Wednesday, July 2, 2025

A New Relativistic Generalization Of MOND (And More)

This six page article is just a conference paper summary of a much more involved modified gravity theory and its implications. The abstract is silent on how well it handles galaxy cluster physics, which deviate (in a quite systemic way) from simple toy-model MOND theories, or the Hubble tension.

We propose an alternative scalar-tensor theory based on the Khronon scalar field labeling a family of space-like three-dimensional hypersurfaces. This theory leads to modified Newtonian dynamics (MOND) at galactic scales for stationary systems, recovers GR plus a cosmological constant in the strong field regime, and is in agreement with the standard cosmological model and the observed cosmic microwave background anisotropies.
Luc Blanchet, Constantinos Skordis, "Khronon-Tensor theory reproducing MOND and the cosmological model" arXiv:2507.00912 (July 1, 2025) (Contribution to the 2025 Gravitation session of the 59th Rencontres de Moriond).

A fuller explanation of the theory can be found here.

Another lengthy paper by P. S. Bhupal Dev et al., examines the constraints dark matter-neutrino interactions which are very strict.
We present a comprehensive analysis of the interactions of neutrinos with the dark sector within the simplified model framework. We first derive the exact analytic formulas for the differential scattering cross sections of neutrinos with scalar, fermion, and vector dark matter (DM) for light dark sector models with mediators of different types. We then implement the full catalog of constraints on the parameter space of the neutrino-DM and neutrino-mediator couplings and masses, including cosmological and astrophysical bounds coming from Big Bang Nucleosynthesis, Cosmic Microwave Background, DM and neutrino self-interactions, DM collisional damping, and astrophysical neutrino sources, as well as laboratory constraints from 3-body meson decays and invisible Z decays. 
We find that most of the benchmarks in the DM mass-coupling plane adopted in previous studies to get an observable neutrino-DM interaction effect are actually ruled out by a combination of the above-mentioned constraints, especially the laboratory ones which are robust against astrophysical uncertainties and independent of the cosmological history. 
To illustrate the consequences of our new results, we take the galactic supernova neutrinos in the MeV energy range as a concrete example and highlight the difficulties in finding any observable effect of neutrino-DM interactions. 
Finally, we identify new benchmark points potentially promising for future observational prospects of the attenuation of the galactic supernova neutrino flux and comment on their implications for the detection prospects in future large-volume neutrino experiments such as JUNO, Hyper-K, and DUNE. We also comment on the ultraviolet-embedding of the effective neutrino-DM couplings.

Monday, June 30, 2025

Razib Khan on Denisovans

Razib Khan does a good job of summing up some of the things that we've learned in recent years about Denisovans, an archaic hominin clade.

[I]n June 2025, Chinese paleogeneticist Qiaomei Fu published data finally connecting specific fossil remains to Denisovans, utilizing both mtDNA and protein sequencing methods. And so now we know that Denisovans and Homo longi, are one and the same. A rather well preserved fossil from Harbin, China, a nearly complete skull, first identified as a new species in a 2021 publication, and colloquially dubbed Dragon Man, turns out to have DNA that we can now see neatly matches the sequences extracted from Denisova cave. For fifteen years, the label Denisovan only applied in a genomic context. No longer. Denisovan physical remains were in fact in plain sight all along.

This is not entirely a surprise. Some geneticists and paleoanthropologists have long assumed that many among the wealth of the fossils languishing yet to be identified, catalogued or named in East Asian collections today were Denisovans (I said as much in a podcast with Vagheesh Narasimhan of UT Austin, when H. longi was announced four years ago). Also, since 2010, we have established that Denisovans are the ancestors of more than Papuans and other Australasians. The Negrito peoples of the Philippines have a substantial contribution from Denisovans, the same as their Papuan neighbors from New Guinea to the south. But when you set aside their majority Austronesian ancestry (a much more recent overlay), it appears their forager ancestors (today some 35% of their ancestry) carried even more Denisovan ancestry than Papuans, on the order of 7-8%. It is also clear that low, but detectable, levels of Denisovan ancestry appear today in populations across South, East and Southeast Asia, at fractions of 0.1-0.3%.

 

Partial skull of Homo longi, AKA a Denisovan

The attested presence of Denisovan ancestry across a vast triangle stretching from Pakistan to Japan to Australia argues that they were present across vast territories. Deeper analysis of the Denisovan fragments in the genomes of Asians, Melanesians and Australians suggest at minimum two admixture events with two very distinct Denisovan populations. One population is clearly related to the genomes we have from Denisova cave. These northern Denisovans mixed with the ancestors of modern East Asians. But the Denisovan ancestry in South and Southeast Asians, as well as in Melanesians and Australians, is clearly from a population with a distinct ancestry; likely one that split off from the northern subspecies as long as more than 350,000 years ago. And the plot thickens, because tentative evidence gleaned from comparing the segments carried by these populations with southern Denisovan ancestry suggests distinct admixtures here as well; one in South Asians, another in Southeast Asians (a common one with Melanesians and Australians), and perhaps even one or two further ones in the outer reaches of prehistoric Sundaland and Sahul.

Are Oxygen Levels Related To Earth's Magnetic Field?

The strength of Earth’s magnetic field seems to rise and fall in line with the abundance of oxygen in the planet’s atmosphere, a study of geological records spanning the past half a billion years has found.

From the journal Nature

Among other things, the overall oxygen levels in the atmosphere impacts how large animals get, with more oxygen favoring larger animals.

It isn't clear what causes drive the correlation, although there probably is a cause.

Criticism Of Numerical Approaches To Indo-European Language Phylogeny

I've long been critical of Gray & Atkinson and the New Zealand school's efforts to do computational linguistics for the Indo-European languages, and specifically questioned Heggarty (2023) when it was released. A big factor in that is mishandling the importance of language contact, which can vary depending upon the relative dominance of the languages in contact and the nature of the words, phonetic values, and grammatical structures involved.
In this paper, we present a brief critical analysis of the data, methodology, and results of the most recent publication on the computational phylogeny of the Indo-European family (Heggarty et al. 2023), comparing them to previous efforts in this area carried out by (roughly) the same team of scholars (informally designated as the “New Zealand school”), as well as concurrent research by scholars belonging to the “Moscow school” of historical linguistics. 
We show that the general quality of the lexical data used as the basis for classification has significantly improved from earlier studies, reflecting a more careful curation process on the part of qualified historical linguists involved in the project; however, there remain serious issues when it comes to marking cognation between different characters, such as failure (in many cases) to distinguish between true cognacy and areal diffusion and the inability to take into account the influence of the so-called derivational drift (independent morphological formations from the same root in languages belonging to different branches)
Considering that both the topological features of the resulting consensus tree and the established datings contradict historical evidence in several major aspects, these shortcomings may partially be responsible for the results. Our principal conclusion is that the correlation between the number of included languages and the size of the list may simply be insufficient for a guaranteed robust topology; either the list should be drastically expanded (not a realistic option for various practical reasons) or the number of compared taxa be reduced, possibly by means of using intermediate reconstructions for ancestral stages instead of multiple languages (the principle advocated by the Moscow school).
Alexei S. Kassian and George Starostin, "Do 'language trees with sampled ancestors' really support a 'hybrid model' for the origin of Indo-European? Thoughts on the most recent attempt at yet another IE phylogeny". 12 (682) Humanities and Social Sciences Communications (May 16, 2025).

From the body text:
Discussion and conclusions

In the previous sections, we have to tried to identify several factors that might have been responsible for the dubious topological and chronological results of Heggarty et al. 2023 experiment, not likely to be accepted by the majority of “mainstream” Indo-European linguists. Unfortunately, it is hard to give a definite answer without extensive tests, since, in many respects, the machine-processed Bayesian analysis remains a “black box”. We did, however, conclude at least that this time around, errors in input data are not a key shortcoming of the study (as was highly likely for such previous IE classifications as published by Gray and Atkinson, 2003; Bouckaert et al. 2012), although failure to identify a certain number of non-transparent areal borrowings and/or to distinguish between innovations shared through common ancestry and those arising independently of one another across different lineages (linguistic homoplasy) may have contributed to the skewed topography.

One additional hypothesis is that the number of characters (170 Swadesh concepts) is simply too low for the given number of taxa (161 lects). From the combinatorial and statistical point of view, it is a trivial consideration that more taxa require more characters for robust classification (see Rama and Wichmann, 2018 for attempts at estimation of optimal dataset size for reliable classification of language taxa). Previous IE classifications by Gray, Atkinson et al. involved fewer taxa and more characters (see Table 1 for the comparison).

Table 1 suggests that the approach maintained and expanded upon in Heggarty et al. 2023 project can actually be a dead-end in classifying large and diversified language families. In general, the more languages are involved in the procedure, the more characters (Swadesh concepts) are required to make the classification sufficiently robust. Such a task, in turn, requires a huge number of man-hours for wordlist compilation and is inevitably accompanied by various errors, partly due to poor lexicographic sources for some languages, and partly due to the human factor. Likewise, expanding the list of concepts would lead us to less and less stable concepts with vague semantic definitions.

Instead of such an “expansionist” approach, a “reductionist” perspective, such as the one adopted by Kassian, Zhivlov et al. (2021), may be preferable, which places more emphasis on preliminary elimination of the noise factor rather than its increase by manually producing intermediate ancestral state reconstructions (produced by means of a transparent and relatively objective procedure). Unfortunately, use of linguistic reconstructions as characters for modern phylogenetic classifications still seems to be frowned upon by many, if not most, scholars involved in such research — in our opinion, an unwarranted bias that hinders progress in this area.

Overall one could say that Heggarty et al. (2023) at the same time represents an important step forward (in its clearly improved attitude to selection and curation of input data) and, unfortunately, a surprising step back in that the resulting IE tree, in many respects, is even less plausible and less likely to find acceptance in mainstream historical linguistics than the trees previously published by Gray & Atkinson (2003) and by Bouckaert et al. (2012). 
Consequently, the paper enhances the already serious risk of discrediting the very idea of the usefulness of formal mathematical methods for the genealogical classification of languages; it is highly likely, for instance, that a “classically trained” historical linguist, knowledgeable in both the diachronic aspects of Indo-European languages and such adjacent disciplines as general history and archaeology, but not particularly well versed in computational methods of classification, will walk away from the paper in question with the overall impression that even the best possible linguistic data may yield radically different results depending on all sorts of “tampering” with the complex parameters of the selected methods — and that the authors have intentionally chosen that particular set of parameters which better suits their already existing pre-conceptions of the history and chronology of the spread of Indo-European languages. 
While we are not necessarily implying that this criticism is true, it at least seems obvious that in a situation of conflict between “classic” and “computational” models of historical linguistics, assuming that the results of the latter automatically override those of the former would be a pseudo-scientific approach; instead, such conflicts should be analyzed and resolved with much more diligence and much deeper analysis than the one presented in Heggarty et al. 2023 study.

Hadron Molecules v. True Composite States

Any time that you have four to six quarks in some sort of bound state, the question that is presented is whether it is a true tetra-, penta-, or hexaquark, or whether it is a hadron molecule with the same valence quarks.

In a true tetra-, penta-, or hexaquark, the valence quarks are bound direct to each other by gluons. In a hadron molecule, mesons or baryons are bound to each other either by something analogous to the nuclear binding force (carried by mesons in atomic nuclei, mostly, but not entirely, pions) or electromagnetically (as in an ordinary molecule made up of atoms bound electromagnetically).

A new preprint looks at four pentaquark states with a valence charm quark and finds that all of them are hadron molecules rather than true pentaquarks.