4 pages. Invited talk at 16th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY08), June 16-21 2008, Seoul, Korea
After a brief review of the muon g-2 status, we discuss hypothetical errors in the Standard Model prediction that could explain the present discrepancy with the experimental value. None of them looks likely. In particular, an hypothetical increase of the hadroproduction cross section in low-energy e^+e^- collisions could bridge the muon g-2 discrepancy, but is shown to be unlikely in view of current experimental error estimates. If, nonetheless, this turns out to be the explanation of the discrepancy, then the 95% CL upper bound on the Higgs boson mass is reduced to about 130 GeV which, in conjunction with the experimental 114.4 GeV 95% CL lower bound, leaves a narrow window for the mass of this fundamental particle.
On April 7, 2001 the Muon g-2 Experiment at Fermilab presented its first results which lead to a 4.2$σ$ discrepancy between the world average of the muon anomalous magnetic dipole moment and the standard model prediction of this quantity. I take issue with the statistical meaning of this finding.
The observed value of the muon magnetic dipole moment, which deviates from the Standard Model prediction by $4.2σ$, can be explained in models with weakly-interacting massive particles (WIMPs) coupled to muons. However, a considerable range of parameter space of such models will remain unexplored in the future LHC experiments and dark matter (DM) direct searches. In this work we discuss the temperature observation of neutron stars (NSs) as a promising way to probe such models given that WIMPs are efficiently captured by NSs through DM-muon or spin-dependent DM-nucleon scattering. The captured …
The confirmation of the discrepancy with the Standard Model predictions in the anomalous magnetic moment by the Muon g-2 experiment at Fermilab points to a low scale of new physics. Flavour symmetries broken at low energies can account for this discrepancy but these models are much more restricted, as they would also generate off-diagonal entries in the dipole moment matrix. Therefore, if we assume that the observed discrepancy in the muon $g-2$ is explained by the contributions of a low-energy flavor symmetry, lepton flavour violating processes can constrain the structure of the lepton mass m…
Very recently, the Muon $g-2$ experiment at Fermilab has confirmed the E821 Brookhaven result, which hinted at a deviation of the muon anomalous magnetic moment from the Standard Model (SM) expectation. The combined results from Brookhaven and Fermilab show a difference with the SM prediction $δa_μ= (251 \pm 59) \times 10^{-11}$ at a significance of $4.2σ$, strongly indicating the presence of new physics. Motivated by this new result we reexamine the contributions to the muon anomalous magnetic moment from both: (i)~the ubiquitous $U(1)$ gauge bosons of D-brane string theory constructions and …
The theoretical predictions in the standard model (SM) and measurements on the anomalous magnetic dipole moments (MDM) of muon and electron have great precision, hence the MDMs of muon and electron have close relation with the new physics (NP) beyond the SM. Recently, a negative $\sim2.4σ$ discrepancy between the measured electron MDM and the SM prediction results from a recent improved determination of the fine structure constant. Combined with the long-lasting muon MDM discrepancy which is about $\sim3.7σ$, it is difficult to explain both the magnitude and opposite signs of the deviations in…
The latest measurements of the anomalous muon magnetic moment $a^{}_μ\equiv (g^{}_μ- 2)/2$ show a $4.2σ$ discrepancy between the theoretical prediction of the Standard Model and the experimental observations. In order to account for such a discrepancy, we consider a possible extension of the type-(I+II) seesaw model for neutrino mass generation with a gauged $L^{}_μ- L^{}_τ$ symmetry. By explicitly constructing an economical model with only one extra scalar singlet, we demonstrate that the gauge symmetry $U(1)^{}_{L^{}_μ- L^{}_τ}$ and its spontaneous breaking are crucially important not only f…
The discrepancy between the measured value and the Standard Model prediction of the muon anomalous magnetic moment is one of the most important issues in the particle physics. It is known that introducing a mediator boson X with the $μτ$ lepton flavor violating (LFV) couplings is one good solution to explain the discrepancy, due to the $τ$ mass enhancement in the one-loop correction. In this paper, we study the signal of this model, i.e. the same-sign leptons, in the Belle II experiment, assuming the flavor-diagonal couplings are suppressed. We show that the Belle II experiment is highly sensi…
We present a model that gives a natural explanation to the charged lepton mass hierarchy and study the contributions to the electron and the muon $g-2$. In the model, we introduce lepton-flavor-dependent $U(1)_F$ symmetry and three additional Higgs doublets with $U(1)_F$ charges, to realize that each generation of charged leptons couples to one of the three additional Higgs doublets. The $U(1)_F$ symmetry is softly broken by $+1$ charges, and the smallness of the soft breaking naturally gives rise to the hierarchy of the Higgs VEVs, which then accounts for the charged lepton mass hierarchy. Si…
There has been a long-standing discrepancy between the experimental measurements of the electron and muon anomalous magnetic moments and their predicted values in the Standard Model. This is particularly relevant in the case of the muon $g-2$, which has attracted a remarkable interest in the community after the long-awaited announcement of the first results by the Muon $g-2$ collaboration at Fermilab, which confirms a previous measurement by the E821 experiment at Brookhaven and enlarges the statistical significance of the discrepancy, now at $4.2 σ$. In this paper we consider an extension of …
Electric dipole moments (EDMs) of elementary particles are powerful probes of new physics with flavor-diagonal CP violation. The reported discrepancy in the muon anomalous magnetic moment motivates us to explore to what extent new physics with flavor-diagonal CP violation to address the discrepancy is probed by searches for the muon EDM. As a benchmark, we focus on a CP-violating two-Higgs-doublet model to explain the muon $g-2$ anomaly where the muon exclusively couples to one Higgs doublet. Since contributions to flavor violating processes as well as the electron EDM are suppressed, the muon…
We propose a Standard Model extension by a $U(1)_{R}$ gauge symmetry where only right-handed chiral fermions can carry a non-trivial charge. Here we show that the simplest anomaly-free solution to accommodate the proton charge radius discrepancy takes right-handed muons $μ_R$ and first generation quarks, $u_R$ and $d_R$. Consistency with the latest muon's $(g-2)$ measurements is achieved through an extra light scalar, which itself must lie in the tens of MeV mass range to be viable.
The discrepancy between the muon $g-2$ measurement and the Standard Model prediction points to new physics around or below the weak scale. It is tantalizing to consider the loop effects of a heavy axion (in the general sense, also known as an axion-like particle) coupling to leptons and photons as an explanation for this discrepancy. We provide an updated analysis of the necessary couplings, including two-loop contributions, and find that the new physics operators point to an axion decay constant on the order of 10s of GeV. This poses major problems for such an explanation, as the axion coupli…
The latest results of CDF-II collaboration show a discrepancy of $7σ$ with standard model expectations. There is, also, a $4.2σ$ discrepancy in the measurement of muon magnetic moment reported by Fermilab. We study the connection between neutrino masses, dark matter, muon ($g-2$) and W-boson mass anomaly within a single coherent framework based on $Z_{4}$ extension of the scotogenic model with vector like lepton (VLL). Neutrino masses are generated at one loop level. The inert doublet, also, provide a solution to W-boson mass anomaly through correction in oblique parameters $S$, $T$ and $U$. T…
Higgs mass and muon anomalous magnetic moment in the U(1) extended MSSM
我们研究了具有额外U（1）规范对称性的MSSM的唯象问题。我们发现，最轻的希格斯玻色子玻色子的质量可以增加到125 GeV，而不引入一个大的超对称尺度或大的A项，在CMSSM和规范介导的超对称破缺（GMSB）模型的框架。这一方案可以同时解释U（1）-扩展的CMSSM/GMSB模型中μ子异常磁矩（μ on g-2）在1 σ水平上的差异。在CMSSM的情况下，暗物质丰度也可以解释。
A number of predictions were made in von Buddenbrock et al (2016 Eur. Phys. J. C 76, 10, 580) pertaining to the anomalous production of multiple leptons at the Large Hadron Collider. Discrepancies in multi-lepton final states have now become statistically compelling with the available Run~2 data. These could be connected with a heavy boson, $H$, decaying predominantly into a SM Higgs boson, $h$, and a singlet scalar, $S$, where $m_H\approx 270$\,GeV and $m_S\approx 150$\,GeV. These can be embedded into a scenario where a Two Higgs Doublet is considered with an additional singlet scalar, 2HDM+S…
The discrepancy between the measured value and the Standard Model prediction for the muon anomalous magnetic moment is one of the important issues in the particle physics. In this paper, we consider a two Higgs doublet model (2HDM) where the extra Higgs doublet couples to muon and tau in lepton flavor violating (LFV) way and the one-loop correction involving the scalars largely contributes to the muon anomalous magnetic moment. The couplings should be sizable to explain the discrepancy, so that the extra Higgs bosons would dominantly decay into $μτ$ LFV modes, which makes the model testable at…
The statistical significance that characterizes a discrepancy between a measurement and theoretical prediction is usually calculated assuming that the statistical and systematic uncertainties are known. Many types of systematic uncertainties are, however, estimated on the basis of approximate procedures and thus the values of the assigned errors are themselves uncertain. Here the impact of the uncertainty {\it on the assigned uncertainty} is investigated in the context of the muon $g-2$ anomaly. The significance of the observed discrepancy between the Standard Model prediction of the muon's an…
The long-standing discrepancy of muon $g-2$ is a hint of new physics beyond the standard model of particle physics. In this letter we show that heavy new physics contribution can be fully tested at a muon collider with center-of-mass energy up to $O(10)\,$TeV. Even if there is no new particle in this energy range, one can measure the $g-2$ directly via the channel to a Higgs boson and a monochromatic photon.
Motivated by the long-standing discrepancy between the Standard Model prediction and the experimental measurement of the muon magnetic dipole moment, we have recently proposed to interpret this muon $g-2$ anomaly in terms of the loop effect induced by a new massive spin-2 field $G$. In the present paper, we investigate the unitarity bounds on this scenario. We calculate the $s$-wave projected amplitudes for two-body elastic scatterings of charged leptons and photons mediated by $G$ at high energies for all possible initial and final helicity states. By imposing the condition of the perturbativ…
The very precise measurement of the anomalous magnetic moment of the muon, recently released by the Muon g-2 experiment at Fermilab, can serve to set stringent constraints on new particles. If the observed 4$σ$ discrepancy from the Standard Model value is indeed real, it will set a tight margin on the scale of the masses and couplings of these particles. Instead, if the discrepancy is simply a result of additional theoretical and experimental uncertainties to be included, strong constraints can be put on their parameters. In this mini-review, we summarize the impact of the latest muon g-2 meas…
Topcolor and the First Muon Collider (Talk presented at the Workshop on Physics at the First Muon Collider and at the Front End of the Muon Collider, Nov. 1997)
