# An introduction to decomposition

- Institution: CERN
- Department: TH String Theory Seminar
- Speaker: Eric Sharpe
- Year: 2022
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3008825)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

In this talk I will review work on 'decomposition,' a property of 2d theories with 1-form symmetries and, more generally, d-dim'l theories with (d-1)-form symmetries. Decomposition is the observation that such quantum field theories are equivalent to ('decompose into') disjoint unions of other QFTs, known in this context as "universes."

Examples include two-dimensional gauge theories and orbifolds with matter invariant under a subgroup of the gauge group. Decomposition explains and relates several physical properties of these theories -- for example, restrictions on allowed instantons arise as a "multiverse interference effect" between contributions from constituent universes.

First worked out in 2006 as part of efforts to understand string propagation on stacks, decomposition has been the driver of a number of developments since. In the first half of this talk, I will review decomposition; in the second half, I will focus on the recent application to anomaly resolution of Wang-Wen-Witten in two-dimensional orbifolds.

String Seminars: https://cern.zoom.us/j/61053603623?pwd=THhlNnU4ZXljQjFxMjVwQlVxVHdQZz09.

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## Lectures

1. [An introduction to decomposition](https://invisiblenetwork.ai/learn/cern/3008825/32d7986327b1), 1 h 12 min (CERN's player)