iiinova — where your digital self keeps evolving

Daniel Green @dangreen.bsky.social · 05/11/2025

Reminder: Effective field theory is a revolutionary development in fundamental physics that has transformed the field over the past 40 years (that also makes many verified experimental predictions). Congrats to @jfdonoghue.bsky.social !

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Daniel Green @dangreen.bsky.social · 29/08/2025

For (cosmic) neutrino mass enthusiasts: Peter Graham, Joel Meyers and I have new paper, breaking down why data prefers "negative" masses and how it might be explained with new fields and/or forces. We point to a number of measurements that would clarify the situation arxiv.org/abs/2508.20999

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Daniel Green @dangreen.bsky.social · 22/08/2025

This issue has been known for a long time: arxiv.org/abs/1701.08750 arxiv.org/abs/1709.07882 (figures from these papers) If the goal is to make an actual discovery (not just get new bounds into PRL), one needs to be honest about what we know.

arxiv.org

The Cosmology of Sub-MeV Dark Matter

Light dark matter is a compelling experimental target in light of stringent constraints on heavier WIMPs. However, for a sub-MeV WIMP, the universe is sufficiently well understood at temperatures belo...

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Daniel Green @dangreen.bsky.social · 22/08/2025

"Putative dark matter particles with masses below around 1 MeV are not ruled out by astronomical observations" Fact check: astrophysics provides a constraint that is 20 orders of magnitude stronger than this new result.

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Daniel Green @dangreen.bsky.social · 22/07/2025

That said, we have learned a lot in the past year and we should have a paper out soon that will better explain the situation.

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Daniel Green @dangreen.bsky.social · 22/07/2025

Forecasts tend to saturate at the optical depth limit post DESI. So there isn’t huge statistics gain coming. If it is just a large statistical fluctuation, there isn’t a guaranteed way to figure that out.

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Daniel Green @dangreen.bsky.social · 22/07/2025

The answer is a bit complicated. The short answer is that you will gain a bit more going from current to full DESI but after that there really isn’t anything planned that will help. Much more likely to find systematics to explain such a change.

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Daniel Green @dangreen.bsky.social · 20/07/2025

Sorry - if you look at the paper I referenced, they let the optical depth be a free parameter without including the low ell data that usually fixes it. They find both the expansion history and neutrino mass look fine, but the optical depth is roughly what we estimated in our paper (6 sigma high)

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Daniel Green @dangreen.bsky.social · 20/07/2025

(3) The optical depth can improve the whole situation but indeed as high as suggested (arxiv.org/abs/2504.16932) (4) this isn’t inconsistent because the current error is not completely determined by tau (yet)

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Daniel Green @dangreen.bsky.social · 20/07/2025

There are a few things going on: (1) yes, when you allow neutrino mass to be negative, the exclusion of the the physical region consistent with oscillations get stronger (99% in our paper). (2) this does depend on how you define (negative mass), so not all the papers agree on the exact value.

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Daniel Green @dangreen.bsky.social · 11/07/2025

In fact, the reason the SPT result is lower than previous ones is that they use a different value for the optical depth (there are multiple values that come from Planck that are just slightly different ways of analyzing the low-ell data). The SPT data isn’t actually driving this.

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Daniel Green @dangreen.bsky.social · 11/07/2025

What you would need is that there is a systematic error, most likely in the optical depth that is 6-7 sigma. You could tell by repeating this measurement. Unfortunately you will need another CMB satellite to check, which is 10-15 years away (if it happens at all)

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Daniel Green @dangreen.bsky.social · 11/07/2025

The logic of “more data” is the it is a statistical fluctuation that will be revealed my just adding more data. That is literally not possible. You can add ever increasing quality CMB and BAO data and it will do nothing to the neutrino mass measurement.

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Daniel Green @dangreen.bsky.social · 11/07/2025

The really critical point is that “more data” is not a solution. Because of the peculiar nature of the neutrino mass measurement, it is limited by measurements that will be very difficult to repeat and may not happen again for 15 years

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Daniel Green @dangreen.bsky.social · 11/07/2025

There is very little about the SPT result that is new - this issue with neutrino mass has been there since DESI Y1 BAO. An initial run-down of the possible explanations is here arxiv.org/abs/2405.00836

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Daniel Green @dangreen.bsky.social · 25/06/2025

The paper is out here: pole.uchicago.edu/public/data/... Of personal interest: the full range of neutrino masses allowed by neutrino oscillations are now excluded at 98% confidence!

pole.uchicago.edu

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Reposted by Daniel Green

Caltech IPAC @caltechipac.bsky.social · 08/05/2025

Let the science begin! 🥁 On May 1, NASA’s SPHEREx space observatory began regular science operations, which consist of taking about 3,600 images per day. Read more here: spherex.caltech.edu/news/nasa-s-...

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Daniel Green @dangreen.bsky.social · 28/03/2025

I think it is also the problem that deep insights into nature happen slowly. Often there are pieces that fall into place over years so by the time we agree something is true it also feels like old news. Unfortunately, Nobel prize announcements may be the only time we get to really celebrate them.

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Reposted by Daniel Green

Ethan Siegel @startswithabang.bsky.social · 26/03/2025

Is dark energy weakening? DESI’s results are ambiguous You've heard the results last week: the DESI collaboration announced evidence for evolving dark energy. But that's not the only interpretation when the full suite of data just doesn't add up. bigthink.com/starts-with-... #space #physics

bigthink.com

Is dark energy weakening? DESI's results are ambiguous

DESI, by mapping galaxies, has claimed they see evidence for dark energy evolving by getting weaker. But that's only one interpretation.

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Daniel Green @dangreen.bsky.social · 23/03/2025

There are shifts in the value from reanalysis, but nothing big enough to matter. I also haven’t seen a believable claim that a 6-7 sigma error in tau (needed for neutrinos) would definitely have no impact on the DE interpretation of DESI+CMB.

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Daniel Green @dangreen.bsky.social · 22/03/2025

SPT crucially uses polarization only so it has completely different systematics (and data) from the other two

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Daniel Green @dangreen.bsky.social · 22/03/2025

That is not true. The issue with the mass is consistent with Planck, ACT and SPT.

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Daniel Green @dangreen.bsky.social · 22/03/2025

If that is how we should think about your data, then your are guaranteed only to find DE. In DR1, rather than worry about the negative neutrino mass, the collaboration added a prior that it is >60 meV to make it look like nothing.

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Daniel Green @dangreen.bsky.social · 22/03/2025

The main point I am making is that DESI does not explore many alternatives to the DE interpretation so we shouldn’t just assume that is even close to the best explanation. It is convenient to say we shouldn’t trust the other analyses because they collaboration didn’t do it.

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Daniel Green @dangreen.bsky.social · 22/03/2025

These are not some qualities, these are two parameters that definite a sinusoidal oscillation. The analyses are almost identical. It may be true that the collaboration only cares about 1 and not the other but if you goal is to really understand your data (and the Universe!) that seems like an issue

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Daniel Green @dangreen.bsky.social · 22/03/2025

This is the same as the Hubble tension models that make the tension with SN less significant but do not change the value of H0. I wouldn’t call those a solution to the tension in the days, even it is make 5->2 sigma. I would not stop and say “this must be the way the Universe works”

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Daniel Green @dangreen.bsky.social · 22/03/2025

You see to be thinking I am advocating the point of view that this is negative neutrino mass. I am not. I am trying to observe that DE does not explain the inconsistencies with the CMB. At best it makes some of them less statistically significant.

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Daniel Green @dangreen.bsky.social · 22/03/2025

The current upper limit is 70 meV. Given neutrino oscillations, this is effective 1 heavy 2 light, but at these small masses it doesn’t matter. The story is totally different at 150 meV or 250 meV.

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Daniel Green @dangreen.bsky.social · 22/03/2025

Zero is inconsistent with neutrino oscillations. This is a 3 sigma tension that moves to 1.6 after extending the parameter space to allow for null energy condition violation

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Daniel Green @dangreen.bsky.social · 22/03/2025

It is only not statistically significant after adding 2 new parameters. So you have a 3> sigma tension and you add 2 parameters to get it to 1.6. Again, I wouldn’t claim this suggests it naturally explains the data. So you blow up the parameter space and the data still prefers unphysical values

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Daniel Green @dangreen.bsky.social · 22/03/2025

This is not a good excuse. You should be able to measure a phase and a frequency. If you think the paper is unreliable (and thus the tension is not meaningful), I would ask why I should trust the frequency.

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Daniel Green @dangreen.bsky.social · 22/03/2025

Disagree. What papers are you referring to? At small mass, you can’t resolve the free streaming scale so it doesn’t matter. Only for large masses does it make a difference but there it is also excluded.

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Daniel Green @dangreen.bsky.social · 22/03/2025

Yes, that is what I am urging people to do, but the press release and everything I see if about DE. In DR1 BAO, the papers did almost nothing but DE. There is really no reason that DESI can't do more itself instead of asking the community to do the analyses (w data that may not be public yet)

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Daniel Green @dangreen.bsky.social · 22/03/2025

I am not claiming that there is more evident for neutrino mass. I am only saying that if there was a clear indication that it was DE, you might hope that it explained all the tensions in the data. Instead, even with w0wa, it seems like there are many analyses of CMB+DESI that are 2ish sigma off.

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Daniel Green @dangreen.bsky.social · 22/03/2025

Can you tell me what the current tension of the phase shift is? It was 2.3 sigma with w0wa in DR1 (2.7 with LCDM), but I only saw an update on >0 for DR2 Also, why are you only quoting the DESY5 data? The Pantheon data is the one that looks the most in tension.

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Daniel Green @dangreen.bsky.social · 22/03/2025

Why not call it 15 million data points? That would sound even better for DESI. I am showing a plot with 7 points and a non-DE model that would clearly improve the fit.

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Daniel Green @dangreen.bsky.social · 22/03/2025

There is a claim that adding 2 new BSM parameters (1 won’t do) explains a 4 sigma tension, but even with these parameters a 3 sigma tension remains (in neutrino mass). If you need 3 new BSM parameters to get a good fit to the data, it seems unlikely to be your best explaination

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Daniel Green @dangreen.bsky.social · 22/03/2025

The signal that is being reported everywhere violates the null energy condition and is (theoretically) a very very unlikely interpretation. But even without that theory prior, there is way too little skepticism of their interpretation. The data is only 7 points, it could be many things

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Daniel Green @dangreen.bsky.social · 22/03/2025

There are other tensions in their data that may or may not be related but were not really investigated. E.g. the measurement of the phase shift (Neff), shows a 2.7 sigma tension with the SM (arxiv.org/abs/2412.05990). Could trade all of the DE signals for just a phase shift?

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Daniel Green @dangreen.bsky.social · 22/03/2025

DESI did not explore a long list of alternatives. Unlike Planck, DESI has only a few analyses published. Analyses by other groups allow for totally different interpretations. E.g. this nice paper (arxiv.org/abs/2503.14470) shows that decaying dark matter could work

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Daniel Green @dangreen.bsky.social · 22/03/2025

PSA: when a collaboration whose name starts with DE says they have found evidence for non-standard dark energy, the community should take that interpretation with more skepticism. DESI does not show that w0wa explains there data. Eg neutrino mass remains negative even with w0wa

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Daniel Green @dangreen.bsky.social · 31/12/2024

Local non-Gaussianity predicted by Maldacena of (n_s-1) was once thought to be a lower bound, but this contribution is unobservable/pure gauge (arxiv.org/abs/1305.0824). Naively, this suggests there would be no lower bound, but these authors showed the equilateral shape survives.

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Daniel Green @dangreen.bsky.social · 31/12/2024

Dec 31 - Lower bound on primordial non-Gaussianity arxiv.org/abs/1612.00033 Cabass et al. show that inflation predicts a lower bound of equilateral NG of 0.1 x (n_s-1), 3-4 orders of magnitude below the current limits, due to gravity. The search for NG has a set range and target

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Daniel Green @dangreen.bsky.social · 30/12/2024

Shapes of NG have a natural inner product defined by the independence of their estimators (arxiv.org/abs/astro-ph...). Prior to this paper, people looked for models where the predicted 3pt function was orthogonal to previous shapes. Most were just be elements of this basis.

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Daniel Green @dangreen.bsky.social · 30/12/2024

Dec 30 - CMB Bispectrum modal decomposition arxiv.org/abs/0912.5516 Fergusson et al. define a basis of orthogonal polynomials on the space of CMB 3pt functions, vastly reducing the need to find models on which to build non-Gaussian templates. Planck bounds the first 2000 terms.

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Daniel Green @dangreen.bsky.social · 29/12/2024

Dispersion relations have a certain UV-IR character that seems to run in the face of naive EFT intuition: the structure of EFT is constrained the nature of the UV completion. Instead, they are a precise distillation of EFT: the UV determines the local interactions (and that's it)

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Daniel Green @dangreen.bsky.social · 29/12/2024

Dec 29 - Dispersion Relations & EFT arxiv.org/abs/hep-ph/9... Donoghue shows how to use subtracted dispersion relations to expose the structure of EFT. Specifically, this technique precisely illustrates UV information can be traded to local contact interactions.

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Daniel Green @dangreen.bsky.social · 28/12/2024

Consistency of physical experiments, such as scattering of a weak probe or positivity of energies In physical detectors, has proven to be a useful window into strongly coupled QFTs arxiv.org/abs/0803.1467 arxiv.org/abs/1212.4103 This paper gives a very clear (first) demonstration of this strategy

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