Past Relativity Seminar

6 November 2012
Dr Ricardo Monteiro
We will discuss the origin of the conjectured colour-kinematics duality in perturbative gauge theory, according to which there is a symmetry between the colour dependence and the kinematic dependence of the S-matrix. Based on this duality, there is a prescription to obtain gravity amplitudes as the "double copy" of gauge theory amplitudes. We will first consider tree-level amplitudes, where a diffeomorphism algebra underlies the structure of MHV amplitudes, mirroring the colour algebra. We will then draw on the progress at tree-level to consider one-loop amplitudes.
8 June 2012
David McGady

Abstract: In this talk, I will discuss the proportionality between tree amplitudes and the ultraviolet divergences in their one-loop corrections in Yang-Mills and (N < 4) Super Yang-Mills theories in four-dimensions. From the point of view of local perturbative quantum field theory, i.e. Feynman diagrams, this proportionality is straightforward: ultraviolet divergences at loop-level are absorbed into coefficients of local operators/interaction vertices in the original tree-amplitude. Ultraviolet divergences in loop amplitudes are also calculable through on-shell methods. These methods ensure manifest gauge-invariance, even at loop-level (no ghosts), at the expense of manifest locality. From an on-shell perspective, the proportionality between the ultraviolet divergences the tree amplitudes is thus not guaranteed. I describe systematic structures which ensure proportionality, and their possible connections to other recent developments in the field.

29 May 2012
Dr M Dunajski
Solitons are localised non-singular lumps of energy which describe particles non perturbatively. Finding the solitons usually involves solving nonlinear differential equations, but I shall show that in some cases the solitons emerge directly from the underlying space-time geometry: certain abelian vortices arise from surfaces of constant mean curvature in Minkowski space, and skyrmions can be constructed from the holonomy of gravitational instantons.