Title: Can the observed<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>C</mml:mi><mml:mi>P</mml:mi></mml:math>asymmetry in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>τ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>K</mml:mi><mml:mi>π</mml:mi><mml:msub><mml:mrow><mml:mi>ν</mml:mi></mml:mrow><mml:mrow><mml:mi>τ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>be due to nonstandard tensor interactions?
Abstract: An intriguing opposite sign of the $CP$-violating asymmetry from that expected within the Standard Model was recently measured in the tau decay modes ${\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{K}_{s}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{\stackrel{(\ensuremath{-})}{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ by the BABAR collaboration. If this result is confirmed with higher precision, the observed decay rate asymmetry ${A}_{CP}$ can only arise from some nonstandard interactions occurring possibly in both the hadronic as well as in the leptonic sectors. We illustrate that, while a simple charged scalar interaction cannot yield this rate asymmetry, it will be possible to generate this in the presence of a tensor interaction. Parametrizing the strength and weak phase of this nonstandard interaction contribution, the observed branching ratio and the decay-rate $CP$ asymmetry for the particular mode ${\ensuremath{\tau}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{K}_{s}{\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}{\stackrel{(\ensuremath{-})}{\ensuremath{\nu}}}_{\ensuremath{\tau}}$ are used to determine the $CP$-violating weak phase and the coupling of a tensorial interaction that can give a consistent sign and magnitude of the asymmetry.