scholarly journals DARK ENERGY: RECENT DEVELOPMENTS

2006 ◽  
Vol 21 (14) ◽  
pp. 1083-1097 ◽  
Author(s):  
N. STRAUMANN
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Particle Physics ◽  
Vacuum Energy ◽  
Large Body ◽  
Vacuum Energy Density ◽  
Fundamental Particle ◽  
Dark Energy Component ◽  
Recent Developments

A six-parameter cosmological model, involving a vacuum energy density that is extremely tiny compared to fundamental particle physics scales, describes a large body of increasingly accurate astronomical data. In the first part of this brief review we summarize the current situation, emphasizing recent progress. An almost infinitesimal vacuum energy is only the simplest candidate for a cosmologically significant nearly homogeneous exotic energy density with negative pressure, generically called Dark Energy. If general relativity is assumed to be also valid on cosmological scales, the existence of such a dark energy component that dominates the recent universe is now almost inevitable. We shall discuss in the second part the alternative possibility that general relativity has to be modified on distances comparable to the Hubble scale. It will turn out that observational data are further restricting theoretical speculations. Moreover, some of the recent proposals have serious defects on a fundamental level (ghosts, acausalities, superluminal fluctuations).

scholarly journals Do we come from a quantum anomaly?

2019 ◽  
Vol 28 (14) ◽  
pp. 1944002 ◽  
Author(s):  
Spyros Basilakos ◽  
Nick E. Mavromatos ◽  
Joan Solà Peracaula
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Energy Density ◽  
Hubble Parameter ◽  
Vacuum Energy ◽  
Vacuum Energy Density ◽  
Quantum Anomaly ◽  
Inflationary Phase ◽  
Axion Field ◽  
The Universe

We present a string-based picture of the cosmological evolution in which (CP-violating) gravitational anomalies acting during the inflationary phase of the universe cause the vacuum energy density to “run” with the effective Hubble parameter squared, [Formula: see text], thanks to the axion field of the bosonic string multiplet. This leads to baryogenesis through leptogenesis with massive right-handed neutrinos. The generation of chiral matter after inflation helps in cancelling the anomalies in the observable radiation- and matter-dominated eras. The present era inherits the same “running vacuum” structure triggered during the inflationary time by the axion field. The current dark energy is thus predicted to be mildly dynamical, and dark matter should be made of axions. Paraphrasing Carl Sagan [ https://www.goodreads.com/author/quotes/10538.Carl_Sagan .]: we are all anomalously made from starstuff.

scholarly journals Space-Time Curvature Of General Relativity And Energy Density Of A Three-Dimensional Quantum Vacuu

2015 ◽  
Vol 69 (1) ◽  
Author(s):  
Davide Fiscaletti ◽  
Amrit Sorli
Keyword(s):  
General Relativity ◽  
Energy Density ◽  
Vacuum Energy ◽  
Three Dimensional ◽  
Space Time ◽  
Vacuum Energy Density ◽  
Quantum Vacuum ◽  
Vacuum Condensate ◽  
Interesting Solution ◽  
Variable Energy

AbstractA three-dimensional quantum vacuum condensate is introduced as a fundamental medium from which gravity emerges in a geometro-hydrodynamic limit. In this approach, the curvature of space-time characteristic of general relativity is obtained as a mathematical value of a more fundamental actual variable energy density of quantum vacuum which has a concrete physical meaning. The fluctuations of the quantum vacuum energy density suggest an interesting solution for the dark energy problem.

scholarly journals DARK ENERGY DENSITY IN MODELS WITH SPLIT SUPERSYMMETRY AND DEGENERATE VACUA

2012 ◽  
Vol 27 (11) ◽  
pp. 1250063 ◽  
Author(s):  
C. FROGGATT ◽  
R. NEVZOROV ◽  
H. B. NIELSEN
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Susy Breaking ◽  
Vacuum Energy Density ◽  
Dark Energy Density ◽  
Hidden Sector ◽  
Split Supersymmetry ◽  
Breaking Scale

In N = 1 supergravity supersymmetric and nonsupersymmetric Minkowski vacua originating in the hidden sector can be degenerate. In the supersymmetric phase in flat Minkowski space, nonperturbative supersymmetry breakdown may take place in the observable sector, inducing a nonzero and positive vacuum energy density. Assuming that such a supersymmetric phase and the phase in which we live are degenerate, we estimate the value of the cosmological constant. We argue that the observed value of the dark energy density can be reproduced in the split SUSY scenario of SUSY breaking if the SUSY breaking scale is of order of 1010 GeV.

scholarly journals ISSUES WITH VACUUM ENERGY AS THE ORIGIN OF DARK ENERGY

2012 ◽  
Vol 27 (27) ◽  
pp. 1250154 ◽  
Author(s):  
HOURI ZIAEEPOUR
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Dark Energy ◽  
Particle Physics ◽  
Vacuum Energy ◽  
A Priori ◽  
Higgs Field ◽  
Scalar Fields ◽  
Vacuum Energy Density ◽  
Quantum Field

In this paper, we address some of the issues raised in the literature about the conflict between a large vacuum energy density, a priori predicted by quantum field theory, and the observed dark energy which must be the energy of vacuum or include it. We present a number of arguments against this claim and in favor of a null vacuum energy. They are based on the following arguments: A new definition for the vacuum in quantum field theory as a frame-independent coherent state; results from a detailed study of condensation of scalar fields in Friedmann–Lemaître–Robertson–Walker (FLRW) background performed in a previous work; and our present knowledge about the Standard Model of particle physics. One of the predictions of these arguments is the confinement of nonzero expectation value of Higgs field to scales roughly comparable with the width of electroweak gauge bosons or shorter. If the observation of Higgs by the LHC is confirmed, accumulation of relevant events and their energy dependence in near future should allow us to measure the spatial extend of the Higgs condensate.

scholarly journals Dynamical dark energy with a constant vacuum energy density

2006 ◽  
Vol 636 (2) ◽  
pp. 80-85 ◽  
Author(s):  
B. Guberina ◽  
R. Horvat ◽  
H. Nikolić
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Vacuum Energy ◽  
Vacuum Energy Density ◽  
Dynamical Dark Energy

scholarly journals THE NATURE OF THE COSMOLOGICAL CONSTANT PROBLEM

2009 ◽  
Vol 24 (08n09) ◽  
pp. 1545-1548 ◽  
Author(s):  
M. D. MAIA ◽  
A. J. S. CAPISTRANO ◽  
E. M. MONTE
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Energy Density ◽  
Cosmological Constant ◽  
Ground State ◽  
Vacuum Energy ◽  
Dimensional Space ◽  
Brane World ◽  
Vacuum Energy Density ◽  
Cosmological Constant Problem

General relativity postulates the Minkowski space-time as the standard (flat) geometry against which we compare all curved space-times and also as the gravitational ground state where particles, quantum fields and their vacua are defined. On the other hand, experimental evidences tell that there exists a non-zero cosmological constant, which implies in a deSitter ground state, which not compatible with the assumed Minkowski structure. Such inconsistency is an evidence of the missing standard of curvature in Riemann's geometry, which in general relativity manifests itself in the form of the cosmological constant problem. We show how the lack of a curvature standard in Riemann's geometry can be fixed by Nash's theorem on metric perturbations. The resulting higher dimensional gravitational theory is more general than general relativity, similar to brane-world gravity, but where the propagation of the gravitational field along the extra dimensions is a mathematical necessity, rather than a postulate. After a brief introduction to Nash's theorem, we show that the vacuum energy density must remain confined to four-dimensional space-times, but the cosmological constant resulting from the contracted Bianchi identity represents a gravitational term which is not confined. In this case, the comparison between the vacuum energy and the cosmological constant in general relativity does not make sense. Instead, the geometrical fix provided by Nash's theorem suggests that the vacuum energy density contributes to the perturbations of the gravitational field.

scholarly journals SUPERSYMMETRIC BAROTROPIC FRW MODEL AND DARK ENERGY

2009 ◽  
Vol 24 (16) ◽  
pp. 1257-1266
Author(s):  
J. J. ROSALES ◽  
V. I. TKACH
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Perfect Fluid ◽  
Vacuum Energy ◽  
Matter Field ◽  
Vacuum Energy Density ◽  
Square Root ◽  
Frw Universe ◽  
Frw Model

Using the superfield approach we construct the n = 2 supersymmetric Lagrangian for the FRW Universe with barotropic perfect fluid as matter field. The obtained supersymmetric algebra allowed us to take the square root of the Wheeler–DeWitt equation and solve the corresponding quantum constraint. This model leads to the relation between the vacuum energy density and the energy density of the dust matter.

Dark energy and dark matter as due to zero point energy

2012 ◽  
Vol 79 (3) ◽  
pp. 327-334 ◽  
Author(s):  
BO LEHNERT
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Energy Density ◽  
Vacuum Energy ◽  
Mass Density ◽  
Zero Point ◽  
Vacuum Energy Density ◽  
Zero Point Energy ◽  
Observable Universe ◽  
Point Energy

AbstractAn attempt is made to explain dark energy and dark matter of the expanding universe in terms of the zero point vacuum energy. This analysis is mainly limited to later stages of an observable nearly flat universe. It is based on a revised formulation of the spectral distribution of the zero point energy, for an ensemble in a defined statistical equilibrium having finite total energy density. The steady and dynamic states are studied for a spherical cloud of zero point energy photons. The ‘antigravitational’ force due to its pressure gradient then represents dark energy, and its gravitational force due to the energy density represents dark matter. Four fundamental results come out of the theory. First, the lack of emitted radiation becomes reconcilable with the concepts of dark energy and dark matter. Second, the crucial coincidence problem of equal orders of magnitude of mass density and vacuum energy density cannot be explained by the cosmological constant, but is resolved by the present variable concepts, which originate from the same photon gas balance. Third, the present approach becomes reconcilable with cosmical dimensions and with the radius of the observable universe. Fourth, the deduced acceleration of the expansion agrees with the observed one. In addition, mass polarity of a generalized gravitation law for matter and antimatter is proposed as a source of dark flow.

On the cosmological constant problem and brane-world geometry

Open Physics ◽  
2011 ◽  
Vol 9 (1) ◽  
Author(s):  
Abraão Capistrano ◽  
Pedro Odon
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Energy Density ◽  
Cosmological Constant ◽  
Vacuum Energy ◽  
Extrinsic Curvature ◽  
Brane World ◽  
Vacuum Energy Density ◽  
Cosmological Constant Problem ◽  
Riemannian Geometries

AbstractThe cosmological constant problem is examined within the context of the covariant brane-world gravity, based on Nash’s embedding theorem for Riemannian geometries. We show that the vacuum structure of the brane-world is more complex than General Relativity’s because it involves extrinsic elements, in specific, the extrinsic curvature. In other words, the shape (or local curvature) of an object becomes a relative concept, instead of the “absolute shape” of General Relativity. We point out that the immediate consequence is that the cosmological constant and the energy density of the vacuum quantum fluctuations have different physical meanings: while the vacuum energy density remains confined to the four-dimensional brane-world, the cosmological constant is a property of the bulk’s gravitational field that leads to the conclusion that these quantities cannot be compared, as it is usually done in General Relativity. Instead, the vacuum energy density contributes to the extrinsic curvature, which in turn generates Nash’s perturbation of the gravitational field. On the other hand, the cosmological constant problem ceases to be in the brane-world geometry, reappearing only in the limit where the extrinsic curvature vanishes.

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