A Meta Post

Today is the 160th day of the year, and I am on track at 80 posts at this blog so far, the historically normal rate of about one post every two days. I have, however, had proportionately more physics posts and proportionately fewer non-physics posts, than usual, and my posts have had somewhat less depth than I'd ideally like them to, on average. There have been 2,981 posts at this blog over its entire duration.

The sister blog to this one, Wash Park Prophet, has 51 posts so far this year, which while far from being a dead blog, is the lowest posting rate there that I've had of all time (a bit more than 2.2 posts per week). I just can't maintain both blogs at my usual pace at my current job (and have shifted some of my output of hit and run posts to Facebook). I have made 9,696 posts at that blog since its inception.

I've made 12,677 posts at these two blogs combined since their inception.

Combined, I've made 131 posts in 160 days, a pace of about four posts every five days. Again, this is nothing to sniff at, but less than I've posted historically.

Cold Dark Matter Still Doesn't Work

The missing local baryon problem

Stacy McGaugh at Triton Station explores one of the many bits of empirical evidence, which he calls the missing local baryon problem, that really convincingly disfavors any kind of cold dark matter paradigm.

Basically, he utilizes a proof by contradiction. 

He assumes a standard cold dark matter model, analyzes the data on the share of the mass of galaxies and galaxy clusters that is made up of ordinary baryonic matter (which is about 15.7% in the cold dark matter paradigm), in line for the percentage for the whole universe in that paradigm. Then, he shows how the proportion of baryonic matter gets systemically lower in a very predictable manner as the absolute amount of baryonic matter in a galaxy falls.

The problem is that in the cold dark matter paradigm, galaxy clusters form as galaxies cluster together, and larger galaxies form from the merger of smaller galaxies. But this leaves open the question of how the proportion of baryonic matter in a pair of merged galaxies that form a larger galaxy can be systemically and precisely greater in a merged larger galaxy than it was in any of the smaller galaxies whose merger formed it.

Keep in mind that Standard Model physics demonstrates that in all but ultra-extreme circumstances (which haven't existed since the first few seconds after the Big Bang, at most) the total number of baryons in any system (less the total number of anti-baryons in any system) is constant (which has been experimentally confirmed to extreme precision), and that baryons profoundly outnumber anti-baryons in the universe (on the order of 10^10 to one), so there is no plausible physical mechanism by which new baryons are being created in galaxy mergers.

Indeed, even the proportion of the baryonic mass of the universe of each kind of atomic element, something that can only occur in nuclear fission and nuclear fusion reactions that happen mostly in mature stars, has changes only incrementally from the proportions of those atoms predicted to have been present fifteen minutes after the Big Bang, and even then, in amounts and by mechanisms mostly associated with the nuclear physics of stars, that are reasonably well understood. This strongly reinforces the idea that the new baryons aren't being created in galaxy mergers.

So, the shortfall of baryons in a dark matter particle paradigm, that is present in every system smaller than a galaxy cluster, would have to come from the intergalactic medium (IGM) of cold interstellar gas between galaxies and the circumgalactic medium (CGM) of cold interstellar gas in the dark matter halos of galaxies.

Fig. 1 of McGaugh et al. (2026): Conceptual elements of a galaxy: the stars (yellow/blue) and atomic gas (green) of NGC 6946 (Spitzer 3.6µ and 21 cm data: F. Walter et al. 2008) are shown embedded in an extended dark matter halo (black). The dark matter density decreases continuously with radius so the halo has no hard edge, but for convenience we adopt the common convention that the radius r200 marks the boundary of the dark matter halo and the dividing line between the circumgalactic medium (CGM) and the intergalactic medium (IGM; orange). The stars and atomic gas illustrated here appear within r < 20 kpc while r(200) ≈ 220 kpc (not shown to scale).

One kpc (i.e. kiloparsec) equals 32,600 light years.

But while this is the only possible solution to the local missing baryon problem in essentially all galaxies (but especially the smaller ones) in the dark matter particle paradigm, there is basically no way to make this work.

Therefore, cold dark matter models are inconsistent with what we observe.

CDM predicts excessive dwarf galaxy masses

Another example demonstrates that in the Local Group that includes the Andromeda galaxy and the Milky Way, one of its minor galaxies should have more mass than its two biggest galaxies and even more mass than the Local Group as a whole, which is contrary to the kinetic dynamics of the system as a whole and contrary to the conservation of matter. As McGaugh explains:

One signature of this misfit is the occurrence of very large V(200) for dwarf galaxies with small V(f). Taken literally, this would mean that some of the smallest dwarf galaxies reside in dark matter halos that outweigh those of giants like the Milky Way. This seems absurd, and it is. For example, by this approach, the dwarf galaxy NGC 3109 residing just outside the Local Group outweighs the Local Group and both its giants, Andromeda and the Milky Way, put together. But it is pretty clear from the local velocity field that the entire Local Group is not orbiting this little dwarf.

Real galaxies rarely have NFW halo distributions 

In dark matter particle paradigms, inferred dark matter halos have a "pseudo-isothermal" distribution, while collisionless cold dark matter must theoretically have, as an inexorable consequence of a very simple statistical mechanics style calculation that applies to dark matter particle with these very simple properties, what is called an NFW distribution, which is a very poor fit to the vast majority of galaxies.

Figure 2 from McGaugh et al. (2026): The observed flat velocity V(f) as it relates to the fitted V(200) for pseudo-isothermal (left panel) and NFW (right panel) halos (Li et al. 2020). Filled points have formal uncertainties < 20% in V(200); open points are less accurate fits. The solid line shows V(f) = V(200). The gray line in the right panel shows Equation (2a) of Katz et al. (2019), which corresponds roughly to f(v) ≈ 1.4.

V(f) is the rotational velocity of a galaxy at about a 65,000 light year radius, V(200) is the velocity of a galaxy at about 715,000 light year radius, and f(v) is equal to V(200)/V(f). 

The bottom line is that pseudo-isothermal dark matter halo distributions are a decent fit to what is observed with f(v) approximately equal to 1 and little scatter in the data (and scatter mostly associated with data points that have high uncertainties), while an NFW dark matter halo distribution has f(v) approximately equal to 1.4 with a great deal of scatter in the data.

This is a problem for the dark matter paradigm because coming up with a dark matter candidate with properties the naturally form pseudo-isothermal halos (for a candidate that isn't excluded by other data) is a challenging enterprise. Indeed, pseudo-isothermal dark matter halo density distributions aren't even theoretically stable.

CDM predicts the wrong slope for the Tully-Fischer scaling law

In a cold dark matter paradigm, the baryonic Tully-Fischer relationship (which roughly speaking related galaxy size to the speed of its flat rotation) has a slope of four when the observed relationship has a slope of three. 

When your power law exponent is a power of three rather than a predicted power of four, you have a seriously flawed functional form for your model.

Gravity based solutions compared

Toy-model MOND has challenges of its own (especially in galaxy clusters, although the intra-cluster medium of cold interstellar gas that was recently estimated makes the discrepancy smaller), but it is much more descriptive of the data, and predictive, than the cold dark matter paradigm. It even fits clusters reasonably well also with a tweak to just one of its parameters, rather than to the model as a whole. 

Deur chalks up the different gravitational behavior of galaxy clusters and galaxies to the different geometries of the mass distributions involved.

Data Combinations For Neutrion Oscillations

The PMNS matrix with non-zero CP conservation and a normal ordering of neutrino masses is still a good description of all of the available raw data from four leading neutrino experiments (without the need for right handed or otherwise sterile neutrinos, or non-standard neutrino interactions, or Majorana neutrino mass). 

This is hardly breaking news but provides yet another confirmation, independent of the major neutrino physics collaborations that this fairly simple model of neutrino physics works.

We present the first combined oscillation analysis of multiple atmospheric neutrino datasets, featuring data from Super-Kamiokande, IceCube-DeepCore, and KM3NeT/ORCA together with reactor data from Daya Bay. 

Such combinations have long been considered infeasible outside experimental collaborations; we demonstrate that a unified physics model can simultaneously describe all datasets with no significant parameter tensions. 

Fitting 839,048 events across 1536 bins with 91 parameters, our combined analysis yields competitive measurements of the neutrino mixing parameters, disfavors CP conservation, and prefers the Normal over the Inverted Mass Ordering.

Philipp Eller, "Atmospheric Neutrino Oscillations: the Full Picture" arXiv:2606.09714 (June 8, 2026).

The body text notes that:

We disfavor the absence of CP violation at ∆χ2 = 8.06 and the Inverted Ordering at ∆χ2 = 9.11.

These preferences are statistically significant at a more than 95% confidence level.

The preference for normal ordering is about three sigma (roughly a 99% confidence level). 

This preference is also corroborated by an independent statistically significant preference for a normal ordering from cosmology data that strengthens that preference when cosmology data is combined with terrestrial experimental data. But quantifying the cosmology data preference is challenging because it is cosmology model dependent (see also here). 

Cosmology data does, however, consistently favor a lightest neutrino mass eigenstate far less massive than the Katrin direct neutrino mass measurement experiments (by two or three orders of magnitude).

Neutrinoless beta decay experiments (which imply Majorana neutrino mass limits) aren't yet powerful enough to make meaningful statements about neutrino masses relative to other data sources for neutrino masses.

A Preon Model

There are lots of issues with preon models that model at least some of the Standard Model fundamental particles as composite (experimental limits on compositeness are strict and naively rule them out for simpler models). But this is a more interesting one than most.

We build a framework for Regge trajectories from the Nambu-Goto action. We compute the 6-preon Regge trajectory in a preon model, include the worldsheet conformal anomaly, and build the parameter-free Veneziano amplitude. The amplitude has s-channel poles matching the spectrum to 0.5%, and at fixed-angle scattering decays exponentially with a negative Gross-Mende coefficient, realized numerically to 0.03%. 

This is a soft, genuinely non-perturbative ultraviolet completion of the preon model - and thereby of the Standard Model, which emerges as its low-energy limit.

Risto Raitio, "Soft UV Completion of a Preon Model" arXiv:2606.06541 (June 4, 2026).

The model used in this case is spelled out in the introduction:

Quarks and leptons arise as three-preon composites bound at the metacolor scale Λ(cr); the three fermion generations emerge not as a postulated multiplicity but as dynamical excitations of these composites; and the chiral, anomaly-free matter content of one Standard Model family is reproduced from a small set of preon charges. In this picture the Standard Model is the low-energy limit of a confining metacolor gauge theory, much as hadronic physics is the low-energy limit of QCD.