Posts by Category

Simple slow-rotation neutron star structure solver External link

I’m releasing into the wild a simple code for computing neutron star structure in the slow-rotation expansion to first and second order. This code was origi...

ssh ipython notebook tunneling magic

How to get remote jupyter to automatically open a local browser.

Elliptic Integrals in Javascript External link

I just created a repo on github for computing complete elliptic integrals in javascript. The README.md is below, and a demo after that. You might ask yoursel...

Whitespace Cleanup on Diff Lines in Emacs

If you’re in the intersection of git, emacs, and persnickety about whitespace.

Nonlinear ringdown in the news

Our latest paper, Nonlinearities in black hole ringdowns, was just published in Physical Review Letters! This article was selected as an ❦ Editors’ Suggesti...

Sloan Research Fellowship

I am honored to have been selected as one of this year’s Sloan Research Fellows!

Titanium Physicists podcast episode 80 External link

Hear me, Katie Bouman, and friends talk about how to snap a picture of a black hole with the Event Horizon Telescope!

On the Starts with a Bang Podcast! External link

I’m on Episode 42 of the Starts with a Bang Podcast

Talk on the Latin American Webinar on Physics External link

Want to hear me talk about numerical relativity and theories beyond GR?

On the Titanium Physicists Podcast AGAIN! External link

I’m on Episode 64 of the Titanium Physicists Podcast

Member-at-large of APS Topical Group on Gravitation

Just one more committee

Quora session on gravitational waves, LIGO, black holes External link

I hosted a Quora session. It went well!

On the Titanium Physicists Podcast! External link

I’m on Episode 62 of the Titanium Physicists Podcast

Moved to Caltech

I’m back in Pasadena!

Notes: Magnetostatic multipole expansion using STF tensors

How to do the STF multipole expansion of the magnetic potential and field (it’s been on my TODO list for a while)

Notes: How to take a derivative of a generalized continued fraction

So you have a function in terms of a continued fraction, and you want to compute its derivative…

Notes: Generalized harmonic form of Einstein’s equations from a gauge-fixed action

The generalized harmonic formulation can be derived by adding a gauge-fixing term to the Einstein-Hilbert action

Notes: A family of ramp functions and the Beta function

Sometimes in a numerical method, you need to be able to continuously turn a calculation on or off in space or time.

(Notes) When is a metric conformal to Ricci-flat?

Integrability conditions when trying to solve for a conformal factor

Note on simple(r) equations for Einstein-dilaton-Gauss-Bonnet and dynamical Chern-Simons theories

Here to save you some algebra and column-inches

Note on commutation coefficients in two ways

An identity between vector commutation coefficients and coframe connection coefficients

Note on exterior, interior, and Lie derivative superalgebra

These three objects form a superalgebra! Whoa!

Note on Lie derivatives and divergences

When can you integrate-by-parts with Lie derivatives?

Note on generating a divergence identity

Special thanks to Ben Mares for coming up with this identity.

Note on a (dimension-dependent) Weyl identity

There is a nice 4-dimensional Weyl identity that I can never seem to remember off the top of my head; so I decided I need to write this note so I don’t have ...

Notes on the Weyl, E/B, and 3+1 decompositions of Riemann, and curvature invariants

The Weyl decomposition, further splitting into E/B, and computing in terms of 3+1 objects

Notes on the pullback connection

In an effort to keep myself organized, I decided I should type up some notes I have laying around.

Imprints of Changing Mass and Spin on Black Hole Ringdown

We numerically investigate the imprints of gravitational radiation-reaction driven changes to a black hole’s mass and spin on the corresponding ringdown ...

Can a radiation gauge be horizon-locking?

In this short Note, I answer the titular question: Yes, a radiation gauge can be horizon-locking. Radiation gauges are very common in black hole perturbat...

Optimizing post-Newtonian parameters and fixing the BMS frame for numerical-relativity waveform hybridizations

Numerical relativity (NR) simulations of binary black holes provide precise waveforms, but are typically too computationally expensive to produce wavefor...

Numerical relativity surrogate model with memory effects and post-Newtonian hybridization

Numerical relativity simulations provide the most precise templates for the gravitational waves produced by binary black hole mergers. However, many of t...

Numerical simulations of black hole-neutron star mergers in scalar-tensor gravity

We present a numerical-relativity simulation of a black hole - neutron star merger in scalar-tensor (ST) gravity with binary parameters consistent with t...

Nonlinearities in black hole ringdowns

This article was selected as an ❦ Editors’ Suggestion, and Featured in APS’s Physics magazine. More press coverage links here.

Fixing the BMS Frame of Numerical Relativity Waveforms with BMS Charges

The Bondi-van der Burg-Metzner-Sachs (BMS) group, which uniquely describes the symmetries of asymptotic infinity and therefore of the gravitational waves...

Gravitational-wave energy and other fluxes in ghost-free bigravity

One of the key ingredients for making binary waveform predictions in a beyond-GR theory of gravity is understanding the energy and angular momentum carri...

Tidally-induced nonlinear resonances in EMRIs with an analogue model

One of the important targets for the future space-based gravitational wave observatory LISA is extreme mass ratio inspirals (EMRIs), where long and accur...

High Precision Ringdown Modeling: Multimode Fits and BMS Frames

Quasi-normal mode (QNM) modeling is an invaluable tool for characterizing remnant black holes, studying strong gravity, and testing general relativity. ...

Action-angle variables of a binary black-hole with arbitrary eccentricity, spins, and masses at 1.5 post-Newtonian order

Accurate and efficient modeling of the dynamics of binary black holes (BBHs) is crucial to their detection through gravitational waves (GWs), with LIGO/V...

Surprises in a classic boundary-layer problem

We revisit a textbook example of a singularly perturbed nonlinear boundary-value problem. Unexpectedly, it shows a wealth of phenomena that seem to have ...

Numerical renormalization group-based approach to secular perturbation theory

Perturbation theory is a crucial tool for many physical systems, when exact solutions are not available, or nonperturbative numerical solutions are intra...

Fixing the BMS frame of numerical relativity waveforms

Understanding the Bondi-Metzner-Sachs (BMS) frame of the gravitational waves produced by numerical relativity is crucial for ensuring that analyses on su...

Comparing Remnant Properties from Horizon Data and Asymptotic Data in Numerical Relativity

We present a new study of remnant black hole properties from 13 binary black hole systems, numerically evolved using the Spectral Einstein Code. The mass...

Constraining gravitational wave amplitude birefringence and Chern-Simons gravity with GWTC-2

We perform a new test of general relativity (GR) with signals from GWTC-2, the LIGO and Virgo catalog of gravitational wave detections. We search for the...

Integrability of eccentric, spinning black hole binaries up to second post-Newtonian order

We show that an eccentric binary of black holes with misaligned spins is integrable at 2PN order. We also construct 4 out of 5 action variables at 1.5PN.

Brans-Dicke theory in Bondi-Sachs form: Asymptotically flat solutions, asymptotic symmetries and gravitational-wave memory effects

We study the structure of asymptotic null infinity in the Brans-Dicke theory of gravity

A fixed point for black hole distributions

Merger dynamics create an attractive fixed-point in the space of distributions

Numerical relativity simulation of GW150914 beyond general relativity

The first astrophysically-relevant numerical simulation of merging black holes in a higher-curvature theory beyond GR.

Location of the last stable orbit in Kerr spacetime

The dividing line between bound and plunging orbits is an algebraic variety

qnm: A Python package for calculating Kerr quasinormal modes, separation constants, and spherical-spheroidal mixing coefficients

qnm is an open-source Python package for computing the Kerr quasinormal mode frequencies, angular separation constants, and spherical-spheroidal mixing coeff...

Numerical binary black hole collisions in dynamical Chern-Simons gravity

The first numerical beyond-GR binary black hole merger simulation.

Surrogate models for precessing binary black hole simulations with unequal masses

A surrogate model extending the parameter space range of fully precessing quasicircular inspirals

The SXS Collaboration catalog of binary black hole simulations

Accurate models of gravitational waves from merging black holes are necessary for detectors to observe as many events as possible while extracting the maximu...

The binary black hole explorer: on-the-fly visualizations of precessing binary black holes

Real-time interactive visualizations of merging black holes in seconds!

High-accuracy mass, spin, and recoil predictions of generic black-hole merger remnants

Modeling black holes remnants directly from numerical relativity

Measuring stochastic gravitational-wave energy beyond general relativity

Gravity theories beyond general relativity (GR) can change the properties of gravitational waves: their polarizations, dispersion, speed, and, importantly, e...

Black holes, gravitational waves and fundamental physics: a roadmap

The grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities an...

Black hole scalar charge from a topological horizon integral in Einstein-dilaton-Gauss-Bonnet gravity

In theories of gravity that include a scalar field, a compact object’s scalar charge is a crucial quantity since it controls dipole radiation, which can be s...

Black-hole kicks from numerical-relativity surrogate models

Modeling black holes’ kicks directly from numerical relativity

Deformation of extremal black holes from stringy interactions

Finding the shape of extremal black holes in beyond-GR theories

Separating metric perturbations in near-horizon extremal Kerr spacetimes

Whenever you’ve got symmetry, you should use it!

Numerical binary black hole mergers in dynamical Chern-Simons: I. Scalar field

One of the first numerical simulations of black hole mergers in beyond-GR effective field theories

Prescriptions for Measuring and Transporting Local Angular Momenta in General Relativity

Angular momentum is tricky to define in GR! Here’s an approach so that observers can all agree with each others’ measurements.

Black Hole Based Tests of General Relativity

Invited review for CQG Focus Issue

Extremal Black Holes in Dynamical Chern-Simons Gravity

Progress in understanding the structure of extremal black holes in Chern-Simons

Challenging the Presence of Scalar Charge and Dipolar Radiation in Binary Pulsars

Not all theories with long-ranged scalar fields produce dipole radiation in binaries

“Slimplectic” Integrators: Variational Integrators for General Nonconservative Systems

A generalization of symplectic integrators to non-conservative dynamics.

Testing General Relativity With Present and Future Astrophysical Observations

A major review on non-GR theories, black holes and neutron stars in non-GR theories, compact binaries in non-GR theories, and pulsar, gravitational-wave, and...

The Principle of Stationary Nonconservative Action for Classical Mechanics and Field Theories

Extending Hamilton’s variational principle to nonconservative systems.

Why I-Love-Q: Explaining why universality emerges in compact objects

Explaining why universality emerges in compact objects.

Rapidly Rotating Black Holes in Dynamical Chern-Simons Gravity: Decoupling Limit Solutions and Breakdown

Numerical solutions for rapidly-rotating dCS black holes show where the weak-coupling expansion breaks down.

Note on Legendre Decomposition of the Pontryagin Density in Kerr

Short note simplifying a calculation in the literature.

Three-Hair Newtonian Relations for Rotating Stars

Universal relations between the Newtonian multipole moments of rotating stars.

Parametrizing and Constraining Scalar Corrections to General Relativity

Connecting observables (pulsar binary pericenter precession and gravitational wave phase) to the parameters and structure of theoretical models.

Isolated and Binary Neutron Stars in Dynamical Chern-Simons Gravity

Chern-Simons corrections to 1) internal structure (including mass shift) and 2) binary dynamics (including pericenter precession) of neutron stars.

Probes of Strong-field Gravity (PhD Thesis) External link

MIT PhD thesis of Leo C. Stein

Post-Newtonian, Quasicircular Binary Inspirals in Quadratic Modified Gravity

The post-Newtonian calculation scheme applied to binary inspirals in a broad class of almost-GR theories.

The Geometry of Hamiltonian Monte Carlo

Applying symplectic geometry to understand and refine Hamiltonian MC.

Bumpy Black Holes in Alternative Theories of Gravity

Parametrizing deviations from purely GR, vacuum black holes.

Nonspinning Black Holes in Alternative Theories of Gravity

The deformation to spherically symmetric black holes under a class of corrections to general relativity.

Effective Gravitational Wave Stress-energy Tensor in Alternative Theories of Gravity

Computing how much energy and momentum gravitational waves carry in a very broad class of almost-GR theories.

Solving the Corner-turning Problem for Large Interferometers

Turning an O(n^2) problem into an O(n log n) problem in radio interferometry, similar in spirit to how the fast Fourier transform operates.

X-Pipeline: An Analysis Package for Autonomous Gravitational-wave Burst Searches

Autonomous gravitational-wave searches—fully automated analyses of data that run without human intervention or assistance—are desirable for a number of re...

Coherent Network Analysis Technique for Discriminating Gravitational-wave Bursts From Instrumental Noise

How to overconstrain the problem of discriminating gravitational wave signals from detector noise and glitches.

APS 2021 talk slides: Energy carried by gravitational waves in bimetric gravity

I haven’t been posting every time I gave a talk, so here is a sporadic update. I contributed a talk to the 2021 April APS meeting. This talk is a status u...

qnm talk (and notebook) at the BHPToolkit spring 2020 workshop

Last week I gave an invited talk at the Spring 2020 workshop of the Black Hole Perturbation Toolkit (BHPToolkit). The BHPToolkit is a collection of open sou...

Recent talks in Rome and Nottingham

Just an update on talks I gave recently. Valeria Ferrari, Leonardo Gualtieri, and Paolo Pani hosted the conference “New Frontiers in Gravitational-Wave Astr...