Radion dynamics and electroweak physics

The dynamics of a stabilized radion in the Randall-Sundrum model with two branes is investigated, and the effects of the radion on electroweak precision observables are evaluated. The radius is assumed to be stabilized using a bulk scalar field as suggested by Goldberger and Wise. First the mass and the wave function of the radion is determined including the back reaction of the bulk stabilization field on the metric, giving a typical radion mass of the order of the weak scale. This is demonstrated by a perturbative computation of the radion wave function. A consequence of the background configuration for the scalar field is that after including the back reaction the Kaluza-Klein states of the bulk scalars couple directly to the standard model fields on the TeV brane. Some cosmological implications are discussed, and in particular it is found that the shift in the radion at late times is in agreement with the four-dimensional effective theory result. The effect of the radion on the oblique parameters is evaluated using an effective theory approach. In the absence of a curvature-scalar Higgs mixing operator, these corrections are small and give a negative contribution to S. In the presence of such a mixing operator, however, the corrections can be sizable due to the modified Higgs and radion couplings.