Deformed Hopfion-Rañada Knots in ModMax Electrodynamics

Abstract: Source-free so-called ModMax theories of nonlinear electrodynamics in the four dimensional Minkowski spacetime vacuum are the only possible continuous deformations -- and as a function of a single real and positive parameter -- of source-free Maxwell linear electrodynamics in the same vacuum, which preserve all the same Poincar\'e and conformal spacetime symmetries as well as the continuous duality invariance of Maxwell's theory. Null field configurations of the latter however, including null electromagnetic knots, are singular for the Lagrangian formulation of any spacetime Poincar\'e and conformal invariant theory of nonlinear electrodynamics. In particular null hopfion-Ra~nada knots are a distinguished and fascinating class on their own of topologically nontrivial solutions to Maxwell's equations. This work addresses the fate of these configurations within ModMax theories. A doubled class of ModMax deformed hopfion-Ra~nada knots is thereby identified, each of which coalescing back in a continuous fashion to the original hopfion-Ra~nada knot when the nonlinear deformation parameter is turned off.