Found 7 result(s)
Regular Seminar Lionel Mason (University of Oxford)
at: 14:00 room MB 503 Maths  abstract: Recently in their celestial holography programme, Strominger and coworkers attempt to provide a holographic description of conventional 4d gravity. In their investigations, they uncovered a hidden winfinity symmetry in their `celestial soft OPEs' for graviton scattering. This talk will explain the origin of this symmetry in terms of old ideas of Newman and Penrose based on lightcone cuts of null infinity and their description in terms of asymptotic twistors and certain sigma models in asymptotic twistor space. W_n symmetries were introduced by Zamolodchikov as higher spin symmetries in 2d conformal field theories. These were given a geometric interpretation for n=infinity as areapreserving diffeomorphisms of the plane. I will explain how the corresponding loop algebra becomes a hidden symmetry of selfdual gravity via Penrose's nonlinear graviton construction. The action of this symmetry on the treelevel Smatrix of full gravity beyond the selfdual sector will then be obtained from its action on a sigma model in the asymtotic twistor space of a general spacetime. This talk is based on https://arxiv.org/abs/2110.06066 and https://arxiv.org/abs/2103.16984. 
Regular Seminar Lionel Mason (Oxford University)
at: 13:15 room S0.13  abstract: Ambitwistor strings are holomorphic string theories whose target space is the space of complex null geoedesics in complexified spacetimes. I will explain how these theories explain the origin of the scattering equations in twistor strings and the CHY formulae in arbitrary dimensions and provide a reformulation of standard gauge, gravity and other theories in a holomorphic infinite tension analogue of conventional string theories. I will show how these results extend to 1loop both on a torus and on a nodal Riemann sphere, and perhaps to higher loops. 
Regular Seminar Lionel Mason (Oxford)
at: 14:00 room 208  abstract: We use an observation of Maldacena to argue that gravity treeamplitudes can be computed by inserting appropriate wavefunctions into the WittenBerkovits twistorstring for conformal gravity. This is used to motivate and partially explain the recent remarkable twistorstringlike formula of Cachazo & Skinner that expresses the complete treelevel Smatrix for N=8 supergravity in terms of an integral over rational curves in twistor space. 
Regular Seminar Lionel Mason (Oxford)
at: 14:00 room E303 Queens Building  abstract: Leading singularities are invariants of multiloop scattering amplitudes (the full amplitude at tree level) obtained by generalized unitarity. In this talk we show how to construct multiloop leading singularities on twistor space for maximally supersymmetric YangMills (and gravity). Building on the treelevel twistorstring representation of scattering amplitudes, they can be represented as integrals over a moduli space of nodal curves in twistor space. We discuss how this might arise from a conjectural twistorstring path integral representation for the full loop amplitude. We also show how the construction relates to the Grassmannian representation of leading singularities conjectured by ArkaniHamed et. al.. This shows firstly that all leading singularities can be represented in the Grassmannian, and secondly that the complexity is limited, in particular we conjecture that there are no new leading singularities at beyond 3p loops for NpMHV amplitudes. 
Regular Seminar Lionel Mason (Oxford University)
at: 13:30 room Huxley 503  abstract: The twistor programme was introduced by Roger Penrose as an approach to quantum gravity in which twistor space should provide the primary geometric background for physics from which spacetime should emerge. This talk will review the programme, i.e., the early successes in formulating the selfdual parts of YangMills and gravity on twistor space. It will go on to review the impact of twistorstring theory, in giving at least a perturbative approach to full Yang Mills and conformal gravity, and outline arguments that prove the equivalence between the twistorstring models and the spacetime theories. Finally, twistorstring models for Einstein gravity will be reviewed. 
String Theory & Geometry Seminar Lionel Mason (Oxford)
at: 13:30 room Billiard Room, 58 Princes Gate  abstract:
