Orientifolds: The Unique Personality Of Each Spacetime Dimension

TL;DR

This paper reviews recent advances in understanding Z_2 orientifolds across various spacetime dimensions, highlighting their unique physical phenomena, connections to nonperturbative effects, and relationships with M- and F-theory.

Contribution

It provides a comprehensive overview of the dynamics and conceptual aspects of orientifolds in different dimensions, emphasizing their unique features and recent developments.

Findings

Physical phenomena vary across dimensions 10 to 1.

Connections between orientifolds, nonperturbative effects, M- and F-theory.

Insights into orientifold moduli space and gauge symmetry.

Abstract

I review some recent developments in our understanding of the dynamics of Z_2 orientifolds of type IIA and IIB strings and M-theory. Interesting physical phenomena that occur in each spacetime dimension from 10 to 1 are summarized, along with some relationships to nonperturbative effects and to M- and F-theory. The conceptual aspects that are highlighted are: (i) orientifolds of M-theory, (ii) exceptional gauge symmetry from open strings, (iii) certain similarities between branes and orientifold planes. Some comments are also made on disconnected components of orientifold moduli space.