The magnetic moment of the muon can receive significant two-loop contributions from a light pseudoscalar. Notably, the spectrum of scalars of 3-3-1 models includes one pseudoscalar. However, this scalar spectrum inevitably gives rise to flavor-changing neutral current (FCNC) processes. In this study, we examine, within the 3-3-1 model with right-handed neutrinos, whether such spectrum of scalars can account for the anomalous magnetic moment of the muon, considering the constraints imposed by $\textit{B}$-meson decays, meson mixing, and invisible Higgs decays. Our principal finding reveals that a pseudoscalar with mass around 66 GeV and $$\tan \beta =58$$ can account for the $$g-2$$ anomaly without conflicting with flavor physics.

Brazil

A. Doff

Spain

João Pinheiro

C. S. Pires

Exploring solutions to the muon g-2 anomaly in a 3-3-1 model under flavor constraints

We study the most general $\textit{G}$ -invariant AdS vacua in 11 dimensional supergravity preserving 4 real supercharges, with the goal of understanding the IR fixed points of the RG flow induced by the cubic deformation of the ABJM theory. We identify a new $\textit{G}$ -invariant background, which completes the web of RG flows connecting its holographic dual with the ABJM theory and the (cubic analogue of) mass-deformed ABJM theory with SU(3) × U(1) isometry. Our holographic study gives non-trivial predictions for the strongly-coupled field theory dual.

Belgium

China

Xuao Zhang

New $\textit{G}$

Despite the prominence of tensor mesons in photon-photon collisions, until recently their contribution to the hadronic light-by-light (HLbL) scattering part of the anomalous magnetic moment of the muon has been estimated to be at the level of only a few 10 , with an almost negligible contribution to the error budget of the Standard Model prediction. A recent reanalysis within the dispersive approach has found that after resolving the issue of kinematic singularities in previous approaches, a larger result is obtained, a few 10 , and with opposite sign as in previous results, when a simple quark model for the transition form factors is employed. In this paper, we present the first complete evaluation of tensor meson contributions within a hard-wall model in holographic QCD, which reproduces surprisingly well mass, two-photon width, and the observed singly virtual transition form factors of the dominant $\textit{f}$ (1270), requiring only that the energy-momentum tensor correlator is matched to the leading OPE result of QCD. Due to a second structure function that is absent in the quark model and in lowest-order resonance chiral theory, the result for $\textit{a}$ turns out to be positive instead of negative, and also with a magnitude of a few 10 . We discuss both pole and non-pole contributions arising from tensor meson exchanges in the holographic HLbL amplitude, finding that keeping all contributions improves dramatically the convergence of a sum over excited tensor mesons and avoids unnaturally large contributions from the first few excited modes at low energies. Moreover, we find that the infinite tower of tensor mesons permits to fill the gap in the symmetric longitudinal short-distance constraint on the HLbL amplitude left by the contribution of axial vector mesons. Matching the corresponding leading-order OPE result leads to two-photon couplings consistent with the observed combined effects of the ground-state $\textit{f}$ $\textit{, a}$ $\textit{,}$ $$ {f}_2^{\prime } $$ multiplet and a total $$ {a}_{\mu}^{\textrm{Tensor}} $$ contribution of +12$\textit{.}$4 × 10 ; with an $\textit{F}$ fit this is reduced slightly to +11$\textit{.}$1 × 10 . A contribution of this size from the tensor sector could explain the tension between the most recent dispersive and lattice results for $$ {a}_{\mu}^{\textrm{HLbL}} $$ .

Italy

Luigi Cappiello

Austria

Josef Leutgeb

Jonas Mager

Anton Rebhan

Tensor meson transition form factors in holographic QCD and the muon $\textit{g −}$ 2

We present results for the dominant light-quark connected contribution to the long-distance window of the hadronic vacuum polarization (HVP) contribution to the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math> from lattice quantum chromodynamics. Specifically, with a new determination of the lattice scale on MILC’s physical-mass HISQ ensembles, using the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi mathvariant="normal">Ω</mi><mo>−</mo></msup></math> baryon mass, we obtain a result of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>a</mi></mrow><mrow><mi>μ</mi></mrow><mrow><mi>l</mi><mi>l</mi><mo>,</mo><mi>LD</mi></mrow></msubsup><mo stretchy="false">(</mo><mrow><mi>conn</mi></mrow><mo stretchy="false">)</mo><mo>=</mo><mn>400.2</mn><mo stretchy="false">(</mo><mn>2.3</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mi>stat</mi></mrow></msub><mo stretchy="false">(</mo><mn>3.7</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mi>syst</mi></mrow></msub><mo stretchy="false">[</mo><mn>4.3</mn><msub><mrow><mo stretchy="false">]</mo></mrow><mrow><mtext>total</mtext></mrow></msub><mo>×</mo><mspace linebreak="goodbreak"></mspace><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>10</mn></mrow></msup></mrow></math>. Summing this result with our recent determinations of the light-quark connected contributions to the short- and intermediate-distance windows, we obtain a subpercent precision determination of the light-quark-connected contribution to HVP of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>a</mi></mrow><mrow><mi>μ</mi></mrow><mrow><mi>l</mi><mi>l</mi></mrow></msubsup><mo stretchy="false">(</mo><mrow><mi>conn</mi></mrow><mo stretchy="false">)</mo><mo>=</mo><mn>655.2</mn><mo stretchy="false">(</mo><mn>2.3</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mi>stat</mi></mrow></msub><mo stretchy="false">(</mo><mn>3.9</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><mi>syst</mi></mrow></msub><mo stretchy="false">[</mo><mn>4.5</mn><msub><mrow><mo stretchy="false">]</mo></mrow><mrow><mtext>total</mtext></mrow></msub><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>10</mn></mrow></msup></mrow></math>. Finally, as a consistency check, we verify that an independent analysis of the full contribution is in agreement with the sum of individual windows. We discuss our future plans for improvements of our HVP calculations to meet the target precision of the Fermilab <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math> experiment.

United States

Alexei Bazavov

Claude W. Bernard

David A. Clarke

United Kingdom

Christine Davies

Carleton DeTar

Aida X. El-Khadra

Elvira Gámiz

Steven Gottlieb

Anthony V. Grebe

Leon Hostetler

William I. Jay

Hwancheol Jeong

Andreas S. Kronfeld

Shaun Lahert

Jack Laiho

G. Peter Lepage

Michael Lynch

Andrew T. Lytle

Craig McNeile

Ethan T. Neil

Curtis T. Peterson

James N. Simone

Jacob W. Sitison

Ruth S. Van de Water

Alejandro Vaquero

Hadronic Vacuum Polarization for the Muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math> from Lattice QCD: Long-Distance and Full Light-Quark Connected Contribution

We point out that the odd-in-velocity contribution to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mi>G</mi><mn>4</mn></msup><mo stretchy="false">)</mo></math> radiated angular momentum for two-body scattering is determined by the radiation-reaction (RR) term in the one-loop waveform. This RR term is actually proportional to the tree-level waveform, and this reduces the calculation of the odd-in-velocity contribution to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mi>G</mi><mn>4</mn></msup><mo stretchy="false">)</mo></math> angular momentum loss, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>J</mi></mrow><mrow><mn>2</mn><mtext> </mtext><mtext> </mtext><mi>rad</mi></mrow></msub></mrow></math>, to two loops, instead of three loops as one would expect by power counting. We exploit this simplification, which follows from unitarity, to obtain a closed-form expression for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>J</mi></mrow><mrow><mn>2</mn><mtext> </mtext><mtext> </mtext><mi>rad</mi></mrow></msub></mrow></math> for generic velocities, which resums all fractional post-Newtonian (PN) corrections to the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mi>G</mi><mn>4</mn></msup><mo stretchy="false">)</mo></math> angular momentum loss starting at 1.5PN.

France

Carlo Heissenberg

Radiation-reaction and angular momentum loss at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><msup><mrow><mi>G</mi></mrow><mrow><mn>4</mn></mrow></msup><mo stretchy="false">)</mo></mrow></math>

The low-energy spectrum relevant to the lattice calculation of the hadronic vacuum polarization contribution to muon anomalous magnetic moment <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>a</mi><mi>μ</mi><mrow><mi>HVP</mi><mo>,</mo><mi>LO</mi></mrow></msubsup></math> is dominantly given by two-pion states satisfying Lüscher’s finite-volume quantization condition. Finite-volume effects from those states may exhibit power-law dependence on the volume, contrary to an exponential suppression as suggested by chiral effective theory. Employing the finite-volume state decomposition of Euclidean correlators, we systematically investigate the volume dependence and identify the different volume scalings depending on the volume and Euclidean-time region. Using phenomenological inputs for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>π</mi><mi>π</mi></math> phase shift and the timelike pion form factor, we obtain an estimate for the finite-volume effects on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>a</mi><mi>μ</mi><mrow><mi>HVP</mi><mo>,</mo><mi>LO</mi></mrow></msubsup></math>, which is consistent with previous works. Numerical results are given for the “window” observables of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>a</mi><mi>μ</mi></msub></math>.

Japan

Sakura Itatani

Hidenori Fukaya

Shoji Hashimoto

Anatomy of finite-volume effects on the hadronic vacuum polarization contribution to the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math>

We present a calculation of the leading two-loop corrections to the axial-vector coupling constant <math altimg='si1.svg'><msub><mrow><mi>g</mi></mrow><mrow><mi>A</mi></mrow></msub></math> in two covariant versions of two-flavor baryon chiral perturbation theory. Taking the low-energy constants from a combined analysis of elastic and inelastic pion-nucleon scattering, we find that these corrections are rather moderate.

Véronique Bernard

Germany

Georgia

Jambul Gegelia

Shayan Ghosh

Ulf-G. Meißner

Calculation of the axial-vector coupling constant <italic>g</italic> <inf><italic>A</italic></inf> to two loops in covariant chiral perturbation theory

The novel Branching-Ratio Method (BRM) for the determination of effective value <math altimg='si1.svg'><msubsup><mrow><mi>g</mi></mrow><mrow><mi mathvariant='normal'>A</mi></mrow><mrow><mi mathvariant='normal'>eff</mi></mrow></msubsup></math> of the weak axial coupling <math altimg='si2.svg'><msub><mrow><mi>g</mi></mrow><mrow><mi mathvariant='normal'>A</mi></mrow></msub></math> for forbidden non-unique (FNU) <math altimg='si3.svg'><msup><mrow><mi>&#946;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup></math>/electron-capture(EC) decays is introduced. The method offers new possibilities for testing the fitness of nuclear Hamiltonians in modeling the physics of complex <math altimg='si3.svg'><msup><mrow><mi>&#946;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup></math>/EC decays. The constraint of simultaneously reproducing the branching to <math altimg='si3.svg'><msup><mrow><mi>&#946;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup></math> and EC transitions offers an additional constraint in tackling the problem of <math altimg='si1.svg'><msubsup><mrow><mi>g</mi></mrow><mrow><mi mathvariant='normal'>A</mi></mrow><mrow><mi mathvariant='normal'>eff</mi></mrow></msubsup></math> determination. In the BRM the ambiguity in the choice of the values of <math altimg='si1.svg'><msubsup><mrow><mi>g</mi></mrow><mrow><mi mathvariant='normal'>A</mi></mrow><mrow><mi mathvariant='normal'>eff</mi></mrow></msubsup></math> and s-NME (small relativistic vector nuclear matrix element) is lifted when constraints of the branching ratios of <math altimg='si3.svg'><msup><mrow><mi>&#946;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup></math> and EC decays are applied. As an example, in the present work we apply BRM to the case of second FNU <math altimg='si3.svg'><msup><mrow><mi>&#946;</mi></mrow><mrow><mo linebreak='badbreak' linebreakstyle='after'>+</mo></mrow></msup></math>/EC decay of 59Ni. This decay is treated with three different nuclear shell-model (NSM) Hamiltonians demonstrating the effects of different nuclear-structure aspects in application of the BRM.

Finland

Aagrah Agnihotri

Romania

Jouni Suhonen

Novel way of evaluating <italic>g</italic> <inf><italic>A</italic></inf> quenching in <italic>&#946;</italic> +/EC decays: Introducing the Branching-Ratio Method (BRM)

In this paper, we consider hard-wall anti–de Sitter/quantum chromodynamics (AdS/QCD) models extended by a string-theory inspired Chern-Simons action in terms of a superconnection involving a bifundamental scalar field which corresponds to the open-string tachyon of brane-antibrane configurations and which is naturally identified with the holographic dual of the quark condensate in chiral symmetry breaking. This realizes both the axial and chiral anomalies of QCD with a Witten-Veneziano mechanism for the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>η</mi><mo>′</mo></msup></math> mass in addition to current quark masses, but somewhat differently than in the Katz-Schwartz AdS/QCD model used previously by us to evaluate pseudoscalar and axial vector transition form factors and their contribution to the hadronic light-by-light (HLBL) piece of the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math>. Compared to the Katz-Schwartz model, we obtain a significantly more realistic description of axial-vector mesons with regard to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo>−</mo><msubsup><mi>f</mi><mn>1</mn><mo>′</mo></msubsup></math> mixing and equivalent photon rates. Moreover, predictions of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mn>1</mn></msub><mo stretchy="false">→</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup></math> branching ratios are found to be in line with a recent phenomenological study. However, pseudoscalar transition form factors compare less well with experiment; in particular the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>π</mi><mn>0</mn></msup></math> transition form factor turns out to be overestimated at moderate nonzero virtuality. For the combined HLBL contribution to the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math> from the towers of axial vector mesons and excited pseudoscalars we obtain, however, a result very close to that of the Katz-Schwartz model.

Superconnections in AdS/QCD and the hadronic light-by-light contribution to the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>

We propose a novel method to determine the strong coupling of quantum chromodynamics (QCD) and fix its running behavior at all scales by using the Bjorken sum rules (BSR). The BSR defines an effective coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msubsup><mrow><mi>α</mi></mrow><mrow><mi>s</mi></mrow><mrow><msub><mrow><mi>g</mi></mrow><mrow><mn>1</mn></mrow></msub></mrow></msubsup><mo stretchy="false">(</mo><mi>Q</mi><mo stretchy="false">)</mo></mrow></math> which includes the nonperturbative higher-twist corrections and perturbative QCD (pQCD) corrections to the leading-twist part. For the leading-twist part of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>α</mi><mi>s</mi><msub><mi>g</mi><mn>1</mn></msub></msubsup><mo stretchy="false">(</mo><mi>Q</mi><mo stretchy="false">)</mo></math>, we adopt the infinite-order scale-setting procedure of the principle of maximum conformality (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>PMC</mi><mi>∞</mi></msub></math>) to deal with its pQCD corrections, which reveals the intrinsic conformality of the series and eliminates conventional renormalization scheme-and-scale ambiguities. Using the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>PMC</mi><mi>∞</mi></msub></math> approach, we not only eliminate the first kind of residual scale dependence due to uncalculated higher-order terms, but also resolve the previous “self-consistency problem.” The light-front holographic QCD model is used for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>α</mi><mi>s</mi><msub><mi>g</mi><mn>1</mn></msub></msubsup><mo stretchy="false">(</mo><mi>Q</mi><mo stretchy="false">)</mo></math> in the infrared region, which also reveals a conformal behavior at <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>Q</mi><mo stretchy="false">→</mo><mn>0</mn></math>. As a combination, we obtain a precise <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>α</mi><mi>s</mi><msub><mi>g</mi><mn>1</mn></msub></msubsup><mo stretchy="false">(</mo><mi>Q</mi><mo stretchy="false">)</mo></math> at all scales, which matches well with the known experimental data with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi></math>-value <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mn>98</mn><mo>%</mo></math>, and determines the strong coupling constant at the scale <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>M</mi><mi>Z</mi></msub></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>α</mi><mi>s</mi></msub><mo stretchy="false">(</mo><msub><mi>M</mi><mi>Z</mi></msub><mo stretchy="false">)</mo><mo>=</mo><mn>0.122</mn><msubsup><mn>0</mn><mrow><mo>−</mo><mn>0.0012</mn></mrow><mrow><mo>+</mo><mn>0.0011</mn></mrow></msubsup><mo stretchy="false">(</mo><mi mathvariant="normal">Δ</mi><mi>κ</mi><msubsup><mo stretchy="false">)</mo><mrow><mo>+</mo><mn>0.0007</mn></mrow><mrow><mo>−</mo><mn>0.0046</mn></mrow></msubsup><mo stretchy="false">(</mo><mrow><mi>the</mi><mo>.</mo></mrow><mo stretchy="false">)</mo></math>, where the first error comes from <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Δ</mi><mi>κ</mi></math> of LFHQCD model and the second error is from the second kind of residual scale dependence.

Qing Yu

Xing-Gang Wu

Hua Zhou

Jian-Ming Shen

Determination of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>α</mi><mi>s</mi></msub><mo stretchy="false">(</mo><msub><mi>M</mi><mi>Z</mi></msub><mo stretchy="false">)</mo></math> via a high-precision effective coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>α</mi><mi>s</mi><msub><mi>g</mi><mn>1</mn></msub></msubsup><mo stretchy="false">(</mo><mi>Q</mi><mo stretchy="false">)</mo></math>