Perturbations in a coupled scalar field cosmology

I analyse the density perturbations in a cosmological model with a scalar field coupled to ordinary matter, such as one obtains in string theory and in conformally transformed scalar-tensor theories. The spectrum of multipoles on the last scattering surface and the power spectrum at the present epoch are compared with observations to derive bounds on the coupling constant and on the exponential potential slope. It is found that the acoustic peaks and the power spectrum are strongly sensitive to the model parameters. The models that best fit the galaxy spectrum and satisfy the cluster abundance normalization have field energy density Omega(phi)similar or equal to 0.05-0.15 and a scalefactor expansion law a similar to t(p), p similar or equal to 0.67-0.69.