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We derive model-independent lower bounds on the stress tensor central charge Cₓ in terms of the operator content of a 4-dimensional conformal field theory. More precisely, Cₓ 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.
Rattazzi et al. (Fri,) studied this question.