arXiv Is Moving

A few weeks ago, arXiv.org announced that it will be leaving Cornell, the university that currently manages it, and establishing its own nonprofit.

From 4 gravitons.

Calculating Light Meson Masses From First Principles In QCD

How good are current Standard Model calculations at predicting the experimental values of the light meson masses?

A new paper that makes that attempt for most light mesons under 1.5 GeVs of mass (except scalar mesons). And, physicists are finally starting to do a pretty good job of describing the meson mass spectrum which has been an elusive target for decades, even for axial vector mesons, which had long been challenging.

As explained in the introduction:

In the present work we employ the procedure described above to compute the masses of relatively light mesons, namely mesonic states no heavier than about 1.5 GeV. Specifically, for mesons composed of u and ¯d quarks, we compute the masses of π±, ρ(770), b1(1235), a1(1260), π±(1300), and ρ±(1450). For the strange sector, we calculate the masses of the states K±, K∗(890), K1A, K1B, and K±(1460). 

In general, the computed masses are in good agreement with the experimental values. In fact, our findings represent a definite improvement over the results obtained within the standard rainbow-ladder truncation [84], where the masses of axial-vector mesons and radially excited states tend to deviate considerably from the observed values.

Notably, this omits the f(0)(500) scalar meson a.k.a. the sigma meson and seven other true scalar mesons with masses under 1.5 Gev. The other omitted scalar mesons are the f(0)(980), f(2)(1270), f(1)(1285), f(0)(1370), f(1)(1420), f(2)(1430) and f(0)(1500). This may be because their internal structures are less well understood.

The actual procedure used is too technical to discuss at this blog, which is aimed at an education layman readership.

The money chart is as follows:

With the exception of spin-1 kaons (where the relationship is inverted for some reason), the experimental values (in red) tend to be at the very high end of the theoretically predicted values using their methods (in blue), and their predictions, in turn, tend to be more massive than those made using a previous "rainbow ladder" truncation method (in green).

The predictions (and measurements) of excited state light meson masses are much less precise than the predictions (and measurements) of ground state light meson masses.

Is The Newtonian Expectation For Galaxy Rotation Curves Modeled Incorrectly?

The conclusion of this paper is a very big deal if true, and I don't dismiss it out of hand.

But given how well established and widely used the models it claims are grossly wrong are, this needs peer review and time for commentary papers in response to it in order to be taken seriously. I wouldn't be surprised if it contains some significant conceptual flaw.

The approximately flat outer parts of spiral galaxy rotation curves are commonly interpreted as evidence for a discrepancy between the observed baryonic mass and the dynamical mass inferred from the measured orbital velocities. In most standard analyses, this discrepancy is quantified using v2(R)=GM(<R)/R, which is exact only under spherical symmetry. However, spiral galaxies are flattened disk systems, for which mass exterior to the galactocentric radius under consideration can contribute non-negligibly to the gravitational field. 

We introduce the Lost and Found (LF) model, a geometrically consistent Newtonian framework based on direct full-disk gravitational integration and a parametrized representation of the disk surface density. In this approach, the gravitational field is computed without imposing spherical symmetry, and the disk mass distribution is represented by two exponential components with a smooth outer truncation. 

We apply the LF model to a heterogeneous sample of disk galaxies spanning a broad range of masses and radial extents. The model reproduces the main observed features of the rotation curves, including the inner rise and the approximately flat outer behavior, without explicitly invoking a dark matter halo or modifying Newtonian gravity. Across the sample, the LF-inferred mass scales nearly linearly with the conventional dynamical mass, with a characteristic reduction factor ηLF ~ 0.67. 

These results indicate that part of the inferred mass discrepancy may arise from the geometric treatment of gravitation in disk galaxies, and motivate a reassessment of mass inference in non-spherical systems.

Adolfo Santa Fe Dueñas, "Galactic Rotation Curves from Full-Disk Newtonian Gravity: The Lost and Found Model" arXiv:2604.06917 (April 8, 2026) (submitted to MNRAS).

Population Discontinuity At The End Of The Neolithic In Paris, France

Bernard's blog, Généalogie génétique, lives. (I had removed it from the blogroll when technical difficulties at the site made it look dead. I'll reinstate it when I have time.)

His latest post examines an ancient DNA paper looks at ancient DNA from a graveyard in Paris, part of which dates to around 3000 BCE in the megalithic Neolithic era, and part of which comes a century later after a long gap in burials there, when the previous megalithic Neolithic civilization there had collapse: forests had regrown, megalithic construction had ceased, and infectious diseases including the black plague had ravaged the population. 

The post-collapse social organization was different too, with the earlier burials reflecting a large extended family/clan social structure of related people, and the later burials reflecting a smaller nuclear family with multiple generations of related people but only a few people in each generation.

In this case, there was population discontinuity in which the prior Neolithic population was replaced by another Neolithic population from the South with a different social organization that moved in after the original megalithic Neolithic culture in Paris collapsed. Both the original group (in brown on the PCA plot below) and the subsequent one (in green) cluster together as European Neolithic populations, distinct from prior European hunter-gather peoples and the later Bronze Age steppe peoples, despite being distinct enough to indicate a population replacement.

This graveyard pins down the timing of this collapse fairly precisely to a single century.

This also makes clear that Neolithic collapse in Western Europe happened before the arrival of Bronze Age people with steppe ancestry. It also illustrates the civilizational vacuum that those Bronze Age people swept into a few centuries later, replacing much of the first farmer wave of people in this part of Europe, in a dynamic distinct from the conquest of a vibrant Neolithic civilization.

The abstract and citation appears below:

At the transition between the third and the fourth millennium BC, there is evidence for a population decline concurrent with the end of megalith building across continental northwestern Europe. In Scandinavia this ‘Neolithic decline’ is followed by a massive population turnover, as farming communities disappeared and were replaced by people with steppe ancestry. In western Europe, however, ancestry associated with Neolithic farmers persisted beyond the Neolithic decline, and it remains unclear whether a similar demographic replacement occurred.

To investigate the population dynamics around the Neolithic decline in present-day France, we sequenced 132 ancient genomes from the allée sépulcrale at Bury. Located in the Paris area, Bury spans two burial phases separated by a hiatus with no burial activity: one phase directly preceding the Neolithic decline in the late fourth millennium BC, ending around 3000 BC, and a later phase some time after the Neolithic decline in the early- to mid-third millennium BC.

Our analysis revealed that the two burial phases at Bury represented largely discontinuous genetic groups of a markedly different social organization as inferred from three large pedigrees. We show that the difference between the two burial phases can be linked to a northwards movement of Neolithic ancestry from the south, which only spread into the Paris Basin after the Neolithic decline, at around 2900 BC. 

Together with genetic evidence of various infectious diseases in the dataset, such as Yersinia pestis and Borrelia recurrentis, as well as evidence for forest regrowth between the two phases, these findings detail a population turnover at the end of the fourth millennium BC, offering a possible explanation for the cessation of megalith building.

Frederik Seersholm, et al, "Population discontinuity in the Paris Basin linked to evidence of the Neolithic decline" Nature Ecology and Evolution (April 3, 2026).

Steppe ancestry starts to appear in Southern France ca. 2650 BCE, with Bell Beaker artifacts found in the Lower Rhine ca. 2600 BCE. This is about 250-300 years after population replacement in the Paris basin.

Notably, however, the source of the Southern France Neolithic migrants to the Paris basin ca. 2900 BCE is, geographically, one of the earliest places of the Bell Beaker phenomena in France and is the geographic source of the French Bell Beaker people. Indeed, southern France is the first place that the Bell Beaker phenomena arose after Iberia (it arose originally in the Tagus River basin in Portugal). 

Also notably, the very first Bell Beaker people had Neolithic, rather than Steppe ancestry, which only came two or three centuries later.

It is thus conceivable that the Southern French replacement population in Paris ca. 2900 BCE may be from the same population that was the source of the pre-Steppe Bell Beaker progenitors.

Density v. Mass In Compact Objects In Space

This comparison of compact object density and mass is purely descriptive and informs astrophysical intuition.

From here.