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110
Dark Energy from Structure  A Status Report
 GEN. REL. GRAV., DARK ENERGY SPECIAL ISSUE
, 2007
"... The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein’s theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effe ..."
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Cited by 58 (9 self)
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The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein’s theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field (‘morphon field’) modeling Dark Energy. The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation. The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard
Is the physics within the Solar system really understood ? arXiv:grqc/0604052; A. Unzicker, Why do we
 Still Believe in Newton’s Law ? Facts, Myths and Methods in Gravitational Physics
"... A collection is made of presently unexplained phenomena within our Solar system and in the universe. These phenomena are (i) the Pioneer anomaly, (ii) the flyby anomaly, (iii) the increase of the Astronomical Unit, (iv) the quadrupole and octupole anomaly, and (v) Dark Energy and (vi) Dark Matter. A ..."
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Cited by 26 (1 self)
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A collection is made of presently unexplained phenomena within our Solar system and in the universe. These phenomena are (i) the Pioneer anomaly, (ii) the flyby anomaly, (iii) the increase of the Astronomical Unit, (iv) the quadrupole and octupole anomaly, and (v) Dark Energy and (vi) Dark Matter. A new data analysis of the complete set of Pioneer data is announced in order to search for systematic effects or to confirm the unexplained acceleration. We also review the mysterious flyby anomaly where the velocities of spacecraft after Earth swing–bys are larger than expected. We emphasize the scientific aspects of this anomaly and propose systematic and continuous observations and studies at the occasion of future flybys. Further anomalies within the Solar system are the increase of the Astronomical Unit and the quadrupole and octupole anomaly. We briefly mention Dark Matter and Dark Energy since in some cases a relation between them and the Solar system anomalies have been speculated. 1
Cosmological Constant  the Weight of the Vacuum
 Phys. Rept
, 2003
"... Recent cosmological observations suggest the existence of a positive cosmological constant Λ with the magnitude Λ(G�/c 3) ≈ 10 −123. This review discusses several aspects of the cosmological constant both from the cosmological (sections 1–6) and field theoretical (sections 7–11) perspectives. The f ..."
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Cited by 26 (2 self)
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Recent cosmological observations suggest the existence of a positive cosmological constant Λ with the magnitude Λ(G�/c 3) ≈ 10 −123. This review discusses several aspects of the cosmological constant both from the cosmological (sections 1–6) and field theoretical (sections 7–11) perspectives. The first section introduces the key issues related to cosmological constant and provides a brief historical overview. This is followed by a summary of the kinematics and dynamics of the standard Friedmann model of the universe paying special attention to features involving the cosmological constant. Section 3 reviews the observational evidence for cosmological constant, especially the supernova results, constraints from the age of the universe and a few others. Theoretical models (quintessence, tachyonic scalar field,...) with evolving cosmological ‘constant ’ are described from different perspectives in the next section. Constraints on dark energy from structure formation and from CMBR anisotropies are discussed in the next two sections. The latter part of the review (sections 7–11) concentrates on more conceptual and fundamental aspects of the cosmological constant. Section 7 provides some alternative interpretations of the cosmological constant which could have a bearing on the possible solution to the problem. Several relaxation mechanisms have been suggested in the literature to reduce the cosmological constant to the currently observed value and some of these attempts are described in section 8. Next section gives a brief description of the geometrical structure of the de Sitter spacetime and the thermodynamics of the de Sitter universe is taken up in section 10. The last section deals with the role of string theory in the cosmological constant problem.
Categorizing different approaches to the cosmological constant problem
"... Abstract. We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified in ..."
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Cited by 22 (1 self)
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Abstract. We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified into five different schemes of which we indicate the advantages and drawbacks. Besides, we add a new approach based on a symmetry principle mapping real to
Dark Energy from backreaction
 JCAP
, 2004
"... We consider the effect of inhomogeneities on the expansion of the Einsteinde Sitter universe. We find that the backreaction of linear scalar metric perturbations results in apparent dark energy with a mixture of equations of state between 0 and –4/3. We discuss the possibility that backreaction cou ..."
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Cited by 20 (0 self)
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We consider the effect of inhomogeneities on the expansion of the Einsteinde Sitter universe. We find that the backreaction of linear scalar metric perturbations results in apparent dark energy with a mixture of equations of state between 0 and –4/3. We discuss the possibility that backreaction could account for presentday acceleration. 1
Probes and tests of strongfield gravity with observations in the electromagnetic spectrum. Living Rev. Relativity
"... Neutron stars and black holes are the astrophysical systems with the strongest gravitational fields in the universe. In this article, I review the prospect of probing with observations of such compact objects some of the most intriguing General Relativistic predictions in the strongfield regime: th ..."
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Cited by 15 (0 self)
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Neutron stars and black holes are the astrophysical systems with the strongest gravitational fields in the universe. In this article, I review the prospect of probing with observations of such compact objects some of the most intriguing General Relativistic predictions in the strongfield regime: the absence of stable circular orbits near a compact object and the presence of event horizons around blackhole singularities. I discuss the need for a theoretical framework within which future experiments will provide detailed, quantitative tests of gravity theories. Finally, I summarize the constraints imposed by current observations of neutron stars on potential deviations from General Relativity. 1 1
Solar system effects in Schwarzschild–de Sitter space–time
 Phys. Lett
"... The Schwarzschild–de Sitter space–time describes the gravitational field of a spherically symmetric mass in a universe with cosmological constant Λ. Based on this space–time we calculate Solar system effects like gravitational redshift, light deflection, gravitational time delay, Perihelion shift, g ..."
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Cited by 9 (2 self)
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The Schwarzschild–de Sitter space–time describes the gravitational field of a spherically symmetric mass in a universe with cosmological constant Λ. Based on this space–time we calculate Solar system effects like gravitational redshift, light deflection, gravitational time delay, Perihelion shift, geodetic or de Sitter precession, as well as the influence of Λ on a Doppler measurement, used to determine the velocity of the Pioneer 10 and 11 spacecraft. For Λ = Λ0 ∼ 10 −52 m −2 the cosmological constant plays no role for all of these effects, while a value of Λ ∼ −10 −37 m −2, if hypothetically held responsible for the Pioneer anomaly, is not compatible with the Perihelion shift. 1
Quantum signatures of Solar System dynamics
"... Abstract Let!(i) be period of rotation of the ith planet around the Sun (or!j(i) be period of rotation of jth satellite around the ith planet). From empirical P observations it is known that within margins of experimental errors i ni!(i) = 0 (or P j nj!j(i) = 0) for some integers ni (or nj), di ..."
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Cited by 7 (7 self)
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Abstract Let!(i) be period of rotation of the ith planet around the Sun (or!j(i) be period of rotation of jth satellite around the ith planet). From empirical P observations it is known that within margins of experimental errors i ni!(i) = 0 (or P j nj!j(i) = 0) for some integers ni (or nj), di¤erent for di¤erent satellite systems. These conditions, known as resonance conditions, make uses of theories such as KAM di ¢ cult to implement. The resonances in Solar System are similar to those encountered in old quantum mechanics where applications of methods of celestial mechanics to atomic and molecular physics were highly successful. With such a successes, the birth of new quantum mechanics is di ¢ cult to understand. In short, the rationale for its birth lies in simplicity with which the same type of calculations can be done using methods of quantum mechanics capable of taking care of resonances. The solution of quantization puzzle was found by Heisenberg. In this paper new uses of Heisenberg’s ideas are found. When superimposed with the equivalence principle of general relativity, they lead to quantum mechanical treatment of observed resonances in the Solar System. To test correctness of theoretical predictions the number of allowed stable orbits for planets and for equatorial stable orbits of satellites of heavy planets is calculated resulting in good agreement with observational data. In addition, the paper brie‡y discusses quantum mechanical nature of rings of heavy planets and potential usefulness of the obtained results for cosmology. Key words Heisenberg honeycombs Quantum and celestial mechanics Group theory Exactly solvable classical and quantum dynamical problems Equivalence principle Cosmological constant (anti) de Sitter spaces 1
Entropy in the Present and Early Universe: New Small Parameters and Dark Energy Problem
, 2010
"... entropy ..."
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