PM1⁄4EM? Partially massless duality invariance

is almost coeval with Maxwell’s equations themselves, although a proof of its validity awaited over a century [1,2]. In addition to countless generalizations of ‘‘duality’’ in field and string theory, it has led to an enormous variety of more precise analogs, in particular to spin 2 [2,3], then to all free massless (integer or half-integer) spin s > 0 systems in flat space [4,5]. In de Sitter (dS) space, electromagnetic (EM) interactions can be mediated by generalized Maxwell systems [9]. These are the maximal depth partially massless (PM) fields of Refs. [10,11] which enjoy many characteristics of EM such as lightlike propagation [12], gauge invariance [11], conformal invariance [13] and stability [14]. Unlike EM, these particular PM models describe higher spin s propagating helicities s; . . . ; 1 [11]. Here we show that they are invariant under Maxwellian duality rotations, whence our title.