Hyperconifold Transitions, Mirror Symmetry, and String Theory

TL;DR

This paper explores hyperconifold transitions in Calabi-Yau threefolds, demonstrating their resolutions, mirror symmetry properties, and physical relevance in string theory, leading to new Calabi-Yau examples with exotic features.

Contribution

It introduces hyperconifold transitions for Z_3 and Z_5 cases, analyzes their mirrors, and connects these geometric transitions to string theory physics.

Findings

Hyperconifold resolutions exist for Z_3 and Z_5 cases.

Mirrors of hyperconifold transitions are ordinary conifold transitions.

Hyperconifold transitions are physically consistent in Type IIB string theory.

Abstract

Multiply-connected Calabi-Yau threefolds are of particular interest for both string theorists and mathematicians. Recently it was pointed out that one of the generic degenerations of these spaces (occurring at codimension one in moduli space) is an isolated singularity which is a finite cyclic quotient of the conifold; these were called hyperconifolds. It was also shown that if the order of the quotient group is even, such singular varieties have projective crepant resolutions, which are therefore smooth Calabi-Yau manifolds. The resulting topological transitions were called hyperconifold transitions, and change the fundamental group as well as the Hodge numbers. Here Batyrev's construction of Calabi-Yau hypersurfaces in toric fourfolds is used to demonstrate that certain compact examples containing the remaining hyperconifolds - the Z_3 and Z_5 cases - also have Calabi-Yau resolutions. The mirrors of the resulting transitions are studied and it is found, surprisingly, that they are ordinary conifold transitions. These are the first examples of conifold transitions with mirrors which are more exotic extremal transitions. The new hyperconifold transitions are also used to construct a small number of new Calabi-Yau manifolds, with small Hodge numbers and fundamental group Z_3 or Z_5. Finally, it is demonstrated that a hyperconifold is a physically sensible background in Type IIB string theory. In analogy to the conifold case, non-perturbative dynamics smooth the physical moduli space, such that hyperconifold transitions correspond to non-singular processes in the full theory.