Past Relativity Seminar

22 July 2015
12:00
Claude LeBrun
Abstract
Given a smooth compact 4-manifold M  which admits Einstein metrics, is its moduli space of Einstein metrics connected?  While the corresponding question in higher dimensions typically has a negative answer, there are interesting 4-manifolds M for which the answer is known to be affirmative. One important class of 4-manifolds for which we do not know the answer, however,  consists of the underlying 4-manifolds of the del Pezzo surfaces. In this lecture, I will explain a  result which provides interesting partial information concerning this case. 
16 June 2015
12:00
Chris White
Abstract
The study of infrared singularities, due to the emission of “soft” (low momentum) gauge bosons, remains a highly active research area in a variety of quantum field theories. After motivating both phenomenological and formal reasons as to why we should care about IR singularities, this talk will review their structure in QED, QCD and quantum gravity, examining the similarities and differences between these three contexts. The role of Wilson lines will be examined, which provide a useful unifying language. Finally, I will examine recent work on moving beyond the soft approximation, and why this might be useful.
10 March 2015
12:00
to
13:30
Abstract

A systematic understanding of the low energy limit of string theory scattering amplitudes is essential for conceptual and practical reasons. In this talk, I shall report on a work where this limit has been analyzed using tropical geometry. Our result is that the field theory amplitudes arising in the low energy limit of string theory are written in a very compact form as integrals over a single object, the tropical moduli space. This picture provides a general framework where the different aspects of the low energy limit of string theory scattering amplitudes are systematically encompassed; the Feynman graph structure and the ultraviolet regulation mechanism. I shall then give examples of application of the formalism, in particular at genus two, and discuss open issues.

No knowledge of tropical geometry will be assumed and the topic shall be introduced during the talk.

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