# nLab duality between type I and heterotic string theory

Contents

### Context

#### Duality in string theory

duality in string theory

general mechanisms

string-fivebrane duality

string-string dualities

M-theory

F-theory

string-QFT duality

QFT-QFT duality:

# Contents

## Idea

one of the dualities in string theory: between type I string theory and heterotic string theory

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## Properties

### Gauge group

For type I string theory on flat target spacetime orientifolds $\mathbb{R}^{9,1}$ RR-field tadpole cancellation requires 32 D-branes to cancel the O-plane charge of -32 (here).

Under the duality between type I and heterotic string theory this translates to the semi-spin gauge group SemiSpin(32) of heterotic string theory.