Status  Confirmed 
Seminar Series  IPHTHEP 
Subjects  hepph 
Date  Tuesday 12 November 2019 
Time  16:00 
Institute  IPHT 
Seminar Room  Salle Claude Itzykson, Bât. 774 
Speaker's Last Name  Alexander Monin 
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Speaker's Institution  EPFL 
Title  When epsilon expansion goes semiclassical 
Abstract  Even for weakly coupled theories processes with many quanta in general become nonperturbative. In the framework of the standard perturbation theory this fact is related to the factorial growth (with the number of external legs) of the number of Feynman diagrams contributing to the process. Thus, in order to study regimes with many quanta a different approach is needed. I'll present such an approach for $O(2)$ invariant $\lambda \phi^4$ theory at the WilsonFisher fixed point. Namely, using the operatorstate correspondence, valid for conformal field theories, I'll show how anomalous dimensions of operators with arbitrary charge $n$ can be computed as a power series in $\lambda$, by expanding around a nontrivial saddle. The result reproduces both $\lambda n \ll 1$ and $\lambda n \gg 1$ limits amenable to the usual perturbative analysis and the large charge expansion correspondingly. 
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