Mainz 2026 – scientific programme
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A: Fachverband Atomphysik
A 5: Ultracold Matter II – Bosons (joint session Q/A)
A 5.2: Talk
Monday, March 2, 2026, 17:15–17:30, P 2
Weakly interacting Bose gases in the canonical ensemble — •Jonata Santos1, Axel Pelster2, and Arnaldo Gammal1 — 1Universidade de São Paulo, Brazil — 2University of Kaiserslautern-Landau, Germany
Based on the canonical description of a non-interacting Bose gas [1] we work out how both thermodynamic and statistical properties change perturbatively with respect to weak two-particle interactions. Up to first order we obtain a recursion formula for the canonical partition function, which consists of the same Feynman diagrams as the grand-canonical description [2] but with different Feynman rules. Resumming this recursion formula for the canonical partition function allows then to characterize the statistics of the ground-state occupancy by its respective cumulants. We demonstrate the applicability of this approach by analyzing a dilute Bose gas with contact interaction in a box trap. And we compare the results obtained by both periodic and Dirichlet boundary conditions in view of their relevance for current experiments with atomic gases, where the box trap is implemented, for instance, with digital mirror devices. [1] K. Glaum, H. Kleinert, and A. Pelster, Phys. Rev. A 06304 (2007). [2] A. Pelster and K. Glaum, Phys. Stat. Sol. B 237, 72 (2003).
Keywords: Bose gas; canonical ensemble; perturbation theory