In the Dark

This morning’s arXiv announcement contained a number of papers related to the Dark Energy Survey Y6 analysis. There is also a Zoom webinar later today at 10.30 Central Time (16.30 GMT’; 13.30 in Greeland). Details can be found here.

You can find links to and abstracts of all the papers here, but I thought it would be useful to provide arXiv links to the latest batch here.

• arXiv:2601.14559 Dark Energy Survey Year 6 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing – this is the key summary paper.
• arXiv:2601.14484 Dark Energy Survey Year 6 Results: MagLim++ Lens Sample Selection and Measurements of Galaxy Clustering
• arXiv:2601.14864 Dark Energy Survey: DESI-Independent Angular BAO Measurement
• arXiv:2601.15175 Dark Energy Survey Year 6 Results: Galaxy-galaxy lensing
• arXiv:2601.14833 Dark Energy Survey Year 6 Results: Magnification modeling and its impact on galaxy clustering and galaxy-galaxy lensing cosmology
• arXiv:2601.14859 Dark Energy Survey Year 6 Results: Weak Lensing and Galaxy Clustering Cosmological Analysis Framework

A number of DES Y6 papers already published – including several in the Open Journal of Astrophysics – are listed here.

I’ll just highlight a couple of points from the first paper listed above, which uses the now standard “3x2pt” analysis, which combines three complementary two-point correlation functions: cosmic shear; galaxy-galaxy lensing and galaxy clustering. The abstract of this paper is as follows:

A notable result is contained in the last sentence. The simplest interpretation of dark energy is that it is a cosmological constant (usually called Λ) which – as explained here – corresponds to a perfect fluid with an equation-of-state p=wρc² with w=-1. In this case the effective mass density  ρ of the dark energy remains constant as the universe expands. To parametrise departures from this constant behaviour, cosmologists have replaced this form with the form w(a)=w₀+w_a(1-a) where a(t) is the cosmic scale factor. A cosmological constant Λ would correspond to a point (w₀=-1, w_a=0) in the plane defined by these parameters, but the only requirement for dark energy to result in cosmic acceleration is that w<-1/3, not that w=-1. Results last year from DESI suggested values of w₀ ≠-1 and w_a≠0 , but the current DES results are consistent with w=-1; they do not constrain w₀ and w_a jointly.

For reference on the left you can find the (w₀, w_a) plane from DESI.

I thought I’d add one of the other cosmological contraint plots:

The results look qualitatively similar to previous plots but the contours have shifted a bit.

This entry was posted on January 22, 2026 at 12:09 pm and is filed under The Universe and Stuff with tags Cosmology, Dark Energy, Dark Energy Spectroscopic Instrument, Dark Energy Survey, DES, DES Year 6, DESI. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.