∆r and the W–boson mass in the Singlet Extension of the Standard Model

The link between the electroweak gauge boson masses and the Fermi constant via the muon lifetime measurement is instrumental for constraining and eventually pin-ning down new physics. We consider the simplest extension of the Standard Model with an additional real scalar SU(2)L ⊗ U(1)Y singlet and compute the electroweak precision parameter ∆r, along with the corresponding theoretical prediction for the W–boson mass. When confronted with the experimental W–boson mass measurement, our predictions impose limits on the singlet model parameter space. We identify re-gions where these correspond to the most stringent experimental constraints that are currently available.