Why Does Cosmology Give Us A Negative Neutrino Mass As A Best Fit Value?

The apparent preference for a best fit value of the neutrino masses from cosmology measurements is probably a matter of some fine methodological adjustments that weren't made for gravitational lensing.

Recent analyses combining cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) challenge particle physics constraints on the total neutrino mass, pointing to values smaller than the lower limit from neutrino oscillation experiments. To examine the impact of different CMB likelihoods from Planck, lensing potential measurements from Planck and ACT, and BAO data from DESI, we introduce an effective neutrino mass parameter (∑m̃ ν) which is allowed to take negative values. 

We investigate its correlation with two extra parameters capturing the impact of gravitational lensing on the CMB: one controlling the smoothing of the peaks of the temperature and polarization power spectra; one rescaling the lensing potential amplitude. In this configuration, we infer ∑m̃ ν=−0.018+0.085−0.089 eV (68% C.L.), which is fully consistent with the minimal value required by neutrino oscillation experiments. 

We attribute the apparent preference for negative neutrino masses to an excess of gravitational lensing detected by late-time cosmological probes compared to that inferred from Planck CMB angular power spectra. We discuss implications in light of the DESI BAO measurements and the CMB lensing anomaly.

Andrea Cozzumbo, et al., "A short blanket for cosmology: the CMB lensing anomaly behind the preference for a negative neutrino mass" arXiv:2511.01967 (November 3, 2025).

A Dark Energy Alternative

There are multiple possible alternatives to a cosmological constant. This is one of the better attempts.

In our local-to-global cosmological framework, cosmic acceleration arises from local dynamics in an inhomogeneous Einstein-de Sitter (iEdS) universe without invoking dark energy. 

An iEdS universe follows a quasilinear coasting evolution from an Einstein-de Sitter to a Milne state, as an effective negative curvature emerges from growing inhomogeneities without breaking spatial flatness. Acceleration can arise from structure formation amplifying this effect. 

We test two realizations, iEdS(1) and iEdS(2), with H(0) = {70.24,74.00} km s^−1 Mpc^−1 and Ω(m,0) = {0.290,0.261}, against CMB, BAO, and SN Ia data. 

iEdS(1) fits better than ΛCDM and alleviates the H0 tension, whereas iEdS(2) fully resolves it while remaining broadly consistent with the data. Both models yield t0≃13.64 Gyr, consistent with globular-cluster estimates.

Peter Raffai, et al., "A Case for an Inhomogeneous Einstein-de Sitter Universe" arXiv:2511.03288 (November 5, 2025).

A New 200,000 Year Old Denisovan Genome

Bernard's blog does a good job of reviewing the recent publication of a 200,000 year old Denisovan genome. 

This Denisovan's life predates the emergence of modern humans from Africa, but overlaps with the existence of the earliest modern humans within Africa.

In a nutshell, the preprint is: Stéphane Peyrégne, et al., "A high-coverage genome from a 200,000-year-old Denisovan" bioRxiv (October 20, 2025). According to Bernard (via Google translate from French):

They sequenced the genome of molar Denisova 25. Initial results showed that the individual was male. Furthermore, the mitochondrial and Y chromosome haplogroups both belong to the Denisovan population.

The Latest Neutrino Oscillation Parameters

Background

Data from W and Z boson decays and from cosmology measurements, strongly favor a model with exactly three active neutrino flavors, as do requirements for mathematical consistent in the Standard Model of Particle Physics, which requires that each generation of Standard Model fermions (i.e. an up-like quark, a down-like quark, an electron-like charged lepton, and a neutrino) must be complete with four members. The lower bound on a fourth active neutrino mass is on the order of 45,000,000,000,000 meV, while we know that none of the other three active neutrino masses are more than about 900 meV, and we have strong indications that the largest of the three active neutrino masses is no more than about 70 meV.

When the Standard Model was first formulated in the 1970s, neutrinos were assumed to be massless fermions. Experiments proved that this couldn't be the case in 1998, and that neutrinos change flavors and oscillate between their three mass eigenstates. Since then, scientists have worked to determine their mass and additional properties arising from the fact that they have mass, which has culminated in a basic three favor, Dirac neutrino model of neutrino oscillation to which the data has been fit.

This neutrino oscillation behavior is characterized by two mass differences Δm(21) and Δm(32), whether the masses are in a "normal" or "inverted" hierarchy, and four parameters of the PMNS matrix: three of which describe the probability of each of the possible transitions between the three neutrino flavors, and one of which δCP describes charge parity violation (i.e. how those transition probabilities differ between neutrinos and antineutrinos).  

The two mass differences have been measured to decent precision. A normal mass hierarchy is favored by the experimental data, but not to terribly great statistical significance (the preference is close to two sigma). The three main mixing angles of the PMNS matrix have been measured to reasonable but modest precision, although it isn't entirely established if one of them is a bit less than 45º or a bit more than 45º (the data increasing favors a value that is a bit more than 45º). Attempts to measure δCP are very imprecise and generally can't entirely rule out the possibility that there is no CP violation in neutrino oscillation, the best fit values of measurements of δCP consistently favor near maximum CP violation in neutrino oscillations.

The world average measured value of those parameters are as follows (according to the Particle Data Group):

In addition, to fully characterize the properties of neutrinos in the basic three flavor, Dirac neutrino model to which experimental data is fitted, one needs to know the absolute rest mass of at least one of the neutrino mass eigenstates. The experimental upper bound on the mass of the lightest absolute neutrino mass eigenstate is about 800 meV. The experimental lower bound on the sum of the three neutrino mass eigenstates is on the order of 58 meV for a "normal" hierarchy of neutrino masses, and 110 meV. for an "inverted" hierarchy of neutrino masses Reasonably robust upper bounds on the sum of the three neutrino masses from cosmology models and astronomy measurements favor an upper bound for the sum of the three neutrino masses to around 130 meV, with some measurements putting it below the 110 meV cap allowed for an inverted hierarchy for neutrino masses with some more aggressive theoretical assumptions.

The New Paper

A new paper combines the latest data from two major neutrino physics collaborations (NOvA and T2K) to tighten up the precision of measurements of the Δm(32) and δCP parameters of neutrino oscillations, which is hard to do with a single collaboration's data, because the observables in each experiment depend upon more than one parameter, and it is hard to tell with just a single experiment's data, which parameter is driving those observables. But, since the mix of parameters that drive the observables in each experiment is different (in part, by design to allow for just this kind of combined data analysis), when the two collaborations' data are combined, these degeneracies in each individual collaboration's data can be minimized.

The new paper below improves the precision of the measurement of Δm(32) a bit, and also makes for a still very imprecise, but improved, measurement of δCP. 

The new combined measurement for Δm(32) is at the very low end of the current the world average plus or minus two sigma range.

The new paper rules out the possibility of zero CP violation in neutrino mixing at the 3 sigma level for an inverted neutrino mass hierarchy assumption, and at a roughly 2.4 sigma level of significance for a normal neutrino mass hierarchy assumption.

The landmark discovery that neutrinos have mass and can change type (or "flavor") as they propagate -- a process called neutrino oscillation -- has opened up a rich array of theoretical and experimental questions being actively pursued today. 

Neutrino oscillation remains the most powerful experimental tool for addressing many of these questions, including whether neutrinos violate charge-parity (CP) symmetry, which has possible connections to the unexplained preponderance of matter over antimatter in the universe. Oscillation measurements also probe the mass-squared differences between the different neutrino mass states (Δm^2), whether there are two light states and a heavier one (normal ordering) or vice versa (inverted ordering), and the structure of neutrino mass and flavor mixing. 

Here, we carry out the first joint analysis of data sets from NOvA and T2K, the two currently operating long-baseline neutrino oscillation experiments (hundreds of kilometers of neutrino travel distance), taking advantage of our complementary experimental designs and setting new constraints on several neutrino sector parameters. 

This analysis provides new precision on the Δm(32)^2 mass difference, finding 2.43+0.04−0.03 (−2.48+0.03−0.04) × 10^−3 eV^2 in the normal (inverted) ordering, as well as a 3σ interval on δCP of [−1.38π, 0.30π] ([−0.92π, −0.04π]) in the normal (inverted) ordering. The data show no strong preference for either mass ordering, but notably if inverted ordering were assumed true within the three-flavor mixing paradigm, then our results would provide evidence of CP symmetry violation in the lepton sector.

NOvA, T2K Collaborations, "Joint neutrino oscillation analysis from the T2K and NOvA experiments" arXiv:2510.19888 (October 22, 2025).

Further Neutrino Property Issues 

Additional parameters are needed if neutrinos are actually Majorana particles (i.e. if they are their own antiparticles), or if they oscillate with a "sterile" right handed neutrino which only interacts via neutrino oscillation (and not via the electromagnetic, weak, or strong forces of the Standard Model) which is often proposed as a way for Dirac neutrinos to acquire mass in what is called a see-saw mechanism. 

Most physicists believe that one of these two possibilities should be possible to give rise to a mechanism for mass generation in neutrinos. Mass generation via the Higgs mechanism is not a good fit for neutrinos since all neutrinos are "left handed" in parity, and all antineutrinos are "right handed" in parity, unlike all other Standard Model fermions which have both left and right parity versions of both their particles and their antiparticles, making four states possible.

The most definitive phenomenological parameter of Majorana neutrinos would be neutrinoless double beta decay, which has not been observed to high precision. But neutrinoless double beta decays involving Majorana neutrinos is a function of their absolute mass scale. It is more rare to the extent that neutrinos are less massive. And, current bounds on neutrinoless double beta decay are not so strong that this can be ruled out for reasonable neutrino mass scales, although it's getting close to that point. Majorana neutrinos would also have a more complicated oscillation behavior involving more mixing parameters than the Dirac neutrino model.

A Dirac neutrino model with a see-saw mechanism involving oscillation with a sterile neutrino would imply that the transition probabilities of the PMNS matrix parameters wouldn't be unitary. In other words, the probabilities of all the three flavor model transitions wouldn't add up to 100%, because some small percentage of neutrino oscillations would be to one or more sterile neutrino flavors. So far, the observed PMNS matrix parameters are consistent with unitarity. But since the measured parameters each have uncertainties, there is room within those uncertainties for transitions to an additional sterile neutrino flavor (or even to multiple sterile neutrino flavors). The upper bound on missing neutrino transition probabilities is quite low, however, and to make a see-saw mechanism work with such small experimentally allowed transition probabilities, the mass of a hypothetical sterile neutrino would have to be very high.

For the record, I don't like either solution and think that we need to find a "third way" mechanism for generating neutrino mass, although I don't know what it would be.

Because Deur Is Awesome, Even At His Day Job

Alexandre Deur's side hustle, described in the sidebar link, is his work on a gravitational explanation for dark matter and dark energy phenomena, which would solve several of the greatest unsolved problems in physics.

His day job is as a QCD physicist at Jefferson Lab, a U.S. Department of Energy particle physics facility in Newport News, Virginia. There, his progress in determining the value of the least accurately known Standard Model model coupling constant, and confirming that its running with energy scale is consistent with the Standard Model, is also a good thing. 

Unsurprisingly, the research done by him and his colleagues confirms that the Standard Model's running of the strong force coupling constant of quantum chromodynamics determined experimentally confirms the Standard Model over a huge range of energy scales (from hundreds of MeVs to about 14,000,000 MeV).

The strong force coupling constant is usually quoted with values converted using the beta-function that describes its running with energy scale in the Standard Model to the Z-boson mass of 91.188 ± 0.002 GeV (according to the Particle Data Group, inverse error weighted world average measurement). Its world average value converted to that energy scale is 0.1180(9).

The numerical values shown below are in a normalized scale, so the numerical value doesn't match the familiar number.

We discuss how the Bjorken sum rule allows access to the QCD running coupling αs at any scale, including in the deep infrared IR domain. The Bjorken sum data from Jefferson Lab, together with the world data on αs reported by the Particle Data Group, allow us to determine the running of α(s)(Q) over five orders of magnitude in four-momentum Q. We present two possible future measurements of the running of α(s)(Q) using the Bjorken sum rule: the first at the EIC, covering the range 1.5 < Q < 8.7 GeV, and the second at Jefferson Lab at 22 GeV, covering the range 1.0 < Q < 4.7 GeV.

A. Deur, "The strong coupling from the IR to the UV extremes: Determination of α(s) and prospects from EIC and JLab at 22 GeV" arXiv:2510.19556 (October 22, 2025) (Contribution to the proceedings of the "QCD at the Extremes" workshop, Sept. 1-11 2025).

The paper above discusses how proposed low energy experiments at the electron-ion collider at the Brookhaven Lab on Long Island, New York (EIC) and JLab would greatly reduce uncertainties in the measurement of the strong force coupling constant measurement at low energies (i.e. below 5,000 MeV) as shown by the chart below.

The Hunter-Gather To Bronze Age Transition In Kazakhstan

Bernard discusses a paper on ancient DNA from Kazakstan. It revealed that the hunter-gatherer population that persisted there until the late Neolithic era in Europe was roughly 95% replaced by Bronze Age early Indo-Europeans herders similar to the Sintashta and Andronovo cultures genetically. The paper is Haechan Gill, et al., "Ancient genomes from eastern Kazakhstan reveal dynamic genetic legacy of Inner Eurasian hunter-gatherers" (2025).

The paper also has many other secondary insights.

The samples from the current study are in yellow, with the Bronze age samples on the left, and in the MLBA clines, and the Neolithic samples in the Steppe HG cline on the right.

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.

BESIII Collaboration, "Search for a hypothetical gauge boson and dark photons in charmonium transitions" arXiv:2510.16531 (October 18, 2025).

Four astrophysics papers

There were several MOND or MOND-adjacent papers in today's preprints that I don't really have time to discuss at great length.

Stacy McGaugh, one of the leading members of the current generation of MOND researchers looks at pattern in the ordinary matter mass v. size relationship for galaxies in a large data set:

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.

Mordehai Milgrom, "The deep-MOND limit -- a study in Primary vs secondary predictions" arXiv:2510.16520 (a talk presented at the MOND workshop, Leiden, September 2025) (October 18, 2025).

The paper by Scholz below is an attempt to devise a "FUNDAMOND":

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

Erhard Scholz, "Einstein gravity extended by a scale covariant scalar field with Bekenstein term and dynamical mass generation" arXiv:2510.17704 (October 20, 2025).

Finally a notable dark matter search paper rules out a significant swath of dark matter particle parameter space, that most people assumed never existed (heavy charged 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.

Daniele Perri, Glennys Farrar, "The window on heavy charged dark matter was never open" arXiv:2510.17026 (October 19, 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.

Tian-yao Fang, Ming-Chung Chu, "Constraining Ultra-Light Dark Matter mass with Dwarf Galaxy Rotation Curves" arXiv:2510.12848 (October 14, 2025).

The best fit particle mass is in line with other studies and very close to the average mass-energy of a graviton, if they exist (and gravitons are, of course, bosons).

In general, ultralight bosonic dark matter proposals are are better fit to the data than any of the other dark matter particle models. 

Even warm dark matter, in the keV mass range, only barely improves upon failed cold dark matter and ultraheavy dark matter models. Self-interacting dark matter models have also not stood up well against the data from galaxy dynamics.

A Quantum Gravity Observation From Sabine

This basic idea has been floating around in quantum gravity circles for a while, but Hossenfelder's take is more cogent and careful than many of these attempts. Her model is basically a superdeterministic one.

I present a simple argument for why a fundamental theory that unifies matter and gravity gives rise to what seems to be a collapse of the wavefunction. The resulting model is local, parameter-free and makes testable predictions.

Sabine Hossenfelder, "How Gravity Can Explain the Collapse of the Wavefunction" arXiv:2510.11037 (October 13, 2025).

The conclusion states:

I have shown here how the assumption that matter and geometry have the same fundamental origin requires the time evolution of a quantum state to differ from the Schr¨odinger equation. This has the consequence that the ideal time evolutions which minimise the action are those with end states that are to good approximation classical. We can then identify these end states with the eigenstates of the measurement device. 

This new model therefore explains why quantum states seem to ‘collapse’ into eigenstates of the measurement observable, and how this can happen while preserving locality. Since the collapse process is governed by quantum gravitational contributions whose strength is known, the resulting model is parameter free. 

Collapse happens in this model whenever the accumulated phase difference between dislocated branches, τm|Φ12|, exceeds ∼ 1. The model’s phenomenology—notably the collapse itself—can be tested in roughly the same parameter range as other tests of the weak field limit of quantum gravity.

A Proposal To Explain The Neutrino Mixing Angles

Many papers try to explain fundamental constants in the Standard Model in terms of deeper relationships. This attempt to gain insight into the neutrino oscillation parameters is more thought provoking than most. 

We propose a geometric hypothesis for neutrino mixing: twice the sum of the three mixing angles equals 180∘, forming a Euclidean triangle. This condition leads to a predictive relation among the mixing angles and, through trigonometric constraints, enables reconstruction of the mass-squared splittings. 

The hypothesis offers a phenomenological resolution to the θ23 octant ambiguity, reproduces the known mass hierarchy patterns, and suggests a normalized geometric structure underlying the PMNS mixing. 

We show that while an order-of-magnitude scale mismatch remains (the absolute splittings are underestimated by ∼10×), the triangle reproduces mixing ratios with notable accuracy, hinting at deeper structural or symmetry-based origins. 

We emphasize that the triangle relation is advanced as an empirical, phenomenological organizing principle rather than a result derived from a specific underlying symmetry or dynamics. 

It is testable and falsifiable: current global-fit values already lie close to satisfying the condition, and improved precision will confirm or refute it. We also outline and implement a simple χ2 consistency check against global-fit inputs to quantify agreement within present uncertainties.

Mohammad Ful Hossain Seikh, "A geometrical approach to neutrino oscillation parameters" arXiv:2510.06526 (October 7, 2025).

Does Non-Perturbative QCD Have A Cosmological Constant Analog?

A new paper explores a potential parallel between non-perturbative quantum chromodynamics (the physics of the strong force that binds quarks into hadronic structures) and gravity. This isn't entirely surprising, as both are non-abelian gauge theories. And, it suggests that features like the cosmological constant may have a natural source in a non-abelian quantum gravity theory.

Einsteins gravity with a cosmological constant Λ in four dimensions can be reformulated as a λϕ^4 theory characterized solely by the dimensionless coupling λ∝G(N)Λ (G(N) being Newton's constant). The quantum triviality of this theory drives λ → 0, and a deviation from this behavior could be generated by matter couplings. Here, we study the significance of this conformal symmetry and its breaking in modeling non-perturbative QCD. The hadron spectra and correlation functions are studied holographically in an AdS(5) geometry with induced cosmological constants on four-dimensional hypersurface. 

Our analysis shows that the experimentally measured spectra of the ρ and a(1) mesons, including their excitations and decay constants, favour a non-vanishing induced cosmological constant in both hard-wall and soft-wall models. Although this behavior is not as sharp in the soft-wall model as in the hard-wall model, it remains consistent. Furthermore, we show that the correction to the Gell-Mann-Oakes-Renner relation has an inverse dependence on the induced cosmological constant, underscoring its significance in holographic descriptions of low-energy QCD.

Mathew Thomas Arun, Nabeel Thahirm, "On the role of cosmological constant in modeling hadrons" arXiv:2510.06380 (October 7, 2025).

A New Paper Argues For Dark Matter Over MOND

This paper argues for dark matter particles rather than modified gravity based upon observations of very low mass dwarf galaxies, although it has a very small sample size of just twelve galaxies.

A tight correlation between the baryonic and observed acceleration of galaxies has been reported over a wide range of mass (10^8 < Mbar/M⊙ < 10^11) - the Radial Acceleration Relation (RAR). This has been interpreted as evidence that dark matter is actually a manifestation of some modified weak-field gravity theory. 

In this paper, we study the radially resolved RAR of 12 nearby dwarf galaxies, with baryonic masses in the range 10^4 < Mbar/M⊙ < 10^7.5, using a combination of literature data and data from the MUSE-Faint survey. We use stellar line-of-sight velocities and the Jeans modelling code GravSphere to infer the mass distributions of these galaxies, allowing us to compute the RAR. We compare the results with the EDGE simulations of isolated dwarf galaxies with similar stellar masses in a ΛCDM cosmology. 

We find that most of the observed dwarf galaxies lie systematically above the low-mass extrapolation of the RAR. Each galaxy traces a locus in the RAR space that can have a multi-valued observed acceleration for a given baryonic acceleration, while there is significant scatter from galaxy to galaxy. 

Our results indicate that the RAR does not apply to low-mass dwarf galaxies and that the inferred baryonic acceleration of these dwarfs does not contain enough information, on its own, to derive the observed acceleration. 

The simulated EDGE dwarfs behave similarly to the real data, lying systematically above the extrapolated RAR. We show that, in the context of modified weak-field gravity theories, these results cannot be explained by differential tidal forces from the Milky Way, nor by the galaxies being far from dynamical equilibrium, since none of the galaxies in our sample seems to experience strong tides. As such, our results provide further evidence for the need for invisible dark matter in the smallest dwarf galaxies.

Mariana P. Júlio, et al., "The radial acceleration relation at the EDGE of galaxy formation: testing its universality in low-mass dwarf galaxies" arXiv:2510.06905 (October 8, 2025) (Accepted for publication in A&A).

How Flat Is The Universe?

The planet Earth is, to a good approximation, a perfect sphere. But, it isn't perfectly spherical.

Space-time in the universe as a whole is, to a good approximation, perfectly Euclidian. But, it has some curvature.

The magnitude by which the Earth differs from being a perfect sphere (in relative terms) is roughly similar to the magnitude by which the universe differs from being perfectly Euclidian. And, both on average and at the greatest extremes, Earth differs less from being perfectly spherical in relative terms, than the space-time of the universe differs from being perfectly Euclidean.

The ABC Conjecture Has Probably Not Been Proven

Woit reports that a claimed proof of the abc conjecture, a major unproven conjecture in the sub-field of mathematics called number theory (the same sub-field of mathematics that includes Fermat's Last Theorem, which has been proven) is probably flawed:

James Douglas Boyd has recently spent a lot of time interacting with Mochizuki and others at RIMS working in anabelian geometry. Material from interviews he conducted are available here (Mochizuki on IUT) and here (on anabelian geometry at RIMS). He also has written a summary of IUT and of the basic problem with the abc proof. These include detailed comments on the issue pointed out by Scholze-Stix and why this is a significant problem for the proof. I’d be curious to hear from anyone who has looked at this closely about whether they agree with Boyd’s characterization of the situation.

There’s also a lot of material [about] the IUT ideas, independent of the problematic abc proof, and about what Mochizuki and others are now trying to do with these ideas.

What is the abc conjecture?

The abc conjecture (also known as the Oesterlé–Masser conjecture) is a conjecture in number theory that arose out of a discussion of Joseph Oesterlé and David Masser in 1985. It is stated in terms of three positive integers a,b and c (hence the name) that are relatively prime and satisfy a+b=c. The conjecture essentially states that the product of the distinct prime factors of abc cannot often be much smaller than c. A number of famous conjectures and theorems in number theory would follow immediately from the abc conjecture or its versions. Mathematician Dorian Goldfeld described the abc conjecture as "The most important unsolved problem in Diophantine analysis".

The abc conjecture originated as the outcome of attempts by Oesterlé and Masser to understand the Szpiro conjecture about elliptic curves, which involves more geometric structures in its statement than the abc conjecture. The abc conjecture was shown to be equivalent to the modified Szpiro's conjecture.

Various attempts to prove the abc conjecture have been made, but none have gained broad acceptance. Shinichi Mochizuki claimed to have a proof in 2012, but the conjecture is still regarded as unproven by the mainstream mathematical community.

There is no 690 GeV resonance

Once again, a long standing, but sub-five sigma "bump" in particle accelerator results turns out to be explained by better analysis of what the background expectation without the new predicted particle should look like, and not "new physics". The low significance bump is also suspiciously close to four times the top quark mass at that energy scale.

I full expect the search for the X17 boson to end the same way.

Sadly, these pet ideas are zombies that persist in preprints, experimental efforts, and published papers long after they should have been abandoned.

In a series of ∼30 papers starting in 1991, it has been claimed that the Higgs field should be heavier than its now-measured value. To reconcile this idea with reality, it was modified to the assertion that the Higgs field describes two physical degrees of freedom, one of which corresponds to a second Higgs particle with mass 690 GeV. Here I summarize the lack of theoretical and experimental evidence for these claims.

James M. Cline, "There is no 690 GeV resonance" arXiv:2509.20115 (September 24, 2025). 

The paper is only three pages, half of which contains 33 references and the first page's heading and abstract, so I'll take the liberty of reproducing the entire short and punchy paper here:

Recently Ref. [1] reiterated the claim, already made in Refs. [2–14], that the Higgs field has an excited state with mass 690 GeV. This appears to be a modification of an earlier idea [15–28], pursued by one of the same authors, that the Higgs mass could or should be above the perturbative unitarity limit ∼ 700 GeV, as heavy as 2 TeV, depending upon the year of publication. The theoretical motivation for this prediction was the claim [29, 30] that λϕ^4 is not trivial, as is usually believed, but rather has a radiatively generated spontaneous symmetric phase (as predicted by the Coleman-Weinberg one-loop potential), in which it is asymptotically free.1 

1 The triviality of ϕ^4 theory, long believed to be the case, was proven in Ref. [31].

It was also claimed that the vacuum expectation value (VEV) of the scalar field gets renormalized by a different factor Z(v) than the fluctuations around the VEV, Z(ϕ), so that the usual relation between the Higgs mass and the VEV is modified by a factor Z(ϕ)/Z(v) which must be determined by lattice simulations, and predicts m(h) = 760 ± 20 GeV [17]. 

With the experimental discovery of the Higgs with mass m(h) = 125GeV, one might have hoped for such claims to be put to rest, but a way to have one’s cake and eat it too was found. It somehow goes back to the aforementioned idea, that pure λϕ^4 theory has spontaneous symmetry breaking `a la Coleman-Weinberg, despite the usual reservations that the perturbative calculation leading to that result cannot be trusted. The authors argue that now there are two mass scales in the potential: one is m(h)^2, the curvature of the potential V at its minimum, and the other is M(H)^4 = ∆V, from the depth of the potential minimum, which was generated by radiative symmetry breaking. It is not clear why this extra scale should correspond to an additional propagating degree of freedom. 

In order for a single field to describe two degrees of freedom, the propagator must have two poles, which usually arises from a higher derivative action containing ghosts. In the present case, the authors claim that nonperturbative effects generate the propagator structure 

G= i/(p^2 − M(H)^2*A(p^2)) (1) 

where A is a function such that A(m(h)^2) = m(h)^2/M(H)^2 and A(M(H)^2) = 1. The detailed form of A(p) is not disclosed, so we are forced to guess.2 

2 Ref. [1] says that this behavior was verified on the lattice in Ref. [13], but that reference purports to show that the form of the inverse propagator is (p^2 − m(h)^2)f(p), where f(p) has the same properties as A(p) in Eq. (1). This is puzzling since f(p) corresponds to wave function renormalization, while A(p) is the self-energy. 

It cannot be linear in p^2 since that would give G = i/0; hence the next simplest analytic possibility is quartic, A = 1 + (p^4/M(H)^4)(M(H)^2/m(h)^2 − 1). With this choice, we find for m(h) ≪ M(H)

G ∼ = −iM(H)^2/((p^2 − M(H)^2)(p^2 − m(h)^2)),  (2) 

which has the wrong sign for the heavy degree of freedom. The heavy particle is a ghost, as expected from a theory with a higher-derivative Lagrangian. The theoretical motivations for the “resonance” (unaptly named, since it is supposed to be coming from an elementary Higgs field, not a composite particle) are problematic. 

Let us turn then to the experimental evidence, which the LHC collaborations must have been very excited to discover. In Ref. [12] the authors discerned a bump in the ATLAS search [32] for heavy resonances decaying to ZZ → 4ℓ at m(H) ∼700GeV. The authors note that H should be dominantly produced through the gluon-gluon fusion (ggF) process, with negligible production from vector boson fusion (VBF). Fig. 1 reproduces the main results from the two papers. The ATLAS ggF limit has a 2-σ excess at 662GeV, which receives no comment in the ATLAS paper, and only upper limits are quoted.

The CMS collaboration took note of Ref. [12]’s prediction of an excess in this channel in their later search [33]. They also reported no significant excess. 

Since the original suggestion [12], there have been an additional ten papers [1–10] by various combinations of the authors emphasizing the predicted excess, lest we should forget. None of them are referred to by the experimental collaborations. In fact, of the 44 citations to these papers, all but 11 are self-cites. The authors find an equally convincing bump in the H → hh channel, leading them to “spell out a definite experimental signature of this resonance that is clearly visible in various LHC data.” A Nobel prize is sure to follow.

Does The Weak Mixing Angle Minimize Magic?

"Magic" is a quantum mechanical property that roughly speaking quantifies the extent to which a quantum computer is more powerful than a conventional computer. 

The "weak mixing angle" is a physically measured quantity in electroweak unification theory, which treats the weak force and electromagnetism as having a common, unified origin and functional relationships to each other, in which three weak isospin fields and a weak hypercharge field are transformed into the photon and the W+, W-, and Z bosons. It quantifies what transformation from an idealized state in the theory is necessary to produce the world that we actually see.

It turns out that quantum magic appears to be minimized at very close to the weak mixing angle at the Z boson mass energy scale. Since the amount of magic at the Z boson mass energy scale can be calculated in the Standard Model, rather than merely measured experimentally, this potentially makes the weak mixing angle a derived constant rather than an experimentally measured fundamental constant. It is also suggestive of how the weak mixing angle arises at a fundamental level.

Qiaofeng Liu, Ian Low, Zhewei Yin, "A Quantum Computational Determination of the Weak Mixing Angle in the Standard Model" arXiv:2509.18251 (September 22, 2025) (abstract presented as an image rather than cut and pasted, to preserve mathematical equation formatting).

In other news, we are about a decade away from fully describing the properties of the neutrino.

The Latest X17 Paper's Model Isn't Confidence Inspiring

Simply put, any protophobic boson makes no sense. Protons are composite objects, and there is no plausible reason for a fundamental boson to be "phobic" towards one kind of hadron produced by quarks and gluons, but not another. The authors' suggestion that such an explanation is "probable" is using a poor definition of that term.

The so-called X17 particle has been proposed in order to explain a very significant resonant behaviour (in both the angular separation and invariant mass) of e+e− pairs produced during a nuclear transition of excited 8Be, 4He and 12C nuclei. Fits to the corresponding data point, as most probable explanation, to a spin-1 object, which is protophobic and has a mass of approximately 16.7 MeV, which then makes the X17 potentially observable in Coherent Elastic neutrino (ν) Nucleus Scattering (CEνNS) at the European Spallation Source (ESS). 

By adopting as theoretical framework a minimal extension of the Standard Model (SM) with a generic U(1)′ gauge group mixing with the hypercharge one of the latter, which can naturally accommodate the X17 state compliant with all available measurements from a variety of experiments, we predict that CEνNS at the ESS will constitute an effective means to probe this hypothesis, even after allowing for the inevitable systematics associated to the performance of the planned detectors therein.

Joakim Cederkäll, et al., "Hunting the elusive X17 in CEνNS at the ESS" arXiv:2509.15121(September 18, 2025).

Do We Really Need Either Dark Matter Or Modified Gravity?

This article isn't hot off the presses, but was referenced in the comments at the Triton Station blog. I am highly skeptical of the conclusion that Newtonian physics without dark matter or modified gravity can explain the dynamics of the Milky Way galaxy adequately, contrary to a wealth of literature to the contrary.

Vertical stellar kinematics+density can be used to trace the dark matter distribution (or the equivalent phantom mass in a Modified Newtonian Dynamics (MOND) scenario) through the Jeans equations. 

In this paper, we want to improve this type of analysis by making use of the recent data of the 6D information from the Gaia DR3 survey in the anticenter and the Galactic poles to obtain the dynamical mass distribution near plane regions, including extended kinematics over a wide region of 8 kpc < R < 22 kpc, ∣z∣ < 3 kpc. 

Our conclusions are as follows: 

(i) the model of the spherical dark matter halos and the MOND model are compatible with the data; 

(ii) the model of the disky matter (with density proportional to the gas density) is excluded; 

(iii) the total lack of dark matter (there is only visible matter) within Newtonian gravity is compatible with the data; for instance, at solar Galactocentric radius, we obtained Σ = 39 ± 18 M⊙ pc^−2 for z = 1.05 kpc, compatible with the expected value for visible matter alone of 44 M⊙ pc^−2, thus allowing zero dark matter. Similarly, for R > R⊙, z = 1.05 kpc, Σ = 28.7 ± 9.6, 23.0 ± 5.7, 16.9 ± 5.8, and 11.4 ± 6.6 M⊙ pc^−2, respectively, for R = 10, 13, 16, and 19 kpc, compatible with visible matter alone. 

Larger error bars in comparison with previous works are not due to worse data or a more awkward technique but to a stricter modeling of the stellar distribution.

Martín López-Corredoira, "Milky Way Dark Matter Distribution or MOND Test from Vertical Stellar Kinematics with Gaia DR3" 978 ApJ 45 (December 24, 2024) DOI 10.3847/1538-4357/ad94f5 (open access).

Where Does Language Complexity Evolve?

I'm not entirely sold on this article's conclusion about the circumstances in which language complexity evolves, at least not based upon the data presented, even though there is good evidence that large numbers of language learners tend to reduce grammatical complexity.

Polysynthetic languages are very common in the New World and just across the Beringian land bridge from it (which could also be connected to the Paleo-Siberian cases), suggesting that most instances of it could be derived from a common source creating a Founder effect. 

Also, while these languages are small and isolated now, this hasn't always been the case. Athabaskan-Eyak-Tlingit and Nahuatl, for example, historically were quite expansive and had lots of contact with other language families.

The second cluster is from Aboriginal Australians and Papuans who derive from the first wave of modern human migration Out of Africa and into Asia around the time of the Toba eruption. 

There is a third cluster in the Caucuses, involving just one of the language families there, which are associated with early migrants from the first wave of Fertile Crescent agriculture in the highlands of West Asia. 

There are apparently other instances in South Asia and East Asia.

A handful of major language expansions, none of which happened to be polysynthetic make up a huge share of all languages spoken today. These include the Indo-European language family, the Afro-Asiatic languages, the Bantu language family, the Dravidian languages, and the arguable Altaic language family. European and Chinese colonial empires further reduced the size of many languages (long after their features were well intact), for reasons unrelated to language complexity. 

There are polysynthetic or borderline polysynthetic languages listed in the following major language families: the Sino-Tibetan languages (seemingly all in the Tibetan-Burmo branch), the Austroasiatic languages (3 Munda languages in Northeast India), the Austronesian languages (5 borderline seemingly Formosan languages) 

If only a minority of pre-expansion languages were polysynthetic, it wouldn't be surprising if the main expanding languages didn't end up including them.

Significance

A global test reveals statistically robust support for the hypothesis that complex word forms are more likely to develop in isolated languages. Polysynthesis, where words are built from many units to convey complex meanings, is more likely to occur in smaller populations and less likely to occur with many languages in contact. By building a global database of polysynthetic languages and analyzing in a phylospatial framework, this study highlights the potential for macroevolutionary methods to test hypotheses about language evolution and contribute to long-standing debates in linguistics.

Abstract

Evolution of complexity in human languages has been vigorously debated, including the proposal that complexity can build in small, isolated populations but is often lost in situations of language contact. If it is generally true that small, isolated languages can build morphological complexity over time, but complexity tends to be lost in situations of language contact, then we should find that forms of language complexity that have evolved multiple times will tend to be associated with population size, isolation, and language age. 

We test this hypothesis by focusing on one particular form of morphological complexity, polysynthesis, where words built from many parts embody complex phrases. By assembling a global database of polysynthetic languages and conducting phylospatial analyses, we show that languages with highly complex word morphology are more likely to have small population sizes, less likely to occur with many other languages in direct contact, and have a greater tendency to be on long phylogenetically isolated lineages. 

These findings are consistent with the hypothesis that languages that evolve in isolation for long periods may be more likely to accrue morphological complexity. Polysynthetic languages also tend to have higher levels of endangerment. Our results provide phylogenetically informed evidence that one particular form of complex language morphology is more likely to occur in small, isolated languages and is prone to loss in contact.

Lindell Bromham, Keaghan Yaxley, Oscar Wilson, and Xia Hua, "Macroevolutionary analysis of polysynthesis shows that language complexity is more likely to evolve in small, isolated populations" 122(24) PNAS e2504483122 (June 12, 2025) (pay per view; but open access supplemental materials).

The languages counted as polysynthetic and borderline, according to the Supplemental Materials, are below the fold.