### Conveners

#### Session 3: Exclusive and inclusive hadronic tau decays

- Sergi Gonzalez-Solis (Indiana University)

#### Session 3: Exclusive and inclusive hadronic tau decays

- Marc Knecht (CNRS)

After a brief review of semileptonic tau decays in the Standard Model, I will discuss the usefulness of these channels in several new physics searches.

The calculation of radiative corrections (radcorr) in semileptonic decays requires a good description of photon-hadron interactions at all energies. We present a calculation of the radcorr to $\tau^- \to P^- \nu_{\tau}$ decays ($P$ a pseudoscalar meson) where photon-hadron form factors obeys the expected QCD constraints at very small and very large virtual photon momenta. The implications for...

The radiative two-pion tau decay process is studied in this work. The resonance chiral theory is used to calculate the relevant form factors. Different light-flavor vector resonance dynamics are revealed in several different two-particle invariant mass distributions. Interesting studies on the T-odd asymmetry distributions arising from the radiative two-pion tau decay process are explored as...

The rare second-class decay mode of the $\tau$ into $\eta\pi\nu$ could be

observed for the first time at Belle II. It is important to try to derive

a reliable evaluation of the branching fraction and of the energy

distribution of this mode within the standard-model. Many predictions

exist already in the literature which, unfortunately, can differ by one to

two orders of magnitude. In...

Pion-kaon ($\pi K$) pairs occur frequently as final states in heavy-particle decays.

A consistent treatment of $\pi K$ scattering and production amplitudes over a wide energy range is therefore mandatory for multiple applications:

in Standard Model tests; to describe crossed channels in the quest for exotic hadronic states; and for an improved spectroscopy of excited kaon resonances.

In...

We present updated determinations of |Vus| using tau decays that include a preliminary updated HFLAV global fit of the tau branching fractions, up-to-date lattice hadronic form factors and decay constants, and novel determinations published in 2019 of the electromagnetic and strong isospin-breaking corrections to the π+→μ+ν[γ] and K+→μ+ν[γ] leptonic decay rates obtained with lattice QCD+QED.

In the framework of precision experiments, the search for electric dipole moments and the precise determination of magnetic dipole moments (g-2)

have since long be of prime interest. Tau leptons play a particular role owing to the large mass as compared to the electron and muon.

The precision of these measurements is, at the one hand, dominated by radiative corrections, which govern the...

Hadronic decays of $\tau$ lepton provide a unique possibility to study dynamics in a three-body hadronic system. Particularly, $\tau^-\to \pi^+\pi^-\pi^-\,\nu$ and $\tau^-\to K^-K^+\pi^-\,\nu$ gives a clear sample of the $a_1(1260)$ decays. While the pionic system is dominated by the $\rho$ intermediate resonance and the system with kaons shows mostly $K^*$ resonances, the two final states are...

The discrepancy between the FOPT and CIPT predictions for the hadronic tau decay rate (and other spectral function moments) has been a subject of intense investigations for many years and constitutes a major theoretical uncertainty for strong coupling determinations from hadronic tau decay spectral data. We demonstrate that the discrepancy may be understood since the Borel representations...

We use a new, more precise, non-strange, inclusive vector

isovector spectral function to determine the strong coupling at the

tau mass scale employing finite energy sum rules. The new spectral

function is obtained from a combination of (i) ALEPH and OPAL results

for the 2 pion and 4 pion tau decay channels, (ii) recent BaBar

results for the tau K Kbar decay distribution, and...

Tau-based finite-energy sum rule (FESR) analyses often assume that scales

s_0~m_tau^2 are large enough that (i) integrated duality violations (DVs)

can be neglected, and (ii) contributions from non-perturbative OPE

condensates of dimension D scale as ~(Lambda_{QCD}/m_tau )^D, allowing the

OPE series to be truncated at low dimension. The latter assumption is not

true in general since the...