Monday, July 15, 2024

A "No Hype" Science Journalism Stand-Out

Science journalism aimed at the educated (or not so educated) layman in the general public is prone to sensationalism and claims of new discoveries that aren't supported by the body text, or at least, aren't supported by the source and the general scientific community. But there are exceptions. 

One stand out is an article from Phys.org which is a source that often offends in this regard but doesn't this time. Its headline accurately states:

Theoretical physicists find Higgs boson does not seem to contain any harbingers of new physics

The headline conclusion, reached after twelve years of study since its discovery was announced on July 4, 2012, is familiar to readers of this blog, but deserves recognition for resisting sensationalism and restating the scientific consensus.  See, e.g., noting decays to a Z boson and a photon and here (summarizing the data to date). 

The article used as its touchstone has the following abstract and citation (and isn't itself, the headline suggests, a broad review article, and is instead one more mundane article confirming that the experimental study of the Higgs boson confirms the theoretical expectations for it):

We evaluate the top-bottom interference contribution to the fully inclusive Higgs production cross section at next-to-next-to-leading order in QCD. Although bottom-quark-mass effects are power suppressed, the accuracy of state-of-the-art theory predictions makes an exact determination of this effect indispensable. The total effect of the interference at 13 TeV is −1.99⁢(1)+0.30−0.15  pb, while the pure ­Łĺ¬⁡(­ŁŤ╝4­ŁĹá) correction is 0.43 pb. With this result, we address one of the leading theory uncertainties of the cross section.
Michał Czakon et al, "Top-Bottom Interference Contribution to Fully Inclusive Higgs Production", Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.132.211902

As additional context, Peter Higgs after whom the Higgs boson  is named, died in April of this year.

There is actually a slight Higgs boson anomaly, that is barely statistically significant locally (2.2 sigma), which would probably lose its statistical significance after considering look elsewhere effects, involving lower than expected Higgs boson decays to fermions (but the expected number of decays to bosons).

There are also a couple of low significance resonance "bumps" that have been touted as possible additional electromagnetically neutral Higgs bosons that have not been confirmed, one a bit below the Higgs boson mass of about 125 GeV, at about 96 GeV, and one or two a bit above it. Even if these "bumps" were confirmed to be real particles, there is no a priori reason to have any  confidence that they have anything to do with the Higgs boson.

Early Neolithic Arabia

 

Archaeologists in Saudi Arabia have excavated eight ancient "standing stone circles" that they say were used as homes. About 345 of these structures were identified through aerial surveys across the Harrat 'Uwayrid, a lava field near the city of AlUla in northwestern Saudi Arabia, the team reported July 2 in the journal Levant. The circles range from 13 to 26 feet (4 to 8 meters) in diameter and have at least one standing stone at the center. The circles date back around 7,000 years and have the remains of stone walls and at least one doorway. They would have had roofs made of either stone or organic materials, the team wrote. . . . 
Around 7,000 years ago, the environment in northern Saudi Arabia was much wetter than it is today, but farming had not yet come into use. "There's no evidence of farming domesticated species of plants like wheat and barley, but gathering wild plants likely took place, and perhaps manipulating the landscape to increase the likelihood and yield of wild species," McMahon said.

When these standing stone circles were in use, another form of stone structure, known today as a mustatil (Arabic for "rectangle"), was being built as well. Excavations at the mustatils suggest they had a ritual purpose that may have included the sacrifice of cattle. The contemporaneous use of the mustatils and standing stone circles indicates that it is "likely that these two megalithic structure types are aspects of a single cultural entity," the team wrote.

Gary Rollefson, a professor emeritus of anthropology at Whitman College and San Diego State University who was not involved in the research but has conducted extensive archaeological work in the region, said he thinks the people who built the standing stone circles and mustatils are descended from people who lived in Jordan and Syria about 500 years earlier.
He told Live Science that the architecture of the standing stone circles is similar to that of structures found in Jordan dating to about 500 years earlier, and the people who built the structures in Jordan also herded sheep, goats and cattle. The migration may have been spurred by an increase in population brought about by new hunting technologies, such as the "kite," a series of stone walls used to force wild animals into a kill zone. These hunting advances dramatically increased the supply of food, which, in turn, led to an increase in the human population in the Jordan/Syria area.

"They were building up a large population in eastern Jordan and [parts of] Syria," Rollefson said, and they needed to find new hunting grounds, which would have led them to gradually go south, into what is now Saudi Arabia.

Via Live Science.

The paper indicates that there were post-Neolithic early herders, rather than primarily being hunter-gatherers.

The paper and its abstract are as follows:

Recent archaeological investigations in AlUla County have provided the first detailed chrono-cultural evidence for long-term Neolithic domestic occupation in this archaeologically unknown region of north-west Arabia. 
This paper presents the preliminary findings drawn from multi-scalar datasets collected through extensive aerial and ground surveys, and the excavations of ‘monumental’ architectural installations, named in this study as ‘Standing Stone Circles’. These structures were individual dwellings, constructed in concentrations of varying numbers with associated domestic installations, such as hearths. The Standing Stone Cicle sites presented in this paper demonstrate a scale of Neolithic occupation not previously recognized in Saudi Arabia. These structures provide evidence of ongoing occupation throughout the 6th and 5th millennia BCE, concurrent with a general florescence of human activity across north-west Arabia. The faunal remains indicate a mixed subsistence economy, dominated by domesticates but supplemented by wild species. 
Broader considerations of the Neolithic economy, and models of pastoralism and mobility, are made possible on the basis of this, and the associated assemblages of stone artefacts and small finds. The data provided in this article offers a general picture of the Neolithic period in AlUla, addressing the significant geographical and temporal gaps within the archaeological knowledge of north-west Arabia. The identification of diagnostic Late Neolithic Levantine projectile point types, in conjunction with architectural parallels with the Levant, provides further insight into the origins of neolithization in north-west Arabia.

Archaic Hominin News

The flow of genes in multiple episodes between Neanderthals and modern humans is now better understood, and we have a new Denisovan genome from 200,000 years ago with better quality than any previous Denisovan genome. Via Razib:

Our understanding of admixture between humans and Neanderthals has changed dramatically over the past decade and a half. Once thought not to have occurred at all, there is now ample evidence for gene flow from Neanderthals to humans and vice versa. Li et al. used a new framework to model the increasingly complex dynamics of introgression between humans and Neanderthals and the ramifications for both populations. They identified regions of human ancestry in Neanderthals, estimated population sizes for Neanderthals were about 20% lower than previously thought, and proposed the possibility of two pulses of gene flow from humans to Neanderthals. This study comprehensively synthesizes our current knowledge of hominin admixture. —Corinne N. Simonti.
From the Denisovan link:
“I’m pleased to tell you about a new Denisovan genome from a 200,000-year-old male,” said [St├ęphane] Peyr├ęgne, a postdoc at the Max Planck Institute for Evolutionary Anthropology.

The genetic sequence he unveiled is the oldest high-quality human genome yet—80,000 years older than the previous record holder: a Neanderthal that lived about 120,000 years ago. The new results come after more than a decade of effort to find fossilized bones and a second genome of a Denisovan, the mysterious archaic human discovered through its DNA 14 years ago. That first Denisovan genome came from a girl’s pinkie finger bone dated between 60,000 to 80,000 years ago. The genomes of both Denisovans and the ancient Neanderthal all came from the same cold, fossil-rich site: Denisova Cave in the Altai Mountains of Siberia.

According to the analysis by Peyr├ęgne and colleagues, the newly sequenced male comes from a distinct population of early Denisovans that interbred multiple times with a group of Neanderthals whose population had not been detected in DNA before. . . . 
Denisovans are primarily known from their DNA. Researchers have the genome of the girl, as well as bits of nuclear and mitochondrial DNA from fragmentary fossils—teeth, a toe bone—of seven additional individuals, all also from Denisova Cave. Scientists have also identified some Denisovan DNA in living humans, including in Papuans and Han Chinese people, acquired from past interbreeding. DNA in sediments showed that Denisovans were first in the cave 300,000 years ago, and later lived in a cave on the Tibetan Plateau. The scanty fossils reveal this archaic human had larger molars than did the Neanderthals and a robust lower face, known from a jawbone in China. . . . archaeologist Maxim Kozlikin of the Russian Academy of Sciences (RAS) found a molar in a deep layer dated to 200,000 years ago, Peyr├ęgne reported in his talk. The RAS team sent the molar to Max Planck, where evolutionary geneticists extracted enough DNA to provide 24-fold coverage of the genome. . . .

the male Denisovan had inherited 5% of his genome from an ancient, previously unknown population of Neanderthals. The male, labeled Denisova 25, came from a separate population of Denisovans from the girl, known as Denisova 3, and from the other Denisovans in the cave. The girl’s DNA is more closely related to the Denisovan sequences in living modern humans, who got them from at least two Denisovan populations.

All this suggests the older male’s population was replaced in the cave by later Denisovans. . . . the male Denisovan’s ancestors interbred multiple times with Neanderthals. Denisovans were apparently replaced in the cave by Neanderthals for a period, based on the Neanderthal fossil dated to about 120,000 years ago. By about 60,000 years ago, though, the Denisovans had moved back in. The two groups may even have met in the cave—DNA from a bone fragment from a female who was more than 50,000 years old shows her mother was a Neanderthal and her father a Denisovan. Later, both DNA and fossils indicate modern humans occupied the cave and Denisovans and Neanderthals disappear. . . .  
Although Denisovans and Neanderthals apparently interbred repeatedly, their lineages are distinct: They diverged from a common ancestor at least 400,000 years ago. The ancestors of Neanderthals settled in Europe and the Middle East, whereas Denisovans headed farther east into Asia where they evolved separately, acquiring roughly 300,000 genetic changes that differentiate them from Neanderthals, according to the new genome. “Neanderthals and Denisovans remain in separate groups,” and mixed at the edges of their geographic ranges. . . . 
an audience member asked whether the male’s genome also had DNA from an even older, unidentified type of human–perhaps Homo erectus—whose DNA has been spotted in the Denisovan girl’s genome. “If there is any Denisova superarchaic ancestry, it’s also present in this genome,” Peyr├ęgne responded. “[That DNA] is shared between Denisova 3 and Denisova 25.”

Friday, July 12, 2024

The Lightest Neutron Star

The maximum neutron star mass is an open question in physics that receives more attention than the minimum neutron star mass. But the range of neutron star masses is quite narrow, with roughly a factor of two separating the least massive ones from the most massive ones, and there are theoretical efforts to establish why this is the case.

Supernova theory has struggled to explain the lightest known neutron star candidate with an accurate mass determination, the 1.174M⊙ companion in the eccentric compact binary system J0453+1559. 
To improve the theoretical lower limit for neutron star birth masses, we perform 3D supernova simulations for five stellar models close to the minimum mass for iron core collapse. We obtain a record-low neutron star mass of 1.192M⊙ and a substantial kick of ∼100kms^−1. Given residual uncertainties in stellar evolution, a neutron star origin for the 1.174M⊙ object remains plausible.
Bernhard M├╝ller, Alexander Heger, Jade Powell, "The minimum neutron star mass in neutrino-driven supernova explosions" arXiv:2407.08407 (July 11, 2024).