On synthetic gravitational waves from multi-?eld in?ation

摘要

We revisit the possibility of producing observable tensor modes through a con-tinuous particle production process during in?ation. Particularly, we focus on the multi-?eld realization of in?ation where a spectator pseudoscalar σ induces a signi?cant ampli?cation of the U(1) gauge ?elds through the coupling ∝ σF_(μν)F~(μν). In this model, both the scalar σ and the Abelian gauge ?elds are gravitationally coupled to the in?aton sector, therefore they can only affect the primordial scalar and tensor ?uctuations through their mixing with gravitational ?uctuations. Recent studies on this scenario show that the sourced contribu-tions to the scalar correlators can be dangerously large to invalidate a large tensor power spectrum through the particle production mechanism. In this paper, we re-examine these recent claims by explicitly calculating the dominant contribution to the scalar power and bispectrum. Particularly, we show that once the current limits from CMB data are taken into account, it is still possible to generate a signal as large as r ≈ 10~(-3) and the limitations on the model building are more relaxed than what was considered before.