The gravitational wave observations of colliding black holes have opened a new window
into the unexplored extreme gravity sector of physics, where the gravitational fields are …

The near-simultaneous multi-messenger detection of the gravitational wave (GW) event
GW170817 and its optical counterpart, the short-ray burst GRB170817A, implies that …

Despite the tremendous success of general relativity so far, modified theories of gravity have
received increased attention lately, motivated from both theoretical and observational …

Positivity bounds—the consequences of requiring a unitary, causal, local UV completion—
place strong restrictions on theories of dark energy and/or modified gravity. We derive and …

The discovery of the electromagnetic counterpart to GW170817 severely constrains the
tensor mode propagation speed, eliminating a large model space of Horndeski theory. We …

Recently the Event Horizon Telescope Collaboration, with very-long baseline interferometric
observations, resolved structure at the scale of∼ 5 Schwarzschild radii about the center of M …

The violent collisions of black holes provide for excellent test-beds of Einstein's general
relativity in the strong/dynamical gravity regime. We here demonstrate the resolving power …

The recent discovery of gravitational-wave events has offered us unique test beds of gravity
in the strong and dynamical field regime. One possible modification to General Relativity is …

We study the orbital evolution of eccentric binary systems in Horndeski gravity. This
particular theory provides a test bed to give insightful comparisons with data. We compute …

We develop an approach to parametrize cosmological perturbations beyond linear order for
general dark energy and modified gravity models characterized by a single scalar degree of …