Unified dark sector and Hubble-tension alleviation in scalar–vector–tensor gravity
6 affiliations
- 1State University of Tetovo
- 2Shiraz University
- 3University of Malta
- 4National Observatory of Athens
- 5Universidad Católica del Norte
- 6University of Science and Technology of China
Abstract
We investigate a scalar–vector–tensor theory in which matter is minimally coupled to a Jordan-frame metric g̃μ ν =(1+Ξ )gμ ν g ~ μ ν = ( 1 + Ξ ) g μ ν , while a massive vector sector interacts with the baryonic current. We show that the conformal scalar coupling modifies the physical expansion rate measured by matter observers, leading to an enhancement of the Hubble constant inferred at low redshift. We stress, however, that the Hubble rate is not a conformal invariant, whereas the acoustic angular scale θ s θ s is, and we derive the exact integral condition that the scalar field evolution must satisfy. We show that a single-signed scalar velocity cannot satisfy it, and we construct instead a two-epoch phenomenological evolution which matches θ s θ s exactly while retaining the late-time enhancement, at the cost of a small pre-recombination shift of the effective gravitational coupling. We stress that the scalar is not separately conserved, and that retaining the scalar–matter energy exchange in its continuity equation supplies a further restriction: positivity of the scalar energy density bounds the early component to zE≲ 13 z E ≲ 13 . Notably, the recombination temperature is unmodified, since particle masses are constant in the Jordan frame, only the expansion rate at that epoch being altered. The scalar potential naturally acts as a dynamical dark-energy sector, while the vector sector provides two distinct contributions. The temporal component, determined algebraically by the baryon current, yields an apparent matter-like term in the background expansion that is not a true fluid but rather a manifestation of the interaction energy. The propagating spatial modes, on the other hand, form a vector condensate that behaves as a collisionless pressureless component and can play the cosmological role of cold dark matter. Hence, the framework connects scalar dynamics, effective dark-energy evolution, and the H0 H 0 tension within a single setup. Finally, local gravitational constraints require a chameleon-type screening mechanism, whose efficiency we discuss critically.
Versions
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BibTeX
@article{jusufi2026unified,
title = {{Unified dark sector and Hubble-tension alleviation in scalar–vector–tensor gravity}},
author = {Kimet Jusufi and Amir A. Khodahami and Ahmad Sheykhi and Jackson Levi Said and Emmanuel N. Saridakis},
journal = {The European Physical Journal C},
year = {2026},
month = oct,
doi = {10.1140/epjc/s10052-026-16406-4},
url = {https://link.springer.com/10.1140/epjc/s10052-026-16406-4},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Unified dark sector and Hubble-tension alleviation in scalar–vector–tensor gravity
AU - Kimet Jusufi
AU - Amir A. Khodahami
AU - Ahmad Sheykhi
AU - Jackson Levi Said
AU - Emmanuel N. Saridakis
PY - 2026
DA - 2026/10/07
JO - The European Physical Journal C
DO - 10.1140/epjc/s10052-026-16406-4
UR - https://link.springer.com/10.1140/epjc/s10052-026-16406-4
AB - We investigate a scalar–vector–tensor theory in which matter is minimally coupled to a Jordan-frame metric g̃_μ ν =(1+Ξ )g_μ ν g ~ μ ν = ( 1 + Ξ ) g μ ν , while a massive vector sector interacts with the baryonic current. We show that the conformal scalar coupling modifies the physical expansion rate measured by matter observers, leading to an enhancement of the Hubble constant inferred at low redshift. We stress, however, that the Hubble rate is not a conformal invariant, whereas the acoustic angular scale θ _s θ s is, and we derive the exact integral condition that the scalar field evolution must satisfy. We show that a single-signed scalar velocity cannot satisfy it, and we construct instead a two-epoch phenomenological evolution which matches θ _s θ s exactly while retaining the late-time enhancement, at the cost of a small pre-recombination shift of the effective gravitational coupling. We stress that the scalar is not separately conserved, and that retaining the scalar–matter energy exchange in its continuity equation supplies a further restriction: positivity of the scalar energy density bounds the early component to z_E≲ 13 z E ≲ 13 . Notably, the recombination temperature is unmodified, since particle masses are constant in the Jordan frame, only the expansion rate at that epoch being altered. The scalar potential naturally acts as a dynamical dark-energy sector, while the vector sector provides two distinct contributions. The temporal component, determined algebraically by the baryon current, yields an apparent matter-like term in the background expansion that is not a true fluid but rather a manifestation of the interaction energy. The propagating spatial modes, on the other hand, form a vector condensate that behaves as a collisionless pressureless component and can play the cosmological role of cold dark matter. Hence, the framework connects scalar dynamics, effective dark-energy evolution, and the H_0 H 0 tension within a single setup. Finally, local gravitational constraints require a chameleon-type screening mechanism, whose efficiency we discuss critically.
SN - 1434-6044
SN - 1434-6052
ER -