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Does Gravity's Rainbow induce Inflation without an Inflaton?  [PDF]
Remo Garattini,Mairi Sakellariadou
Physics , 2012, DOI: 10.1103/PhysRevD.90.043521
Abstract: We study aspects of quantum cosmology in the presence of a modified space-time geometry. In particular, within the context of Gravity's Rainbow modified geometry, motivated from quantum gravity corrections at the Planck energy scale, we show that the distortion of the metric leads to a Wheeler-De Witt equation whose solution admits outgoing plane waves. Hence, a period of cosmological inflation may arise without the need for introducing an inflaton field.
Brane-world inflation without inflaton on the brane  [PDF]
Yoshiaki Himemoto,Misao Sasaki
Physics , 2000, DOI: 10.1103/PhysRevD.63.044015
Abstract: Inspired by the Randall-Sundrum brane-world scenario, we investigate the possibility of brane-world inflation driven not by an inflaton field on the brane, but by a bulk, dilaton-like gravitational field. As a toy model for the dilaton-like gravitational field, we consider a minimally coupled massive scalar field in the bulk 5-dimensional spacetime, and look for a perturbative solution in the anti-de Sitter (AdS) background. For an adequate range of the scalar field mass, we find a unique solution that has non-trivial dependence on the 5th dimensional coordinate and that induces slow-roll inflation on the brane.
Modified teleparallel gravity: inflation without inflaton  [PDF]
Rafael Ferraro,Franco Fiorini
Physics , 2006, DOI: 10.1103/PhysRevD.75.084031
Abstract: Born-Infeld strategy to smooth theories having divergent solutions is applied to teleparallel equivalent of General Relativity. Differing from other theories of modified gravity, modified teleparallelism leads to second order equations, since teleparallel Lagrangian only contains first derivatives of the vierbein. We show that Born-Infeld-modified teleparallelism solves the particle horizon problem in a spatially flat FRW universe by providing an initial exponential expansion without resorting to an inflaton field.
Quantum fluctuations in brane-world inflation without inflaton on the brane  [PDF]
Norichika Sago,Yoshiaki Himemoto,Misao Sasaki
Physics , 2001, DOI: 10.1103/PhysRevD.65.024014
Abstract: A Randall-Sundrum type brane-cosmological model in which slow-roll inflation on the brane is driven solely by a bulk scalar field was recently proposed by Himemoto and Sasaki. We analyze their model in detail and calculate the quantum fluctuations of the bulk scalar field $\phi$ with $m^2=V''(\phi)$. We decompose the bulk scalar field into the infinite mass spectrum of 4-dimensional fields; the field with the smallest mass-square, called the zero-mode, and the Kaluza-Klein modes above it with a mass gap. We find the zero-mode dominance of the classical solution holds if $|m^2|\bar\ell^2\ll1$, where $\bar{\ell}$ is the curvature radius of the effectively anti-de Sitter bulk, but it is violated if $|m^2|\bar\ell^2\gg1$, though the violation is very small. Then we evaluate the vacuum expectation value $<\delta\phi^2>$ on the brane. We find the zero-mode contribution completely dominates if $|m^2|\bar{\ell}^2\ll 1$ similar to the case of classical background. In contrast, we find the Kaluza-Klein contribution is small but non-negligible if the value of $|m^2|\bar{\ell}^2$ is large.
Of Inflation and the Inflaton  [PDF]
Robert Brout
Physics , 2010,
Abstract: Due to intra-field gravitational interactions, field configurations have a strong negative component to their energy density at the planckian and transplanckian scales, conceivably resulting in a sequestration of the transplanckian field degrees of freedom. Quantum fluctuations then allow these to tunnel into cisplanckian configurations to seed inflation and conventional observed physics: propagating modes of QFT in a geometry which responds to the existence of these new modes through the energy constraint of general relativity, H^2 = \rho/3. That this tunnelling results in geometries and field configurations that are homogeneous allows for an estimate of the mass of the inflaton, m=O(10^{-6}), and the amplitude of the inflaton condensate, \phiav=O(10), both consistent with phenomenology.
Inflation during oscillations of the inflaton  [PDF]
Andrew R Liddle,Anupam Mazumdar
Physics , 1998, DOI: 10.1103/PhysRevD.58.083508
Abstract: Damour and Mukhanov have recently devised circumstances in which inflation may continue during the oscillatory phase which ensues once the inflaton field reaches the minimum of its potential. We confirm the existence of this phenomenon by numerical integration. In such circumstances the quantification of the amount of inflation requires particular care. We use a definition based on the decrease of the comoving Hubble length, and show that Damour and Mukhanov overestimated the amount of inflation occurring. We use the numerical calculations to check the validity of analytic approximations.
A Permutation on Hybrid Natural Inflation  [PDF]
Christopher D. Carone,Joshua Erlich,Marc Sher,Raymundo Ramos
Physics , 2014, DOI: 10.1103/PhysRevD.90.063521
Abstract: We analyze a model of hybrid natural inflation based on the smallest non-Abelian discrete group S_3. Leading invariant terms in the scalar potential have an accidental global symmetry that is spontaneously broken, providing a pseudo-Goldstone boson that is identified as the inflaton. The S_3 symmetry restricts both the form of the inflaton potential and the couplings of the inflaton field to the waterfall fields responsible for the end of inflation. We identify viable points in the model parameter space. Although the power in tensor modes is small in most of the parameter space of the model, we identify parameter choices that yield potentially observable values of r without super-Planckian initial values of the inflaton field.
Type II Seesaw Higgs Triplet as the inflaton for Chaotic Inflation and Leptogenesis  [PDF]
Chian-Shu Chen,Chia-Min Lin
Physics , 2010, DOI: 10.1016/j.physletb.2010.11.016
Abstract: In this paper, we consider a chaotic inflation model where the role of inflaton is played by the Higgs triplet in type II seesaw mechanism for generating the small masses of left-handed neutrinos. Leptogenesis could happen after inflation. This model is constructed without introducing supersymmetry (SUSY).
Alchemical Inflation: inflaton turns into Higgs  [PDF]
Kazunori Nakayama,Fuminobu Takahashi
Physics , 2012, DOI: 10.1088/1475-7516/2012/11/007
Abstract: We propose a new inflation model in which a gauge singlet inflaton turns into the Higgs condensate after inflation. The inflationary path is characterized by a moduli space of supersymmetric vacua spanned by the inflaton and Higgs field. The inflation energy scale is related to the soft supersymmetry breaking, and the Hubble parameter during inflation is smaller than the gravitino mass. The initial condition for the successful inflation is naturally realized by the pre-inflation in which the Higgs plays a role of the waterfall field.
Effects of the imaginary inflaton component in supergravity new inflation  [PDF]
David Nolde
Physics , 2013, DOI: 10.1088/1475-7516/2013/11/028
Abstract: When models of new inflation are implemented in supergravity, the inflaton is a complex and not a real scalar field. As a complex scalar field has two independent components, supergravity models of new inflation are naturally two-field models. In this paper, we use the delta N formalism to analyse how the two-field behaviour modifies the usual single-field predictions. We find that the model reduces to the single-field limit if the inflaton mass term is sufficiently small. Otherwise, the imaginary inflaton component reduces the amplitude A_s and the spectral index n_s of the scalar curvature perturbations. However, the perturbations remain nearly Gaussian, and the reduced bispectrum f_NL is too small to be observed.
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