Category Archives: Research


Today I gave my talk at the KITP workshop on Quantum Gravity Foundations; UV to IR. It was on Nonlocality in the Effective Field Theory of Gravity, reviewing many of our past results but centered on the theme that low energy quantum effects are nonlocal. This is a change from classical GR where we have a spacetime manifold, a local equation governing it, geodesics and crisp events. The workshop here is quite interesting and the setting is great. Today is also the start of my long sabbatical.

Highlighted in PRL

It is nice that our recent paper on quantum effects on light bending got highlighted in Physical Review Letters. This paper calculates the quantum correction to the interaction of light. The effect is small but conceptually there are interesting consequences. For example massless particles no longer follow null geodesics, and massless particles with different spin bend at different angles.

Regge physics again

With the help of Grigory Ovanesyan and Basem El-Menoufi, we have made a nice step of progress in understanding Regge behavior in Soft Collinear Effective Theory (SCET). The paper is here. The issue turns out to be a very subtle one for effective field theory, involving the overlap of different field modes, and it may be important for understanding the limits of factorization theorems.

Nonlocal effects in quantum gravity

Basem and I have a paper exploring the nonlocal effects that come from loops of light fields in gravity. I think that this is an important new area. Already, it seems to have major effects, such as the avoidance of singularities in general relativity, providing a quantum exception to the classical Hawking-Penrose theorems. There seems to be much to do in this area of nonlocal properties of field theory.

Renormalization group approaches to quantum gravity

I participated in a workshop on this topic at the Perimeter Institute. I am a bit of an outsider as I have used the effective field theory treatment to criticize naive applications of running gravitational couplings. The connection of a field like that of Asymptotic Safety to real Loretzian effective field theory is something that needs a better understanding, and I now have a collaboration working on some progress in this area.

The talks at the workshop can be found here.

Besides the science, they produced the Renormalization Souvenir Poster smallbest conference photo ever.