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1. Kaon leptonic and semileptonic decays with Nf=2+1+1 HISQ fermions

   Merino, R; Bazavov, A; Bernard, C; DeTar, C; El-Khadra, AX; Gámiz, E; Gottlieb, S; Grebe, A; Heller, UM; Hostetler, L; et al (March 2026, PoS(LATTICE2025) 238)

   Mathur, Nilmani; Padmanath, Madanagopalan; Raychowdhury, Indrakshi (Ed.)

   Precision tests of the Standard Model (SM) currently show a deficit in first-row Cabibbo-Kobayashi-Maskawa (CKM) unitarity. In this talk, we discuss progress towards a correlated analysis of the lattice-QCD inputs needed to test this relation with kaon data using highly improved staggered quarks (HISQ) on the MILC Nf=2+1+1 configurations. We present the status of a new analysis of light-meson decay constant data where chiral-continuum fits are guided by staggered chiral perturbation theory (SChPT). The goal of SChPT is twofold: it allows us to use data not only at physical pion mass but also at unphysical masses. Moreover, it provides values of ChPT low energy constants (LECs) as well as their correlations. We also present a reanalysis of our previous kaon semileptonic form factor calculation, aiming to estimate correlations between the form factor and light-meson decay constants. We discuss the new methodology, new data included, and present some preliminary results. 

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2. B to π, B(s) to D(s)ℓν form factors from 2+1+1 flavor Lattice QCD

   Cassar, N; Chauhan, A; DeTar, C; El-Khadra, AX; Gámiz, E; Gottlieb, S; Jay, W; Kronfeld, A; Laiho, J; Lytle, A; et al (June 2026, PoS(LATTICE2025)252)

   Mathur, Nilmani; Padmanath, Madanagopalan; Raychowdhury, Indrakshi (Ed.)

   We present a lattice QCD calculation of the hadronic form factors for the semileptonic decays B→π and B(s)→D(s)ℓν, computed using the highly improved staggered quark action for both valence and sea quarks on the MILC collaboration’s 2+1+1-flavor ensembles with lattice spacings ranging from 0.09fm to 0.03fm, many with physical pion masses. On our finest ensembles, we compute the form factors directly at the physical b-quark mass. We discuss the computational setup and analysis strategies for two- and three-point correlation functions. For B(s)→D(s), we present preliminary results of chiral-continuum fits for the scalar and vector form factors. The goal of this project is a percent-level determination of the scalar and vector form factors to enable high-precision determinations of |Vub| and|Vcb|. This work fits into a broader program of lattice-QCD studies of weak B-meson decays by the MILC and Fermilab Lattice collaborations. 

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3. Semileptonic form factors for $$B\rightarrow D^*\ell \nu $$ at nonzero recoil from $$2+1$$-flavor lattice QCD: Fermilab Lattice and MILC Collaborations

   https://doi.org/10.1140/epjc/s10052-022-10984-9  

   Bazavov, A.; DeTar, C. E.; Du, D.; El-Khadra, A. X.; Gámiz, E.; Gelzer, Z.; Gottlieb, S.; Heller, U. M.; Kronfeld, A. S.; Laiho, J.; et al (December 2022, The European Physical Journal C)

   Abstract We present the first unquenched lattice-QCD calculation of the form factors for the decay $$B\rightarrow D^*\ell \nu $$ B → D ∗ ℓ ν at nonzero recoil. Our analysis includes 15 MILC ensembles with $$N_f=2+1$$ N f = 2 + 1 flavors of asqtad sea quarks, with a strange quark mass close to its physical mass. The lattice spacings range from $$a\approx 0.15$$ a ≈ 0.15 fm down to 0.045 fm, while the ratio between the light- and the strange-quark masses ranges from 0.05 to 0.4. The valence b and c quarks are treated using the Wilson-clover action with the Fermilab interpretation, whereas the light sector employs asqtad staggered fermions. We extrapolate our results to the physical point in the continuum limit using rooted staggered heavy-light meson chiral perturbation theory. Then we apply a model-independent parametrization to extend the form factors to the full kinematic range. With this parametrization we perform a joint lattice-QCD/experiment fit using several experimental datasets to determine the CKM matrix element $$|V_{cb}|$$ | V cb | . We obtain $$\left| V_{cb}\right| = (38.40 \pm 0.68_{\text {th}} \pm 0.34_{\text {exp}} \pm 0.18_{\text {EM}})\times 10^{-3}$$ V cb = ( 38.40 ± 0 . 68 th ± 0 . 34 exp ± 0 . 18 EM ) × 10 - 3 . The first error is theoretical, the second comes from experiment and the last one includes electromagnetic and electroweak uncertainties, with an overall $$\chi ^2\text {/dof} = 126/84$$ χ 2 /dof = 126 / 84 , which illustrates the tensions between the experimental data sets, and between theory and experiment. This result is in agreement with previous exclusive determinations, but the tension with the inclusive determination remains. Finally, we integrate the differential decay rate obtained solely from lattice data to predict $$R(D^*) = 0.265 \pm 0.013$$ R ( D ∗ ) = 0.265 ± 0.013 , which confirms the current tension between theory and experiment. 

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4. Gapless spin liquid and pair density wave of the Hubbard model on three-leg triangular cylinders

   https://doi.org/10.1088/1367-2630/ac3a83  

   Peng, Cheng; Jiang, Yi-Fan; Wang, Yao; Jiang, Hong-Chen (December 2021, New Journal of Physics)

   Abstract We study the ground state properties of the Hubbard model on three-leg triangular cylinders using large-scale density-matrix renormalization group simulations. At half-filling, we identify an intermediate gapless spin liquid phase, which has one gapless spin mode and algebraic spin–spin correlations but exponential decay scalar chiral–chiral correlations, between a metallic phase at weak coupling and Mott insulating dimer phase at strong interaction. Upon light doping the gapless spin liquid, the system exhibits power-law charge-density-wave (CDW) correlations but short-range single-particle, spin–spin, and chiral–chiral correlations. Similar to CDW correlations, the superconducting correlations also decay in power-law but oscillate in sign as a function of distance, which is consistent with the striped pair-density wave. When further doping the gapless spin liquid phase or doping the dimer order phase, another phase takes over, which has similar CDW correlations but all other correlations decay exponentially. 

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5. Hadronic vacuum polarization of the muon on 2+1+1-flavor HISQ ensembles: an update.

   https://doi.org/10.22323/1.396.0526  

   Lahert, Shaun; DeTar, Carleton; El-Khadra, Aida X; Gámiz, Elvira; Gottlieb, Steven; Kronfeld, Andreas; Neil, Ethan; Peterson, Curtis T.; Van de Water, Ruth (May 2022, The 38th International Symposium on Lattice Field Theory (LATTICE2021))

   We give an update on the status of the Fermilab Lattice-HPQCD-MILC calculation of the con- tribution to the muon’s anomolous magnetic moment from the light-quark, connected hadronic vacuum polarization. We present preliminary, blinded results in the intermediate window for this contribution a^ll_{\mu W}. The calculation is performed on Nf = 2 + 1 + 1 highly-improved staggered quark (HISQ) ensembles from the MILC collaboration with physical pion mass at four lattice spacings between 0.15 fm and 0.06 fm. We also present preliminary results for a study of the two- pion contributions to the vector-current correlation function performed on the 0.15 fm ensemble contribution, 𝑎𝑙𝑙 . The calculation is performed on the 0.15 fm ensemble where we see a factor of four improvement over traditional noise reduction techniques. 

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