Statut  Confirmé 
Série  IPNTHEO 
Domaines  nuclth 
Date  Mercredi 23 Mai 2018 
Heure  11:30 
Institut  IPN 
Salle  Bâtiment 100, Salle A015 
Nom de l'orateur  Werner 
Prenom de l'orateur  F. 
Addresse email de l'orateur  
Institution de l'orateur  Laboratoire Kastler Brossel 
Titre  Can one sum up all Feynman diagrams for the unitary Fermi gas? 
Résumé  The unitary Fermi gas is a textbook model of strongly correlated fermions that accurately describes ultracoldatom experiments and is also relevant to neutron matter [1]. I will present our longterm project on reliable and accurate computation of equilibrium properties of the unitary Fermi gas by systematic summation of Feynman diagrams. Thanks to a diagrammatic Monte Carlo algorithm, we accurately sample all skeleton diagrams (built on dressed singleparticle and pair propagators) up to order $\sim9$. The diagrammatic series is divergent and there is no small parameter so that a resummation method is needed. Previously we used Abelian resummation methods, which are applicable under the assumption that the diagrammatic series has a nonzero radius of convergence; this led to good agreement with experimental data for the equation of state [2] and Tan's contact [3]. In our more recent work [4], we compute analytically the largeorder asymptotics of the diagrammatic series, and find that even though the radius of convergence is actually zero, the series is resummable by a generalised conformalBorel transformation. Our new data for the equation of state and the contact are consistent with the old ones, but the resummation procedure is now mathematically justified and the error bars are significantly smaller. I will also discuss the computational complexity of diagrammatic Monte Carlo algorithms [5], including the new algorithm of [6]. 1] G. C. Strinati, P. Pieri, G. Roepke, P. Schuck, and M. Urban, Physics Reports 1, 738 (2018) [2] K. Van Houcke, F. Werner, E. Kozik, N. Prokof'ev, B. Svistunov, M. Ku, A. Sommer, L. Cheuk, A. Schirotzek, M. Zwierlein, Nature Phys. 8, 366 (2012) [3] K. Van Houcke, F. Werner, E. Kozik, N. Prokof'ev, B. Svistunov, arXiv:1303.6245 [4] R. Rossi, T. Ohgoe, K. Van Houcke, F. Werner, arXiv:1802.07717 [5] R. Rossi, N. Prokof'ev, B. Svistunov, K. Van Houcke, F. Werner, EPL 118, 10004 (2017) [6] R. Rossi, Phys. Rev. Lett. 119, 045701 (2017) 
Numéro de preprint arXiv  
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