scholarly journals Implications of a Nonzero Cosmological Constant and Luminosity Selection Effects on Cosmological Tests

1998 ◽  
Vol 51 (3) ◽  
pp. 585 ◽  
Author(s):  
A. A. Ubachukwu
Keyword(s):  
Cosmological Constant ◽  
The Other ◽  
Linear Size ◽  
Low Density ◽  
Selection Effects ◽  
Flat Universe ◽  
Size Evolution ◽  
Significant Difference ◽  
Cosmological Tests ◽  
The Universe

This paper examines the implications of a nonzero cosmological constant Λ 0 on the amount of linear size evolution and the luminosity selection effects usually required in the interpretation of the angular diameter–redshift (θ–z) test. This is based on three typical cases chosen on various plausible assumptions which can be made concerning the contribution of Λ 0 to the density of the universe (parametrised by ?0). The results show that a fairly strong linear size evolution will be required to interpret the θ–z data of extended steep spectrum quasars for all three cases, if luminosity effects are neglected. However, this evolution is significantly steeper in a matter-dominated universe with ?M = ?0 = 1 than in both the flat universe with ?Λ = 0·8, ?M = 0·2 and an open universe with ?M = 0·2, Λ = 0. Furthermore, when the luminosity selection effects present in the sample are considered, a milder size evolution is obtained for the ?M = 1, ?Λ = 0 model while little or no size evolution is found for the other two cases. There is therefore no significant difference in our results for an open low density universe with ?Λ = 0 and a flat universe dominated by ?Λ predicted by inflation. The present results therefore imply that an open low density universe with ?M = 0·2 and ?Λ = 0 is compatible with an inflationary model of the universe with ?M = 0·2 and ?Λ = 0 · 8. This leads to a contradiction since the universe cannot be open and spatially closed at the same time (the existence of one should preclude the other).

COSMOLOGICAL TERM AS A CORRECTION OF METRIC TENSOR FIELD

2001 ◽  
Vol 10 (06) ◽  
pp. 893-904 ◽  
Author(s):  
TAKAO FUKUI
Keyword(s):  
Cosmological Constant ◽  
Tensor Field ◽  
Cosmological Term ◽  
The Other ◽  
Metric Tensor ◽  
Linear Correction ◽  
The Universe

Models of the universe with a cosmological term which is introduced as a correction of the metric tensor field are studied. By revisiting with these models some of the conventional success, we infer that a model with a linear correction is a favourable candidate for a model of the universe. The cosmological constant and the flatness problems are examined in the model. There might be a possibility to solve the other cosmological problems only with the metric tensor field.

scholarly journals Thermodynamic Prescription of Cosmological Constant in the Randall-Sundrum II Brane

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Tanwi Bandyopadhyay
Keyword(s):  
Cosmological Constant ◽  
Uncertainty Principle ◽  
Generalized Uncertainty Principle ◽  
Friedmann Equation ◽  
Entropy Function ◽  
Flat Universe ◽  
Corrected Entropy ◽  
Cosmological Scenario ◽  
Equipartition Law ◽  
The Universe

In this work, we apply the quantum corrected entropy function derived from the Generalized Uncertainty Principle (GUP) to the holographic equipartition law to study the cosmological scenario in the Randall-Sundrum (RS) II brane. An extra driving term has come up in the effective Friedmann equation for a homogeneous, isotropic, and spatially flat universe. Further, thermodynamic prescription of the universe constraints this term eventually with an order equivalent to that of the cosmological constant.

scholarly journals Nuclear Constraints on the Age of the Universe

1983 ◽  
Vol 6 ◽  
pp. 241-253 ◽  
Author(s):  
David N. Schramm
Keyword(s):  
Cosmological Constant ◽  
Nuclear Physics ◽  
Big Bang ◽  
Distance Scale ◽  
The Other ◽  
Single Measurement ◽  
Age Of The Universe ◽  
The Big Bang ◽  
The Universe ◽  
Fair Degree

In this paper a review will be made of how one can use nuclear physics to put rather stringent limits on the age of the universe and thus the cosmic distance scale. As the other papers in this session have demonstrated there is some disagreement on the distance scale and thus the limits on the age of the universe (if the cosmological constant Λ = 0.) However, the disagreement is only over the last factor of 2, the basic timescale seems to really be remarkably well agreed upon. The universe is billions of years old - not thousands, not quintillions but billions of years. That our universe has a finite age is philosophically intriguing. That we can estimate that age to a fair degree of accuracy is truly impressive.No single measurement of the time since the Big Bang gives a specific, unambiguous age. Fortunately, we have at our disposal several methods that together fix the age with surprising precision.

scholarly journals A NEW COSMOLOGICAL CONSTANT MODEL

1996 ◽  
Vol 11 (01) ◽  
pp. 1-7 ◽  
Author(s):  
JORGE L. LOPEZ ◽  
D.V. NANOPOULOS
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Hubble Parameter ◽  
Particle Physics ◽  
Time Dependent ◽  
Low Density ◽  
Universe Model ◽  
Planck Time ◽  
Age Of The Universe ◽  
The Universe

We propose a new cosmological model with a time-dependent cosmological constant (Λ∝1/t2), which starting at the Planck time as [Formula: see text], evolves to the present-day allowed value of [Formula: see text]. This scenario is supported by noncritical string theory considerations. We compute the age of the Universe and the time dependence of the scale factor in this model, and find general agreement with recent determinations of the Hubble parameter for substantial values of ΩΛ. This effectively low-density open Universe model differs from the traditional cosmological constant model, and has observable implications for particle physics and cosmology.

scholarly journals Phenomenological models of Universe with varying G and Λ

Open Physics ◽  
2014 ◽  
Vol 12 (5) ◽  
Author(s):  
Martiros Khurshudyan
Keyword(s):  
Cosmological Constant ◽  
Phenomenological Models ◽  
Gravitational Constant ◽  
Fluid Model ◽  
Cosmological Parameters ◽  
The Other ◽  
Barotropic Fluid ◽  
Two Component ◽  
And Behavior ◽  
The Universe

AbstractIn this article we will consider several phenomenological models for the Universe with varying G and Λ(t), where G is the gravitational ”constant” and Λ(t) is a varying cosmological ”constant”. Two-component fluid model are taken into account. An interaction of the phenomenological form between a barotropic fluid and a quintessence DE is supposed. Three different forms of Λ(t) will be considered. The problem is analysed numerically and behavior of different cosmological parameters investigated graphically. Conclusion and discussions are given at the end of the work. In an Appendix information concerning to the other cosmological parameters is presented.

scholarly journals Luminosity Selection Effects and Linear Size Evolution in the Quasar/Galaxy Unification Scheme

1998 ◽  
Vol 51 (1) ◽  
pp. 143
Author(s):  
A. A. Ubachukwu ◽  
J. N. Ogwo
Keyword(s):  
High Redshift ◽  
Radio Galaxies ◽  
Linear Size ◽  
Selection Effects ◽  
Size Evolution

The implications of linear size evolution and luminosity selection effects in the quasar/galaxy unification scheme have been investigated. We show that both radio galaxies and quasars undergo similar size evolution above some low redshift cut-off zc = 0·2–0·3. However, this evolution can be attributed largely to the strong luminosity selection effects present in the sample. We also observe that there is a marked difference in the luminosity–redshift slope between low and high redshift sources, which may be responsible for the conflicting results in the literature as to whether or not radio galaxies and quasars have similar linear size versus luminosity/redshift relationships. Our present result seems consistent with the quasar/galaxy unification scheme in which the two classes of object are expected to have similar linear size versus luminosity/redshift relationships.

scholarly journals ASYMPTOTICALLY VANISHING COSMOLOGICAL CONSTANT IN THE MULTIVERSE

2011 ◽  
Vol 26 (18) ◽  
pp. 3107-3120 ◽  
Author(s):  
HIKARU KAWAI ◽  
TAKASHI OKADA
Keyword(s):  
Wave Function ◽  
Partition Function ◽  
Cosmological Constant ◽  
Space Time ◽  
The Other ◽  
Wkb Method ◽  
Leading Order ◽  
Lorentzian Space ◽  
Euclidean Wormholes ◽  
The Universe

We study the problem of the cosmological constant in the context of the multiverse in Lorentzian space–time, and show that the cosmological constant will vanish in the future. This sort of argument was started by Sidney Coleman in 1989, and he argued that the Euclidean wormholes make the multiverse partition function a superposition of various values of the cosmological constant Λ, which has a sharp peak at Λ = 0. However, the implication of the Euclidean analysis to our Lorentzian space–time is unclear. With this motivation, we analyze the quantum state of the multiverse in Lorentzian space–time by the WKB method, and calculate the density matrix of our universe by tracing out the other universes. Our result predicts vanishing cosmological constant. While Coleman obtained the enhancement at Λ = 0 through the action itself, in our Lorentzian analysis the similar enhancement arises from the front factor of eiS in the universe wave function, which is in the next leading order in the WKB approximation.

scholarly journals Linear Size Evolution and Luminosity Selection Effects in Quasars

1997 ◽  
Vol 50 (5) ◽  
pp. 967
Author(s):  
A. A. Ubachukwu
Keyword(s):  
Linear Size ◽  
Selection Effects ◽  
Large Sample ◽  
Size Evolution

We have quantitatively estimated the amount of luminosity selection effects present in the observed linear size-redshift data for a large sample of extended steep spectrum quasars. We show that ~90% of the observed dependence of sizes of quasars on redshift can be interpreted in terms of luminosity selection effects alone. This gives quantitative support to earlier results which show that little or no intrinsic linear size evolution appears to be occurring among quasars.

The cosmological constant

1983 ◽  
Vol 310 (1512) ◽  
pp. 303-310 ◽  
Keyword(s):  
Phase Transition ◽  
Symmetry Breaking ◽  
Cosmological Constant ◽  
Anthropic Principle ◽  
The Other ◽  
Planck Length ◽  
Upper Limit ◽  
Distant Galaxies ◽  
Effective Cosmological Constant ◽  
The Universe

The cosmological constant is the quantity in physics that is most accurately measured to be zero: observations of departures from the Hubble law by distant galaxies place an upper limit of the order of 10 -120 in dimensionless units. On the other hand, the various symmetry breaking mechanisms that we believe are operating in the Universe would give an effective cosmological constant many orders of magnitude larger, unless they are incredibly finely balanced. One answer would be to appeal to the anthropic principle, but a more attractive possibility is that there is a phase transition N = 8 supergravity to a foam-like state which breaks supersymmetry and which appears flat on scales larger than the Planck length.

scholarly journals A measurement of the cosmic expansion within our lifetime

2021 ◽  
Author(s):  
Fulvio Melia
Keyword(s):  
Standard Model ◽  
Cosmological Constant ◽  
Physical Properties ◽  
Particle Physics ◽  
The Other ◽  
Model Parameters ◽  
Cosmic Expansion ◽  
Redshift Drift ◽  
The Standard Model ◽  
The Universe

Abstract The most exciting future observation in cosmology will feature a monitoring of the cosmic expansion in real time, unlike anything that has ever been attempted before. This campaign will uncover crucial physical properties of the various constituents in the Universe, and perhaps answer a simpler question concerning whether or not the cosmic expansion is even accelerating. An unambiguous yes/no response to this query will significantly impact cosmology, of course, but also the standard model of particle physics. Here, we discuss---in a straightforward way---how to understand the so-called `redshift drift' sought by this campaign, and why its measurement will help us refine the standard-model parameters if the answer is `yes.' A `no' answer, on the other hand, could be more revolutionary, in the sense that it might provide a resolution of several long-standing problems and inconsistencies in our current cosmological models. An outcome of zero redshift drift, for example, would obviate the need for a cosmological constant and render inflation completely redundant.

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