Speaker
Description
The ratios $R_{\tau/P}\equiv \Gamma(\tau\to P \nu_\tau[\gamma])/\Gamma(P\to \mu \nu_\mu[\gamma]) (P=\pi, K)$ provide sensitive tests of lepton universality $|g_\tau/g_\mu|=1$ and are a useful tool for new physics searches. We improve previous computations of the corresponding radiative corrections, within Chiral Perturbation Theory with resonances, complying with known QCD limits. We find $\delta R_{\tau/\pi} = (0.18 \pm 0.57)\%$ and $\delta R_{\tau/K} = (0.97 \pm 0.58)\%$, where the uncertainties are induced fundamentally by the counterterms. We test lepton universality, obtaining $|g_{\tau}/g_{\mu}|(\pi) = 0.9964 \pm 0.0038$ and $|g_{\tau}/g_{\mu}|(K) = 0.9857 \pm 0.0078$, and analyze the CKM unitarity, getting results at $2.1\sigma$ and $1.5\sigma$ from unitarity via $|V_{us}/V_{ud}$| and $|V_{us}|$, respectively. We also update the search for non-standard interactions in one-meson $\tau$ decays.
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