Monday, December 31, 2018

Fundamental Constant Measurements At Year End And More

Happy New Year's Eve. Rather than clean up the formatting, I am simply cutting and pasting for expediency. I provide some brief commentary on a variety of notable end of the year physics pre-prints.


The CMS experiment at the Large Hadron Collider (LHC) has new measurements of the top quark mass using Run-2 data in two channels and a new measurement of the strong force coupling constant. The top quark mass measurements tend to corroborate earlier LHC data and run on the low side of Tevatron measurements and some of the earliest LHC measurements in some select channels (the broad spread of the measurements in those channels makes me suspect that the margin of error in all of the measurements may be underestimated). We still have no top quark mass measurements from ATLAS using Run-2 data.

Some theoretical benchmarks are here. An extended Koide's rule fit would suggest a value of the top quark mass of 173.26 GeV.

The low top quark mass measurements disfavor the conclusion that the sum of the Yukawas for fundamental fermions is equal to the sum of the Yukawas for the fundamental bosons which would call for a top quark mass of 174.03 GeV (although it has far less impact on the hypothesis that the sum of the Yukawas for all the fundamental particles of the Standard Model is exactly equal to 1 which is still a closer fit to the data with a target value of about 173.73 GeV with the ultimately measured value of the Higgs boson mass potentially somewhat influencing this value). But, the uncertainties in the latest measurements are still quite large (up to about +1.35 GeV at two sigma for individual measurements which would allow a value of 173.6 GeV or even a bit more).

The strong force coupling constant value measured is low compared to the global average measured value, but is consistent with it because the latest run to measurement in this channel has a high level of uncertainty. Even CMS does not use this newly measured value for further calculations, showing a great lack of faith in it.

tt production cross section, the top quark mass, and the strong coupling constant using dilepton events in pp collisions at s= 13 TeV

A measurement of the top quark-antiquark pair production cross section σtt in proton-proton collisions at a centre-of-mass energy of 13 TeV is presented. The data correspond to an integrated luminosity of 35.9 fb1, recorded by the CMS experiment at the CERN LHC in 2016. Dilepton events (e±μμ+μ, e+e) are selected and the cross section is measured from a likelihood fit. For a top quark mass parameter in the simulation of mMCt= 172.5 GeV the fit yields a measured cross section σtt= 803 ± 2 (stat) ± 25 (syst) ± 20 (lumi) pb, in agreement with the expectation from the standard model calculation at next-to-next-to-leading order. A simultaneous fit of the cross section and the top quark mass parameter in the simulation is performed. The measured value of mMCt=172.33 ± 0.14 (stat) +0.660.72 (syst) GeV is in good agreement with previous measurements. The resulting cross section is used, together with the theoretical prediction, to determine the top quark mass and to extract a value of the strong coupling constant with different sets of parton distribution functions.
The strong force coupling constant is low compared to other recent measurements but has a large margin of error. Four different values are determined by different methodologies and a combined final result is not reported because the margin of error is so high. The global average value is used for calculations in the remainder of the paper.
Table 5: Values of αS(mZ) with their uncertainties obtained from a comparison of the measured σtt value to the NNLO prediction in the MS scheme using different PDF sets. The first uncertainty is the combination of the experimental and PDF uncertainties, and the second is from the variation of the renormalization and factorization scales. 
PDF set αS(mZ) 
ABMP16 0.1139 ± 0.0023 (fit + PDF) +0.0014 −0.0001 (scale) 
NNPDF3.1 0.1140 ± 0.0033 (fit + PDF) +0.0021 −0.0002 (scale) 
CT14 0.1148 ± 0.0032 (fit + PDF) +0.0018 −0.0002 (scale) 
MMHT14 0.1151 ± 0.0035 (fit + PDF) +0.0020 −0.0002 (scale) 
The values of αS(mZ) obtained using different PDF sets are consistent among each other and are in agreement with the world-average value [29] within the uncertainties, although suggesting a smaller value of αS(mZ). The value of αS(mZ) is also in good agreement with the recent result of the analysis in Ref. [84] of jet production in deep-inelastic scattering using the NNLO calculation by the H1 experiment, and is of comparable precision.
The current particle data group value is 0.1181 +/- 0.0011.

Measurement of the top quark mass in the all-jets final state at s= 13 TeV and combination with the lepton+jets channel

A top quark mass measurement is performed using 35.9 fb1 of LHC proton-proton collision data collected with the CMS detector at s= 13 TeV. The measurement uses the tt all-jets final state. A kinematic fit is performed to reconstruct the decay of the \ttbar~system and suppress the multijet background. Using the ideogram method, the top quark mass (mt) is determined, simultaneously constraining an additional jet energy scale factor (JSF). The resulting value of mt= 172.34 ± 0.20 (stat+JSF) ± 0.70 (syst) GeV is in good agreement with previous measurements. In addition, a combined measurement that uses the ttlepton+jets and all-jets final states is presented, using the same mass extraction method, and provides an mt measurement of 172.26 ± 0.07 (stat+JSF) ± 0.61 (syst) GeV. This is the first combined mt extraction from the lepton+jets and all-jets channels through a single likelihood function.
Some other miscellaneous physics papers (some fairly speculative) are as follows:


A new 41 page review article recaps the basic mathematical outline of the Standard Model at a level beyond that mathematical abilities of an educated layman, but in a fair more comprehensible manner than a semester or year length presentation directed at specialists.

Quantum Field Theory and the Electroweak Standard Model

These lecture notes cover the basics of Quantum Field Theory (QFT) and peculiarities in the construction of the Electroweak (EW) sector of the Standard Model (SM). In addition, the present status, issues, and prospects of the SM are discussed.
A new experimental test of muon properties that can be predicted theoretically to extreme accuracy will be possible to test soon. Past muon property measurements have led to persistent unexplained anomalies. This paper takes a hard look at how much uncertainty there is in the theoretical prediction before the experiment is conducted and experiment and theoretical predictions are compared.

Hyperfine Splitting in Muonium: Accuracy of the Theoretical Prediction

Last twenty years theory of hyperfine splitting in muonium developed without any experimental input. Finally, this situation is changing and a new experiment on measuring hyperfine splitting in muonium is now in progress at J-PARC. The goal of the MuSEUM experiment is to improve by an order of magnitude experimental accuracy of the hyperfine splitting and muon-electron mass ratioUncertainty of the theoretical prediction for hyperfine splitting will be crucial for comparison between the forthcoming experimental data and the theory in search of a possible new physics. In the current literature estimates of the error bars of the theoretical prediction differ by a factor of two. We explain the origin of this discrepancy and present an estimate of these error bars.
A good review of non-fundamental issues in the hadron spectrum that the QCD calculations necessary to clarify are challenging to do. There are a surprising number of hadrons that have been experimentally measured but not neatly fit into SM hadron types (without ruling out the possibility that they are one of those types). The Z mesons can all be explained as meson molecules as can one of the X mesons. Another X meson looks like a true tetraquark. Y(4220) is the hardest to characterize. It might be a charmonium hybrid, but several other possibilities are ruled out and the potential that it is a tetraquark is unknown. There are numerous XYX mesons that have been less well characterized and aren't addressed in the paper.

The XYZ mesons: what they aren't

I discuss the properties of some representative XYZ mesons in the context of the most commonly proposed models for their underlying nature.
There were basically no surprises as of about 2003. From the body text:
One of the big surprises from the B-factory experiments [after 2003] was the discovery of mesons with decay final states that include a c- and a ¯c-quark that cannot be assigned to any of the remaining unassigned levels of the charmonium spectrum. . . . Sure enough, as the B-factory programs unfolded, and BESIII started up, additional cc¯ charmonium states were found, along with a larger number of charmoniumlike states, both neutral and charged. . . . The properties of these states, which are collectively known as the XYZ mesons, have been extensively reviewed and are generally well known. What is not well known is what they are, and this has turned out to be a very challenging issue. Here I address a more modest question: what aren’t they?
Proposed theoretical models for these new states include: 
molecules: loosely bound deuteron-like meson-meson structures; 
QCD tetraquarks: colored quark ([cqi]) and diantiquark ([¯cq¯j]) configurations (qi = u, d, s) tightly bound by the exchange of colored gluons; 
charmonium hybrids: a cc¯ pair plus an excited “valence” gluon (and electrically neutral); 
threshold effects: enhancements caused by threshold cusps, rescattering processes, etc.; 
hadrocharmonium: a colorless hadron cloud of light quarks & gluons, bound to a a cc¯ charmonium core state via van-der-Waals forces. 
Here I briefly discuss each of these possibilities, with emphasis on their experimental consequences. I restrict the discussion to six candidate XYZ mesons that are experimentally well established and whose J PC values are known: i.e., the isospin zero X(3872), X(3915), and Y(4220), and the isospin one Zc(3900), Zc(4020) and Z(4430).
The paper concludes this this table and analysis. Blue is possible, Red is ruled out. Green is weakly possible. And, of course, ??? means that we don't know.

Can tetraquarks be stable? This paper considers the question. One heavy-light mix tetraquark might be relatively stable, but no heavy tetarquarks can be stable.

Basics of doubly heavy tetraquarks

We outline the most important results regarding the stability of doubly heavy tetraquarks QQq¯q¯ with an adequate treatment of the four-body dynamics. We consider both color-mixing and spin-dependent effects. Our results are straightforwardly applied to the case of all-heavy tetraquarks QQQ¯Q¯We conclude that the stability is favored in the limit MQ/mq1 pointing to the stability of the bbu¯d¯ state and the instability of all-heavy tetraquarks.
Highly speculative. Probably garbage. The paper pretty much rules out its own hypothesis.

Neutron lifetime and dark decay of the neutron and hydrogen

The tension between the neutron lifetimes measured in the beam and trap experiments suggests that the neutron n might have a new invisible decay channel nnX into mirror neutron, its dark partner from parallel hidden sector and nearly degenerate in mass with the neutron, with mnmn 1 MeV, and X being ordinary and mirror photons as well as more exotic massless bosons. I discuss some phenomenological and astrophysical consequences of this scenario, which depends on the mass range of mirror neutron n. Namely, the case mn<mp+me leads to a striking possibility is that the hydrogen atom 1H (protium), constituting 75 per cent of the baryon mass in the Universe, could in fact be unstable: If instead mn>mp+me, then the decay npeν¯e is allowed and ncan represent unstable but very long living dark matter component. Nevertheless, this decay would produce substantial diffuse gamma background. This explanation, however, is in tension with the latest results of the experiments measuring β-asymmetry in the neutron decay.

This is a proposal for a new kind of neutrino physics measurement to clarify the reactor anomaly sterile neutrino hypothesis (I strongly suspect that the reactor anomaly is not due to a sterile neutrino).

On θ23 Octant Measurement in 3+1 Neutrino Oscillations in T2HKK

It has been pointed out that the mixing of an eV-scale sterile neutrino with active flavors can lead to loss of sensitivity to θ23 octant (sign of sin2θ231/2) in long baseline experiments, because the main oscillation probability P0=4sin2θ23sin2θ13sin2Δ13 can be degenerate with the sum of the interferences with the solar oscillation amplitude and an active-sterile oscillation amplitude in both neutrino and antineutrino oscillations, depending on CP phases. In this paper, we show that the above degeneracy is resolved by measuring the same beam at different baseline lengths. We demonstrate that Tokai-to-Hyper-Kamiokande-to-Korea (T2HKK) experiment (one 187~kton fiducial volume water Cerenkov detector is placed at Kamioka, L=295~km, and another detector is put in Korea, L1000~km) exhibits a better sensitivity to θ23 octant in those parameter regions where the experiment with two detectors at Kamioka is insensitive to it. Therefore, if a hint of sterile-active mixings is discovered in short baseline experiments, T2HKK is a better option than the plan of placing two detectors at Kamioka. We also consider an alternative case where one detector is placed at Kamioka and a different detector is at Oki Islands, L=653~km, and show that this configuration also leads to a better sensitivity to θ23 octant.

Astronomy data continues to place observational bounds on hypothetical dark matter particle properties.

Galactic Center Gas Clouds and Novel Bounds on Ultra-Light Dark Photon, Vector Portal, Strongly Interacting, Composite, and Super-Heavy Dark Matter

Cold gas clouds recently discovered hundreds of parsecs from the center of the Milky Way Galaxy have the potential to detect dark matter. With a detailed treatment of gas cloud microphysical interactions, we determine Galactic Center gas cloud temperatures, free electron abundances, atomic ionization fractions, heating rates, cooling rates, and find how these quantities vary with metallicity. Considering a number of different dark sector heating mechanisms, we set new bounds on ultra-light dark photon dark matter for masses 10221010 eV, vector portal dark matter coupled through a sub-MeV mass boson, and up to 10 60   GeV mass dark matter that interacts with baryons.
And more dark matter property constraints (also whoever was drafting the abstract didn't know how to use spell check): 

More stringent constraints on the unitarised fermionic dark matter Higgs portal

We revisit the simplest model of Higgs portal fermionic dark matter. The dark matter in this scenario is thermally produced in the early universe due to the interactions with the Higgs boson which is described by a non-renormalisable dimension-5 operator. The dark matter-Higgs scattering amplitude grows as s, signalling a breakdown of the effective description of the Higgs-dark matter interactions at large enough (compared to the mass scale Λ of the dimention-5 operator) energies. Therefore, in order to reliably compute Higgs-dark matter scattering cross sections, we employ the K-matrix unitarisation procedure. To account for the desired dark matter abundance, the unitarised theory requires appreaciably smaller Λ than the non-unitarised version, especially for dark matter masses around and below the Higgs resonance, mχ65 GeV, and mχ few TeV. Consequently, we find that the pure scalar CP-conserving model is fully excluded by current direct dark matter detection experiments.
Most dark matter particle proposals are for thermal dark matter, but not all of them.

Non-thermal Dark Matter from Modified Early Matter Domination

Thermal freeze-out or freeze-in during a period of early matter domination can give rise to the correct dark matter abundance for σannvf<3×1026 cm3 s1. In the standard scenario, a single field that behaves like matter drives the early matter dominated era. However, in realistic models, this epoch may involve more than one field. In this paper, we study the effect of such a modification on the production of dark matter during early matter domination. We show that even a subdominant second field that decays much faster than the dominant one can considerably enhance the temperature of the universe during an early matter-dominated phase. This in turn affects dark matter production via freeze-out/in and opens up the allowed parameter space toward significantly larger dark matter masses. As a result, one can comfortably obtain the correct relic abundance for PeV-scale dark matter for reheating temperatures at or below 10 GeV.
Someone thinks that dark matter annihilation signals might be coming from the galactic center. This is probable not true. It is not possible to tell, in their model, with current telescopes, but that could change soon.

Signatures of Synchrotron Radiation from the Annihilation of Dark Matter at the Galactic Centre

We propose a fermionic dark matter model by extending Standard Model with a Dirac fermion and a real pseudoscalar. The fermion dark matter particle interacts with the Standard Model sector via the Higgs portal through a dimension five interaction term as also through a pseudoscalar interaction term. The parameter space of the model is then constrained by using the vacuum stability and perturbativity condition as also with the LHC constraints. They are finally constrained by the PLANCK results for dark matter relic densities. The direct detection limits are then ensured to have satisfied by the model. We then explore within the framework of the model, the possible signatures of synchrotron radiation from the annihilations of dark matter in the Galactic Centre region when the end product is e+e. We consider the observational data from the radio telescopes namely SKA, GMRT and Jodrell Bank telescopes and compare our calculated synchrotron flux density with them and also with the results predicted by these experiments. We predict that the low frequency radio telescopes like GMRT, SKA, if operate at the peak frequencies obtained from our calculations should get a better r.m.s sensitivity.
Another paper considers potential warm dark matter annihilation or decay signatures in the Milky Way.

Surface brightness profile of the 3.5 keV line in the Milky Way halo

We report a detection of 3.5 keV line in the Milky Way in 5 regions offset from the Galactic Center by distances from 10' to 35 degrees. We build an angular profile of this line and compare it with profiles of several astrophysical lines detected in the same observations. We compare our results with other detections and bounds previously obtained using observations of the Milky Way.
Baryon number and lepton number are still perfectly conserved in all experimental measurements conducted to date, once again constraining the possibilities for baryongenesis and leptogenesis at any time other than in the very first instants after the Big Bang. This is bad news for popular GUT and TOE models and (in connection with other experimental data on the subject) may force cosmologists to accept that the initial conditions of the universe did not involve zero baryon number and zero lepton number as one would expect if the Big Bang arose from pure energy.

Model-independent Bounds on the Standard Model Effective Theory from Flavour Physics

Meson-antimeson mixing provides the most stringent constraints on baryon- and lepton-number conserving New Physics, probing scales higher than 105 TeV. In the context of the effective theory of weak interactions, these constraints translate into severe bounds on the coefficients of ΔF=2 operators. Generalizing to the effective theory invariant under the Standard Model gauge group, valid above the electroweak scale, the bounds from ΔF=2 processes also affect ΔF=1 and even ΔF=0 operators, due to log-enhanced radiative corrections induced by Yukawa couplings. We systematically analyze the effect of the renormalization group evolution above the electroweak scale and provide for the first time the full set of constraints on all relevant dimension-six operators.
A die hard is still convinced that supersymmetry can provide a workable dark matter candidate and fit experimental constraints with a WIMP dark matter candidate. But, WIMP dark matter is actually almost completely ruled out by astronomy data that the author doesn't consider.

The Higgs and WIMP DM Lamp Posts for New Weak Scale Physics: EFT Perspectives and the NMSSM

Nausheen R. Shah (Wayne State U.)
I will show, via effective field theory (EFT) techniques, that obtaining an observationally consistent relic density while evading stringent direct detection limits and maintaining h125 phenomenology in an extended Higgs sector can be easily achieved. I will then map such an EFT to the low energy limit of the NMSSM with the Higgsinos integrated out. Both the singlino and the singlet-like CP-odd and even scalars in the NMSSM may play a relevant role in such a scenario, while being difficult to probe via conventional searches. The singlet sector of the general NMSSM can be mapped on to a 2HDM+S, and I will discuss prospects of probing this at the LHC using signatures such as mono-Higgs and mono-Z. This proceeding is mostly based on Refs. arXiv:1712.09873 and arXiv:1808.02667.
Galactic globular clusters don't have the properties that they are expected to have. There may be a prosaic reason that this is the case (failure to properly account for stellar collisions in current predictions).

Radial trends in Galactic globular clusters and their possible origin

Valery V. Kravtsov (1 and 2) ((1) SAI, Lomonosov Moscow State University, Moscow, Russia, (2) INCT, Universidad de Atacama, Copiapo, Chile)
The relaxation time at the half-mass radius of Galactic globular clusters (GGCs) is typically within a few Gyr. Hence, the majority of GGCs are expected to be well relaxed systems, given their age is around 12-13 Gyr. So any initial radial segregation between stars of the same initial mass on the main sequence (MS), in particular, the progenitors of the present day sub-giant and red-giant branch (SGB, RGB) stars should already have dissipated. However, a body of evidence contradicting to these expectations has been accumulated to date. The paradox could be solved by taking into account the effect of stellar collisions. They occur at particularly high rate in collapsing nuclei of GGCs and seem to be mainly responsible for unrelaxed central regions and the radial segregation observed. We draw attention that actually observed collisional blue stragglers should be less numerous than their lower-mass counterparts formed and accumulated at and below the present day MS turnoff. The effect of this is that MS/SGB/RGB stars of a given luminosity are not of the same mass but fall in a range of mass.
Satellite dwarf galaxies without dark matter could be proof of MOND's external field effect (which should be correlated with distance to the Milky Way), one of its boldest deviations from general relativity, which can make sense in a quantum gravity theory, but is hard to justify in a conventional geometric theory or a dark matter particle theory.

On the absence of dark matter in dwarf galaxies surrounding the Milky Way

It is widely accepted that Milky Way (MW) dwarfs are the most dark matter (DM) dominated galaxies. Their DM content is estimated through its projected density along the line of sight (los). Here we demonstrate that this quantity correlates with their distance to the MW, falsifying the calculations of DM in dwarfs. Moreover, we show that the acceleration deduced from the los velocity dispersion is entirely due to MW tidal shocks. This regime is expected in the astronomical context for which MW dwarfs are descendants of infalling gas-rich galaxies. It implies that they have no DM, or, alternatively that DM could not play a role in them, questioning, e.g., their use as targets for DM searches.
A modified gravity paper looking at theoretical prediction in one kind of modified gravity for key observables in elliptical galaxies that match up with observations. f(R) gravity has the virtue of having a lot of theoretical consistency issues worked out that are not present in phenomenological models like MOND.

Fundamental plane of elliptical galaxies in f(R) gravity: the role of luminosity

The global properties of elliptical galaxies are connected through the so-called fundamental plane of ellipticals, which is an empirical relation between their parameters: effective radius, central velocity dispersion and mean surface brightness within the effective radius. We investigated the relation between the parameters of the fundamental plane equation and the parameters of modified gravity potential f(R). With that aim, we compared theoretical predictions for circular velocity in f(R) gravity with the corresponding values from a large sample of observed elliptical galaxies. Besides, we consistently reproduced the values of coefficients of the fundamental plane equation as deduced from observations, showing that the photometric quantities like mean surface brightness are related to gravitational parameters. We show that this type of modified gravity, especially its power-law version - Rn, is able to reproduce the stellar dynamics in elliptical galaxies. Also, it is shown that Rn gravity fits the observations very well, without need for a dark matter.