# Gravity Seminars

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

**Meeting ID: **981 6665 1049 **Passcode: **726235

Monday, April 26, 2021

1:00 PM

Online, Room Zoom

## "High-performance Gravitational Wave Extraction in SpECTRE"

**Jordan Moxon , California Institute of Technology**

[Host: Alexander Grant]

Numerical relativity stands as the primary method of generating precise waveform predictions for comparable-mass compact binary coalescences used in gravitational wave data analysis pipelines. To produce those predictions, the spacetime in the vicinity of the binary system must be simulated to high precision, and then the waveform information must be extracted from the dynamical spacetime near the binary. Cauchy Characteristic Evolution (CCE) offers a wave extraction method capable of efficiently determining a complete, asymptotically well-behaved metric at Scri+. For our implementation of CCE in SpECTRE, we have developed a number of mathematical refinements of the CCE system that improves spectral convergence and eases the computation of detailed dynamical spacetime information at Scri+. Our implementation in SpECTRE is far faster than previous CCE codes, is free from logarithmic pathologies, and computes full waveform information: news, strain, and all five Weyl scalars. I will discuss the numerical methods used to improve the performance of SpECTRE CCE, as well as several projects that have used the system to study gravitational wave memory and other subtle waveform effects that become available with full access to waveform data at Scri+.

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

**Meeting ID:** 981 6665 1049

**Password:** 726235

**Meeting ID:**

**Password:**Monday, April 5, 2021

1:00 PM

Online, Room via Zoom

Note special room.

## "Formation and dynamics of extreme mass ratio inspirals with environmental effects"

**Huan Yang , Perimeter Institute and University of Guelph**

[Host: Alexander Grant]

In this talk I will discuss relevant environment effects (i.e., accretion disk, tidal gravitational field from close objects) that influence the formation and dynamics of extreme mass ratio inspirals (EMRIs), which are important sources for LISA. I will show that disk-assisted EMRIs may be more commonly seen by LISA. They can be distinguished from EMRIs formed through cluster multibody scattering by eccentricity measurements. The disk force and tidal gravitational field from nearby objects may also leave observable imprints on the waveform of the EMRIs, which provide new opportunities in probing the stellar distributions and constraining the accretion physics at galactic centers.

**Join Zoom Meeting:**##### https://virginia.zoom.us/j/97049511556

**Meeting ID: **970 4951 1556

**Password:** 707548

**Meeting ID:**

**Password:**Monday, March 22, 2021

6:00 PM

Online, Room via Zoom

Note special time.

Note special room.

## "Adventures in Gravitational-wave Astronomy: testing for hair, memory, and eccentricity"

**Paul Lasky , Monash University**

[Host: Alexander Saffer]

Since the first gravitational-wave detection of a binary black hole merger in 2015, the LIGO and Virgo detectors have observed gravitational waves from more than 50 merging systems. That number is expected to increase significantly over the coming years as these experiments become even more sensitive. The increased number of detections, and the improved sensitivity of these instruments, allows us to probe the ultra-strong regime of gravity, as well as the formation history of these systems. I will discuss ongoing efforts to test general relativity in the ultra strong-field regime, including tests of the no-hair theorem and searches for gravitational-wave memory -- a permanent deformation of spacetime following the passage of a gravitational wave. I will also discuss efforts to detect orbital eccentricity in these systems, which has led to potentially the first observation of a second-generation black hole merger.

**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.

**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/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.

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.]