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arXiv1993

Where is the large radius limit?

By properly accounting for the invariance of a Calabi-Yau sigma-model under shifts of the $B$-field by integral amounts (analagous to the $θ$-angle in QCD), we show that the moduli spaces of such sigma-models can often be enlarged to include ``large radius limit'' points. In the simplest cases, there are holomorphic coordinates on the enlarged moduli space which vanish at the limit point, and which appear as multipliers in front of instanton contributions to Yukawa couplings. (Those instanton contributions are therefore suppressed at the limit point.) In more complicated cases, the instanton contributions are still suppressed but the enlarged space is singular at the limit point. This singularity may have interesting effects on the effective four-dimensional theory, when the Calabi-Yau is used to compactify the heterotic string.

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arXiv1994

Differential Geometry of Toda Systems

In the present paper we give a differential geometry formulation of the basic dynamical principle of the group--algebraic approach \cite{LeS92} --- the grading condition --- in terms of some holomorphic distributions on flag manifolds associated with the parabolic subgroups of a complex Lie group; and a derivation of the corresponding nonlinear integrable systems, and their general solutions. Moreover, the reality condition for these solutions is introduced. For the case of the simple Lie groups endowed with the canonical gradation, when the systems in question are reduced to the abelian Toda equations, we obtain the generalised Plücker representation for the pseudo--metrics specified by the Kähler metrics on the flag manifolds related to the maximal nonsemisimple parabolic subgroups; and the generalised infinitesimal Plücker formulas for the Ricci curvature tensors of these pseudo--metrics. In accordance with these formulas, the fundamental forms of the pseudo--metrics and the Ricci curvature tensors are expressed directly in terms of the abelian Toda fields, which have here the sense of Kähler potentials.

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arXiv1993

Spacetime Topology Change: The Physics of Calabi-Yau Moduli Space

We review recent work which has significantly sharpened our geometric understanding and interpretation of the moduli space of certain $N$=2 superconformal field theories. This has resolved some important issues in mirror symmetry and has also established that string theory admits physically smooth processes which can result in a change in topology of the spatial universe.

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arXiv1994

Infinite Dimensional Geometry and Quantum Field Theory of Strings. I. Infinite Dimensional Geometry of Second Quantized Free String

There are investigated several objects of an INFINITE DIMENSIONAL GEOMETRY appearing from the second quantization of a free string. The paper contains 2 chapters: 1st is devoted to the infinite dimensional geometry of flag, fundamental and $Π$-spaces for Virasoro-Bott group and its nonassociative deformation defined by Gelfand-Fuchs 3-cocycle (Gelfand-Fuchs loop) as well as of infinite-dimensional non-Euclidean symplectic grassmannian, to the constructions of Verma modules, their models and skladens over Virasoro algebra; an infinite dimensional geometry of the configuration space for the second quantized free string in flat and curved backgrounds as well as author version of Bowick- Rajeev formalism of the separation of internal and external degrees of freedom of a closed string are described in 2nd chapter. In the 1st chapter the main objects are infinite dimensional Lie algebras, groups and loops, homogeneous, Kähler, Finsler, contact and symmetric spaces, complex, real and CR-manifolds, determinant sheaves, manifolds with subsymmetries, polarizations and Fock spaces, bibundles and objects of integral geometry, nonholonomic spaces, deformations of geometric structures and moduli spaces. In the 2nd chapter they are gauge fields, Faddeev-Popov ghosts, Gauss-Manin connections, Kostant-Blattner-Sternberg pairings, BRST-operators.

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arXiv1994

Infinite Dimensional Geometry and Quantum Field Theory of Strings. II. Infinite Dimensional Noncommutative Geometry of a Self-Interacting String Field

A geometric interpretation of quantum self-interacting string field theory is given. Relations between various approaches to the second quantization of an interacting string are described in terms of the geometric quantization. An algorithm to construct a quantum nonperturbative interacting string field theory in the quantum group formalism is proposed. problems of a metric background (in)dependence are discussed.

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arXiv1994

String Theory on K3 Surfaces

The moduli space of N=(4,4) string theories with a K3 target space is determined, establishing in particular that the discrete symmetry group is the full integral orthogonal group of an even unimodular lattice of signature (4,20). The method combines an analysis of the classical theory of K3 moduli spaces with mirror symmetry. A description of the moduli space is also presented from the viewpoint of quantum geometry, and consequences are drawn concerning mirror symmetry for algebraic K3 surfaces.

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arXiv1995

Enumeration of rational curves via torus actions

This paper contains an attempt to formulate rigorously and to check predictions in enumerative geometry of curves following from Mirror Symmetry. The main tool is a new notion of stable map. We give an outline of a contsruction of Gromov-Witten invariants for all algebraic projective or closed symplectic manifolds. Mirror Symmetry in the basic example of rational curves on a quintic 3-folds is reduced to certain complicated but explicit identity. The strategy of computations can be described as follows: 1) we reduce counting problems to questions concerning Chern classes on spaces of curves on the ambient projective space, 2) using Bott's residue formula we pass to the space of (degenerate) curves invariant under the action of the group of diagonal matrices, 3) we get a sum over trees and evaluate it using the technique of Feynman diagrams. Our computation scheme gives ``closed'' formulas for generating functions in topological sigma-model for a wide class of manifolds, covering many Calabi-Yau and Fano varieties.

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arXiv1994

The Role of Solvable Groups in Quantization of Lie Algebras

The elements of the wide class of quantum universal enveloping algebras are prooved to be Hopf algebras $H$ with spectrum $Q(H)$ in the category of groups. Such quantum algebras are quantum groups for simply connected solvable Lie groups $P(H)$. This provides utilities for a new algorithm of constructing quantum algebras especially useful for nonsemisimple ones. The quantization procedure can be carried out over an arbitrary field. The properties of the algorithm are demonstrated on examples.

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arXiv1994

Group-like Structures in Quantum Lie Algebras and the Process of Quantization

For a certain class of Lie bialgebras $(A,A^*)$ the corresponding quantum universal enveloping algebras $U_q(A)$ are prooved to be equivalent to quantum groups Fun$_q(F^*)$, $F^*$ being the factor group for the dual group $G^*$. This property can be used to simplify the process of quantization. The described class appears to be wide enough to contain all the standard quantizations of infinite series. The properties of the groups $F^*$ are explicitly demonstrated for the standard deformations $U_q(SL(n))$. It is shown that for different $A^*$ (remaining in the described class of Lie bialgebras) the same algorithm leads to the nonstandard quantizations.

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arXiv1994

Topics in Hidden Symmetries

These three topics are an attempt to explicate some curiosities of the inverse problem of representation theory (i.e. having a set of operators to describe the "correct" algebraic object, which is represented by them) on simple examples related to the Lie algebra sl(2,C). Such consideration maybe regarded as toy one for analogous infinite dimensional problems in the modern quantum field theory (conformal field theory, integrable models, field theory in non-trivial backgrounds). Some constructions inspired by these topics and related to infinite dimensional hidden symmetries, which are produced by vertex operator fields, will be discussed in the forthcoming article.

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arXiv1994

Mirror Symmetry Constructions: A Review

We review various constructions of mirror symmetry in terms of Landau-Ginzburg orbifolds for arbitrary central charge $c$ and \CY\ hypersurfaces and complete intersections in toric varieties. In particular it is shown how the different techniques are related

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arXiv1995

Lagrangian Formalism Over Graded Algebras

This paper provides a description of an algebraic setting for the Lagrangian formalism over graded algebras and is intended as the necessary first step towards the noncommutative C-spectral sequence (variational bicomplex). A noncommutative version of integration procedure, the notion of adjoint operator, Green's formula, the relation between integral and differential forms, conservation laws, Euler operator, Noether's theorem is considered.

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arXiv1994

Localization of $\frak{u}$-modules. I. Intersection cohomology of real arrangements

This paper is the first in a series. The main goal of the series is to present a geometric construction of certain remarkable tensor categories arising from quantum groups coresponding to the value of deformation parameter $q$ equal to a root of unity. In the present paper we study perverse sheaves over a complex affine space which are smooth along the stratification determined by a finite arrangement of complex affine hyperplanes defined by real equations. In particular, we construct explicitely (in terms of combinatorial data) complexes computing cohomology of Goresky-MacPherson extensions of one-dimensional local systems over the complement of hyperplanes.

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arXiv1994

Local systems over complements of hyperplanes and the Kac-Kazhdan conditions for singular vectors

In this note we strenghten a theorem by Esnault-Schechtman-Viehweg which states that one can compute the cohomology of a complement of hyperplanes in a complex affine space with coefficients in a local system using only logarithmic global differential forms, provided certain "Aomoto non-resonance conditions" for monodromies are fulfilled at some "edges" (intersections of hyperplanes). We prove that it is enough to check these conditions on a smaller subset of edges. We show that for certain known one dimensional local systems over configuration spaces of points in a projective line defined by a root system and a finite set of affine weights (these local systems arise in the geometric study of Knizhnik-Zamolodchikov differential equations), the Aomoto resonance conditions at non-diagonal edges coincide with Kac-Kazhdan conditions of reducibility of Verma modules over affine Lie algebras.

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arXiv1994

Monopoles and Four-Manifolds

Recent developments in the understanding of $N=2$ supersymmetric Yang-Mills theory in four dimensions suggest a new point of view about Donaldson theory of four manifolds: instead of defining four-manifold invariants by counting $SU(2)$ instantons, one can define equivalent four-manifold invariants by counting solutions of a non-linear equation with an abelian gauge group. This is a ``dual'' equation in which the gauge group is the dual of the maximal torus of $SU(2)$. The new viewpoint suggests many new results about the Donaldson invariants.

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arXiv1995

Holomorphic Yang-Mills Theory and Variation of the Donaldson Invariants

We study the path integrals of the holomorphic Yang-Mills theory on compact Kähler surface with $b_2^+ = 1$. Based on the results, we examine the correlation functions of the topological Yang-Mills theory and the corresponding Donaldson invariants as well as their transition formulas.

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arXiv1995

On S-Duality in Abelian Gauge Theory

U(1) gauge theory on ${\bf R}^4$ is known to possess an electric-magnetic duality symmetry that inverts the coupling constant and extends to an action of $SL(2,{\bf Z})$. In this paper, the duality is studied on a general four-manifold and it is shown that the partition function is not a modular-invariant function but transforms as a modular form. This result plays an essential role in determining a new low-energy interaction that arises when N=2 supersymmetric Yang-Mills theory is formulated on a four-manifold; the determination of this interaction gives a new test of the solution of the model and would enter in computations of the Donaldson invariants of four-manifolds with $b_2^+\leq 1$. Certain other aspects of abelian duality, relevant to matters such as the dependence of Donaldson invariants on the second Stieffel-Whitney class, are also analyzed.

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arXiv1995

Thermodynamic Bethe Ansatz and Dilogarithm Identities I

We consider the (A_n,A_1) Y-system arising in the Thermodynamic Bethe Ansatz. We prove the periodicity of solutions of this Y-system conjectured by Al.B. Zamolodchikov, and the dilogarithm identities conjectured by F. Gliozzi and R. Tateo.

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