Dark Energy in Light of the Early JWST Observations: Case for a Negative Cosmological Constant?

Early data from the James Webb Space Telescope (JWST) has uncovered theexistence of a surprisingly abundant population of very massive galaxies atextremely high redshift, which are hard to accommodate within the standardΛCDM cosmology. We explore whether the JWST observations may bepointing towards more complex dynamics in the dark energy (DE) sector.Motivated by the ubiquity of anti-de Sitter vacua in string theory, we considera string-inspired scenario where the DE sector consists of a negativecosmological constant (nCC) and a evolving component with positive energydensity on top, whose equation of state is allowed to cross the phantom divide.We show that such a scenario can drastically alter the growth of structurecompared to ΛCDM, and accommodate the otherwise puzzling JWSTobservations if the dynamical component evolves from the quintessence-likeregime in the past to the phantom regime today: in particular, we demonstratethat the presence of a nCC (which requires a higher density for the evolvingcomponent) plays a crucial role in enhancing the predicted cumulative comovingstellar mass density. Our work reinforces the enormous potential held byobservations of the abundance of high-z galaxies in probing cosmologicalmodels and new fundamental physics, including string-inspired ingredients.