A four-dimensional residue calculus for quaternionic slice regular functions

Abstract

We develop a 4-dimensional residue calculus for quaternionic slice semiregular functions. Its local singularities are isolated real poles and 2-dimensional spheres. For the latter, we introduce a spherical residue and characterize it as a spherical Laurent coefficient, as the sum of two classical residues on any full complex slice, and by a finite differential procedure involving alternating spherical and slice derivatives. The residue theorem expresses a weighted boundary flux on a circular domain as the sum of the real and spherical residues it contains. Beyond this formula, polynomially weighted flux moments recover every coefficient of every finite principal part, including the companion coefficient at a spherical pole, invisible to ordinary residue summation. Once the polar components and order bounds are fixed, the quotient of the real polynomial ring by the global pole polynomial is the finite-dimensional algebra of weights. We prove that the residue pairing is well defined and nondegenerate, and identifies formal principal parts with the full quaternion-valued real dual of this algebra. Hermite interpolation and the Chinese remainder theorem provide global weights selecting each local coefficient. We separate the regularity domain of the function from the geometry of integration: for a smooth noncircular integration domain compactly contained in a circular ambient domain, away from the reals and with boundary disjoint from the polar set, we establish an exact residue formula with an explicit volume correction governed by the Cauchy-Fueter operator. The theory includes higher-order poles, exceptional points, product domains, and zero divisors. Applications give formulas for rational and oscillatory integrals on the imaginary hyperplane and characterize the rational data on the 3-dimensional imaginary subspace of the quaternions admitting a canonical slice regular extension.