Talks

I will describe a proposal for a generalization of the BMS group in which the conformal isometries of the sphere (Lorentz group) are replaced by arbitrary sphere diffeomorphisms. I describe the computation of canonical charges and show that the associated Ward identities are equivalent to the Cachazo-Strominger subleading soft graviton formula. Based on joint work with Alok Laddha.

Scalar fields are a useful proxy for other complex interactions, but also an attractive extension of General Relativity and a possible dark matter component. I will discuss some aspects of the gravitational interaction of scalar fields, in particular (i) the formation and growth of self-gravitating structures and their interaction with compact stars. and (ii) superradiance around black holes and how it can be used to constraint particle masses.

A new analysis of electron-proton scattering data (those published in 2010 by the Mainz A1 collaboration and previous world compilations) to determine the proton electric and magnetic radii is presented. The analysis enforces model-independent constraints of form factor analyticity and investigates a wide range of possible systematic effects. Employing standard models for radiative corrections, our improved analysis yields proton electric radii for the Mainz and world data sets that are consistent, although a simple combination yields a value r_E = 0.904(15) fm that is 4-sigma larger than the CREMA muonic hydrogen determination. Remaining possible deficiencies are discussed that, if addressed, could reconcile the values from muonic hydrogen spectroscopy and ep-scattering.