### 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)