Parameters Of Standard Model Research Articles

Dependency of the cosmographic tension of standard model to statistical errors of observational data ‎

In this work, we study the standard model of cosmology in the context of cosmographic approach. We want to determine whether the cosmographic tension of the standard model that is reported in recent studies, depends on the statistical errors of the observational data or not. To do this, we produce three catalogues of mock data for the distance modulus of type Ia supernovae using a canonical value for matter density in the framework of standard model. In the first catalogue, the errors of mock data have been chosen equal to the errors of real data in Pantheon catalogue. In the second and third catalogues, the errors of mock data have been chosen equal to half and twice the real errors in Pantheon sample, respectively. In the next step, using the generated mock data, we minimize the least square function in the context of Markov Chain Monte Carlo method and put constraints on the cosmographic parameters in both model independent cosmographic approach and standard model. Our results show that decreasing the error of mock data can remove the cosmographic tension of the standard model. Also, the larger errors increase the deviation of standard model from cosmographic method. Hence, the cosmographic tension of the standard model which is recently reported by the Hubble diagrams of quasars and Gamma-Ray-Burst can be essentially due to large error bars of these observational data and so not a physical tension.

Global analysis of electroweak data in the Standard Model

We perform a global fit of electroweak data within the Standard Model, using state-of-the art experimental and theoretical results, including a determination of the electromagnetic coupling at the electroweak scale based on recent lattice calculations. In addition to the posteriors for all parameters and observables obtained from the global fit, we present indirect determinations for all parameters and predictions for all observables. Furthermore, we present full predictions, obtained using only the experimental information on Standard Model parameters, and a fully indirect determination of Standard Model parameters using only experimental information on electroweak data. Finally, we discuss in detail the compatibility of experimental data with the Standard Model and find a global p-value of 0.5.

Top quark pair and single top cross sections and ttX (CMS)

Latest results on inclusive and differential top quark pair and single top quark production cross sections are presented using proton-proton collision data collected by the CMS experiment. The differential cross sections are measured as a function of various kinematic observables of the top quarks and the jets and leptons of the event final state. The results are confronted with precise theory calculations and used to constrain Standard Model parameters. Measurements are performed also with high p_TpT top quarks, i.e., in boosted regimes.

Recent results on top quark mass and properties and rare/anomalous top quarks interactions in CMS

The amount of data collected by the CMS experiment at the CERN LHC in the second data taking period provides the possibility to study absolute and differential cross sections of top quark interaction processes with high precision. Utilizing these results, fundamental standard model parameters such as the top quark mass are extracted. Moreover, given standard model measurements are interpreted in the context of beyond the standard model theories. Recent results on top quark properties and rare or anomalous top quark interactions by CMS are presented in these proceedings. Furthermore, the implications of experimental results to effective field theory are discussed.

Precision QCD Physics at the LHC

This review describes the current status of precision quantum chromodynamics (QCD) studies at the LHC. We introduce the main experimental and theoretical methods, and we discuss their cross-stimulated developments and recent advances. The different types of QCD observables that are measured at the LHC, including cross sections and event- and jet-level properties, for various final states, are summarized. Their relation to fundamental QCD dynamics and their impact on Standard Model parameter determinations are discussed using specific examples. The impact of QCD-related observables on direct and indirect searches for rare processes within and New Physics beyond the Standard Model is outlined.

Identifying microstructural changes in diffusion MRI; How to circumvent parameter degeneracy

Biophysical models that attempt to infer real-world quantities from data usually have many free parameters. This over-parameterisation can result in degeneracies in model inversion and render parameter estimation ill-posed. However, in many applications, we are not interested in quantifying the parameters per se, but rather in identifying changes in parameters between experimental conditions (e.g. patients vs controls). Here we present a Bayesian framework to make inference on changes in the parameters of biophysical models even when model inversion is degenerate, which we refer to as Bayesian EstimatioN of CHange (BENCH).We infer the parameter changes in two steps; First, we train models that can estimate the pattern of change in the measurements given any hypothetical direction of change in the parameters using simulations. Next, for any pair of real data sets, we use these pre-trained models to estimate the probability that an observed difference in the data can be explained by each model of change.BENCH is applicable to any type of data and models and particularly useful for biophysical models with parameter degeneracies, where we can assume the change is sparse. In this paper, we apply the approach in the context of microstructural modelling of diffusion MRI data, where the models are usually over-parameterised and not invertible without injecting strong assumptions. Using simulations, we show that in the context of the standard model of white matter our approach is able to identify changes in microstructural parameters from conventional multi-shell diffusion MRI data. We also apply our approach to a subset of subjects from the UK-Biobank Imaging to identify the dominant standard model parameter change in areas of white matter hyperintensities under the assumption that the standard model holds in white matter hyperintensities.

Complete theory of radiative corrections to Kℓ3 decays and the Vus update

We fill up the missing piece in our own re-analysis of the long-distance electromagnetic radiative corrections to semileptonic kaon decays by performing a rigorous study in the K → πμ+νμ(γ) channels. With appropriate experimental and lattice inputs, we achieve a precision level of 10−4 in these channels. This is comparable to our previous analysis in the K → πe+νe(γ) channels. With this new result, we present an updated global analysis to extract the Standard Model parameter |Vus| from semileptonic kaon decays. We obtain |Vus| = 0.22308(55) and 0.22356(73), using the lattice average of the K0→ π− transition form factor at Nf = 2 + 1 + 1 and Nf = 2 + 1, respectively.

Precise equivalent circuit model for Li-ion battery by experimental improvement and parameter optimization

The equivalent circuit model (ECM) is a type of lithium-ion battery model that is widely used in electric vehicle battery management systems (BMS). BMS is an important component that affects the performance of electric vehicles, and accurate battery model is the foundation of BMS. For different usage scenarios, improving the accuracy of battery model in BMS plays a crucial role in improving the energy utilization of electric vehicles and ensuring the safe use of batteries. The accuracy of the battery model is strongly influenced by the accuracy of the battery model parameters, therefore, this study aimed at elucidating on these factors. In this paper, experimental procedures for model parameter identification are designed and optimized by orthogonal analysis in terms of model accuracy, model consistency, and maximum model error. Model parameters that can synthetically balance the three model evaluation indices are finally obtained through experiments. By combining the obtained experimental contents and analysis results, we quantitatively investigated the sensitivity of different model performances to the three model parameters in ECM under different state of charge (SOC) using a combination of polynomial fitting and derivative solving sensitivity by single-factor sensitivity analysis. This study provides a basis for future battery modeling, model error analysis, and model parameter identification. In addition, we propose the optimization parameter as an indicator for optimizing the parameters in the battery model in conjunction with parameter sensitivity to model performance and degree of deviation from standard model parameters. The validation shows that the optimized battery model parameters using this method can improve the model's specific performance.

Quantum gravity effects in the infrared: a theoretical derivation of the low-energy fine structure constant and mass ratios of elementary particles

We have recently proposed a pre-quantum, pre-spacetime theory as a matrix-valued Lagrangian dynamics on an octonionic spacetime. This theory offers the prospect of unifying internal symmetries of the standard model with pre-gravitation. We explain why such a quantum gravitational dynamics is in principle essential even at energies much smaller than Planck scale. The dynamics can also predict the values of free parameters of the low-energy standard model: these parameters arising in the Lagrangian are related to the algebra of the octonions, which define the underlying non-commutative spacetime on which the dynamical degrees of freedom evolve. These free parameters are related to the exceptional Jordan algebra \(J_3(8)\), which describes the three fermion generations. We use the octonionic representation of fermions to compute the eigenvalues of the characteristic equation of this algebra and compare the resulting eigenvalues with known mass ratios for quarks and leptons. We show that the ratios of the eigenvalues correctly reproduce the [square root of the] known mass ratios. In conjunction with the trace dynamics Lagrangian, these eigenvalues also yield a theoretical derivation of the low-energy fine structure constant.

Reproducibility of the Standard Model of diffusion in white matter on clinical MRI systems

Estimating intra- and extra-axonal microstructure parameters, such as volume fractions and diffusivities, has been one of the major efforts in brain microstructure imaging with MRI. The Standard Model (SM) of diffusion in white matter has unified various modeling approaches based on impermeable narrow cylinders embedded in locally anisotropic extra-axonal space. However, estimating the SM parameters from a set of conventional diffusion MRI (dMRI) measurements is ill-conditioned. Multidimensional dMRI helps resolve the estimation degeneracies, but there remains a need for clinically feasible acquisitions that yield robust parameter maps. Here we find optimal multidimensional protocols by minimizing the mean-squared error of machine learning-based SM parameter estimates for two 3T scanners with corresponding gradient strengths of 40and80mT/m. We assess intra-scanner and inter-scanner repeatability for 15-minute optimal protocols by scanning 20 healthy volunteers twice on both scanners. The coefficients of variation all SM parameters except free water fraction are ≲10% voxelwise and 1−4% for their region-averaged values. As the achieved SM reproducibility outcomes are similar to those of conventional diffusion tensor imaging, our results enable robust in vivo mapping of white matter microstructure in neuroscience research and in the clinic.

SpaceMath version 1.0 A Mathematica package for beyond the standard model parameter space searches

We present a pedagogical Mathematica package, so-called SpaceMath, for Beyond the Standard Model parameter space searches. This software is directed mainly for the training of human resources related to elementary particle physics phenomenology, however, it is sophisticated enough to be used in researches. In this first version, SpaceMath v1.0 works with Higgs Boson Data whose results are the most up-to-date experimental measurements made at the Large Hadron Collider. In addition, we also include the expected results at future colliders, namely, High Luminosity LHC and High Energy LHC. SpaceMath v1.0 is able to find allowed regions for free parameters of extension models using the Higgs Boson Data within a friendly interface and an intuitive environment in which the user enters the couplings symbolically, sets parameters and execute Mathematica in the traditional way. As result, both tables as plots with values and areas agree with experimental data are generated. We present examples using SpaceMath v1.0 to analyze the free Two-Higgs Doublet Model and the Simplest Little Higgs Model parameter spaces, step by step, in order to start new users in a fast and efficient way. Finally, to validate SpaceMath v1.0, widely known results are reproduced.

Impact of SM parameters and of the vacua of the Higgs potential in gravitational waves detection

In this work we discuss two different phases of a complex singlet extension of the Standard Model (SM) together with an extension that also includes new fermion fields, in particular, a Majoron model equipped with an inverse seesaw mechanism. All considered scenarios contain a global U(1) symmetry and allow for first-order phase transitions while only two of them are strong enough to favour the detection of primordial gravitational waves (GWs) in planned experiments such as LISA. In particular, this is shown to be possible in the singlet extension with a non vanishing real VEV at zero temperature and also in the model with extra fermions. In the singlet extension with no additional fermions, the detection of GWs strongly depends on the U(1) symmetry breaking pattern of the scalar potential at zero temperature. We study for the first time the impact of the precision in the determination of the SM parameters on the strength of the GWs spectrum. It turns out that the variation of the SM parameters such as the Higgs boson mass and top quark Yukawa coupling in their allowed experimental ranges has a notable impact on GWs detectability prospects.

A measurement of the cosmic expansion within our lifetime

The most exciting future observation in cosmology will feature a monitoring of the cosmic expansion in real time, unlike anything that has ever been attempted before. This campaign will uncover crucial physical properties of the various constituents in the universe, and perhaps answer a simpler question concerning whether or not the cosmic expansion is even accelerating. An unambiguous yes/no response to this query will significantly impact cosmology, of course, but also the standard model of particle physics. Here, we discuss—in a straightforward way—how to understand the so-called ‘redshift drift’ sought by this campaign, and why its measurement will help us refine the standard-model parameters if the answer is ‘yes.’ A ‘no’ answer, on the other hand, could be more revolutionary, in the sense that it might provide a resolution of several long-standing problems and inconsistencies in our current cosmological models. An outcome of zero redshift drift, for example, would obviate the need for a cosmological constant and render inflation completely redundant.

Massless preheating and electroweak vacuum metastability

Current measurements of Standard Model parameters suggest that the electroweak vacuum is metastable. This metastability has important cosmological implications, because large fluctuations in the Higgs field could trigger vacuum decay in the early universe. For the false vacuum to survive, interactions which stabilize the Higgs during inflation -- e.g., inflaton-Higgs interactions or non-minimal couplings to gravity -- are typically necessary. However, the post-inflationary preheating dynamics of these same interactions could also trigger vacuum decay, thereby recreating the problem we sought to avoid. This dynamics is often assumed catastrophic for models exhibiting scale invariance since these generically allow for unimpeded growth of fluctuations. In this paper, we examine the dynamics of such "massless preheating" scenarios and show that the competing threats to metastability can nonetheless be balanced to ensure viability. We find that fully accounting for both the backreaction from particle production and the effects of perturbative decays reveals a large number of disjoint "islands of (meta)stability" over the parameter space of couplings. Ultimately, the interplay among Higgs-stabilizing interactions plays a significant role, leading to a sequence of dynamical phases that effectively extend the metastable regions to large Higgs-curvature couplings.

NNLO interpolation grids for jet production at the LHC

Fast interpolation-grid frameworks facilitate an efficient and flexible evaluation of higher-order predictions for any choice of parton distribution functions or value of the strong coupling alpha _{mathrm {s}}. They constitute an essential tool for the extraction of parton distribution functions and Standard Model parameters, as well as studies of the dependence of cross sections on the renormalisation and factorisation scales. The APPLfast project provides a generic interface between the parton-level Monte Carlo generator and both the APPLgrid and the fastNLO libraries for the grid interpolation. The extension of the project to include hadron–hadron collider processes at next-to-next-to-leading order in perturbative QCD is presented, together with an application for jet production at the LHC.

Higher-order QCD corrections to H \u2192 b overline{b} from rational approximants

We use rational approximants to study missing higher orders in the massless scalar-current quark correlator. We predict the yet unknown six-loop coefficient of its imaginary part, related to Γ(H → b overline{b} ), to be c5 = −6900 ± 1400. With this result, the perturbative series becomes almost insensitive to renormalization scale variations and the intrinsic QCD truncation uncertainty is tiny. This confirms the expectation that higher-order loop computations for this quantity will not be required in the foreseeable future, as the uncertainty in Γ(H → b overline{b} ) will remain largely dominated by the Standard Model parameters.

Sensitivity of musculoskeletal models to variation in muscle architecture parameters.

Musculoskeletal models, like all theoretical models of physical processes, depend on the assumptions needed to construct the model. For musculoskeletal models, these assumptions include, among other things, the kinematic data, the kinetic data and the muscle parameters. The former (dynamic) data can be acquired relatively easily from living subjects, but the latter are usually based on limited information, frequently determined from cadaver studies performed on elderly individuals. Previously, we determined the sensitivity of forces to dynamic differences among 10 humans walking on a straight path. Here, we assess the sensitivity of the muscle and joint reaction forces developed in human walking to variable muscle parameters obtained from 10 living adults, whose data were recently reported, and compared the results with the values from a standard model that depends on cadaveric data. We found that, while the force patterns across the stance cycle were similar among muscle parameter models, differences of as much as 15% in the force magnitude were produced. Whether or not the variation between the standard model and other muscle parameters is important depends on why the forces are required.

On the cosmological implications of the electroweak vacuum instability: constraining the non-minimal coupling with inflation

Our current measurements of the Standard Model parameters imply that the Higgs field resides in a metastable electroweak vacuum, where the vacuum can decay to a lower ground state, with cataclysmic repercussions for our Universe. According to our observations, no such event has happened in the observable universe, in spite of the various energetic processes that could have triggered it. This work serves as an overview of a method that uses the metastability of the false vacuum during cosmological inflation to provide constraints on the Higgs curvature coupling ξ. Considering also the effects of the time-dependent Hubble rate on the effective Higgs potential and on our past light-cone space-time geometry, results in state-of-the-art lower ξ-bounds from quadratic and quartic chaotic inflation, and Starobinsky-like power-law inflation.

Association of Environmental Uncertainty With Altered Decision-making and Learning Mechanisms in Youths With Obsessive-Compulsive Disorder

Adults with obsessive-compulsive disorder (OCD) display perseverative behavior in stable environments but exhibit vacillating choice when payoffs are uncertain. These findings may be associated with intolerance of uncertainty and compulsive behaviors; however, little is known about the mechanisms underlying learning and decision-making in youths with OCD because research into this population has been limited. To investigate cognitive mechanisms associated with decision-making in youths with OCD by using executive functioning tasks and computational modeling. In this cross-sectional study, 50 youths with OCD (patients) and 53 healthy participants (controls) completed a probabilistic reversal learning (PRL) task between January 2014 and March 2020. A separate sample of 27 patients and 46 controls completed the Wisconsin Card Sorting Task (WCST) between January 2018 and November 2020. The study took place at the University of Cambridge in the UK. Decision-making mechanisms were studied by fitting hierarchical bayesian reinforcement learning models to the 2 data sets and comparing model parameters between participant groups. Model parameters included reward and punishment learning rates (feedback sensitivity), reinforcement sensitivity and decision consistency (exploitation), and stickiness (perseveration). Associations of receipt of serotonergic medication with performance were assessed. In total, 50 patients (29 female patients [58%]; median age, 16.6 years [IQR, 15.3-18.0 years]) and 53 controls (30 female participants [57%]; median age, 16.4 years [IQR, 14.8-18.0 years]) completed the PRL task. A total of 27 patients (18 female patients [67%]; median age, 16.1 years [IQR, 15.2-17.2 years]) and 46 controls (28 female participants [61%]; median age, 17.2 [IQR, 16.3-17.6 years]) completed the WCST. During the reversal phase of the PRL task, patients made fewer correct responses (mean [SD] proportion: 0.83 [0.16] for controls and 0.61 [0.31] for patients; 95% CI, -1.31 to -0.64) and switched choices more often following false-negative feedback (mean [SD] proportion: 0.09 [0.16] for controls vs 0.27 [0.34] for patients; 95% CI, 0.60-1.26) and true-positive feedback (mean [SD] proportion: 0.93 [0.17] for controls vs 0.73 [0.34] for patients; 95% CI, -2.17 to -1.31). Computational modeling revealed that patients displayed enhanced reward learning rates (mean difference [MD], 0.21; 95% highest density interval [HDI], 0.04-0.38) but decreased punishment learning rates (MD, -0.29; 95% HDI, -0.39 to -0.18), reinforcement sensitivity (MD, -4.91; 95% HDI, -9.38 to -1.12), and stickiness (MD, -0.35; 95% HDI, -0.57 to -0.11) compared with controls. There were no group differences on standard WCST measures and computational model parameters. However, patients who received serotonergic medication showed slower response times (mean [SD], 1420.49 [279.71] milliseconds for controls, 1471.42 [212.81] milliseconds for patients who were unmedicated, and 1738.25 [349.23] milliseconds for patients who were medicated) (control vs medicated MD, -320.26 [95% CI, -547.00 to -88.68]) and increased unique errors (mean [SD] proportion: 0.001 [0.004] for controls, 0.002 [0.004] for patients who were unmedicated, and 0.008 [0.01] for patients who were medicated) (control vs medicated MD, -0.007 [95% CI, -3.14 to -0.36]) on the WCST. The results of this cross-sectional study indicated that youths with OCD showed atypical probabilistic reversal learning but were generally unimpaired on the deterministic WCST, although unexpected results were observed for patients receiving serotonergic medication. These findings have implications for reframing the understanding of early-onset OCD as a disorder in which decision-making is associated with uncertainty in the environment, a potential target for therapeutic treatment. These results provide continuity with findings in adults with OCD.

Hint of a truncated primordial spectrum from the CMB large-scale anomalies

Context. Several satellite missions have uncovered a series of potential anomalies in the fluctuation spectrum of the cosmic microwave background temperature, including: (1) an unexpectedly low level of correlation at large angles, manifested via the angular correlation function, C(θ); and (2) missing power in the low multipole moments of the angular power spectrum, Cℓ. Aims. Their origin is still debated, however, due to a persistent lack of clarity concerning the seeding of quantum fluctuations in the early Universe. A likely explanation for the first of these appears to be a cutoff, kmin = (3.14 ± 0.36)×10−4 Mpc−1, in the primordial power spectrum, 𝒫(k). Our goal in this paper is twofold: (1) we examine whether the same kmin can also self-consistently explain the missing power at large angles, and (2) we confirm that the introduction of this cutoff in 𝒫(k) does not adversely affect the remarkable consistency between the prediction of Planck-ΛCDM and the Planck measurements at ℓ > 30. Methods. We have used the publicly available code CAMB to calculate the angular power spectrum, based on a line-of-sight approach. The code was modified slightly to include the additional parameter (i.e., kmin) characterizing the primordial power spectrum. In addition to this cutoff, the code optimized all of the usual standard-model parameters. Results. In fitting the angular power spectrum, we found an optimized cutoff, kmin = (2.04−0.79+1.4) × 10−4 Mpc−1, when using the whole range of ℓ’s, and kmin = (3.3−1.3+1.7) × 10−4 Mpc−1, when fitting only the range ℓ ≤ 30, where the Sachs-Wolfe effect is dominant. Conclusions. These are fully consistent with the value inferred from C(θ), suggesting that both of these large-angle anomalies may be due to the same truncation in 𝒫(k).