Celestial amplitudes and conformal soft theorems. (27th September 2019)

• Record Type: Journal Article
• Authors: Adamo, Tim; Mason, Lionel; Sharma, Atul
• Is Part Of: Classical and quantum gravity. Volume 36:Number 20(2019:Oct.)
• Publication Date: 2019-09-27
• Subjects: scattering amplitudes -- asymptotic symmetries -- ambitwistor strings -- soft theorems; Quantum gravity -- Periodicals; Gravitation -- Periodicals; Relativity (Physics) -- Periodicals; Space and time -- Periodicals; Periodicals; 521.1
• DOI: 10.1088/1361-6382/ab42ce
• Languages: English
• ISSNs: 0264-9381

Abstract

Abstract: Scattering amplitudes in d + 2 dimensions can be expressed in terms of a conformal basis, for which the S-matrix behaves as a CFT correlation function on the celestial d -sphere. We explain how compact expressions for the full tree-level S-matrix of gauge theory, gravity and other QFTs extend to this conformal basis, and are easily derived from ambitwistor strings. Using these formulae and their worldsheet origins, we prove various tree-level 'conformal soft theorems' in gauge theory and gravity in any dimension; these arise from limits where the scaling dimension of an external state in the scattering process takes special values. These conformally soft limits are obscure from standard methods, but they are easily derived with ambitwistor strings. Additionally, we make an identification between the residues of conformally soft vertex operator insertions in ambitwistor strings and charges generating asymptotic symmetries.