Twin Peaks

The on-shell imaginary part of the retarded selfenergy of massive $\vr^4$ theory in 1+1 dimensions is logarithmically infrared divergent. This leads to a zero in the spectral function, separating its usual bump into two. The twin peaks interfere in time-dependent correlation functions, which causes oscillating modulations on top of exponential-like decay, while the usual formulas for the decay rate fail. We see similar modulations in our numerical results for a mean field correlator, using a Hartree ensemble approximation.