Anomalous Magnetic Moment Research Articles

Calculation of the total 10th order QED contribution to the electron magnetic moment

The total 5-loop quantum electrodynamics universal contribution to the anomalous magnetic moments of the leptons was calculated by the author. The obtained value A1(10)=5.891(61) provides the first complete verification of the previously known value obtained by T. Aoyama, M. Hayakawa, T. Kinoshita, and M. Nio (AHKN). The discrepancy is 5σ. The computation includes the recalculation of the part that the author calculated in 2019 using a slightly different method and the calculation of the remaining part of the coefficient. A comparison with the AHKN values in 32 gauge-invariant classes is provided. In addition, the results are divided into 95 small gauge-invariant classes that subdivide the former ones. Such a detailization is provided for the first time. The method described in previous works of the author was used, in general. However, the Monte Carlo integration method is new and is described in detail. Some useful technical information and information on numerical cancellations is also given. Published by the American Physical Society 2024

NICA Facilities for the Search for EDM Light Nuclei

To search for proton Electric Dipole Moments (EDM) using proton storage ring with purely electrostatic elements, the concept of frozen spin method has been proposed by Brookhaven National Laboratory. This method is based on two facts: in the equation of spin precession, the magnetic field dependence is entirely eliminated, and at the ‘‘magic’’ energy, the spin precession frequency coincides with the precession frequency of the particle momentum. In case of deuteron, we have to use the electrical and magnetic field simultaneously, keeping the frozen spin direction along the momentum as in the pure electrostatic ring. Later, Yu. Senichev proposed the concept of quasi-frozen spin, in which the spin oscillates around the direction of the pulse within half the value of the advanced phase of rotation in magnetic arcs, each time returning back in deflectors with an electrostatic field. Due to the low value of the anomalous magnetic moment of deuteron, an effective contribution to the expected EDM effect is reduced only by a few percent compared with frozen spin method. In this work, we consider the adapted structure of the NICA and Nuclotron synchrotrons, in which the ‘‘quasi-frozen spin’’ option can be implemented. The advantage of the ‘‘quasi-frozen spin’’ concept is the possibility of using synchrotrons already existing in the world that are not focused on studying EDM, which makes this method the only one possible for the accelerators of the NICA complex.

QCD bounds on leading-order hadronic vacuum polarization contributions to the muon anomalous magnetic moment

QCD bounds on the leading-order (LO) hadronic vacuum polarization (HVP) contribution to the anomalous magnetic moment of the muon [aμHVP,LO, aμ=(g−2)μ/2] are determined by imposing Hölder inequalities and related inequality constraints on systems of finite-energy QCD sum rules. This novel methodology is complementary to lattice QCD and data-driven approaches to determining aμHVP,LO. For the light-quark (u, d, s) contributions up to five-loop order in perturbation theory in the chiral limit, LO in light-quark mass corrections, next-to-leading order in dimension-four QCD condensates, and to LO in dimension-six QCD condensates, we find that (657.0±34.8)×10−10≤aμHVP,LO≤(788.4±41.8)×10−10, bridging the range between lattice QCD and data-driven values. Published by the American Physical Society 2024

First constraints on the Lμ− Lτ explanation of the muon g-2 anomaly from NA64-e at CERN

The inclusion of an additional U(1) gauge Lμ − Lτ symmetry would release the tension between the measured and the predicted value of the anomalous muon magnetic moment: this paradigm assumes the existence of a new, light Z′ vector boson, with dominant coupling to μ and τ leptons and interacting with electrons via a loop mechanism. The Lμ − Lτ model can also explain the Dark Matter relic abundance, by assuming that the Z′ boson acts as a “portal” to a new Dark Sector of particles in Nature, not charged under known interactions. In this work we present the results of the Z′ search performed by the NA64-e experiment at CERN SPS, that collected ~ 9 × 1011 100 GeV electrons impinging on an active thick target. Despite the suppressed Z′ production yield with an electron beam, NA64-e provides the first accelerator-based results excluding the g − 2 preferred band of the Z′ parameter space in the 1 keV <mZ′\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {m}_{Z^{\\prime }} $$\\end{document} ≲ 2 MeV range, in complementarity with the limits recently obtained by the NA64-μ experiment with a muon beam.

Confronting electroweak MSSM through one-loop renormalized neutralino-Higgs interactions for dark matter direct detection and the muon g−2

We compute the next-to-leading order (NLO) corrections to the vertices where a pair of the lightest neutralino couples to CP-even (light or heavy) Higgs scalars. In particular, the lightest neutralino is assumed to be a dominantly binolike mixed state, composed of bino and Higgsino or bino, wino, and Higgsino. After computing all the three-point functions in the electroweak minimal supersymmetric Standard Model (MSSM), we detail the contributions from the counterterms that arise in renormalizing these vertices in one-loop order. The amendment of the renormalized vertices impacts the spin-independent direct detection cross sections of the scattering of nucleons with dark matter. We perform a comprehensive numerical scan over the parameter space where all the points satisfy the present B-physics constraints and accommodate the muon’s anomalous magnetic moment. Finally, we exemplify a few benchmark points, which indulge the present searches of supersymmetric particles. After including the renormalized one-loop vertices, the spin-independent DM-nucleon cross sections may be enhanced up to 20% compared to its tree-level results. Finally, with the NLO cross section, we use the recent LUX-ZEPLIN (LZ) results on the neutralino-nucleon scattering to display the relative rise in the lowest allowed band of the Higgsino mass parameter in the M1−μ plane of the electroweak MSSM. Published by the American Physical Society 2024

Massless spin 2 field in 50-component approach: exact solutions with cylindrical symmetry, eliminating the guage degrees of freedom

We begin with some known results of the 50-component theory for a spin-2 field described in cylindrical coordinates. This theory is based on the use of a 2nd-rank symmetric tensor and a 3rd-rank tensor symmetric in two indices. In the massive case, this theory describes a spin-2 particle with an anomalous magnetic moment. According to the Fedorov – Gronskiy method, which is based on projective operators, all 50 functions involved in the description of the spin-2 field for the case of the free particle can be expressed in terms of only 7 different functions constructed from Bessel functions. This leads to a homogeneous system of linear algebraic equations for 50 numerical parameters. We have found 6 independent solutions to these equations. Additionally, we have obtained explicit expressions for 4 guage solutions defined in accordance with the Pauli – Fierz approach. These solutions are exact and correspond to non-physical states that do not affect observable quantities, such as the energy-momentum tensor. Finally, we have constructed two classes of solutions that represent physically observable states.

Charmonium production in hot magnetized hyperonic matter: Effects of the baryonic Dirac sea and pseudoscalar-vector mixing

We investigate the medium modifications of the masses of pseudoscalar open charm (D and D¯) mesons and the charmonium state [ψ(3770)] in hot isospin asymmetric strange hadronic medium in the presence of an external magnetic field within a chiral effective model. The in-medium partial decay widths of ψ(3770) to charged and neutral DD¯ mesons are computed from the medium modifications of the masses of the initial and final state mesons. These are computed using two light quark pair creation models—(I) the P03 model and (II) a field theoretical (FT) model of composite hadrons with quark (and antiquark) constituents. The production cross sections of ψ(3770), arising from scattering of the D and D¯ mesons, are computed from the relativistic Breit-Wigner spectral function expressed in terms of the in-medium masses and the decay widths of the charmonium state. The effects of the magnetic field are considered due to the Dirac sea (DS) of the baryons, the mixing of the pseudoscalar (S=0) and vector (S=1) meson (PV mixing), the Landau level contributions for the charged hadrons. The anomalous magnetic moments (AMMs) of the baryons are also taken into account in the present study. For magnetized nuclear matter, at ρB=ρ0, the effect of Dirac sea leads to inverse magnetic catalysis (IMC), which is drop of the magnitude of the light quark condensates (proportional to the scalar fields) with increase in the magnetic field, contrary to the opposite effect of magnetic catalysis (MC) at ρB=0. The inclusion of hyperons to the nuclear medium is observed to lead to magnetic catalysis. There are observed to be significant effects from the DS and PV mixing on the properties of the charm mesons. The production cross sections of ψ(3770) arising due to scattering of D+D−(D0D¯0) mesons in the hot magnetized strange hadronic matter are observed to have distinct peak positions, when the magnetic field is large. This is because the production cross sections have contributions from the transverse as well as longitudinal components of ψ(3770), which have nondegenerate masses due to PV [ψ(3770)−ηc′] mixing. These can have observable consequences on the dilepton spectra as well as on the production of the charm mesons in ultrarelativistic peripheral heavy ion collision experiments, where the produced magnetic field is huge. Published by the American Physical Society 2024

Nonlocal QED and lepton g-2 anomalies

Quantum electrodynamics is generally extended to a nonlocal QED by introducing the correlation functions. The gauge link is introduced to guarantee that the nonlocal QED is locally U(1) gauge invariant. The corresponding Feynman rules as well as the proof of Ward–Takahashi identity are presented. As an example, the anomalous magnetic moments of leptons are studied in nonlocal QED. At one-loop level, besides the ordinary diagrams, there are many additional Feynman diagrams which are generated from the gauge link. It shows the nonlocal QED can provide a reasonable explanation for lepton g-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$g-2$$\\end{document} anomalies.

Exact classical approach to the electron's self-energy and anomalous g-factor

An exact classical approach to the calculation of electron's self-energy and anomalous g-factor is reported. The electron's intrinsic dynamics, related electrodynamics and occurrence of anomalous magnetic moment are completely determined. A unique regularization of the electromagnetic field scalar potential underlying all results is derived. A fundamental transcendental equation satisfied by the electron's anomalous g-factor is obtained, with solution , matching the experimentally measured value reported in the literature to 0.59 parts per trillion. Field representation of the electron intrinsic and orbital dynamics in atoms is discussed.

Testing Z boson rare decays Z→H1γ,A1γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\rightarrow H_1 \\gamma , A_1 \\gamma $$\\end{document} with (g-2)μ,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(g-2)_\\mu ,$$\\end{document}MW,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ M_W,$$\\end{document} and BR(hSM→Zγ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$BR(h_{\ extrm{SM}}\\rightarrow Z\\gamma )$$\\end{document} in the NMSSM

We study the rare decay process of Z boson into photon, accompanied by a CP-even or CP-odd scalar. We present the analytical delineation of the processes through the model-independent parametrizations of the new physics couplings and, finally, consider the Next-to-Minimal Supersymmetric Standard Model to mark out the parameter space where the branching fraction can have the maximum value. As a part of the necessary phenomenological and experimental cross-checks, we aim to fit the anomalous magnetic moment of the muon and W boson mass anomaly through the supersymmetric contributions. We also find that the decays Z→H1γ,A1γ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Z\\rightarrow H_1 \\gamma , A_1 \\gamma $$\\end{document} can serve as an excellent complementary test to BR(hSM→Zγ).\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$BR(h_{\ extrm{SM}}\\rightarrow Z\\gamma ).$$\\end{document} In fact, to facilitate future searches, we unveil a few benchmark points that additionally satisfy the deviation of BR(hSM→Zγ)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$BR(h_{\ extrm{SM}}\\rightarrow Z\\gamma )$$\\end{document} from the SM value based on the recent measurements of ATLAS and CMS. Future proposals such as ILC, CEPC, and FCC-ee are anticipated to operate for multiple years, focusing on center-of-mass energy near the Z pole. Consequently, these projects will be capable of conducting experiments at the Giga-Z(109\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(10^{9}$$\\end{document} of Z bosons) and Tera-Z(1012\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(10^{12}$$\\end{document} of Z bosons) phases, which may probe the aforesaid rare decay processes, thus the model as well. These unconventional yet complementary searches offer different routes to explore the supersymmetric models with extended Higgs sectors like NMSSM.

Flavor-violating ALPs, electron g−2 , and the Electron-Ion Collider

We revisit the possibility that light axionlike particles (ALPs) with lepton-flavor-violating couplings could give significant contributions to the electron’s anomalous magnetic moment ge−2. Unlike flavor diagonal lepton-ALP couplings, which are exclusively axial, lepton-flavor-violating couplings can have arbitrary chirality. Focusing on the e−τ ALP coupling, we find that the size of the contribution to ge−2 depends strongly on the chirality of the coupling. A significant part of the parameter space for which such a coupling can explain experimental anomalies in ge−2 can be probed at the Electron-Ion Collider, which is uniquely sensitive to the chirality of the coupling using the polarization of the electron beam. Published by the American Physical Society 2024

Interpreting the W-mass and muon (gμ − 2) anomalies within a 2-Higgs doublet model

In this study, we investigate the anomalous magnetic moment of the muon (gμ−2) as reported by Fermilab (FNAL), along with the recent measurement of the W-boson mass by the CDF-II collaboration. Both findings show significant deviations from the predictions of the Standard Model (SM), hinting at the possibility of new physics. Our focus is on the Type III two-Higgs-doublet model (2HDM), wherein both Higgs doublets couple with all fermions, leading to the induction of flavour-changing neutral currents (FCNCs) at the tree level. Within this framework, we investigate a lepton-flavour-violating (LFV) scenario, aiming to explain both observed anomalies, while satisfying the up-to-date theoretical and experimental constraints.

Two-loop contributions of axion-like particles to electromagnetic and chromomagnetic form factors

Axions and axion-like particles emerge in many models for physics beyond the Standard Model. Thus, they have gained increasing research interest in both experimental and theoretical physics apart from their original proposition as a solution to the strong CP-problem. Among other aspects it has recently been shown that ALPs can potentially provide a solution to the long-lasting discrepancy between theory and experiment of the anomalous magnetic moment of the muon. Provided that the ALP has flavor-violating couplings to leptons, they can also mediate flavor-violating decays like μ→eγ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mu \\rightarrow e\\gamma $$\\end{document}. Both processes are mediated through related form factors that we compute to two-loop order. We further show numerical implications of our calculations and how they might affect constraints on ALP couplings derived from experiments.

Measurement of the e+e−→π+π− cross section from threshold to 1.2 GeV with the CMD-3 detector

The cross section of the process e+e−→π+π− has been measured in the center of mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on a full dataset collected below 1 GeV during three data taking seasons, corresponding to an integrated luminosity of about 62 pb−1. In the dominant ρ-resonance region, a systematic uncertainty of 0.7% has been reached. At energies around ϕ-resonance the π+π− production cross section was measured for the first time with high beam energy resolution. The forward-backward charge asymmetry in the π+π− production has also been measured. It shows a strong deviation from the theoretical prediction based on the conventional scalar quantum electrodynamics framework, and it is in good agreement with the generalized vector-meson-dominance and dispersive-based predictions. The impact of the presented results on the evaluation of the hadronic contribution to the anomalous magnetic moment of muon is discussed. Published by the American Physical Society 2024

Measurement of the Pion Form Factor with CMD-3 Detector and Its Implication to the Hadronic Contribution to Muon (g-2).

The cross section of the process e^{+}e^{-}→π^{+}π^{-} has been measured in the center-of-mass energy range from 0.32 to 1.2GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. The measurement is based on an integrated luminosity of about 88 pb^{-1}, of which 62 pb^{-1} represent a complete dataset collected by CMD-3 at center-of-mass energies below 1GeV. In the dominant region near the ρ resonance a systematic uncertainty of 0.7% was achieved. The implications of the presented results for the evaluation of the hadronic contribution to the anomalous magnetic moment of the muon are discussed.

Effects of center-of-mass correction and nucleon anomalous magnetic moments on nuclear charge radii

Effects of center-of-mass correction and nucleon anomalous magnetic moments on nuclear charge radii

Hadronic light-by-light scattering contributions to (g−2)μ from axial-vector and tensor mesons in the holographic soft-wall model

We compute the light axial-vector and tensor meson two-photon transition form factors in the soft-wall holographic model of quantum chromodynamics (QCD) in the flavor-symmetric case. They are used to evaluate the axial-vector and tensor meson contributions to the anomalous magnetic moment of the muon via the hadronic light-by-light scattering process. As expected, these contributions are smaller than the one from pseudoscalar mesons. The result for axial-vector mesons is higher than the value found in other approaches. Published by the American Physical Society 2024

Mass Interaction Principle as a Foundational Framework for Quantum Mechanics

This paper proposes mass interaction principle (MIP) as: the particles will be subjected to the random frictionless Brownian motion by the collision of space time particle(STP) ubiquitous in spacetime. The change in the amount of action of the particles during each collision is an integer multiple of the Planck constant h. The motion of particles under the action of STP is a Markov process. Under this principle, we infer that the statistical inertial mass of a particle is a statistical property that characterizes the difficulty of particle diffusion in spacetime. Within the framework of MIP, all the essences of quantum mechanics are derived, which proves that MIP is the origin of quantum mechanics. Due to the random collisions between STP and the matter particles, matter particles are able to behave exactly as required by the supervisor and shepherd for all microscopic behaviors of matter particles. More importantly, we solve a world class puzzle about the anomalous magnetic moment of muon in the latest experiment,and give a self-consistent explanation to the lifetime discrepancy of muon between standard model prediction and experiments at the same time. Last but not least, starting from MIP, we prove the principle of entropy increasing and clarify the physical root of entropy at absolute zero. Within the framework of MIP, we comprehensively discussed the Copenhagen interpretation. It leads to an important conclusion that Copenhagen interpretation is unnecessary for the quantum mechanical system. We found that Maxwell’s classical electromagnetic theory is applicable to the microscopic world not as previously thought. The key is that Brownian motion and classical electromagnetic theory must be combined together to completely solve the problem of electrons outside the nucleus not radiating electromagnetic waves.

Lepton pair production in muon-nucleus scattering

The MUonE experiment aims at providing a novel determination of the leading hadronic contribution to the muon anomalous magnetic moment through the study of elastic muon-electron scattering. Since the initial-state electrons are bound in a low-Z atomic target, the interaction between the incoming muons and the nuclei is expected to be the main source of experimental background. In this article, we study the production of a real lepton pair from the muon-nucleus scattering, discussing its numerical impact in the MUonE kinematic configuration. The process is described as a scattering of a muon in an external Coulomb field with the addition of a form factor to describe the nuclear charge distribution. The calculation is implemented in the fully differential Monte Carlo event generator Mesmer, without introducing any approximation on the angular variables.

Singlet-doublet fermion Dark Matter with Dirac neutrino mass, (g − 2)μ and ∆Neff

We study the possibility of generating light Dirac neutrino mass via scotogenic mechanism where singlet-doublet fermion Dark Matter (DM) plays non-trivial role in generating one-loop neutrino mass, anomalous magnetic moment of muon: (g − 2)μ as well as additional relativistic degrees of freedom ∆Neff within reach of cosmic microwave background (CMB) experiments. We show that the Dirac nature of neutrinos can bring interesting correlations within the parameter space satisfying the (g − 2)μ, DM relic density and the effective relativistic degrees of freedom ∆Neff. While we stick to thermal singlet-doublet DM with promising detection prospects, both thermal and non-thermal origin of ∆Neff have been explored. In addition to detection prospects of the model at DM, (g − 2)μ and other particle physics experiments, it remains verifiable at future CMB experiments like CMB-S4 and SPT-3G.