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) https://doi.org/10.1017/qua.2018.46

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.