Resolve the lightcone singularity and extend the SO(3,1)-action

Abstract

Papadopoulos showed in 2021: The action of the Lorentz group SO(3,1) on the lightcone of Minkowski space lifts to an SO(3,1)-action on the blow-up of the lightcone. From this, he draws conclusions regarding further hypothetical vacuum states in quantum field theories. The present note shows that the possbility to lift the SO(3,1)-action to the blow-up is a pure mathematical result. It does not depend on the context from physics, in particular it does not make use of the Dirac equation. Instead, it is a simple application of the blow-up theory from algebraic geometry. Lifting is possible because the group action is linear and the exceptional divisor of the blow-up is the projectivized tangent cone.