Nonperturbative 2D Gravity, Punctured Spheres and $\Theta$-Vacua in String Theories

G. Bonelli, P. A. Marchetti, M. Matone

We consider a model of 2D gravity with the coefficient of the Einstein-Hilbert action having an imaginary part $\pi /2$. This is equivalent to introduce a $\Theta$-vacuum structure in the…