Boundary inflation and the WMAP data

Inflation in a five-dimensional brane world model with two boundary branes is studied. We make use of the moduli space approximation whereby the low energy theory reduces to a four-dimensional biscalar-tensor gravity plus a minimally coupled scalar field. After a detailed analysis of the inflationary solutions, we derive the evolution equations of the linear perturbations separating the adiabatic mode from two entropy modes. We then examine the primordial scalar and tensor power spectra and show that their tilt depends on the scalar-tensor coupling constant. Finally, the induced cosmic microwave background (CMB) anisotropies are computed and we present a Monte Carlo Markov chains exploration of the parameter space using the first year WMAP data. We find a marginalized probability bound for the associated Eddington parameter at the end of inflation 1-γ<2×10^-3, at 95% confidence level. This suggests that future CMB data could provide crucial information helping to distinguish scalar-tensor and standard inflationary scenarios.