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# Rethinking Quantum Field Theory

Sep 27 – 30, 2016
DESY Hamburg
Europe/Berlin timezone

## Large-Charge Perturbation Theory

Sep 29, 2016, 2:00 PM
15m
Seminar room 1 (DESY Hamburg)

### Seminar room 1

#### DESY Hamburg

Notkestrasse 85, 22607 Hamburg
String & Mathematical Physics

### Speaker

Mr Orestis Loukas (University of Bern)

### Description

I will introduce the basic concepts of Large-Charge Perturbation Theory (LCPT) in d+1 space-time dimensions. Given a Quantum Field Theory with a globally conserved charge Q, LCPT aims at providing analytic insight to sectors, which remain inaccessible via ordinary perturbative methods, but where Q is assumed to be large. To this end, the scalar O(2) model with $\phi^N$ self-interaction will be implemented as a toy-example. I will construct the large-charge vacuum of this theory as a generalized coherent state and derive its effective potential at fixed (and large) charge Q. Subsequently, we shall investigate the perturbative treatment of fluctuations around the large-Q vacuum proving the existence of a consistent “1/Q-expansion”.

### Primary author

Mr Orestis Loukas (University of Bern)

### Co-authors

Dr Domenico Orlando (University of Bern) Dr Luis Álvarez-Gaumé (CERN) Dr Susanne Reffert (University of Bern)

 Slides