Albandea, D., & Hernandez, P. (2025). Chiral and isospin breaking in the two-flavor Schwinger model. Phys. Rev. D, 111(7), 074503–11pp.
Abstract: The Schwinger model with two massive fermions is a nontrivial theory for which no analytical solution is known. The strong coupling limit of the theory allows for different semiclassical approximations to extract properties of its low-lying spectrum. In particular, analytical results exist for the fermion condensate, the fermion mass dependence of the pseudoscalar meson mass or its decay constant. These approximations, nonetheless, are not able to quantitatively predict isospin breaking effects in the light spectrum, for example. In this paper we use lattice simulations to test various analytical predictions and study isospin breaking effects from nondegenerate quark masses. We also introduce a low-energy effective field theory based on a nonlinear sigma model with a dilaton field, which leads to the correct fermion mass dependence of the pion mass, the correct sigma-to-pi mass ratio and a prediction of the isospin breaking effects, which we test numerically.
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Lopez Castro, G., Miranda, A., & Roig, P. (2025). Isospin breaking corrections in 2π production in tau decays and e plus e – annihilation: Consequences for the muon g -2 and conserved vector current tests. Phys. Rev. D, 111(7), 073004–26pp.
Abstract: We revisit the isospin-breaking corrections relating the e+e- hadronic cross section and the tau decay spectral function, focusing on the dipion channel, that gives the dominant contribution to the hadronic vacuum polarization piece of the muon g – 2. We test different types of electromagnetic and weak form factors and show that both, the Gounaris-Sakurai and a dispersive-based approach, describe accurately z lepton and e+e- data (less when KLOE measurements are included in the fits) and comply reasonably well with analyticity constraints. From these results we obtain the isospin-breaking contribution to the conserved vector current (CVC) prediction of the BR(z -> vz) and to the 2hadronic vacuum polarization (HVP) contribution to the muon g – 2, in agreement with previous determinations and with similar precision. Our results abound in the utility of using tau data-based results in the updated data-driven prediction of the muon g – 2 in the Standard Model.
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Estrada, E. J., Marquez, J. M., Portillo-Sanchez, D., & Roig, P. (2025). Proton-box contribution to aμHLbL. Phys. Rev. D, 111(9), 093008–9pp.
Abstract: We analyze the proton-box contribution to the hadronic light-by-light part of the muon's anomalous magnetic moment, which is the first reported baryonic contribution to this piece. We follow the quark-loop analysis, incorporating the relevant data-driven and lattice proton form factors. Although the heavy mass expansion would yield a contribution of O & eth;10-10 & THORN;, the damping of the form factors in the regions where the kernel peaks explains our finding μap-box 1/4 1.82 & eth;7 & THORN; x 10-12, 2 orders of magnitude smaller than the forthcoming uncertainty on the a μmeasurement and on its Standard Model prediction.
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Majumdar, A., Papoulias, D. K., Prajapati, H., & Srivastava, R. (2025). Constraining low scale dark hypercharge symmetry at spallation, reactor, and dark matter direct detection experiments. Phys. Rev. D, 111(7), 073006–24pp.
Abstract: Coherent elastic neutrino-nucleus (CEVNS) and elastic neutrino-electron scattering (EVES) data are exploited to constrain “chiral” U(1)X gauged models with light vector mediator mass. These models fall under a distinct class of new symmetries called dark hypercharge symmetries. A key feature is the fact that the Z' boson can couple to all Standard Model fermions at tree level, with the U(1)X charges determined by the requirement of anomaly cancellation. Notably, the charges of leptons and quarks can differ significantly depending on the specific anomaly cancellation solution. As a result, different models exhibit distinct phenomenological signatures and can be constrained through various experiments. In this work, we analyze the recent data from the COHERENT experiment, along with results from dark matter (DM) direct detection experiments such as XENONnT, LUX-ZEPLIN, and PandaX-4T, and place new constraints on three benchmark models. Additionally, we set constraints from a performed analysis of TEXONO data and discuss the prospects of improvement in view of the next-generation DM direct detection DARWIN experiment.
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Gariazzo, S., Giare, W., Mena, O., & Di Valentino, E. (2025). How robust are the parameter constraints extending the ΛCDM model? Phys. Rev. D, 111(2), 023540–24pp.
Abstract: We present model-marginalized limits on the six standard.CDM cosmological parameters (Omega(c) h(2), Omega(b) h(2), theta(MC), tau(reio), n(s) and A(s)), as well as on selected derived quantities (H-0, Omega(m), sigma(8), S-8 and r(drag)), obtained by considering several extensions of the.CDM model and three independent cosmic microwave background (CMB) experiments: the Planck satellite, the Atacama Cosmology Telescope, and South Pole Telescope. We also consider low redshift observations in the form of baryon acoustic oscillation (BAO) data from the SDSS-IV eBOSS survey and supernovae (SN) distance moduli measurements from the Pantheon-Plus catalog. The marginalized errors are stable against the different minimal extensions of the Lambda CDM model explored in this study. The largest impact on the parameter accuracy is produced by varying the effective number of relativistic degrees of freedom (N-eff) or the lensing amplitude (A(lens)). Nevertheless, the marginalized errors on some derived parameters such as H-0 or Omega(m) can be up to 2 orders of magnitude larger than in the canonical Lambda CDM scenario when considering only CMB data. In these cases, low redshift measurements are crucial for restoring the stability of the marginalized cosmological errors computed here. Overall, our results underscore remarkable stability in the mean values and precision of the main cosmological parameters once both high and low redshift probes are fully accounted for. The marginalized values can be used in numerical analyses due to their robustness and slightly larger errors, providing a more realistic and conservative approach.
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