Perturbative gauge theory at null infinity

Abstract

Abstract:We describe a theory living on the null conformal boundary I of fourdimensional Minkowski space, whose states include the radiative modes of Yang-Mills theory. The action of a Kac-Moody symmetry algebra on the correlators of these states leads to a Ward identity for asymptotic 'large' gauge transformations which is equivalent to the soft gluon theorem. The subleading soft gluon behavior is also obtained from a Ward identity for charges acting as vector fields on the sphere of null generators of I . Correlation functions of the Yang-Mills states are shown to produce the full classical S-matrix of YangMills theory. The model contains additional states arising from non-unitary gravitational degrees of freedom, indicating a relationship with the twistor-string of Berkovits & Witten.

Burg-Metzner-Sachs symmetry, string theory, and soft theorems

“…In the case of ambitwistor string theory, the appearance of the soft limits is quite well understood already [28][29][30][31]. Some results for the case of gauge theories may be found in [32][33][34][35][36].…”

Celestial amplitudes and conformal soft theorems

“…Thus, they can equally well describe scattering in the conformal basis, leading to CHY formulae for celestial scattering amplitudes. Ambitwistor strings and CHY formulae have been used to study energetic soft limits and their connection to asymptotic symmetries [9,[36][37][38][39][40], so it is no surprise that they are also useful in the conformal basis.…”

New ambitwistor string theories

“…For example, in the case of the critical type II gravity model in 10 dimensions, the ambitwistor model leads to proposals for how the formulae might be extended to loop amplitudes [12][13][14]. They also give new insights into the relationship [15,16] between asymptotic symmetries and soft theorems [17][18][19][20]. Recently, CHY discovered new formulae for a large collection of theories.…”