Exponentiation of higher-point and higher-genus Virasoro conformal blocks in the semiclassical limit

A bstract A long-standing conjecture claims that Virasoro conformal blocks exponentiate in the semiclassical limit c → ∞ with h / c finite. However, this has been proven only for four-point blocks on the sphere and one-point blocks on the torus. Here we extend the proof to general conformal blocks for higher-point functions and higher-genus backgrounds in arbitrary channels. The statement is to be understood at the level of a formal power series. Our proof builds upon a novel extension of the oscillator method for the computation of conformal blocks to cases where three internal lines meet at a vertex. This extension also gives a new constructive method to compute global conformal blocks in 2d CFTs at general genus.