Seonglae ChoThe simplest model for explaining the accelerating expansion of the universe is the cosmological constant, but it suffers from fine-tuning and coincidence problems, and it is difficult to realize a stable de Sitter vacuum in quantum gravity.
DESI DR2 observations suggest that dark energy may be dynamical—i.e., varying with time. The authors theoretically derive dynamical dark energy from the metastring, an intrinsically non-commutative and T-duality–covariant formulation of string theory, and compare it with the DESI results.
In the metastring framework, in addition to the usual spacetime coordinate , there exists a dual spacetime coordinate , and the two do not commute: , where is a fundamental length scale (of Planck order). Expanding the Tseytlin action to leading order in , the first term from integrating over defines Newton’s constant , while the second term generates a positive cosmological constant (dark energy) from the curvature of dual spacetime . Consequently, the dark-energy density is given by an integral over dual energies : , where is the density of states, is the FRW scale factor, and are -dependent IR/UV cutoffs. From the appendix derivation, the equation-of-state parameter can be written as , where is the dark-energy density parameter.
Assuming dark-energy quanta obey infinite statistics (quantum Boltzmann statistics)—the most general statistics compatible with Lorentz invariance and nonlocality—the density of states is taken to have a Wien form, (with dimensionless constants , and the present-day IR cutoff). Using the naive UV–IR cutoff relations yields for all , which is ruled out by DESI (which prefers ). To address this, introducing the more general relations and (with ) leads to , consistent with DESI.
DESI DR2 observation
2020
2025