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We revisit a particular ghost-free bimetric model which is related to bothpartial masslessness (PM) and conformal gravity. Linearly, the model propagatessix instead of seven degrees of freedom not only around de Sitter but alsoaround flat spacetime. Nonlinearly, the equations of motion can be recast inthe form of expansions in powers of curvatures, and exhibit a remarkable amountof structure. In this form, the equations are shown to be invariant underscalar gauge transformations, at least up to six orders in derivatives, thelowest order term being a Weyl scaling of the metrics. The terms attwo-derivative order reproduce the usual PM gauge transformations on de Sitterbackgrounds. At the four-derivative order, a potential obstruction that coulddestroy the symmetry is shown to vanish. This in turn guarantees the gaugeinvariance to at least six-orders in derivatives. This is equivalent to addingup to 10-derivative corrections to conformal gravity. More generally, weoutline a procedure for constructing the gauge transformations order by orderas an expansion in derivatives and comment on the validity and limitations ofthe procedure. We also discuss recent arguments against the existence of a PMgauge symmetry in bimetric theory and show that, at least in their presentform, they are evaded by the model considered here. Finally, we argue that abimetric approach to PM theory is more promising than one based on theexistence of a fundamental PM field.

Extended Weyl Invariance in a Bimetric Model and Partial Masslessness