No abstract

Recently, a novel class of models for inflation has been found in which the inflationary dynamics is driven solely by (non-canonical) kinetic terms rather than by potential terms. As an obvious extension, we show that a scalar field with non-canonical kinetic terms alone behaves like an energy component which is time-varying and has negative pressure presently, i.e. quintessence. We present a model which has a constant equation of state, that is, a "kinetic" counterpart of the Ratra-Peebles model of a quintessence field with a potential term. We make clear the structure of the phase plane and show that the quintessential solution is a late-time attractor. We also give a model for the "phantom" component which has an equation of state with w = p/ρ < −1.

We propose a chaotic inflation model in supergravity. In the model the Kahler potential has a Nambu-Goldstone-type shift symmetry of the inflaton chiral multiplet which ensures the flatness of the inflaton potential beyond the Planck scale. We show that chaotic inflation naturally takes place by introducing a small breaking term of the shift symmetry in the superpotential. This may open a new branch of model building for inflationary cosmology in the framework of supergravity.

We propose a new class of inflation model, G-inflation, which has a Galileon-like nonlinear derivative interaction of the form G(φ, (∇φ) 2 )2φ in the Lagrangian with the resultant equations of motion being of second order. It is shown that (almost) scale-invariant curvature fluctuations can be generated even in the exactly de Sitter background and that the tensor-to-scalar ratio can take a significantly larger value than in the standard inflation models, violating the standard consistency relation. Furthermore, violation of the null energy condition can occur without any instabilities. As a result, the spectral index of tensor modes can be blue, which makes it easier to observe quantum gravitational waves from inflation by the planned gravitational-wave experiments such as LISA and DECIGO as well as by the upcoming CMB experiments such as Planck and CMBpol.Inflation in the early universe [1] is now a part of the standard cosmology to solve the horizon and flatness problem as well as to account for the origin of density/curvature fluctuations. It is most commonly driven by a scalar field dubbed as inflaton, and the research on inflationary cosmology has long been focused on the shape of the inflaton potential in the particle physics context. Its underlying physics is now being probed using precision observations of the cosmic microwave background [2] and large scale structure which are sensitive only to the dynamical nature of the inflaton. Reflecting this situation, a number of novel inflation models have been proposed extending the structure of the kinetic function, such as k-inflation [3], ghost condensate [4], and DBI inflation [5].In this Letter, we propose a new class of inflation models, for which the scalar field Lagrangian is of the formwhere K and G are general function of φ and X := −∇ µ φ∇ µ φ/2. The most striking property of this generic Lagrangian (1) is that it gives rise to derivatives no higher than two both in the gravitational-and scalar-field equations. In the simplest form the nonlinear term may be given by G2φ ∝ X2φ, which has recently been discussed in the context of the so-called Galileon field [6,7]. The general form G(φ, X)2φ may be regarded as an extension of the Galileon-type interaction X2φ while maintaining the field equations to be of second-order [8]. So far the phenomenological aspects of the Galileon-type scalar field have been studied mainly in the context of dark energy and modified gravity [9]. In this Letter, we discuss primordial inflation induced by this type of fields. * This paper is the original version of the article published in Phys. Rev. Lett. 105, 231302 (2010) with the title "Inflation driven by the Galileon field."Now let us start investigating our model in detail. Assuming that φ is minimally coupled to gravity, the total action is given byThe energy-momentum tensor T µν derived from the action readsThe equation of motion of the scalar field is equivalent to ∇ ν T ν µ = 0. Here and hereafter we use the notation K X for ∂K/∂X etc.Taking the homogeneous and isotro...

We investigate the non-Gaussianity of primordial curvature perturbation in the modulated reheating scenario where the primordial perturbation is generated due to the spacial fluctuation of the inflaton decay rate to radiation. We use the $\delta N$ formalism to evaluate the trispectrum of curvature perturbation as well as its bispectrum. We give expressions for three non-linear parameters $f_{NL}, \tau_{NL}$ and $g_{NL}$ in the modulated reheating scenario. If the intrinsic non-Gaussianity of scalar field fluctuations and third derivative of the decay rate with respect to scalar fields are negligibly small, $g_{NL}$ has at least the same order of magnitude as $f_{NL}$. We also give general inequality between $f_{NL}$ and $\tau_{NL}$ which is true for other inflationary scenarios as long as primordial non-Gaussianity comes from super-horizon evolution.Comment: references adde