Wednesday, October 31, 2018

Large Hadron Collider Run 2 Ends Soon

The Large Hadron Collider (LHC) will shut down in December and won't start up again until 2021. In the meantime there will be basically no new high energy physics experimental data and scientists will have to pour over the data that has been already collected instead. 
Since 2015 the LHC experiments have been taking data from proton-proton collisions at 13 TeV. This is “Run 2” of the LHC, “Run 1” was at the lower energy of 8 TeV. The proton-proton Run 2 ended this morning, with the LHC shifting to other tasks, first machine development, later heavy ions. It will shut down completely in December for the start of “Long Shutdown 2 (LS2)”, which will last for over two years, into early 2021. During LS2 there will be maintenance performed and improvements made, including bringing the collision energy of the machine up to the design energy of 14 TeV. 
ATLAS is reporting 158 inverse fb of collisions delivered by the machine during Run 2, of which 149 inverse fb were recorded, the CMS numbers should be similar. Most data analysis reported to date by ATLAS and CMS has only used the 2015 and 2016 data (about 36 inverse fb) although a few results have included data through 2017 (about 80 inverse fb). My impression is that for many searches they have been waiting for the full run 2 dataset to be available. Perhaps results of searches with the full dataset might start becoming available by the time of summer 2019 conferences. 
The LHC run 3 is planned for 2021-2023, producing perhaps 300 inverse fb of data, results perhaps available in 2024. It will thus be quite a long time after run 2 results start appearing before better ones due simply to more data become available.
From Not Even Wrong.

Tuesday, October 30, 2018

An Oldie But Goodie

The top quark was experimentally discovered in 1995 although experimenters were hot on its path a couple of years earlier, and the Higgs boson was discovered and its mass was first measured in 2012. The masses predicted in this 1993 paper are close to the values ultimately measured.
A model for composite electroweak bosons is re-examined to establish approximate ranges for the initial predictions of the top and Higgs masses. Higher order corrections to this 4-fermion theory at a high mass scale where the theory is matched to the Standard Model have little effect, as do wide variations in this scale. However, including all one loop evolution and defining the masses self-consistently, at their respective poles, moves the top mass upward by some 10 GeV to near 175 GeV and the Higgs mass down by a similar amount to near 125 GeV.
David E. Kahana, Sidney H. Kahana, "Top and Higgs Masses in Dynamical Symmetry Breaking" (December 21, 1993).

Of course, this doesn't mean that the approach taken to make these predictions in 1993 was necessary an accurate explanation of why those particles have the masses that they do. Hundreds of predictions with significant margins of error were made and somebody had to be right as a matter of random chance, since a general ballpark in which the mass values had to fall was already known.

Arguably, this is little more than numerology. But, it is particularly interesting numerology as the ultimate prediction was correct long in advance.

While an accurate prediction doesn't insure that the reasoning used to produce that prediction is valid, if the reasoning used by an investigator produces an inaccurate prediction then we known that there was something wrong with that investigator's method or source data that informed the prediction.

India's Caste Endogamy Was Very Extreme

The interracial intermarriage rate in Jim Crow America was about 1%. At that rate, if introgression of non-white individuals into whites continued for 50 years, the average person with white ancestry would be 40% non-white. (I suspect this exaggerated figure is due to improper use of a 1% introgression rate per year rather than per generation, but even a few generations of modest introgression does have a notable effect over a very long time period)
In India, caste cemented itself, not just at the Varna level, but at the Jati level about 1500 years ago. This implied an endogamy rate on the order of 99.8% (with 10% introgression over that time period) to 99.9% (with 5% introgression over that time period) to 99.98% (with 1% introgression over that time period).

I think the source is Razib or someone he quoted, but I could be mistaken. I accidentally failed to hit the publish button on this post back on April 17, 2018.

Sunday, October 28, 2018

A Pre-Clovis Spear Point In Texas

A pre-Clovis spear point found in Texas from about 15,000 years ago largely reaffirms the existing paradigm for how the founding population of the Americas settled these regions after the Last Glacial Maximum. 

In particular, it clarifies that there were populations in the interior of North America before there was an ice free land corridor from Beringia to North America in the north. Somebody either walked across a glacier for many miles, or took a boat down the Pacific coast and them migrated inland before the ice free land corridor opened.

In other New World pre-history news, a new paper (whose results were previously blogged here) notes that a one study outlier genetic finding in the Amazon has no trace in ancient DNA:
Intriguingly, a signal of Australasian ancestry that has been observed in some Amazonian groups is not evident in any of the ancient Siberian or Beringian samples sequenced here, or in previous studies.
Pontus Skoglund‏ notes that: "the signal is found in Tianyuan at 40kya, stronger than Australasians in its connection to Amazonians in fact. No less mysterious though!" He cites this source. This Tianyuan connection is also stronger than the connection to the Andamanese people.

My own theory is that the genetic trace seen is the product of one or two individuals or a nuclear family who were newcomers to the Beringian community that were in the first wave of advance to settle South America.

Friday, October 26, 2018

Quote of the Day

[Professor Steven] Weinberg raises an eyebrow and points to his office. 
His office, it turns out, is half the size of mine, an observation that vaporizes what little ambition I ever had to win the Nobel Prize.
- Sabine Hossenfelder, "Lost in Math" (2018) at page 96.

For what it is worth, "Lost in Math" is a treasure trove of dry wit for those with some familiarity with modern physics, and this is merely one of many gems that her book contains.

An abstract from today that sums up the attitudes in the field about high energy physics that she is critiquing is this one:
The standard model of particle physics is an extremely successful theory of fundamental interactions, but it has many known limitations. It is therefore widely believed to be an effective field theory that describes interactions near the TeV scale. A plethora of strategies exist to extend the standard model, many of which contain predictions of new particles or dynamics that could manifest in proton-proton collisions at the Large Hadron Collider (LHC). As of now, none have been observed, and much of the available phase space for natural solutions to outstanding problems is excluded. If new physics exists, it is therefore either heavy (i.e. slightly above the reach of current searches) or hidden (i.e. currently indistinguishable from standard model backgrounds). We summarize the existing searches, and discuss future directions at the LHC.
Salvatore Rappoccio, "The experimental status of direct searches for exotic physics beyond the standard model at the Large Hadron Collider" (October 24, 2018).

Thirty three pages of null results follow. The review begins with the following introduction:
Particle physics is at a crossroads. The standard model (SM) explains a wide range of phenomena spanning interactions over many orders of magnitude, yet no demonstrated explanation exists for a variety of fundamental questions. Most recently, the discovery of the Higgs boson [1, 2, 3, 4, 5, 6, 7, 8, 9] at the ATLAS [10] and CMS [11] detectors has elucidated the mechanism of electroweak symmetry breaking, but there is no explanation for why the scale of its mass is so much different from naive quantum-mechanical expectations (the “hierarchy problem”) [12, 13, 14, 15, 16, 17, 18, 19, 20]. Dark matter (DM) remains an enigma, despite extensive astronomical confirmation of its existence [21, 22, 23]. Neutrino masses are observed to be nonzero [24, 25, 26, 27], and elements of the Pontecorvo-Maki-Nakagawa-Sakata matrix [28, 29] have been measured, but these masses are not easily accounted for in the SM [30]. Unification of the strong and electroweak forces is expected, but not yet observed nor understood [31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44]; such models often predict the existence of yet-to-be-observed leptoquarks (LQs) or proton decay [45]. Furthermore, there are unexpected observations that are not explained in the SM, such as the baryon asymmetry [46], anomalies in the decays of bottom-quark hadrons [47], a discrepancy in the anomalous magnetic moment of the muon (g-2) [48], and the strong CP problem [49, 50, 51]. Even further, there are open questions about long-standing observations, such as whether or not there is an extended Higgs sector [52], why there are multiple generations of fermions with a large mass hierarchy [32, 53, 54, 55], and why no magnetic monopoles are observed to exist [56]. For these reasons, the SM is considered to be an effective field theory, and that physics beyond the SM (BSM) should exist.  
In this Review, we will (non-exhaustively) discuss a subset of these questions that have been investigated recently at the LHC with 13 TeV proton-proton collisions by the ATLAS, CMS, and LHCb [57] experiments. From a collider standpoint, we will discuss the solution to the hierarchy problem, dark matter, the origins of neutrino masses, unification, and compositeness. We will also discuss the possibilities for improvements of these searches at the High-Luminosity LHC (HL-LHC) or other future colliders. One very popular group of theories to explain several of these phenomena involve supersymmetric (SUSY) extensions to the SM [12, 13]. With a few exceptions, this Review will focus on answers to the above questions that do not involve SUSY, although it remains a theoretically attractive solution. This Review will also primarily not focus on solutions that involve an extended Higgs sector, nor open anomalies in hadron spectroscopy.  
Many models of BSM physics that can be tested at the LHC involve spectacular signatures that distinguish them from SM backgrounds. It is therefore worthwhile to discuss the searches for new physics with their unique signatures in mind. As such, we will first broadly discuss the signatures used for LHC BSM searches, and then discuss the implications on various scenarios.
I have highlighted the problems identified and underlined those that are legitimate problems as opposed to mere quibbled with what the laws of Nature actually happen to be. The decision to omit SUSY limitations and extended Higgs sectors is a telling sign of the decreasing popularity of these theories.

The decision to ignore "open anomalies in hadron spectroscopy" is a reflection of the extent to which QCD is so inexact, compared to other aspects of high energy physics, that anomalies often don't mean very much. 

Tuesday, October 23, 2018

Siberia Has Experienced Repeated Population Replacement

The first wave of archaic hominin migration out of Africa which expanded as far into Southern Asia as Indonesia and China, Homo erectus, probably never reached Northern Asia in any significant numbers.

But, before modern humans arrived in Northern Asia, Denisovans and Neanderthals (archaic hominins) reached at least as far as the Altai Mountains. We don't know with much precision when they arrived there or by precisely what route, but both were present in the Altai region around 90,000 years ago when a child with one Denisovan parent and one Neanderthal parent was born. Sometime after 40,000 years ago, they became extinct (or at least almost extinct) in the region. We don't know if they ever overlapped with modern humans in that region, but the timing of the latest evidence of their presence in Northern Asia and the earliest evidence of a modern human presence in Northern Asia is suspiciously close in time. Ancient Altai Neanderthal DNA shows evidence as admixture with modern humans that was estimated to have taken place ca. 100,000 years ago, but these admixture events probably took place with their ancestors in Southwest Asia, rather than Northern Asia.

Ancient DNA and archaeology establishes that the original modern humans in Siberia (who arrived there about 38,000 years ago), the "Ancient North Siberians" (ANS) were wiped out during the Last Glacial Maximum (about 20,000 years ago) except for refugia populations in Beringia (and possibly also the Altai Mountains region) who contributed to Ancient Paleosiberian gene pools.

Ancient DNA also confirms the hypothesis that Siberia was the source for both the "Ancient Paleosiberian" (AP) population that emerged after the Last Glacial Maximum which gave rise to the founding population of the Americas (which has only a few relict tribes in Siberia itself who are their descendants), and for the East Asian shifted "Neosiberian" populations that largely replaced the Ancient Paleosiberians around 11,000 years ago who were a genetic source for Na-Dene and Inuit Native Americans ancestors' migration to the Americas and most modern indigenous Siberians. 

In the last 7000 years or so, there have been more waves of migration across Northern Asia, although some of these waves did not reach all of the way to far Northeastern Siberia. 

First, Uralic populations migrated West and East from central Siberia (starting ca. 5000 BCE).

Then, Tocharian Indo-Europeans migrated from the Pontic-Caspian steppe as far east as the Tarim Basin which they reached ca. 2000 BCE, and a trickle of Pontic-Caspian steppe people made it as far as Bronze Age China. 

Ethnically and linguistically Turkish populations migrated west starting in the first few centuries BCE and CE, and extending their reach from a source in Northeast Asia to a maximum extend in Turkey (with a substantial Turkish immigrant population arriving Germany after World War II). The Oghuz Turks started to arrive in Anatolia around the 9th century CE and this demographic shift (in Anatolia, a significant introgression into the pre-existing population but not a population replacement) was consolidated by the 11th century Seljuk Empire which was both Turkic and Persian that controlled almost all of Anatolia.

Islamic culture accompanied by significant (but not replacement level) ethnically Iranian/Middle Eastern migration followed that in an eastward direction, overlapping with the westward Turkish migration, and ultimately leaving a lasting impact as far east as what is currently Western China, during the Tang Dynasty.

By the 13th century CE there was a Mongolian wave of western migration (which also expanded to the East from Mongolia). The eastward Mongolian expansion had a more lasting impact than the western expansion.

A few centuries later, the Russians, initially with a Scandinavian elite and Slavic masses, migrated east again, leaving us with the current status quo, more or less. This expansion wiped out all but a few thousand of the remaining Ancient Paleosiberian populations in Siberia. The Russians made it all of the way to Alaska, uniting all of Siberia and former Beringia and Alaska politically as well as biogeographically, until 1867 when the Alaska Purchase transferred Alaska to the United States.

The paper recounting the new ancient DNA discoveries has the following abstract and citation:
Far northeastern Siberia has been occupied by humans for more than 40 thousand years. Yet, owing to a scarcity of early archaeological sites and human remains, its population history and relationship to ancient and modern populations across Eurasia and the Americas are poorly understood. 
Here, we report 34 ancient genome sequences, including two from fragmented milk teeth found at the ~31.6 thousand-year-old (kya) Yana RHS site, the earliest and northernmost Pleistocene human remains found. 
These genomes reveal complex patterns of past population admixture and replacement events throughout northeastern Siberia, with evidence for at least three large-scale human migrations into the region. 
The first inhabitants, a previously unknown population of "Ancient North Siberians" (ANS), represented by Yana RHS, diverged ~38 kya from Western Eurasians, soon after the latter split from East Asians. 
Between 20 and 11 kya, the ANS population was largely replaced by peoples with ancestry from East Asia, giving rise to ancestral Native Americans and "Ancient Paleosiberians" (AP), represented by a 9.8 kya skeleton from Kolyma River. AP are closely related to the Siberian ancestors of Native Americans, and ancestral to contemporary communities such as Koryaks and Itelmen. Paleoclimatic modelling shows evidence for a refuge during the last glacial maximum (LGM) in southeastern Beringia, suggesting Beringia as a possible location for the admixture forming both ancestral Native Americans and AP. 
Between 11 and 4 kya, AP were in turn largely replaced by another group of peoples with ancestry from East Asia, the "Neosiberians" from which many contemporary Siberians derive. We detect additional gene flow events in both directions across the Bering Strait during this time, influencing the genetic composition of Inuit, as well as Na Dene-speaking Northern Native Americans, whose Siberian-related ancestry components is closely related to AP. 
Our analyses reveal that the population history of northeastern Siberia was highly dynamic, starting in the Late Pleistocene and continuing well into the Late Holocene. The pattern observed in northeastern Siberia, with earlier, once widespread populations being replaced by distinct peoples, seems to have taken place across northern Eurasia, as far west as Scandinavia. 
Sikora et al., The population history of northeastern Siberia since the Pleistocene, bioRxiv (October 22, 2018), doi:

Monday, October 22, 2018

Books About Prussia

My paternal line ancestor came from Prussia in 1847 to dodge the draft (Germany did not yet exist).  Some of my ancestors are also connected to one of the classical music composers called Bach's family. Most of the ancestors who stayed ended up just barely on the East German side of the divided Germany after World War II.

Razib notes some good books about Prussia, which a quote here for future reference:
Tim Blanning’s Frederick the Great: King of Prussia is an excellent book. So is The Pursuit of Glory: The Five Revolutions that Made Modern Europe: 1648-1815. Finally, Iron Kingdom: The Rise and Downfall of Prussia, 1600–1947. One of the most interesting things about Frederick the Great: King of Prussia is how Blanning recounts the importance of personally playing and repeatedly listening to music in the life of the German monarch. He was apparently a very competent flutist.
In the greater scheme of things, Prussia is particularly notable for having an absurdly micromanaging legal code (with dictates, for example, regarding when one should do which chores in a household like laundry) and for encouraging a largely industrial employer based welfare state, not so different from the Japanese economy of the 1980s. Some interesting historical economics also flows from the previously highly balkanized state of what became Germany, comparing economic development with litmus tests like opera house construction and public clocktowers.

Genetically, my father's side makes him look like a broadly Northern European mutt, in significant part because the significant clusters and ancestral populations of Northern Europe don't align very well with the current political boundaries there, and partially because Northern Europe has had considerable population exchange in the modern era in this region.

Fuzzy Dark Matter Model Tightly Constrained By Astronomy Measurements; MOG Allegedly Ruled out

Fuzzy dark matter is a dark matter particle theory that involves very light bosons as dark matter particles (in contrast, for example, to warm dark matter which uses keV mass scale sterile fermions).  A new preprint purports to confine the allowed mass range of fuzzy dark matter particles to within a factor of ten using astronomy measurement from the Milky Way and one other galaxy. This same method could conceivably rule out the entire parameter space of fuzzy dark matter theories with the right observation.
The fuzzy dark matter (FDM) model treats DM as a bosonic field with astrophysically large de Broglie wavelength. A striking feature of this model is O(1fluctuations in the dark matter density on time scales which are shorter than the gravitational timescale. Including for the first time the effect of core oscillations, we demonstrate how such fluctuations lead to heating of star clusters, and thus an increase in their size over time. From the survival of the old star cluster in Eridanus II we infer ma0.61×1019 eV    within modelling uncertainty if FDM is to compose all of the DM, and derive constraints on the FDM fraction at lower masses. The subhalo mass function in the Milky Way implies ma0.8×1021 eV to successfully form Eridanus II. The window between 1021 eVma1020 eV is affected by narrow band resonances, and the limited applicability of the diffusion approximation. Some of this window may be consistent with observations of Eridanus II and more detailed investigations are required.
David J. E. Marsh, Jens C. Niemeyer, "Strong Constraints on Fuzzy Dark Matter from Ultrafaint Dwarf Galaxy Eridanus II" (October 19, 2018).

By comparison a graviton from a falling apple near Earth should have energy of 10^-30 ergs. One erg equals 6.242 * 10^11  eV, so a graviton from a falling apple (which is also a boson) ought to have an energy on the other of 6*10^-19 eV which is quite close in order of magnitude to the estimated energy of fuzzy dark matter particles in this study.

For the energy range, a graviton based quantum gravity theory (such as Deur's analysis) and a fuzzy dark matter theory, ought to be very similar.

Meanwhile, another paper purports to rule out John Moffat's MOG theory, which uses a scalar, vector, tensor function, based upon detailed Milky Way observations. Until now, this has been one of the most robust modified gravity theories to date, explaining phenomena where Milgrom's MOND theory fails, such as cluster physics and cosmology data and passing other tests that competing modified gravity theories have failed. 

This could be correct, but previous efforts to falsify modified gravity theories have resulted from a misunderstanding of the application of those theories, so it may be premature to rule it out based upon this study alone. A lack of a comparison of the errors observed to the measurement errors and any theoretical errors in the abstract, in particular, is a cause of skepticism of this result.
We perform a test of John Moffat's Modified Gravity theory (MOG) within the Milky Way, adopting the well known "Rotation Curve" method. We use the dynamics of observed tracers within the disk to determine the gravitational potential as a function of galactocentric distance, and compare that with the potential that is expected to be generated by the visible component only (stars and gas) under different "flavors" of the MOG theory, making use of a state-of-the-art setup for both the observed tracers and baryonic morphology. Our analysis shows that in both the original and the modified version (considering a self-consistent evaluation of the Milky Way mass), the theory fails to reproduce the observed rotation curve. We conclude that in none of its present formulation, the MOG theory is able to explain the observed Rotation Curve of the Milky Way.

Carolina Negrelli, Maria Benito, Susana Landau, Fabio Iocco, Lucila Kraiselburd, "Testing MOG theory in the Milky Way" (October 16, 2018).

As the introduction to the pre-print explains:
A dark component of matter has become one of the pillars of current ΛCDM model: it is invoked to explain the mismatch between the observed dynamical mass, and that inferred by observations of the visible component, of astrophysical objects over a large range of mass and spatial scales, from Galaxy Clusters [1–4] to Spiral [5–7] and Dwarf Galaxies [8], including our own, [9], and provides a consistent explanation to the power spectrum of the Cosmic Microwave Background [10], and to the formation of astrophysical structures [11]. Yet, the very nature of this dark matter is currently unknown, and none of the proposed candidates (from stable particles in extensions of the Standard Model, to primordial Black Holes [12, 13]) has been unambiguously detected yet. 
An alternative proposal to explain the mismatch observed in the data relies on a modification of the theory of gravity. Several proposals, such as MOND, TeVeS and MOG [14–16], have been able to give an explanation to phenomena around data coming from numerous and diverse sources: motion of globular and galaxy clusters [17–19] and rotation curves of spiral and dwarf galaxies [20, 21]. 
While some analysis indicate that TeVeS and MOG have difficulties explaining the Bullet cluster data [22] or to reconcile gas profile and strong–lensing measurements in well known cluster systems [23], others claim that MOG can fit both Bullet and the Train Wreck merging clusters [24, 25]. It has been pointed out that the detection of a neutron star merger by the LIGO experiment rules out MOND-like theories [26]. Recent analysis state the former being correct for bi-metric theories such as MOND and TeVeS, but not for MOG [27]. Some of the above controversies are yet to be resolved, so it is currently unclear if MOG phenomenology can offer a solution at all scales. 
In this work, we adopt an agnostic approach, and only focus on the prediction of MOG theory on the scale of Spiral Galaxies, with a specific one: our own host. In order to test the predictions of MOG theory within the Milky Way, we use state–of–the–art compilations of kinematical tracers and observationally inferred morphologies, adopted in recent studies of Dark Matter distribution [9, 28, 29], and already used to test MOND phenomenology [30].
They money figures from the MOG paper are as follows:

The authors claim a 5 sigma discrepancy, but eyeballing the data, the discrepancies between the SG flavor of MOG and the Milky Way data appear to be statistically significant only in the area where there is a transition from the Newtonian regime to the modified gravity regime at about 15 to 25 kiloparsecs from the central region, although the fit is less strong in closer core than at the edges of the galaxy (something that is also generically true of particle dark matter theories).

A previous paper by some of the same authors about MOND in 2015 (which was ultimately published) was the following, which found that MOND with a simple interpolation function did fit the Milky Way data.
Modified Newtonian dynamics (MOND) is an empirical theory originally proposed to explain the rotation curves of spiral galaxies by modifying the gravitational acceleration, rather than by invoking dark matter. Here,we set constraints on MOND using an up-to-date compilation of kinematic tracers of the Milky Way and a comprehensive collection of morphologies of the baryonic component in the Galaxy. In particular, we find that the so-called "standard" interpolating function cannot explain at the same time the rotation curve of the Milky Way and that of external galaxies for any of the baryonic models studied, while the so-called "simple" interpolating function can for a subset of models. Upcoming astronomical observations will refine our knowledge on the morphology of baryons and will ultimately confirm or rule out the validity of MOND in the Milky Way. We also present constraints on MOND-like theories without making any assumptions on the interpolating function.
Fabio Iocco, Miguel Pato, Gianfranco Bertone, "Testing modified Newtonian dynamics in the Milky Way" (October 26,2015)

Tuesday, October 16, 2018

New Astronomy Constraints On Extra Dimensions And Graviton Lifetimes

The observation of GW170817 in both gravitational and electromagnetic waves provides a number of unique tests of general relativity. One question we can answer with this event is: Do large-wavelength gravitational waves and short-frequency photons experience the same number of spacetime dimensions? 
In models that include additional non-compact spacetime dimensions, as the gravitational waves propagate, they "leak" into the extra dimensions, leading to a reduction in the amplitude of the observed gravitational waves, and a commensurate systematic error in the inferred distance to the gravitational wave source. Electromagnetic waves would remain unaffected. 
We compare the inferred distance to GW170817 from the observation of gravitational waves, dGWL, with the inferred distance to the electromagnetic counterpart NGC 4993, dEML. We constrain dGWL=(dEML/Mpc)γ with γ=1.01+0.04−0.05 (for the SHoES value of H0) or γ=0.99+0.03−0.05 (for the Planck value of H0), where all values are MAP and minimal 68% credible intervals. 
These constraints imply that gravitational waves propagate in D=3+1 spacetime dimensions, as expected in general relativity. In particular, we find that D=4.02+0.07−0.10 (SHoES) and D=3.98+0.07−0.09 (Planck). Furthermore, we place limits on the screening scale for theories with D>4 spacetime dimensions, finding that the screening scale must be greater than ∼20 Mpc. We also place a lower limit on the lifetime of the graviton of t>4.50×10^8 yr.
Pardo et al. 2018, "Limits on the number of spacetime dimensions from GW170817"

In many beyond the Standard Model theories, all particles and forces except gravity are confined to the 3+1 dimensions of General Relativity, but gravity can escape those dimensions to higher dimensions, which partially explains its relative weakness as a force. This result disfavors theories of that class.

Ancient Egyptian Astronomers

An ancient Egyptian Calendar of Lucky and Unlucky Days, the Cairo Calendar (CC), assigns luck with the period of 2.850 days. Previous astronomical, astrophysical and statistical analyses of CC support the idea that this was the period of the eclipsing binary Algol three millennia ago. However, next to nothing is known about who recorded Algol's period into CC and especially how. Here, we show that the ancient Egyptian scribes had the possible means and the motives for such astronomical observations. Their principles of describing celestial phenomena as activity of gods reveal why Algol received the title of Horus.

Monday, October 15, 2018

Quote of the Day

One of the most frequent critical remarks I have gotten on my book is that I seem confident. I was supposed, it seems, to begin each paragraph with “I'm sorry, but.”

But I am not sorry. I mean what I say. Yes, in the foundations of physics we are financing some 15,000 or so theorists who keep producing useless scientific articles because they believe the laws of nature must be beautiful. That's exactly what I am saying.

Mistaken Statistics

From xkcd. Mouseover: "Don't forget to add another term for "probability that Modified Bayes' Theorem is correct.""

Hunter-Gatherer Labels Encompass More Than One Kind Of Society

[M]any people who use “hunter-gatherers” as a category are actually lumping things that are quite different from each other. If you want to use ethnographic studies of today’s people to say anything about prehistoric people, you need to understand that any living group may be like ancient people in some ways, and very different from ancient people in other ways. Lumping across the entire category of “hunter-gatherers” doesn’t work if some of those living hunter-gatherers have economies, subsistence patterns, and social organization that is unlike anything that archaeology tells us about prehistoric groups. 
Here’s a teaser from a box that discusses the work of Steven Pinker:  
Despite the apparent magnitude of the Ju/’hoan/!Kung homicide rate, these still represent only 1.0–1.6% of overall deaths, compared to the 8–58% figure referenced in Pinker’s TED Talk.
Via John Hawks.

While the term "hunter-gatherer" can be useful in anthropology to characterize cultures and populations, it is stretched too far when used not just to apply to terrestrial hunter-gatherers, but also to maritime food production from fishing and coastal seafood collection as staples (e.g. the Native Americans of the Pacific Northwest, of the Baltic Sea area, and the Jomon of Japan prior to the arrival of farming and herding as leading means of food production).

This distinction is important, because, in pre-history, maritime food producers had relatively sedentary lifestyles, more permanent buildings and structures, and more staying power vis-a-vis farmers. The transition from terrestrial hunting and gathering to nomadic pastoralism also appears to be possible with less demographic replacement, than the transition from terrestrial hunting and gathering to farming. But, this doesn't hold true to the same extent for a transition from maritime food production to farming.

There is also a tendency to mischaracterize nomadic pastoralists as hunter-gatherers, and to fail to distinguish between terrestrial hunting and gathering society focused on big game hunting (e.g. the Neanderthals and the Clovis culture) and terrestrial hunting and gathering societies with more of a focus on small game and gathering (e.g. Cro-Magnons in Europe).

Paper Doubts Ancient African Megalakes Other Than Lake Chad

Wetlands and small lakes with one big lake still sounds a lot more like modern Wisconsin than it does like the modern Sahara.  
The Sahara was wetter and greener during multiple interglacial periods of the Quaternary, when some have suggested it featured very large (mega) lakes, ranging in surface area from 30,000 to 350,000 km2. In this paper, we review the physical and biological evidence for these large lakes, especially during the African Humid Period (AHP) 11–5 ka. Megalake systems from around the world provide a checklist of diagnostic features, such as multiple well-defined shoreline benches, wave-rounded beach gravels where coarse material is present, landscape smoothing by lacustrine sediment, large-scale deltaic deposits, and in places, tufas encrusting shorelines. Our survey reveals no clear evidence of these features in the Sahara, except in the Chad basin. Hydrologic modeling of the proposed megalakes requires mean annual rainfall ≥1.2 m/yr and a northward displacement of tropical rainfall belts by ≥1000 km. Such a profound displacement is not supported by other paleo-climate proxies and comprehensive climate models, challenging the existence of megalakes in the Sahara. Rather than megalakes, isolated wetlands and small lakes are more consistent with the Sahelo-Sudanian paleoenvironment that prevailed in the Sahara during the AHP. A pale-green and discontinuously wet Sahara is the likelier context for human migrations out of Africa during the late Quaternary.
J. Quade, et al., "Megalakes in the Sahara? A Review" 90(2) Quaternary Research 253 (September 2018) (published online June 14, 2018)

Thursday, October 11, 2018

More Problems For Sting Theory

In string theory, a paradigm shift could be imminent. In June, a team of string theorists published a conjecture which sounded revolutionary: String theory is said to be fundamentally incompatible with our current understanding of 'dark energy'. A new study has now found out that this conjecture seems to be incompatible with the existence of the Higgs particle.
From Science Daily discussing the following paper:
According to a conjecture recently put forward in [1], the scalar potential V of any consistent theory of quantum gravity satisfies a bound |∇V|/V≥O(1). This forbids de Sitter solutions and supports quintessence models of cosmic acceleration. Here, we point out that in the simplest models incorporating the standard model in addition to quintessence, with the two sectors decoupled as suggested by observations, the proposed bound is violated by 50 orders of magnitude. However, a very specific coupling between quintessence and just the Higgs sector may still be allowed and consistent with the conjecture.
Frederik Denef, Arthur Hebecker, Timm Wrase. "de Sitter swampland conjecture and the Higgs potential." 98 (8) Physical Review D (August 7, 2018). DOI: 10.1103/PhysRevD.98.086004

These papers don't by themselves, entirely rule out string theory, but they do take, what was just a year ago a "landscape" of string theories too vast to sort though, and rule out almost all of those possibilities. 

Some Puerto Ricans Have Berber Ancestry Via The Canary Islands

Maju, after a long silence on genetics issues at his blog, has conducted some very credible independent research that suggests that many Puerto Ricans have some (post-Columbian) North African Berber ancestry through admixture of that ancestry in the people of the Canary Islands who then migrated to the Caribbean islands about 500 years ago.

Wednesday, October 10, 2018

The Citation Gap In Physics Publications

Usually, I write about scientific discoveries rather than the scientific process, but today I'll take a moment to look at what is behind the gender gap in physics paper citations.

Sabine Hossenfelder, at her blog, makes a convincing effort to determine why papers by men are cited such much more often than women in physics, as a rebuttal to another investigator who concluded that women are cited less often because they are inferior physicists.

Essentially, almost all of the gap is attributable to women dropping out of active research positions in the profession entirely very early in their careers. This is common among both men and women, but it is more common among women. Among researchers who have published at least five papers, including one in the last three years, there is basically no gender based citation gap. As she explains:
[T]he vast majority of people who use the arXiv publish only one or two papers and are never heard of again. This is in agreement with the well-known fact that the majority of physicists drop out of academic careers.
The first one or two papers of a junior researcher who never publishes again is much less likely to be cited by someone else than a paper published by someone who continues to actively publish for a long time. And, women are much more likely to leave the academic physics profession than men, in part, because many leave to spend time raising children and never return to research physics positions afterwards.

Monday, October 8, 2018

A New Reference Page On Deur's Approach To Quantum Gravity

I have added a new reference page on this blog, linked in the sidebar, that explains Deur's approach to quantum gravity. This provides a single link to this theory which can be updated as necessary, so that people who use it alway get the most up to date developments about this theory.

More Higgs Boson Based Limitations On BSM Physics

The way that this is described in the abstract is ass backward, but the bottom line is that the Higgs boson mass poses serious problems to a model that has a particle with a large Yukawa coupling to the Higgs boson that is heavier than the top quark.
We revisited the scenario of electroweak baryogenesis in the presence of large Yukawa couplings, in which it was found previously that a strongly first order electroweak phase transition can occur with the Higgs mass at its observed value of 125 GeV. 
Given the sensitivity of the running of the Higgs quartic coupling on the Yukawa coupling constants, we find that the addition of order one Yukawa couplings beyond the top quark drastically lowers the scale at which the Higgs potential becomes unstable. Specifically, even with only one additional order one Yukawa coupling, the scalar potential becomes unstable already at the TeV scale, assuming the Standard Model values for the Higgs sector parameters at the electroweak scale. 
Furthermore, by assuming the Standard Model values for the Higgs sector parameters at the TeV scale, the quartic coupling constant is driven to be larger than its Standard Model value at the electroweak scale. This in turn predicts a much lighter Higgs mass than the measured value of 125 GeV. In this scenario, the strength of the electroweak phase transition is also significantly weakened.
Arianna Braconi, Mu-Chun Chen, Geoffrey Gaswint, "Revisiting Electroweak Phase Transition with Varying Yukawa Coupling Constants" (October 5, 2018).

The conclusion of the paper connects the dots, noting that:
All together, these limitations render this simplest setup with large varying Yukawa couplings not a viable mechanism for baryogenesis.
This shouldn't be surprising. 

Thursday, October 4, 2018

The Diet Of Early Anatolian Farmers

A new study looks a protein residues on pots and vessels from one of the earliest farming sites in Anatolia to figure out what these early farmers ate. There are no huge surprises, but this data paints a more vivid sense of the early Neolithic diet.
[R]esearchers analyzed vessel sherds from the West Mound of Çatalhöyük, dating to a narrow timeframe of 5900-5800 BC towards the end of the site's occupation. The vessel sherds analyzed came from open bowls and jars, as shown by reconstructions and had calcified residues on the inside surfaces. In this region today, limescale residue on the inside of cooking pots is very common. The researchers used state-of-the-art protein analyses on samples taken from various parts of the ceramics, including the residue deposits, to determine what the vessels held. 
Food proteins left behind in ceramic bowls and jars 
The analysis revealed that the vessels contained grains, legumes, meat and dairy products. The dairy products were shown to have come mostly from sheep and goats, and also from the bovine (cattle) family. While bones from these animals are found across the site and earlier lipid analyses have identified milk fats in vessels, this is the first time researchers have been able to identify which animals were actually being used for their milk. In line with the plant remains found, the cereals included barley and wheat, and the legumes included peas and vetches. The non-dairy animal products, which might have included meat and blood, came primarily from the goat and sheep family, and in some cases from bovines and deer. Interestingly, many of the pots contain evidence of multiple food types in a single vessel, suggesting that the residents mixed foods in their cuisine, potentially as porridges or soups, or that some vessels were used sequentially for different food items, or both. 
Early cheese-making 
One particular vessel however, a jar, only had evidence for dairy products, in the form of proteins found in the whey portion of milk. "This is particularly interesting because it suggests that the residents may have been using dairy production methods that separated fresh milk into curds and whey. It also suggests that they had a special vessel for holding the whey afterwards, meaning that they used the whey for additional purposes after the curd was separated," states Jessica Hendy, lead author, of the Max Planck Institute for the Science of Human History. These results show that dairying has been ongoing in this area since at least the 6th millennium BC, and that people used the milk of multiple difference species of animal, including cow, sheep and goat.
From here citing:

Jessica Hendy, et al., "Ancient proteins from ceramic vessels at Çatalhöyük West reveal the hidden cuisine of early farmers." 9(1) Nature Communications (2018) DOI: 10.1038/s41467-018-06335-6

A New Top Quark Mass Calculation From ATLAS

There is a new paper determining the top quark mass from ATLAS experiment data from the Large Hadron Collider (LHC), although it uses only fairly early data.
The mass of the top quark is measured to be mtop=172.08±0.39(stat)±0.82(syst) GeV. A combination with previous ATLAS mtopmeasurements gives mtop=172.69±0.25(stat)±0.41(syst) GeV.
From here.

From the introduction:
The mass of the top quark mtop is an important parameter of the Standard Model (SM). Precise measurements of mtop provide crucial information for global fits of electroweak parameters [1–3] which help to assess the internal consistency of the SM and probe its extensions. In addition, the value of mtop affects the stability of the SM Higgs potential, which has cosmological implications [4–6]. 
Many measurements of mtop in each tt¯ decay channel were performed by the Tevatron and LHC collaborations. The most precise measurements per experiment in the tt¯ → lepton + jets channel are mtop = 172.85 ± 0.71 (stat) ± 0.84 (syst) GeV by CDF [7], mtop = 174.98 ± 0.58 (stat) ± 0.49 (syst) GeV by D0 [8], mtop = 172.33 ± 0.75 (stat) ± 1.03 (syst) GeV by ATLAS [9] and mtop = 172.35 ± 0.16 (stat) ± 0.48 (syst) GeV by CMS [10]. Combinations are performed, by either the individual experiments, or by several Tevatron and LHC experiments [11]. In these combinations, selections of measurements from all tt¯ decay channels are used. The latest combinations per experiment are mtop = 173.16 ± 0.57 (stat) ± 0.74 (syst) GeV by CDF [12], mtop = 174.95 ± 0.40 (stat) ± 0.64 (syst) GeV by D0 [13], mtop = 172.84 ± 0.34 (stat) ± 0.61 (syst) GeV by ATLAS [14] and mtop = 172.44 ± 0.13 (stat) ± 0.47 (syst) GeV by CMS [10]. 
In this paper, an ATLAS measurement of mtop in the tt¯ → lepton + jets channel is presented. The result is obtained from pp collision data recorded in 2012 at a centre-of-mass energy of √ s = 8 TeV with an integrated luminosity of about 20.2 fb−1 . The analysis exploits the decay tt¯ → W+W−bb¯ → `νqq¯ 0bb¯, which occurs when one W boson decays into a charged lepton (` is e or µ including τ → e, µ decays) and a neutrino (ν), and the other into a pair of quarks. In the analysis presented here, mtop is obtained from the combined sample of events selected in the electron+jets and muon+jets final states. Single-top-quark events with the same reconstructed final states contain information about the top quark mass and are therefore included as signal events
The combined error in the combination is ± 0.48 GeV, which is very low. This excludes masses in excess of 173.65 GeV at the 95% confidence level, which is barely consistent with Particle Data Group indirect measurement of 173.5 GeV.

Both the new calculation and the combined measurement are lighter than previous results from all sources as of a year ago. There was a paper reviewing the most recent mass measurement in both collaborations in January of 2018. At that time, ATLAS was using only Run-1 data.

It is worth observing the range of the combined measurements from the two Tevatron experiments and the two LHC experiments: 172.44 GeV to 174.95 GeV. The spread from the midpoint of that range is ± 1.255 GeV. I think it is safe to say that somebody's error bars are probably underestimated.

It isn't at all clear why such old data is being used in a 2018 publication. As of the most recent information available ATLAS and CMS have each collected almost three times as much data as the 20.2 fb-1 relied upon in this paper.

ATLAS: 57.5 fb-1
CMS: 59.21 fb-1

Also, much of that has been at higher 13 TeV energies than the centre-of-mass energy of √ s = 8 TeV relied upon in this paper, which should also produce better data. Many papers using more recent data have been published concerning top quark physics. For example, this paper from ATLAS and this one in which:  "The data analysed correspond to 79.8 fb−1 of proton--proton collisions at a centre-of-mass energy of s√=13 TeV recorded by the ATLAS experiment at the LHC."

While the percentage error in the top quark mass determination isn't particularly high for QCD, in many circumstances, what matters is the absolute magnitude of the uncertainty, rather than the percentage uncertainty, and in terms of absolute magnitude of the error bars, the uncertainty in the top quark mass dwarfs the uncertainty in all of the other mass measurements in the Standard Model.

A May 3, 2018 paper from CMS also looks at this topic (largely identical in result and data to a January 17, 2018 paper from CMS) using more data and higher energy data:
The mass of the top quark is measured using a sample of tt events containing one isolated muon or electron and at least four jets in the final state, collected by the CMS detector using proton-proton collisions at s= 13 TeV at the CERN LHC. The events are selected from data corresponding to an integrated luminosity of 35.9 fb1. For each event the mass is reconstructed from a kinematic fit of the decay products to a \ttbar hypothesis. Using the ideogram method, the top quark mass is determined simultaneously with an overall jet energy scale factor (JSF), constrained by the mass of the W boson in qq decays. The measurement is calibrated on samples simulated at next-to-leading order matched to a leading-order parton shower. The top quark mass is found to be 172.25±0.08 (stat+JSF)±0.62 (syst) GeV. The dependence of this result on the kinematic properties of the event is studied and compared to predictions of different models of tt production, and no indications of a bias in the measurements are observed.
Other Physics News

A paper in June summed up efforts to more accurately measure the strong force coupling constant. The abstract of the paper notes that:
The latest experimental and theoretical developments in the high-precision determination of the strong coupling αs are briefly reviewed. Six groups of observables: (i) lattice QCD data, (ii) hadronic τ decays, (iii) deep-inelastic e±p data and parton distribution functions (PDF) fits, (iv) event shapes and jet rates in e+e collisions, (v) Z boson hadronic decays, and (vi) top-quark cross sections in pp collisions, are used to extract the current world-average at the Z pole mass, αs(m2Z)=0.1181±0.0011 at next-to-next-to-leading-order (NNLO), or beyond, accuracy. Additional NNLO extractions have recently appeared based on new lattice studies, the R(s) ratio in e+ehadrons, updated PDF fits, energy-energy correlations in e+e collisions, jet cross sections in e±p collisions, and the full set of pptt¯ cross sections at the LHC. Inclusion of these new data into the world-average would slightly increase its value and reduce its uncertainty to αs(m2Z)=0.1183±0.0008. Future αs extraction perspectives with permille uncertainties at future high-luminosity e+e machines -- via W and Z hadronic decays, parton fragmentation functions, and photon F2(x,Q2) structure function in γγ collisions -- are also discussed.