  In condensed matter, limited symmetry constraints allow free fermionic
excitations to exist beyond the conventional Weyl and Dirac electrons of
high-energy physics. These excitations carry a higher pseudospin, providing a
natural generalization to the Weyl fermion. How do electrons beyond the
conventional Dirac and Weyl fermions localize under disorder? In this Letter,
we solve the problem of localization of free fermionic excitations carrying an
arbitrary pseudospin-s. We derive exact analytical expressions for fermionic
wavefunctions, scattering time, renormalized velocity, Cooperon, and the
magnetoconductivity. We discover that the gapless Cooperon mode solely depends
on the pseudospin even when Fermi surface is composed of multiple pockets,
leading to weak localization (antilocalization) behavior for even (odd) s.
Remarkably, we find the localization correction to scale exponentially with s,
i.e., faster moving electrons are strongly susceptible to disorder effects.
This opens up intriguing possibility for Anderson localization and many-body
localization in these materials.
