English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We consider the ``second-class current'' decay $\tau^-\to\pi^-\eta\nu_\tau$from several points of view. We first focus on the decay rate as expectedwithin standard weak interaction and QCD due to isospin violation. The decaycontributions divide into $P$- and $S$-wave parts. The former can be reliablyestimated using the $\rho\eta\pi$ coupling inferred from the rates andDalitz-plot distributions of $\eta\to 3\pi$ decays. The somewhat larger$S$-wave part, which was previously computed using chiral perturbation theory,is estimated from a simple $\bar qq$ model. Both estimates of the $S$-wave partdepend on whether the $a_0(980)$ scalar particle is a $\bar qq$ or some other(4-quark) state. Finally, we discuss genuinely new, non-$V-A$ scalar weakinteractions. The $\tau^-\to\pi^-\eta\nu_\tau$ decay provides information onthis question, which nicely complements that from precision $\beta$ decayexperiments. % In summary, we discuss the possible implications of putativevalues of the branching fraction ${\cal B}(\tau^-\to\pi^-\eta\nu_\tau)$. In thecase of larger values, in particular of the $S$-wave part, not only willdetection of the decay be more likely and more reliable, its implications willbe more far-reaching and interesting.

Estimate of the branching fraction $\tau^- \to \eta \pi^-\nu_\tau$, the $a_0^-(980)$, and non-standard weak interactions