Assisted dark energy

We study cosmological dynamics of a multi-field system for a general Lagrangian density having scaling solutions. This allows the possibility that scaling radiation and matter eras are followed by a late-time cosmic acceleration through an assisted inflation mechanism. Using the bound coming from Big-Bang-Nucleosynthesis (BBN) and the condition under which each field cannot drive inflation as a single component of the universe, we find the following features: (i) a transient or eternal cosmic acceleration can be realized after the scaling matter era, (ii) a "thawing" property of assisting scalar fields is crucial to determine the evolution of the field equation of state w_φ, and (iii) the field equation of state today can be consistent with the observational bound w_φin the presence of multiple scalar fields.