Dispatches From Turtle Island
Observations That Transcend Law and Politics
Tuesday, October 21, 2025
The Hunter-Gather To Bronze Age Transition In Kazakhstan
A Search For X17 Comes Up Empty And Assorted Astrophysics Papers
Today's preprint harvest was abundant and I have a little time to blog this morning.
An X17 paper
BESIII searched for an X17 boson and didn't find it.
We report a direct search for a new gauge boson, X, with a mass of 17 MeV/c^2, which could explain the anomalous excess of e+e− pairs observed in the 8Be nuclear transitions. The search is conducted in the charmonium decay χcJ→XJ/ψ (J = 0,1,2) via the radiative transition ψ(3686)→γχcJ using (2712.4 ± 14.3) × 10^6 ψ(3686) events collected with the BESIII detector at the BEPCII collider. No significant signal is observed, and the new upper limit on the coupling strength of charm quark and the new gauge boson, ϵc, at 17 MeV/c^2 is set to be |ϵc| < 1.2 × 10^−2 at 90% confidence level. We also report new constraints on the mixing strength ϵ between the Standard Model photon and dark photon γ′ in the mass range from 5 MeV/c^2 to 300 MeV/c^2. The upper limits at 90% confidence level vary within (2.5−17.5) × 10^−3 depending on the γ′ mass.
The mass-size relations of galaxies are generally studied considering only stars or only gas separately. Here we study the baryonic mass-size relation of galaxies from the SPARC database, using the total baryonic mass (Mbar) and the baryonic half-mass radius (R50,bar). We find that SPARC galaxies define two distinct sequences in the Mbar−R50,bar plane: one that formed by high-surface-density (HSD), star-dominated, Sa-to-Sc galaxies, and one by low-surface-density (LSD), gas-dominated, Sd-to-dI galaxies. The Mbar−R50,bar relation of LSD galaxies has a slope close to 2, pointing to a constant average surface density, whereas that of HSD galaxies has a slope close to 1, indicating that less massive spirals are progressively more compact.
Our results point to the existence of two types of star-forming galaxies that follow different evolutionary paths: HSD disks are very efficient in converting gas into stars, perhaps thanks to the efficient formation of non-axisymmetric structures (bars and spiral arms), whereas LSD disks are not.
The HSD-LSD dichotomy is absent in the baryonic Tully-Fisher relation (Mbar versus flat circular velocity Vf) but moderately seen in the angular-momentum relation (approximately Mbar versus Vf×R50,bar), so it is driven by variations in R50,bar at fixed Mbar. This fact suggests that the baryonic mass-size relation is the most effective empirical tool to distinguish different galaxy types and study their evolution.
Zichen Hua, Federico Lelli, Enrico Di Teodoro, Stacy McGaugh, James Schombert, "The baryonic mass-size relation of galaxies. I. A dichotomy in star-forming galaxy disks" arXiv:2510.17770 (October 20, 2025) (accepted by Astronomy & Astrophysics).
The creator of MOND muses in a public lecture about what a fundamental theory explaining MOND (a FUNDAMOND) has to look like:
In default of a fundamental MOND theory -- a FUNDAMOND -- I advocate that, alongside searching for one, we should try to identify predictions that follow from wide classes of MOND theories, if not necessarily from all. In particular, predictions that follow from only the basic tenets of MOND -- ``primary predictions'' -- are shared by all MOND theories, and are especially valuable. Such predictions permit us to test the MOND paradigm itself, or at least large parts of it, without yet having a FUNDAMOND.
Concentrating on the deep-MOND limit, I discuss examples of either type of predictions.
For some examples of primary predictions, I demonstrate how they follow from the basic tenets (which I first formulate). I emphasize that even predictions that pertain to the deep-MOND limit - namely, those that concern gravitating systems that have low accelerations everywhere -- require the full set of MOND tenets, including the existence of a Newtonian limit close to the deep-MOND regime. This is because Newtonian dynamics is a unique theory that all MOND theories must tend to in the limit of high accelerations, and it strongly constrains aspects of the deep-MOND regime, if the transition between the limits is fast enough, which is one of the MOND tenets.
Under carefully chosen assumptions a single general relativistic scalar field is able to induce MOND-like dynamics in the weak field approximation of the Einstein frame (gauge) and to modify the light cone structure accordingly.
This is shown by a Lagrangian model formulated in the framework of integrable Weyl geometry. It contains a Bekenstein-type (``aquadratic'') term and a second order term generating additional mass energy for the scalar field. Both are switched on only if the gradient of the scalar field is spacelike and below a MOND-typical threshold, like in the superfluid model of Berezhiani/Khoury. The mass term induces non-negligible energy and pressures of the scalar field and leads to gravitational light deflection compatible with MOND-ian free fall trajectories. In the weak field (Newton-Milgrom) approximation the Bekenstein term implies a deep MOND equation for the scalar field. In this model the external field effect of the MOND approach has to be reconsidered. This has important consequences for hierarchical systems like clusters, which may suffice for explaining their dynamics without additional dark matter
There is a claim in the literature that charged dark matter particles in the mass range 100(qX/e)^2 TeV≤mX≤10^8(qX/e) TeV are allowed, based on arguing that heavy charged particles cannot reach the Earth from outside the magnetized region of the Milky Way (Chuzhoy-Kolb, 2009). We point out that this claim fails for physical models for the Galactic magnetic field. We explicitly confirm our argument by simulating with the software CRPropa the trajectories of heavy charged dark matter in models of the Galactic magnetic field.
Thursday, October 16, 2025
The Population Genetics Of Egypt Have Been Stable For A Long Time
An ancient DNA sample from ca. 2500 BCE in Egypt reveals a great deal of continuity in the population genetics of Egypt then and the population genetics of Egypt today.
I didn't have a lot of time to look carefully at this study, but prior studies have shown a modest increase in sub-Saharan African admixture since then, due to the trans-Saharan slave trade in more recent time periods.
Ultralight Dark Matter
While ultra-light bosonic dark matter (ULDM) in a Bose-Einstein condensate (BEC) state could naturally account for the central core in some galaxies and resolve the core-cusp problem, the dark matter density distribution in the outer regions of galaxies remains less explored. We propose a trial wavefunction to model the ULDM distribution beyond the BEC core. We derive the corresponding rotation velocity curve, which shows excellent agreement with those of 12 dwarf spheroidal galaxies. The best-fit ULDM particle mass for each dwarf galaxy falls within a strikingly narrow range of m = (1.8−3.2) × 10^−23 eV.