An Improved Standard Model Prediction Of BR(B -> tau nu) And Its Implications For New Physics

TL;DR

This paper refines the Standard Model prediction for the B -> tau nu decay rate using updated parameters and explores implications for new physics, including specific models like 2HDM and MSSM.

Contribution

It provides an improved Standard Model prediction for BR(B -> tau nu) and analyzes how new physics could alter this prediction, especially under minimal flavour violation scenarios.

Findings

Standard Model prediction: (0.84 +- 0.11) x 10^{-4}

Experimental measurement: (1.73 +- 0.34) x 10^{-4}

Discussion of new physics effects in decay amplitude and CKM parameters

Abstract

The recently measured B -> tau nu branching ratio allows to test the Standard Model by probing virtual effects of new heavy particles, such as a charged Higgs boson. The accuracy of the test is currently limited by the experimental error on BR(B -> tau nu) and by the uncertainty on the parameters fB and |Vub|. The redundancy of the Unitarity Triangle fit allows to reduce the error on these parameters and thus to perform a more precise test of the Standard Model. Using the current experimental inputs, we obtain BR(B -> tau nu)_SM = (0.84 +- 0.11)x10^{-4}, to be compared with BR(B -> tau nu)_exp = (1.73 +- 0.34)x10^{-4}. The Standard Model prediction can be modified by New Physics effects in the decay amplitude as well as in the Unitarity Triangle fit. We discuss how to disentangle the two possible contributions in the case of minimal flavour violation at large tan beta and generic loop-mediated New Physics. We also consider two specific models with minimal flavour violation: the Type-II Two Higgs Doublet Model and the Minimal Supersymmetric Standard Model.