From weak to strong: Constrained extrapolation of perturbation series with applications to dilute Fermi systems

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We develop a method that uses truncation-order-dependent reexpansions constrained by generic strong-coupling information to extrapolate perturbation series to the nonperturbative regime. The method is first benchmarked against a zero-dimensional model field theory and then applied to the dilute Fermi gas in one and three dimensions. Overall, our method significantly outperforms Padé and Borel extrapolations in these examples. The results for the ground-state energy of the three-dimensional Fermi gas are robust with respect to changes in the form of the reexpansion and compare well with quantum Monte Carlo simulations throughout the BCS regime and beyond.