Analysis of a remarkable singularity in a nonlinear DDE

We investigate the dynamics of the nonlinear DDE (delay-differential equation) d2xdt2(t)+x(t-T)+x(t)3=0, where T is the delay. For T=0, this system is conservative and exhibits no limit cycles. For T>0, no matter how small T is, an infinite number of limit cycles exist, their amplitudes going to infinity in the limit as T approaches zero. We investigate this situation in three ways: (1) harmonic balance, (2) Melnikov's integral, and (3) adding damping to regularize the singularity.