# Gravity Seminars This Term

**Join Zoom Meeting:**##### https://virginia.zoom.us/j/99269571512

**Meeting ID:** 992 6957 1512

**Password:** 474477

**Meeting ID:**

**Password:**Monday, February 8, 2021

1:00 PM

Online, Room Zoom

## "The classical evolution of binary black hole systems in scalar-tensor theories"

**Justin Ripley , University of Cambridge**

[Host: Alexander Saffer]

In this talk I will discuss recent work on numerically solving for the binary black hole dynamics of black holes in Einstein scalar Gauss-Bonnet (ESGB) gravity. This modified gravity theory can be motivated by effective field theory reasoning, and admits scalarized black hole solutions. These two facts make it a promising theory to constrain using binary black hole, gravitational wave observations. I will discuss how recent advances in mathematical relativity--in particular, the development of the "modified harmonic formulation"--have opened up the possibility of constructing fully nonlinear solutions to the equations of motion of ESGB gravity (in addition to a class of scalar-tensor modified theories known as "Horndeski" theories). I will discuss numerical simulations of single and binary black hole systems in these theories, and the gravitational and scalar radiation they emit.

**Join Zoom Meeting:**##### https://virginia.zoom.us/j/98692700509

**Meeting ID:** 986 9270 0509

**Password: **525364

**Meeting ID:**

**Password:**Monday, February 22, 2021

1:00 PM

Online, Room Zoom

## "Testing the Schwarzschild/Kerr black hole hypothesis with gravitational and electromagnetic waves"

**Alejandro Cardenas-Avendano , University of Illinois Urbana-Champaign**

[Host: Alexander Saffer]

Over the past years, electromagnetic and gravitational observations have been used to understand the nature of black holes and the material around them. Our ability to learn about the underlying physics, however, depends heavily on our understanding of the gravity theory that describes the geometry around these compact objects, and for the electromagnetic observations, also on the complex astrophysics that produces the observed radiation. In this talk, I will discuss our current ability to constrain and detect deviations from general relativity using (i) the electromagnetic radiation emitted by an accretion disk around a black hole, and (ii) the gravitational waves produced when comparable-mass black holes collide, and when a small compact object falls into a supermassive one in an extreme mass-ratio inspiral. I will also compare the constraining capabilities of these two types of observations to show how current gravitational wave observations have already placed constraints on possible modifications to general relativity, that are more stringent than what can be achieved with current and near-future electromagnetic observations.

**Join Zoom Meeting:**##### https://virginia.zoom.us/j/98166651049

**Meeting ID: **981 6665 1049

**Password:** 726235

**Meeting ID:**

**Password:**Monday, March 8, 2021

1:00 PM

Online, Room Zoom

## "Recent developments in the post-Minkowskian approach to the spinning black hole binary problem"

**Justin Vines , Max Planck Institute for Gravitational Physics (Albert Einstein Institute)**

[Host: Alexander Grant]

The detection and analysis of gravitational wave signals from coalescing binary systems crucially relies on analytic perturbative approaches to the two-body problem in general relativity (as well as on numerical approaches). While the post-Newtonian (weak-field and slow-motion) approximation is most directly relevant to observations by LIGO et al., recent developments have revived interest in the more inclusive post-Minkowskian (weak-field but arbitrary-speed) approximation -- particularly in relation to highly advanced techniques developed by particle physicists for computing relativistic quantum scattering amplitudes and associated classical observables. This interplay between high-energy quantum physics and gravitational-wave science has led to several new results and useful insights, particularly regarding relationships between complimentary approximation schemes; this importantly also includes the "self-force" or "post-test-body" approach, treating small mass ratios but arbitrary field strengths and speeds. We will review some of these developments, focusing on the post-Minkowskian treatment of the spinning black hole binary problem.

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To add a speaker, send an email to dn2ep@Virginia.EDU Include the seminar type (e.g. Gravity Seminars), date, name of the speaker, title of talk, and an abstract (if available). [Please send a copy of the email to phys-speakers@Virginia.EDU.]