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.
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)....
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...
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...
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...
We pursue a comprehensive approach towards the estimation of the Hubble constant by addressing two separate but interlinked sources of uncertainty: peculiar velocities and the calibration of the distance ladder. Peculiar velocities introduce noise in the Hubble diagram and can potentially bias the Hubble constant estimates derived from direct distance tracers. Traditionally, their impact is...
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...
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...
In this talk I will review how modified gravity parametrizations can, in principle, be exploited to not only test general relativity, but also tackle the problematic tensions that riddle cosmology in its current state, considering these issues by the point of view of both background observables and perturbations. More precisely, I will aim to provide insight into questions such as: can...
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...
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,...
