systematically include Post-Newtonian corrections to the action for the purpose of making precision gravitational wave predictions which are sensitive to environmental conditions.

June 11, 2024

Amanda Farah, University of Chicago

July 2, 2024

Mikołaj Korzyński, Polish Academy of Sciences

Previous seminars