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Theoretical and Observational Approaches to the Hubble Tension in Cosmology
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Theoretical and Observational Approaches to the Hubble Tension in Cosmology

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: 30 September 2026 | Viewed by 6379

Special Issue Editors

Dr. Indranil Banik

E-Mail Website
Guest Editor
Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX, UK
Interests: cosmology; galactic dynamics; milgromian dynamics
Dr. Harry Desmond

E-Mail Website
Guest Editor
Institute of Cosmology and Gravitation, University of Portsmouth, Dennis Sciama Building, Burnaby Road, Portsmouth PO1 3FX, UK
Interests: cosmology; galaxy formation; distance ladder; modified gravity

Special Issue Information

Dear Colleagues,

Cosmology is currently in a crisis known as the Hubble tension, where the redshifts of extragalactic objects increase with distance about 10% faster than expected in the standard cosmological model (ΛCDM) with parameters calibrated to fit the pattern of anisotropies in the cosmic microwave background (CMB). This Special Issue aims to provide a platform for researchers to share the latest updates on theoretical and observational approaches to the Hubble tension, especially including researchers who present their work at the related parallel session of the National Astronomy Meeting 2025 in Durham, UK (https://conference.astro.dur.ac.uk/event/7/program). Recent observational advances allow distances to be measured in several ways beyond the traditional route using supernovae calibrated by the Leavitt law of Cepheid variable stars, a technique which has continued to see steady improvements in precision and more thorough cross-checks for systematics. The cosmic expansion history can also be constrained using, e.g., baryon acoustic oscillations (BAOs) as standard rulers and stellar populations as cosmic clocks. This latter approach has made significant strides in recent years, both using the absolute ages of galactic stars as a lower limit on the cosmic age, and using the differential ages of stars in passive galaxies at two different redshifts to estimate the time difference between those redshifts. An important aim of this Special Issue is to exploit the increasing sensitivity of various techniques to give readers an idea of which ones actually show a tension with the ΛCDM. This will give a deeper insight into the origin of the Hubble tension. Various proposals have been put forward, for instance, that distances are underestimated in the local Universe, or that the expansion rate is genuinely faster than expected. This would normally invalidate fits to the CMB anisotropies, but new physics prior to recombination could potentially avoid this issue. The expansion history can also be modified at late times, perhaps due to a changing dark energy density—as hinted at by some observations. The solution might even preserve the standard ΛCDM expansion history at all epochs, but involve redshifts being inflated in the nearby Universe by a large local void, merely giving the illusion of a Hubble tension. This Special Issue provides an opportunity to discuss the latest refinements to these approaches and a clearer assessment of their viability in light of observational advances. In this respect, we particularly welcome contributions that combine the latest evidence to argue against previously proposed solutions that may have been viable until recently.

Dr. Indranil Banik
Dr. Harry Desmond
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1500 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • cosmology
  • distance scale
  • supernovae
  • galaxies
  • variable stars
  • stellar populations
  • recombination

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Published Papers (4 papers)

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40 pages, 2191 KB  
Article
Comparing Measures of the Hubble and BAO Tensions in ΛCDM and Possible Solutions in f(Q) Gravity
by José Antonio Nájera, Indranil Banik, Harry Desmond and Vasileios Kalaitzidis
Galaxies 2026, 14(2), 19; https://doi.org/10.3390/galaxies14020019 - 9 Mar 2026
Viewed by 1170
Abstract
We test whether f(Q) symmetric teleparallel gravity theories can solve the Hubble tension consistently with DESI DR2 BAO. We consider three f(Q) functional forms: logarithmic, exponential, and hyperbolic tangent. We extend these models by allowing a cosmological [...] Read more.
We test whether f(Q) symmetric teleparallel gravity theories can solve the Hubble tension consistently with DESI DR2 BAO. We consider three f(Q) functional forms: logarithmic, exponential, and hyperbolic tangent. We extend these models by allowing a cosmological constant, and compare to phenomenological models with a flexible exponential, hyperbolic secant, and polynomial decay addition to the standard ΛCDM H(z). We test these models against DESI DR2 BAO, CMB (Planck 2018 + SPT-3G + ACT DR6), local H0, and Cosmic Chronometer data. The logarithmic and hyperbolic tangent f(Q) models do not provide an adequate solution, but the exponential model does. Furthermore, it slightly reduces the (Ωm,H0rd) parameter space tension between CMB and BAO datasets to 2.56σ, down from 2.65σ for ΛCDM. Although ΛCDM faces only 1.66σ tension in DESI data space, the 1σ higher tension in parameter space suggests a real anomaly. The models assisted by the cosmological constant perform slightly better still, at the cost of undermined theoretical motivation. They also perform poorly once local H0 measurements are included. The phenomenological models fit all data reasonably well, yet the best-fitting models predict isotropically averaged BAO distances exceeding the DESI DR2 measurements at all redshifts. This highlights the difficulties of finding a theoretically motivated solution to the Hubble tension while remaining consistent with BAO data. Full article
(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)
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36 pages, 1121 KB  
Article
A Common Origin of the H0 and S8 Cosmological Tensions and a Resolution Within a Modified ΛCDM Framework
by Dimitris M. Christodoulou, Demosthenes Kazanas and Silas G. T. Laycock
Galaxies 2026, 14(2), 16; https://doi.org/10.3390/galaxies14020016 - 27 Feb 2026
Cited by 1 | Viewed by 1262 | Correction
Abstract
The two most severe cosmological tensions in the Hubble constant H0 and the matter clustering amplitude S8 have the same relative discrepancy of 8.3%, which suggests that they may have a common origin. Modifications of gravity and exotic dark fields with [...] Read more.
The two most severe cosmological tensions in the Hubble constant H0 and the matter clustering amplitude S8 have the same relative discrepancy of 8.3%, which suggests that they may have a common origin. Modifications of gravity and exotic dark fields with numerous free parameters introduced in the Einstein field equations often struggle to simultaneously alleviate both tensions; thus, we need to look for a common cause within the standard ΛCDM framework. At the same time, linear perturbation analyses of matter in the expanding ΛCDM universe have always neglected the impact of comoving peculiar velocities v (generally thought to be a second-order effect), the same velocities that, in physical space, cannot be fully accounted for in the observed late-time universe when the cosmic distance ladder is used to determine the local value of H0. We have reworked the linear density perturbation equations in the conformal Newtonian gauge (sub-horizon limit) by introducing an additional drag force per unit mass −Γ(t)v in the Euler equation with Γ≡γ(2H), where γ≪1 is a positive dimensionless constant and 2H(t) is the time-dependent Hubble friction. We find that a damping parameter of γ=0.083 is sufficient to resolve the S8 tension by suppressing the growth of structure at low redshifts, starting at z★≃3.5–6.5 to achieve S8≃0.78–0.76, respectively. Furthermore, we argue that the physical source causing this additional friction (a tidal field generated by nonlinear structures in the late-time universe) is also responsible for a systematic error in the local determinations of H0—the inability to subtract peculiar tidal velocities along the lines of sight when determining the Hubble flow via the cosmic distance ladder. Finally, the dual action of the tidal field on the expanding background—reducing both the matter and the dark energy sources of the squared Hubble rate H2, thereby holding back the cosmic acceleration a¨—is of fundamental importance in resolving cosmological tensions and can also substantially alleviate the density coincidence problem. Full article
(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)
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10 pages, 703 KB  
Article
On the Analysis Dependence of DESI Dynamical Dark Energy
by Eoin Ó Colgáin, Saeed Pourojaghi and M. M. Sheikh-Jabbari
Galaxies 2025, 13(6), 133; https://doi.org/10.3390/galaxies13060133 - 9 Dec 2025
Cited by 2 | Viewed by 1516
Abstract
We continue scientific scrutiny of the DESI dynamical dark energy (DE) claim by explicitly demonstrating that the result depends on the analysis pipeline. Concretely, we define a likelihood that converts the w0waCDM model back into the (flat) ΛCDM [...] Read more.
We continue scientific scrutiny of the DESI dynamical dark energy (DE) claim by explicitly demonstrating that the result depends on the analysis pipeline. Concretely, we define a likelihood that converts the w0waCDM model back into the (flat) ΛCDM model, which we fit to DESI constraints on the ΛCDM model from DR1 Full-Shape (FS) modeling and BAO. We further incorporate CMB constraints. Throughout, we find that w0 and wa are within 1σ of the ΛCDM model. Our work makes it explicit that, in contrast to DR1 and DR2 BAO, there is no dynamical DE signal in FS modeling, even when combined with BAO and CMB. Moreover, one confirms late-time accelerated expansion today (q0<0) at ≳3.4σ in FS modeling + BAO. On the contrary, DR1 and DR2 BAO fail to confirm q0<0 under similar assumptions. Our analysis highlights the fact that trustable scientific results should be independent of the analysis pipeline. Full article
(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)
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2 pages, 186 KB  
Correction
Correction: Christodoulou et al. A Common Origin of the H0 and S8 Cosmological Tensions and a Resolution Within a Modified ΛCDM Framework. Galaxies 2026, 14, 16
by Dimitris M. Christodoulou, Demosthenes Kazanas and Silas G. T. Laycock
Galaxies 2026, 14(2), 25; https://doi.org/10.3390/galaxies14020025 - 20 Mar 2026
Viewed by 510
Abstract
In the original publication [...] Full article
(This article belongs to the Special Issue Theoretical and Observational Approaches to the Hubble Tension in Cosmology)
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