Description
Organisers: Indranil Banik, Harry Desmond, Eleonora Di Valentino, Tom Shanks
Cosmology is currently in a crisis due to the Hubble tension, the observation that redshift rises about 10% faster with distance than predicted in ฮCDM with parameters calibrated to fit the CMB anisotropies. This session would bring together researchers working on various aspects of the Hubble tension. Recent observational advances allow distances to be measured in several ways beyond the traditional route using the Leavitt law and supernovae, while precise CMB results can now be obtained without Planck data. Besides the CMB, cosmological constraints have recently been provided by novel probes such as the dispersion measure of fast radio bursts, cosmic chronometers, and accurate estimates of the age of the Universe from the oldest stars. Proposed solutions to the Hubble tension either argue that distances in the nearby Universe have been systematically underestimated, raise the present expansion rate at the background level, or assign the steep local redshift gradient to peculiar velocities, as would arise from outflows due to a large local void โ as indeed suggested by galaxy number counts and bulk flows. Solutions at the background level can modify the sound horizon at recombination, as done by early dark energy models. Or they can involve a late-time modification, possibly due to the dark energy density changing with time. This is actually suggested by the latest baryon acoustic oscillation data. The proposed parallel session would allow especially early career researchers working on these and other aspects of the Hubble tension to present their work and learn from each other.
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09/07/2025, 14:15Theoretical and observational approaches to the Hubble tensionTalk
A promising explanation for the Hubble tension is that we live near the centre of a large local underdensity or void. This is suggested by observations of source number counts across the whole electromagnetic spectrum, with near-infrared results implying that the density is about 20% below average out to 300 Mpc across 90% of the sky and most of the galaxy luminosity function (ApJ, 775, 62)....
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09/07/2025, 14:33Theoretical and observational approaches to the Hubble tensionTalk
There have been several studies investigating the cosmological implications of the Hubble tension, both in terms of the impact on early and late universe physics. I will summarise some of our previous work on investigating late-time solution with the first simultaneous analysis of local and high-redshift Type Ia supernovae and exploring a wide range of exotic cosmological solutions. In this...
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09/07/2025, 14:51Theoretical and observational approaches to the Hubble tensionTalk
An alternative approach to resolving the Hubble tension that relies on minimal assumptions of cosmology and does not propagate the uncertainty associated with calibrations of the distance ladder is based on the relationship between the Hubble parameter $H(z)$ and the differential age-redshift relation. This relationship allows us to quantify the expansion between two coevolving populations of...
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09/07/2025, 15:09Theoretical and observational approaches to the Hubble tensionTalk
The Hubble tension is a significant (~4 sigma) discrepancy between the universe's expansion rate measured from supernovae and the rate predicted by the standard ฮCDM cosmological model based on CMB observations. Inspired by this tension, more detailed analyses of late-universe data have also revealed possible large-scale variation in the redshiftโdistance relationship across the sky, based on...
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09/07/2025, 15:27Theoretical and observational approaches to the Hubble tensionTalk
Perhaps the most pressing problem in current cosmology is the cause of the Hubble tension. We revisit a two-rung distance ladder, composed only of Cepheid periods and magnitudes, anchor distances in the Milky Way, Large Magellanic Cloud and NGC 4258, and host galaxy redshifts. Following Kenworthy et al. 2022, for the most accurate and up-to-date measurements, we adopt the SH0ES data, where the...
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Theoretical and observational approaches to the Hubble tensionPoster
As cosmological measurements become increasingly precise, tensions and discrepancies are emerging between different observables. One of the most prominent is the disagreement between measurements of the Hubble constant ($H_0$) from early Universe data, such as the Cosmic Microwave Background (CMB), and late Universe measurements, particularly from the Local Distance Ladder (LDL). A wide range...
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Enrico Specogna (University of Sheffield)Theoretical and observational approaches to the Hubble tensionPoster
In this work we reflect on the departure from the standard growth of structures induced by two seemingly different, yet comparable extensions to the standard cosmological model: modified gravity and massive neutrinos. Can current Cosmic Microwave Background anisotropy and lensing data tell the difference between a phenomenological modification in the growth of the large-scale structure,...
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Theoretical and observational approaches to the Hubble tensionPoster
Cosmological simulations provide a powerful framework for investigating the growth and evolution of large-scale structures (LSS) in the Universe, with their ability to approximate a diverse range of physical processes and test models that can be evaluated by observations. This research addresses the challenges of understanding how matter clustering in galaxy groups and clusters is affected by...
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Jose Antonio Najera (Institute of Cosmology and Gravitation, University of Portsmouth, UK)Theoretical and observational approaches to the Hubble tensionPoster
Redshift-independent distances are crucial to build the distance ladder and make model-independent determinations of the Hubble constant. Only a few standard candle or ruler methods have been used to calibrate the first two rungs of the distance ladder (for example Cepheids, TRGBs, Tully-Fisher, and JAGB). However a great range of methods have been used to measure distances directly. I will...
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Theoretical and observational approaches to the Hubble tensionPoster
The observational evidence for a local ~200Mpc, underdensity goes back to the 1990's and, like the "Hubble tension", remains unexplained by the standard cosmology. Wong et al (2022, MNRAS, 511, 5742) show that the Local Hole covers >90% of the sky out to ~200Mpc with an ~20% underdensity, consistent with previous independent observations (e.g. Keenan, Barger and Cowie, 2013, ApJ, 775,...
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