Power-law Bianchi type I inflation with multiple vector fields

We seek power-law Bianchi type I solutions for an inflationary universe in a model with one scalar field non-minimally coupled to three vector fields aligned along the three axes. As a result, we find four types of power-law solutions that are classified according to the number of non-vanishing vector fields. Moreover, we find that all these solutions are stable for certain conditions on the parameters (stability regions), which are described both quantitatively and qualitatively. The attractor property of these solutions is also confirmed by numerical calculations.