Wednesday, May 29, 2024

Maximum Particle Energy From Quantum Gravity

An upper bound on the energies of massive particles would be very important because it was set an upper bound a many kinds of high energy physics, including but not limited to sphaleron interactions, which are critical to baryogenesis and leptogenesis, and to the stability of the Higgs vacuum.
Beginning from the standard Arnowitt-Deser-Misner (ADM) formulation of general relativity we construct a tentative model of quantum gravity from the point of view of an observer with constant proper acceleration, just outside of a horizon of spacetime. In addition of producing the standard results of black-hole thermodynamics, our model makes an entirely new prediction that there is a certain upper bound for the energies of massive particles. For protons, for instance, this upper bound is around 1.1×10^21eV. The result is interesting, because this energy is roughly of the same order of magnitude as are the highest energies ever measured for protons in cosmic rays.
Jarmo Mäkelä, "A Possible Quantum Effect of Gravitation" arXiv:2405.18502 (May 28, 2024).

Tuesday, May 28, 2024

Tau Lepton Properties

A recent recap paper provides the state of the art properties of the tau lepton. The tau lepton mass, previously noted in this blog post, is consistent with Koide's rule to the extent of current experimental precision.

BelleII provides the most precise measurement of the τ lepton mass: 1777.09 ± 0.08 ± 0.11 MeV/c2, where the first uncertainty is statistical, and the second one is systematic. . . . 

The τ lepton lifetime . . . [has a] Current world’s best result of [290.17 ± 0.53 ± 0.33] × 10^−15 s, where the first uncertainty is statistical, and the second one is systematic. 

. . . 

[The predicted electric dipole moment of the tau lepton is indistinguishable from zero in the Standard Model. The anomalous magnetic dipole moment of the tau lepton in the Standard Model is] 117721(5) × 10^−8. . . . [The tau EDM is experimentally limited to be] |ℜ,ℑ(dτ)| < (0.1–1) × 10^−18 ecm. [The bounds on the anomalous magnetic dipole moment will be measured at Belle II in the near future.] 

. . . 

[Lepton flavor universality between electrons and muons have been tested in tau decays are are consistent within two sigma of the predicted universality.] we provide a result of Rµ = 0.9675 ± 0.0007 ± 0.0036, where the first uncertainty is statistical, and the second one is systematic, leading to |gµ/ge| = 0.9974±0.0019. This is the most precise test in a single measurement. Here, the systematic uncertainty is larger than the statistical one, with the leading contribution coming from particle identification (0.32%) and trigger efficiency (0.10%). 

. . . 

No CPV is observed in the charged leptons sector (in the SM, it is predicted only in the quarks sector). . . . [the BaBar observed a] value is 2.8σ away from the SM prediction. [Belle II will be measuring this in the near future.]

[Heavy neutral leptons, i.e. fourth generation neutrinos are highly constrained by tau decays at Belle II (ignoring constraints from other sources) as shown in the figure below]

From Denis Bodrov, "Tau physics at Belle and Belle II" arXiv:2405.16512 (May 26, 2024).

Thursday, May 23, 2024

The Past, Present, And Future Of Modern Physics

The Past

Modern physics started a little more than a century ago in the early 1900s. 

The state of physics immediately before that point is still taught in universities as a classical approximation of more fundamental physical laws found in modern physics which is often called "classical physics."

Classical physics consists of Newtonian mechanics and Newtonian gravity and calculus, dating to the late 1600s, Maxwell's equations of electromagnetism and classical optics, the laws of thermodynamics and their derivation from statistical mechanics, fluid mechanics, and the proton-neutron-electron model of the atom exemplified in the Periodic Table of the Elements.

Modern physics starts with a scientific understanding of radioactive decay, special relativity, general relativity, and quantum mechanics, which was developed between about 1896 and 1930. It also includes nuclear physics and neutrino physics, that begin in earnest in the 1930s, the Standard Model of Particle Physics and hadron physics that were formulated in the modern sense in the early 1970s, with the three generations of fermions established by 1975. Various beyond the Standard Model extensions of that model mostly date to the 1980s or later, even though the first hints of some of them were considered earlier. The penultimate Standard Model particle to be experimentally confirmed was the top quark in 1994. The fact that neutrinos were massive and oscillate was confirmed by 1998. All particles predicted by the Standard Model of Particle Physics were discovered by 2012 when the Higgs boson was discovered. Subsequent research has confirmed that the particle discovered is a good match to the Standard Model Higgs boson.

Some of the notable developments in Standard Model physics since 2012 have been the experimental exclusion of many extensions of the Standard Model over ever increasing ranges of energies and parameter spaces, the discovery of many hadrons predicted in the Standard Model including tetraquarks and pentaquark together with measurements of their properties, progress in calculating parton distribution functions from first principles, and refinement of our measurements of the couple dozen experimentally determined physical constants of the Standard Model.

Modern physics also includes modern astrophysics and cosmology including the Big Bang Theory and the concept of black holes which coincided with general relativity, dark matter phenomena first observed and neutron stars were first proposed in the 1930s, neutron stars were first observed in the 1967 and the first observation of a black hole was in 1971, cosmological inflation hypotheses date to 1980, the possibility of dark energy phenomena was part of general relativity but it wasn't confirmed until 1998, the LambdaCDM model of cosmology was proposed in the mid-1990s and became the paradigm when dark energy was observationally confirmed in 1998. Quantum gravity hypotheses and hypotheses to explain baryogenesis and leptogenesis have seen serious development mostly since 1980 although early hypotheses along these lines have been around since the inception of modern physics.

The Present

As of 2024, modern physics is dominated by the "core theories" of special relativity, general relativity, and the Standard Model of Particle Physics, none of which have been clearly contradicted by observational evidence after more than a century of looking in the case of relativity and half a century of the Standard Model which has been refined since its original scheme only to expand it to exactly three generation of fermions and to attempt to integrate massive neutrinos and neutrinos oscillation.

On one hand, there are many areas of wide consensus in modern physics. Special relativity has been exhaustively confirmed experimentally and observationally. The predictions of General Relativity including the Big Bang, black holes, strong field behavior in contexts like the dynamics of massive binary systems and compact objects, and its predictions like the precession of Mercury and frame dragging in the solar system context have been observationally confirmed to high precision. Half a century of high energy physics experiments and cosmic ray and neutron star observations have never definitively contradicted the Standard Model (apart from expanding it to exactly three generation of fermions and adding massive neutrinos) and have made myriad predictions to exquisite precision.

There are a variety of open questions and matters of ongoing investigation in modern physics, however.

Two important phenomena predicted by the Standard Model: sphaleron interactions and glue balls (i.e. hadrons made entirely of gluons), have not yet been observed. We still don't know the absolute masses of the neutrino mass eigenstates or even if they have a "normal" or "inverted" mass hierarchy, the quadrant of one of the neutrino mass oscillation parameters, more than the vaguest estimate of the CP violating phase among the potential seven experimentally observed neutrino related physical constants, or the mechanism by which neutrino mass arises. We've seen patterns in the experimentally measured parameters of the Standard Model but have no solid theory to explain their values. While we can predict the "spectrum" of pseudoscalar and vector mesons and of three quark baryons with their properties for the most part, we are still struggling to explain the observed spectrum of scalar and axial vector mesons, we are in the early stage of working out the spectrum of possible four and five quark hadrons including both true four and five quark bound systems and "hadron molecules". And we can't even really predict, a priori, why the exact handful of light pseudoscalar and vector mesons are blends of valence quark combinations rather than individual particles although we can explain their structures with post-dictions. While in principle parton distribution functions can be calculated from first principles in the Standard Model, we've only managed to actually do that, somewhat crudely and in only a few special cases, in the last few years.

Investigation of just what triggers wave function collapse, how quantum entanglement works, the extent to which virtual particles and quantum tunneling must obey special and general relativity, and the correct "interpretation" of quantum mechanics is ongoing. At an engineering level, we are in the very early days of developing quantum computers.

We have a good working model of the residual strong force that binds nucleons in an atom, but have not derived all of nuclear physics or even the residual strong force, from the first principles of quantum chromodynamics (QCD), the Standard Model theory of the strong force. While we understand the principles behind sustainable nuclear fusion power generation, we don't have the engineering realization of it quite worked out. We have mapped out the periodic table of the elements and isotopes all of the way to quite ephemeral elements and isotopes that are only created synthetically, but we can't confidently predict whether or not there are as yet undiscovered elements that are in an island of stability. We are on the brink of mastering condensed matter physics issues like how to create high temperature superconductors and the structure and equation of state of neutron stars.

The search for deviations from the Standard Model in high energy physics has been relentless, particularly since 1994, when all Standard Model particles except the top quark had been discovered. Mostly this has been a tale of crushed dreams. Experiments have largely ruled out huge portions of the parameter space of supersymmetry, multiple Higgs doublet theories, technicolor, leptoquarks, preon theories, fourth or greater generation fermion theories, all manner of grand unified theories of particle physics, proton decay, neutron-antineutron oscillation, flavor changing neutral currents at the tree level, neutrinoless double beta decay or other affirmative evidence for Majorana neutrinos, lepton flavor violation, lepton unitarity violations, non-standard neutrino interactions, and sterile neutrinos. No dark matter candidates have been observed experimentally. We've even observationally ruled out changes in many of its fundamental constants for a period looking back of many billions of years.

There have been some statistically significant, but tiny, discrepancies between the experimentally measured value of the anomalous magnetic moment of the muon and the value predicted by the Standard Model, although this increasingly looks like it is a function of erroneous calculations of the predicted value rather than evidence of new physics. While most experimental anomalies suggesting new particles have been ruled out there have been some very weak experimental hints of a 17 MeV particle (X17) whose alleged experimental hints may have other explanations, and an electromagnetically neutral second scalar Higgs boson at about 95 GeV, neither of which have been fully ruled out, but neither of which is likely to amount to anything, and their have been weak experimental hints, that are to some extent mutually inconsistent between different experiments of one or two possible "sterile neutrinos" (which could also be a dark matter candidate). The anomalous magnetic moment of the electron measured experimentally isn't a perfect fit to its theoretically predicted value although it is very close. The experimentally measured couplings of the Standard Model Higgs boson aren't a perfect fit to the theoretical predictions although they are reasonably close to within experimental uncertainties. While early hints of lepton universality violations were ruled out when the experimental data improved, there are still some minor lepton flavor ratio anomalies out there. Still, there is every reason to think that these anomalies won't last and that the particle content of the Standard Model is complete with the possible exceptions of one or more particles involved in the mechanism that generates neutrino masses, a massless or nearly massless graviton, and one or more dark matter candidates with properties that make them almost impossible to detect in a particle collider.

Thus, while there are a few details and implementations left to work out, the Standard Model, high energy physics, and nuclear physics are close to being complete and we don't expect any new discoveries in this area to identify anything deeply wrong with what we know now, even though if we are really lucky, more research and greater precision might grant us a deeper understanding of why the Standard Model has the properties that it does.

The situation in astrophysics and cosmology is much less settled, and while the handful of particle colliders on the planet provide us with a trickle of new high energy physics data in some very narrow extensions of existing high energy physics parameter space, a host of new "telescopes" in the broad sense of the term is providing torrents of new astronomy observations that our existing modern physics theories struggle to explain. The leading paradigm in astrophysics and cosmology, the LambdaCDM "Standard Model of Cosmology" is a dead man walking, mostly for lack of a consensus on what to replace it with.

"Telescopes" aren't just visual light telescopes on the surface of the Earth anymore, and even those are vastly improved. Modern "telescopes" see the entire range of the electromagnetic spectrum from ultra-low frequency radio waves to ultra-high energy gamma waves, not just from Earth but also based in space, with extreme resolutions. We have neutrino "telescopes". We have "cosmic ray detectors" which observe non-photon particles that rain down on Earth from space. We have gravitational wave "telescopes" that have made many important discoveries, including the observation of many intermediate size black holes. In some cases we can do "multi-messenger astronomy" which combined signals from multiple kinds of telescopes that come from a single event (something that has places strong bounds on both the speed of neutrinos and the speed of gravitational waves, which have both been as predicted by special and general relativity).

We have overwhelming observational evidence of dark matter phenomena. But we have no dark matter particle candidate and no gravity based explanation for dark matter phenomena that fits all of the data and has secured wide acceptance, although we have an ever filling cemetery of ruled out explanations for dark matter, like MACHOs, primordial black holes, supersymmetric WIMPs, and cold dark matter particles that form NFW halos. Attempts to explain dark matter through the gravitomagnetic effects of general relativity in galaxies have also failed. And there are dozens of distinct types of observations contrary to the predictions of LambdaCDM. Fairly sophisticated comparisons of predictions with observations strong disfavor warm dark matter candidates and thermal relic GeV mass scale self-interacting dark matter candidates. QCD axions and QCD bound exotic hadrons are also largely ruled out. Toy model MOND can't be the exclusive explanation for dark matter phenomena, and neither can some of its relativistic generalizations like TeVeS, although MOND is a very simple theory that explains almost all dark matter phenomena observed up to the galaxy scale with a single new parameter and has with some mild generalizations explained the cosmic radio background (CMB) observations and the impossible early galaxies problem. But while MOND may be on the right track it doesn't quite get many features of galaxy clusters right (although a similar scaling law can work there) and has trouble with some out of disk plane feature of spiral galaxies. The data on wide binaries, which would distinguish between a variety of dark matter particle and gravitational based theories to explain dark matter phenomena are current inconclusive and have received contradictory interpretation. A variety of gravitational explanations of dark matter phenomena are promising, however, as are dark matter particle theories with extreme low mass dark matter candidates like axion-like particles which have wave-like properties.

We have inconsistent measurements of the Hubble constant which is one of two observations that contribute to our estimate of the amount of dark energy in a simple LambdaCDM model where dark energy is simply a specific constant value of the cosmological constant suggesting that the cosmological constant, lambda, may not actually be constant.

The allowed parameter space for cosmological inflation continues to narrow with the non-detection of primordial gravitational waves at ever greater precisions. There are strong, but not conclusive suggestions that the universe may be anisotropic and inhomogeneous even at the largest scales, contrary to the prevailing cosmology paradigm.

There are no widely accepted satisfactory answer to the question of baryogenesis and leptogenesis, although improvements in the precision and energy scale reach of the Standard Model and improved astronomy observations increasingly push any meaningful baryogenesis and leptogenesis closer to the Big Bang, with any significant changes in the aggregate baryon number and lepton number of the universe pretty much pushed to the first microsecond after the Big Bang at this point.

None of the unknowns in astrophysics and cosmology have any real practical engineering implications. But the Overton window of possibilities that are being seriously investigated in these fields is vastly broader than in high energy physics or quantum mechanics.

The Future

The good news is that the torrent of astronomy data that is pouring in from many independent research groups is providing us with the data we need to more definitively rule out or confirm various competing hypotheses in astrophysics and cosmology. We have a lot of shiny new tools both in the form in many different kinds of vastly improved "telescopes" and in the form of profoundly improved computational power and artificial intelligence tools to analyze this vast amount of new data to allow us to have scientific advances in these fields which are not just driven by observations and not group think or the sociology of the discipline, even though it may take the deaths of a generation or two of astrophysicists for the field to fully free itself from outdated ideas that are no longer supported by the data.

Even if we don't reach a consensus around a new observationally supported and theoretically consistent paradigm in my lifetime of two or three more decades, I am very hopeful that we will do so within the lives of my children and of my grandchildren to be.

I have strong suspicions about what the new paradigm will look like.

Dark matter phenomena will be explained most likely by a gravitational explanation with strong similarities to work of Alexandre Deur, whether or not his precise attempt to derive his conclusions from non-perturbative general relativity effects holds up. The consensus will also probably likely be that quantum gravity does exist, although it may take quite a while to prove that with observations.

Also, like Deur, and unlike the vast majority of other explanations, I think that the ultimate explanation for dark energy phenomena will conserve mass-energy both globally and locally and will not be a true physical constant. The cosmological constant of general relativity will probably ultimately be abandoned even though it is a reasonable first order approximation of what we observe. This will also mean that the aggregate mass-energy of the universe at any given time will be finite and conserved; it will be a non-zero boundary condition at t=0 of the Big Bang.

Thus, I suspect that a century from now, the consensus will be that there are no dark matter particles and there is no dark energy substances, and that these were just products of theoretical misconceptions akin the the epicycles to explain celestial mechanics that preceded the discovery that their motions could be explained to all precision available at the time with Newtonian gravity.

It will take time, but I expect that cosmological inflation will ultimately be ruled out.

I expect that new advances in astrophysics will rule out faster than light travel or information transfer and wormholes.

I don't think that we will have a conclusive explanation of baryogenesis and leptogenesis, even within my grandchildren's lives, but I do think that a mirror universe hypothesis that there is an antimatter universe that exists before the Big Bang in which time runs in the opposite direction will become one of the leading explanations. This is because I think that we will make significantly more progress towards ruling out new high energy physics and any possibility of matter creation in periods closer and closer to the Big Bang. This will make non-zero baryon number and lepton number in increasingly short time frames immediately after, although not at, the Big Bang impossible.

I think that there are even odds that we will discover that sphaleron interactions are actually physically impossible in any physical possible scenario doesn't their theoretical possibility in the Standard Model, possibly due to a maximum local mass-energy density.

In the area of high energy physics, I don't expect any new particles to be discovered (apart from possible evidence for the existence of a massless graviton), and I expect the Standard Model to stand the test of time. I do expect some refinements of our theories of wave function collapse and quantum interpretations. I don't expect new high energy physics at higher energies. I don't expect that we will find new heavy elements in islands of stability.

I expect that neutrinos will be found to have Dirac rather than Majorana mass that is somehow made possible without new particles despite the current lack of a clear path to do so. Most likely, our understanding of neutrino mass and of the Higgs field Yukawas of the Standard Model particles will involve a dynamical balancing of the Higgs vev between particles that can transform into each other in W boson interactions via W boson interactions, as opposed to giving such a central role to the coupling of these particles to a Higgs boson. Self-interactions with the fields to which the various fundamental particles couple will also play a role in generating their masses.

I expect that, as our measurements of the fundamental particle masses get more precise, that the sum of the square of the masses of the fundamental particles will indeed be found to equal the square of the Higgs vev. Vast amounts of ink will be spilled once this is confirmed, over why fundamental boson masses give rise to slightly more than half of the Higgs vev, while fundamental fermions give rise to slightly less than half of it. This could reduce the number of free independently experimentally measured mass and coupling constant parameters of the Standard Model from eighteen (fifteen masses and three coupling constants) minus one for the electroweak relationship between the W and Z boson masses and coupling constants, to eight or fewer (three coupling constants, the W, two fermion masses, and two lepton masses).

I expect that we will have a good first principles explanation of the full spectrum of observed hadrons and that we will have first principles calculations of all of their parton distribution functions.

I expect that we will be able to work out the residual strong force that binds nucleons exactly from first principles, and that we will be able to calculate with quantum computers that there are no undiscovered islands of stability in heavy elements or isotopes.

There are even odd that we will discover a deeper explanation for the values of the parameters in the CKM and PMNS matrixes by sometime in my grandchildren's lives, and better than even odds that we will be able to reduce the number of free parameters in those two matrixes to less than the current eight. I wouldn't be surprised if the CP violating parameters of the CKM and PMNS matrixes were found to have an independent source from the other six parameters of those matrixes.

I don't think that we will develop a Lie group Grand Unified Theory or Theory of Everything, or that string theory will ever work, although I do think that we are more likely than not to develop a theory of quantum gravity that can be integrated into the Standard Model more cleanly. Indeed, gravitationally based dark matter phenomena may turn out to be a quantum gravity effect that is actually absent from classical general relativity.

Wednesday, May 22, 2024

The Luna Structure In India

Image from Wikipedia.

The biggest meteor impact on Earth in the last 10,000 years struck Western India around 6905 BP (i.e. 4955 BCE). 

The impact clearly wasn't related to the fall of the Harappan culture. Indeed, perhaps it destroyed a previous civilizations in the area in a way that made way for it to move in. On the other hand, the location is quite far from the core of the Harappan region, and the civilization didn't really take off for another 1600 years or so, so the link between this civilization and the archaeological culture doesn't really ring true. 

But "[a]round 6500 BCE, agriculture emerged in Balochistan, on the margins of the Indus alluvium," which is a better fit geographically and temporally to this impact. This period was also known as the Mehrgarh, aceramic Neolithic period, in the Indus Valley Civilization. The agriculture that emerged was an expansion of the geographic range of the Fertile Crescent Neolithic. But this first appearance of agriculture in the region was still far north of the Luna structure.

It also isn't obviously related to any major regional or global climate event. This time period is mostly remembered for being in the middle of the Holocene Climatic Optimum that occurred in the interval roughly 9,500 to 5,500 years BP, with a thermal maximum around 8000 years BP. 

It also far predates the South Indian Neolithic Revolution of ca. 2500 BCE, and the arrival of rice as a major food crop in the Harappan culture.
The Luna structure of India has been rumored to be an impact crater for more than a decade without any convincing evidence. This structure (1.5–1.8 km) is prominently visible in the low-lying Banni Plains of the tectonically active Kutch Basin as a circular morphological feature with a less-prominent rim. Luna area is strewn with melt-like rocks having high specific gravity and displaying wide range of magnetic properties. It contains minerals like wüstite, kirschsteinite, ulvöspinel, hercynite, and fayalite. The whole rock analysis denotes PGE enrichment, with notably higher average concentrations of Ru (19.02 ppb), Rh (5.68 ppb), Pd (8.64 ppb), Os (6.03 ppb), Ir (10.63 ppb) and Pt (18.31 ppb). The target is not exposed at Luna, owing to the overlying thick sequence of Quaternary sediments. The mineralogical and geochemical signatures points to an impact into a target, which is rich in clay with elevated calcium and silica (sand/silt) content. Geochemical data suggests an iron or stony-iron meteorite as the potential projectile at Luna. The silt layer containing plant remnants, underlying the strewn layer, yielded a radiocarbon age of 6905 years, making Luna the biggest crater to result from an iron bolide within the last 10,000 years. . . .
In this study, we introduce the Luna structure (23°42′16″ N; 69°15′35′E) with 1.5–1.8 km diameter, as a potential hypervelocity impact crater. The structure remains submerged (and inaccessible) for a greater part of the year owing to its presence in the low-lying Banni Plains of the Kutch Basin of western India. Interestingly, the Luna region was one amongst the several settlements linked to the ancient Harappan Civilization (7000-1900 BP). . . . We present strong petrographic, mineralogical, and geochemical evidence to confirm the impact origin of Luna structure, along with an age estimate. 
K.S. Sajinkumar, et al., "The Luna structure, India: A probable impact crater formed by an iron bolide" 240 Planetary and Space Science 105826 (January 2024).

Monday, May 20, 2024

Quantum Tunneling Is Not Superluminal

Figuring out how long it takes an atom to engage in quantum tunneling is very experimentally challenging, because the distances are short, the time elapsed is tiny and hard to measure, and the things observed are on the wave-particle boundary. But a couple of scientists came up with an experimental design that addresses the challenges. 

The possibility of superluminal travel had seemed particularly plausible because the correct propagator path integral used to determine the probability of a photon moving from points A to point B using quantum mechanics includes both superluminal and subluminal paths in the calculation, which is pretty much the only time in all of physics that calls for physicists to even contemplate that massless particles move at anything other than the speed of light, in all of physics. It is also a good place to look because quantum tunneling is one of the most famous circumstances where key conservation laws, that are ironclad in classical physics, apply to end states of an interaction but not to the intermediate states. 

But they found that quantum tunneling does not appear to happen at faster than the speed of light, as some theorists had suggested might be possible in this situation. Their experiment showed no signs of superluminal or instantaneous movement of particles.
What time does a clock tell after quantum tunneling? 
Predictions and indirect measurements range from superluminal or instantaneous tunneling to finite durations, depending on the specific experiment and the precise definition of the elapsed time. Proposals and implementations use the atomic motion to define this delay, although the inherent quantum nature of atoms implies a delocalization and is in sharp contrast to classical trajectories. 
Here, we rely on an operational approach: We prepare atoms in a coherent superposition of internal states and study the time read-off via a Ramsey sequence after the tunneling process without the notion of classical trajectories or velocities. Our operational framework (i) unifies definitions of tunneling delay within one approach, (ii) connects the time to a frequency standard given by a conventional atomic clock that can be boosted by differential light shifts, and (iii) highlights that there exists no superluminal or instantaneous tunneling.
Patrik Schach and Enno Giese, "A unified theory of tunneling times promoted by Ramsey clocks" 10(16) Science Advances (April 19, 2024).

Four Waves Of New World Languages?

The "four wave" idea is that there were four waves of people in the founding population from two eras. These were in  turn followed two much later waves that aren't included in the four, a Na-Dene wave, followed much later by an Inuit wave. And, there is indeed genetic evidence of a two component founding population, although no previous study have felt they had sufficient evidence to make a corresponding linguistic division with linguistic features that persisted to the present.

The abstract of a new historical linguistics paper states:
The known languages of the Americas comprise nearly half of the world's language families and a wide range of structural types, a level of diversity that required considerable time to develop. This paper proposes a model of settlement and expansion designed to integrate current linguistic analysis with other prehistoric research on the earliest episodes in the peopling of the Americas. 
Diagnostic structural features from phonology and morphology are compared across 60 North American languages chosen for coverage of geography and language families and adequacy of description. 
Frequency comparison and graphic cluster analysis are applied to assess the fit of linguistic types and families with late Pleistocene time windows when entry from Siberia to North America was possible. The linguistic evidence is consistent with two population strata defined by early coastal entries ~24,000 and ~15,000 years ago, then an inland entry stream beginning ~14,000 ff. and mixed coastal/inland ~12,000 ff. 
The dominant structural properties among the founder languages are still reflected in the modern linguistic populations. The modern linguistic geography is still shaped by the extent of glaciation during the entry windows. Structural profiles imply that two linguistically distinct and internally diverse ancient Siberian linguistic populations provided the founding American populations.
Final two paragraphs of the paper conclude:
The results are compatible with the two-origin analysis (Two Main Biological Components, or 2MBC) of Walter Neves and various colleagues (Neves & Pucciarelli, 1991; Neves et al., 2007; Hubbe et al., 2010; Hubbe et al., 2020, and several others; overviews in Rothhammer & Dillehay, 2009; Hubbe, 2015; von Cramon-Taubadel et al., 2017), which infer a distinction of early versus later populations in South and Central America from craniometric data; the early population has Australasian/Melanesian affinities while the later one has Siberian affinities. Skoglund et al., 2016 find South American genomic evidence for two populations and the same affinities. These findings are a good match for the distinction here of early versus late strata. 
Whether the physical diversity matches the linguistic diversity is not yet clear. The start times implied are too late, but this is probably not essential. The geographically patterned structural distribution is not addressed as Neves and colleagues deal only with Central and South America, and Skoglund et al., 2016 find too little data for North America. Pitblado, 2011 reviews other evidence for two origins.

Thus the modern facts speak for a structurally differentiated linguistic population in ancient Siberia. Its descendants entered through a chronologically and geographically sequenced series of openings beginning in the peak LGM, first coastal and then inland, rapidly moving well to the south and well inland. Whether the early and late South American populations continue the North American early and late strata, and whether the North American geographical patterning continues to South America, warrant further work.

The introduction explains that:
Archeological evidence shows that there were human entries to the Americas well before the end of the last glaciation (Dillehay, 1997; Dillehay et al., 20082015) and quite possibly by the peak of glaciation c. 24,000 years ago. The linguistic evidence requires entries during or before the last glacial maximum (LGM) (Nichols, 2015a2015b), enough to give rise to the ~200 independent language families of the Americas and their structural diversity. (Before recent extinctions the Americas hosted close to half of the known linguistic lineages.) Glaciation blocked entry to North America, but recent paleoceanographic data and models show two periods during the terminal Pleistocene when coastal entries were possible: ~24.5–22 ka and ~16.4–14.8 ka (Praetorius et al., 2023). Overland entries to intermontane North America via the ice-free corridor between the shrinking Cordilleran and Laurentide glaciers became possible in the same general time frame as the second of these openings (Perego et al., 2009, Anderson & Bissett, 2015:79–80), and movement into the interior via the Columbia and Snake to the upper Missouri drainage and via the Colorado and Gila was always possible (Anderson et al., 2013; Anderson & Bissett, 2015).

Drawing on these sources, this paper proposes a two-stratum, four-opening model for the origin and expansion of the American linguistic population. The first and second openings (~24,000 and ~15,000 years ago, following Praetorius et al., 2023resulted in coastal entries south of the ice sheets (i.e. south of the Columbia River). The resultant linguistic populations have mingled in Oregon and California; their descendants cannot so far be clearly distinguished on linguistic evidence, and will be jointly called the early stratum. The third opening was the formation of the ice-free corridor ~14,000 years ago, resulting in colonization of the North American interior by people from Beringia and unglaciated northwestern Alaska; this produced a later stratum which gave rise inter alia to the Clovis phenomenon and whose linguistic descendants are structurally quite distinct from the early stratum found in California and Oregon. The fourth opening was the retreat of the coastal ice sheet, making possible coastal and near-coastal settlement of the Pacific Northwest ~12,000 years ago. Descendants of fourth-opening languages share many of the distinctive properties of third-opening languages but can be distinguished on other salient properties. Still later came the entries of two known language families: Athabaskan-Eyak-Tlingit (AET, a.k.a. Na-Dene), mostly interior-oriented, and Eskimo-Aleut, primarily coastal.

Inland Northeastern Asia during the terminal Pleistocene must have been a linguistic spread zone like attested recent arctic and subarctic regions. Relevant modern examples are non-food-producing arctic regions (North America; northern Eurasia prior to the introduction of large-scale reindeer herding) and also non-food-producing desert regions (southern Africa, the Australian arid interior, and part of the Great Basin). A spread zone usually has a sparse and often mobile human population and a linguistic population shaped by convergence and diffusion with occasional large spreads altering the genealogical and/or typological profile of the region. In the roughly 8000–10,000 years between the two coastal openings there must have been the normal gradual grammatical and lexical changes in the northeastern Asian languages, and occasional immigration, emigration, or extinction of languages, over time substantially changing the linguistic typological profile of the area. (Note that the linguistic comparative method, used to establish relatedness and reconstruct ancestral states, can rarely reach back more than ~6000 years, so daughters from an 8000-year-old split can be as unrecognizably different as two unrelated languages.) A few representatives of the Siberian linguistic population as it changed over time can be assumed to have made viable entries to subglacial North America.

With deglaciation after the third and fourth openings, occasional further entries must have occurred. A total of about 12 entries at a mean of 2000-year intervals, beginning about 25,000 years ago, would generate the genealogical and structural diversity attested in the Americas and allow time for expansion as far south as Monte Verde, Chile, a site with clear evidence of human habitation at over 14,000 years ago (for the expansion rate, Nichols, 2008; for Monte Verde, Dillehay et al., 2015; Erlandson et al., 2008; Dillehay, 1997). The most recent two postglacial entries are identifiable with specific language families: the AET family, which dispersed in Alaska at least 5000 years ago and has well-argued likely connections to the Yeniseian family of north central Siberia (Vajda, 20102018, Fortescue & Vajda, 2022), age of entry unknown but likely early postglacial (Kari, 2019 gives some hydronymic evidence)6and the ~4000-year-old Eskimo-Aleut family of coastal Siberia, Alaska, Canada, and Greenland, whose Eskimoan and Aleut branches split in Siberia, spread eastward separately to Alaska, and later recontacted there (Berge, 20172018). The AET and Eskimo-Aleut families are different in structural type from each other and from most of the other families in North America. Geographically, I put them in the Pacific Northwest group.

The first entrants to North America expanded the human frontier, and as the continent was settled the frontier expanded east and south. Behind the gradually advancing frontier was probably a dynamic and variable ethnolinguistic situation. Though the sociolinguistics of interaction between small, mobile groups in very sparsely inhabited land with an open frontier is unknown, the model sketched here attempts to capture one element of the picture: language viability and spreads from the entry points. In this model an entering group settles in an attractive resource-rich area (the term of Beaton, 1991 is megapatch) not far from the entry point, and there they prosper, adapt to the environment and resources, and expand demographically. By the time another entrant appears the first settlers are well entrenched, more numerous than the newcomers, and in a position to fend off or absorb the small group of newcomers. The newcomers move on, skirting earlier entrants. Offshoots from the first settlement also move away and found new colonies. Thus the early settlement functions as a staging area (using the term of Anderson & Gillam, 2000, Anderson et al., 2013; those staging areas are archeologically supported while those proposed here are supported by linguistic intangibles). Gradually the human frontier expands far to the south and east, but it continues to be the case that descendants of the earlier settlers remain entrenched in or near the staging area more often than they move on.

This paper is an exploratory study showing that there is enough linguistic evidence to support the model and raise research questions and hypotheses. It is intended to help geneticists, archeologists, and linguists formulate research questions and hypotheses relevant to each other's work. Meanwhile, pending larger-scale and more definitive work, the results are used here as an analytic framework.
The paper is: 

Johanna Nichols, "Founder effects identify languages of the earliest AmericansAmerican Journal of Biological Anthropology (March 30, 2024) (open access) via Language Log.

Thursday, May 16, 2024

Another Gravitational Explanation Of Dark Matter And Dark Energy Phenomena

Another interesting gravitational explanation of dark matter and dark energy phenomena.
We argue that the effect of cold dark matter in the cosmological setup can be explained by the coupling between the baryonic matter particles in terms of the long-range force having a graviton mass mg via the Yukawa gravitational potential. Such a quantum-corrected Yukawa-like gravitational potential is characterized by the coupling parameter α, the wavelength parameter λ, which is related to the graviton mass via m(g)=ℏ/(λc), that determines the range of the force and, finally, a Planck length quantity l(0) that makes the potential regular at the centre. The corrected Friedmann equations are obtained using Verlinde's entropic force interpretation of gravity based on the holographic scenario and the equipartition law of energy. The parameter α modifies Newton's constant as G(eff)→G(1+α). We argue that dark matter is an apparent effect as no dark matter particle exists in this picture. Furthermore, the dark energy is also related to graviton mass and α; in particular, we point out that the cosmological constant can be viewed as a self-interaction effect between gravitons. We further show that there exists a precise correspondence with Verlinde's emergent gravity theory, and due to the long-range force, the theory can be viewed as a non-local gravity theory. To this end, we performed the phase space analyses and estimated λ≃103[Mpc] and α∈(0.0385,0.0450), respectively. Finally, from these values, for the graviton mass, we get mg≃10^−68 kg, and cosmological constant Λ≃10^−52m^−2. Further, we argue how this theory reproduces the MOND phenomenology on galactic scales via the acceleration of Milgrom a(0)≃10^−10m/s^2.
Kimet Jusufi, Genly Leon, Alfredo D. Millano, "Dark Universe Phenomenology from Yukawa Potential?" arXiv:2304.11492 (May 14, 2024) (Phys. Dark Univ. 42 (2023), 101318).

Monday, May 13, 2024

Tunisian Arabic v. Maltese

The Tunisian dialect of the Arabic language is basically the same as the Maltese language, except that Tunisian is written in Arabic script, while Maltese is written in the Latin alphabet.

Friday, May 10, 2024

A Notable Modified Gravity Paper And The Running Of Gravitational Couplings

It is unclear to me why gravitational mass should differ from gravitational mass-energy for this purpose. Massless particles gravitate if they have energy.
Some time ago, it has been suggested that gravitons can acquire mass in the process of spontaneous symmetry breaking of diffeomorphisms through the condensation of scalar fields [Chamseddine and Mukhanov, JHEP, 2010]. Taking this possibility into account, in the present paper, first we show how the graviton mass intricately reshapes the gravitational potential akin to a Yukawa-like potential at large distances. Notably, this long-range force modifies the Newton's law in large distances and might explain the phenomena of dark matter. The most important finding in the present paper is the derivation of a modified Newtons law of gravity by modifying the Verlindes entropic force relation due to the graviton contribution. The graviton contribution to the entropy basically measures the correlation of graviton and matter fields which then reproduces the Bekenstein-Hawking entropy at the horizon. This result shows the dual description of gravity: in the language of quantum information and entropy the gravity can be viewed as an entropic force, however in terms of particles and fields, it can be viewed as a longe range force. Further we have recovered the corrected Einstein field equations as well as the ΛCDM where dark matter emerges as an apparent effect.
Kimet Jusufi, et al., "Modified gravity/entropic gravity correspondence due to graviton mass" arXiv:2405.05269 (April 25, 2024).

There is also a preprint on the beta function of gravity in a quantum gravity scenario that is particularly relevant globally to the running of Standard Model constants at extremely high energies and the cosmology of the immediate post-Big Bang period and in strong gravitational regimes.
We study the beta functions for the dimensionless couplings in quadratic curvature gravity, and find that there is a simple argument to restrict the possible form of the beta functions as derived from the counterterms at an arbitrary loop. The relation to the recent different results on beta functions is also commented on.
Hikaru Kawai, Nobuyoshi Ohta, "An Observation on the Beta Functions in Quadratic Gravity" arXiv:2405.05706 (May 9, 2024).

Tuesday, May 7, 2024

Connecting Denisovan DNA To Bones

A new study looks at what Denisovan ancient DNA codes for in order to determine which hominin remains that have been located are the best fit to that DNA. These remains would have been contemporaneous with the earliest modern humans and with Neanderthals.

The Dali and Harbin specimens that are a good fit to the expectation from the Denisovan DNA samples are from China. 

Dali Man was discovered in 1978 in Dali County, Shaanxi Province, China and dates to 280,000 to 240,000 years ago. 

The Harbin specimen was recovered in Harbin city in northeastern China and has a minimum uranium-series age of 146,000 year ago.

The Kabwe specimen, also known as the "Broken Hill skull" and "Rhodesian Man", which is also a good fit to Denisovan DNA expectations, was discovered in 1921 in Zambia, which is outside the range of places where Denisovan admixture is found in modern humans. It has traditionally been classified as Homo heidelbergensis, a species which is widely hypothesized to be a lineage ancestral to Denisovans, Neanderthals, and modern humans. This specimen is dated to 324,000 to 274,000 years ago.
Denisovans are an extinct group of humans whose morphology is mostly unknown. The scarcity of verified Denisovan fossils makes it challenging to study how they differed in their anatomy, and how well they were adapted to their environment. To gain insight into their evolutionary history, we used a genetic phenotyping approach, where Denisovan anatomy was inferred by detecting gene regulatory changes that likely altered Denisovan skeletal morphology. 
We then scanned Middle Pleistocene skulls for unclassified specimens that match our Denisovan profile and thus might have been related to Denisovans. We found that the Harbin, Dali, and Kabwe specimens show a particularly good match to the predicted Denisovan profile. We conclude that our genetic phenotyping approach could help classify unidentified specimens, and that Harbin, Dali, and Kabwe likely belonged to individuals closely linked to the Denisovan lineage.
Nadav Mishol, et al., "Candidate Denisovan fossils identified through gene regulatory phenotyping" bioRxiv (April 19, 2024) (emphasis and links in the abstract added editorially).

The First Farmers Of Cyprus Were Mostly Anatolian

Neolithic Cyprus was settled from Turkey, not Greece, by a sister population to the first farmers of Europe, very early in the Fertile Crescent derived Neolithic era. 
Archaeological evidence supports sporadic seafaring visits to the Eastern Mediterranean island of Cyprus by Epipaleolithic hunter-gatherers over 12,000 years ago, followed by permanent settlements during the early Neolithic. The geographical origins of these early seafarers have so far remained elusive. 
By systematically analysing all available genomes from the late Pleistocene to early Holocene Near East (c. 14,000–7000 cal BCE), we provide a comprehensive overview of the genetic landscape of the early Neolithic Fertile Crescent and Anatolia and infer the likely origins of three recently published genomes from Kissonerga-Mylouthkia (Cypriot Late Pre-Pottery Neolithic B, c. 7600–6800 cal BCE). These appear to derive roughly 80% of their ancestry from Aceramic Neolithic Central Anatolians residing in or near the Konya plain, and the remainder from a genetically basal Levantine population. 
Based on genome-wide weighted ancestry covariance analysis, we infer that this admixture event took place roughly between 14,000 and 10,000 BCE, coinciding with the transition from the Cypriot late Epipaleolithic to the Pre-Pottery Neolithic A (PPNA). Additionally, we identify strong genetic affinities between the examined Cypro-LPPNB individuals and later northwestern Anatolians and the earliest European Neolithic farmers
Our results inform archaeological evidence on prehistoric demographic processes in the Eastern Mediterranean, providing important insights into early seafaring, maritime connections, and insular settlement.
Alexandros Heraclides, et al., "Palaeogenomic insights into the origins of early settlers on the island of Cyprus" 14 Scientific Reports 9632 (April 26, 2024) (open access).

Some comments about early pottery

Pottery appears to have been an East Asian innovation, that arose prior to farming and herding in sedentary fishing based communities like the Jomon and people with similar lifestyles in what is now China and Korea, that gradually migrated to the West across North Asia, mostly arriving in West Asia and Europe after herding and farming had been developed there.

Also, it is worth noting that Western anthropologists use the term "Neolithic" to refer to the commencement of widespread use of domesticated plants and animals, while Soviet and post-Soviet anthropologists use the term "Neolithic" to refer to the commencement of widespread use of pottery.

Friday, May 3, 2024

A Neutrino Mass Puzzle

The differences between the three neutrino masses is known to considerable precision and is most easily communicated in meV units. But the absolutely masses are not very meaningfully constrained from direct measurements of the neutrino masses. Cosmology based constraints on the sum of the three neutrino masses are much more restrictive. 

But a new preprint based upon newly released DESI data shows that we are at the brink of being over constrained, as the sum of the three neutrino masses estimated from cosmology is likely to fall below the minimum sum of the three neutrino masses from neutrino oscillation data. 

This suggests that the cosmology based bounds may be unreliable. This isn't all that stunning given that myriad problems with the LambdaCDM model, even though the sum of the neutrino masses estimates from cosmology are quite robust over a wide range of assumptions.

On the other hand, cosmology based bounds aren't the only factors that favor a normal neutrino mass hierarchy over an inverted neutrino mass hierarchy. A normal neutrino mass hierarchy leaves two possibilities: either a near minimal sum of the three neutrino masses, independent of cosmology considerations, or a nearly degenerate set of neutrino masses, as the main possibilities. The large size of the PMNS matrix mixing angles relative to those in the CKM matrix for quarks suggests that the hierarchy of neutrino masses may indeed be less steep than that of the quarks. But there is no established theory to quantify that intuition.
The baryon acoustic oscillation (BAO) analysis from the first year of data from the Dark Energy Spectroscopic Instrument (DESI), when combined with data from the cosmic microwave background (CMB), has placed an upper-limit on the sum of neutrino masses, ∑mν<70 meV (95%). In addition to excluding the minimum sum associated with the inverted hierarchy, the posterior is peaked at ∑mν=0 and is close to excluding even the minimum sum, 58 meV at 2σ. 
In this paper, we explore the implications of this data for cosmology and particle physics. The sum of neutrino mass is determined in cosmology from the suppression of clustering in the late universe. 
Allowing the clustering to be enhanced, we extended the DESI analysis to ∑mν<0 and find ∑mν=−160±90 meV (68%), and that the suppression of power from the minimum sum of neutrino masses is excluded at 99% confidence. 
We show this preference for negative masses makes it challenging to explain the result by a shift of cosmic parameters, such as the optical depth or matter density. 
We then show how a result of ∑mν=0 could arise from new physics in the neutrino sector, including decay, cooling, and/or time-dependent masses. These models are consistent with current observations but imply new physics that is accessible in a wide range of experiments. 
In addition, we discuss how an apparent signal with ∑mν<0 can arise from new long range forces in the dark sector or from a primordial trispectrum that resembles the signal of CMB lensing.
Nathaniel Craig, Daniel Green, Joel Meyers, Surjeet Rajendran, "No νs is Good News" arXiv:2405.00836 (May 1, 2024).

Another preprint today greatly loosens the bound on the muon neutrino mass from more direct measurements to about 150 keV, which is a huge step backwards from the previous direct detection bound of 420 eV proposed in the year 2014.

The tightest bound on the lightest neutrino mass eigenstate is about 0.8 eV (and is likely to drop to 0.2 eV as experimental methods improve). Combining the current bound and the mass differences permitted from neutrino oscillation data keeps all three neutrino mass eigenstates at under 1 eV in either a normal or an inverted neutrino mass hierarchy (and the sum of the three neutrino masses under 2.6 eV). So the neutrino mass bounds from the new preprint and from the 2014 study are meaningless.

If the lightest neutrino mass were constrained to be 0.2 eV or less, the sum of the three neutrino masses in either hierarchy, could be constrained to be no more than about 0.71 eV (0.66 eV in a normal hierarchy), which while not competitive with the potentially discredited cosmology bounds, would still be far less of a setback.

The background from the muon neutrino mass preprint states the following:
As a result of the discovery of neutrino flavor oscillations, neutrinos are thought to have a non-zero mass, as opposed to the standard model (SM). The detection of neutrino oscillations in the atmospheric Super-Kamiokande and solar Sudbury Neutrino Observatory (SNO) experiments provided initial evidence supporting the existence of nonzero neutrino masses. In the 21st century, several neutrino oscillation experiments were conducted, providing precise measurements for the phenomenon of neutrino oscillation. However, these experiments revealed that two out of the three flavors are heavy, and the massive flavor possesses a mass of at least 0.05 eV. Nonetheless, it should be noted that these experiments could only determine mass-squared differences between the flavors and were unable to directly measure the individual mass of each flavor. 
It is crucial to highlight that the theoretical concept of neutrino oscillation was initially proposed by the Russian scientist Bruno Pontecorvo to elucidate the absence of detected atmospheric and solar neutrinos. 

Measuring neutrino mass is of a great importance due to its implications regarding not only refining our understanding about the nature of the universe and dark matter, but also conceivably providing insights into some new physics beyond SM. Therefore, one of the main objectives of particle physicists has been to measure neutrino masses for several years. Consequently, numerous experiments have been conducted since 1991 to measure the mass of neutrinos based on tritium beta decay, from Los Alamos to the Karlsruhe Tritium Neutrino experiment in 2022. 
At Los Alamos, researchers established an upper limit of 11 eV at a 95% confidence level for the mass of the electron anti-neutrino, m(¯ νe). In the first run in 2019, the KATRIN experiment significantly improved the sensitivity of m(¯ νe), setting a new upper bound of 1.1 eV at 90% confidence level (CL), which represents an improvement by a factor of about two compared to the previous limit. Furthermore, in the second run in 2022, they achieved a more precise upper bound of 0.9 eV at 90% CL. The results from the KATRIN 2019 (first run) were then combined with those from KATRIN 2022 (second run), resulting in a more accurate upper limit of 0.8 eV at a 90% CL for m(¯ νe). 
On the other hand, the most successful attempts to measure the mass of muon neutrinos, as the second flavor, were in 1982, involving the measurement of muon neutrinos from pion decay in flight and achieving an upper bound of less than 500 keV, and in 1996, measuring muon neutrinos from the decay of pions at rest, resulting in an upper limit of less than 170-190 keV.

A True Garbage Physics Paper

How do we create incentives in High Energy Physics to discourage such utterly garbage filled advocacy of discredited dead end speculation?
At present, the Standard Model (SM) agrees with almost all collider data. Yet, three finetuning issues -- the Higgs mass problem, the strong CP problem and the cosmological constant problem -- all call for new physics. The most plausible solutions at present are weak scale SUSY, the PQWW axion and the string landscape. A re-evaluation of EW finetuning in SUSY allows for a higgsino-like LSP and naturalness upper bounds well beyond LHC limits. Rather general arguments from string theory allow for statistical predictions that m_h~ 125 GeV with sparticles beyond present LHC limits. The most lucrative LHC search channel may be for light higgsino pair production. Dark matter turns out to be a SUSY DFSZ axion along with a diminished abundance of higgsino-like WIMPs.
Howard Baer, "Beyond the Standard Model: An overview" arXiv:2405.00872 (May 1, 2024) (contribution to the 2024 QCD session of the 58th Rencontres de Moriond).

Wednesday, May 1, 2024

Japan's Sun God

I saw a reference to the story of Amaterasu being lured out of her cave and looked up the story. 

Japan's Shinto religion is often described as animistic, rather than polytheistic, and it does have many small gods (kami). But the story of Amaterasu has strong echos of the Greek gods, with odd births and amoral gods. I had been unaware that the story including siblings having children together, a moderately unusual theme in legends. As the reference below notes, it is also one of the only religions with a female sun god and a male moon god.

Of course, the existing Japanese royal family is one of the oldest still extant royal dynasties on Earth, and the only one of which I am aware that claims divine ancestry.

Amaterasu, (Japanese: “Great Divinity Illuminating Heaven”), the celestial sun goddess from whom the Japanese imperial family claims descent, and an important Shintō deity. 
She was born from the left eye of her father, Izanagi, who bestowed upon her a necklace of jewels and placed her in charge of Takamagahara (“High Celestial Plain”), the abode of all the kami
One of her brothers, the storm god Susanoo, was sent to rule the sea plain. Before going, Susanoo went to take leave of his sister. As an act of good faith, they produced children together, she by chewing and spitting out pieces of the sword he gave her, and he by doing the same with her jewels. Susanoo then began to behave very rudely—he broke down the divisions in the rice fields, defiled his sister’s dwelling place, and finally threw a flayed horse into her weaving hall. Indignant, Amaterasu withdrew in protest into a cave, and darkness fell upon the world.

The other 800 myriads of gods conferred on how to lure the sun goddess out. They collected cocks, whose crowing precedes the dawn, and hung a mirror and jewels on a sakaki tree in front of the cave. The goddess Amenouzume (q.v.) began a dance on an upturned tub, partially disrobing herself, which so delighted the assembled gods that they roared with laughter. Amaterasu became curious how the gods could make merry while the world was plunged into darkness and was told that outside the cave there was a deity more illustrious than she. She peeped out, saw her reflection in the mirror, heard the cocks crow, and was thus drawn out from the cave. The kami then quickly threw a shimenawa, or sacred rope of rice straw, before the entrance to prevent her return to hiding.

Amaterasu’s chief place of worship is the Grand Shrine of Ise, the foremost Shintō shrine in Japan. She is manifested there in a mirror that is one of the three Imperial Treasures of Japan (the other two being a jeweled necklace and a sword). The genders of Amaterasu and her brother the moon god Tsukiyomi no Mikato are remarkable exceptions in worldwide mythology of the sun and the moon. See also Ukemochi no Kami.

From the Encyclopedia Britannica. Simple English Wikipedia's retelling of the story is here.

Fun fact: The most energetic particle in a cosmic ray ever seen by astronomers has been named after Amaterasu.