Anomaly cancellation in K3 orientifolds

TL;DR

This paper analyzes anomaly cancellation mechanisms in six-dimensional Type IIB Z_N orientifolds, focusing on the Green-Schwarz process involving RR tensors and scalars, and explores related phenomena like gauge symmetry breaking and tensionless strings.

Contribution

It provides a detailed string theory computation of anomaly inflow and the associated couplings, elucidating the role of RR fields and supersymmetry in anomaly cancellation in K3 orientifolds.

Findings

Explicit anomaly inflow calculations from string theory.

Identification of RR couplings responsible for anomaly cancellation.

Discussion of tensionless strings when couplings diverge.

Abstract

We study in detail the pattern of anomaly cancellation in D=6 Type IIB Z_N orientifolds, occurring through a generalized Green-Schwarz mechanism involving several RR antisymmetric tensors and scalars fields. The starting point is a direct string theory computation of the inflow of anomaly arising from magnetic interaction of D-branes, O-planes and fixed-points, which are encoded in topological one-loop partition functions in the RR odd spin-structure. All the RR anomalous couplings of these objects are then obtained by factorization. They are responsible for a spontaneous breaking of U(1) factors through a Higgs mechanism involving the corresponding hypermultiplets. Some of them are also related by supersymmetry to gauge couplings involving the NSNS scalars sitting in the tensor multiplets. We also comment on the possible occurrence of tensionless strings when these couplings diverge.