STEREO Rules Out Sterile Neutrinos

There are no sterile neutrinos. Anomalies between predictions and results that have been used to suggest that possibility (including but not limited to those in the study below) are due to flaws in how the nuclear sources of the neutrinos were modeled. 

Anomalies in past neutrino measurements have led to the discovery that these particles have non-zero mass and oscillate between their three flavors when they propagate. In the 2010's, similar anomalies observed in the antineutrino spectra emitted by nuclear reactors have triggered the hypothesis of the existence of a supplementary neutrino state that would be sterile i.e. not interacting via the weak interaction. The STEREO experiment was designed to study this scientific case that would potentially extend the Standard Model of Particle Physics. Here we present a complete study based on our full set of data with significantly improved sensitivity. Installed at the ILL (Institut Laue Langevin) research reactor, STEREO has accurately measured the antineutrino energy spectrum associated to the fission of 235U. This measurement confirms the anomalies whereas, thanks to the segmentation of the STEREO detector and its very short mean distance to the core (10~m), the same data reject the hypothesis of a light sterile neutrino. Such a direct measurement of the antineutrino energy spectrum suggests instead that biases in the nuclear experimental data used for the predictions are at the origin of the anomalies. Our result supports the neutrino content of the Standard Model and establishes a new reference for the 235U antineutrino energy spectrum. We anticipate that this result will allow to progress towards finer tests of the fundamental properties of neutrinos but also to benchmark models and nuclear data of interest for reactor physics and for observations of astrophysical or geo-neutrinos.

H. Almazán, et al., "Interpreting Reactor Antineutrino Anomalies with STEREO data" arXiv:2210.07664 (October 14, 2022).

No Statistically Significant Evidence Of Dark Matter At XENON1T

A new paper goes to great length to describe the results of dark matter searches at XENON1T. 

All hints of a signal of dark matter in excess of the expected background results had a local significance of less than 2 sigma (1.7 sigma and 1.8 sigma in two of many bins of the parameter space studied), which is not statistically significant. The significance would have been even lower had the look elsewhere effect been considered.

Less Than Explicit Proofs

How Often Do Bottom Quark To Up Quark Transitions Occur?

The CKM matrix measures the probability of one kind of quark transitioning into another kind of quark in a W boson mediated interactions.

The global average value for the V(ub) element according to the Particle Data Group without doing a global fit on the entire matrix is:

This is a relative precision of about 5%. According to the latest measurement from the Belle II experiment "the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element,

V(ub) = (3.55±0.12±0.13±0.17)×10^−3, is extracted. Here, the first uncertainty is statistical, the second is systematic and the third is theoretical." 

The magnitude of the probability of a bottom to up quark transition (which mutes the complex number components of the CKM matrix element that reflects CP violation in the transition probability) is the square of the magnitude of this CKM matrix element (i.e. this happens in about 13 per million transitions).

Combining the uncertainties in quadrature, the measurement is 3.55 ± 0.245 x 10^-3. This is consistent with the PDG value at the one sigma level.

Replicating the existing value from other experiments was no small feat.

We present an analysis of the charmless semileptonic decay B0→π−ℓ+νℓ, where ℓ=e,μ, from 198.0 million pairs of BB¯ mesons recorded by the Belle II detector at the SuperKEKB electron-positron collider. The decay is reconstructed without identifying the partner B meson. The partial branching fractions are measured independently for B0→π−e+νe and B0→π−μ+νμ as functions of q2 (momentum transfer squared), using 3896 B0→π−e+νe and 5466 B0→π−μ+νμ decays.

It Isn't Easy For A Non-Expert To Know If A Question Is Easy Or Hard

 

The 2022 Nobel Prize In Medicine

This year's Nobel Prize in Medicine goes to the person who first sequenced Neanderthal DNA from about 40,000 years ago, an incredible scientific achievement that deserves recognition. As the New York Times explains:

Svante Pääbo, a Swedish scientist who peered back into human history by retrieving genetic material from 40,000-year-old bones, producing a complete Neanderthal genome and launching the field of ancient DNA studies, was awarded the Nobel Prize in Physiology or Medicine on Monday.

New Snowmass Papers On BSM Physics

A new Snowmass paper surveys the lastest work in BSM physics, most of which is utter garbage. 

The opening paragraph states (I highlight the non-problems in the list and insert comments in brackets):

Despite its phenomenal successes, the Standard Model (SM) can only be considered a low energy, effective field theory (EFT) description of particle physics [not really true anymore given the Higgs boson mass] which leaves many unanswered questions about the nature of reality at distance scales shorter than ∼ TeV^−1. 

Among these so-far unanswered questions are the origin of the neutrino masses, an explanation for the quark and lepton flavor structures, the absence of measurable CP violation in QCD, and why the scales associated with gravity and weak interactions are so disparate. The SM also does not explain the observed asymmetry between matter and antimatter in the Universe. It is known that the cosmological dark matter cannot be composed of SM fields and the origin of the periods of accelerated expansion of the Universe are a mystery [ignores the possible new gravitational physics that could explain these phenomena and the old school cosmological constant]. Any explanation for these above mentioned puzzles must involve physics beyond the SM [doubtful].

Some headings from the paper (particularly garbage-full topics in bold):

2 Naturalness [naturalness is fundamentally hokum] 

2.1 Supersymmetry

2.2 Warped Extra Dimensions and Composite Higgs Theories

2.3 Neutral Naturalness

2.4 Cosmological Selection

2.5 Strong CP and Axions

2.6 Quantum Gravity Implications: Swampland

3 Dark Matter

3.1 Interaction Mechanisms

classic freeze-out

Forbidden DM

Asymmetric dark matter

Sommerfeld enhancement

Inelastic dark matter  

3.2 Models

Supersymmetric dark matter [there is no parameter space left for it]

Dark matter in composite Higgs theories [the composite Higgs is dead]

Strong-coupled composite dark matter [basically ruled out]

Atomic/Mirror dark matter

Light dark matter

Axion and wave-like dark matter

Other models of dark matter: . . . sterile neutrino dark matter, ultraheavy dark matter, dynamical dark matter, and hidden sectors and a multi-temperature universe.

4 Baryogenesis [rests heavily on the utterly unsupported premise that aggregate baryon number has to be zero at the Big Bang]

5 Flavor Model Building [full text reproduced below for lack of subheadings]

Flavor violating processes, in particular those involving flavor changing neutral currents (FCNC) have exquisite sensitivity to new sources of flavor and CP violation beyond those of the SM. This high sensitivity to new physics has its origin in the small amount of flavor breaking that is present in the SM. In the SM, the only sources of flavor violation are the hierarchical Yukawa couplings of the Higgs. The origin of the SM arrangement of the various quark and charged lepton masses, the hierarchical structure of the CKM matrix, and the absence of visible hierarchies in the PMNS matrix is often referred to as the SM flavor puzzle. Various classes of ideas exist to solve this puzzle: horizontal flavor symmetries, warped extra dimentions, partial compositeness, and radiative fermion masses. In the SM, the quark FCNCs are suppressed by a loop factor and by small CKM matrix elements. As long as theoretical uncertainties in the SM predictions are under control, quark flavor violating processes can indirectly explore very high mass scales, in some cases far beyond the direct reach of collider experiments. In the lepton sector, SM predictions for FCNCs are suppressed by the tiny neutrino masses and below any imaginable experimental sensitivities. Electroweak contributions to electric dipole moments are also predicted to be strongly suppressed in the SM, several orders of magnitude below the current bounds. Charged lepton flavor violation and electric dipole moments are thus null tests of the SM. Any observation of such processes would be an unambiguous sign of new physics.

In the SM, the Yukawa couplings of the Higgs to the fermions are the only sources of flavor violation. Therefore, the Higgs might be the window into understanding flavor, with the precision Higgs program at the LHC, and in the future also at a Higgs factory, able to provide valuable inputs. In particular, Higgs decays involving tau, h → τµ and h → τe, are cases where the direct searches at the LHC are the most sensitive probes.

In addition to long-standing puzzles, in the last several years a number of “flavor anomalies” have created considerable excitement in the community. Discrepancies between SM predictions and experimental measurements are seen in B decays as well as in the anomalous magnetic moment of the muon. If the new physics origin for these experimental anomalies could be established, it would have a transformative impact on the field. First and foremost, such an indirect sign of new physics would establish a new mass scale in particle physics. This scale could become the next target for direct exploration at future high-energy colliders. With sufficient energy, discoveries would, at least in principle, be guaranteed. Second, the couplings of the new physics constitute new sources of flavor violation beyond the SM Yukawa couplings. Existing low energy constraints suggest that such new physics couplings have a hierarchical flavor structure. This provides a new perspective on the Standard Model flavor puzzle and invites the construction of flavor models that link the structure of the SM and BSM sources of flavor violation. At present, the global analyses point towards a small consistent set of dimension-6 effective operators (C9 and/or C10) to explain the B-physics anomalies. The leading candidate UV models generating these operators involve Z(0) (e.g. Lµ − Lτ ) gauge bosons or leptoquarks.

The new Snowmass paper on quantum gravity, string theory, and black holes is also full of dubious assertions.

In short, until we vote a lot of physicists in this camp off the island, physics will continue to be plagued with high IQ idiots pursuing dubious and unsound theories.

The 2022 Nobel Prize In Physics

This year's Nobel prize in Physics was awarded to three physicists who, independently and sequentially, experimentally confirmed that quantum entanglement was a real phenomena that worked in practice the way that quantum theory predicted that it would.

Data Will Eventually Save The Day In Astrophysics

This short summary paper only analyzes the data about mass and light distributions in a galaxy cluster relative to the ΛCDM Standard Model of Cosmology. 

Once again, it shows that the ΛCDM model doesn't fit the data: In real life, inferred dark matter sub-halos are more compact than predicted in the ΛCDM model. 

Each new finding, on multiple fronts where the ΛCDM model is contradicted, leaves less and less room to argue that this model is not deeply flawed.

But even more importantly, thanks to the multiple new high quality telescopes out there collecting a veritable torrent of new data on systems like this one at high precision, we have a lot of high precision measurements of gravitationally bound systems that can be fit to different models, such as gravitationally based ones, once we've finally buried the dead horse of ΛCDM and begun to seriously consider alternatives.

I'm comfortable that because so many independent groups are collecting so much data, which is being widely shared, and because theorists are not as monolithic as they are in the high energy physics field, that eventually we will get the right answers, even if the sociology and culture of the astrophysics discipline means that it takes us longer to get to the right answer than it should.

Strong gravitational lensing (SL) has emerged as a very accurate probe of the mass distribution of cluster- and galaxy-scale dark matter (DM) haloes in the inner regions of galaxy clusters. The derived properties of DM haloes can be compared to the predictions of high-resolution cosmological simulations, providing us with a test of the Standard Cosmological Model. 

The usual choice of simple power-law scaling relations to link the total mass of members with their luminosity is one of the possible inherent systematics within SL models of galaxy clusters, and thus on the derived cluster masses. Using new information on their structural parameters (from HST imaging) and kinematics (from MUSE data), we build the Fundamental Plane (FP) for the early-type galaxies of the cluster Abell S1063. We take advantage of the calibrated FP to develop an improved SL model of the total mass of the cluster core. 

The new method allows us to obtain more accurate and complex relations between the observables describing cluster members, and to completely fix their mass from their observed magnitudes and effective radii. Compared to the power-law approach, we find a different relation between the mass and the velocity dispersion of members, which shows a significant scatter. Thanks to a new estimate of the stellar mass of the cluster members from HST data, we measure the cumulative projected mass profiles out to a radius of 350 kpc, for all baryonic and DM components of the cluster. 

Finally, we compare the physical properties of the sub-haloes in our model and those predicted by high-resolution hydrodynamical simulations. We obtain compatible results in terms of the stellar-over-total mass fraction of the members. On the other hand, we confirm the recently reported discrepancy in terms of sub-halo compactness: at a fixed total mass value, simulated sub-haloes are less compact than what our SL model predicts.

Giovanni Granata, "Improved strong lensing modelling of galaxy clusters using the Fundamental Plane: detailed mapping of the baryonic and dark matter mass distribution of Abell S1063" arXiv:2209.11776 (September 21, 2022) (published in The Hypatia Colloquium 2022 book of proceedings).

The body text explains that:

Galaxy clusters are the most massive gravitationally bound structures in the Universe, and around 85 − 90% of their total mass is under the form of dark matter (DM). As a consequence, they are excellent astrophysical laboratories to test our hypoteses on the nature of DM itself. Thanks to several dedicated photometric and spectroscopic surveys, strong gravitational lensing (SL) has become the most accurate probe of the total mass distribution in the cores (out to a few hundreds of kiloparsecs from the centre) of massive galaxy clusters. SL can be combined with baryonic mass diagnostics to disentangle the mass distribution of cluster- and galaxy-scale DM haloes from the total mass distribution of the cluster. The resulting DM mass profiles can be compared to the predictions of high-resolution cosmological simulations, based on the Λ cold dark matter (CDM) Cosmological Model. 

The remarkable improvement in the accuracy of SL models, driven by recent observational campaigns, has allowed us to map robustly the mass distribution of the DM haloes hosting the member galaxies (usually referred to as sub-haloes). On this scale, a significant discrepancy between the predictions of SL models and highresolution simulations has recently emerged: at a fixed galaxy total mass, sub-haloes extracted from SL models are more compact than their simulated counterparts [2].

[2] Meneghetti, M., et al., 2020, Science, 369, 1347 . . . 

As anticipated, comparing the physical properties of the DM sub-haloes as predicted by SL models to the most recent cosmological simulations is a test of the foundations of the Λ CDM cosmological model on which the simulations are based, and of the micro-physics of DM. 

We first compare the stellar-to-total mass fractions of the cluster members with the predictions of recent HOD studies based on DM-only N-body simulations [7]. We find a significant discrepancy: the stellar mass fraction values predicted by SL models are almost an order of magnitude higher than those predicted by the HOD procedure. This discrepancy is resolved if one considers, instead, hydrodynamical simulations, which include gas particles and stars, as well as the effects of the interaction between baryons and DM during the formation of clusters. We consider high-resolution simulations of clusters with a mass similar to that of AS1063 from [8]. We perform two-dimensional projections to simulate the lensing observational conditions. In this case, we find compatible stellar mass fraction values from the SL model and the simulation suite. 

Secondly, we examine how sub-haloes extracted from lensing models compare to their simulated counterparts in terms of maximum circular velocity, which is a proxy for their compactness. [2] recently found that hydrodynamical simulations predict high-mass sub-haloes (total mass M > 10^10 M) to be significantly less compact than forecast by a sample of state-of-the-art SL models, including the model of Abell S1063 presented in [4]. 

The new technique we adopt significantly impacts the relation between the total mass and the maximum circular velocity of the sub-haloes, obtaining again a different slope compared to [4] and allowing for the inclusion of a scatter. However, as shown in Figure 2, our results agree with those from [4] in the mass range considered, thus confirming the reported discrepancy. Several tests to infer the origin of this discrepancy are being performed, focusing both on SL modelling and on the implementation of the cosmological simulations. However, no conclusive answer has been obtained so far. This leaves several open questions, and could point towards a new fundamental challenge for the Λ CDM paradigm.

[1] is the result from the modeling of strong gravitational lensing observations in this study (blue), [4] is the distribution predicted by the ΛCDM model (red).

See also here ("At z~2 there is ~40% less dark matter mass on average within R(e) compared to expected values based on cosmological stellar-mass halo-mass relations.")

A Rare Physics Op-Ed

The Guardian Newspaper has a rare opinion-editorial article about the value of certain kinds of theoretical and phenomenological physics research headlined:

No one in physics dares say so, but the race to invent new particles is pointless: In private, many physicists admit they do not believe the particles they are paid to search for exist – they do it because their colleagues are doing it. 

It was written by Sabine Hossenfelder who, as usual, is spot on in challenging the practice she describes not as entirely invalid, but as having minimal value. It begins playfully:

Imagine you go to a zoology conference. The first speaker talks about her 3D model of a 12-legged purple spider that lives in the Arctic. There’s no evidence it exists, she admits, but it’s a testable hypothesis, and she argues that a mission should be sent off to search the Arctic for spiders.

The second speaker has a model for a flying earthworm, but it flies only in caves. There’s no evidence for that either, but he petitions to search the world’s caves. The third one has a model for octopuses on Mars. It’s testable, he stresses.

She continues:

Almost every particle physics conference has sessions just like this, except they do it with more maths. It has become common among physicists to invent new particles for which there is no evidence, publish papers about them, write more papers about these particles’ properties, and demand the hypothesis be experimentally tested. Many of these tests have actually been done, and more are being commissioned as we speak. It is wasting time and money.

Since the 1980s, physicists have invented an entire particle zoo, whose inhabitants carry names like preons, sfermions, dyons, magnetic monopoles, simps, wimps, wimpzillas, axions, flaxions, erebons, accelerons, cornucopions, giant magnons, maximons, macros, wisps, fips, branons, skyrmions, chameleons, cuscutons, planckons and sterile neutrinos, to mention just a few. We even had a (luckily short-lived) fad of “unparticles”.

All experiments looking for those particles have come back empty-handed, in particular those that have looked for particles that make up dark matter, a type of matter that supposedly fills the universe and makes itself noticeable by its gravitational pull. However, we do not know that dark matter is indeed made of particles; and even if it is, to explain astrophysical observations one does not need to know details of the particles’ behaviour. The Large Hadron Collider (LHC) hasn’t seen any of those particles either, even though, before its launch, many theoretical physicists were confident it would see at least a few.

Talk to particle physicists in private, and many of them will admit they do not actually believe those particles exist. . . .  

[T]he biggest contributor to this trend is a misunderstanding of Karl Popper’s philosophy of science, which, to make a long story short, demands that a good scientific idea has to be falsifiable. Particle physicists seem to have misconstrued this to mean that any falsifiable idea is also good science.

In the past, predictions for new particles were correct only when adding them solved a problem with the existing theories. For example, the currently accepted theory of elementary particles – the Standard Model – doesn’t require new particles; it works just fine the way it is. The Higgs boson, on the other hand, was required to solve a problem. The antiparticles that Paul Dirac predicted were likewise necessary to solve a problem, and so were the neutrinos that were predicted by Wolfgang Pauli. The modern new particles don’t solve any problems.

In some cases, the new particles’ task is to make a theory more aesthetically appealing, but in many cases their purpose is to fit statistical anomalies. Each time an anomaly is reported, particle physicists will quickly write hundreds of papers about how new particles allegedly explain the observation. . . . 

Ambulance-chasing is a good strategy to further one’s career in particle physics. . . . since ambulance-chasers cite each other’s papers, they can each rack up hundreds of citations quickly. But it’s a bad strategy for scientific progress. . . .  

I believe there are breakthroughs waiting to be made in the foundations of physics; the world needs technological advances more than ever before, and now is not the time to idle around inventing particles, arguing that even a blind chicken sometimes finds a grain. As a former particle physicist, it saddens me to see that the field has become a factory for useless academic papers.

Also, note that criticism of physics scholarship really has two parts: 

(1) particles "to make a theory more aesthetically appealing", which aren't actually needed (like axions, see-saw mechanism neutrinos, supersymmetric particles and extra Higgs bosons), and 

(2) particles to explain statistical anomalies (often from one or two recent experiments) which have not adequately exhausted explanations that don't require new physics (like the X17 particle, leptoquarks to explain lepton universality violations in semi-leptonic B meson decays, sterile neutrinos, and new particles proposed to explain a W boson mass measurement out of step with other recent W boson mass measurements).

But, both are out of hand and a waste of time and money that would be better spent focusing on more well motivated proposals.

The author further discusses the Op-Ed at her blog.