Abstract

We study the duality between four-dimensional N=2 compactifications of heterotic and type IIA string theories. Via adiabatic fibration of the duality in six dimensions, type IIA string theory compactified on a K3-fibred Calabi-Yau threefold has a potential heterotic dual compactification. This adiabatic picture fails whenever the K3 fibre degenerates into multiple components over points in the base of the fibration. Guided by monodromy, we identify such degenerate K3 fibres as solitons generalizing the NS5-brane in heterotic string theory. The theory of degenerations of K3 surfaces can then be used to find which solitons can be present on the heterotic side. Similar to small instanton transitions, these solitons escort singular transitions between different Calabi-Yau threefolds. Starting from well-known examples of heterotic--type IIA duality, such transitions can take us to type IIA compactifications with unknown heterotic duals.

Highlights

  • This adiabatic picture fails whenever the K3 fibre degenerates into multiple components over points in the base of the fibration. We identify such degenerate K3 fibres as solitons generalizing the NS5-brane in heterotic string theory

  • The duality between heterotic string theory and Type II string theories hints at non-trivial relations between seemingly totally unrelated mathematical objects

  • Heterotic string compactifications involve gauge field moduli, whereas only the compactification geometry must be specified for Type II compactifications

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Summary

Introduction

The duality between heterotic string theory and Type II string theories hints at non-trivial relations between seemingly totally unrelated mathematical objects. Starting with the heterotic-type IIA duality in six dimensions, the key principle in understanding the correspondence of discrete data is the idea of adiabatically fibering the dual six dimensional theories over a base P1 [4,5,6]. Armed with this principle, the problem of discrete data correspondence roughly splits into two fronts. We refer to [9] for definitions and explanations concerning the methods of toric geometry used in this article

A quick review
Examples of algebraic K3 surfaces
Choices of lattice-polarized K3 fibration and duality
Discrete choices in K3 fibrations
Duality dictionary in a case study: degree-2 K3 in the fibre
Degenerations of K3 surfaces and soliton solutions
Corridor branches and reducible fibres
Warm-up
Corridor branches among models with a degree-2 K3 surface
More transitions and degenerate fibres
Branches with type III or non-Kulikov degenerations
Heterotic string interpretation
Recap and speculations
Analogy and difference to 7-branes in F-theory
A K3-fibred Calabi-Yau threefolds as toric hypersurfaces
Geometry of generic fibres
Singular fibres
Hodge numbers of divisors of a Calabi-Yau threefold
B Mathematics of degenerations of K3 surfaces
Degenerations of K3 surfaces
Monodromy action
Baily-Borel compactification
C Picard-Lefschetz monodromy and collapsing dP7

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