Gravitational waves in a string-like fluid cosmology

The coupling of a string-like fluid with ordinary matter and gravity may le ad to a closed Universe with the dynamic of an open one. This can provide a n alternative solution for the age and horizon problems. A study of density perturbations of the string-like fluid indicates the existence of instabil ities in the small-wavelength limit when a hydrodynamic approach is employe d. Here, we extend this study to gravitational waves, where the hydrodynami cal approach plays a less important role, and we argue that traces of the e xistence of this fluid must be present in the anisotropies of the cosmic ba ckground radiation.