Scalar and tensor power spectra in a universe with positive curvature index and maximally symmetric spatial section

Asgari, Ali A.; Abbassi, Amir H.

doi:10.1016/j.dark.2015.03.001

Cited by 7 publications

(5 citation statements)

References 36 publications

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“…For example Ellis and his collaborators [11,12] analyzed the spatially closed inflationary model and revealed the causal and dynamical discrepancies between spatially flat and closed models. Furthermore, the spectra coming out from spatially closed inflationary model is different from ordinary inflationary scenario [13]. Similar treatment is observed in spatially open model [14,15].…”

Section: Effect Of the Curvature Parameter In Various Cosmological Er...supporting

confidence: 60%

Imprints of intrinsic and exterior curvatures in cosmology

Asgari,

Abbassi

2017

Preprint

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Nowadays, according to the observational evidences the curvature parameter of the universe is neglected and spatially flat FLRW model is on the top of interest for cosmologists. However, due to some discrepancies between Λ-CDM model anticipations and observations, one may think out the curvature parameter as the solution even though it may be very small. So, in this article we investigate the eras in which the curvature influence was or is more significant. In addition, a geometrical interpretation of the Hubble parameter is dedicated. We find that the Hubble parameter is more appropriate to be defined as the mean curvature of the spatial section of the universe because the concept of the scale factor in a nonhomogeneous universe is not precisely clear. Moreover, we realize that by employing the linear perturbations, two principle curvatures of the absolute space change into what depends on the local Hubble parameter.

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Section: Effect Of the Curvature Parameter In Various Cosmological Er...supporting

confidence: 60%

Imprints of intrinsic and exterior curvatures in cosmology

Asgari,

Abbassi

2017

Preprint

Self Cite

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“…This assumes we are starting after the Universe has inflated sufficiently that it is negligible. If this is not the case then one may expect signatures such as a correction to the normalization of the power spectrum[167,168], and possibly a non-standard running of the spectral index[169].…”

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confidence: 99%

Pixelated Dark Energy

Heckman

Lawrie

Lin

et al. 2019

Fortschritte der Physik

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We study the phenomenology of a recent string construction with a quantum mechanically stable dark energy. A mild supersymmetry protects the vacuum energy but also allows O(10−100) TeV scale superpartner masses. The construction is holographic in the sense that the 4D spacetime is generated from “spacetime pixels” originating from five‐branes wrapped over metastable five‐cycles of the compactification. The cosmological constant scales as Λ∼1/N in the pixel number. An instability in the construction leads to cosmic expansion. This also causes more five‐branes to wind up in the geometry, leading to a slowly decreasing cosmological constant which we interpret as an epoch of inflation followed by (pre‐)heating when a rare event occurs in which the number of pixels increases by an order one fraction. The sudden appearance of radiation triggers an exponential increase in the number of pixels. Dark energy has a time varying equation of state with wa=−3normalΩm,0false(1+w0false)/2, which is compatible with current bounds, and could be constrained further by future data releases. The pixelated nature of the Universe also implies a large‐l cutoff on the angular power spectrum of cosmological observables with l max ∼Ofalse(Nfalse). We also use this pixel description to study the thermodynamics of de Sitter space, finding rough agreement with effective field theory considerations.

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“…which is the Mukhanov-Sasaki equation for general K, has been derived in [18] for K = +1. We leave solutions of equation (24) for next works and now turn to investigate the evolution of R q in post-inflation epoch.…”

Section: Special Solutionsmentioning

confidence: 99%

Curvature and topology dependency of the cosmological spectra

2019

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In this article we investigate dependency of two important cosmological random fields defined on spatial slices of the FLRW universe and their spectra on the geometry and topology of the background universe. Our discussion includes the post-inflationary universe i.e. radiation-dust mixture era. For this purpose, we first extract an explicit equation describing evolution of the comoving curvature perturbation in the FLRW universe with arbitrary spatial sectional curvature. We may realize when K = 0, curvature scale may be as significant as the perturbations scales to recognize the behavior of the spectral indices. We also focus on the entropy perturbation in order to extract behavior of the isocurvature spectral index in terms of the curvature index and time. Our analysis shows that the adiabatic and entropy spectral indices of the cosmological perturbations (spectra of curvature and entropy perturbations) in sub-horizon scales could be function of topology. It may be significant because reveals imprints of geometry on the statistical information deduced by observations. Moreover, an accurate analysis makes clear that time-average of isocurvature index in case K = 0 is about zero,so that imprint of entropy perturbation in time duration may be negligible. We also consider evolution of the cosmological indices for super-curvature modes in case K = −1 . In the most results dependency to curvature, initial conditions and scale modes are thoroughly vivid.

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Scalar and tensor power spectra in a universe with positive curvature index and maximally symmetric spatial section

Cited by 7 publications

References 36 publications

Imprints of intrinsic and exterior curvatures in cosmology

Imprints of intrinsic and exterior curvatures in cosmology

Pixelated Dark Energy

Curvature and topology dependency of the cosmological spectra

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