Friday, June 27, 2025

Theories To Explain The Fundamental Fermion Masses

A new review paper which will be a chapter in an Encyclopedia of Particle Physics summarizes various theories that have been advanced to explain the fundamental fermion masses in the Standard Model, and while it isn't complete, its table of contents is a nice summary of some of the leading approaches.

2 Fermion masses and mixing angles 
2.1 The Standard Model 
2.2 Neutrino masses 
Majorana neutrino masses
The seesaw mechanism
Type-I seesaw
Type-III seesaw
Type-II seesaw
Dirac neutrino mass
2.3 The data 

3 In search of an organizing principle 

4 Grand Unified Theories 
4.1 SU(5) GUTs 
4.2 SU(10) GUTs 

5 Fermion masses from quantum corrections 
5.1 Radiative fermion masses 
5.2 Infrared fixed points 

6 CompositeFermions 
6.1 Massless composite fermions 
6.2 Partial compositeness 

7 Flavor Symmetries 
7.1 The Froggatt-Nielsen Model 
7.2 Variants and alternatives 

8 Fermion masses in String Theory 
8.1 Aiming at the SM from strings 
8.2 Eclectic flavor symmetries from heterotic orbifolds 
8.3 Flavor in models with D-branes 
8.4 Metaplectic flavor symmetries from magnetized branes

The LP & C relationship, and the kind of dynamical balancing rules that I favor don't get a mention, although they come closest to the quantum corrections approach. 

Thursday, June 26, 2025

Missing Baryon Problem Solved

Connor et al. assess that about 3/4 of all baryons are in the intergalactic medium (IGM), give or take 10% – the side bars illustrate the range of uncertainty. Many of the remaining baryons are in other forms of space plasma associated with but not in galaxies: the intracluster medium (ICM) of rich clusters, the intragroup medium (IGroupM) of smaller groups, and the circumgalactic medium (CGM) associated with individual galaxies. All the stars in all the galaxies add up to less than 10%, and the cold (non-ionized) atomic and molecular gas in galaxies comprise about 1% of the baryons.

For a long time at least half to a third of the ordinary atoms that other observations and Big Bang Nucleosynthesis predicted exist hadn't been found. (And, to be clear, this "missing baryon problem" was separate and distinct from the "dark matter" problem.)

Now, they are all accounted for. The missing ones were in the intergalactic medium (i.e. in the deep space between galaxies at a density of about one hydrogen atom per cubic meter). 

Stacy McGaugh at his blog Triton Station explains how this happened. The money chart is above.

Wednesday, June 25, 2025

Conformal Cosmology

An interesting GR based response to dark matter and dark energy that makes one subtle adjustment to the standard analysis. I'll have to give it a more careful read before saying more about it.

This paper is published in a peer reviewed journal (although not a high profile one) and the author has seven prior peer reviewed journal publications since 2016, one with Pavel Kroupa, a leading astronomer in the MOND literature, as a co-author. So, this is not the work of a crackpot non-astronomer.
The cosmic time dilation observed in Type Ia supernova light curves suggests that the passage of cosmic time varies throughout the evolution of the Universe. This observation implies that the rate of proper time is not constant, as assumed in the standard FLRW metric, but instead is time-dependent. Consequently, the commonly used FLRW metric should be replaced by a more general framework, known as the Conformal Cosmology (CC) metric, to properly account for cosmic time dilation. 
The CC metric incorporates both spatial expansion and time dilation during cosmic evolution. As a result, it is necessary to distinguish between comoving and proper (physical) time, similar to the distinction made between comoving and proper distances. In addition to successfully explaining cosmic time dilation, the CC metric offers several further advantages: (1) it preserves Lorentz invariance, (2) it maintains the form of Maxwell's equations as in Minkowski space-time, (3) it eliminates the need for dark matter and dark energy in the Friedmann equations, and (4) it successfully predicts the expansion and morphology of spiral galaxies in agreement with observations.
Vaclav Vavrycuk, "Time dilation observed in Type Ia supernova light curves and its cosmological consequences" arXiv:2506.19099 (June 23, 2025) (published in 13 Galaxies 55 (2025)).

Kroupa has also published a new cosmology paper (although I'm not optimistic about this MOND plus sterile neutrinos in clusters approach).
The νHDM is the only cosmological model based on Milgromian Dynamics (MOND) with available structure formation simulations. While MOND accounts for galaxies, with a priori predictions for spirals and ellipticals, a light sterile neutrino of 11 eV can assist in recovering scaling relations on the galaxy-cluster scales. In order to perform MONDian cosmological simulations in this theoretical approach, initial conditions derived from a fit to the angular power spectrum of Cosmic Microwave Background (CMB) fluctuations are required. 
In this work, we employ CosmoSIS to perform a Bayesian study of the νHDM model. Using the best-fit values of the posterior, the CMB power spectrum is reevaluated. The excess of power in the transfer function implies a distinct evolution scenario, which can be used further as an input for a set of hydro-dynamical calculations. The resulting values H0 ≈ 56 km/s/Mpc and Ωm0≈0.5 are far from agreement with respect to the best fit ones in the canonical Cold Dark Matter model, but may be significant in MONDian cosmology. The assumed Planck CMB initial conditions are only valid for the ΛCDM cosmology. This work constitutes a first step in an iterative procedure needed to disentangle the model dependence of the derived initial density and velocity fields.
Nick Samaras, Sebastian Grandis, Pavel Kroupa, "On the initial conditions of the νHDM cosmological model" arXiv:2506.19196 (June 23, 2025) (accepted for publication in MNRAS).

Tuesday, June 24, 2025

Muon g-2 Limits On BSM Physics

A new preprint explores how the lack of a muon g-2 anomaly constrains beyond the Standard Model particle physics models. The new constraints are strict but aren't easily summarized in a few words. Another paper looks at the impact on supersymmetry theories.

Friday, June 20, 2025

Homo Longi Were Denisovans

The archaic hominin skull from China provisionally classified as a member of the species Homo Longi has been linked to Denisovan DNA and proteins. This also makes it possible to know what a Denisovan looked like as shown in the image below.


The connection has been suspected, but not proven, for some time.

Monday, June 16, 2025

Population Replacement In The Columbian Highlands

In Europe, the first farmers of Europe, derived from Western Anatolian farmers, largely replaced Europe's original hunter-gatherers (who actually show continuity between the periods before and immediately after the Last Glacial Maximum), and in turn, received very substantial genetic admixture from late Copper Age/early Bronze Age Indo-Europeans from more or less where Ukraine is today. This diluted both first farmer ancestry, and the already highly diluted European hunter-gather ancestry that was admixed into those first farmer populations. In some places, like Britain, the population replacement of first farmers by Indo-Europeans was nearly complete.

Something similar apparently happened in East and Southeast Asia.

A new study established that the Americas did not break from this pattern, with some of its early agriculturists replacing pre-existing hunter-gatherer populations in a similarly genocidal pattern. If anything, this replacement was even more complete.

Sometime between 4000 BCE and 0 CE, in the Columbian highlands, probably coinciding with a new archaeological culture whose artifacts appear around 1000 BCE to 800 BCE, a millennium after maize cultivation began around 1800 BCE (but possibly before the full blown ceramic culture emerged), a clade of indigenous South American hunter-gatherers (with ancestry dating back to the initial wave of human settlement of South America) were replaced by a different group of indigenous South Americans.

The 1800 BCE date is from A. Gómez, et al., "A Holocene pollen record of vegetation change and human impact from Pantano de Vargas, an intra-Andean basin of Duitama, Colombia." 145 Rev. Palaeobot. Palynol. 143–157 (2007) (full paper available here), and really only definitively points to deforestation and Amaranth cultivation at that point in the highlands of Columbia.

From Wikipedia.

The population that replaced them, which is genetically linked to the speakers of Chibchan languages and probably originated in Central America, has remained the dominant population of the region in genetic continuity with their ancestors since this population replacement occurred, although later populations admixed with them and brought new languages in some parts of the region. 

There is no evidence that anyone from the pre-agricultural, pre-ceramic culture that was replaced in the Columbian highlands survived, or even significantly admixed with surviving populations.

The new agriculturalist culture did not really come into its own archaeologically until 1000 BCE to 800 BCE, so we can't know for sure if the replacement took place suddenly (although the lack of admixture between the new and old populations suggests that it did) or more gradually, or how long after maize cultivation, a thousand years earlier than this culture's pots appeared, the population replacement happened. 

Conservatively, it happened in some short time period between 1800 BCE and 800 BCE (about 3,000 to 4,000 years after it happened in Europe). Realistically, it probably happened on the later side of that time range when other components of the emerging farmer culture, like pottery and possibly other key domesticated plants and/or animals, joined with improved maize cultivation to give rise to a technologically dominant new culture.

The introduction and discussion sections of a new study released May 28, 2025 in the journal Scientific Advances by Kim-Louise Krettek, et al., explain that:

Genetic studies on ancient and present-day Indigenous populations have substantially contributed to the understanding of the settlement of the Americas. Those studies revealed that the population ancestral to non-Arctic Native Americans derives from a genetic admixture between ancient East Asian and Siberian groups somewhere in North-East Asia before 20,000 years before the present (yr B.P.). Around 16,000 yr B.P., after its arrival in North America, this genetic ancestry split into two lineages known as northern Native American and southern Native American. While northern Native American ancestry is largely confined to ancient and current populations of North America, the southern Native American lineage expanded further south and constitutes the main ancestry component of ancient and present-day Indigenous South Americans. 
Southern Native American ancestry diversified within North America into at least three sublineages, i.e., one related to the Clovis-associated Anzick-1 individual from western Montana (USA), one found in ancient California Channel Islands individuals and the last one representing the main ancestry source of modern-day Central and South Americans.  
Each of these sublineages provided a wave of ancestry into the gene pool of ancient South Americans. Individuals from Chile and Brazil dating back to around 12,000 and 10,000 yr B.P., respectively, were more genetically related to the Anzick-1 genome than individuals from the eastern Southern American coast, Southern Cone and the Andes from 10,000 yr B.P. onward. In addition, the California Channel Islands ancestry was found in the Central Andes by 4200 yr B.P. and became widespread in the region thereafter. However, the exact timing of these population movements into the southern subcontinent remains largely unsolved to date. 
The Isthmo-Colombian area, stretching from the coast of Honduras to the northern Colombian Andes, is critical to understanding the peopling of the Americas. Besides being the land bridge between North and South America, it is at the center of the three major cultural regions of Mesoamerica, Amazonia, and the Andes. At the time of European contact, the region was inhabited by a complex mosaic of human populations, mainly speakers of Chibchan, Chocoan, Carib, and Arawakan languages. 
Among those populations, those who were speakers of Chibchan languages were the most widespread in the region in terms of demography, cultural diversity, and territorial distribution. Chibchan is a language family with multiple, highly distinct branches, many of which are still spoken today in different regions of the Isthmo-Colombian area. The homeland and antiquity of the Proto-Chibchan language and the ancestor of all Chibchan languages remain subjects of debate. High intrafamily variation in terms of lexicon and grammar suggests that the language family is ancient and began diversifying several thousand years ago. The locus of that incipient diversification, however, is still uncertain. Most scholars believe that this protolanguage began to diversify in Lower Central America, where the largest number of these languages is spoken today. However, some evidence suggests that Proto-Chibchan might have originated in South America and then diversified in Central America at a much later date. 
Genetic studies of ancient and present-day Isthmo-Colombian Indigenous populations revealed a distinctive ancestry component primarily associated with speakers of Chibchan languages. However, whereas mitochondrial DNA (mtDNA) studies suggested a migration of Chibchan-related ancestry from Central America into Colombia and Venezuela, genome-wide studies favored an opposite, south-to-north population movement. According to the latter model, speakers of Chibchan languages from Central America are not direct descendants of the first settlers in the region but, instead, derive from a more recent back migration from South to Central America. 
The southernmost region of the Isthmo-Colombian area is the Altiplano Cundiboyacense (hereafter Altiplano). This plateau with an average altitude of 2600 m in the Eastern Cordillera of the Colombian Andes was inhabited by ancient hunter-gatherer groups from the Late Pleistocene. During the Early and Middle Holocene phases of the Preceramic period (~11,500 to 4000 yr B.P.), populations on the Altiplano underwent multiple cultural transformations, most notably increased sedentism and a transition from a hunter-gatherer subsistence to the introduction of horticultural practices and forest management. However, it was not until the early Late Holocene, ~3800 yr B.P., that the first clear evidence of maize cultivation appeared. 
During the subsequent Formative period (~3000 to 1000 yr B.P.), a distinct type of pottery emerged on the Altiplano that is referred to as the Herrera ceramic complex, also known in the literature as the Herrera period (2800 to 1200 yr B.P.). It is still highly debated whether Herrera-associated groups on the Altiplano derived from an in situ development of local hunter-gatherers or were a consequence of population dispersals into the region. 
Around 1200 yr B.P., a cultural phase, known as the Muisca period, began on the Altiplano and lasted until the imposition of the Hispanic Colonial regime in the mid-16th century. Most available evidence is suggestive of population continuity with the preceding Herrera period. The Muisca period is characterized by a relatively continuous process of demographic growth, development of agriculture and trade, and social and political complexification. These factors played a considerable role in shaping the Muisca culture and gave rise to the Chibchan-speaking population that dominated the Altiplano until European colonization. 
While several studies have reported mtDNA data from ancient Colombian individuals, genome-wide data from this region are still entirely lacking to date. In this study, we generated mtDNA and genome-wide data of 21 ancient individuals from two areas of the Altiplano (Bogotá plateau and Los Curos). Our data, spanning a time transect between around 6000 and 500 yr B.P., provide an opportunity to explore several key questions: 
(i) Which southern Native American genetic ancestry do Preceramic individuals from the Altiplano derive from? 
(ii) Were the cultural transformations associated with the Herrera and Muisca periods accompanied by migrations and demographic changes? 
(iii) How is the genetic ancestry observed in speakers of Chibchan languages related to that of ancient individuals from the Altiplano? 
(iv) What are the genetic relationships between the generated ancient genomes and the existing genomic data of present-day Indigenous communities from Colombia and neighboring regions?

In this study, we generated genome-wide data from 21 individuals spanning a time transect of almost 6000 years from the Altiplano, which represents the southern edge of the Isthmo-Colombian area. Our findings contribute to a better understanding of the population history of this area, a key region in the peopling process of South America. We show that the hunter-gatherer population from the Altiplano dated to around 6000 yr B.P. lack the genetic ancestry related to the Clovis-associated Anzick-1 genome and to ancient California Channel Island individuals, suggesting their affiliation to the southern Native American lineage that became the primary source of ancestry of South Americans by 9000 yr B.P. 
However, unlike ancient genomes from the Andes and the Southern Cone that are associated with the same wave of ancestry, the analyzed Preceramic individuals from Colombia do not share distinct affinity with any ancient or modern-day population from Central and South America studied to date. Colombia_Checua_6000BP can thus be modeled as a previously undescribed distinct lineage deriving from the radiation event that gave rise to multiple populations across South America during its initial settlement. 
The cultural transition between the Preceramic and Herrera periods is associated with a seemingly complete replacement of the local genetic profile. This challenges the model where local hunter-gatherers developed in situ as suggested by morphometric studies and an ancient mtDNA time transect. Instead, our study provides evidence for a major genetic turnover on the Altiplano occurring after 6000 yr B.P. but before 2000 yr B.P. Since the mechanisms and precise temporal scale of this replacement event remain uncertain, we cannot directly associate it with the emergence of maize cultivation ~3800 yr B.P. However, our data do support the archaeological hypothesis that the introduction of pottery associated with the Herrera ceramic complex was mediated through population dispersals. 
Our results show that the incoming genetic ancestry on the Altiplano is related to ancient and present-day populations speaking Chibchan languages from Central America. This can be explained most parsimoniously by Chibchan-related migrations from Lower Central America to South America, rather than back-migration to the isthmus. 
A separate study found evidence for a previously unknown south-to-north expansion of Chibchan-related ancestry from Lower Central America into the Mayan territories of Belize by 5600 yr B.P. Therefore, rather than modeling Central American populations associated with Chibchan languages as deriving from a mixture between North and South American ancestries, these results are consistent with an origin of Chibchan-related ancestries in Lower Central America, followed by bidirectional gene flow toward both Meso- and South America. This model of an original “Chibchan homeland” in Central America is supported not only by mtDNA studies on present-day populations who speak Chibchan languages but also from linguistic observations, indicating that the isthmus region exhibits the highest diversity within this language family. 
From an archaeological perspective, the Chibchan-related ancestry is first identified in 2000-year-old individuals associated with Herrera ceramics. In addition, previously sequenced Ceramic-associated individuals from Venezuela dated to 2400 yr B.P. also showed a high affinity to Central American populations speaking Chibchan languages. Despite the similar ancestry pattern and temporal frame, the two populations do not appear to form a simple sister group. This could be in line with linguistic evidence that suggests multiple, distinct Chibchan language expansions into South America, but additional studies will be necessary to further clarify this issue. 
After the arrival of the Chibchan-related ancestry, which completely reshaped the genetic landscape of the region, we find evidence of a long period of genetic continuity in the genetic profile of the local populations for over 1500 years (from at least 2000 to 500 yr B.P.). The stability in genetic ancestry encompasses the end of the Herrera period and the beginning of the Muisca period. This points to a scenario in which populations speaking languages from the Chibchan lineage would have settled the Altiplano before the emergence of traits normally associated with the Muisca culture, and it shows that this cultural transition took place without a substantial migration from regions with a distinct genetic ancestry composition. In addition, such a genetic continuity extends through different cultural phases within the Muisca period and persists until the Spanish colonization. Colonial linguistic documentation established that Muisca people spoke a now extinct Chibchan language. Our findings not only confirm their genetic link with speakers of Chibchan languages from Central America but also suggest that ancestral Chibchan languages, possibly basal to the Magdalenic branch that gave rise to the documented Muisca language, might have already been spoken on the Altiplano during the pre-Muisca Herrera period. 
While the representation of Indigenous populations in our dataset is certainly not exhaustive, the observed spatial pattern in the genetic affinity of post-2000 yr B.P. ancient Colombians with present-day Indigenous populations raises questions regarding the uneven distribution of populations speaking Chibchan languages across the Isthmo-Colombian area at the time of the Hispanic colonization, also referred to as a Chibchan “archipelago”. 
One possible explanation is that this distribution resulted from separate dispersals from Central America to different locations of northern South America rather than a single expansion wave, as suggested by the internal branching pattern of the Chibchan language family. However, it is also possible that the initial spread was more widespread and got later fragmented by post-Chibchan migration and admixture events. The observation that Chibchan-affiliated populations from northern Colombia have a significantly reduced genetic affinity to post-2000–yr B.P. ancient Colombians than to Lower Central Americans supports the role of population admixture in shaping the genetic diversity of northern South America.

Also, while the earlier South American hunter-gatherer clade that went extinct probably dated to the founding wave of the modern humans in South America, they did not have notable Australasian or Melanesian ancestry, disfavoring the existence of a dramatically genetically distinct founding population of the Americas that preceded the main founding wave of modern humans and has Australasian or Melanesian genetic affinities that ancient.

Chinese Script v. English Statistics

The average number of strokes in a Chinese character is roughly 12.

The average number of strokes in a letter of the English alphabet is 1.9.

The average number of syllables in an English word is 1.66 (and 5 letters).

The average number of syllables in a Chinese word is roughly 2 (and 24 strokes).

The average number of words in an English sentence is 15-20.

The average number of words in a Chinese sentence is 25 (ballpark figure; see here)

Chinese has more than 100,000 characters.

English has 26 letters.

Total number of English words; over 600,000 (Oxford English Dictionary)

Total number of Chinese words: a little over 370,000 (Hànyǔ dà cídiǎn 漢語大詞典 [Unabridged dictionary of Sinitic])

From Language Log.

Quantum Gravity Can't Violate CPT

The reasoning in this article is sound and means that quantum gravity should preserve Charge-Parity-Time (CPT) symmetry, not just in an emergent low energy approximation, but at all energy scales.
CPT symmetry is at the heart of the Standard Model of particle physics and experimentally very well tested, but expected to be broken in some approaches to quantum gravity. It thus becomes pertinent to explore which of the two alternatives is realized: (i) CPT symmetry is emergent, so that it is restored in the low-energy theory, even if it is broken beyond the Planck scale, (ii) CPT symmetry cannot be emergent and must be fundamental, so that any approach to quantum gravity, in which CPT is broken, is ruled out. 

We explore this by calculating the Renormalization Group flow of CPT violating interactions under the impact of quantum fluctuations of the metric. We find that CPT symmetry cannot be emergent and conclude that quantum-gravity approaches must avoid the breaking of CPT symmetry. 
As a specific example, we discover that in asymptotically safe quantum gravity CPT symmetry remains intact, if it is imposed as a fundamental symmetry, but it is badly broken at low energies if a tiny amount of CPT violation is present in the transplanckian regime.
Astrid Eichhorn, Marc Schiffer, "No dynamical CPT symmetry restoration in quantum gravity" arXiv:2506.12001 (June 13, 2025).

Monday, June 9, 2025

Ancient UP Agriculture

Drone based LIDAR has made a major new find in North America:
A new study has found that a thickly forested sliver of Michigan’s Upper Peninsula is the most complete ancient agricultural location in the eastern United States. The Sixty Islands archaeological site is recognized as the ancestral home of the Menominee Nation. Known to the members of the tribe as Anaem Omot (Dog’s Belly), the area is a destination of pilgrimage, where remains of the settlement date to as far back as 8,000 B.C.

Located along a two-mile stretch of the Menominee River, Sixty Islands is defined by its cold temperatures, poor soil quality and short growing season. Although the land has long been considered unsuitable for farming, an academic paper published on Thursday in the journal Science revealed that the Menominee’s forbears cultivated vast fields of corn and potentially other crops there.
From the New York Times.

I'll update if time permits after reading the full paper.

The Latest Neutrino Mixing Data

The work to measure the mixing properties of neutrinos continues. A normal mass ordering and near maximal CP violation continues to be preferred.
T2K has made improved measurements of three-flavor neutrino mixing with 19.7(16.3) × 10^20 protons on target in (anti-)neutrino-enhanced beam modes. A new sample of muon-neutrino events with tagged pions has been added at the far detector, increasing the neutrino-enhanced muon-neutrino sample size by 42.5%. In addition, new samples have been added at the near detector, and significant improvements have been made to the flux and neutrino interaction modeling. T2K data continues to prefer the normal mass ordering and upper octant of sin^2θ(23) with a near-maximal value of the charge-parity violating phase with best-fit values in the normal ordering of δCP=−2.18+1.22−0.47, sin^2θ(23)=0.559+0.018−0.078 and Δm(23)^2=(+2.506+0.039−0.052)×10^−3 eV^2.
The T2K Collaboration, "Results from the T2K experiment on neutrino mixing including a new far detector μ-like sample" arXiv:2506.05889 (June 6, 2025).

The preference for the upper quadrant was about 2.3 sigma, and the preference for a normal ordering was about 2.7 sigma. With regard to CP-violation:
The data preferred values of δCP close to −π/2 radians, excluding values around +π/2 radians at >3σ, and excluding the CP-conserving values of 0 and π at 90% confidence. However [with further analysis] . . . the result to no longer exclude δCP = π at 90% confidence. The result was statistically limited and can be expected to improve as more data is accumulated.

Friday, June 6, 2025

New World Y1K Demographic Trends

Viewing event 350 years apart as part of the same trend is further in the direction of lumping than I'm comfortable with, but it is good to have a perspective on the pre-Columbian Americas that isn't static, with the implicit assumption that it was always the way it was when Europeans first encountered it.
[A] team led by archaeologist Robert Kelly of the University of Wyoming has studied this period using a previously assembled database of some 100,000 radiocarbon dates from across the United States. (See “Save the Dates.”) They used the dates to track population movements and demographic decline during this turbulent era, which was marked by drought, warfare, and disease. “We knew in a piecemeal fashion that these conditions drove demographic changes in different regions,” says Kelly. “But the radiocarbon data gives us a powerful new tool to understand population decline across the continent.”

After dividing the United States into 18 watersheds, the team analyzed the frequency of radiocarbon dates in each region and demonstrated that a cascading demographic collapse began in the central Rockies around a.d. 800 and later accelerated in multiple regions of central North America after 1150. The team’s analysis shows that the population of watersheds in California, the Pacific Northwest, the Great Lakes, and New England actually grew during the same period. This was likely because groups made their way from regions stricken by drought and warfare toward the coasts. Nonetheless, the radiocarbon data suggests that the overall Native American population declined by at least 30 percent from its peak before 1150.
From Archaeology Magazine.

The Latest Wide Binary Paper Shows Newtonian Behavior

The Wide Binary analysis debate continues. This paper doesn't see MOND-like behavior in wide binaries.
Of the 44 pairs observed with HARPS, 27% show sign of multiplicity or are not suitable for the test, and 32 bona-fide WBs survive our selection. Their projected separation s is up to 14 kAU, or 0.06 parsec. We determine distances, eccentricities and position angles to reproduce the velocity differences according to Newton's law, finding reasonable solutions for all WBs but one, and with some systems possibly too near pericenter and/or at too high inclination. Our (limited) number of WBs does not show obvious trends with separation or acceleration and is consistent with Newtonian dynamics. We are collecting a larger sample of this kind to robustly assess these results.

Thursday, June 5, 2025

Conformal Gravity As A Dark Matter Alternative

One proposed modification of General Relativity that has been proposed to explain dark matter phenomena is Conformal Gravity, which basically preserves angles in transformations adding an additional symmetry to GR.

A new paper suggests that Conformal Gravity fails in elliptical galaxies.
As an alternative gravitational theory to General Relativity (GR), the Conformal Gravity (CG) has recently been successfully verified by observations of Type Ia supernovae (SN Ia) and the rotation curves of spiral galaxies
The observations of galaxies only pertain to the non-relativistic form of gravity. In this context, within the framework of the Newtonian theory of gravity (the non-relativistic form of GR), dark matter is postulated to account for the observations. On the other hand, the non-relativistic form of CG predicts an additional potential: besides the Newtonian potential, there is a so-called linear potential term, characterized by the parameter γ∗, as an alternative to dark matter in Newtonian gravity. 
To test CG in its non-relativistic form, much work has been done by fitting the predictions to the observations of circular velocity (rotation curves) for spiral galaxies. 
In this paper, we test CG with the observations from elliptical galaxies. Instead of the circular velocities for spiral galaxies, we use the velocity dispersion for elliptical galaxies. By replacing the Newtonian potential with that predicted by non-relativistic form of CG in Hamiltonian, we directly extend the Jeans equation derived in Newtonian theory to that for CG. By comparing the results derived from the ellipticals with that from spirals, we find that the extra potential predicted by CG is not sufficient to account for the observations of ellipticals. Furthermore, we discover a strong correlation between γ∗ and the stellar mass M∗ in dwarf spheroidal galaxies. This finding implies that the variation in γ∗ violates a fundamental prediction of Conformal Gravity (CG), which posits that γ∗ should be a universal constant.
Li-Xue Yue, Da-Ming Chen, "Test of conformal gravity as an alternative to dark matter from the observations of elliptical galaxies" arXiv:2506.03955 (June 4, 2025).

The Missing Baryons Are Probably In Deep Space

The missing baryon problem is that we can't find where all of the ordinary matter that should exist is located. New studies such as this one strongly suggest that it is mostly spread diffusely between galaxies.
Fast radio bursts (FRBs) are emerging as powerful cosmological probes for constraining the baryon fraction in the intergalactic medium (IGM), offering a promising avenue to address the missing baryon problem. In this paper, we analyze constraints on the IGM baryon fraction (fIGM) using 92 localized FRBs, incorporating a corrected probability distribution function for the IGM dispersion measure within three different cosmological models. We find that variations in the underlying cosmological model have a negligible impact on the inferred values of fIGM. While the NE2001 Galactic electron density model yields slightly higher fIGM values compared to the YMW16 model, the results are consistent within the 1σ confidence level. Additionally, there is no statistically significant evidence for redshift evolution in fIGM. Our analysis constrains fIGM to the range 0.8∼0.9, providing strong support for the idea in which the majority of the missing baryons reside in the diffuse IGM.
Yang Liu, Yuchen Zhang, Hongwei Yu, Puxun Wu, "Constraining the Baryon Fraction in the Intergalactic Medium with 92 localized Fast Radio Bursts" arXiv:2506.03536 (June 4, 2025).

Tuesday, June 3, 2025

The Final Fermilab Muon g-2 Measurement

From this morning's seminar: The new experimental result from Fermilab Runs 1-6 combined is:

0.01165920705(148) which is 127 parts per billion. This exceeded their goal of 140 ppb.


Including the Brookhaven result in the global experimental average only slightly tweaks this result (by 10 * 10^-12 higher) because the average is inverse error weighted and the Brookhaven result has four times more uncertainty and is only modestly higher itself. Runs 4-6 whose results were announced today, slightly pulled up the total value. It's result was 5 * 10^-12 higher than the overall average.


A crude breakdown of the sources of the uncertainty in the final results was as follows (the 125 ppb uncertainty total differs from everything else that puts it at 127 ppb).


The 127 ppb uncertainty in the experimental result (i.e. 0.01165920705(148)) compares to a 530 ppb uncertainty in the 2025 White Paper predicted value of muon g-2 which is a(SM)(μ) = 116592033(62) × 10^−11 (530 ppb).

The experimental value minus the SM prediction is (375 ± 637) × 10^−12 which is a difference of about 0.6 sigma, which is a very strong global confirmation of the Standard Model of Particle Physics at low to moderate energies.

The world average value minus the SM prediction is (385 ± 637) × 10^−12 which is also a difference of about 0.6 sigma, which is a very strong global confirmation of the Standard Model of Particle Physics at low to moderate energies.

Most likely, the discrepancy is mostly due to the leading order hadronic vacuum polarization (LO HVP) calculation in the Standard Model prediction being about 0.5% low in a calculation with a ± 0.9% uncertainty.

This result disfavors the hypothetical X17 particle, since a 16.9 MeV fundamental boson would very likely have a significant effect on the anomalous magnetic moment of the 105.7 MeV muon.

The link to the Fermilab paper reporting this is here. It's abstract states:
A new measurement of the magnetic anomaly aµ of the positive muon is presented based on data taken from 2020 to 2023 by the Muon g−2 Experiment at Fermi National Accelerator Laboratory (FNAL). This dataset contains over 2.5 times the total statistics of our previous results. From the ratio of the precession frequencies for muons and protons in our storage ring magnetic field, together with precisely known ratios of fundamental constants, we determine aµ = 1165920710(162) × 10^−12 (139ppb) for the new datasets, and aµ = 1165920705(148) × 10^−12 (127ppb) when combined with our previous results. The new experimental world average, dominated by the measurements at FNAL, is aµ(exp) = 1165920715(145) × 10^−12 (124ppb). The measurements at FNAL have improved the precision on the world average by over a factor of four.

Monday, June 2, 2025

More On 22,000 Year Old Footprints In New Mexico

According to a new study, ancient footprints and drag marks at White Sands National Park in New Mexico suggest the earliest known North Americans used wooden travois-like "vehicles" to transport goods, and possibly even people, 22,000 years ago.

This account is based upon:

A travois is crafted from one or more wooden poles and is one of the simplest prehistoric vehicles. Although these devices likely played vital roles in the lives of ancient peoples, they have low preservation potential in the archaeological record. Here we report linear features associated with human footprints, some of which are dated to ∼22,000 years old, preserved in fine-grained sediments at White Sands National Park (New Mexico, USA). Using a range of examples, we identify three morphological types of trace in late Pleistocene sediments. Type I features occur as single, or bifurcating, narrow (depth > width) grooves which extend in planform from 2 to 50 m in length and trace either straight, gently curved or more irregular lines. They are associated with human footprints, which are truncated longitudinally by the groove and are not associated with other animal tracks. Type II examples are broader (width > depth) and form shallow runnels that typically have straight planforms and may truncate human footprints to one side. Type III examples consist of two parallel, equidistant grooves between 250 and 350 mm apart. They trace gently curving lines that can extend for 30+ m. Human footprints are associated with these features and may occur between, and to the side of, the parallel grooves. We review a range of possible interpretations including both human and non-human explanations and conclude that the most parsimonious explanation is that they represent drag marks formed by travois consisting of a single pole or crossed poles pulled by humans, presumably during the transport of resources. As such this unique footprint record may represent one of the earliest pieces of evidence for the use of transport technology.
Bennett, M. R., et al., "The ichnology of White Sands (New Mexico): Linear traces and human footprints, evidence of transport technology?" Quaternary Science Advances, 17(100274), 100274 (2025) (open access) doi:10.1016/j.qsa.2025.100274

The dating was confirmed in this 2023 paper:

Editor’s summary 
Traditionally, researchers believed that humans arrived in North America around 16,000 to 13,000 years ago. Recently, however, evidence has accumulated supporting a much earlier date. In 2021, fossilized footprints from White Sands National Park in New Mexico were dated to between 20,000 and 23,000 years ago, providing key evidence for earlier occupation, although this finding was controversial. Pigati et al. returned to the White Sands footprints and obtained new dates from multiple, highly reliable sources (see the Perspective by Philippsen). They, too, resolved dates of 20,000 to 23,000 years ago, reconfirming that humans were present far south of the ice sheets during the Last Glacial Maximum. 
—Sacha Vignieri 
Abstract 
Human footprints at White Sands National Park, New Mexico, USA, reportedly date to between ~23,000 and 21,000 years ago according to radiocarbon dating of seeds from the aquatic plant Ruppia cirrhosa. These ages remain controversial because of potential old carbon reservoir effects that could compromise their accuracy. We present new calibrated 14C ages of terrestrial pollen collected from the same stratigraphic horizons as those of the Ruppia seeds, along with optically stimulated luminescence ages of sediments from within the human footprint–bearing sequence, to evaluate the veracity of the seed ages. The results show that the chronologic framework originally established for the White Sands footprints is robust and reaffirm that humans were present in North America during the Last Glacial Maximum.

Jeffrey S. Pigati, et al., "Independent age estimates resolve the controversy of ancient human footprints at White Sands" 382 (6666) Science 73-75 (October 5, 2023).