Ippei Obata

Chiral primordial gravitational waves from dilaton induced delayed chromonatural inflation

We study inflation driven by a dilaton and an axion, both of which are coupled to a SU(2) gauge field. We find that the inflation driven by the dilaton occurs in the early stage of inflation during which the gauge field grows due to the gauge kinetic function. When the energy density of magnetic fields catches up with that of electric fields, chromo-natural inflation takes over in the late stage of inflation, which we call delayed chromo-natural inflation. Thus, the delayed chromo-natural inflation driven by the axion and the gauge field is induced by the dilaton. The interesting outcome of the model is generation of chiral primordial gravitational waves on small scales. Since the gauge field is inert in the early stage of inflation, it is viable in contrast to the conventinal chromo-natural inflation. We find the parameter region where chiral gravitational waves are generated in a frequency range higher than nHz, which are potentially detectable in future gravitational wave interferometers and pulsar timing arrays such as DECIGO, eLISA and SKA.

Does anisotropic inflation produce a small statistical anisotropy

Anisotropic inflation is an interesting model with an U(1) gauge field and it predicts the statistical anisotropy of the curvature perturbation characterized by a parameter

Oscillating Chiral Tensor Spectrum from Axionic Inflation

g_*

Chiral primordial blue tensor spectra from the axion-gauge couplings

. However, we find that the background gauge field does not follow the classical attractor solution due to the stochastic effect. We develop the stochastic formalism of a vector field and solve Langevin and Fokker-Planck equations. It is shown that this model is excluded by the CMB constraint

Dynamics of electroweak gauge fields during and after Higgs inflation

g_*\le 10^{-2}

Statistically anisotropic tensor modes from inflation

with a high probability about

Chromo-Natural Inflation in the Axiverse

99.999\%

Chiral primordial Chiral primordial gravitational waves from dilaton induced delayed chromonatural inflation

.

Publisher’s Note: Chiral primordial gravitational waves from dilaton induced delayed chromonatural inflation [Phys. Rev. D 93 , 123502 (2016)]

We study the axionic inflation with a modulated potential and examine if the primordial tensor power spectrum exhibits oscillatory feature, which is testable with future space-based gravitational wave experiments such as DECIGO and BBO. In the case of the single-field axion monodromy inflation, it turns out that it is difficult to detect the oscillation in the spectrum due to suppression of the sub-Planckian decay constant of axion. On the other hand, in the case of aligned chromo-natural inflation where the axion is coupled to a SU(2) gauge field, it turns out that the sizable oscillation in the tensor spectrum can occur due to the enhancement of chiral gravitational waves sourced by the gauge field. We expect that this feature will be a new probe to axion phenomenologies in early universe through the chiral gravitational waves.

Footprint of Two-Form Field: Statistical Anisotropy in Primordial Gravitational Waves.

We suggest the new feature of primordial gravitational waves sourced by the axion-gauge couplings, whose forms are motivated by the dimensional reduction of the form field in the string theory. In our inflationary model, as an inflaton we adopt two types of axion, dubbed the model-independent axion and the model-dependent axion, which couple with two gauge groups with different sign combination each other. Due to these forms both polarization modes of gauge fields are amplified and enhance both helicies of tensor modes during inflation. We point out the possibility that a primordial blue-tilted tensor power spectra with small chirality are provided by the combination of these axion-gauge couplings, intriguingly both amplitudes and chirality are potentially testable by future space-based gravitational wave interferometers such as DECIGO and BBO project.