Ambitwistor strings and the scattering equations at one loop
Abstract
Ambitwistor strings are chiral, infinite tension analogues of conventional string theory whose target space is the space of complex null geodesics and whose spectrum consists exclusively of massless states. At genus zero, these strings underpin the CachazoHeYuan formulæ for tree level scattering of gravitons, gluons and scalars. In this paper we extend these formulæ in a number of directions. Firstly, we consider Ramond sector vertex operators and construct simple amplitudes involving spacetime fermions. These agree with tree amplitudes in ten dimensional supergravity and super YangMills. We then show that, after the usual GSO projections, the ambitwistor string partition function is modular invariant. We consider the scattering equations at genus one, and calculate one loop scattering amplitudes for NSNS external states in the Type II ambitwistor string. We conjecture that these give new representations of (the integrand of) one loop supergravity amplitudes and we show that they have the expected behaviour under factorization of the worldsheet in both nonseparating and separating degenerations.
 Publication:

Journal of High Energy Physics
 Pub Date:
 April 2014
 DOI:
 10.1007/JHEP04(2014)104
 arXiv:
 arXiv:1312.3828
 Bibcode:
 2014JHEP...04..104A
 Keywords:

 Scattering Amplitudes;
 Superstrings and Heterotic Strings;
 Supergravity Models;
 Differential and Algebraic Geometry;
 High Energy Physics  Theory
 EPrint:
 34 pages, no figures. v2: improvements to discussion, references updated