# Infinite-dimensional representations of 2-groups

- Responsibility
- John C. Baez ... [et al.].
- Language
- English.
- Imprint
- Providence, R.I. : American Mathematical Society, c2012.
- Physical description
- v, 120 p. : ill ; 26 cm.
- Series
- Memoirs of the American Mathematical Society ; no. 1032.

## Access

## Creators/Contributors

- Contributor
- Baez, John C., 1961-

## Contents/Summary

- Bibliography
- Includes bibliographical references.
- Publisher's Summary
- A "$2$-group" is a category equipped with a multiplication satisfying laws like those of a group. Just as groups have representations on vector spaces, $2$-groups have representations on "$2$-vector spaces", which are categories analogous to vector spaces. Unfortunately, Lie $2$-groups typically have few representations on the finite-dimensional $2$-vector spaces introduced by Kapranov and Voevodsky. For this reason, Crane, Sheppeard and Yetter introduced certain infinite-dimensional $2$-vector spaces called "measurable categories" (since they are closely related to measurable fields of Hilbert spaces), and used these to study infinite-dimensional representations of certain Lie $2$-groups. Here they continue this work. They begin with a detailed study of measurable categories. Then they give a geometrical description of the measurable representations, intertwiners and $2$-intertwiners for any skeletal measurable $2$-group. They study tensor products and direct sums for representations, and various concepts of subrepresentation. They describe direct sums of intertwiners, and sub-intertwiners--features not seen in ordinary group representation theory and study irreducible and indecomposable representations and intertwiners. They also study "irretractable" representations--another feature not seen in ordinary group representation theory. Finally, they argue that measurable categories equipped with some extra structure deserve to be considered "separable $2$-Hilbert spaces", and compare this idea to a tentative definition of $2$-Hilbert spaces as representation categories of commutative von Neumann algebras.

(source: Nielsen Book Data)

## Subjects

## Bibliographic information

- Publication date
- 2012
- Series
- Memoirs of the American Mathematical Society, 0065-9266 ; no. 1032
- Note
- "September 2012, volume 219, number 1032 (end of volume)."
- ISBN
- 9780821872840 (alk. paper)
- 0821872842 (alk. paper)