Double Delta Expansions — an Open Problem
According to Bender et al (Phys. Rev. Lett. 58, 2615 (1987)), it is possible to treat coupling constants non-perturbatively, using an ad hoc new parameter δ. Inspiration: The formalism uses parametric differentiation of functional integrals. Question: Could the formalism of functional integrals also provide a similar recipe which would use a doublet of the expansion parameters? Hint: My preliminary, second-order study with δ replaced by (ρ, η) (Phys. Lett. A 164, 145 (1992)).