MOND-Like Behavior Applies To All Galaxies

As explained in a Triton Station blog post, the MOND-like behavior of galaxies called the "radial acceleration relation" holds true for galaxies of all sizes and shapes. 

The post notes that "an apparent offset between early type galaxies (ETGs, aka ellipticals) and late type galaxies (LTGs, aka spirals)" turns out to be a statistical artifact of analyzing the samples in an inconsistent manner.

Figure 3 from Mistele et al. (2024). The baryonic Tully–Fisher relation implied by weak lensing for the entire sample (yellow symbols, left column) and for ETGs and LTGs separately (red and blue symbols, right column). The Vflat values are weighted averages of the Vc values shown in Figure 1 for 50 kpc < R < 300 kpc (first row) and 50 kpc < R < 1000 kpc (second row). Vertical error bars represent a 0.1 dex systematic uncertainty on M*/L. For comparison, we also show the best fit to the kinematic data from Lelli et al. (2019; solid gray line) and the corresponding binned kinematic data (white diamonds).

We combine kinematic and gravitational lensing data to construct the Radial Acceleration Relation (RAR) of galaxies over a large dynamic range. 

We improve on previous weak-lensing studies in two ways. First, we compute stellar masses using the same stellar population model as for the kinematic data. Second, we introduce a new method for converting excess surface density profiles to radial accelerations. This method is based on a new deprojection formula which is exact, computationally efficient, and gives smaller systematic uncertainties than previous methods. 

We find that the RAR inferred from weak-lensing data smoothly continues that inferred from kinematic data by about 2.5 dex in acceleration. Contrary to previous studies, we find that early- and late-type galaxies lie on the same joint RAR when a sufficiently strict isolation criterion is adopted and their stellar and gas masses are estimated consistently with the kinematic RAR.

T. Mistele, S. McGaugh, F. Lelli, J. Schombert and P. Li, "Radial acceleration relation of galaxies with joint kinematic and weak-lensing data" Journal of Cosmology and Astroparticle Physics (April 4, 2024) (open access). DOI 10.1088/1475-7516/2024/04/020.

Other papers also establish that these dynamics are present in galaxies are early as they can be detected with the James Webb Space Telescope (JWST), which has an ability to see faint, highly redshifted objects that is unparalleled. This is true even in galaxies that are visible before the LambdaCDM model says that they should exist at all.

Bottom Quark Mass And The LP & C Relation

The pole masses of the top quark, Higgs boson, Z boson, W boson, tau lepton, muon, and electron are relatively straight forward to measure directly, and are known to decent to excellent relative precision.

In contrast, the bottom, charm, strange, down, and up quarks are always confined in a hadron. This means that their masses can't be measured directly and instead have to be reverse engineered from hadron properties according to some self-consistent scheme, one in which the pole masses of isolated particles is not even necessarily well defined.

The most common scheme for determining the masses of the five less massive quarks is the MS-bar mass a.ka. the modified minimal subtraction scheme. But this isn't the only scheme for determining their masses. Another one is the "on-shell mass" of bottom and charm quarks which can be determined more or less exactly and to almost the same precision as the MS-bar mass upon which a lot of good data has been assembled. And, it more fundamental, and hence more appropriate to use for theoretical purposes (although the "on-shell" mass of the three lightest quarks is ill-defined). As explained in the introduction of the linked paper:

In perturbative QCD (pQCD) theory, two schemes are frequently adopted for renormalizing the quark masses, e.g. the on-shell (OS) scheme and the modified minimal subtraction (MS) scheme. 

The OS mass, also known as the pole mass, offers the advantage of being grounded in a physical definition which is gauge-parameter independent and scheme independent. It ensures that the inverse heavy-quark propagator exhibits a zero at the location of the pole mass to any order in the perturbative expansion. 

On the other hand, the MS scheme focuses solely on removing the subtraction term 1/ǫ+ln(4π)−γE from the quantum corrections to the quark two-point function. And by combining this with the bare mass, one can derive the expression for the renormalized MS mass.

In high-energy processes, the MS mass is preferred for its lack of intrinsic uncertainties. It has been found that for the high-energy processes involving the bottom quark, such as the B meson decays, when their typical scales are lower than the bottom quark mass, the using of MS mass becomes less suitable and the OS mass is usually adopted. 

Practically, the perturbative series using the OS mass is plagued by renormalon ambiguities, resulting in a perturbative series with poor convergence. Thus for precision tests of the Standard Model, accurate determination of the OS mass is important. 

It is noted that the OS mass can be related to the MS mass by using the perturbative relation between the bare quark mass (mq,0) and the renormalized mass in either the OS or MS scheme, where q denotes the heavy charm, bottom, and top quark, respectively.

The MS-bar mass of the bottom quark is 4.18 + 0.03 - 0.02 GeV. A new paper determines that this is equivalent to an on-shell mass of the bottom quark of 5.36 + 0.10 - 0.07 GeV. The new preprint that makes this conversion and its abstract are as follows:

Shun-Yue Ma, Xu-Dong Huang, Xu-Chang Zheng, Xing-Gang Wu, "Precise determination of the bottom-quark on-shell mass using its four-loop relation to the MS bar scheme running mass" arXiv:2406.18025 (June 26, 2024).

The on-shell mass of the charm quark (calculated somewhat less precisely) is 2.486 + 0.126 - 0.109 GeV.

Why care which definition of quark mass is used?

One reason is that this is relevant to a hypothesized relationship between the masses of the Standard Model fundamental particles and the Higgs vacuum expectation value (Higgs vev) known as the LP & C relation. 

This hypothesis holds that the sum of the square of the fundamental particle masses is equal to the square of the Higgs vev. This is equivalent to saying that the Higgs field Yukawas of the fundamental particles in the Standard Model add up to exactly one.

Putting best fit measurements into this formula comes up just a little short in a way that is principally due to the top quark mass being too light, when MS-bar scheme running masses are used for the other five quarks.

The current best fit measurement of the top quark mass is 172.690 ± 0.3 GeV.

But, to make the LP & C relation work with the best fit masses of all of the other fundamental particles, the preferred value is 173.615 GeV, which is about a 3.1 sigma tension.

If the on-shell mass of the bottom quark is used instead, however, this eases up these tensions somewhat. 

For example, fitting the top quark mass alone requires a top quark mass of 173.583 GeV when using the on-shell mass of the bottom quark, which is a little bit less than a 3.0 sigma tension. Using the on-shell masses of the charm quark as well would require a top quark mass of 173.570 GeV, which is a bit more than a 2.9 sigma tension.

Another way to make the numbers fit while reducing the tensions for the mass measurements of individual particles is to use top quark masses and Higgs boson masses. In the case of the Higgs boson, the current world average mass is 125.25 ± 0.17 GeV.

If both the top quark mass and Higgs boson mass are increased above their best fit measurements by equal numbers of standard deviations, which reduces the tension to about 2.6 sigma, and that could be reduced to a tension of about 2.5 sigma or less for both the top quark and the Higgs boson, using on-shell masses, which is significantly more mild than a 3.1 sigma tension in the top quark mass.

With all three adjustments, the LP & C relation could fit with a top quark mass of 173.44 GeV and the Higgs boson mass of 125.675 GeV, neither of which is a huge stretch, which means that the LP & C relation is still a viable theory, even though it is not perfectly consistent with the latest mass measurements.

Using the MS-bar mass rather than the on-shell masses of the three light quarks turns out to be immaterial in evaluating the LP & C relation, in which the uncertainties are dominated by the uncertainties in the largest absolute fundamental particle masses.

Alternatively, the LP & C relation could hold because the list of Standard Model fundamental particles is not complete, in which case it estimates the sum of the square of the masses of the missing fundamental particles, subject to the relative uncertainties in the known fundamental particle masses, in a global test of the completeness of the Standard Model.

The best fit to this gap, if concentrated in a single particle, would be a particle with a mass of about 17.5 GeV, but with a great uncertainty, mostly due to the uncertainties in the top quark and Higgs boson masses, and to a lesser extent the W boson mass uncertainty.

The trouble is, of course, that this mass range is well-explored, has produced no fundamental particles in this mass range, and would wildly throw off the observed branching fractions of the Higgs boson, Z boson, and W boson if it did exist, so it probably doesn't.

On-shell masses also make sense to use when exploring generalizations of Koide's rule to quark masses.

McGaugh On Structure Formation

McGaugh reminds the world that the early structure formation seen in the James Webb Space Telescope (JWST) was predicted long ago by MOND and is inconsistent with the ΛCDM model.

Galaxies in the early universe appear to have grown too big too fast, assembling into massive, monolithic objects more rapidly than anticipated in the hierarchical ΛCDM structure formation paradigm. 

The available data are consistent with there being a population of massive galaxies that form early (z≳10) and follow an approximately exponential star formation history with a short (≲1 Gyr) e-folding timescale on the way to becoming massive (M∗≈10¹¹M⊙) galaxies by z=0, consistent with the traditional picture for the evolution of giant elliptical galaxies. Observations of the kinematics of spiral galaxies as a function of redshift similarly show that massive disks and their scaling relations were in place at early times, indicating a genuine effect in mass that cannot be explained as a quirk of luminosity evolution. 

That massive galaxies could form by z=10 was explicitly predicted in advance by MOND. We discuss some further predictions of MOND, such as the early emergence of clusters of galaxies and the cosmic web.

Stacy S. McGaugh, James M. Schombert, Federico Lelli, Jay Franck, "Accelerated Structure Formation: the Early Emergence of Massive Galaxies and Clusters of Galaxies" arXiv:2406.17930 (June 25, 2024) (submitted to Apj).

A Good Reason To Like The Mirror Universe Scenario

 

A mirror universe scenario overcomes this meme. 

Deur's approach (whether or not it modifies general relativity) also solves the conservation of mass-energy issue associated with "dark energy" using the same mechanism that he used to explain dark matter phenomena, and explains the "cosmic coincidence" problem as a bonus prize.

NFW And Einasto DM Halos Don't Work

Neither of the leading models for dark matter particle distributions in dark matter halos can accommodate the observed reality that galaxies have an inner core, rather than an inner cusp. 

[A]n ideal spherically symmetric stellar system with isotropic velocities and an inner core cannot reside in a Navarro, Frenk, and White (NFW) gravitational potential. . . . stellar cores are also inconsistent with Einasto potentials. This result may have implications to constrain the nature of DM through interpreting the stellar cores often observed in dwarf galaxies.

From  Jorge Sanchez Almeida, "Einasto gravitational potentials have difficulty to hold spherically symmetric stellar systems with cores" arXiv:2406.13613 (June 19, 2024) (RNAAS complementing our previous paper Sanchez Almeida et al. (2023, ApJ, 954, 153; doi: https://doi.org/10.3847/1538-4357/ace534)).

Absolute Neutrino Mass Bound Tightened

The old KATRIN bound on the lightest neutrino mass was 0.8 eV. Now it is down to 0.45 eV. This pushes the limit on the sum of the three neutrino masses to 1.41 eV in a normal hierarchy and 1.46 eV in an inverted hierarchy. 

After a full run of data collection, KATRIN is expected to lower that bound to 0.2 eV. This would push the limit on the sum of the three neutrino masses to 0.66 eV in a normal hierarchy and 0.71 eV in an inverted hierarchy. 

This is about six times less tight a bound on the neutrino masses than the cosmology based neutrino mass bounds, which approach 0.12 eV or less for the sum of the three neutrino masses, but this is a much less model dependent limit than cosmology based limit.

The fact that neutrinos carry a non-vanishing rest mass is evidence of physics beyond the Standard Model of elementary particles. Their absolute mass bears important relevance from particle physics to cosmology. In this work, we report on the search for the effective electron antineutrino mass with the KATRIN experiment. KATRIN performs precision spectroscopy of the tritium β-decay close to the kinematic endpoint. Based on the first five neutrino-mass measurement campaigns, we derive a best-fit value of m^2(ν)=−0.14+0.13−0.15 eV^2, resulting in an upper limit of mν < 0.45 eV at 90 % confidence level. With six times the statistics of previous data sets, amounting to 36 million electrons collected in 259 measurement days, a substantial reduction of the background level and improved systematic uncertainties, this result tightens KATRIN's previous bound by a factor of almost two.

M. Aker, et al., "Direct neutrino-mass measurement based on 259 days of KATRIN data" arXiv:2406.13516 (June 19, 2024).

The best fit value for the electron neutrino mass is slightly below zero, when in reality, it can't have a value of less than zero. So, the probability density is heavily concentrated around a value indistinguishable from zero (a bit more than 74% in a Gaussian probability distribution which clearly isn't the true appropriate probability distribution).

So, while the limits of the experiment probably can't rule out of mass of more than 0.2 eV at a 90% confidence interval with a full run of KATRIN experiment, the best fit value after the full run is still likely to be indistinguishable or almost indistinguishable from zero. 

This would imply a best fit value for the sum of the three neutrino masses of about 0.06 eV in a normal hierarchy and 0.11 eV in an inverted hierarchy. And, almost every available observational dataset favors a normal hierarchy over an inverted hierarchy, although not truly decisively.

Measuring The Mean Lifetime Of A Short Lived Particle

The LHCb experiment has measured the mean lifetime of a particle called the bottom xi or cascade B baryon, a spin 1/2 baryon with a down quark, a strange quark, and a bottom quark as valence quarks, with a mass of 5,797.0 ± 0.6 MeV (between the mass of a helium atom and a lithium atom), which is the eighth most massive baryon ever observed (the most massive is the bottom omega baryon with a mass of 6,046.1 ± 1.7 MeV, which is a spin-1/2 baryon with two strange quarks and a bottom quark as valence quarks). 

Its mean lifetime is: 1.578 ± 0.018 ± 0.010 ± 0.011 ps which with a combined uncertainty is 1.578 ± 0.023 ps. A picosecond is 10^-12 seconds (i.e. a trillionth of a second). As the linked article's abstract explains:

This measurement improves the precision of the current world average of the Ξ_b^- lifetime by about a factor of two, and is in good agreement with the most recent theoretical predictions.

It is astounding that we can measure such a tiny span of time to better than 2% precision. The uncertainty in its lifetime is on the order of 40 trillionths of second. 

The measured value is about 0.2% less than the best theoretical prediction to date, and the theoretical prediction also has an uncertainty of about 2%, so the measured value is basically a perfect match to the theoretically predicted value.

There are at least fifteen possible decays of bottom xi baryons whose branching fractions are summarized by the particle data group. This history of this particle's discovery can be found here. The first experimental observation of this particle, which took place at Fermilab, was announced just over seventeen years ago, on June 12, 2007.

There are baryons which decay a trillion times faster, as little as 5.63 ± 0.14 x 10^-24 seconds, usually to a pion and either a proton or a neutron, for the four kinds of spin-3/2 delta baryons which have only up and down quarks as valence quarks and masses of 1232 ± 2 MeV. 

There is nothing terribly notable about this most recent measurement of the mean lifetime of the bottom xi except that it was first publicly announced today in a preprint on arXiv.

Sterile Neutrinos Largely Ruled Out Up To 3eV

A reactor neutrino study has largely ruled out sterile neutrinos up to 3 eV, and possibly up to 4.5 eV. This rules out the Gallium anomaly (explained here), which already has many explanations that do not require new physics.

The preprint and its abstract are as follows:

The PROSPECT experiment is designed to perform precise searches for antineutrino disappearance at short distances (7-9 ~m) from compact nuclear reactor cores. This Letter reports results from a new neutrino oscillation analysis performed using the complete data sample from the PROSPECT-I detector operated at the High Flux Isotope Reactor in 2018. 

The analysis uses a multi-period selection of inverse beta decay neutrino interactions with reduced backgrounds and enhanced statistical power to set limits on electron-flavor disappearance caused by mixing with sterile neutrinos with 0.2-20 eV^2 mass splittings. 

Inverse beta decay positron energy spectra from six different reactor-detector distance ranges are found to be statistically consistent with one another, as would be expected in the absence of sterile neutrino oscillations. The data excludes at 95% confidence level the existence of sterile neutrinos in regions above 3~eV^2 previously unexplored by terrestrial experiments, including all space below 10~eV^2 suggested by the recently strengthened Gallium Anomaly. The best-fit point of the Neutrino-4 reactor experiment's claimed observation of short-baseline oscillation is ruled out at more than five standard deviations.

M. Andriamirado, et al., "Final Search for Short-Baseline Neutrino Oscillations with the PROSPECT-I Detector at HFIR" arXiv:2406.10408 (June 14, 2024).

Neutrino-less double beta decay has also been further constrained: 

We present a search for neutrinoless double-beta (0νββ) decay of 136Xe using the full KamLAND-Zen 800 dataset with 745 kg of enriched xenon, corresponding to an exposure of 2.097 ton yr of 136Xe. This updated search benefits from a more than twofold increase in exposure, recovery of photo-sensor gain, and reduced background from muon-induced spallation of xenon. 

Combining with the search in the previous KamLAND-Zen phase, we obtain a lower limit for the 0νββ decay half-life of T(0ν1/2) > 3.8×10^26 yr at 90% C.L., a factor of 1.7 improvement over the previous limit. The corresponding upper limits on the effective Majorana neutrino mass are in the range 28-122 meV using phenomenological nuclear matrix element calculations.

S. Abe, et al., "Search for Majorana Neutrinos with the Complete KamLAND-Zen Dataset" arXiv:2406.11438 (June 17, 2024).

Analysis 

This is still a long way from ruling out neutrinos with purely Majorana mass in either the inverted hierarchy (which requires a half-life about 1000 times as long), or the normal hierarchy. (which requires a half-life 100,000 to 1,000,000 times as long).

This upper bound on Majorana mass implies a maximum sum of the three neutrino masses, if neutrinos have purely Majorana mass and an inverted hierarchy, of about 0.5 eV.

The upper bound on the sum of the three neutrino masses due to direct measurements of the lightest neutrino mass at Katrin of 0.8 eV is currently about 2.51 eV. When Katrin runs its course, this should fall to a lightest neutrino mass of less than 0.2 eV  and a sum of the three neutrino masses of less than 0.71 eV.

The lower bound on the sum of the neutrino masses based upon neutrino oscillation data is about 0.059 eV in the normal hierarchy and 0.109 eV in the inverted hierarchy.

Cosmology bounds on the sum of the three neutrino masses are much tighter, but with the DESI data set, the bounds on the sum of the three neutrino masses from all sources are on the verge of being over constrained (i.e. the cosmology bounds favor a sum of the three neutrino masses under 0.059 eV), which suggests that the cosmology model used to set these bound may be flawed. 

Were There More Kinds of Archaic Hominins In China?

John Hawks' latest blog post, "Julurens: a new cousin for Denisovans and Neanderthals" with a subtitle, "A new study suggests that the Middle Pleistocene record in China includes more groups than have previously been recognized," suggests that the hominin landscape in the era of Denisovans and Neanderthals in what is now called China may have been more complex than previously realized. He explains that:

A new article from Xiujie Wu and Christopher Bae presents a new look at some fossils of the later Middle Pleistocene. They focus on fossil samples from Xujiayao in north China and Xuchang in central China. These fossils, which date to between 220,000 and 100,000 years ago, contrast with the so-called “Dragon Man” skull from Harbin and other similar remains. Wu and Bae suggest that the Xujiayao and Xuchang fossils may be something different and call them the Julurens—a name that means “big heads”.

Who were the Julurens? Here I give a quick rundown of the key fossils. I also dive into the broader question of how variation in the fossil record may relate to the DNA evidence, especially the Denisovans.

Diagram showing recent estimates of population mixture among Pleistocene human groups. The deep divergence among “Denisovan” lineages follows the analysis of Jacobs and coworkers (2019).

Read the whole article.

Do All Galaxies Have A Billion Year Rotation Period?

This isn't breaking news, but it is new to me.

H I-selected galaxies obey a linear relationship between their maximum detected radius Rmax and rotational velocity. This result covers measurements in the optical, ultraviolet, and H I emission in galaxies spanning a factor of 30 in size and velocity, from small dwarf irregulars to the largest spirals. Hence, galaxies behave as clocks, rotating once a Gyr at the very outskirts of their discs. Observations of a large optically selected sample are consistent, implying this relationship is generic to disc galaxies in the low redshift Universe. A linear radius–velocity relationship is expected from simple models of galaxy formation and evolution. 

The total mass within Rmax has collapsed by a factor of 37 compared to the present mean density of the Universe. Adopting standard assumptions, we find a mean halo spin parameter λ in the range 0.020–0.035. The dispersion in λ, 0.16 dex, is smaller than expected from simulations. This may be due to the biases in our selection of disc galaxies rather than all haloes. The estimated mass densities of stars and atomic gas at Rmax are similar (∼0.5 M⊙ pc−2), indicating outer discs are highly evolved. The gas consumption and stellar population build time-scales are hundreds of Gyr, hence star formation is not driving the current evolution of outer discs. The estimated ratio between Rmax and disc scalelength is consistent with long-standing predictions from monolithic collapse models. Hence, it remains unclear whether disc extent results from continual accretion, a rapid initial collapse, secular evolution, or a combination thereof.

Gerhardt R Meurer, Danail Obreschkow, O Ivy Wong, Zheng Zheng, Fiona M Audcent-Ross, D J Hanish, "Cosmic clocks: a tight radius–velocity relationship for H I-selected galaxies"476(2) Monthly Notices of the Royal Astronomical Society (MNRAS) 1624–1636 (March 9, 2018, in print May 2018).

Flat Rotation Curves Extend A Long Way

This evidence, if established more definitively, is a strong blow to basically all dark matter particle theories and a useful data point to distinguish different gravity based explanations of dark matter phenomena.

We use a new deprojection formula to infer the gravitational potential around isolated galaxies from weak gravitational lensing. The results imply circular velocity curves that remain flat for hundreds of kpc, greatly extending the classic result from 21 cm observations. Indeed, there is no clear hint of a decline out to 1 Mpc, well beyond the expected virial radii of dark matter halos. Binning the data by mass reveals a correlation with the flat circular speed that closely agrees with the Baryonic Tully-Fisher Relation known from kinematic data. These results apply to both early and late type galaxies, indicating a common universal behavior.

Tobias Mistele, Stacy McGaugh, Federico Lelli, James Schombert, Pengfei Li, "Indefinitely Flat Circular Velocities and the Baryonic Tully-Fisher Relation from Weak Lensing" arXiv:2406.09685 (June 14, 2024) (accepted for publication in ApJL).

Problems For The X17 Particle Hypothesis

I would be extremely surprised if the existence of a new hypothetical X17 particle was confirmed. This paper supports that skepticism.

Recent findings of an unexpected, narrow resonance in the e+e− decay spectra of excited states of 8Be, 4He and 12C by the ATOMKI collaboration have received considerable experimental and theoretical attention, whereby a new, 17-MeV vector-like or axial-vector-like boson termed X17 was conjectured as an explanation of the anomaly. 

Further analysis of all existing constraints disfavors a vector X17 scenario. 

For a similar analysis of the axial-vector scenario, a calculation of the reduced matrix element of a spin-dipole operator between the excited nuclear state C(17.23) and the carbon ground state is required. In the present work, we compute the aforementioned reduced matrix element under the assumption that the state C(17.23) is well represented by the 2s1/21p−13/2 particle-hole shell-model excitation of the ground state, as supported by experimental data. Within such a framework, our results indicate that, like the vector scenario, the axial-vector interpretation of X17 shows strong tensions with the other existing constraints on the nucleon coupling of a conjectured X17.

Cornelis J.G. Mommers, Marc Vanderhaeghen, "Constraining the axial-vector X17 interpretation with 12C data" arXiv:2406.08143 (June 12, 2024).

The Mayans Ritually Sacrificed Young Boys, Many Related

The team behind the new study was able to extract and sequence ancient DNA from 64 out of around 100 individuals, whose remains were found scattered in a water chultún — an underground storage chamber discovered in 1967 about 400 meters (437 yards) from the sacred sinkhole in Chichén Itzá.

With radiocarbon dating, the team found that the underground cavern was used for 500 years, although most of the children whose remains the team studied were interred there between AD 800 and 1,000 — during the height of Chichén Itzá’s political power in the region.

All the children were boys, who had been drawn from the local Maya population at that time, according to the DNA analysis, and at least a quarter of them were closely related to at least one other child in the chultún. The group also included two pairs of twins as well as siblings and cousins. Most of the boys were between 3 and 6 years old when they died.

Analysis of variants or isotopes of carbon and nitrogen in the bones also suggested that the related children had similar diets. Together, according to the authors, these findings suggested that related male children were likely selected in pairs for ritual sacrifices linked to the chultún.

“It is surprising to me to see family members, given the enormous time breadth of the deposit, which by radiocarbon dates is now confirmed to have been used over a time span of 500 years, during which these bodies slowly accumulated,” said Vera Tiesler, a bioarchaeologist and professor at the Autonomous University of Yucatán, in an email. She wasn’t involved in the research.

While the study authors believe this finding reveals the only known burial of sacrificed male children, Tiesler said that the ancient Maya ritual calendar was complex, likely with different “victim profiles” for different religious occasions throughout the year and time cycles.

From CNN discussing the following paper:

The ancient city of Chichén Itzá in Yucatán, Mexico, was one of the largest and most influential Maya settlements during the Late and Terminal Classic periods (AD 600–1000) and it remains one of the most intensively studied archaeological sites in Mesoamerica. However, many questions about the social and cultural use of its ceremonial spaces, as well as its population’s genetic ties to other Mesoamerican groups, remain unanswered. 

Here we present genome-wide data obtained from 64 subadult individuals dating to around AD 500–900 that were found in a subterranean mass burial near the Sacred Cenote (sinkhole) in the ceremonial centre of Chichén Itzá. 

Genetic analyses showed that all analysed individuals were male and several individuals were closely related, including two pairs of monozygotic twins. Twins feature prominently in Mayan and broader Mesoamerican mythology, where they embody qualities of duality among deities and heroes, but until now they had not been identified in ancient Mayan mortuary contexts. 

Genetic comparison to present-day people in the region shows genetic continuity with the ancient inhabitants of Chichén Itzá, except at certain genetic loci related to human immunity, including the human leukocyte antigen complex, suggesting signals of adaptation due to infectious diseases introduced to the region during the colonial period.

Rodrigo Barquera, et al., "Ancient genomes reveal insights into ritual life at Chichén Itzá" Nature (June 12, 2024) (open access).

The discussion in the paper of the possible religious beliefs associated with the sacrifices or of the 16th century Spanish accounts of the practice (some of which, like the gender of the sacrifice victims, is provable wrong), is intriguing. See also the Dresden Codex which has origins at the same Mayan site:

The Dresden Codex is a Maya book, which was believed to be the oldest surviving book written in the Americas, dating to the 11th or 12th century. However, in September 2018 it was proven that the Maya Codex of Mexico, previously known as the Grolier Codex, is, in fact, older by about a century. The codex was rediscovered in the city of Dresden, Germany, hence the book's present name. It is located in the museum of the Saxon State Library. The codex contains information relating to astronomical and astrological tables, religious references, seasons of the earth, and illness and medicine. It also includes information about conjunctions of planets and moons. . . . 

The Dresden Codex is described by historian J. Eric S. Thompson as writings of the indigenous people of the Yucatán Peninsula in southeastern Mexico. Maya historians Peter J. Schmidt, Mercedes de la Garza, and Enrique Nalda confirm this. Thompson further narrows the probable origin of the Dresden Codex to the area of Chichen Itza, because certain picture symbols in the codex are only found on monuments in that location. He also argues that the astronomical tables would support this as the place of origin. Thompson claims that the people of the Yucatán Peninsula were known to have done such studies around 1200 A.D. Thompson also notes the similar ceramic designs in the Chichen Itza area which are known to have ceased in the early thirteenth century. British historian Clive Ruggles suggests, based on the analyses of several scholars, that the Dresden Codex is a copy and was originally written between the twelfth and fourteenth centuries. Thompson narrows the date closer to 1200 to 1250. Maya archaeologist Linton Satterthwaite puts the date when it was made as no later than 1345.

A natural response to these human sacrifices is to ask "why" and to put it in the context of some narrative, which can be done only incompletely.

WIMP Exclusions And Other Constraints On Dark Matter Properties

For clarity, I don't think that dark matter particles exist. I think that dark matter phenomena is due to a gravitational effect or a fifth force. But ruling out dark matter particle candidates strengthens that case.

WIMPs (weakly interacting massive particles), which are predicted by supersymmetry, for example, which should be possible to detect in sensitive dark dark matter detection experiments, are strongly disfavored as dark matter candidates given the latest data.

Additional data, not considered in this chart, strongly disfavor GeV and heavier dark matter candidates based upon galaxy dynamics, separate and apart from the direct dark matter detection observations shown below.

This is a blow not just to the WIMP dark matter particle candidate (that has quietly ceased to be the subject of many publications about dark matter), but also to supersymmetry, which has a WIMP candidate as one of its core predictions, and to many versions of string theory, for which supersymmetry is a low energy approximation. Non-detection of any sign of supersymmetric particles at the Large Hadron Collider (LHC) further disfavors supersymmetric WIMPs and supersymmetry.

The original WIMP prediction assumed an interaction cross-section comparable to that of a neutrino which would have arisen from the Standard Model  weak force, and a mass on the order of 100 GeV which would have been optimal for resolving the "hierarchy problem" at the electro-weak scale, which was the initial motivation for supersymmetry.

An interaction of 10-1000 GeV mass dark matter particles with ordinary matter, if such a particle exists, has to be at least 10,000,000 times weaker than the interactions between neutrinos and ordinary matter. If it has a mass of about 40 GeV the interaction has to be about 100,000,000 times weaker. This excludes not just weak force mediated interactions but also Higgs field mediated interactions. 

An interaction weaker than a weak force interaction is experimentally excluded down to about 2 GeV of WIMP mass.

The bottom line is that if dark matter particles exist and have a mass in  the 10-1000 GeV mass range, they have absolutely no non-gravitational interactions with ordinary matter. This is a dark matter particle property that faces another observational constraint. There is a tight correlation between inferred dark matter particle distributions in inferred dark matter halos with ordinary matter distributions. This correlation is much stronger than should be possible from gravitational interactions alone.

So, WIMPs are pretty definitively not the correct explanation for dark matter phenomena. 

Many new dark matter particle papers argue that WIMPs are "well-motivated" dark matter candidates based upon citations to older papers. But this is no longer the case.

The interaction cross section as a function of WIMP mass. The original expectation of 10^-39cm² is at top. Gray areas are regions that were experimentally excluded by 2008 (before the blue-green prediction) and by 2022, which is the most recent update as of this writing. The most sensitive limit is 10^-47 cm², eight orders of magnitude below the original prediction.

Via Triton Station. 

At masses much below 10 GeV, and certainly at masses below 1 MeV, direct dark matter detection experiments of that kind that are the basis for the chart below lose most of their observational power because the background noise from neutrinos overwhelms any possible signal from dark matter interactions with the detector. 

The chart below showing this background and the caption are also via Triton Station.

WIMP experimental limits (via Hamdan 2021) with the expected neutrino background in orange. Once this sensitivity is reached, any WIMP signal becomes obscured by the neutrino background.

To subtract this background to try to improve the signal would require a better understanding of the neutrino background than we have at this time and would even then degrade the precision of the measurement. 

Fermionic Dark Matter Can't Be Less Massive Than A Neutrino

Stacy McGaugh also makes a notable observation in a comment which rules out a very different part of the dark matter parameters space:

neutrinos are fermions and subject to a close-packing limit imposed by the Pauli Exclusion Principle. A less well-known problem for neutrinos as dark matter is that there are some regions where the dark matter density is too high to be explained by fermions of neutrino mass. They can’t be packed in tightly enough.

Thus, we can pretty much categorically rule out all fermionic dark matter candidates which are less massive than neutrinos (realistically, having less than meV mass). So, light dark matter candidates must be bosons.

Dark Matter Must Be Wave-Like And Thus Light

Another large generic exclusion of dark matter parameter space is that there is observational evidence that dark matter particles, if they exist, must be "wave-like" which suggests that it must have a particle mass of not more than about 10 keV. The same line of research favors a dark matter particle mass of much, much less than the neutrino mass, which we know, from McGaugh's comment, must also be a boson (realistically spin-0, spin-1, or spin-2). 

The requirement that dark matter be wave-like also rules out, for example, all hadronic dark matter candidates and primordial black holes, in addition to providing another means to exclude WIMPs down to the MeV mass or so, even if they are sterile (i.e. having no non-gravitational interactions). 

The requirement that dark matter be wave-like also generically rules out "thermal freeze out" dark matter candidates, other than warm dark matter with a dark matter particle mass on the order of 1-10 keV, which would have too high of a mean velocity at the necessarily low dark matter particle masses.

Two New Archaic Ancestry Papers

Neither of two new papers about archaic admixture, and in one case, more general issues in South Asian historical genetics, are paradigm changing. But both papers refine the story we already have with more fine detail and more certainty.

India has been underrepresented in whole genome sequencing studies. We generated 2,762 high coverage genomes from India––including individuals from most geographic regions, speakers of all major languages, and tribal and caste groups––providing a comprehensive survey of genetic variation in India. With these data, we reconstruct the evolutionary history of India through space and time at fine scales. 

We show that most Indians derive ancestry from three ancestral groups related to ancient Iranian farmers, Eurasian Steppe pastoralists and South Asian hunter-gatherers. We uncover a common source of Iranian-related ancestry from early Neolithic cultures of Central Asia into the ancestors of Ancestral South Indians (ASI), Ancestral North Indians (ANI), Austro-asiatic-related and East Asian-related groups in India. 

Following these admixtures, India experienced a major demographic shift towards endogamy, resulting in extensive homozygosity and identity-by-descent sharing among individuals. 

At deep time scales, Indians derive around 1-2% of their ancestry through gene flow from archaic hominins, Neanderthals and Denisovans. By assembling the surviving fragments of archaic ancestry in modern Indians, we recover ∼1.5 Gb (or 50%) of the introgressing Neanderthal and ∼0.6 Gb (or 20%) of the introgressing Denisovan genomes, more than any other previous archaic ancestry study. Moreover, Indians have the largest variation in Neanderthal ancestry, as well as the highest amount of population-specific Neanderthal segments among worldwide groups. 

Finally, we demonstrate that most of the genetic variation in Indians stems from a single major migration out of Africa that occurred around 50,000 years ago, with minimal contribution from earlier migration waves. 

Together, these analyses provide a detailed view of the population history of India and underscore the value of expanding genomic surveys to diverse groups outside Europe.

Elise Kerdoncuff, et al., "50,000 years of Evolutionary History of India: Insights from ∼2,700 Whole Genome Sequences" bioRxiv (February 20, 2024).

Gene flow from Neandertals has shaped the landscape of genetic and phenotypic variation in modern humans. We identify the location and size of introgressed Neandertal ancestry segments in more than 300 genomes spanning the last 50,000 years. We study how Neandertal ancestry is shared among individuals to infer the time and duration of the Neandertal gene flow. 

We find the correlation of Neandertal segment locations across individuals and their divergence to sequenced Neandertals, both support a model of single major Neandertal gene flow. Our catalog of introgressed segments through time confirms that most natural selection–positive and negative–on Neandertal ancestry variants occurred immediately after the gene flow, and provides new insights into how the contact with Neandertals shaped human origins and adaptation.

Leonardo N. M. Iasi, et al., "Neandertal ancestry through time: Insights from genomes of ancient and present-day humans" bioRxiv (May 13, 2024).

According to a news report on the second paper:

The best explanation for most Neanderthal DNA seen in the modern human genome was a single major period of interbreeding about 47,000 years ago that lasted about 6,800 years, the researchers found.

Peak Denisovan Ancestry Is Found In The Philippines

A few years ago, it was discovered that Denisovan ancestry makes up the largest percentage of a modern population in a group of people in the Philippines (these peoples also have the typical level of Neanderthal ancestry found in non-African modern humans).

This implies the co-existence of the earliest modern human Negrito people and Denisovans during the early to middle Upper Paleolithic era (ca. 50,000 years ago).  

The extinction of the last Neanderthals in Europe was about 29,000 years ago, although Neanderthal admixture with modern humans was mostly 100,000 to 35,000 or so years ago.

This was perhaps 50,000 years after the extinction of Homo erectus, based upon the youngest known Homo erectus remains, although an extinction date 70,000 years ago in line with the Toba eruption and first contact wiht modern humans is a plausible possible extinction date that later discoveries could support.

Multiple lines of evidence show that modern humans interbred with archaic Denisovans. 

Here, we report an account of shared demographic history between Australasians and Denisovans distinctively in Island Southeast Asia. Our analyses are based on ∼2.3 million genotypes from 118 ethnic groups of the Philippines, including 25 diverse self-identified Negrito populations, along with high-coverage genomes of Australopapuans and Ayta Magbukon Negritos. 

We show that Ayta Magbukon possess the highest level of Denisovan ancestry in the world—∼30%–40% greater than that of Australians and Papuans—consistent with an independent admixture event into Negritos from Denisovans. Together with the recently described Homo luzonensis, we suggest that there were multiple archaic species that inhabited the Philippines prior to the arrival of modern humans and that these archaic groups may have been genetically related. 

Altogether, our findings unveil a complex intertwined history of modern and archaic humans in the Asia-Pacific region, where distinct Islander Denisovan populations differentially admixed with incoming Australasians across multiple locations and at various points in time.

Maximillian Larena, et al., "Philippine Ayta possess the highest level of Denisovan ancestry in the world" 31(19) Current Biology 4219-4230 (August 12, 2021 in print October 11, 2021) (open access). 

The body text discusses the estimated timing of admixture and divergence and the amount of East Asian admixture in the relevant populations:

East Asian-related Admixture in Negritos 

To determine the presence of East Asian admixture among Philippine Negritos, we implemented the test D(Mbuti;EastAsian,Papuan,X); with Balangao Cordilleran utilized as a surrogate for the least admixed East Asian source. We find that all Philippine Negritos display varied levels of gene flow from East Asians, with Ayta Magbukon presenting as the least admixed. 

To estimate the levels of East Asian and Australasian-related ancestries in Negritos, we implemented the qpAdm tool of Admixtools v5.0 software package. We first prepared a new dataset with reference ancient samples, by merging Phil_1KGP_SGDP_1.92M dataset with published ancient DNA data to produce the Phil_1KGP_SGDP_Ancient_1.92M dataset, which was then haploidized and filtered to keep transversion sites only, producing the Phil_1KGP_SGDP_Ancient_Transv_317K dataset with 317,220 SNPs. 

The ‘left’ populations include Balangao Cordilleran of the Philippines as the surrogate for the least admixed East Asian source and Papuan as the surrogate for the least admixed Australasian source. The outgroup or ‘right’ populations include Juhoansi, Mbuti, Mota, Loschbour, Anzick1, Ust’Ishim, Sumiduouro, and Karitiana. 

Overall, there is a wide variation in the magnitude of admixture with East Asians. For instance, Ayta Magbukon and Ayta Ambala presented as the least admixed Negrito populations, with an East Asian-related ancestry of only ∼10%–30%. On the other hand, both Agta Bulusan and Agta Matnog have the highest levels of admixture, possessing ∼79%–85% East Asian-related ancestry. To estimate the date of admixture, we utilized MALDER, which applies a weighted linkage disequilibrium (LD) statistic-based method and allows detection of multiple admixture events. Philippine non-Negritos, Amis, Atayal, mainland East Asians, and Australopapuans were set as putative source populations, while all Philippine Negrito groups were set as target populations. The mean date of admixture between Negritos and East Asians among all ethnic groups within the Philippines was estimated to ∼2,281 years (95% CI: 2,083 – 2,523 years). 

This time frame is largely historically consistent with the arrival of Austronesian mariners in the Philippines. 

Divergence Time between Negritos and Papuans 

To estimate the divergence time between Philippine Negritos versus Papuans, we utilized the ‘TT’ method, which is based on computing sample configurations in a population divergence model. This approach estimates the number of generations since a population divergence for a pair of individuals (or populations), and the method produces direct estimates in generations that are unaffected by the effective population size of the population of each of the individuals in the comparison. We utilized the publicly available genome sequence data on Papuans and our newly generated sequence data on Ayta Magbukon. 

The estimated divergence time between Ayta Magbukon Negrito and Papuans is ∼85 kya (95% CI: 76 – 95 kya). This unusually old divergence time may be attributed to the deeply diverging Denisovan ancestries found in both Papuans and Ayta Magbukon. 

To correct the effect of archaic introgression, we filtered out all the archaic sequences (that were identified using the S’ method) in both Ayta Magbukon and Papuans. The estimated divergence time between Ayta Magbukon Negritos and Papuans, using the filtered data, is 53 kya (95% CI: 41-64 kya). This estimated date falls shortly after the divergence between Australasians and East Asians/West Eurasians, which was previously estimated to ∼58 kya (95% CI: 51 – 72 kya).

The Denisovan populations that were sources for populations in the Philippines and Papuan populations respectively, might have been 100,000 or more years diverged from each other. 

Y-DNA Claims Purporting To Support The Elamo-Dravidian Linguistic Hypothesis

I've long been unimpressed with the lingustic Elamo-Dravidian hypothesis, but there is a paper trying to make that case from Y-DNA that I'll note for balance, although I still don't find the claim to be convincing. It isn't clear that Elamite was a language in the L1-M22 population when it migrated to South Asia, nor is it clear that their language became dominant in South Asia after they arrived by the time it expanded 2,000 to 4,000 years later after stasis in the interim period.

West and South Asian populations profoundly influenced Eurasian genetic and cultural diversity. We investigate the genetic history of the Y chromosome haplogroup L1-M22, which, while prevalent in these regions, lacks in-depth study. 

Robust Bayesian analyses of 165 high-coverage Y chromosomes favor a West Asian origin for L1-M22 ∼20.6 thousand years ago (kya). Moreover, this haplogroup parallels the genome-wide genetic ancestry of hunter-gatherers from the Iranian Plateau and the Caucasus.

We characterized two L1-M22 harboring population groups during the Early Holocene. One expanded with the West Asian Neolithic transition. The other moved to South Asia ∼8-6 kya but showed no expansion. This group likely participated in the spread of Dravidian languages. These South Asian L1-M22 lineages expanded ∼4-3 kya, coinciding with the Steppe ancestry introduction.

Our findings advance the current understanding of Eurasian historical dynamics, emphasizing L1-M22’s West Asian origin, associated population movements, and possible linguistic impacts.

Ajai Kumar Pathak, et al., "Human Y chromosome haplogroup L1-M22 traces Neolithic expansion in West Asia and supports the Elamite and Dravidian connection" 27(6) Cell 110016 (May 16, 2024 published in journal on June 21, 2024) (open access) DOI:https://doi.org/10.1016/j.isci.2024.110016 (the paper also notably acknowledges ChatGPT 3.5 editing assistance).

Ancient Celtic Elite DNA

The earliest Celtic rulers in Europe for a period of about 350 year may have been mostly from the same matrilineally inherited royal dynasty.

The early Iron Age (800 to 450 BCE) in France, Germany and Switzerland, known as the ‘West-Hallstattkreis’, stands out as featuring the earliest evidence for supra-regional organization north of the Alps. Often referred to as ‘early Celtic’, suggesting tentative connections to later cultural phenomena, its societal and population structure remain enigmatic. 

Here we present genomic and isotope data from 31 individuals from this context in southern Germany, dating between 616 and 200 BCE. We identify multiple biologically related groups spanning three elite burials as far as 100 km apart, supported by trans-regional individual mobility inferred from isotope data. These include a close biological relationship between two of the richest burial mounds of the Hallstatt culture. Bayesian modelling points to an avuncular relationship between the two individuals, which may suggest a practice of matrilineal dynastic succession in early Celtic elites. We show that their ancestry is shared on a broad geographic scale from Iberia throughout Central-Eastern Europe, undergoing a decline after the late Iron Age (450 BCE to ~50 CE).

Joscha Gretzinger et al., "Evidence for dynastic succession among early Celtic elites in Central Europe" Nature Human Behavior (June 3, 2024) (open access).

The paper is explored further at Bernard's Blog who notes that (per Google translate into English from French): "the results of this study suggest an avuncular society among the early Celts of the fifth or fourth century BCE era, in agreement with the historical writings of the Romans."

The Google translate in English of the French Wikipedia link to avuncular society (with minor grammatical and spelling edits) states:

The term avuncular is a technical term used, in the anthropology of kinship, to designate a privileged relationship between Ego, reference person, and his “maternal uncle” or, conversely, between Ego and his uterine nephew or niece.

The term avuncular itself derives from the Latin avunculus, a kinship term used to designate, in this language, the mother's brother (MB) as opposed to the father's brother patruus (FB). In certain societies with marked matrilineal filiation, the role which is assigned to the father in other societies can be assumed by the maternal uncle who becomes the “social father” of his sister's children. The notion of avuncular is, however, not reserved for the designation of this formula of descent (which is, moreover, rather rare) and it can also describe a formula of matrimonial alliance. The marriage of a man with his sister's daughter is thus called avuncular marriage. If the term avuncular applies to the links which unite the mother's brother and the sister's son or daughter, it can however also, in a more loose way, be used to designate the relationship between a paternal uncle and a child of his brother.

This marks a distinct shift from Bronze Age Indo-Europeans in Europe, including among the Bell Beaker people who are likely ancestral to the Celtic people, who exhibit a strict patriarchal, patrilocal clan structure.

Razib Khan also notes that the paper "makes it clear that Proto-Celtic Hallstatt southern Germany saw significant genetic change with the spread of Germanic languages from the north."

A Survey Of Notable Non-MOND Modified Gravity Theories

Some of the more notable theories beyond general relativity or applying general relativity in non-conventional (and not widely accepted) ways that are gravity based models to explain dark matter and/or dark energy phenomena which are not MOND or a close elaboration of it include the following theories:

* Moffat's MOG, see, e.g., J.W. Moffat (2015); MOG also explains the cosmic microwave background power spectrum. J.W. Moffat (2001); John W. Moffat, "Wide Binaries and Modified Gravity (MOG)" arXiv:2311.17130 (November 28, 2023), Mahmood Roshan, "Stellar Bar evolution in the absence of dark matter halo" (January 25, 2018);

* Verlinde's entropic/emergent gravity, see e.g., Erik P. Verlinde, "Emergent Gravity and the Dark Universe" arXiv:1611.02269 (November 7, 2016), Jungjai Lee, Hyun Seok Yang, "Dark Energy and Dark Matter in Emergent Gravity" arXiv:1709.04914 (September 14, 2017, last revised November 1, 2022) (published at 81(9) Journal of the Korean Physical Society 910-920 (2022)); A. Schlatter, R. E. Kastner, "Gravity from Transactions: A Review of Recent Developments" arXiv:2209.04025 (September 8, 2022);

* Deur's work, see, e.g., A. Deur, "Effect of the field self-interaction of General Relativity on the Cosmic Microwave Background Anisotropies" arXiv:2203.02350 (March 4, 2022)), with a somewhat similar approach from Yuta Ito, "Gravitational Amplification of Test-Mass Potential in the Self-gravitating Isothermal Gaseous Systems" arXiv:2303.02631 (March 5, 2023);

* f(R) gravity, Eddington-inspired-Born-Infeld (EiBI) and general relativity with renormalization group effects (RGGR) (three different modified gravity theories discussed in one paper) see Alejandro Hernandez-Arboleda, Davi C. Rodrigues, Aneta Wojnar, "Normalized additional velocity distribution: a fast sample analysis for dark matter or modified gravity models" arXiv:2204.03762 (April 7, 2022);

* f(R) gravity, see, e.g., Vesna Borka Jovanović, Predrag Jovanović, Duško Borka, Salvatore Capozziello, "Fundamental plane of elliptical galaxies in f(R) gravity: the role of luminosity" (December 28, 2018);

* f(Q) gravity, see, e.g., Gaurav N. Gadbail, "Cosmological dynamics of interacting dark energy and dark matter in f(Q) gravity" arXiv:2406.02026 (June 4, 2024);

* f(T) gravity, see, e.g., A. R. P. Moreira, "Geometrically contracted structure in teleparallel f(T) gravity" arXiv:2212.08948 (December 17, 2022);

* scalar-tensor gravity theories, see, e.g., Thomas P. Sotiriou, Valerio Faraoni, "Modified gravity with R-matter couplings and (non-)geodesic motion" arXiv:0805.1249 (September 27, 2008);

* long range quantum gravity, see, e.g., Matteo Tuveri, Mariano Cadoni "Galactic dynamics and long-range quantum gravity" arXiv:1904.11835 (April 26, 2019);

* modified general relativity, see, e.g., Gary Nash, "Modified general relativity" arXiv:1904.10803 (April 22, 2019);

* metric skew tensor gravity, see, e.g., W.M. Stuckey, Timothy McDevitt, A.K. Sten, Michael Silberstein, "The Missing Mass Problem as a Manifestation of GR Contextuality" 27(14) International Journal of Modern Physics D 1847018 (2018). DOI: 10.1142/S0218271818470181;

* curvature and topology based model of gravity, see, e.g., Valeri P. Frolov, "Limiting curvature models of gravity" arXiv:2111.14318 (November 29, 2021); Richard Lieu, arXiv:2406.04355 "The binding of cosmological structures by massless topological defects" (May 16, 2024);

* conformal gravity a.k.a. Weyl Conformal gravity, see, e.g., Philip D. Mannheim, "Is dark matter fact or fantasy? -- clues from the data" (March 27, 2019), James G. O'Brien, et al., "Radial Acceleration and Tully-Fisher Relations in Conformal Gravity" (December 7, 2018), Philip D. Mannheim, "Making the Case for Conformal Gravity" (October 27, 2011), and Leonardo Modesto, Tian Zhou, Qiang Li, "Geometric origin of the galaxies' dark side" arXiv:2112.04116 (December 8, 2021);

* GR with torsion added, see, e.g., S. H. Pereira, et al., "Dark matter from torsion in Friedmann cosmology" arXiv:2202.01807 (February 3, 2022);

* negative mass models, see, e.g., Hector Socas-Navarro, "Can a negative-mass cosmology explain dark matter and dark energy?" arXiv:1902.08287 (February 21, 2019);

* the effort of Naman Kumar to explain the dark energy with an anti-matter mirror universe, see, e.g., Naman Kumar, "On the Accelerated Expansion of the Universe" 30 Gravitation and Cosmology 85-88 arxiv.org:2406.04392 (April 4, 2024);

* string theory/brane theory approaches, see, e.g., Naman Kumar, "Variable Brane Tension and Dark Energy" arXiv:2404.17941 (April 27, 2024);

* non-Verlinde efforts based on entropy and Mach's principle, see, e.g., Santanu Das, "Aspects of Machian Gravity (III): Testing Theory against Galaxy Cluster mass" arXiv:2312.06312 (December 11, 2023) and Kimet Jusufi, Ahmad Sheykhi, Salvatore Capozziello, "Apparent dark matter as a non-local manifestation of emergent gravity" arXiv:2303.14127 (March 23, 2023), Rubén Arjona, et al., "A GREAT model comparison against the cosmological constant" arXiv:2111.13083 (November 25, 2021). Report number: IFT-UAM/CSIC-2021-136m, and Andre Maeder "Dynamical Effects of the Scale Invariance of the Empty Space: The Fall of Dark Matter?" 849(2) The Astrophysical Journal 158 (November 10, 2017) (pre-print here);

* general co-variance breaking gravity, see, e.g., Alexander P. Sobolev, "Foundations of a Theory of Gravity with a Constraint and its Canonical Quantization" 52 Foundations of Physics Article number: 3 arXiv:2111.14612 (open access, pre-print November 25, 2021, publication date anticipated 2022) DOI: 10.1007/s10701-021-00521-1;

* Pascoli's K-model, see, e.g., Gianni Pascoli, "A comparative study of MOND and MOG theories versus the κ-model: An application to galaxy clusters" arXiv:2307.01555 (July 4, 2023);

* gravitomagnetic and other perturbative GR effect approaches, see, e.g., Kostas Glampedakis, David Ian Jones, "Pitfalls in applying gravitomagnetism to galactic rotation curve modelling" arXiv:2303.16679 (March 29, 2023), A. N. Lasenby, M. P. Hobson, W. E. V. Barker, "Gravitomagnetism and galaxy rotation curves: a cautionary tale" arXiv:2303.06115 (March 10, 2023), Yogendra Srivastava, Giorgio Immirzi, John Swain, Orland Panella, Simone Pacetti, "General Relativity versus Dark Matter for rotating galaxies" arXiv:2207.04279 (July 9, 2022), G. O. Ludwig, "Galactic rotation curve and dark matter according to gravitomagnetism" 81 The European Physical Journal C 186 (February 23, 2021) (open access), F.I. Cooperstock, S. Tieu, "Galactic dynamics via general relativity: a compilation and new developments." 22 Int. J. Mod. Phys. A 2293–2325 (2007). arXiv:astro-ph/0610370 see also follow up papers in 2007, in 2011, and 2015; H. Balasin, D. Grumiller, "Non-Newtonian behavior in weak field general relativity for extended rotating sources." 17 Int. J. Mod. Phys. D 475–488 (2008) (arXiv version here); M. Crosta, M. Giammaria, M.G. Lattanzi, E. Poggio, "On testing CDM and geometry-driven Milky Way rotation curve models with Gaia DR2." 496 Mon. Not. R. Astron. Soc. 2107–2122 (2020) (open access); Missing Mass Problem as a Manifestation of GR Contextuality" 27(14) International Journal of Modern Physics D 1847018 (2018). DOI: 10.1142/S0218271818470181, Federico Re, "Fake dark matter from retarded distortions" (May 30, 2020), Felipe J. Llanes-Estrada, "Elongated Gravity Sources as an Analytical Limit for Flat Galaxy Rotation Curves" 7(9) Universe 346 arXiv:2109.08505 (September 16, 2021) DOI: 10.3390/universe7090346, P. Tremblin, et al., "Non-ideal self-gravity and cosmology: the importance of correlations in the dynamics of the large-scale structures of the Universe" arXiv:2109.09087 (September 19, 2021) (submitted to A&A, original version submitted in 2019), Priidik Gallagher, Tomi Koivisto, "The Λ and the CDM as integration constants" arXiv (March 9, 2021), and Johan Hansson, et al., Nonlinear Effects of Gravity in Cosmology arXiv:1805.11043 (2016);

* non-local gravity theories, see, e.g., Ivan Kolář, Tomáš Málek, Anupam Mazumdar, "Exact solutions of non-local gravity in class of almost universal spacetimes" arXiv: 2103.08555; Reza Pirmoradian, Mohammad Reza Tanhayi, "Non-local Probes of Entanglement in the Scale Invariant Gravity" arXiv: 2103.02998, J. R. Nascimento, A. Yu. Petrov, P. J. Porfírio, "On the causality properties in non-local gravity theories" arXiv: 2102.01600, Salvatore Capozziello, Maurizio Capriolo, Shin'ichi Nojiri, "Considerations on gravitational waves in higher-order local and non-local gravity" arXiv: 2009.12777, Jens Boos, "Effects of Non-locality in Gravity and Quantum Theory" arXiv: 2009.10856, Jens Boos, Jose Pinedo Soto, Valeri P. Frolov, "Ultrarelativistic spinning objects in non-local ghost-free gravity" arXiv: 2004.07420;

* massive graviton theories, see, e.g., Kimet Jusufi, Genly Leon, Alfredo D. Millano, "Dark Universe Phenomenology from Yukawa Potential?" arXiv:2304.11492 (May 14, 2024) (Phys. Dark Univ. 42 (2023), 101318), Kimet Jusufi, et al., "Modified gravity/entropic gravity correspondence due to graviton mass" arXiv:2405.05269 (April 25, 2024), and O. Costa de Beauregard, "Massless or massive graviton?" 3 Foundations of Physics Letters 81-85 (1990));

* varying G and running gravitational coupling constant approaches, see, e.g., Hikaru Kawai, Nobuyoshi Ohta, "An Observation on the Beta Functions in Quadratic Gravity" arXiv:2405.05706 (May 9, 2024), Dimitris M. Christodoulou, Demosthenes Kazanas, "Gravitational Potential and Nonrelativistic Lagrangian in Modified Gravity with Varying G" (November 21, 2018);

* fifth force models, see, e.g., Marcus Högås, Edvard Mörtsell, "The Hubble tension and fifth forces: a cosmic screenplay" arXiv:2309.01744 (September 4, 2023); and

* Einstein-Aether theories, see, e.g., Vincenzo F. Cardone, Ninfa Radicella, "Can MONDian vector theories explain the cosmic speed up?" arXiv:0908.0095 (August 1, 2009) ("Generalized Einstein - Aether vector field models have been shown to provide, in the weak field regime, modifications to gravity which can be reconciled with the successful MOND proposal.").

* Quantized inertia, see, e.g., McCulloch, Mike E., "Testing Quantised inertia on Proxima Centauri." 352(1) MNRAS L67-69 (2024).

https://academic.oup.com/mnrasl/article/532/1/L67/7682393

See also McGaugh's tree of gravity based theories (with regrettably very small print):

Another summary from a conference paper illustration is: