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Researchers at Istanbul Technical University report that an overlooked branch of teleparallel gravity suggests dark energy may have switched from negative to positive about 9.5 billion years ago. Scientists exploring an overlooked branch of an alternative gravity theory suggest dark energy may have switched from negative to positive roughly 9.5 billion years ago. The work, a 2025 study in Physical Review D led by Prof. Özgür Akarsu, revisited teleparallel f(T) gravity, which describes gravity through torsion rather than spacetime curvature. Earlier studies of an exponential form of the theory kept dark energy's density positive, as general relativity assumes. The neglected branch allows negative effective density in the early Universe, which reaches zero at about redshift 1.5, roughly 9.5 billion years ago, before becoming positive. Co-authors include Dr. N. Merve Uzun, Bilal Bulduk, Prof. Nihan Katırcı of Doğuş University and Prof. Antonio De Felice of Kyoto University's Yukawa Institute. The team says the model keeps the six parameters of the standard ΛCDM model and needs no extra adjustable parameter, and its departures from general relativity are suppressed in dense environments, keeping it compatible with Solar System gravity measurements. ScienceDaily reported that the group's earlier sign-switching ΛCDM work agreed with DESI observations and might ease the Hubble tension, the disagreement over the present expansion rate, but lacked a physical mechanism. Akarsu said the sign change arises naturally from the theory itself. The evidence from DESI is not yet strong enough to establish a discovery, so the result remains theoretical.