Minimal Higgs inflation

In this paper we propose two simple minimal Higgs inflation scenarios through a simple modification of the Higgs potential, as opposed to the usual non-minimal Higgs-gravity coupling prescription. The modification is done in such a way that it creates a flat plateau for a huge range of field values at the inflationary energy scale $\mu \simeq (\lambda)^{1/4} \alpha$. Assuming the perturbative Higgs quartic coupling, $\lambda \simeq {\cal O}(1)$, for both the models inflation energy scale turned out to be $\mu \simeq (10^{14}, 10^{15})$ GeV, and prediction of all the cosmologically relevant quantities, $(n_s,r,dn_s^k)$, fit extremely well with observations made by PLANCK. Considering observed central value of the scalar spectral index, $n_s= 0.968$, our two models predict efolding number, $N = (52,47)$. Within a wide range of viable parameter space, we found that the prediction of tensor to scalar ratio $r (\leq 10^{-5})$ is far below the current experimental sensitivity to be observed in the near future. The prediction for the running of scalar spectral index, $dn_s^k$, approximately remains the same as was predicted by the usual chaotic and quartic inflation scenario. We also the computed the background field dependent unitarity scale $\Lambda(h)$, which turned out to be much larger than the aforementioned inflationary energy.Comment: 5 pages,2 figures, unitarity issue discusse

Kinetic Gravity Braiding and axion inflation

We constructed a new class of inflationary model with the higher derivative axion field which obeys constant shift symmetry. In the usual axion (natural) inflation, the axion decay constant is predicted to be in the super-Planckian regime which is believed to be incompatible with an effective field theory framework. With a novel mechanism originating from a higher derivative kinetic gravity braiding (KGB) of an axion field we found that there exist a huge parameter regime in our model where axion decay constant could be naturally sub-Planckian. Thanks to the KGB which effectively reduces the Planck constant. This effectively reduced Planck scale provides us the mechanism of further lowering down the speed of an axion field rolling down its potential without introducing super-Planckian axion decay constant. We also find that with that wide range of parameter values, our model induces almost scale invariant power spectrum as observed in CMB experiments.Comment: 4 pages, 1 figure, Matched with published versio

Semi-realistic Bouncing Domain Wall Cosmology

In this paper we constructed a semi-realistic cosmological model in a dynamic domain wall framework. Our universe is considered to be a (3+1) dimensional dynamic domain wall in a higher dimensional Einstein-Maxwell-Born-Infeld background. One of our interesting outcomes from the effective Hubble equation for the domain wall dynamics is that it contains an additional component of "dark matter" which is induced from the charge of the bulk Born-Infeld gauge field. In this background spacetime we have studied the cosmological dynamics of the domain wall. In addition to the Born-Infield gauge field if we consider additional pure gauge field, a non-singular bounce happens at the early stage with a smooth transition between contracting and expanding phase.Comment: 19 pages, 2 figures, Typos corrected and little change in titl

Cosmological Behavior of a Parity and Charge-Parity Violating Varying Alpha Theory

In this report we construct a phenomenological model in which the time variation of the fine structure constant, $\alpha$, is induced by a parity and charge-parity (PCP) violating interaction. Such a PCP violation in the photon sector has a distinct physical origin from that in the conventional models of this kind. We calculate the cosmological birefringence so induced in our model and show that it in turn produces a new non-vanishing multipole moment correlation between the temperature and the polarization anisotropies in the CMB spectrum. We have also calculated the amount of optical rotation due to a strong background magnetic field and the effect of our new PCP violating term on the variation of $\alpha$ during the cosmic evolution. We found that only in the radiation dominated era can the contribution of the new PCP violating term to the variation of $\alpha$ be non-vanishing.Comment: 20 pages, No figure, Matched with the published versio