Found 6 result(s)

### 28.10.2015 (Wednesday)

#### Ambitwistor strings and the scattering equations at one loop

Regular Seminar Lionel Mason (Oxford University)

 at: 13:15 KCLroom S0.13 abstract: Ambitwistor strings are holomorphic string theories whose target space is the space of complex null geoedesics in complexified space-times. 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 1-loop both on a torus and on a nodal Riemann sphere, and perhaps to higher loops.

### 08.10.2013 (Tuesday)

#### TBA

Regular Seminar Lionel Mason (Oxford)

 at: 16:00 City U.room C343 abstract:

### 11.10.2012 (Thursday)

#### Gravity tree amplitudes and twistor-string theory

Regular Seminar Lionel Mason (Oxford)

 at: 14:00 QMWroom 208 abstract: We use an observation of Maldacena to argue that gravity tree-amplitudes can be computed by inserting appropriate wave-functions into the Witten-Berkovits twistor-string for conformal gravity. This is used to motivate and partially explain the recent remarkable twistor-string-like formula of Cachazo & Skinner that expresses the complete tree-level S-matrix for N=8 supergravity in terms of an integral over rational curves in twistor space.

### 28.01.2010 (Thursday)

#### Leading singularities, twistor-strings and grassmannians

Regular Seminar Lionel Mason (Oxford)

 at: 14:00 QMWroom E303 Queens Building abstract: Leading singularities are invariants of multi-loop scattering amplitudes (the full amplitude at tree level) obtained by generalized unitarity. In this talk we show how to construct multi-loop leading singularities on twistor space for maximally super-symmetric Yang-Mills (and gravity). Building on the tree-level twistor-string 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 twistor-string path integral representation for the full loop amplitude. We also show how the construction relates to the Grassmannian representation of leading singularities conjectured by Arkani-Hamed 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.

### 10.05.2007 (Thursday)

#### The twistor programme and twistor strings (From twistor-strings to quantum gravity)

Regular Seminar Lionel Mason (Oxford University)

 at: 13:30 ICroom 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 space-time should emerge. This talk will review the programme, i.e., the early successes in formulating the self-dual parts of Yang-Mills and gravity on twistor space. It will go on to review the impact of twistor-string theory, in giving at least a perturbative approach to full Yang Mills and conformal gravity, and outline arguments that prove the equivalence between the twistor-string models and the space-time theories. Finally, twistor-string models for Einstein gravity will be reviewed.

### 31.10.2005 (Monday)

#### Twistor String Theory

String Theory & Geometry Seminar Lionel Mason (Oxford)

 at: 13:30 ICroom Billiard Room, 58 Princes Gate abstract: