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Alvarado, F., Alvarez-Ruso, L., Hernandez, E., Nieves, J., & Penalva, N. (2024). The Λc → Λ ℓ+ ν ℓ weak decay including new physics. J. High Energy Phys., 10(10), 137–24pp.
Abstract: We investigate the Lambda(c) -> Lambda & ell;(+)nu(& ell;) decay with a focus on potential new physics (NP) effects in the & ell; = μchannel. We employ an effective Hamiltonian within the framework of the Standard Model Effective Field Theory (SMEFT) to consider generalized dimension-6 semileptonic c -> s operators of scalar, pseudoscalar, vector, axial-vector and tensor types. We rely on Lattice QCD (LQCD) for the hadronic transition form factors, using heavy quark spin symmetry (HQSS) to determine those that have not yet been obtained on the lattice. Uncertainties due to the truncation of the NP Hamiltonian and different implementations of HQSS are taken into account. As a result, we unravel the NP discovery potential of the Lambda(c) -> Lambda semileptonic decay in different observables. Our findings indicate high sensitivity to NP in lepton flavour universality ratios, probing multi-TeV scales in some cases. On the theoretical side, we identify LQCD uncertainties in axial and vector form factors as critical for improving NP sensitivity, alongside better SMEFT uncertainty estimations.
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Bijnens, J., Hermansson-Truedsson, N., & Rodriguez-Sanchez, A. (2025). Constraints on the hadronic light-by-light tensor in corner kinematics for the muon g-2. J. High Energy Phys., 03(3), 094–36pp.
Abstract: The dispersive approach to the hadronic light-by-light contribution to the muon g – 2 involves an integral over three virtual photon momenta appearing in the light-by-light tensor. Building upon previous works, we systematically derive short-distance constraints in the region where two momenta are large compared to the third, the so-called Melnikov-Vainshtein or corner region. We include gluonic corrections for the different scalar functions appearing in the Lorentz decomposition of the underlying tensor, and explicitly check analytic agreement with alternative operator product expansions in overlapping regimes of validity. A very strong pattern of cancellations is observed for the final g – 2 integrand. The last observation suggests that a very compact expression only containing the axial current form factors can provide a good approximation of the corner region of the hadronic light-by-light tensor.
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Davier, M., Diaz-Calderon, D., Malaescu, B., Pich, A., Rodriguez-Sanchez, A., & Zhang, Z. (2023). The Euclidean Adler function and its interplay with Delta alpha(had)(QED) and alpha(s). J. High Energy Phys., 04(4), 067–57pp.
Abstract: Three different approaches to precisely describe the Adler function in the Euclidean regime at around 2 GeVs are available: dispersion relations based on the hadronic production data in e(+)e(-) annihilation, lattice simulations and perturbative QCD (pQCD). We make a comprehensive study of the perturbative approach, supplemented with the leading power corrections in the operator product expansion. All known contributions are included, with a careful assessment of uncertainties. The pQCD predictions are compared with the Adler functions extracted from ?a( QED)(had)(Q(2)), using both the DHMZ compilation of e(+)e(-) data and published lattice results. Taking as input the FLAG value of a(s), the pQCD Adler function turns out to be in good agreement with the lattice data, while the dispersive results lie systematically below them. Finally, we explore the sensitivity to a(s) of the direct comparison between the data-driven, lattice and QCD Euclidean Adler functions. The precision with which the renormalisation group equation can be tested is also evaluated.
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Estrada, E. J., & Roig, P. (2026). Tensor meson pole contributions to the HLbL piece of aμHLbL within RχT. J. High Energy Phys., 01(1), 070–26pp.
Abstract: We compute the tensor meson pole contributions to the Hadronic Light-by-Light piece of a μin the purely hadronic region, using Resonance Chiral Theory. Given the differences between the dispersive and holographic groups determinations and the resulting discussion of the corresponding uncertainty estimate for the Hadronic Light-by-Light section of the muon g – 2 theory initiative second White Paper, we consider timely to present an alternative evaluation. In our approach, in addition to the lightest tensor meson nonet, two vector meson resonance nonets are considered, in the chiral limit.Disregarding operators with derivatives, only the form factor FT 1 is non-vanishing, as assumed in the dispersive study. All parameters are determined by imposing a set of short-distance QCD constraints, and the radiative tensor decay widths. In this case, we obtain the following results for the different contributions (in units of 10-11): aa2-pole μ= – (1.02(10)stat(+0.00 -0.12) syst), af2-pole μ= – (3.2(3)stat(+0.0 -0.4) syst) and af' 2 -pole μ= -(0.042(13)stat), which add up to aa2+f2+ f' 2 -pole μ= – (4.3+0.3 -0.5), in close agreement with the holographic result when truncated to FT 1 only. However, with an ad-hoc extended Lagrangian, that also generates FT 3, as in the holographic approach, we have found: aa2-pole μ= +0.47(1.43)norm(3)stat(+0.06 -0.00)syst, af2-pole μ= +1.18(4.18)norm(12)stat(+0.24 -0.00) syst and af' 2 -pole μ= +0.040(78)norm(2)stat, summing to aa2+f2+ f' 2 -pole μ= +1.7(4.4), which agree with these recent determinations within uncertainties (dominated by the FT 3 normalization). We point out that R.T generates all five form factors, differently to previous approaches. The contributions to a μof F2,4,5 cannot be evaluated in the current basis, preventing for the moment a complete calculation of aT-poles μwithin our framework.
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Estrada, E. J., Gonzalez-Solis, S., Guevara, A., & Roig, P. (2024). Improved π0, η, η′ transition form factors in resonance chiral theory and their aμHLbL contribution. J. High Energy Phys., 12(12), 203–48pp.
Abstract: Working with Resonance Chiral Theory, within the two resonance multiplets saturation scheme, we satisfy leading (and some subleading) chiral and asymptotic QCD constraints and accurately fit simultaneously the pi 0, eta, eta ' transition form factors, for single and double virtuality. In the latter case, we supplement the few available measurements with lattice data to ensure a faithful description. Mainly due to the new results for the doubly virtual case, we improve over existing descriptions for the eta and eta '. Our evaluation of the corresponding pole contributions to the hadronic light-by-light piece of the muon g – 2 read: a μpi 0-pole=61.9 +/- 0.6-1.5+2.4x10-11, a μeta-pole=15.2 +/- 0.5-0.8+1.1x10-11 and a μeta '-pole=14.2 +/- 0.7-0.9+1.4x10-11, for a total of a μpi 0+eta+eta '-pole=91.3 +/- 1.0-1.9+3.0x10-11, where the first and second errors are the statistical and systematic uncertainties, respectively.
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