Sankarshana Srinivasan tells us about his work building the framework to constrain (or detect!) modified gravity using upcoming surveys. Building on earlier work developing model independent modified gravity simulations, Shankar now shows how a clever transform (the BNT transform) is able to better isolate the weak-lensing kernel, meaning one can more cleanly cut out the fully messy non-linear scales without losing too much usable information. We’re all looking forward to the talk in 3-5 years’ time applying these methods to Euclid and LSST data!

Paper: arXiv: 2409.06569

Cosmology Talk on earlier work in this series by Dan Thomas: The first model independent cosmological simulations of modified gravity

Angus Wright, Benjamin Stölzner, Robert Reischke, Marika Asgari and Konrad Kuijken tell us about the final cosmology results from the Kilo Degree Survey (KiDS-Legacy). After exhaustive improvement of their analysis, and consistency tests, and a six month wander in the B-Mode wilderness they emerge with no S8 tension at all.

Angus: anguswright.github.io
Benjamin: inspirehep.net/authors/1944983
Robert: inspirehep.net/authors/2219647
Marika: ncl.ac.uk/…marikaasgari.html
Konrad: universiteitleiden.nl/…koen-kuijken

KiDS: kids.strw.leidenuniv.nl

Papers:
2503.19442
2503.19441
2503.19440

Teresa Matamoro, Mike Walmsley and Phil Holloway tell us about three key areas Euclid has shed a scientific light on in their Q1 data release today. These are active galactic nuclei, galaxy morphology and strong lensing.

Teresa: linkedin/teresamatamoro…

Mike: walmsley.dev

Phil: physics.ox.ac.uk/…

ESA details on the Q1 release: cosmos.esa.int/…

Euclid Consortium details on the Q1 release: euclid-ec.org…

Papers:

[2503.15326] Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine C – Finding lenses with machine learning

[2503.15324] Euclid Quick Data Release (Q1): The Strong Lensing Discovery Engine A — System overview and lens catalogue

[2503.15320] Euclid Quick Data Release (Q1). The active galaxies of Euclid

[2502.06505] Euclid: A complete Einstein ring in NGC 6505

[2404.02973] Scaling Laws for Galaxy Images

The space observatory Euclid is producing and sharing results. In this video Guadalupe Cañas-Herrera and Hervé Aussel tell us about Euclid, its science goals and the Q1 data set they have released today (19-Mar-2025).

Guadalupe: gcanasherrera.com

Hervé: inspirehep.net/authors/1038805

ESA details on the Q1 release: cosmos.esa.int/…

Euclid Consortium details on the Q1 release: euclid-ec.org…

Papers:

[2503.15302] Euclid Quick Data Release (Q1) – Data release overview

[2503.15306] Euclid Quick Data Release (Q1). Photometric redshifts and physical properties of galaxies through the PHZ processing function

[2503.15307] Euclid Quick Data Release (Q1): From spectrograms to spectra: the SIR spectroscopic Processing Functio

[2503.15308] Euclid Quick Data Release (Q1) – Characteristics and limitations of the spectroscopic measurements

[2503.15321] Euclid Quick Data Release (Q1). Active galactic nuclei identification using diffusion-based inpainting of Euclid VIS images

Cristhian Garcia Quintero and Paul Martini tell us about the baryon acoustic oscillation measurements in data release two (DR2) of the Dark Energy Spectroscopic Instrument (three years of data). As with the first data release they are seeing evidence for evolving dark energy. They now see it when combining with just CMB, or with “just” Dark Energy Survey supernovae and clustering data.

Relevant papers on the arXiv: Continue reading →

Arnaud de Mattia, Hector Gil-Marín and Pauline Zarrouk tell us about the latest DESI key papers. These ones are covering the “full shape” of the galaxy power spectrum. This is in contrast to their results from April, which were centred around the Baryon Acoustic Oscillation (BAO) feature.

The analysis is an absolute tour de force, explaining why the video is so long. DESI have done a lot of analysis and it takes a while to unpack. (The raw recording of this video was more than 200 minutes long!)

The results aren’t quite so eye-opening as the BAO ones were in April. The evidence for evolving dark energy is still there, but the significance of this evidence hasn’t changed much. They are however able to do a bunch of tests of modified gravity and find that, unlike ΛCDM, General Relativity appears to be in great shape (at least as far as DESI observations are concerned). Continue reading →

Daniele Sorini tells us about his research looking into how the value of dark energy affects star formation in the universe. He builds an analytic model of star formation in the universe, which allows him to follow the universe to very late times and ask “if Λ was different, how many total stars could form over the entire history of the universe?”

This is the crucial question one wants to ask when examining anthropic explanations of Λ scientifically. Previous studies have asked this question using simulations, forcing them to stop after a finite amount of time.

Fascinatingly, Daniele finds that there is a value of Λ where star formation peaks, which is about 0.1 times the value in our universe. Previous simulation-based studies maybe didn’t spot this because they simply didn’t do simulations with Λ less than our observed value, except for Λ=0, but also they didn’t go to late enough times. Continue reading →

Ana Alexandre and Valentin Thoss tell us about their recent papers examining the consequences of a potential “memory burden” effect on decaying primordial blackholes (PBHs).

This memory burden effect would be a consequence of quantum gravity and would substantially slow down the Hawking evaporation of blackholes. The consequences for primordial blackholes would be very important because it would open a whole window of PBH masses as dark matter candidates. (Masses that are normally ignored because PBHs of these masses are presumed to have decayed by today.)

All fundamental physicists would agree that Hawking radiation must breakdown at some point at/before a blackhole reaches the Planck mass. This proposed memory burden effect goes a step further and claims that the breakdown must happen no later than when a blackhole has decayed to half of its original mass. This is not universally agreed upon, but it’s still worth examining the consequences if it is true. Continue reading →

Abigail Lee tells us about how she has used the J-region Asymptotic Giant Branch (JAGB) to measure extragalactic distances, ultimately using them as a rung on the distance ladder to measure the expansion rate of the universe.

The JAGB method is new, at least compared to cepheids and “tip of the red giant” (TRGB) methods, but is also very promising. The stars it uses are bright, so they can be seen at large distances, and they’re numerous, which means they can be observed far from the centres of galaxies (minimising “crowding” from other stars in the same pixels). So, even ignoring Hubble tensions, this is a very exciting time to be involved in extragalactic distance measurements.

Abby used data from JWST to detect the JAGB mode brightness, which is then the distance indicator of the method. With more telescope time, and more local calibrators, JAGB will only go from strength to strength.

When the measured distances are compared to JWST measurements of TRGB and cepheids it has very little scatter with TRGB, but a little more from cepheids. The ultimate Hubble parameter is also on the smaller side, consistent with CMB + ΛCDM and on the border of being inconsistent with SH0ES cepheid+HST based measurements.

Abby: abiglee7.github.io

The paper: arXiv: 2408.03474

Wendy Freedman and Barry Madore give a status update on the Chicago-Carnegie Hubble Program (CCHP). There has been much progress!

In this status update there are three independent distance ladder measurements of the expansion rate (i.e. the Hubble parameter) all using JWST data. There is the very well-known Cepheid method, the now also well known Tip of the Red Giant (TRGB) method, and making its debut, the J-Region Asymptotic Giant Branch (JAGB) method.

The TRGB and JAGB methods agree strikingly well and appear to be consistent with the CMB + ΛCDM value for the expansion rate. The Cepheid method also agrees to within less than 5%, which is still striking, but there is some deviation.

The deviation pushes the Cepheid value for H0 up, making it consistent with the SH0ES value, although the error bars on this CCHP result are large enough that their Cepheid value is also consistent with the lower TRGB and JAGB methods. Most curiously (to this relative outsider) the JAGB value does not appear to be consistent with SH0ES, even when considering statistical and systematic errors at once. The striking consistency between TRGB and JAGB, means that one’s naive guess might be that there is some unknown systematic in the Cepheid method (in both the CCHP and SH0ES measurements). However, naive guesses are naive so, time will tell. Continue reading →