Equivalence of Geometric h<1/2 and Standard c>25 Approaches to Two-Dimensional Quantum Gravity

We show equivalence between the standard weak coupling regime c>25 of the two-dimensional quantum gravity and regime h<1/2 of the original geometric approach of Polyakov [1,2], developed in [3,4,5].Comment: 10 pages, late

On real projective connections, V.I. Smirnov's approach, and black hole type solutions of the Liouville equation

We consider real projective connections on Riemann surfaces and corresponding solutions of the Liouville equation. It is shown that these solutions have singularities of special type (of a black hole type) on a finite number of simple analytical contours. The case of the Riemann sphere with four real punctures, considered in V.I. Smirnov's thesis (Petrograd, 1918), is analyzed in detail.Comment: 13 pages, final versio

Generating Functional in CFT and Effective Action for Two-Dimensional Quantum Gravity on Higher Genus Riemann Surfaces

We formulate and solve the analog of the universal Conformal Ward Identity for the stress-energy tensor on a compact Riemann surface of genus $g>1$, and present a rigorous invariant formulation of the chiral sector in the induced two-dimensional gravity on higher genus Riemann surfaces. Our construction of the action functional uses various double complexes naturally associated with a Riemann surface, with computations that are quite similar to descent calculations in BRST cohomology theory. We also provide an interpretation for the action functional in terms of the geometry of different fiber spaces over the Teichm\"{u}ller space of compact Riemann surfaces of genus $g>1$.Comment: 38 pages. Latex2e + AmsLatex2.1. One embedded figure. One section on the relation with the geometry of fiber spaces on the Teichmueller space and several important references adde

Generating Functional in CFT on Riemann Surfaces II: Homological Aspects

We revisit and generalize our previous algebraic construction of the chiral effective action for Conformal Field Theory on higher genus Riemann surfaces. We show that the action functional can be obtained by evaluating a certain Deligne cohomology class over the fundamental class of the underlying topological surface. This Deligne class is constructed by applying a descent procedure with respect to a \v{C}ech resolution of any covering map of a Riemann surface. Detailed calculations are presented in the two cases of an ordinary \v{C}ech cover, and of the universal covering map, which was used in our previous approach. We also establish a dictionary that allows to use the same formalism for different covering morphisms. The Deligne cohomology class we obtain depends on a point in the Earle-Eells fibration over the Teichm\"uller space, and on a smooth coboundary for the Schwarzian cocycle associated to the base-point Riemann surface. From it, we obtain a variational characterization of Hubbard's universal family of projective structures, showing that the locus of critical points for the chiral action under fiberwise variation along the Earle-Eells fibration is naturally identified with the universal projective structure.Comment: Latex, xypic, and AMS packages. 53 pages, 1 figur