Dark energy might not be constant after all

[Filip Larsen]

https://arstechnica.com/science/2024/04/dark-energy-might-not-be-constant-after-all/
https://www.desi.lbl.gov/2024/04/04...recise-measurement-of-the-expanding-universe/

Interesting preliminary indications from DESI (which I did not know about until now).

The Dark Energy Spectroscopic Instrument (DESI)​

The Dark Energy Spectroscopic Instrument (DESI) will measure the effect of dark energy on the expansion of the universe. It will obtain optical spectra for tens of millions of galaxies and quasars, constructing a 3D map spanning the nearby universe to 11 billion light years.

 

[exponent137]

One question:
In https://arxiv.org/pdf/2404.03002.pdf
it is written in the abstract:

"upper limit Sum mν < 0.072 (0.113) eV at 95% confidence for a Sum mν > 0 (Sum mν > 0.059) eV prior."

To which value we can believe more, 0.072 eV, or to 0.113 eV?

 

[Hill]

One question:
In https://arxiv.org/pdf/2404.03002.pdf
it is written in the abstract:

View attachment 342927

"upper limit Sum mν < 0.072 (0.113) eV at 95% confidence for a Sum mν > 0 (Sum mν > 0.059) eV prior."

To which value we can believe more, 0.072 eV, or to 0.113 eV?

As noted in the main text,

 

[exponent137]

So, is 0.113 eV the more correct answer? Let us ignore IH. What is the point of 0.072 eV? To show that the results are more precise?

 

[Bandersnatch]

So, is 0.113 eV the more correct answer? Let us ignore IH. What is the point of 0.072 eV? To show that the results are more precise?

It's not that it's 'more correct'. The result is dependent on what one assumes is the correct lower bound for the sum of neutrino masses. If you assume one thing, it's that. If you assume another, it's the other thing.
They have to assume something, because it's not known. But there are good reasons to pick some specific values, for which they show the corresponding results.

The relevant bit is in section 7.1 (second paragraph).

 

[ohwilleke]

One question:
In https://arxiv.org/pdf/2404.03002.pdf
it is written in the abstract:

View attachment 342927

"upper limit Sum mν < 0.072 (0.113) eV at 95% confidence for a Sum mν > 0 (Sum mν > 0.059) eV prior."

To which value we can believe more, 0.072 eV, or to 0.113 eV?

The second. The merely non-zero Bayesian prior for the sum of the three neutrino masses is contrary to the whole point of using Bayesian statistics (which is to incorporate information that you already know in a prior), and should just be ignored as meaningless.

 

[exponent137]

It's not that it's 'more correct'. The result is dependent on what one assumes is the correct lower bound for the sum of neutrino masses. If you assume one thing, it's that. If you assume another, it's the other thing.
They have to assume something, because it's not known. But there are good reasons to pick some specific values, for which they show the corresponding results.

The relevant bit is in section 7.1 (second paragraph).

I read. One option is for the degenerate case. I suppose that this option is contrary to the measured mass differences of neutrinos? If it is in contradiction with measurements, why it is used? Maybe because it gives some simplified information?

 

[exponent137]

The AI gave me the date of the announcement of the upper limit on the neutrino mass from KATRIN:

https://indico.kit.edu/event/5330/

 

[ohwilleke]

The AI gave me the date of the announcement of the upper limit on the neutrino mass from KATRIN:

https://indico.kit.edu/event/5330/

Probably not the final announcement, just the latest update. And, of course, this is really a limit driven by experimental measurement limits. The best upper limit on neutrino mass from KATRIN is far in excess of any reasonable estimate of that number.

 

[Ibix]

The problem is on your end, so the search engine is directly on Chrome. Dark matter is decreasing - BBC

It's 404 for me too. I suspect it may be a region issue if the link works for you.

Are you referring to this article: https://www.bbc.co.uk/news/articles/c17xe5kl78vo? In case that link doesn't work for you, it cites this MNRAS paper and talks with one of the authors, Prof Young Wook Lee.

If so, you should probably read this more recent MNRAS paper, which essentially says that the results in the first paper are based on errors in analysis.

 

[renormalize]

Dark matter is decreasing - BBC

That's not verifed.
I managed to track down the paper to which the Quanta Magazine link refers, as well as this more recent one that cites it: Status of the S8 Tension: A 2026 Review of Probe Discrepancies. I quote from the article:

This is a rapidly evolving area of cosmology and the jury is clearly still out regarding whether dark energy is constant or not.

 

[berkeman]

Thread is closed temporarily for Moderation...

 

[PeterDonis]

A number of posts have been deleted. The thread topic has been sufficiently addressed and the thread will remain closed.