Testing multi-field inflation with LiteBIRD

We investigate expected constraints on the primordial tensor power spectrum from the future cosmic microwave background polarization experiment LiteBIRD as a test of multi -field inflation, where we specifically consider spectator models as representative examples. We argue that the measurements of the tensor -to -scalar ratio and the tensor spectral index, in combination with the constraints on the scalar spectral index from the Planck observation, are useful in testing multi -field inflation models. We also discuss implications for multi -field inflationary model building.