second derivative of H_{x,t} is exactly the probability density function of S_t
I’m not sure if I understood this part correctly, but I’d suggest to think of your problem from a generative perspective:
- You assume that there’s some timeseries S_t - how would you model just this part? Gaussian Process, Random Walk…
- from this timeseries, you can calculate another (plus unknown constant C_1)
- from this timeseries, you can then calculate H_{x,t} (again plus unknown constant C_2)
- finally create a likelihood function that compares H_{x,t} with data