|V_{cd}|, |V_{cs}| and f_{D_s} from (semi) leptonic $D_{(s)}$-decays : signals of New Physics ?

TL;DR

This paper compares recent experimental measurements of D_{(s)} leptonic decays with theoretical predictions from lattice QCD and QCD sum rules, finding potential hints of New Physics if CKM matrix unitarity is assumed.

Contribution

It provides updated determinations of CKM matrix elements and decay constants from experimental data, highlighting possible deviations from Standard Model predictions under certain assumptions.

Findings

Measured |V_cd| and |V_cs| are consistent with SM within 1σ.

Assuming |V_cs|< 1 or |V_cs|=|V_ud| reveals 1.5-3σ deviations from SM.

Results suggest potential signals of New Physics beyond the Standard Model.

Abstract

We confront the recent improved measurements of the D_{(s)} (semi) leptonic decays with lattice QCD (LQCD) with n_f=3 flavours and QCD spectral sum rules (QSSR) predictions. D\to\mu\nu_\mu leptonic width data compared with theoretical determinations of f_D, leads to the value of the CKM mixing angle : |V_cd|= 0.230 (10)_exp (9)_th. Measured ratio of the D semi-leptonic widths combined with LQCD and QSSR predictions leads to the average |V_cd|/|V_cs|= 0.2175(88), and then to |V_cs|= 1.068(47). We consider the previous determinations as improvements of the existing estimates. Using the average data of the D_s\to \mu\nu_\mu (resp. D_s\to \tau\nu_\tau) branching ratios, one obtains : |V_cs|f_{D_s}^\mu= (259 +- 12) {MeV} (resp) |V_cs|f_{D_s}^\tau= (274 +- 13) {MeV}, which can be compared with the average of the Standard Model (SM) values from LQCD and QSSR f_{D_s}=(240 +- 7) MeV. If one uses the present determination of |V_cs|, there is an agreement with the SM prediction within 1\sigma. If instead, we impose the unitarity constraint |V_cs|< 1, or assume (as frequently done) |V_cs|=|V_ud|, we would obtain a deviation from the SM expectations ranging from 1.5 to 3 \sigma, eventually signaling some New Physics beyond the SM.