From de Sitter to anti-de Sitter singularity regularization: Theory and phenomenology

Recent investigations of vacuum polarization in extremely compact stars suggest that, in such regimes, the effective matter content of spacetime may acquire a vacuum-energy equation of state with negative energy density, mimicking a negative cosmological constant. Motivated by this observation, we introduce a general algorithm to modify well-known spherically symmetric regular black hole metrics by replacing their usual de Sitter cores (dSC) with Anti-de Sitter cores (AdSC). Like their dSC counterparts, these AdSC solutions may exhibit two, one, or no horizons depending on the value of a regularization parameter l. We present explicit examples of AdSC-Bardeen and AdSC-Dymnikova metrics, analyze their main properties, and investigate some of their phenomenological signatures using test fields. In particular, we compare their fundamental quasinormal modes and echo signals with those of the dSC cases, highlighting potential avenues for distinguishing them observationally.