119157556
Inflation beyond T-models and primordial B-modes
Abstract We describe extended theories which shares the gauge transformation symmetry of the T-models, and takes the T-models as well as Starobinsky model as special cases. We derive a general relation between the two slow-roll parameters, and find that a large class of models can be embedded. Such models include more general Starobinsky-like inflation as well as the chaotic inflation with a large tensor-to-scalar ratio consistent with the BICEP2 result.
118390460
1/R correction to gravity in the early universe
To explain the accelerated expansion of the late universe, the 1/R correction to Einstein gravity is usually considered, where R is the Ricci scalar. This correction term, if stable, is generally believed to be negligible during inflation. However, if the 1/R term is inflaton dependent, it will dramatically change the story of inflation. The entropy perturbation will naturally appear and drive the evolution of curvature perturbation outside the Hubble horizon. In a large class of models, the entropy perturbation can be made nearly scale invariant. In Einstein gravity the single-field inflation with a quartic potential has been ruled out by recent observations, but it revives when the 1/R term is turned on. The evolution of non-Gaussianities on a large scale are also studied and applied to inflation with 1/R correction. In some specific models, a large non-Gaussianity can be naturally generated outside the horizon. A recent study ruled out almost all f(R) models during the matter-dominated phase. Taking this into consideration, we are left with a limited class of model which recovers the Einstein gravity soon after reheating.
119238882
On the possibility of blue tensor spectrum within single field inflation
We present a series of theoretical constraints on the potentially viable inflation models that might yield a blue spectrum for primordial tensor perturbations. By performing a detailed dynamical analysis we show that, while there exists such possibility, the corresponding phase space is strongly bounded. Our result implies that, in order to achieve a blue tilt for inflationary tensor perturbations, one may either construct a non-canonical inflation model delicately, or study the generation of primordial tensor modes beyond the standard scenario of single slow-roll field.
118471930
Equilateral non-Gaussianity from heavy fields
The effect of self-interactions of heavy scalar fields during inflation on the primordial non-Gaussianity is studied. We take a specific constant-turn quasi-single field inflation as an example. We derive an effective theory with emphasis on non-linear self-interactions of heavy fields and calculate the corresponding non-Gaussianity, which is of equilateral type and can be as relevant as those computed previously in the literature. We also derive the non-Gaussianity by directly using the in-in formalism, and verify the equivalence of these two approaches.
119250849
Power spectra of scalar and tensor modes in modified Horava-Lifshitz gravity
In Horava-Lifshitz gravity, the extra dynamical scalar mode could play significant role in cosmology. However it has been pointed out that such a scalar may suffer from the strong coupling problem in IR. We address this issue in this paper. Our analysis shows that the scalar mode could decouple naturally at \lambda=1 due to the extra gauge symmetry. On the other hand, the fact that the scalar mode becomes ghost when 1/3<\lambda<1 is a real challenge to the theory. We try to overcome this problem by modifying the action such that the RG flow lies outside the problematic region. We discuss the cosmological implications of the action and calculate the power spectra of scalar and tensor modes.
118608368
Scale invariant power spectrum in Hořava-Lifshitz cosmology without matter
In this paper we investigate the physical implications of the dynamical scalar mode in pure Hořava-Lifshitz gravity on cosmology. We find that it can produce a scale-invariant power spectrum in UV era if the detailed balance condition on the action is relaxed. This indicates that the physical scalar mode may seed the large scale structure and Hořava-Lifshitz cosmology could be a qualified alternative to inflationary scenario.
17751676
The phase structure of the early universe in the minimal SU(5) grand unified theory
Abstract Using the most general, gauge invariant and renormalizable Higgs potential which avoids domain walls, we study the possible phases that can appear at high temperatures in the minimal SU(5) grand unified theory. We emphasize the important role of the fundamental representation of Higgs field for the phase structure at temperatures of 10 14 GeV.
118191225
Cosmological Consequences of Grand Unified Theories
120447542
Inflation-driving scalar field
Abstract The quantum mechanical behavior of the Higgs field which drives inflation of the early universe is discussed. The standard picture of the new inflationary universe cannot be realized in the minimal SU(5) model. A realistic model in which inflation is driven by a complex gauge singlet Higgs field containing the axion is presented.
115847230
A Slow Rollover Phase Transition in the Schrdinger Picture
121075245
Perturbative Calculations in a Unified Gauge Field Model of Strong, Weak and Electromagnetic Interactions