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Q: Fachverband Quantenoptik und Photonik

Q 20: Quantum Gases I

Q 20.3: Poster

Tuesday, March 15, 2022, 16:30–18:30, P

Wilsonian Renormalization in the Symmetry-Broken Polar Phase of a Spin-1 Bose Gas — •Niklas Rasch, Aleksandr Mikheev, and Thomas Gasenzer — Kirchhoff-Institut für Physik, Universität Heidelberg, Germany

Wilsonian renormalization group theory (WRG) is applied to the spin-1 Bose gas both in the thermal and in the symmetry-broken polar phase. WRG is employed in a 1-loop perturbative expansion. In the thermal phase all relevant flow equations are derived and analysed for their fixed-point behaviour and critical exponents. To describe the thermal phase transition, the symmetry is broken explicitly and flow equations in the polar phase are computed including the renormalization of the condensate density. A general scheme is established for investigating the flow equations in a cut-off independent manner at fixed macroscopic density. We find cut-off independent critical temperatures as well as the decrease in condensate density towards criticality and predictions for the condensate depletion. Nevertheless, anomalous scaling is observed in most couplings impeding convergence and physical predictions. This is overcome by introducing anomalous couplings for the temporal and spatial derivatives for which additional flow equations are derived. Including them leads to the disappearance of cut-off dependencies and predictions for all couplings.