MS Seminar (Mathematics - String Theory)

Speaker: Kallol Sen (Kavli IPMU)
Title: Conformal bootstrap in Mellin space
Date: Wed, Sep 21, 2016, 13:15 - 14:30
Place: Seminar Room B
Abstract: We describe in more detail our approach to the conformal bootstrap which uses the Mellin representation of $CFT_d$ four point functions and expands them in terms of crossing symmetric combinations of $AdS_{d+1}$ Witten exchange functions. We consider arbitrary external scalar operators and set up the conditions for consistency with the operator expansion. Namely, we demand cancellation of spurious powers (of the cross ratios, in position space) which translate into spurious poles in Mellin space. We discuss two contexts in which we can immediately apply this method by imposing the simplest set of constraint equations. The first is the $\e$ expansion. We mostly focus on the Wilson-Fisher fixed point as studied in an epsilon expansion about $d=4$. We reproduce Feynman diagram results for operator dimensions to $O(\e^3)$ rather straightforwardly. This approach also yields new analytic predictions for OPE coefficients to the same order which fit rather nicely with recent numerical estimates for the Ising model (at $\e =1$). We will also mention some leading order results for a scalar theory near six dimensions. The second context is a large spin expansion, in any dimension, for a class of operators, where we are able to reproduce and go a bit beyond some of the results recently obtained using the (double) light cone expansion. We also have a preliminary discussion about numerical implementation of the above bootstrap scheme in the absence of a small parameter.