BIG BANG NUCLEOSYNTHESIS WITH A CONSTANT VACUUM ENERGY MOTIVATED BY CYCLIC COSMOLOGY

2011 ◽  
Vol 26 (02) ◽  
pp. 331-339
Author(s):  
S. KALITA ◽  
H. L. DUORAH ◽  
K. DUORAH
Keyword(s):  
Energy Density ◽  
Extra Dimension ◽  
Vacuum Energy ◽  
Mass Difference ◽  
Big Bang ◽  
Upper Bounds ◽  
Rapid Expansion ◽  
Vacuum Energy Density ◽  
Temperature Relation ◽  
Freeze Out

Abundances of primordial deuterium, [Formula: see text] and helium, Yp, are examined by modifying the early universe expansion rate and hence the time–temperature relation, including a constant vacuum energy motivated by the cyclic scenario of brane cosmology. Enhancement of abundances with respect to standard BBN prediction is found. Rapid expansion leads to early freeze-out of weak interaction and hence to an enhanced neutron fraction at elevated freeze-out temperature, which in turn results in more helium. Nucleosynthesis at a much lower temperature (due to rapid expansion) faces a larger Coulomb barrier and leaves more deuterium behind, which is also implied by a lower baryon-to-photon ratio (η) as we increase the vacuum energy density. The change in the helium fraction agrees within orders of magnitudes with that found by the effect of more neutrino flavors on Yp. Elevation of the neutron fraction at freeze-out is revealed by decrease in the neutron–proton mass difference (Q) from 1.293 MeV to 1.279 MeV, which is consistent with the study of the influence of extra dimension size on BBN. The lowest Q value corresponds to the highest vacuum energy and also to the largest size of the extra dimension. The upper limit on vacuum energy density is found by estimating the contribution from nonbaryonic dark matter by using X-ray emission from galaxy clusters and taking a flat spatial geometry, which is found to be the cosmological constant (Λ) observed today, so that the abundances do not run beyond the observational upper bounds. The allowed range of ΩΛ, 0.786 ≤ Ω Λ ≤ 0.844, makes Yp and [Formula: see text] lie within the observational upper bounds, which yields a Big Bang equivalence of the Λ universe. This is expected to further motivate the cyclic scenario, which incorporates a small and constant vacuum energy density tied to spacetime.

scholarly journals The evolution of the universe in asymmetric cosmic time

2021 ◽  
Vol 4 (3) ◽  
Keyword(s):  
Energy Density ◽  
Nuclear Force ◽  
Vacuum Energy ◽  
Cosmic Time ◽  
Big Bang ◽  
Vacuum Energy Density ◽  
De Sitter ◽  
Planck Time ◽  
The Big Bang ◽  
The Universe

The Cosmic Time Hypothesis (CTH) presented in this paper is a purely axiomatic theory. In contrast to today's standard model of cosmology, the ɅCDM model, it does not contain empirical parameters such as the cosmological constant Ʌ, nor does it contain sub-theories such as the inflation theory. The CTH was developed solely on the basis of the general theory of relativity (GRT), aiming for the greatest possible simplicity. The simplest cosmological model permitted by ART is the Einstein-de Sitter model. It is the basis for solving some of the fundamental problems of cosmology that concern us today. First of all, the most important results of the CTH: It solves one of the biggest problems of cosmology the problem of the cosmological constant (Ʌ)-by removing the relation between and the vacuum energy density ɛv (Λ=0, ɛv > 0). According to the CTH, the vacuum energy density ɛv is not negative and constant, as previously assumed, but positive and time-dependent (ɛv ̴ t -2). ɛv is part of the total energy density (Ɛ) of the universe and is contained in the energy-momentum tensor of Einstein's field equations. Cosmology is thus freed from unnecessary ballast, i.e. a free parameter (= natural constant) is omitted (Ʌ = 0). Conclusion: There is no "dark energy"! According to the CTH, the numerical value of the vacuum energy density v is smaller by a factor of ≈10-122 than the value calculated from quantum field theory and is thus consistent with observation. The measurement data obtained from observations of SNla supernovae, which suggest a currently accelerated expansion of the universe, result - if interpreted from the point of view of the CTH - in a decelerated expansion, as required by the Einstein-de Sitter universe. Dark matter could also possibly not exist, because the KZH demands that the "gravitational constant" is time-dependent and becomes larger the further the observed objects are spatially and thus also temporally distant from us. Gravitationally bound local systems, e.g. Earth - Moon or Sun - Earth, expand according to the same law as the universe. This explains why Hubble's law also applies within very small groups of galaxies, as observations show. The CTH requires that the strongest force (strong nuclear force) and the weakest (gravitational force) at Planck time (tp ≈10-43 seconds after the "big bang") when all forces of nature are supposed to have been united in a single super force, were of equal magnitude and had the same range. According to the KZH, the product of the strength and range of the gravitational force is constant, i.e. independent of time, and is identical to the product of the strength and range of the strong nuclear force. At Planck time, the universe had the size of an elementary particle (Rp = rE ≈10-15 m). This value also corresponds to the range of the strong nuclear force (Yukawa radius) and the Planck length at Planck time. The CTH provides a possible explanation for Mach's first and second principles. It solves some old problems of the big bang theory in a simple and natural way. The problem of the horizon, flatness, galaxy formation and the age of the world. The inflation theory thus becomes superfluous. • The CTH provides the theoretical basis for the theory of Earth expansion • In Cosmic Time, there was no Big Bang. The universe is infinitely old. • Unlike other cosmological models, the CTH does not require defined "initial conditions" because there was no beginning. • The CTH explains why the cosmic expansion is permanently in an unstable state of equilibrium, which is necessary for a long-term flat (Euclidean), evolutionarily developing universe.

scholarly journals Quintessence and effective AdS brane geometries

2015 ◽  
Vol 30 (13) ◽  
pp. 1550065 ◽  
Author(s):  
K. Priyabrat Pandey ◽  
Abhishek K. Singh ◽  
Sunita Singh ◽  
Supriya Kar
Keyword(s):  
Black Hole ◽  
Energy Density ◽  
Extra Dimension ◽  
Vacuum Energy ◽  
Bound State ◽  
Second Order ◽  
The Other ◽  
Vacuum Energy Density ◽  
Curvature Scalar

A geometric torsion dynamics leading to an effective curvature in a second-order formalism on a D4-brane is revisited with a renewed interest. We obtain two effective AdS 4 brane geometries on a vacuum created pair of [Formula: see text]-brane. One of them is shown to describe an AdS Schwarzschild spinning black hole and the other is shown to describe a spinning black hole bound state. It is argued that a D-instanton in a vacuum created anti-D3-brane within a pair may describe a quintessence. It may seem to incorporate a varying vacuum energy density in a brane universe. We consider the effective curvature scalar on S1 × S1 to analyze torsionless geometries on a vacuum created pair of [Formula: see text]-brane. The emergent AdS 3 brane is shown to describe a Schwarzschild and a Reissner–Nordstrom (RN) geometries in the presence of extra dimension(s).

C-field cosmological model for barotropic fluid distribution with bulk viscosity and decaying vacuum energy (Λ) in FRW space–time

2013 ◽  
Vol 91 (9) ◽  
pp. 728-732 ◽  
Author(s):  
Raj Bali ◽  
Seema Saraf
Keyword(s):  
Energy Density ◽  
Cosmological Model ◽  
Bulk Viscosity ◽  
Vacuum Energy ◽  
Big Bang ◽  
Fluid Distribution ◽  
Vacuum Energy Density ◽  
Massless Scalar ◽  
Barotropic Fluid ◽  
The Creation

A solution of Einstein’s field equations that admits barotropic fluid distribution and a negative-energy massless scalar creation field as a source in the presence of bulk viscosity and time-dependent vacuum energy density (Λ) is investigated. It is shown that a cosmological model based on this solution satisfies observational tests and is thus a viable alternative to the standard Big Bang model. The present model is free from real singularity and particle horizon. The creation field increases with time, which matches the result as obtained by Hoyle and Narlikar (Proc. Roy. Soc. A, 282, 178 (1964)). The vacuum energy density, Λ ∼ t–2, matches the result as obtained by Bertolami (Nuovocim. B, 93, 36 (1986)). The spatial volume increases exponentially with time. Thus the model has an inflationary scenario. The deceleration parameter q < 0 indicating that the model represents accelerating expansion of the universe. The presence of the creation field prevents matter density from vanishing and it remains constant for large t. We also observe that bulk viscosity slows down the rate of decrease of volume expansion.

scholarly journals FROM INFLATION TO DARK ENERGY THROUGH A DYNAMICAL Λ: AN ATTEMPT AT ALLEVIATING FUNDAMENTAL COSMIC PUZZLES

2013 ◽  
Vol 22 (12) ◽  
pp. 1342008 ◽  
Author(s):  
SPYROS BASILAKOS ◽  
JOSÉ ADEMIR SALES LIMA ◽  
JOAN SOLÀ
Keyword(s):  
Energy Density ◽  
Vacuum Energy ◽  
Big Bang ◽  
Vacuum Energy Density ◽  
Late Time ◽  
De Sitter ◽  
New Class ◽  
Sitter Spacetime ◽  
Inflationary Phase ◽  
De Sitter Vacuum

After decades of successful hot big-bang paradigm, cosmology still lacks a framework in which the early inflationary phase of the universe smoothly matches the radiation epoch and evolves to the present "quasi" de Sitter spacetime. No less intriguing is that the current value of the effective vacuum energy density is vastly smaller than the value that triggered inflation. In this paper, we propose a new class of cosmologies capable of overcoming, or highly alleviating, some of these acute cosmic puzzles. Powered by a decaying vacuum energy density, the spacetime emerges from a pure nonsingular de Sitter vacuum stage, "gracefully" exits from inflation to a radiation phase followed by dark matter and vacuum regimes, and, finally, evolves to a late-time de Sitter phase.

Quantum fields and gravity: Expanding space-times

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040039
Author(s):  
Claudio Parmeggiani
Keyword(s):  
Energy Density ◽  
Vacuum Energy ◽  
Fock Space ◽  
Zero Point ◽  
Big Bang ◽  
Space Time ◽  
Vacuum Energy Density ◽  
Dimensional Manifold ◽  
Quantum Fields ◽  
Point Energy

We discuss a proposal for a somewhat new formulation of quantum field theory (set in a four-dimensional manifold, the space-time) that includes an analysis of its implications for the evolution of Einstein-Friedmann cosmological models. The proposed theory displays two peculiar features: (i) a local Hilbert-Fock space is associated with each space-time point: we are dealing with a vector bundle whose fibers are Hilbert spaces; the operator-valued sections of the bundle are the quantum fields; (ii) the vacuum energy density is finite, being regularized in a space-time curvature dependent way, independently at each point. In fact everything is finite: self-masses, self-charges, quantum fluctuations: they depend on the space-time curvature and diverge only for a flat metric. In an Einstein-Friedmann model the vacuum (zero-point) energy density is consequently time-dependent and in general not negligible. Then it is shown that, for some choices of the parameters of the theory, the big-bang singularity is resolved and replaced by a bounce driven by the vacuum energy density, which becomes (very) large and negative near the bounce (negative by the contribution of the Fermi fields). But for large times (now, say) the Bose fields’ positive vacuum energy eventually overcomes the negative one and we are finally left with the present vacuum energy: positive and reasonably small.

scholarly journals LOCAL CONTRIBUTION OF A QUANTUM CONDENSATE TO THE VACUUM ENERGY DENSITY

2003 ◽  
Vol 18 (10) ◽  
pp. 683-690 ◽  
Author(s):  
GIOVANNI MODANESE
Keyword(s):  
Energy Density ◽  
Vacuum Energy ◽  
Casimir Effect ◽  
Landau Equation ◽  
Vacuum Energy Density ◽  
Negative Effects ◽  
Ginzburg Landau ◽  
Physical Conditions ◽  
Local Contribution ◽  
Gravitational Vacuum

We evaluate the local contribution gμνL of coherent matter with Lagrangian density L to the vacuum energy density. Focusing on the case of superconductors obeying the Ginzburg–Landau equation, we express the relativistic invariant density L in terms of low-energy quantities containing the pairs density. We discuss under which physical conditions the sign of the local contribution of the collective wave function to the vacuum energy density is positive or negative. Effects of this kind can play an important role in bringing the local changes in the amplitude of gravitational vacuum fluctuations — a phenomenon reminiscent of the Casimir effect in QED.

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