We study the conformal field theory of the D1/D5 system compactified on X (X is T4 or K3). It is described by a sigma model whose target space is the moduli space of instantons on X. For values of the parameters where the branes can separate, the spectrum of dimensions in the conformal field theory exhibits a continuum above a gap. This continuum leads to a pathology of the conformal field theory, which explains a variety of problems in various systems. In particular, we explain the apparent discrepancy between different methods of finding the spectrum of chiral fields at certain points in the moduli space of the system.

http://cds.cern.ch/record/383066/files/9903224.pdf

The D1/D5 System And Singular CFT

http://cds.cern.ch/record/241379/files/arXiv:hep-th_9210010.pdf

W symmetry in conformal field theory

Worldsheet approach to heterotic instantons and solitons

https://escholarship.org/content/qt9j2016wx/qt9j2016wx.pdf?t=p2at96

Two-dimensional black hole and singularities of CY manifolds

We describe all almost contact metric, almost hermitian and G2-structures admitting a connection with totally skew-symmetric torsion tensor, and prove that there exists at most one such connection. We investigate its torsion form, its Ricci tensor, the Dirac operator and the ∇-parallel spinors. In particular, we obtain solutions of the type II string equations in dimension n = 5,6 and 7.

https://www.intlpress.com/site/pub/files/_fulltext/journals/ajm/2002/0006/0002/AJM-2002-0006-0002-a005.pdf

Parallel spinors and connections with skew-symmetric torsion in string theory

Superconformal algebras in two dimensions with N=4

Extended supersymmetric σ-Models on group manifolds (I). The complex structures

Extended supersymmetric σ-models on group manifolds (II). Current algebras

Complex structures on parallelised group manifolds and supersymmetric σ-models

We investigate the general algebras which contain the two-dimensional conformal algebra (Virasoro algebra) and N fermionic generators. We demand that the latter are of the "Neveu-Schwarz type". String theories are known with N = 2 and N = 4 extensions. We show under which assumptions these are unique. We construct all possible N = 2 algebras, containing the previously known ones. General conditions are given for extensions to arbitrary N, and special examples are worked out.

A. Sevrin

Papers

Superconformal algebras in two dimensions with N=4

Extended supersymmetric σ-Models on group manifolds (I). The complex structures

Extended supersymmetric σ-models on group manifolds (II). Current algebras

Complex structures on parallelised group manifolds and supersymmetric σ-models

Infinite dimensional extended superconformal lie algebras