On the crossing relation in the presence of defects

Understand

The OPE of local operators in the presence of defect lines is considered both in the rational CFT and the $c>25$ Virasoro (Liouville) theory.

• The duality transformation of the 4-point function with inserted defect operators is explicitly computed.
• The two channels of the correlator reproduce the expectation values of the Wilson and 't Hooft operators, recently discussed in Liouville theory in relation to the AGT conjecture.