Found 3 result(s)

02.11.2016 (Wednesday)

Unitarity and positivity constraints for CFT at large N

Triangular Seminar L. Fernando Alday (Oxford)

at:
15:00 IC
room Blackett LT2
abstract:

We consider the four-point correlator of the stress tensor multiplet in N = 4 SYM in the limit of large c=N^2, but finite \lambda=g^2 N. For finite values of \lambda single-trace intermediate operators arise at order 1/c and this leads to specific poles in the Mellin representation of the correlator. The sign of the residue at these poles is fixed by unitarity. We consider solutions consistent with crossing symmetry and this pole structure. We show that in a certain regime all solutions result in a negative contribution to the anomalous dimension of twist four operators. This positivity condition can also be proven by assuming the correct Regge behaviour for the Mellin amplitude. The positivity constraints arising from CFT for the Mellin amplitude take a very similar form to the causality constraint for the forward limit of the S-matrix.

09.10.2013 (Wednesday)

Higher Spin correlators

Triangular Seminar Alday Fernando (Oxford)

at:
15:00 City U.
room AG07
abstract:

I will discuss the three-point correlator of two protected scalar operators and one higher spin twist-two operator in N = 4 SYM, in the limit of large spin. This structure constant can be extracted from the OPE of the four-point correlator of protected scalar operators. Based on the OPE structure, symmetry arguments and intuition from the available perturbative results, it is possible to predict the structure constant at all loops in perturbation theory. Furthermore, this allows also to propose an expression for the all loops four-point correlator in a particular limit.

23.02.2011 (Wednesday)

An OPE for Polygonal null Wilson Loops

Regular Seminar Luis Fernando Alday (Oxford)

at:
13:15 KCL
room 423
abstract: