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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Chaotic inflationary universe and the anisotropy of the large-scale structure

It has been realized that the inflationary universe is in fact chaotic, that globally it is strongly inhomogeneous, and that the inflation in the universe as a whole is eternal. In such a picture the region available to modern observations is just a tiny part of the universe, in which inflation finished about 10(exp 10) years ago. In spite of the great popularity of the chaotic inflationary universe models, it is usually taken for granted that their specific features (such as strong global inhomogeneity of the universe) can hardly lead to any observable consequences. The argument is that all that is seen is just a tiny part of the universe, a region about 10(exp 28) cm, and the typical scales of considerable inhomogeneities are much greater than this size. In contrast to this opinion, an attempt is made to show that such observable consequences can really exist. The phenomenon closely connected with the origin of structure (galaxies, clusters, etc.) in the observable region is discussed. The main idea considered is the vacuum fluctuations evolution on the inhomogeneous background.

Chibisov, G. V.↗
DOE OSTI2017

Electroweak vacuum instability and renormalized Higgs field vacuum fluctuations in the inflationary universe

In this work, we investigated the electroweak vacuum instability during or after inflation. In the inflationary Universe, i.e., de Sitter space, the vacuum field fluctuations < δ φ {sup 2} > enlarge in proportion to the Hubble scale H {sup 2}. Therefore, the large inflationary vacuum fluctuations of the Higgs field < δ φ {sup 2} > are potentially catastrophic to trigger the vacuum transition to the negative-energy Planck-scale vacuum state and cause an immediate collapse of the Universe. However, the vacuum field fluctuations < δ φ {sup 2} >, i.e., the vacuum expectation values have an ultraviolet divergence, and therefore a renormalization is necessary to estimate the physical effects of the vacuum transition. Thus, in this paper, we revisit the electroweak vacuum instability from the perspective of quantum field theory (QFT) in curved space-time, and discuss the dynamical behavior of the homogeneous Higgs field φ determined by the effective potential V {sub eff}( φ ) in curved space-time and the renormalized vacuum fluctuations < δ φ {sup 2} >{sub ren} via adiabatic regularization and point-splitting regularization. We simply suppose that the Higgs field only couples the gravity via the non-minimal Higgs-gravity coupling ξ(μ). In this scenario, the electroweak vacuum stability is inevitably threatened by the dynamical behavior of the homogeneous Higgs field φ, or the formations of AdS domains or bubbles unless the Hubble scale is small enough H < Λ {sub I} .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1986

The behavior of the Higgs field in the new inflationary universe

Answers are provided to questions about the standard model of the new inflationary universe (NIU) which have raised concerns about the model's validity. A baby toy problem which consists of the study of a single particle moving in one dimension under the influence of a potential with the form of an upside-down harmonic oscillator is studied, showing that the quantum mechanical wave function at large times is accurately described by classical physics. Then, an exactly soluble toy model for the behavior of the Higgs field in the NIU is described which should provide a reasonable approximation to the behavior of the Higgs field in the NIU. The dynamics of the toy model is described, and calculative results are reviewed which, the authors claim, provide strong evidence that the basic features of the standard picture are correct.

Guth, Alan H.↗
NASA NTRS1983

The origin of density fluctuations in the 'new inflationary universe'

Cosmological mysteries which are not explained by the Big Bang hypothesis but may be approached by a revamped inflationary universe model are discussed. Attention is focused on the isotropy, the large-scale homogeneity, small-scale inhomogeneity, the oldness/flatness of the universe, and the baryon asymmetry. The universe is assumed to start in the lowest energy state, be initially dominated by false vacuum energy, enter a de Sitter phase, and then cross a barrier which is followed by the formation of fluctuation regions that lead to structure. The scalar fields (perturbation regions) experience quantum fluctuations which produce spontaneous symmetry breaking on a large scale. The scalar field value would need to be much greater than the expansion rate during the de Sitter epoch. A supersymmetric (flat) potential which satisfies the requirement, yields fluctuations of the right magnitude, and allows inflation to occur is described.

Turner, M. S.↗
DOE OSTI2018

Inflationary universe in deformed phase space scenario

We consider a noncommutative (NC) inflationary model with a homogeneous scalar field minimally coupled to gravity. The particular NC inflationary setting herein proposed, produces entirely new consequences as summarized in what follows. We first analyze the free field case and subsequently examine the situation where the scalar field is subjected to a polynomial and exponential potentials. We propose to use a canonical deformation between momenta, in a spatially flat Friedmann–Lemaî tre–Robertson–Walker (FLRW) universe, and while the Friedmann equation (Hamiltonian constraint) remains unaffected the Friedmann acceleration equation (and thus the Klein–Gordon equation) is modified by an extra term linear in the NC parameter. This concrete noncommutativity on the momenta allows interesting dynamics that other NC models seem not to allow. Let us be more precise. This extra term behaves as the sole explicit pressure that under the right circumstances implies a period of accelerated expansion of the universe. We find that in the absence of the scalar field potential, and in contrast with the commutative case, in which the scale factor always decelerates, we obtain an inflationary phase for small negative values of the NC parameter. Subsequently, the period of accelerated expansion is smoothly replaced by an appropriate deceleration phase providing an interesting model regarding the graceful exit problem in inflationary models. This last property is present either in the free field case or under the influence of the scalar field potentials considered here. Moreover, in the case of the free scalar field, we show that not only the horizon problem is solved but also there is some resemblance between the evolution equation of the scale factor associated to our model and that for the R{sup 2} (Starobinsky) inflationary model. Therefore, our herein NC model not only can be taken as an appropriate scenario to get a successful kinetic inflation, but also is a convenient setting to obtain inflationary universe possessing the graceful exit when scalar field potentials are present.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1986

The new inflationary universe, 1984

The present status of the new inflationary theory in cosmology is discussed. The standard scenario of the very early universe, the problems of this scenario, and the basics of the new inflationary theory are reviewed. The ways in which this theory solves the problems connected with the standard scenario are described.

Guth, Alan H.↗
DOE OSTI2017

Inflationary universe in the presence of a minimal measurable length

In this paper, we will study the effect of having a minimum measurable length on inflationary cosmology. We will analyze the inflationary cosmology in the Jacobson approach. In this approach, gravity is viewed as an emergent thermodynamical phenomena. We will demonstrate that the existence of a minimum measurable length will modify the Friedmann equations in the Jacobson approach. We will use this modified Friedmann equation to analyze the effect of minimum measurable length scale on inflationary cosmology. This analysis will be performed using the Hamiltonian-Jacobi approach. We compare our results to recent data, and find that our model may agree with the recent data. - Highlights: • We study the inflationary cosmology in the Jacobson thermodynamic approach. • We analyze the short distance correction to inflation from a minimum measurable length. • This analysis is done using the Hamiltonian-Jacobi approach. • This model of inflationary cosmology is consistent with the observational data.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Evolution of perturbations in an inflationary universe

The evolution of inhomogeneous density perturbations in a model of the very early universe that is dominated for a time by a constant energy density of a false quantum-mechanical vacuum is analyzed. During this period, the universe inflates exponentially and supercools exponentially, until a phase transition back to the true vacuum reheats the matter and radiation. Focus is on the physically measurable, coordinate-independent modes of inhomogeneous perturbations of this model and it is found that all modes either are constant or are exponentially damped during the inflationary era.

Frieman, J. A.↗
DOE OSTI2020

Fuzzy Euclidean wormholes in the inflationary universe

In this paper, we investigate complex-valued Euclidean wormholes in the Starobinsky inflation. Due to the properties of the concave inflation potential, the classicality condition at both ends of the wormhole can be satisfied, as long as the initial condition of the inflation field is such that it is located sufficiently close to the hilltop. Furthermore, we compare the probabilities of classicalized wormholes with the Hartle–Hawking compact instantons and conclude that the Euclidean wormholes are probabilistically preferred than compact instantons, if the inflation lasts more than 50 e-foldings. Our result assumes that the Euclidean path integral is the correct effective description of quantum gravity. This opens a new window for various future investigations that can be either confirmed or refuted by future experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1991

Phase transitions triggered by quantum fluctuations in the inflationary universe

The dynamics of a second-order phase transition during inflation, which is induced by time-variation of spacetime curvature, is studied as a natural mechanism to produce topological defects of typical grand unification scales such as cosmic strings or global textures. It is shown that their distribution is almost scale-invariant with small- and large-scale cutoffs. Also discussed is how these cutoffs are given.

Nagasawa, Michiyasu↗
NASA NTRS1987

The large-scale peculiar velocity field in flat models of the universe

The inflationary universe scenario predicts a flat universe and both adiabatic and isocurvature primordial density perturbations with the Zel'dovich spectrum. The two simplest realizations, models dominated by hot or cold dark matter, seem to be in conflict with observations. Flat models with two components of mass density, where one of the components of mass density is smoothly distributed, are examined, and the large-scale peculiar velocity field for these models is computed. For the smooth component the authors consider relativistic particles, a relic cosmological term, and light strings. At present the observational situation is unsettled, but, in principle, the large-scale peculiar velocity field is a very powerful discriminator between these different models.

Vittorio, Nicola↗
NASA NTRS1990

Gravitational lensing limits on the cosmological constant in a flat universe

Inflationary cosmological theories predict, and some more general aesthetic criteria suggest, that the large-scale spatial curvature of the universe k should be accurately zero (i.e., flat), a condition which is satisfied when the universe's present mean density and the value of the cosmological constant Lambda have certain pairs of values. Available data on the frequency of multiple image-lensing of high-redshift quasars by galaxies suggest that the cosmological constant cannot make a dominant contribution to producing a flat universe. In particular, if the mean density of the universe is as small as the baryon density inferred from standard cosmic nucleosynthesis calculations or as determined from typical dynamical studies of galaxies and galaxy clusters, then a value of Lambda large enough to produce a k = 0 universe would result in a substantially higher frequency of multiple-image lensing of quasars than has been observed so far. Shortcomings of the available lens data and uncertainties concerning galaxy properties allow some possibility of escaping this conclusion, but systematic searches for a gravitational lenses and continuing investigations of galaxy mass distributions should soon provide decisive information. It is also noted that nonzero-curvature cosmological models can account for the observed frequency of galaxy-quasar lens systems and for a variety of other constraints.

Turner, Edwin L.↗
DOE OSTI2017

G-warm inflation

A warm inflationary universe in the context of Galileon model or G-model is studied. Under a general formalism we study the inflationary dynamics and the cosmological perturbations considering a coupling of the form G (φ, X )= g (φ) X . As a concrete example, we consider an exponential potential together with the cases in which the dissipation and Galilean coefficients are constants. Also, we study the weak regime given by the condition R <1+3 gH φ-dot , and the strong regime in which 1< R +3 gH φ-dot . Additionally, we obtain constraints on the parameters during the evolution of G-warm inflation, assuming the condition for warm inflation in which the temperature T > H , the conditions or the weak and strong regimes, together with the consistency relation r = r ( n {sub s} ) from Planck data.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Logamediate Inflation in f ( T ) Teleparallel Gravity

We study logamediate inflation in the context of f ( T ) teleparallel gravity. f ( T )-gravity is a generalization of the teleparallel gravity which is formulated on the Weitzenbock spacetime, characterized by the vanishing curvature tensor (absolute parallelism) and the non-vanishing torsion tensor. We consider an f ( T )-gravity model which is sourced by a canonical scalar field. Assuming a power-law f ( T ) function in the action, we investigate an inflationary universe with a logamediate scale factor. Our results show that, although logamediate inflation is completely ruled out by observational data in the standard inflationary scenario based on Einstein gravity, it can be compatible with the 68% confidence limit joint region of Planck 2015 TT,TE,EE+lowP data in the framework of f ( T )-gravity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Prospects for cosmological collider physics

It is generally expected that heavy fields are present during inflation, which can leave their imprint in late-time cosmological observables. The main signature of these fields is a small amount of distinctly shaped non-Gaussianity, which if detected, would provide a wealth of information about the particle spectrum of the inflationary Universe. Here we investigate to what extent these signatures can be detected or constrained using futuristic 21-cm surveys. We construct model-independent templates that extract the squeezed-limit behavior of the bispectrum, and examine their overlap with standard inflationary shapes and secondary non-Gaussianities. We then use these templates to forecast detection thresholds for different masses and couplings using a 3D reconstruction of modes during the dark ages ( z ∼ 30–100). We consider interactions of several broad classes of models and quantify their detectability as a function of the baseline of a dark ages interferometer. Our analysis shows that there exists the tantalizing possibility of discovering new particles with different masses and interactions with future 21-cm surveys.

79 ASTRONOMY AND ASTROPHYSICS↗