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arXiv · 2512.19294

$f_K/f_{\pi}$ in iso-symmetric QCD and the CKM matrix unitarity

Alessandro Conigli·Julien Frison·Alejandro Sáez
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Abstract

We present lattice results for $f_K/f_{\pi}$ in the iso-symmetric limit of pure QCD (isoQCD) with $N_f=2+1$ flavours, along with a determination of $|V_{us}|/|V_{ud}|$ and a study on the unitarity of the first row of the Cabibbo-Kobayashi-Maskawa (CKM) matrix after introducing strong isospin-breaking and QED effects. The results obtained are based on a combination of a Wilson unitary action and the mixed-action setup introduced in arXiv:2309.14154, arXiv:2510.20450. The combination of the two regularisations enables a more precise control over the continuum-limit extrapolation.

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Alessandro Conigli, Julien Frison, Alejandro Sáez. 2025-12-22. $f_K/f_{\pi}$ in iso-symmetric QCD and the CKM matrix unitarity. https://doi.org/10.1140/epjc/s10052-026-15670-8

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