Powerful and deceptive Feynman diagrammatic series

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• Dr Evgeny Kozik, King's College London
• Thursday 22 January 2015, 13:45-15:00
• Theory Library.

If you have a question about this talk, please contact Kevin Ralley.

Diagrammatic Monte Carlo (DiagMC) is a recently introduced approach to correlated fermionic systems based on unbiased stochastic summation of Feynman diagrams to high order. I will discuss the new technique and show how DiagMC can be used to address the Hubbard model on the square lattice in the region of moderate on-site repulsion U -which expresses the thermodynamic grand potential in terms of the interacting single-particle Green’s function G--is at least double valued with a distinct unphysical branch. Although, despite this pathology, the skeleton (bold-line) series in terms of G is found to converge (at least at moderate temperatures), at stronger interactions its convergence is to the unphysical branch, which reveals a new scenario of breaking down of diagrammatic expansions.

This talk is part of the Theoretical Physics Seminars series.

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• Bham Talks
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