Ramsay. He (?) makes it very clear that it's a debut puzzle.
Unusual and very interesting one. I was somehow on the wavelength and quickly wrote in much of the grid, but many parsings are complex (though I fear some may not be to everyone's liking).
Math(s) nerds will enjoy 19d. The Riemann zeta function is a rare guest in cryptics!
Looking forward to more from Ramsay.