Harappan, Dravidian and Indo-Aryan Legacies

Razib Khan has made some interesting posts at Brown Pundits and at his other online forums in early 2021, one of which I agree with completely, and another of which I think is probably not on target. I started writing this responsive post at the time, but go derailed. I've completed it and posted it now with only modest revision.

In the post that I fully agree with, regarding the Y-DNA of Brahmins in India, he writes at Brown Pundits (some linked added by me):

I was talking to a person of South Indian Brahmin origin today about their genetics. Over the course of the conversation, he showed me Y and mtDNA haplogroup types amongst his jati. The vast majority of the Y haplogroups were not R1a.

Brahmin groups in India seem to be about 15% to 30% steppe in their overall genome. But their Y chromosomes are usually 50% or so R1a1a-Z93. The lineage associated with Indo-Iranian pastoralists.

So what’s going on with the other haplogroups? For example, J2, L, C, G, and H?

From what I can see J2 and L are the next most frequent haplogroups after R1a1a-Z93. This tells us something. These are haplogroups found in ancient “Indus Periphery” samples. And, these two haplogroups are found at high concentrations in the northwest of the subcontinent.

It doesn’t take a Brahmin to connect the dots here. Some of the gotra as early as the Vedic period were almost certainly derived from high-status individuals in the post-IVC society. Warriors and priests in the fallen civilization of the IVC, which had likely degraded itself to a level of barbarism by the time the Indo-Aryans became ascendant.

The notion that the mostly Indo-Aryan steppe people who were a leading component of the Brahmin class also included elites from the Harappan culture which was already in some stage of collapse when they migrated to South Asia seems very likely.

Relevant Y-DNA Haplogroups

Y-DNA H is the most definitively autochthonous Y-DNA haplogroup of India and South Asia, is most common in Sri Lanka (25%), South India (26-27%) and Bangladesh (36%), fairly common in North India (25% but varying from 10% to 44% by caste with lower frequencies in high caste and higher frequencies in low caste) and Nepal (6%-39% with large regional variation and the high frequencies restricted to villages with founder effect issues). 

Y-DNA H frequencies are much lower in even nearby adjacent populations Pakistani populations have 3-8% (except the genetically distinctive the Kalash with 20%) and Afghanistan has 6-7%. But it is found in 30%-60% of men in most Roma populations of Europe (a.k.a. Gypsy, with all collective names for this people being somewhat problematic) which are derived from India.

Y-DNA L has a South Asian centered distribution but a quite different distribution than Y-DNA L, suggestive of West Asia origins. It has higher frequency among members of Dravidian castes (ca. 17-19%) (as opposed to sub-caste Dalit and "tribal" people of India) but is somewhat rarer in members of Indo-Aryan castes (ca. 5-6%). It is also present at high frequencies among the Kalash.

Y-DNA J2 and G have a distribution suggestive of West Asian origins.

Haplogroup J2 has been present in South Asia mostly as J2a-M410 and J2b-M102, since neolithic times (9500 YBP). J2-M172 was found to be significantly higher among Dravidian castes at 19% than among Indo-European castes at 11%. J2-M172 and J-M410 is found 21% among Dravidian middle castes, followed by upper castes, 18.6%, and lower castes 14%. . . . 

In Pakistan, the highest frequencies of J2-M172 were observed among the Parsis at 38.89%, the Dravidian speaking Brahui's at 28.18% and the Makrani Balochs at 24%. It also occurs at 18.18% in Makrani Siddis and at 3% in Karnataka Siddis. J2-M172 is found at an overall frequency of 16.1% in the people of Sri Lanka.

What role did Harappans play in Dravidian ethnogenesis?

I am much more skeptical of Razib Khan's conjecture in another post at Brown Pundits. He writes:

Peter Bellwood in First Farmers presents a hypothesis for the expansion of the Dravidian languages into southern India in the late Neolithic through the spread of an agro-pastoralist lifestyle through the western Deccan, pushing southward along the Arabian sea fringe. At the time I was skeptical, but now I am modestly confident that this is close to the reality. 

[The South Indian Neolithic was probably the source of the expansion of the Dravidian languages, from a focal point in southern India, not "into it", and given that it involved a mix of Sahel African domesticates, Fertile Crescent Neolithic domesticates, and a few local domesticates, I suspect that there were maritime impact from Africa, and as well as borrowings from IVC agriculturists. But the IVC culture didn't spread south sooner because the Fertile Crescent package of crops didn't thrive well enough to support a Neolithic culture by itself in southern India so the input of Sahel African domesticates was probably the critical final piece of the puzzle.]

There is always talk about “steppe” ancestry on this weblog. But there are groups that seem “enriched” from IVC ancestry, as judged by the Indus Periphery samples. The confidence is lower since we don’t have nearly as good a sample coverage…but I think I can pass on what we’ve seen so far: groups in southern Pakistan, non-Brahmin elites in South India, and some Sudra groups in Gujarat and Maharashtra, seem to be relatively enriched for IVC-like ancestry. Then there is the supposed existence of Dravidian toponyms in Sindh, Gujarat, and Maharashtra. And, their total absence in the Gangetic plain.

[Discussed below.] 

There have been decades of debate about Brahui. I’ve looked closely at Brahui genetics, and they are no different from the Baloch. Combined with evidence from Y chromosomes (the Baloch and Brahui have some of the highest frequencies of haplogroups found in IVC-related ancient DNA), I doubt the thesis they are medieval intruders (if they are, their distinctive genes were totally replaced).

[The case that they are medieval intruders whose distinctive genes were totally replaced is the stronger one as discussed below.] 

Genetically, we know that some southern tribes, such as the Pulliyar, have some IVC-related ancestry. But other groups, such as Reddy in Andhra Pradesh, have a lot more. How does this cline emerge? 

[Discussed below.] 

My conjecture is that there were several movements of “Dravidian” people from Sindh and Gujarat into southern India, simultaneous with the expansion of Vedic Aryans to the north into the Gangetic plain. The region the Vedic Aryans intruded upon, Punjab, was not inhabited by Dravidian speakers. Like Mesopotamia, the Indus Valley Civilization was probably multi-lingual, despite broad cultural affinities developed over time.

[I disagree with almost all of this as discussed below.] 

I don't disagree that he is correct on the distribution of Dravidian toponyms or the enhanced levels of IVC-type genetics where he notes it. But I do disagree with the narrative he provides for those facts.

The strongest evidence for a ca. 1000 CE origin for the Brahui, rather than a deep and ancient one, is linguistic. The Brahui language contains linguistic innovations not present in the Dravidian languages until after about 1000 CE that are specific to the North Dravidian language of which it is one.

All of the communities with North Dravidian language speakers also have traditions of an origin in the Deccan Peninsula, which are more likely to have persisted over time in a more recent migration.

Brahui is spoken beyond and outside the range of widespread Dravidian toponyms, which once established tend to be stable.

Obviously, the genetics suggests a scenario of elite language shift with only a little, possibly no longer discernible due to dilution, demic contribution to the population genetics of the founding elite. But, this is not unprecedented. Something similar took place in Hungary in about the same era. In Turkey, also in roughly the same era, there was language shift with a quite modest ethnically Turk genetic contribution, and more than twenty centuries before that, language shift to the Hittite language was also elite dominated. In South Asia, there was more demic impact, but the language shift to Sanskrit derived Indo-Aryan languages was still elite dominated. This also happened in post-Columbian Latin America.

In the Indus River Valley itself and adjacent areas, IVC ancestry is likely due to Harappan migration (a society that was not Dravidian language speaking although it had contacts with Dravidian language speakers) prior to the arrival of the Indo-Aryans, and this is probably the source of IVC ancestry in the Brahui.

The archaeological evidence and ancient seals and limits historical accounts from Mesopotamia, all tend to disfavor the conclusion that the "Indus Valley Civilization was probably multi-lingual", and instead tend to favor a linguistic, cultural, and political unity maintains from the outset of its adoption of Fertile Crescent agriculture that persisted until close to its collapse. There isn't evidence of war or war-like fortifications in the core IVC region until very late, which political unity which usually leads to linguistic and cultural unity, can produce.

There is also essentially no evidence for the narrative that "there were several movements of “Dravidian” people from Sindh and Gujarat into southern India, simultaneous with the expansion of Vedic Aryans to the north into the Gangetic plain." 

The evidence instead suggests that the migrations went the other way and ultimately collapsed in some areas, leaving only toponyms and a few isolated linguistic communities like the Brahui and other Northern Dravidian enclaves from a high water mark of Dravidian expansion from South India.

Moorjani, et al., "Genetic Evidence for Recent Population Mixture in In India" 93 American Journal of Human Genetics 422-438 (September 5, 2013) estimated the admixture history of India based upon an analysis of a moderate sized samples of modern Indian genomes. 

Moorjani found that the timing of admixture was later than the South Asian Neolithic era and was in some cases consistent with only a single wave of admixture based not only on Linkage Disequilibrium methods (which are less prone to uncertainty that mutation rate methods) but also by confirming that the components that did admix were consistent with being from the same autosomal gene pools as opposed to different ones as would be expected if there were two waves of admixture from different sources. 

Ancestral North Indian (ANI) ancestry is a mix of steppe ancestry and ancestry from co-opted IVC people. The admixture into Dravidian peoples is older, reflecting a broad sweep of the subcontinent that went unchecked, but presumably was then beaten back in a Dravidian reconquest of Southern India, which accounts for both the fact that these regions don't speak Indo-Aryan languages now (although the pro-Hindu religion stuck), and the deceptively young apparent age of the Dravidian language family due to the extinction of all Dravidian dialects except the relict core from which the reconquest was mounted. In contrast, in linguistically Indo-Aryan North India, there was a second pulse of steppe introgression that came later. 

The higher ratio of IVC genetics to steppe ancestry in South Indian Brahmins likely reflects a narrative in which lower status post-IVC local elites sought positions leading the conquest of South India at a greater rate than higher status steppe elites, because they had better opportunities for promotion there, and may also, more conjecturally, found the climate less out of their comfort zone than the steppe elites who were already at the fringe of their comfort zones in North India. 

The abstract and body text of Moorjani (2013) notes that:

Genetic evidence indicates that most of the ethno-linguistic groups in India descend from a mixture of two divergent ancestral populations: Ancestral North Indians (ANI) related to West Eurasians (people of Central Asia, the Middle East, the Caucasus, and Europe) and Ancestral South Indians (ASI) related (distantly) to indigenous Andaman Islanders. The evidence for mixture was initially documented based on analysis of Y chromosomes and mitochondrial DNA and then confirmed and extended through whole-genome studies.

Archaeological and linguistic studies provide support for the genetic findings of a mixture of at least two very distinct populations in the history of the Indian subcontinent. The earliest archaeological evidence for agriculture in the region dates to 8,000–9,000 years before present (BP) (Mehrgarh in present-day Pakistan) and involved wheat and barley derived from crops originally domesticated in West Asia. The earliest evidence for agriculture in the south dates to much later, around 4,600 years BP, and has no clear affinities to West Eurasian agriculture (it was dominated by native pulses such as mungbean and horsegram, as well as indigenous millets). 

Linguistic analyses also support a history of contacts between divergent populations in India, including at least one with West Eurasian affinities. Indo-European languages including Sanskrit and Hindi (primarily spoken in northern India) are part of a larger language family that includes the great majority of European languages. In contrast, Dravidian languages including Tamil and Telugu (primarily spoken in southern India) are not closely related to languages outside of South Asia. Evidence for long-term contact between speakers of these two language groups in India is evident from the fact that there are Dravidian loan words (borrowed vocabulary) in the earliest Hindu text (the Rig Veda, written in archaic Sanskrit) that are not found in Indo-European languages outside the Indian subcontinent.

Although genetic studies and other lines of evidence are consistent in pointing to mixture of distinct groups in Indian history, the dates are unknown. Three different hypotheses (which are not mutually exclusive) seem most plausible for migrations that could have brought together people of ANI and ASI ancestry in India. The first hypothesis is that the current geographic distribution of people with West Eurasian genetic affinities is due to migrations that occurred prior to the development of agriculture. Evidence for this comes from mitochondrial DNA studies, which have shown that the mitochondrial haplogroups (hg U2, U7, and W) that are most closely shared between Indians and West Eurasians diverged about 30,000–40,000 years BP. The second is that Western Asian peoples migrated to India along with the spread of agriculture; such mass movements are plausible because they are known to have occurred in Europe as has been directly documented by ancient DNA. Any such agriculture related migrations would probably have begun at least 8,000–9,000 years BP (based on the dates for Mehrgarh) and may have continued into the period of the Indus civilization that began around 4,600 years BP and depended upon West Asian crops. The third possibility is that West Eurasian genetic affinities in India owe their origins to migrations from Western or Central Asia from 3,000 to 4,000 years BP, a time during which it is likely that Indo-European languages began to be spoken in the subcontinent. A difficulty with this theory, however, is that by this time India was a densely populated region with widespread agriculture, so the number of migrants of West Eurasian ancestry must have been extraordinarily large to explain the fact that today about half the ancestry in India derives from the ANI. It is also important to recognize that a date of mixture is very different from the date of a migration; in particular, mixture always postdates migration. Nevertheless, a genetic date for the mixture would place a minimum on the date of migration and identify periods of important demographic change in India. . . . 

Most Indian groups descend from a mixture of two genetically divergent populations: Ancestral North Indians (ANI) related to Central Asians, Middle Easterners, Caucasians, and Europeans; and Ancestral South Indians (ASI) not closely related to groups outside the subcontinent. The date of mixture is unknown but has implications for understanding Indian history. We report genome-wide data from 73 groups from the Indian subcontinent and analyze linkage disequilibrium to estimate ANI-ASI mixture dates ranging from about 1,900 to 4,200 years ago. In a subset of groups, 100% of the mixture is consistent with having occurred during this period. . . . 

By using f4 ratio estimation that analyzes allele frequency correlation patterns to infer mixture proportions, we estimate that ANI ancestry along the Indian cline ranges from as low as 17% (Paniya) to as high as 71% (Pathan). Traditionally lower caste, Dravidian, and tribal groups tend to have lower proportions of ANI ancestry than traditionally upper caste and Indo-European groups (p < 0.001). . . . 

To date ANI-ASI mixture, we capitalized on the fact that admixture between two populations generates allelic association (linkage disequilibrium [LD]) between pairs of SNPs. The LD decays at a constant rate as recombination breaks down the contiguous chromosomal blocks inherited from the ancestral mixing populations. The expected value of the admixture LD is related to the genetic distance between SNPs (the probability of recombination per generation between them) and the time that has elapsed since mixture. We previously reported simulations showing that dating population mixture based on the scale of admixture LD is robust to the use of imperfect surrogates for the ancestral populations, fine-scale errors in the genetic map, and a history of founder events in the admixed population, and is able to provide unbiased estimates for the dates of events up to 500 generations ago. We confirmed this by using new simulations with demographic parameters relevant to India. 

We estimated admixture dates for all the groups on the Indian cline with more than five samples (a minimum sample size is important for measuring LD with precision). We observe a decay of LD with genetic distance for all groups. By fitting an exponential function using least-squares (via rolloff), our point estimates for the dates range from 64 to 144 generations ago, or 1,856 to 4,176 years assuming 29 years per generation.

We highlight two implications of these dates. 

First, nearly all groups experienced major mixture in the last few thousand years, including tribal groups like the Bhil, Chamar, and Kallar that might be expected to be more isolated. 

Second, the date estimates are typically more recent in Indo-Europeans (average of 72 generations) compared to Dravidians (108 generations). A jackknife estimate of the difference is highly significant at 35 ± 8 generations (Z = 4.5 standard errors from zero). A possible explanation is a secondary wave of mixture in the history of many Indo-European groups, which would decrease the estimated admixture date. . . . 

A caveat for these dating analyses is that they assume that the entire admixture occurred instantaneously (or over a small number of generations). However, population mixture can be noninstantaneous, such that the date we obtain from our method may actually be an average of multiple dates spread out over a substantial period. One way to detect a history of noninstantaneous gene flow is to fit a sum of exponential functions to the decay of admixture LD and to show that this provides a better fit to the data than a single exponential function, as we in fact find for the Kashmiri Pandit, Kshatriya, Sindhi, and Pathan. However, even if we fail to detect a nonexponential decay, we cannot rule out noninstantaneous gene flow, because the decay can be noisy, making the statistical detection of a mixture of exponential functions difficult. 

A particularly important scenario we could not rule out by this method is that several thousand years ago, Indian groups were already admixed, and thus the LD decay we detect is the result of mixture of already admixed ancestral groups with different proportions of ANI ancestry. If the initial admixture was more than 10,000 years old, the associated admixture LD would have decayed to such a short distance that our methods would have poor power to detect it. The LD we measure might in this case reflect only the final admixture events, complicating interpretation of the results. . . . 

[W]e identified previously undetected complexity in Indian history, with many sets of Indian groups not consistent with a simple ANI-ASI admixture. . . . . we find that the Indian groups consistent with simple ANI-ASI mixture are most often from tribal and traditionally lower-caste groups. Middle- and upper-caste groups tend to have evidence of more complex histories, with signals of multiple layers of ANI ancestry from slightly different ANI ancestral populations. Further evidence for multiple waves of admixture in the history of many traditionally middle- and upper-caste groups (as well as Indo-European and northern groups) comes from the more recent admixture dates we observe in these groups and the fact that a sum of two exponential functions often produces a better fit to the decay of admixture LD than does a single exponential. Evidence for multiple components of West Eurasian-related ancestry in northern Indian populations has also been reported by Metspalu et al. based on clustering analysis. 

Focusing on the largest set of Indo-Europeans (four groups) and the largest set of Dravidians (five groups) consistent with mixture of the same ANI and ASI ancestral populations, we find that the expected and observed admixture LD amplitudes are equivalent to within the limits of our resolution. . . . our data are consistent with all of the ANI ancestry in some selected sets of Indians (including groups speaking both Indo-European and Dravidian languages) being due to admixture events that we can date to within the past few thousand years. Accounting for statistical uncertainty, we estimate that the ANI ancestry that cannot be explained by a single wave of admixture in the last few thousand years has a 95% confidence interval (truncated to 0) of 0%–19% for Indo-Europeans and 0%–16% for Dravidians. Thus, all the ANI ancestry in some groups is consistent with deriving from admixture events that have occurred in the past few thousand years. 

Our analysis documents major mixture between populations in India that occurred 1,900–4,200 years BP, well after the establishment of agriculture in the subcontinent. We have further shown that groups with unmixed ANI and ASI ancestry were plausibly living in India until this time. This contrasts with the situation today in which all groups in mainland India are admixed. 

These results are striking in light of the endogamy that has characterized many groups in India since the time of mixture. For example, genetic analysis suggests that the Vysya from Andhra Pradesh have experienced negligible gene flow from neighboring groups in India for an estimated 3,000 years. Thus, India experienced a demographic transformation during this time, shifting from a region where major mixture between groups was common and affected even isolated tribes such as the Palliyar and Bhil to a region in which mixture was rare. Our estimated dates of mixture correlate to geography and language, with northern groups that speak Indo-European languages having significantly younger admixture dates than southern groups that speak Dravidian languages. This shows that at least some of the history of population mixture in India is related to the spread of languages in the subcontinent. 

One possible explanation for the generally younger dates in northern Indians is that after an original mixture event of ANI and ASI that contributed to all present-day Indians, some northern groups received additional gene flow from groups with high proportions of West Eurasian ancestry, bringing down their average mixture date. This hypothesis would also explain the nonexponential decays of LD in many northern groups and their higher proportions of ANI ancestry. . . .

The dates we report have significant implications for Indian history in the sense that they document a period of demographic and cultural change in which mixture between highly differentiated populations became pervasive before it eventually became uncommon. The period of around 1,900–4,200 years BP was a time of profound change in India, characterized by the deurbanization of the Indus civilization, increasing population density in the central and downstream portions of the Gangetic system, shifts in burial practices, and the likely first appearance of Indo-European languages and Vedic religion in the subcontinent. The shift from widespread mixture to strict endogamy that we document is mirrored in ancient Indian texts. The Rig Veda, the oldest text in India, has sections that are believed to have been composed at different times. The older parts do not mention the caste system at all, and in fact suggest that there was substantial social movement across groups as reflected in the acceptance of people with non-Indo-European names as kings (or chieftains) and poets. The four-class (varna) system, comprised of Brahmanas, Ksatriyas, Vaisyas, and Sudras, is mentioned only in the part of the Rig Veda that was likely to have been composed later (book 10). The caste (jati) system of endogamous groups having specific social or occupational roles is not mentioned in the Rig Veda at all and is referred to only in texts composed centuries after the Rig Veda, for example, the law code of Manu that forbade intermarriage between castes. Thus, the evolution of Indian texts during this period provides confirmatory support as well as context for our genetic findings. 

It is also important to emphasize what our study has not shown. Although we have documented evidence for mixture in India between about 1,900 and 4,200 years BP, this does not imply migration from West Eurasia into India during this time. On the contrary, a recent study that searched for West Eurasian groups most closely related to the ANI ancestors of Indians failed to find any evidence for shared ancestry between the ANI and groups in West Eurasia within the past 12,500 years (although it is possible that with further sampling and new methods such relatedness might be detected). 

An alternative possibility that is also consistent with our data is that the ANI and ASI were both living in or near South Asia for a substantial period prior to their mixture. Such a pattern has been documented elsewhere; for example, ancient DNA studies of northern Europeans have shown that Neolithic farmers originating in Western Asia migrated to Europe about 7,500 years BP but did not mix with local hunter gatherers until thousands of years later to form the present-day populations of northern Europe. 

The most remarkable aspect of the ANI-ASI mixture is how pervasive it was, in the sense that it has left its mark on nearly every group in India. It has affected not just traditionally upper-caste groups, but also traditionally lower-caste and isolated tribal groups, all of whom are united in their history of mixture in the past few thousand years. 

The Self-Coupling of the Higgs Boson

In the Standard Model, all of the properties of the Higgs boson, except its mass, can be calculated from first principles, and the global average measurement of its rest mass is 125.10 ± 0.14 GeV, a precision of about one part per 894.

In the Standard Model, the strength of the interactions of the Higgs boson with the fundamental particles, their so called "Yukawas" is proportional to the rest mass of those particles. The Higgs field also gives mass to the Higgs boson itself in proportion to its rest mass in the Standard Model.

The strength of the coupling of the Higgs boson with itself that is observed experimentally can can compared to a benchmark Standard Model value it has at its measured value, with the value equal to exactly one if the the experimentally measured value matched the predicted one. 

If the experimentally measured value were higher, it would be proportionately more than one. If the experimentally measured value were lower, it would be proportionately less than one. It the experimentally measured value were opposite in direction to the exacted value (e.g. by analogy, if the electromagnetic force were repulsive when it was expected to be attractive) then the value is negative.

Tommaso Dorigo reports on the best measurement of the Higgs boson self-coupling to date, from was published by the CMS Collaboration at the Large Hadron Collider (LHC) back in November. Their measurement bounds the Higgs self-coupling to be between -2.7 and 8.6 (relative to a benchmark value of 1.0) within 95% confidence intervals. 

This is consistent with the Standard Model prediction, but with lots of uncertainty because it is a hard measurement to make of something that can only happen with any frequency towards the high end of the energy scales that the LHC can produce. Also, while this isn't a terribly tight constraint (many of its interactions are constrained much more tightly), it is sufficiently tight to rule out a large swath of beyond the Standard Model theories that predicted more dramatic deviations from the Standard Model prediction.

Combining the observed strength of all Higgs boson interactions observed to date, in which 1.0 is the Standard Model prediction, the experimentally observed values so far have been 1.13 ± 0.06, a slight tension with the Standard Model prediction, but still remarkably close to properties predicted theoretically in the 1960s, more than half a century ago, when scientists still used slide rules and punch card mainframe computers to do calculations.

String Theory Is Still Vaporware

String Theory has many problems. 

It has six (or in some accounts seven) space-time dimensions too many. It predicts lots of new supersymmetric particles and forces (even without adding in gravity) that we haven't observed (experimental exclusions for such particles were reviewed at this post). It needs to explain why we don't observe proton decay. It predicts a scalar-tensor theory of gravity that isn't observed. It is happiest in an "anti-deSitter" universe which is roughly equivalent to a negative cosmological constant when the measured value of the cosmological constant of General Relativity is positive. The physics journalist for Forbes magazine recaps these issues.

Ethan Siegel has an excellent piece on the basic problem with string theory (to the extent it’s well-defined, it has too large a (super)symmetry group and too many dimensions, no explanation for how to recover 4 space-time dimensions and observed symmetry groups).

Here’s why the hope of String Theory, when you get right down to it, is nothing more than a broken box of dreams.

From Not Even Wrong. 

[T]here are a lot of symmetries that you could imagine would be respected, but simply aren’t. You could imagine that the three forces of the Standard Model would unify into a single one at high energies in some sort of grand unification. You could imagine that for every fermion, there would be a corresponding boson, as in supersymmetry. And you can imagine that, at the highest energies of all, that even gravity gets unified with the other forces in a so-called “theory of everything.”

That’s the brilliant, beautiful, and compelling idea at the core of String Theory. It’s also has absolutely no experimental or observational evidence in favor of it at all. . . .  

Many ideas — such as grand unification and supersymmetry — would involve adding new particles and interactions, but would also lead to experimental consequences like proton decay or the presence of additional particles or decay pathways not seen at colliders. The fact that these predictions haven’t panned out helps us place constraints on both of these ideas. 

String theory, though, goes many steps farther than either grand unification or what we know as supersymmetry does.

For grand unification, the idea is to take the three forces in the Standard Model and embed them into a larger, more symmetric structure. Instead of the particles we know with the interactions we know — with multiple disjoint frameworks corresponding to each of the forces — grand unification tries to fit the Standard Model inside a larger structure.

This might just sound like words to you, but the group theory representation of the Standard Model is SU(3) × SU(2) × U(1), where the SU(3) is the color (strong force) part, the SU(2) is the weak (left-handed) part, and the U(1) is the electromagnetic part. If you want to unify these forces into a larger framework, you’ll need a bigger group.

You can take the route of Georgi-Glashow [SU(5)] unification, which predicts new, super-heavy bosons that couple to both quarks and leptons simultaneously. You can take the route of Pati-Salam [SU(4) × SU(2) × SU(2)] unification, which adds in the right-handed particles, making the Universe left-right symmetric instead of preferring a left-handed neutrino. Or you can go even larger: to SU(6), SO(10), or still larger groups, so long as they contain the Standard Model within them.

The problem, of course, is that the larger you go, the more stuff there is to get rid of, and the more explaining there is to do if we want to understand why these extra components to reality don’t show themselves, either directly or indirectly, in our experiments, measurements, and observations of the Universe. The proton doesn’t decay, so either the simplest model of grand unification is wrong, or you have to pick a more complicated model and find a way to evade the constraints that rule out the simpler models.

If you want to talk about unification and group theory in the context of String Theory, however, your group suddenly has to become enormous! You can fit it into one of the SO groups, but only if you go all the way up to SO(32). You can fit it into two of the exceptional groups crossed together — E(8) × E(8) — but that’s enormous, as each E(8) contains and is larger than SU(8), mathematically. This isn’t to say it’s impossible that String Theory is correct, but that these large groups are enormous, like a block of uncut marble, and we want to get just a tiny, perfect statuette (our Standard Model, and nothing else) out of it.

Similarly, there’s an analogous problem that arises with supersymmetry. Typically, the supersymmetry you hear about involves superpartner particles for every particle in existence in the Standard Model, which is an example of a supersymmetric Yang-Mills field theory where N=1. The biggest problem is that there should be additional particles that show up at the energy scales that reveal the heaviest Standard Model particles. There should be a second Higgs, at least, below 1,000 GeV. There should be a light, stable particle, but we haven’t observed it yet. Even without String Theory, there are many strikes against N=1 supersymmetry.

The Standard Model, without supersymmetry, is simply the N=0 case. But if we want String Theory to be correct, we need to make nature even more symmetric than standard supersymmetry predicts: String Theory contains a gauge theory known as N=4 supersymmetric Yang-Mills theory. There’s even more stuff to hand-wave away if we want String Theory to be correct, and it all has to disappear to not conflict with the observations we’ve already made of the Universe we have.

But one of the biggest challenges for String Theory is something that’s often touted as it’s big success: the incorporation of gravity. It’s true that String Theory does, in a sense, allow gravity to be merged with the other three forces into the same framework. But in the framework of String Theory, when you ask, “what is my theory of gravity,” you don’t get the answer that Einstein tells us is correct: a four-dimensional tensor theory of gravity. . . . 

So what does String Theory give you? Unfortunately, it doesn’t give you a four-dimensional tensor theory of gravity, but rather a 10-dimensional scalar-tensor theory of gravity. Somehow, you have to get rid of the scalar part, and also get rid of six extra (spatial) dimensions.

We had, as proposed 60 years ago, an alternative to Einstein’s General Relativity that did incorporate a scalar as well: Brans-Dicke gravity. According to Einstein’s original theory, General Relativity was needed to explain the orbit of Mercury, and why its perihelion (where it came closest to the Sun) precessed at the rate that it did. We observed a total precession of ~5600 arc-seconds per century, where ~5025 were due to the precession of the equinoxes and ~532 were due to the other planets. Einstein’s General Relativity predicted the other ~43, and that was the slam-dunk prediction he finally made in 1915 that catapulted the eclipse expedition into infamy. The 1919 revelation that light bent starlight was the ultimate confirmation of our new theory of gravity.

But by the late 1950s, some observations of the Sun had indicated that it wasn’t spherical, but rather was compressed along its poles into an oblate spheroid. If that were the case, Brans and Dicke argued, then that observed amount of departure from a perfect sphere would create an additional 5 arc-seconds of precession per century that differed from Einstein’s predictions. How to fix it? Add in a scalar component to the theory, and a new parameter: ω, the Brans-Dicke coupling constant. If ω was about 5, everything would still turn out right.

Of course, the Sun actually is a perfect sphere to a much better degree than even the Earth, and those observations were incorrect. Given the modern constraints that we have, we now know that ω must be greater than about 1000, where the limit as ω → ∞ gives you back standard General Relativity. For String Theory to be correct, we have to “break” this 10 dimensional Brans-Dicke theory down to a four dimensional Einsteinian theory, which means getting rid of six dimensions and this pesky scalar term and the coupling, ω, all of which must go away.

What all of this means is that if String Theory is correct, we have to start with a Universe that’s highly symmetric and very unlike the Universe we have today. This Universe, at some early time at very high energies, had 10 dimensions to it, had a scalar gravity component in addition to the tensor component, was unified into some very large group like SO(32) or E(8) × E(8), and was described by a maximally supersymmetric (N = 4) Yang-Mills theory.

If String Theory is correct, then somehow — and nobody knows how — this ultra-symmetric state broke, and it broke incredibly badly. Six of the dimensions disappeared, and the scalar gravity component stopped mattering. The large, unified group broke very badly, leaving only our relatively tiny Standard Model, SU(3) × SU(2) × U(1), behind. And that supersymmetric Yang-Mills Theory broke so badly that we don’t see any evidence for a single supersymmetric particle today: just the regular Standard Model. . . . 

It may be interesting and promising, but until we can solve String Theory in a meaningful way to get the Universe we observe out of it, we have to admit to ourselves what String Theory truly is: a large, unbroken box that must somehow crumble in this particular, intricate fashion, to recover the Universe we observe. Until we understand how this occurs, String Theory will only remain a speculative dream.

There are additional problems that aren't discussed in the article. 

One is the fact that we live in a universe with deSitter rather than anti-deSitter topology. Another is the fact that there are myriad possible versions called vacua, the vast majority of which have an anti-deSitter topology which are called the "swampland" because most of them are starkly incompatible with observed reality.

Another is the fact that experimental evidence has established that supersymmetry, which is a necessary sub-component of string theory, was conceived to solve a problem that we now know that it doesn't solve in the way that it was intended to, called the "hierarchy problem" because even if supersymmetric particles and extra Higgs bosons exist, the Large Hadron Collider has established that they are too heavy to solve the "problem" that they were devised to solve.

There may be glimmers of useful mathematical or physical insight that one can gain from studying it, but it is along the lines of the insights into English grammar and vocabulary that you get from studying French for a year or two, that has no meaningful connection to the real world and doesn't allow you to do anything worthwhile.

But in the end analysis, there is a substantial and growing faction of the fundamental physics community, including both professional physicists and educated laypeople like myself, who have concluded that String Theory and Supersymmetry are both dead ends that have wasted immense amounts of time and resources of a lot of very smart people.

The History of Chess

The map below shows the spread of chess out of India. Ironically, Russia, home of many of the greatest chess legends, was one of the last places that chess arrived.

The BBC On "Cracks In Cosmology"

A January 13, 2021 article in issue 358 of BBC Science Focus Magazine entitled "The Cracks in Cosmology: Why Our Universe Doesn't Add Up?" by Marcus Chown nicely sums of the LambdaCDM Standard Model of Cosmology and some key lines of observational evidence indicating that it is flaws.

The model, in his simplified terms in which he explains it, consists of the Big Bang, plus inflation, plus dark matter, plus dark energy. Inflation smooths out the universe, dark energy speeds its expansion, dark matter shapes the cosmic background radiation patterns, aids in galaxy formation, and leads to phenomena like galactic rotation curves that aren't Keplerian and galactic clusters that are much heavier than their visible matter.

He identifies three notable recent flaws in this model in observations newly made in 2020.

First, he points to the gravitational lensing of subhalos in galactic clusters recently observed to be much more compact and less "puffy" than LambdaCDM would predict.

Secondly, he points to a KIDS telescope observation of very large scale structure which shows it to be 8.3% smoother (i.e. less clumpy) than predicted by LambdaCDM.

Third, he points to the Hubble tension (see, e.g., here) that shows that Hubble's constant, which is a measure of the expansion rate of the universe, is about 10% smaller when measured via cosmic microwave background radiation (with a small margin of error) than when measured by a wide variety of measures at times much more removed from the Big Bang that the time at which the cosmic microwave background came into being.

He then provides a laundry list of ways that the model or the data collection could be flawed.

Other Problems With LambdaCDM

Honestly, these aren't even necessarily the most serious of the problems, and many of the big problems have been known for a long time. Among problems with the Cold Dark Matter model, especially at the galaxy and galactic cluster scale. 

* The halo shapes are usually wrong (too cuspy and not in the NFW distribution predicted by the theory). 

* The correspondence between the distribution of ordinary matter and inferred dark matter in galaxies is too tight; truly collisionless dark matter should have less of a tight fit in its distribution to ordinary matter distributions than is observed. This is also the case in galaxy clusters. 

* It doesn't explain systemic variation in the amount of apparent dark matter in elliptical galaxies, or why spiral galaxies have smaller proportions of ordinary matter than elliptical galaxies in same sized inferred dark matter halos, or why thick spiral galaxies have more inferred dark matter than thin ones.

* It doesn't explain why satellite galaxies are consistently located in a two dimensional plane relative to the core galaxy. 

* Not as many satellite galaxies are observed as predicted, or why the number of satellite galaxies is related to budge mass in spiral galaxies.

* The aggregate statistical distribution of galaxy types and shapes, called the "halo mass function" is wrong.

* Galaxies are observed sooner after the Big Bang than expected (see also here).

* The temperature of the universe measured by 21cm background radio signals is consistent with no dark matter and inconsistent with sufficient dark matter for LambdaCDM to work. 

* It doesn't explain strong statistical evidence of an external field effect that violates the strong equivalence principle. 

* Observations are inconsistent with the "Cosmological principle" that LambdaCDM predicts, which is "the notion that the spatial distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale.

* It doesn't do a good job of explaining the rare dwarf galaxies (that are usually dark matter dominated) that seem to have no dark matter. 

* It doesn't explain deficits of X-ray emissions in low surface brightness galaxies.

* It predicts too few galaxy clusters.

* It gets globular cluster formation wrong (see also here).

* It doesn't explain evidence of stronger than expected gravitational effects in wide binary stars.

* There are too many galaxy clusters colliding at speeds that are too high relative to each other. 

* It doesn't explain the "cosmic coincidence" problem (that the amount of ordinary matter, dark matter and dark energy are of the same order of magnitude at this moment in the history of the Universe since the Big Bang).

* There are potential unresolved system problems in current dark energy measurements.

* Every measure of detecting it directly has come up empty (including not just dedicated direct detection experiments but particle collider searches, searches for cosmic ray signals of dark matter annihilation, and indirect searches combined with direct searches and also here). But it requires particles and forces of types not present in the Standard Model or general relativity to fit what is observed.

* It has made very few ex ante predictions and those it has made have often been wrong, while MOND has a much better track record despite being far simpler (which should matter).

* There are alternative modified gravity theories to toy model MOND that explain pretty much everything that dark matter particle theories do (including, e.g., the cosmic coincidence problem, clusters, the Bullet Cluster, galaxy formation, the cosmic background radiation pattern observed), with fewer problems and anomalies.

Spinach

Linguistically, at least, the words for the leafy green vegetable known as "Spinach" in both Indo-European languages like English and French, Afro-Asiatic languages, and in Chinese, derives from a Persian word. This is consistent with what we know about the origins of this domesticated plant, which was domesticated there about two thousand years ago, and then dispersed globally over the last fifteen hundred years or so:

Spinach (Spinacia oleracea) is a leafy green flowering plant native to central and western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. . . . 

Spinach is thought to have originated about 2000 years ago in ancient Persia from which it was introduced to India and ancient China via Nepal in 647 AD as the "Persian vegetable". In AD 827, the Saracens introduced spinach to Sicily. The first written evidence of spinach in the Mediterranean was recorded in three 10th-century works: a medical work by al-Rāzī (known as Rhazes in the West) and in two agricultural treatises, one by Ibn Waḥshīyah and the other by Qusṭus al-Rūmī. Spinach became a popular vegetable in the Arab Mediterranean and arrived in Spain by the latter part of the 12th century, where Ibn al-ʻAwwām called it raʼīs al-buqūl, 'the chieftain of leafy greens'. Spinach was also the subject of a special treatise in the 11th century by Ibn Ḥajjāj.

Spinach first appeared in England and France in the 14th century, probably via Spain, and gained common use because it appeared in early spring when fresh local vegetables were not available. Spinach is mentioned in the first known English cookbook, the Forme of Cury (1390), where it is referred to as 'spinnedge' and/or 'spynoches'. During World War I, wine fortified with spinach juice was given to injured French soldiers with the intent to curtail their bleeding.

The Persian (i.e. Iranian) word for Spinach, however, has origins much deeper than its domestication about the year 0 CE (when "Middle Iranian" was one of the main languages spoken in Persia, with the cutoff between Middle Iranian and Old Iranian often put at around 400 BCE):

Kulturwort of Iranian origin. According to Asatrian, there were probably two forms in late Middle Iranian, *ispanāg (or *ispināg) and (the dialectal) *ispanāx (or *ispināx), yielding Arabized forms إِسْفَنَاج / إِسْفِنَاج‎ (ʾisfanāj / ʾisfināj) and إِسْفَنَاخ / إِسْفِنَاخ‎ (ʾisfanāḵ / ʾisfināḵ), which were popularized in Persian and Arabic, respectively (alternative forms with پ‎ (p) are directly from Middle Iranian). 

The Old Iranian form would be *spināka-, *spinaka- (compare Northern Kurdish sping), from the root *spin- (Northwestern Iranian), *sin- (Southwestern Iranian), ultimately from the Proto-Iranian *spai- (*spi-), from Proto-Indo-European *spey- (“thorn-like”) (*spi-), which are also reflected in Latin spina, Persian سنجد‎ (senjed), Ossetian сындз (synʒ), синдзӕ (sinʒæ, “thorn”), Baluchi (šinž), Central Iranian šeng, Kermani šank (“thorn”). Also akin to Semnani esbenāγa.

According to Cabolov, related to Northern Kurdish siping (“meadow salsify, possibly also spinach”) and Persian سپند‎ (sipand, “wild rue”).

The derivation of the root word for Spinach from words meaning thorny or spiky reflects the appearance of its seeds:

Spinach seeds are generally referred to as round – which is relatively smooth – or prickly, with seeds that are sharp and pointed borne in a capsule with several spines. If you have ever tried removing the seeds of prickly spinach from the stalk by hand, you quickly learned why it is called prickly. It hurts.

According to the UN Food & Agriculture Organization, in 2018, world production of spinach was 26.3 million tonnes, with China alone accounting for 90% of the total.

New Muon g-2 Measurement Expected February 2021

FNAL-E989 first announcement in February 2021

Per Asian Twitter via Physics Forums.

This is arguably the most important fundamental physics measurement since the discovery of the Higgs boson. It has the potential to either (1) unambiguously establish that the Standard Model of Particle Physics is missing undiscovered new physics of some well quantified type (still only enough to generate parts be million irregularities on the measured value), if the consensus theoretical estimate and the experimental measurement of muon g-2 differ by five sigma or more, or instead, (2) profoundly limit any form of low energy new physics, if the consensus theoretical estimate and the experimental measurement of muon g-2 differ by two sigma or less.

In the second case, any impact of new fundamental particles or new forces in the Standard Model on muon g-2 must be almost exactly offsetting, and/or any undiscovered new physics must be extremely slight.

This is because the theoretical value of muon g-2 is a function of the strong coupling constant, the weak coupling constant, the strong force coupling constant, and the properties of essentially all of the fundamental particles of the Standard Model, through intermediate loops included in the calculation of this derived muon property. Essentially anything that can interact with a muon in the Standard Model, and anything that interacts with something that interacts with a muon in the Standard Model, ever so slightly tweaks the value of muon g-2.

For example, as one June 2020 paper explains:

The longstanding muon g-2 anomaly may indicate the existence of new particles that couple to muons, which could either be light (< GeV) and weakly coupled, or heavy (>> 100 GeV) with large couplings. If light new states are responsible, upcoming intensity frontier experiments will discover further evidence of new physics. However, if heavy particles are responsible, many candidates are beyond the reach of existing colliders. We show that, if the g-2 anomaly is confirmed and no explanation is found at low-energy experiments, a high-energy muon collider program is guaranteed to make fundamental discoveries about our universe. New physics scenarios that account for the anomaly can be classified as either "Singlet" or "Electroweak" (EW) models, involving only EW singlets or new EW-charged states respectively. We argue that a TeV-scale future muon collider will discover all possible singlet model solutions to the anomaly. If this does not yield a discovery, the next step would be a O(10 TeV) muon collider. Such a machine would either discover new particles associated with high-scale EW model solutions to the anomaly, or empirically prove that nature is fine-tuned, both of which would have profound consequences for fundamental physics.

Rodolfo Capdevilla, David Curtin, Yonatan Kahn, Gordan Krnjaic, "A Guaranteed Discovery at Future Muon Colliders" arXiv (June 29, 2020).

In contrast, if the theoretical prediction for muon g-2 is confirmed, even very weakly coupled sub-GeV particles, and also high mass new particles (above 100 GeV up to tens of TeV) with anything more than extremely weak couplings are largely ruled out. Thus, any new fundamental particles would have to be confined to a scale that would not be detectable at a next generation collider.

In the intermediate range, where a tension between the new experimentally measured value of muon g-2 and the theoretically predicted value of muon g-2 continues to be more than two sigma but less than five sigma, the case for new physics relative to merely something like underestimated error bars in either the experimental measurement or the theoretical prediction or both, is still diminished. 

This is because that can only happen if the best fit value of the experimental measurement becomes significantly closer to the theoretical prediction than it was fifteen years ago, even though a tension remains.

If that happened, the source of any new physics leading to a tension would also be expected to be smaller than the previous tension would have predicted, implying either a much weaker coupling to Standard Model physics, or a much higher mass scale for new physics, than previously surmised. 

An ongoing tension would still motivate searches for new physics by providing some observational motivation for them. But a lot of new physics models proposed to explain the tension observed fifteen years ago would end up on the cutting room floor. 

Anything other than a definitive confirmation of the necessity of new physics to explain the muon g-2 anomaly would, in particular, be a huge blow to the prospects of supersymmetry (SUSY) models (see, e.g., here) or models with additional types of Higgs bosons (see, e.g. here) at scales potentially discoverable by a next generation particle collider (i.e. with new particles having masses of tens of TeVs or less).

UPDATE January 31, 2021:

A periodical reports a March 2021 date, which would be another modest postponement.

Locked cabinets, sealed envelopes, and secret codes surround a big question in particle physics: Could the magnetism of a particle called the muon point to new vistas in physics?

Behind the scenes drama here.

The Meaning Of The Name Of The Founder Of Zoroastrianism

The founder of the Zoroastrian religion is known as Zoroaster and also the variant form Zarathustra. What did his name mean?

In Avestan, Zaraϑuštra is generally accepted to derive from an Old Iranian *Zaratuštra-; The element half of the name (-uštra-) is thought to be the Indo-Iranian root for "camel", with the entire name meaning "he who can manage camels".

Not terribly profound, but suggestive of Central Asian affinities, just like the Indo-Iranian people of whom he was a part. 

Belle Experiment At LHCb Finds No Evidence Of Lepton Flavor Universality Violations

Executive Summary: No New Physics

A compilation of all of the Belle collaboration data to date shows no statistically significant evidence of lepton flavor universality violations in B meson decays, which are prohibited by the Standard Model. Evidence of anomalies from earlier data with a smaller sample size has grown less significant as more data has been collected.

This doesn't quite, by itself, but the nail in the coffin of this hint of beyond the Standard Model physics, but it comes close. Upcoming work by a successor Belle II collaboration, measuring the previously anomalous quantities to greater precision, will be more definitive.

One Small Anomaly In Something Else Was Seen

There was one modest statistical tension in the latest Belle data between a Standard Model expectation that is distinct from a lepton universality violation, which is that there would be no semi-leptonic decays of B mesons to kaons with a muon-electron mix, rather than a lepton and anti-lepton of the same flavor as expected, out of four channels tested, with no signal in the other three channels of semi-leptonic B meson decays studied. 

But given look elsewhere effects, the marginal strength of the signal near the boundary of what the experiment can detect (the best fit to its frequency was one per 20 million events in one decay channel), and the small absolute number of events involved, this result is not very notable and is probably just a statistical fluke. 

Unlike the lepton universality violations looked for in the new study, there was no statistically significant evidence of this anomaly from prior experiments at Belle or in other collaborations before the study was done, further heightening the look elsewhere effect impact on its significant. This and a lack of replication casts doubt about the reality of this marginally statistically significant tension with the Standard Model. 

Background

In the Standard Model of Particle Physics, electrons, muons and tau leptons should have exactly the same properties apart from their masses, something called "lepton flavor universality" subject to distinctions to slight to measure caused by interactions in intermediate loops of decays and interactions with oscillating neutrinos whose different types do not behave identically (with their differences described by the PMNS matrix).

One of the hottest areas of fundamental physics in recent years has been the detection of anomalies in B meson decays (a B meson is a two valence quark particle in which at least one of the valence quarks is a b quark) into leptons, that seems to deviation from lepton universality. Individually, none of these anomalies is significant enough to amount to a discovery of new physics, although it is possible (although challenging) to imagine new physics that could explains the anomalies seen in multiple channels which start to look very significant if they are all evidence of the same new physics phenomena. 

A Headache Avoided

This new result from Belle is reassuring, because previously observed anomalies were hard to explain. This is because the decays in which the anomalies were observed are generally believed to arise from a process (W boson decays) that are shared with many other kinds of decays where larger data sets have shown no evidence for the same anomaly, and the Standard Model process assumed to be at work in B meson decays otherwise comes very close to accurately explaining the B meson decays that were observed (e.g. it predicted the overall number of decays accurately).

Lepton universality violations are not seen in W boson decays at the LHC, are not found in tau lepton decays or pion decays (also here), and are not found in anti-B meson and D* meson decays or in Z boson decays, even though all of those examples involve the same kind of weak force decay believed to be involved in B meson decays.

If the old lepton universality anomaly was real, something very big had to have been wrong with our understanding of hadron decays in the Standard Model, even though the Standard Model works basically perfectly in all other hadron decay contexts.

But you would expect statistical flukes (possibly amplified by understated systemic errors) to be seen in early B meson decays data, if they are seen anywhere. This is because the high energies necessary to create B mesons means that the data sets for these decays are the smallest of the various decays where lepton universality could be studied. So the fact that there was an early anomaly in early B meson decay data that has faded as more data has been collected, makes sense.

If the lepton flavor universality violation anomaly seen in prior studies was a real "new physics" effect, it should have gotten stronger, not weaker, as the size of the data set increased. 

The New Results In Detail

A new pre-print is entitled "Test of lepton family universality and search for lepton and baryon number violation at Belle" (and incidentally follows the desirable practice of listing only the corresponding author the the collaboration as authors, rather than comprehensively listing every scientist in the collaboration individually).

The Lepton Flavor Universality Violation Measurement 

The headline result is its test of lepton flavor universality. This updated result analyzes: "the results obtained from a multidimensional fit performed on the full Υ(4𝑆) data sample of Belle. . . .  Following four channels are studied: 𝐵 + → 𝐾+ 𝑒 + 𝑒 − , 𝐵 + → 𝐾+𝜇 +𝜇 − , 𝐵 0 → 𝐾 0 𝑆 𝑒 + 𝑒 − , and 𝐵 0 → 𝐾 0 𝑆 𝜇 +𝜇 − based on 711 fb−1 Υ(4𝑆) data corresponding to 772 × 10^6 𝐵𝐵 events."

In other words, it looked the semi-leptonic decays of two kinds of B mesons, (1) the decay of charged B mesons into a charged kaon and either an electron-positron pair, or a muon-antimuon pair, and (2) the decay of neutral B mesons into a neutral kaon and either an electron-positron pair, or a muon-antimuon pair. In all it analyzed 772 million B meson decays, the complete set of B meson decays from excited Y(4,S) resonances into B meson pairs from the experiment to date.

If the Standard Model is correct, the ratio of semi-leptonic B meson decays to muon-antimuon pairs to semi-leptonic B meson decays to electron-positron pairs (called R(K) should be equal to exactly one, subject only to random statistical errors (since the laws of quantum physics govern probabilities rather than being deterministic), to asymmetries induced from neutrino interaction loops which should be much smaller than the statistical uncertainties, and to systemic experimental measurement errors that are well quantified in heavily used experimental setup.

The results were also segregated into "q squared" bins that reflect the energy scale of the interaction produce the B mesons in each decay. The number of events in each bin has an uncertainty in it because most of the 772 million decays don't involve the semi-leptonic decays a B mesons to kaons studied, and the scientists had to segregate out background events from the decays that they were actually studying, which can't be distinguished with perfect accuracy. In the end, there were only about 275 charged B meson decays and 49 neutral B meson decays in the sample analyzed.

From the fit we obtain 137 ± 14 and 138 ± 15 events in 𝐵 + → 𝐾+𝜇 +𝜇 − and 𝐵 + → 𝐾+ 𝑒 + 𝑒 − decays, respectively. Similarly, the yields for the neutral channels 𝐵 0 → 𝐾 0 𝑆 𝜇 +𝜇 − and 𝐵 0 → 𝐾 0 𝑆 𝑒 + 𝑒 − are 27.3 + 6.6 − 5.8 and 21.8 + 7.0 − 6.1 events. 

These results were consistent with the Standard Model expectation of a ratio of one to one at the two sigma level used to distinguish between normal statistical variation in experiments like this and tensions that are considered anomalies that deviate from the Standard Model expectation. 

The previous data had shown a 2.4 sigma tension with the Standard Model in the neutral kaon decay channel and a 2.5 sigma tension in the charged kaon decay channels studied by Belle.  Moreover, the direction of the deviation from a perfect one to one ratio in the neutral B meson decay where it was stronger in the current study in terms of the deviation of the best fit ratio from one to one (although with more uncertainty) than in the charged B meson decay in the current study, was in the opposite direction of the previous anomalies. The previous data showed too few muon events in neutral B meson decays relative to the electron events, while this study showed too many. 

Another 3.4 sigma tension seen in the prior data was restricted to a somewhat odd ball measurement, that normally wouldn't attract attention, in a narrow energy scale bin, and can be viewed as a physicists version of p-hacking to find a statistical fluke in a way that doesn't properly account for look elsewhere effects. 

This particular study from Belle didn't examine the fourth channel in which a 3.7 sigma tension with the Standard Model was observed in previous data, involving a different kind of semi-leptonic B meson decay than the decays to kaons reviewed in this pre-print.

Semi-Leptonic Mixed Lepton Flavor Decays

The search also looked for semi-leptonic decays to kaons with a mix of electrons and muons which should not happen in the Standard Model. 

The maximum frequency of such decays consistent with observation was constrained by an additional order of magnitude relative to prior studies to not more than parts per 100 million in three of four channels.

But, in the only notable result of the study, there was 3.2 sigma evidence (a result in tension with the Standard Model) of some anomalous decays in the charged B meson to charged kaon together with a muon and a positron channel at an apparent rate of one such decay per 20 billion charged B meson decays, but with considerable uncertainty in the magnitude of the anomaly that at the low end could be very close to zero. Once look elsewhere effects are considered, this results is somewhat less notable.

Baryon Number Violating Tau Decays

Baryon number violating decays in about 841 million tau lepton decays (in which the net number of quarks less antiquarks before and after the decay changes) which are not allowed by the Standard Model, were not observed. Their frequency, if they happen at all, was constrained to be fewer than something on the order of single digit numbers of events per 10 million tau lepton decays.

Physics In 2020

I made 90 posts about physics at this blog in 2020. A few topics dominated the discussion, and I collect some of those posts.

There were many increasingly accurate measurements of Standard Model physical constants. I tracked these results against some speculative theoretical expectations, but the uncertainties in the top quark mass measurement which won't be dramatically better for the foreseeable future, and to a lesser extent, some of the other measurements limited the extent to which these expectations could be meaningfully confirmed.

* Top quark mass (Tevatron)

* Top quark mass

* Charm quark mass

* Higgs boson mass

* Higgs boson self-coupling

* Tau lepton mass

* CKM Matrix elements

* W boson properties 

* Annual Particle Data Group summary

* Standard model constants overview

The neutrino data, in particular, strongly disfavors the sterile neutrino hypothesis although it hasn't quite put a nail in the coffin of that conjecture and continues to favor a "normal mass hierarchy" for neutrinos with no evidence of Majorana neutrinos such a neutrinoless double beta decay. Efforts to determine the CP violating phase in neutrino oscillation have confirmed that there is some CP violation in this process and favors near maximal CP violation in neutrino oscillation, but has large margins of error. These measurements are likely to improvement meaningfully in the coming year.

* Reactor data disfavors sterile neutrinos

* Neutrino properties from astronomy

* Number of neutrino species

* Neutrino properties overview 

* Neutrino CP violation

* Neutrinoless double beta decay

Modified gravity approaches to explaining dark matter and dark energy continued to be successful, while the paradigmatic lambdaCDM theory of cosmology continued to fall short. Demonstration of violations of the strong equivalence principle towards the end of the year topped the list. Advances of modified gravity and dings for lambdaCDM in the area of early cosmology were also significant.

* MOND galaxy formation

* Supermassive black hole formation timing

* A new prediction from Deur 

* Galaxy shape impacts inferred amount of DM

* Deur on galaxy shape and inferred amount of DM

* The MOND constant in a solar system context

* MOND and out of equilibrium galaxies  

* Gravitational Wave Telescope Constraints

* MOND does CMB predictions

* Explaining DM phenomena with GR

* Explaining DM phenomena with GR II

* Strong equivalence principle violated

* Strong equivalence principle violated II

* Another modified gravity theory

* A testable quantum gravity prediction

* Newton's constant holds at short ranges 

* Massive gravity

* Sabine Hossenfelder splits the difference

* Wrong Mix of Dark Matter in CDM

* Galaxy formation simulations disfavor CDM

* DM simulation fails

* CDM can't explain satellite galaxy alignment

* Primordial black hole DM disfavored 

* You need a fifth force or modified gravity

* Unexpected Hubble lensing data in clusters 

* Constraints on thermal freeze out DM

* Any primordial gravitational waves are small

* LambdaCDM fails at cosmology scale

* Exclusions of BSM particles at the LHC

* WIMPs not detected

  

A variety of experimental anomalies and measurement tensions were explored. 

The biggest one that is that there will be two new muon g-2 measurements, the last of which was fifteen years ago and the next of which will be announced early this year. The new measurement (and the new theoretical prediction) will be much more accurate than the last, in which the measurement which differed by about three sigma (about 2 parts per million) from the theoretically expected value. The calculation of muon g-2 is sensitive in a global way to almost all aspects of Standard Model physics and can be calculated and measured with extreme precision. The closer that the experimentally measured value of muon g-2 is, the less room there is for new physics beyond the Standard Model. On the other hand, big differences would be strong evidence that scientists are missing something in the Standard Model.

* General discussion of muon g-2

* Summary of predictions of muon g-2

* Coming muon g-2 experiments

Another area where there have been tensions is in suggestions that premise of charged lepton universality (i.e., that the electron, muon and tau lepton are identical apart from mass) is violated. The tensions have appeared in B meson decays, but not in other kinds of decays that should implicate the same properties.

* Why they probably aren't real

* How big are the tensions

The Xenon1T experiment reported some anomalous outcomes that were almost immediately determined to be meaningless because the results failed to consider an important source of background contamination in its results, although that hasn't prevented theorists for coming up with esoteric and unlikely theoretical explanations for it. 

A Hungarian group has argued that there is a beyond the Standard Model X17 particle, but that hasn't been panning out either (see also a lengthy discussion with citations to journal articles in the comments to this post).