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Soft Theorems from Conformal Field Theory

Lipstein, A.

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Strominger and collaborators recently proposed that soft theorems for gauge and gravity amplitudes can be interpreted as Ward identities of a 2d CFT at null infinity. In this paper, we will consider a specific realization of this CFT known as ambitwistor string theory, which describes 4d Yang-Mills and gravity with any amount of supersymmetry. Using 4d ambtwistor string theory, we derive soft theorems in the form of an infinite series in the soft momentum which are valid to subleading order in gauge theory and sub-subleading order in gravity. Furthermore, we describe how the algebra of soft limits can be encoded in the braiding of soft vertex operators on the worldsheet and point out a simple relation between soft gluon and soft graviton vertex operators which suggests an interesting connection to color-kinematics duality. Finally, by considering ambitwistor string theory on a genus one worldsheet, we compute the 1-loop correction to the subleading soft graviton theorem due to infrared divergences.


Lipstein, A. (2015). Soft Theorems from Conformal Field Theory. Journal of High Energy Physics, 2015(6), Article 166.

Journal Article Type Article
Acceptance Date Jun 4, 2015
Online Publication Date Jun 24, 2015
Publication Date 2015-06
Deposit Date Dec 30, 2015
Publicly Available Date Mar 29, 2016
Journal Journal of High Energy Physics
Print ISSN 1126-6708
Publisher Scuola Internazionale Superiore di Studi Avanzati (SISSA)
Peer Reviewed Peer Reviewed
Volume 2015
Issue 6
Article Number 166
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