Monday, October 31, 2022
A new paper describes a novel way of measuring time. It involves no new scientific discoveries and is simply a clever engineer application of existing science. But it has the potential to be useful in a wide variety of scientific and engineering applications.
[A]ccording to researchers from Uppsala University in Sweden. . . . experiments on the wave-like nature of something called a Rydberg state have revealed a novel way to measure time that doesn't require a precise starting point.Rydberg atoms are the over-inflated balloons of the particle kingdom. Puffed-up with lasers instead of air, these atoms contain electrons in extremely high energy states, orbiting far from the nucleus. . . . In some applications, a second laser can be used to monitor the changes in the electron's position, including the passing of time. These 'pump-probe' techniques can be used to measure the speed of certain ultrafast electronics, for instance.
We have investigated the rich dynamics of complex wave packets composed of multiple high-lying Rydberg states in He. A quantitative agreement is found between theory and time-resolved photoelectron spectroscopy experiments. We show that the intricate time dependence of such wave packets can be used for investigating quantum defects and performing artifact-free timekeeping. The latter relies on the unique fingerprint that is created by the time-dependent photoionization of these complex wave packets. These fingerprints determine how much time has passed since the wave packet was formed and provide an assurance that the measured time is correct. Unlike any other clock, this quantum watch does not utilize a counter and is fully quantum mechanical in its nature. The quantum watch has the potential to become an invaluable tool in pump-probe spectroscopy due to its simplicity, assurance of accuracy, and ability to provide an absolute timestamp, i.e., there is no need to find time zero.
Thursday, October 27, 2022
Brookhaven's E821 (2006): 116,592,089(63)
Combined measurement: 116,592,061(41)
Theory Initiative calculation: 116,591,810(43)
BMW calculation: 116,591,954(55)
When a new experimental anomaly that seems to contradict the Standard Model of Particle Physics fails to secure even ambulance chasing paper writers to propose new physics to explain it, it probably isn't really new physics.
This is the situation in the case of an anomaly described in a new article in the journal Nature regarding how quarks within protons act in electromagnetic fields of particular strengths in an overall low energy system (the anomalous effect peaks at a momentum exchange scale of about 18.7 MeV, which is about 350 MeV squared).
The money chart of the paper which shows the anomaly is Figure 4 below:
But, for a variety of reasons, there is good reason to think that the anomaly observed, whatever its source, isn't beyond the Standard Model (BSM) physics.
The New Anomaly
New experiments seem to show that the quarks respond more than expected to an electric field pulling on them, physicist Nikolaos Sparveris and colleagues report October 19 in Nature. The result suggests that the strong force isn’t quite as strong as theory predicts.It’s a finding at odds with the standard model of particle physics, which describes the particles and forces that combine to make up us and everything around us. The result has some physicists stumped about how to explain it — or whether to even try.At the Thomas Jefferson National Accelerator Facility in Newport News, Va., the team probed protons by firing electrons at a target of ultracold liquid hydrogen. Electrons scattering off protons in the hydrogen revealed how the protons’ quarks respond to electric fields (SN: 9/13/22). The higher the electron energy, the deeper the researchers could see into the protons, and the more the electrons revealed about how the strong force works inside protons.For the most part, the quarks moved as expected when electric interactions pulled the particles in opposite directions. But at one point, as the electron energy was ramped up, the quarks appeared to respond more strongly to an electric field than theory predicted they would.But it only happened for a small range of electron energies, leading to a bump in a plot of the proton’s stretch.“Usually, behaviors of these things are quite, let’s say, smooth and there are no bumps,” says physicist Vladimir Pascalutsa of the Johannes Gutenberg University Mainz in Germany.Pascalutsa says he’s often eager to dive into puzzling problems, but the odd stretchiness of protons is too sketchy for him to put pencil to paper at this time. “You need to be very, very inventive to come up with a whole framework which somehow finds you a new effect” to explain the bump, he says. “I don’t want to kill the buzz, but yeah, I’m quite skeptical as a theorist that this thing is going to stay.”It will take more experiments to get theorists like him excited about unusually stretchy protons, Pascalutsa says. He could get his wish if Sparveris’ hopes are fulfilled to try the experiment again with positrons, the antimatter version of electrons, scattered from protons instead.
From Science News discussing primarily the following paper whose abstract and citations are set forth below.
The Paper and Its Abstract
The abstract of the new article in Nature state:
The visible world is founded on the proton, the only composite building block of matter that is stable in nature. Consequently, understanding the formation of matter relies on explaining the dynamics and the properties of the proton’s bound state. A fundamental property of the proton involves the response of the system to an external electromagnetic field. It is characterized by the electromagnetic polarizabilities that describe how easily the charge and magnetization distributions inside the system are distorted by the electromagnetic field. Moreover, the generalized polarizabilities map out the resulting deformation of the densities in a proton subject to an electromagnetic field. They disclose essential information about the underlying system dynamics and provide a key for decoding the proton structure in terms of the theory of the strong interaction that binds its elementary quark and gluon constituents. Of particular interest is a puzzle in the electric generalized polarizability of the proton that remains unresolved for two decades. Here we report measurements of the proton’s electromagnetic generalized polarizabilities at low four-momentum transfer squared. We show evidence of an anomaly to the behaviour of the proton’s electric generalized polarizability that contradicts the predictions of nuclear theory and derive its signature in the spatial distribution of the induced polarization in the proton. The reported measurements suggest the presence of a new, not-yet-understood dynamical mechanism in the proton and present notable challenges to the nuclear theory.
Background Regarding QCD
The paper also provides a general background introduction to Quantum Chromodynamics (QCD) to give the paper context before it launches into its body text.
Explaining how the nucleons—protons and neutrons—emerge from the dynamics of their quark and gluon constituents is a central goal of modern nuclear physics. The importance of the question arises from the fact that the nucleons account for 99% of the visible matter in the universe. Moreover, the proton holds a unique role of being nature’s only stable composite building block.
The dynamics of quarks and gluons is governed by quantum chromodynamics (QCD), the theory of the strong interaction. The application of perturbation methods renders aspects of QCD calculable at large energies and momenta— namely at high four-momentum transfer squared (Q2)—and offers a reasonable understanding of the nucleon structure at that scale. Nevertheless, to explain the emergence of the fundamental properties of nucleons from the interactions of its constituents, the dynamics of the system have to be understood at long distances (or low Q2), where the QCD coupling constant αs becomes large and the application of perturbative QCD is not possible. The challenge arises from the fact that QCD is a highly nonlinear theory, because the gluons—the carriers of the strong force—couple directly to other gluons. Here theoretical calculations can rely on lattice QCD, a space-time discretization of the theory based on the fundamental quark and gluon degrees of freedom, starting from the original QCD Lagrangian.
An alternative path is offered by effective field theories, such as the chiral effective field theory, which use hadronic degrees of freedom and are based on the approximate and spontaneously broken chiral symmetry of QCD. Although steady progress has been made in recent years, we have yet to achieve a good understanding of how the nucleon properties emerge from the underlying dynamics of the strong interaction. To do this, the theoretical calculations require experimental guidance and confrontation with precise measurements of the system’s fundamental properties.
In conclusion, we have studied the proton’s response to an external electromagnetic field and its dependence on the distance scale within the system. We show evidence of a local enhancement in the proton’s electric generalized polarizability that the nuclear theory cannot explain. We provide a definitive answer to the existence of an anomaly in this fundamental property and we have measured with high precision the magnitude and the dynamical signature of this effect. The reported data suggest the presence of a dynamical mechanism in the system that is currently not accounted for in the theory. They pose a challenge to the chiral effective field theory, the prevalent effective theory for the strong interaction, and they serve as high-precision benchmark data for the upcoming lattice quantum chromodynamics calculations.
The measurements of the proton’s electromagnetic generalized polarizabilities complement the counterpart of the spin-dependent generalized polarizabilities of the nucleon. Together, the two components of the generalized polarizabilities provide a puzzling picture of the nucleon’s dynamics that emerge at long-distance scales.
Proton has the unique role of being nature’s only stable composite building block. Consequently, the observed anomaly in a fundamental system property comes with a unique scientific interest. It calls for further measurements so that the underlying dynamics can be mapped with precision and highlights the need for an improved theory so that a fundamental property of the proton can be reliably described.
Why Aren't New Physics Explanations Popular For This Kind Of Effect
Neither plain vanilla quantum electrodynamics (QED), which is the Standard Model theory of electromagnetism, nor quantum chromodynamics, which is the Standard Model theory of the strong force, which are the two principle Standard Model theories implicated in this experiment, are popular parts of fundamental physics in which to suggest beyond the Standard Model modifications.
This is for opposite reasons.
QED is validated at such extreme precision (often at parts per billion levels or more) with reasonably moderate amounts of calculations, which have been exhaustively tested, that there is no wiggle room for significant new physics in the context of something as ordinary as a proton in an electric field.
QCD, meanwhile, is so hard to calculate with that one of perhaps half a dozen main workable operationalizations of it must be used in practice, and the precision of those calculations is so low (general at the 10% to parts per thousand level) and is so inconsistent between methods, that it is almost more art than science to do QCD calculations that reproduce real world observations reasonably well. As a result theoretical calculation uncertainties frequently swamp any proposed new physics effects in a theory with few moving parts that can be easily manipulated by a physicist to explain observational anomalies.
So, even if there is an anomalous effect that is real and not just due to systemic error or statistical variation, it is hard to say that this is because of new physics as opposed to an oversimplification of true QCD dynamics made in the interests of actually being able to do QCD calculations.
Instead, theorists proposing new theories are far more fond of introducing new particles and forces, outside the three Standard Model forces with its dozen kinds of fundamental fermions, three massive weak force bosons, Higgs boson, photons, and gluons.
But introducing a new particle into the dynamics of the proton, the most carefully studied composite particle made of quarks that exists, that has never been observed in any other context over many decades of ultra-precise experimental measurements of its properties is very hard to do without contradicting other experiments that should also be affected by the same new particle that weren't observed in the other experiments.
Also, if they tweak any Standard Model force, the weak force whose interactions require ten of the Standard Model's parameters to describe, is more attractive that the electromagnetic or strong forces, which have fundamentally very simple structures even when the application of those forces to physical situations is complicated.
But this experiment is a poor candidate to demonstrate a weak force effect since it doesn't involve any kind of particle decay and because it isn't small enough for the weak force to be a good candidate to explain it.
Tweaks to General Relativity which is the state of the art theory of gravity are also popular with theorists, but this isn't part of the Standard Model, and gravitational effects are negligible at the scale of a single proton.
Tuesday, October 25, 2022
I have been Chair of the CWRU Department of Astronomy for over seven years now. Prof. Mihos served in this capacity for six years before that. No sane faculty member wants to be Chair; it is a service obligation we take on because there are tasks that need doing to serve our students and enable our research.
Academia is an area where the urge to "move up" into the direct management level position of department chair is not strong.
This fact is widely known by those in academia (incidentally, it also applies to the position of chief judge in most courts), and little known outside it.
After their birth a significant fraction of all stars pass through the tidal threshold (prah) of their cluster of origin into the classical tidal tails. The asymmetry between the number of stars in the leading and trailing tails tests gravitational theory. All five open clusters with tail data (Hyades, Praesepe, Coma Berenices, COIN-Gaia 13, NGC 752) have visibly more stars within dcl = 50 pc of their centre in their leading than their trailing tail. Using the Jerabkova-compact-convergent-point (CCP) method, the extended tails have been mapped out for four nearby 600-2000 Myr old open clusters to dcl>50 pc. These are on near-circular Galactocentric orbits, a formula for estimating the orbital eccentricity of an open cluster being derived.
Applying the Phantom of Ramses code to this problem, in Newtonian gravitation the tails are near-symmetrical. In Milgromian dynamics (MOND) the asymmetry reaches the observed values for 50 < dcl/pc < 200, being maximal near peri-galacticon, and can slightly invert near apo-galacticon, and the Küpper epicyclic overdensities are asymmetrically spaced. Clusters on circular orbits develop orbital eccentricity due to the asymmetrical spill-out, therewith spinning up opposite to their orbital angular momentum.
This positive dynamical feedback suggests Milgromian open clusters to demise rapidly as their orbital eccentricity keeps increasing. Future work is necessary to better delineate the tidal tails around open clusters of different ages and to develop a Milgromian direct n-body code.
A specific modification of Newtonian dynamics known as MOND has been shown to reproduce the dynamics of most astrophysical systems at different scales without invoking non-baryonic dark matter (DM). There is, however, a long-standing unsolved problem when MOND is applied to rich clusters of galaxies in the form of a deficit (by a factor around two) of predicted dynamical mass derived from the virial theorem with respect to observations.
In this article we approach the virial theorem using the velocity dispersion of cluster members along the line of sight rather than using the cluster temperature from X-ray data and hydrostatic equilibrium. Analytical calculations of the virial theorem in clusters for Newtonian gravity+DM and MOND are developed, applying pressure (surface) corrections for non-closed systems. Recent calibrations of DM profiles, baryonic ratio and baryonic (β model or others) profiles are used, while allowing free parameters to range within the observational constraints. It is shown that solutions exist for MOND in clusters that give similar results to Newton+DM -- particularly in the case of an isothermal β model for β=0.55−0.70 and core radii rc between 0.1 and 0.3 times r(500) (in agreement with the known data).
The disagreements found in previous studies seem to be due to the lack of pressure corrections (based on inappropriate hydrostatic equilibrium assumptions) and/or inappropriate parameters for the baryonic matter profiles.
Infectious diseases are among the strongest selective pressures driving human evolution. This includes the single greatest mortality event in recorded history, the first outbreak of the second pandemic of plague, commonly called the Black Death, which was caused by the bacterium Yersinia pestis. This pandemic devastated Afro-Eurasia, killing up to 30–50% of the population.
To identify loci that may have been under selection during the Black Death, we characterized genetic variation around immune-related genes from 206 ancient DNA extracts, stemming from two different European populations before, during and after the Black Death. Immune loci are strongly enriched for highly differentiated sites relative to a set of non-immune loci, suggesting positive selection.
We identify 245 variants that are highly differentiated within the London dataset, four of which were replicated in an independent cohort from Denmark, and represent the strongest candidates for positive selection. The selected allele for one of these variants, rs2549794, is associated with the production of a full-length (versus truncated) ERAP2 transcript, variation in cytokine response to Y. pestis and increased ability to control intracellular Y. pestis in macrophages.
Finally, we show that protective variants overlap with alleles that are today associated with increased susceptibility to autoimmune diseases, providing empirical evidence for the role played by past pandemics in shaping present-day susceptibility to disease.
PDG contains various mesons denoted with the letter ρ . These are the isovector resonances with quantum number of isospin (I = 1), of parity (P = −1), and of charge conjugation (C = −1). For instance, the vector mesons ρ(770) with quantum number JPC = 1 −−, the excited vector mesons ρ(1450), ρ(1700), and the tensor meson ρ3 (1690) with quantum number JPC = 3 −−.Despite the prediction of the ρ2 in the Relativistic Quark model, it is still missing experimentally. We only have the following data which were observed from different experimental groups and listed as “further states” in PDG: ρ2 (1940) and ρ2 (2225) with the total decay widths Γ tot ρ2 (1940) ≃ 155±40 MeV and Γ tot ρ2 (2225) ≃ 335+100 −50 MeV accordingly.Axial tensor mesons are studied in recent LQCD [Lattice QCD] simulations, where the authors consider the mass of ρ2 is about 1.7 GeV as the ρ3 (1690). We present the results about the missing ρ2 within a chiral effective model which is so-called the extended Linear Sigma Model (eLSM).
We have studied ρ2 axial-tensor meson, chiral partner of the tensor meson ρ2 (1320) in the framework of a chiral model for low-energy QCD. We predict its mass to be around 1.663 GeV. A phenomenological note on the missing ρ2 meson similar to the Relativistic Quark model prediction. Because of the chiral symmetry, the parameter determined in the tensor sector allows to make predictions for unknown ground-state axial-tensor resonance. The effective model fitting to the LQCD results is also presented.
The ρ2 meson is the missing isovector member of the meson nonet with the quantum numbers JPC=2−−. It belongs to the class of ρ-mesons such as the vector meson ρ(770), the excited vector ρ(1700) and the tensor ρ3(1690). Yet, despite the rich experimental and theoretical studies for other ρ-meson states, no resonance that could be assigned to the ρ2 meson has been measured. In this note, we present the results for the mass and dominant decay channels of the ρ2 meson within the extended Linear Sigma Model.
In this proceeding, we present results from a global fit of Dirac fermion dark matter (DM) effective field theory (EFT) based on arXiv:2106.02056 using the GAMBIT framework. Here we show results only for the dimension-6 operators that describe the interactions between a gauge-singlet Dirac fermion and Standard Model quarks. Our global fit combines the latest constraints from Planck, direct and indirect DM detection, and the LHC. For DM mass below 100 GeV, it is impossible to simultaneously satisfy all constraints while maintaining the EFT validity at high energies. For higher masses, however, large regions of parameter space remain viable where the EFT is valid and saturates the observed DM abundance.
1. Direct detection: The Wilson coefficients are evaluated at µ = 2 GeV using DirectDM and matched onto a set of non-relativistic EFT operators. These are used in DDCalc v2.2.0 to compute predicted events rates and corresponding likelihoods for XENON1T, LUX (2016), PandaX (2016) and (2017), CDMSlite, CRESST-II and CRESST-III, PICO-60 (2017) and (2019), and DarkSide-50 experiments.2. Relic density: Using CalcHEP v3.6.27, GUM and DarkSUSY v6.2.2, we compute the DM relic density via a thermal freeze-out scenario. Both cases where χ makes up all ( fχ ≡ Ωχ/0.12 ≈ 1) or a sub-component ( fχ ≤ 1) of the total DM abundance are studied.3. Fermi-LAT searches for gamma rays: Observations of dwarf spheroidal galaxies of the Milky Way place strong constraints on the DM annihilation rate. Using Fermi-LAT searches for gamma rays from DM annihilation in dwarfs, we use the gamLike v1.0.1 package within DarkBit to compute the resulting likelihood function.4. Solar capture: Neutrinos from DM annihilation in the Sun can be detected at the IceCube experiment. Using Capt’n General, we compute the DM capture rate in the Sun and utilise the nulike package to obtain an event-by-event level likelihood for the 79-string IceCube data.5. Energy injection bounds: Using the CosmoBit module of GAMBIT, we compute bounds on our model based on predicted rates of DM annihilation in the early universe. These annihilations lead to energy injection and observable effects in the cosmic microwave background.6. ATLAS and CMS monojet searches: By combining the ColliderBit module of GAMBIT with FeynRules v2.0, MadGraph_aMC@NLO v2.6.6, Pythia v8.1 and Delphes v3.4.2, we compute a likelihood based on monojet searches performed at the ATLAS and CMS experiments.
Friday, October 21, 2022
It is reported that the Large High Altitude Air Shower Observatory (LHAASO) observed thousands of very-high-energy photons up to ∼18 TeV from GRB 221009A. We study the survival rate of these photons by considering the fact that they are absorbed by the extragalactic background light.
By performing a set of 10^6 Monte-Carlo simulations, we explore the parameter space allowed by current observations and find that the probability of predicting that LHAASO observes at least one photons of 18 TeV from GRB 221009A within 2000 seconds is 4-5%.
Hence, it is still possible for the standard physics to interpret LHAASO's observation in the energy range of several TeV. Our method can be straightforwardly generalized to study more data sets of LHAASO and other experiments in the future.
Thursday, October 20, 2022
The genetic inheritance patterns of complex traits can be summarized with just just two numbers per complex trait.
Genome-wide association studies have revealed that the genetic architectures of complex traits vary widely, including in terms of the numbers, effect sizes, and allele frequencies of significant hits. However, at present we lack a principled way of understanding the similarities and differences among traits. Here, we describe a probabilistic model that combines mutation, drift, and stabilizing selection at individual sites with a genome-scale model of phenotypic variation. In this model, the architecture of a trait arises from the distribution of selection coefficients of mutations and from two scaling parameters. We fit this model for 95 diverse, highly polygenic quantitative traits from the UK Biobank. Notably, we infer similar distributions of selection coefficients across all these traits. This shared distribution implies that differences in architectures of highly polygenic traits arise mainly from the two scaling parameters: the mutational target size and heritability per site, which vary by orders of magnitude across traits. When these two scale factors are accounted for, the architectures of all 95 traits are nearly identical.
The discoveries of solar and atmospheric neutrino oscillations have motivated a broad experimental program dedicated to studying neutrino mixing. While most measurements are consistent with three-flavor (3ν) neutrino oscillations as described by the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) formalism, several experimental anomalies hint at the existence of a sterile neutrino with a mass at the eV scale.
The SAGE and GALLEX experiments, and more recently, the BEST experiment, have observed lower than expected ν(e) rates from radioactive sources, which is known as the gallium anomaly.
Reactor neutrino experiments have measured lower anti-ν(e) rates than the expectation based on reactor anti-neutrino flux calculations. This observation is referred to as the reactor anomaly.
An oscillation signal in the reactor anti-ν(e) energy spectrum over distances of a few meters was reported by the Neutrino-4 collaboration.
In addition to these observed anti-ν(e) deficits, excesses of anti-ν(e)-like events were also observed in some anti-ν(µ) dominated accelerator neutrino experiments. The LSND collaboration observed an anomalous excess of anti-ν(e)-like events, and the MiniBooNE collaboration observed an excess of low-energy electron-like events.These anomalies are in strong tension with other experimental results within the 3(active) + 1(sterile) oscillation framework as seen in a global fit of the data.
In addition, recent experimental measurements and improvements of the reactor anti-neutrino flux calculation lead to a plausible resolution of the reactor anti-neutrino anomaly.
The Neutrino-4 anomaly is largely excluded by the results from other very short baseline reactor neutrino experiments, for example, PROSPECT, STEREO, DANSS, NEOS, although it is consistent with the gallium anomaly.
The parameter space to the right of the red lines are excluded by the latest MicroBooNE data reported in the paper below at a 95% confidence level. The shaded area are parameters for a sterile neutrino in a 3-1 model that are not ruled out by the referenced prior experiments due to anomalies in their data.
We present a search for eV-scale sterile neutrino oscillations in the MicroBooNE liquid argon detector, simultaneously considering all possible appearance and disappearance effects within the 3+1 active-to-sterile neutrino oscillation framework. We analyze the neutrino candidate events for the recent measurements of charged-current νe and νμ interactions in the MicroBooNE detector, using data corresponding to an exposure of 6.37×10^20 protons on target from the Fermilab booster neutrino beam. We observe no evidence of light sterile neutrino oscillations and derive exclusion contours at the 95% confidence level in the plane of the mass-squared splitting Δm241 and the sterile neutrino mixing angles θμe and θee, excluding part of the parameter space allowed by experimental anomalies. Cancellation of νe appearance and νe disappearance effects due to the full 3+1 treatment of the analysis leads to a degeneracy when determining the oscillation parameters, which is discussed in this paper and will be addressed by future analyses.
Monday, October 17, 2022
Several recent studies have shown that velocity differences of very wide binary stars, measured to high precision with GAIA, can potentially provide an interesting test for modified-gravity theories which attempt to emulate dark matter; in essence, MOND-like theories (with external field effect included) predict that wide binaries (wider than ∼7 kAU) should orbit ∼15% faster than Newtonian for similar orbit parameters; such a shift is readily detectable in principle in the sample of 9,000 candidate systems selected from GAIA EDR3 by Pittordis and Sutherland (2022). However, the main obstacle at present is the observed ``fat tail" of candidate wide-binary systems with velocity differences at ∼1.5−6× circular velocity; this tail population cannot be bound pure binary systems, but is likely to be dominated by triple or quadruple systems with unresolved or undetected additional star(s).While this tail can be modelled and subtracted, obtaining an accurate model for the triple population is crucial to obtain a robust test for modified gravity. Here we explore prospects for observationally constraining the triple population: we simulate a population of hierarchical triples ``observed" as in PS22 at random epochs and viewing angles; then evaluate various possible methods for detecting the third star, including GAIA astrometry, RV drift, and several imaging methods from direct Rubin images, speckle imaging and coronagraphic imaging. Results are encouraging, typically 90 percent of the triple systems in the key regions of parameter space are detectable; there is a moderate ``dead zone" of cool brown-dwarf companions at ∼25−100 AU separation which are not detectable with any of our baseline methods. A large but feasible observing campaign can clarify the triple/quadruple population and make the gravity test decisive.
A number of recent studies have shown that velocity differences of wide stellar binaries offer an interesting test for modified-gravity theories similar to MoND, which attempt to eliminate the need for dark matter (see e.g. Hernandez et al. (2012a), Hernandez et al. (2012b) Hernandez et al. (2014), Matvienko & Orlov (2015), Scarpa et al. (2017) and Hernandez (2019)). Such theories require a substantial modification of standard GR below a characteristic acceleration threshold a0 ∼ 1.2×10−10 m s−2 (see review by Famaey & McGaugh (2012)). A key advantage of wide binaries is that at separations > 7 kAU, the relative accelerations are below this threshold, so MoND-like theories predict significant deviations from GR; while wide binaries should contain negligible dark matter, so DM theories predict no change from GR/Newtonian gravity. Thus in principle the predictions of DM vs modified gravity in wide binaries are unambiguously different, unlike the case for galaxy-scale systems where the DM distribution is uncertain.
Wide binaries in general have been studied since the 1980s ((Weinberg et al. 1987; Close et al. 1990)), but until recently the precision of ground-based proper motion measurements was a serious limiting factor: wide binaries could be reliably selected based on similarity of proper motions, see e,g, Yoo et al. (2004), L´epine & Bongiorno (2007), Kouwenhoven et al. (2010), Jiang & Tremaine (2010), Dhital et al. (2013), Coronado et al. (2018). However, the typical proper motion precision ∼ 1 mas yr−1 from ground-based or Hipparcos measurements was usually not good enough to actually measure the internal velocity differences, except for a limited number of nearby systems.
The launch of the GAIA spacecraft (Gaia Collaboration 2016) in 2014 offers a spectacular improvement in precision; the proper motion precision of order 30 µas yr−1 corresponds to transverse velocity precision 0.0284 km s−1 at distance 200 parsecs, around one order of magnitude below wide-binary orbital velocities, so velocity differences can be measured to good precision over a substantial volume; and this will steadily improve with future GAIA data extending eventually to a 10-year baseline. Recent studies of WBs from GAIA include e.g. El-Badry et al. (2021) and Hernandez et al. (2022).
In earlier papers in this series, Pittordis & Sutherland (2018) (hereafter PS18) compared simulated WB orbits in MoND versus GR, to investigate prospects for the test in advance of GAIA DR2. This was applied to a sample of candidate WBs selected from GAIA DR2 data by Pittordis & Sutherland (2019) (hereafter PS19), and an expanded sample from GAIA EDR3 by Pittordis & Sutherland (2022) (hereafter PS22). To summarise results, simulations show that (with MoND external field effect included), wide binaries at & 10 kAU show orbital velocities typically 15 to 20 percent faster in MOND than GR, at equal separations and masses. This leads to a substantially larger fraction of “faster” binaries with observed velocity differences between 1.0 to 1.5 times the Newtonian circular-orbit value. In Newtonian gravity, changing the eccentricity distribution changes the shape of the distribution mainly at lower velocities, but has little effect on the distribution at the high end from 1.0 to 1.5 times circular velocity. Therefore, the predicted shift from MOND is distinctly different from changing the eccentricity distribution within Newtonian gravity; so given a large and pure sample of several thousand WBs with precise 2D velocity difference measurements, we could decisively distinguish between GR and MOND predictions.
The main limitation at present is that PS19 and PS22 showed the presence of a “fat tail” of candidate binaries with velocity differences ∼ 1.5 to 6× the circular-orbit velocity; these systems are too fast to be pure bound binaries in either GR or MOND, and a likely explanation (Clarke 2020) is higher-order multiples e.g. triples where either one star in the observed “binary” is itself an unresolved closer binary, or the third star is at resolvable separation but is too faint to be detected by GAIA; the third star on a closer orbit thus substantially boosts the velocity difference of the two observed stars in the wide “binary”.
In PS22 we made a simplified model of this triple population, then fitted the full distribution of velocity differences for WB candidates using a mix of binary, triple and flyby populations. These fits found that GR is significantly preferred over MOND if the rather crude PS22 triple model is correct, but we do not know this at present. Allowing much more freedom in the triple modelling is computationally expensive due to many degrees of freedom, and is likely to lead to significant degeneracy between gravity modifications and varying the triple population. Therefore, observationally constraining the triple population, or eliminating most of it by additional observations, is the next key step to make the WB gravity test more secure.
In this paper we explore prospects for observationally constraining the triple population: we generate simulated triple systems “observed” at random epochs, inclinations and viewing angles, and then test whether the presence of the third star is detectable by any of various methods including direct, speckle or coronagraphic imaging; radial velocity drift; or astrometric non-linear motion in the future GAIA data; we see below that prospects are good, in that 80 to 95% of triple systems in the PS22 sample should be potentially detectable as such by at least one of the methods.
Should Wide Binaries Be Different In Deur's Analysis?
Quoting from the sidebar:
How strong are the gravitational self-interaction?
This is a function, roughly speaking, of system mass and system size:Near a proton GMp/rp=4×10-38 with Mp the proton mass and rp its radius. ==>Self-interaction effects are negligible. . . .For a typical galaxy: Magnitude of the gravity field is proportionate to GM/sizesystem which is approximately equal to 10-3.
In Southern mainland China, mainland Southeast Asia, and northern India (the Munda people), the first wave of farmers were linguistically Austroasiatic, a language family that originates in the South Chinese rice farming Neolithic revolution. There were also later waves of migration of farmers from South China, most recently the Thai people.
A TreeMix analysis places the Jomon as an offshoot of the Hoabinhian people (a Mesolithic wave of people in Southeast Asia and Southern China ca. 12,000 to 10,000 BCE), with the Kusunda people (who are hunter-gathers in Western Nepal who historically spoke a language that is an isolate and were animistic religiously) as an intermediate population.Y-DNA haplogroup D has a cryptic distribution found in isolated pockets across Asia including Siberia and Tibet that tends to favor a Northern route origin.The mtDNA haplogroups N9b and M7a also tell story so deep in history (both are very basal in the Eurasian mtDNA tree and derived from African mtDNA haplogroup L3) that it is hard to reconstruct. Both mtDNA M and mtDNA N show distributions that tend to favor a Southeast Asian route to Japan, but perhaps this is because the northern bearers of this haplogroup went extinct, and were then almost fully replaced in the Last Glacial Maximum.
On the other hand, there have continuously been modern humans in Japan since before the 12,000 BCE migration associated with the Hoabinhian people, so at least some Jomon ancestry probably precedes that wave of migration. But different selective pressures in Japan and Southeast Asia could also lead to selection for a different physical appearance.
Taiwan is known as the homeland of the Austronesian-speaking groups, yet other populations already had lived here since the Pleistocene. Conventional notions have postulated that the Palaeolithic hunter-gatherers were replaced or absorbed into the Neolithic Austronesian farming communities. Yet, some evidence has indicated that sparse numbers of non-Austronesian individuals continued to live in the remote mountains as late as the 1800s.
The cranial morphometric study of human skeletal remains unearthed from the Xiaoma Caves in eastern Taiwan, for the first time, validates the prior existence of small stature hunter-gatherers 6000 years ago in the preceramic phase. This female individual shared remarkable cranial affinities and small stature characteristics with the Indigenous Southeast Asians, particularly the Negritos in northern Luzon.
This study solves the several-hundred-years-old mysteries of ‘little black people’ legends in Formosan Austronesian tribes and brings insights into the broader prehistory of Southeast Asia.