Anisotropic inflation with derivative couplings

Abstract

We study anisotropic power-law inflationary solutions when the inflaton and its derivative couple to a vector field. This type of coupling is motivated by D-brane inflationary models, in which the inflaton, and a vector field living on the D-brane, couple disformally (derivatively). We start by studying a phenomenological model where we show the existence of anisotropic solutions and demonstrate their stability via a dynamical system analysis. Compared to the case without a derivative coupling, the anisotropy is reduced and thus can be made consistent with current limits, while the value of the slow-roll parameter remains almost unchanged. We also discuss solutions for more general cases, including D-brane-like couplings.

Anisotropic power-law inflation for a conformal-violating Maxwell model

“…In particular, Ref. [108] points out that no small-anisotropy inflationary solutions exists for f (X ) ∝ X −n in contrast to our model with f (X ) ∝ X n .…”

“…[63,[109][110][111], Ref. [108] proposes an extension of the KSW model with f (φ) → f (φ, X ) similar to ours. In particular, Ref.…”

On the Validity of the Cosmic No-hair Conjecture in some Conformal-violating Maxwell Models

“…We have presented basic results of our recent studies on the validity of the cosmic no-hair conjecture in some conformal-violating Maxwell models [27][28][29][30][31][32][33][34][35][36][37]. In particular, we have examined two types of conformal-violating Maxwell term, one is .…”

“…to see whether a spatial anisotropy of spacetime exists or not [36][37]. As a result, an action of a new conformal-violating Maxwell model is given by [36][37]…”

“…Hence, we might think that the violation of isotropy is closely related to the violation of conformal invariance during the inflationary phase of our universe. In the light of this observation, we has proposed a new model [36][37], in which the kinetic term of scalar field defined as 2 X       is coupled to the electromagnetic field as  …”