Complex HVPT and hyperasymptotics

Complex hypervirial perturbation theory (HVPT) is applied to the problem of a harmonic oscillator with a perturbation gx3exp(i), for which the traditional Rayleigh?Schodinger perturbation theory has to be supplemented by hyperasymptotics for obtaining accurate resonance energies in the negative region. Complex HVPT gives accurate results for positive and for negative up to about . The case of a quartic perturbed oscillator is also treated.