Semileptonic tau decays beyond the Standard Model

Abstract

Hadronic τ decays are studied as probe of new physics. We determine the dependence of several inclusive and exclusive τ observables on the Wilson coefficients of the low-energy effective theory describing charged-current interactions between light quarks and leptons. The analysis includes both strange and non-strange decay channels. The main result is the likelihood function for the Wilson coefficients in the tau sector, based on the up-to-date experimental measurements and state-of-the-art theoretical techniques. The likelihood can be readily combined with inputs from other low-energy precision observables. We discuss a combination with nuclear beta, baryon, pion, and kaon decay data. In particular, we provide a comprehensive and model-independent description of the new physics hints in the combined dataset, which are known under the name of the Cabibbo anomaly.

Sterile neutrinos in light of the Cabibbo-angle anomaly

“…where G F = 1.1663788(6) × 10 −5 GeV −2 , K = 8120.27648(26)×10 −10 GeV −4 s, and the index i runs 10 C, 14 O, 26m Al, 34 Cl, 34 Ar, 38m K, 42 Sc, 46 V, 50 Mn, and 54 Co, shown in Fig. 2.…”

“…There have been several attempts to resolve this anomaly by TeV-scale new physics models [5,7,8,[10][11][12][13][14][15][16][17][23][24][25][26][27][28][29][30][31][32][33][34][35]. In this article, we develop deeper the extensions of neutrino sector concerning the anomaly.…”

“…There are several attempts to resolve this anomaly with TeV scale NP, e.g., higher dimension operators in the effective field theory [5][6][7][8]. In this contribution, we take a different approach because it is also conceivable that the anomaly suggests new light particles, in particular, sterile neutrino that has a small mixing with the electron neutrino.…”

The Euclidean Adler Function and its Interplay with $Δα^{\mathrm{had}}_{\mathrm{QED}}$ and $α_s$

“…The O 6,V −A contribution is a genuine vacuum condensate whose nonzero value, O 6,V −A ≈ −0.0035 (9) GeV 6 [100], is well established and understood beyond perturbation theory, and its effect is unrelated to the perturbative series, which is identical for the vector and axial channels. Nonperturbative effects in the observed spectrum (see for example [109,110]) are known to be suppressed for the V + A combination with respect to the V − A, which motivates to assume |O 6,V +A | < |O 6,V −A | [111]. This inequality holds (by far) in the large-N C limit, which gives O ∞ 6,V +A = − 2 9 O ∞ 6,V −A , reproducing the old vacuum saturation approximation, which is also known to work well in predicting O 6,V −A and some rigorous inequalities [2].…”

Radiative corrections and new physics tests in semileptonic tau decays

“…These, for the one-meson tau decays have been discussed in Refs. [41][42][43]. Accounting for both radiative corrections δ τ P and possible NP effects ∆ τ P , they can be written iii…”