An Orientifold of Type-IIB Theory on $K3$

TL;DR

This paper constructs a new six-dimensional N=1 supersymmetric orientifold of Type-IIB string theory on K3, featuring a specific orientifold symmetry, anomaly cancellation, and gauge group structures.

Contribution

It introduces a novel orientifold of Type-IIB on K3 with detailed analysis of its spectrum, anomaly cancellation, and gauge groups, expanding the landscape of consistent string compactifications.

Findings

Contains nine tensor multiplets and twelve hypermultiplets in the closed-string sector.

Achieves anomaly cancellation via a generalized Green-Schwarz mechanism.

Supports gauge groups SO(16) or U(8)×U(8) depending on moduli.

Abstract

A new orientifold of Type-IIB theory on $K3$ is constructed that has $N=1$ supersymmetry in six dimensions. The orientifold symmetry consists of a $Z_2$ involution of $K3$ combined with orientation-reversal on the worldsheet. The closed-string sector in the resulting theory contains nine tensor multiplets and twelve neutral hypermultiplets in addition to the gravity multiplet, and is anomaly-free by itself. The open-string sector contains only 5-branes and gives rise to maximal gauge groups $SO(16)$ or $U(8)\times U(8)$ at different points in the moduli space. Anomalies are canceled by a generalization of the Green-Schwarz mechanism that involves more than one tensor multiplets.