Dynamical instability of polytropic spheres in spacetimes with a cosmological constant

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

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New Limits on a Cosmological Constant from Statistics of Gravitational Lensing

The Astrophysical Journal ◽

10.1086/306575 ◽

1999 ◽

Vol 510 (1) ◽

pp. 42-53 ◽

Cited By ~ 74

Author(s):

Masashi Chiba ◽

Yuzuru Yoshii

Keyword(s):

Cosmological Constant ◽

Gravitational Lensing

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Neutral signature gauged supergravity solutions

Journal of High Energy Physics ◽

10.1007/jhep02(2021)030 ◽

2021 ◽

Vol 2021 (2) ◽

Author(s):

J. Gutowski ◽

W. A. Sabra

Keyword(s):

Cosmological Constant ◽

Geometric Structure ◽

Base Space ◽

Killing Spinor ◽

Positive Cosmological Constant ◽

3 Dimensional

Abstract We classify all supersymmetric solutions of minimal D = 4 gauged supergravity with (2) signature and a positive cosmological constant which admit exactly one Killing spinor. This classification produces a geometric structure which is more general than that found for previous classifications of N = 2 supersymmetric solutions of this theory. We illustrate how the N = 2 solutions which consist of a fibration over a 3-dimensional Lorentzian Gauduchon-Tod base space can be written in terms of this more generic geometric structure.

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Bootstrapped Newtonian Cosmology and the Cosmological Constant Problem

Symmetry ◽

10.3390/sym13020358 ◽

2021 ◽

Vol 13 (2) ◽

pp. 358

Author(s):

Roberto Casadio ◽

Andrea Giusti

Keyword(s):

Black Holes ◽

Cosmological Constant ◽

Quantum Cosmology ◽

Quantum Physics ◽

Gravitational Interaction ◽

Newtonian Gravity ◽

Cosmological Constant Problem ◽

Newtonian Cosmology ◽

Natural Solution ◽

The Impact

Bootstrapped Newtonian gravity was developed with the purpose of estimating the impact of quantum physics in the nonlinear regime of the gravitational interaction, akin to corpuscular models of black holes and inflation. In this work, we set the ground for extending the bootstrapped Newtonian picture to cosmological spaces. We further discuss how such models of quantum cosmology can lead to a natural solution to the cosmological constant problem.

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Constraining the Swiss-Cheese IR-Fixed Point Cosmology with Cosmic Expansion

Universe ◽

10.3390/universe7080263 ◽

2021 ◽

Vol 7 (8) ◽

pp. 263

Author(s):

Ayan Mitra ◽

Vasilios Zarikas ◽

Alfio Bonanno ◽

Michael Good ◽

Ertan Güdekli

Keyword(s):

Fixed Point ◽

Cosmological Constant ◽

Cosmic Acceleration ◽

Fine Tuning ◽

Clusters Of Galaxies ◽

Swiss Cheese ◽

Coincidence Problem ◽

Cosmological Expansion ◽

Cosmic Evolution ◽

Previous Assumption

A recent work proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a Swiss-cheese cosmology model, which relativistically integrates the contribution of all these anti-gravity sources on a galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides an explanation for both the fine tuning and the coincidence problem. The present work relaxes the previous assumption on the running of the cosmological constant and allows for a generic scaling around the infrared fixed point. Our analysis reveals that, in order to produce a cosmic evolution consistent with the best ΛCDM model, the IR-running of the cosmological constant is consistent with the presence of an IR-fixed point.

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