# nLab pp-wave spacetime

Contents

### Context

#### Gravity

gravity, supergravity

# Contents

## Idea

A pp-wave spacetime is a spacetime, i.e. an exact solution to Einstein's equations for gravity, containing nothing but radiation (gravitational waves and/or electromagnetic waves) with one fixed wave vector.

The Ricci flat pp-wave spacetimes are examples of universal spacetimes.

## Properties

### As Penrose limits

Every spacetime looks like a pp-wave near a lightlike geodesic. This is called the Penrose limit. (see Blau 11)

### Relation to BMN matrix model

The BMN matrix model (BMN 02, Section 5 and Appendix B) is a deformation of the BFSS matrix model by mass-terms which correspond to a deformation of the Minkowski spacetime background to a pp-wave spacetime.

## References

### pp-Waves as Penrose limits of $AdS_p \times S^q$ spacetimes
• Michael Gutperle, Nicholas Klein, A Penrose limit for type IIB $AdS_6$ solutions (arXiv:2105.10824)