During this century, two great physical theories have emerged. Each theory remains unchallenged within its respective domain.

Introduction to superstrings

Axion hair and dynamical torsion from anomalies

https://cds.cern.ch/record/266050/files/9407078.pdf

Bosonization in higher dimensions

The euclidean path integral remains, in spite of its familiar problems, an important approach to quantum gravity. One of its most striking and obscure features is the appearance of gravitational instantons or wormholes. These renormalize all terms in the Lagrangian and cause a number of puzzles or even deep inconsistencies, related to the possibility of nucleation of "baby universes". In this review, we revisit the early controversies surrounding these issues as well as some of the more recent discussions of the phenomenological relevance of gravitational instantons. In particular, wormholes are expected to break the shift symmetries of axions or Goldstone bosons non-perturbatively. This can be relevant to large-field inflation and connects to arguments made on the basis of the Weak Gravity or Swampland conjectures. It can also affect Goldstone bosons which are of physical interest in the context of the strong CP problem or as dark matter.

/pdf/euclidean-wormholes-baby-universes-and-their-impact-on-x1wvsaouu1.pdf

Euclidean wormholes, baby universes, and their impact on particle physics and cosmology

We define and study projective special para-Kahler manifolds and show that they appear as target manifolds when reducing five-dimensional vector multiplets coupled to supergravity with respect to time. The dimensional reductions with respect to time and space are carried out in a uniform way using an -complex notation. We explain the relation of our formalism to other formalisms of special geometry used in the literature. In the second part of the paper we investigate instanton solutions and their dimensional lifting to black holes. We show that the instanton action, which can be defined after dualising axions into tensor fields, agrees with the ADM mass of the corresponding black hole. The relation between actions via Wick rotation, Hodge dualisation and analytic continuation of axions is discussed.

https://www.math.uni-hamburg.de/home/cortes/0905.2844v1.pdf

Special geometry of Euclidean supersymmetry III: the local r-map, instantons and black holes

Wormholes and duality

Scalar field wormholes

String theory is spacetimes with boundaries is shown to be equivalent, in some instances, to string theory or orbifolds. This equivalence is used to calculate the Casimir energy of the string between two infinite parallel plates in spacetime. The calculation mimics some features of string theory in Rindler and Schwarzschild spacetimes and supports the conjecture that string theories avoid the singularity problem by giving particle production rates that diverge in the presence of large, but finite, fields.

A. Kshirsagar

Papers

Wormholes and duality

Scalar field wormholes

Strings, strong fields and boundaries