Topological inflation with graceful exit

Physical Review D, 1990

We consider the production of topological defects, especially cosmic strings, in extended inflation models. In extended inflation, the Universe passes through a fist-order phase transition via bubble percolation, which naturally allows defects to form at the end of inflation. The correlation length, which determines the number density of the defects, is related to the mean size of bubbles when they collide. This mechanism allows a natural combination of inflation and large-scale structure via cosmic strings.

1982

We present a natural scenario for obtaining an open universe (Ω0 < 1) through inflation. In this scenario, there are two epochs of inflationary expansion—an epoch of ‘old inflation, ’ during which the inflaton field is stuck in a false vacuum, followed by an epoch of ‘new inflation, ’ during which the inflaton field slowly rolls toward its true minimum. During the first epoch, inflation solves the smoothness and horizon problems. Then an open universe (with negative spatial curvature) is created by the nucleation of a single bubble. In effect Ω is instantaneously ‘reset ’ to zero. During the subsequent ‘new ’ inflation Ω rises toward unity. The value of Ω today is calculable in terms of the parameters of the potential, and we show that obtaining values significantly different from zero or unity (though within the range 0 < Ω < 1) does not require significant fine tuning. We compute the spectrum of density perturbations by evolving the Bunch-Davies vacuum modes across the bu...

Physical Review D, 2020

2016

In this paper we will discuss a model which describes the cause of inflation by a topological transition. The guiding principle is the choice of an exotic smoothness structure for the space-time. Here we consider a space-time with topology S 3 × R. In case of an exotic S 3 × R, there is a change in the spatial topology from a 3-sphere to a homology 3-sphere which can carry a hyperbolic structure. From the physical point of view, we will discuss the path integral for the Einstein-Hilbert action with respect to a decomposition of the space-time. The inclusion of the boundary terms produces fermionic contributions to the partition function. The expectation value of an area (with respect to some surface) shows an exponential increase, i.e. we obtain inflationary behavior. We will calculate the amount of this increase to be a topological invariant. Then we will describe this transition by an effective model, the Starobinski or R 2 model which is consistent with the current measurement of the Planck satellite. The spectral index and other observables are also calculated.

Spectrum of initial scalar and tensor perturbations created during an inflationary stage producing a closed or open FRW universe now is discussed. In the closed case, the CMB temperature anisotropy ∆T /T generated by scalar perturbations is enhanced for low multipoles. It is argued that in the open case there is no suppression of low multipoles. A possibility of the existence of a preferred space direction in the open case is noted.

We propose a background-independent formulation of cosmic inflation. The inflation in this picture corresponds to a dynamical process to generate space and time while the conventional inflation is simply an (exponential) expansion of a preexisting spacetime owing to the vacuum energy carried by an inflaton field. We observe that the cosmic inflation is triggered by the condensate of Planck energy into vacuum responsible for the dynamical emergence of spacetime and must be a single event according to the exclusion principle of noncommutative spacetime caused by the Planck energy condensate in vacuum. The emergent spacetime picture admits a background-independent formulation so that the inflation can be described by a conformal Hamiltonian system characterized by an exponential phase space expansion without introducing any inflaton field as well as an {\it ad hoc} inflation potential. This implies that the emergent spacetime may incapacitate all the rationales to introduce the multiverse hypothesis. In Part I we will focus on the physical foundation of cosmic inflation from the emergent spacetime picture to highlight the main idea. Its mathematical exposition will be addressed in Part II with a generalization of the emergent spacetime picture to matrix string theory.

Physics Letters B, 2006

Using the Ponce de Leon background metric, which describes a 5D universe in an apparent vacuum:Ḡ AB = 0, we study the effective 4D evolution of both, the inflaton and gauge-invariant scalar metric fluctuations, in the recently introduced model of space time matter inflation.

2006

In generic models of cosmological inflation, quantum fluctuations strongly influence the spacetime metric and produce infinitely many regions where the end of inflation (reheating) is delayed until arbitrarily late times. The geometry of the resulting spacetime is highly inhomogeneous on scales of many Hubble sizes. The recently developed string-theoretic picture of the "landscape" presents a similar structure, where an infinite number of de Sitter, flat, and anti-de Sitter universes are nucleated via quantum tunneling. Since observers on the Earth have no information about their location within the eternally inflating universe, the main question in this context is to obtain statistical predictions for quantities observed at a random location. I describe the problems arising within this statistical framework, such as the need for a volume cutoff and the dependence of cutoff schemes on time slicing and on the initial conditions. After reviewing different approaches and mathematical techniques developed in the past two decades for studying these issues, I discuss the existing proposals for extracting predictions and give examples of their applications.

OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), 2006

We derive constraints on a simple quintessential inflation model, based on a spontaneously broken 4 theory, imposed by the Wilkinson Microwave Anisotropy Probe three-year data (WMAP3) and by galaxy clustering results from the Sloan Digital Sky Survey (SDSS). We find that the scale of symmetry breaking must be larger than about 3 Planck masses in order for inflation to generate acceptable values of the scalar spectral index and of the tensor-to-scalar ratio. We also show that the resulting quintessence equation of state can evolve rapidly at recent times and hence can potentially be distinguished from a simple cosmological constant in this parameter regime.

Physics Letters B, 2014

Models of cosmic inflation posit an early phase of accelerated expansion of the universe, driven by the dynamics of one or more scalar fields in curved spacetime. Though detailed assumptions about fields and couplings vary across models, inflation makes specific, quantitative predictions for several observable quantities, such as the flatness parameter (Ω k = 1 − Ω) and the spectral tilt of primordial curvature perturbations (ns − 1 = d ln PR/d ln k), among others-predictions that match the latest observations from the Planck satellite to very good precision. In the light of data from Planck as well as recent theoretical developments in the study of eternal inflation and the multiverse, we address recent criticisms of inflation by Ijjas, Steinhardt, and Loeb. We argue that their conclusions rest on several problematic assumptions, and we conclude that cosmic inflation is on a stronger footing than ever before.