The Phenomenology of the Dark Dimension and Non-Supersymmetric Strings
Abstract
Swampland principles, combined with the smallness of dark energy Λ, lead to the dark dimension scenario, with one extra dimension of micron size. We review this scenario and its predictions: KK graviton dark matter (or the KK tower of the quintessence field into which the gravitons convert), neutrino masses tied to Λ1/4 via a bulk B−L gauge symmetry, QCD axion decay constant fa∼ Λ1/12∼ 109−1010 GeV at the 5d Planck scale M5, connecting electroweak hierarchy to Λ1/6, and a relation between the GUT and weak scales with M5 as the geometric mean. The dark dimension also provides a concrete realization of an evolving dark sector: the evolution of its diameter correlates the variation of dark energy with that of the dark matter mass, fitting the recent DESI DR2 (+CMB+supernovae) data while avoiding the phantom crossing that the w0waCDM parametrization would suggest---the apparent phantom behavior instead arises from the evolving dark matter mass. The fits suggest that the dark energy field sits in the interior of moduli space, near an unstable critical point. Motivated by this, we review recent progress on non-supersymmetric string vacua: isolated critical points protected by duality symmetries, in non-geometric flux compactifications and in Scherk--Schwarz compactifications of M-theory, and an emerging duality web for non-supersymmetric strings. This note is based on two talks given by the author at String Phenomenology 2026 (Paris) and Strings 2026 (Shanghai).
Related
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- Anomalous Dimensions, Matching, and Phenomenology of Dirac Fermionic Dark Matter Effective Interactions
- Spectral Fractional Bosonic Strings: Exact Polyakov Measure and the Critical Dimension
BibTeX
@misc{vafa2026phenomenology,
title = {{The Phenomenology of the Dark Dimension and Non-Supersymmetric Strings}},
author = {Cumrun Vafa},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.04909},
eprint = {2610.04909},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.04909},
}
RIS
TY - UNPB
TI - The Phenomenology of the Dark Dimension and Non-Supersymmetric Strings
AU - Cumrun Vafa
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.04909
UR - https://arxiv.org/abs/2610.04909
AB - Swampland principles, combined with the smallness of dark energy Λ, lead to the dark dimension scenario, with one extra dimension of micron size. We review this scenario and its predictions: KK graviton dark matter (or the KK tower of the quintessence field into which the gravitons convert), neutrino masses tied to Λ^1/4 via a bulk B−L gauge symmetry, QCD axion decay constant f_a∼ Λ^1/12∼ 10^9−10^10 GeV at the 5d Planck scale M_5, connecting electroweak hierarchy to Λ^1/6, and a relation between the GUT and weak scales with M_5 as the geometric mean. The dark dimension also provides a concrete realization of an evolving dark sector: the evolution of its diameter correlates the variation of dark energy with that of the dark matter mass, fitting the recent DESI DR2 (+CMB+supernovae) data while avoiding the phantom crossing that the w_0w_aCDM parametrization would suggest---the apparent phantom behavior instead arises from the evolving dark matter mass. The fits suggest that the dark energy field sits in the interior of moduli space, near an unstable critical point. Motivated by this, we review recent progress on non-supersymmetric string vacua: isolated critical points protected by duality symmetries, in non-geometric flux compactifications and in Scherk--Schwarz compactifications of M-theory, and an emerging duality web for non-supersymmetric strings. This note is based on two talks given by the author at String Phenomenology 2026 (Paris) and Strings 2026 (Shanghai).
ER -