Critical interface: Twisting spin glasses at T-c

We consider two identical copies of a finite dimensional spin glass coupled at their boundaries. This allows to identify the analog for a spin glass of twisted boundary conditions in ferromagnetic system and it leads to a definition of an interface free energy that should scale with a positive power of the system size in the spin-glass phase. In this paper we study within mean-field theory the behavior of this interface at the spin-glass critical temperature T-c. We show that the leading scaling of the interface free energy may be obtained by simple scaling arguments using a cubic field theory of critical spin glasses and neglecting the replica symmetry-breaking dependence.