  In the string axiverse scenario, primordial black holes (PBHs) can sustain
non-negligible spin parameters as they evaporate. We show that tracking both
the mass and spin evolution of a PBH in its final hour can yield a purely
gravitational probe of new physics beyond the TeV scale, allowing one to
determine the number of new scalars, fermions, vector bosons, and spin-3/2
particles. Furthermore, we propose a multi-messenger approach to accurately
measure the mass and spin of a PBH from its Hawking photon and neutrino primary
emission spectra, which is independent of putative interactions between the new
degrees of freedom and the Standard Model particles, as well as from the
Earth-PBH distance.
