Closing the Generation Gap

TL;DR

This paper explores phase transitions in four-dimensional M theory vacua that alter net generation numbers, revealing loopholes that allow chirality changes despite initial obstructions, with implications for string theory topology changes.

Contribution

It introduces new mechanisms for chirality-changing phase transitions in four-dimensional M theory, expanding understanding of topology change and matter generation.

Findings

Demonstrates phase transitions changing net generation numbers.

Identifies loopholes avoiding obstructions to chirality change.

Constructs explicit four-dimensional examples involving wrapped M-theory fivebranes.

Abstract

I describe recent examples of phase transitions in four-dimensional M theory vacua in which the net generation number changes. There are naive obstructions to transitions lifting chiral matter, but loopholes exist which enable us to avoid them. I first review how chirality arises in the heterotic limit of M theory, previously known forms of topology change in string theory, and chirality-changing phase transitions in six dimensions. This leads to the construction of the four-dimensional examples, which involve wrapped M-theory fivebranes at an $E_8$ wall.