Quintessential implications of the presence of AdS in the dark energy sector

We explore the implications for an Anti-de Sitter (AdS) vacuum, equivalently a negative cosmological constant (nCC), in the dark energy (DE) sector using current cosmological observations. Our joint analysis uses DESI BAO, DESY5 supernovae, and P-ACT CMB (ACT-DR6 + Planck) measurements. We also use the KiDS weak-lensing measurement to cross-check consistency with the inferred value of $S_{8}$. Within the Chevallier--Polarski--Linder parametrization for the evolving component of the DE, the inclusion of an AdS term provides a theoretically motivated mechanism that opens up a finite non-phantom region in the CPL parameter space while remaining compatible with current observations. A negative cosmological constant also implies a finite cosmic lifetime, thereby linking observational DE phenomenology to broader questions in quantum gravity and string theory.