Exponential decay rate applied to the self-exciting kernel each step. Must be in (0, 1).
Excitation amplitude; scales how much each event raises the intensity.
Baseline intensity (the unconditional floor).
https://screamer.readthedocs.io/en/latest/ for the Python reference and full details.
Conditional intensity of an exponential-kernel Hawkes process: lambda_t = mu + kappa_t.