The intrinsic cohomology ring of the universal compactified Jacobian over the moduli space of stable curves

The purpose of this paper is to study the cohomology rings of universal compactified Jacobians. Over the moduli space Mg of nonsingular curves, we show that the cohomology ring of the universal Jacobian is independent of the degree. Over the moduli space M₆, ₍ of Deligne-Mumford stable marked curves with n 1, on the one hand we show that the cohomology ring of a universal fine compactified Jacobian is sensitive to the choice of a nondegenerate stability condition which answers a question of Pandharipande; on the other hand, we prove that the cohomology ring admits a degeneration via the perverse filtration which is independent of the (nondegenerate) stability condition. The latter defines the intrinsic cohomology ring of the universal compactified Jacobian which only relies on g, n. Our main tools include the support theorems, the recently developed Fourier theory for dualizable abelian fibrations, and the universal double ramification cycle relations associated with the universal Picard stack.