Central charge bounds in 4D conformal field theory

We derive model-independent lower bounds on the stress tensor central charge C_T in terms of the operator content of a 4-dimensional conformal field theory. More precisely, C_T is bounded from below by a universal function of the dimensions of the lowest and second-lowest scalars present in the conformal field theory. The method uses the crossing symmetry constraint of the 4-point function, analyzed by means of the conformal block decomposition.