scholarly journals ON THE PROBLEM OF VACUUM ENERGY IN FLRW UNIVERSES AND DARK ENERGY

2013 ◽  
Vol 28 (36) ◽  
pp. 1350166
Author(s):  
BADIS YDRI ◽  
ADEL BOUCHAREB
Keyword(s):  
Dark Energy ◽  
Vacuum Energy ◽  
Hubble Constant ◽  
De Sitter ◽  
Planck Constant ◽  
Point Function ◽  
Dark Energy Density ◽  
Tadpole Diagram ◽  
Order Of Magnitude ◽  
The Universe

We present a (hopefully) novel calculation of the vacuum energy in expanding FLRW spacetimes based on the renormalization of quantum field theory in nonzero backgrounds. We compute the renormalized effective action up to the two-point function and then apply the formalism to the cosmological backgrounds of interest. As an example we calculate for quasi de Sitter spacetimes the leading correction to the vacuum energy given by the tadpole diagram and show that it behaves as [Formula: see text] where H0 is the Hubble constant and Λ P is the Planck constant. This is of the same order of magnitude as the observed dark energy density in the universe.

scholarly journals Primordial Dark Energy from a Condensate of Spinors in a 5D Vacuum

2013 ◽  
Vol 2013 ◽  
pp. 1-7
Author(s):  
Pablo Alejandro Sánchez ◽  
Mauricio Bellini
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Inflationary Universe ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Dark Energy Density ◽  
Sitter Spacetime ◽  
Interesting Candidate ◽  
Expansion Of The Universe ◽  
The Universe

We explore the possibility that the expansion of the universe can be driven by a condensate of spinors which are free of interactions in a 5D relativistic vacuum defined in an extended de Sitter spacetime which is Riemann flat. The extra coordinate is considered as noncompact. After making a static foliation on the extra coordinate, we obtain an effective 4D (inflationary) de Sitter expansion which describes an inflationary universe. We found that the condensate of spinors studied here could be an interesting candidate to explain the presence of dark energy in the early universe. The dark energy density which we are talking about is poured into smaller subhorizon scales with the evolution of the inflationary expansion.

scholarly journals Quantum Mechanical Explanation for Dark energy, Cosmic Coincidence, Flatness, Age and Size of Universe

2019 ◽  
Author(s):  
Biswaranjan Dikshit
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Vacuum Energy ◽  
Quantum Mechanical ◽  
Coincidence Problem ◽  
Dark Energy Density ◽  
Astronomical Observations ◽  
The Universe ◽  
Matter Energy ◽  
Cosmic Coincidence Problem

Although general relativity has been successful in explaining many astronomical phenomena, few problems about the contents and evolution of the universe have remained mysterious since last century. Most important of them is the cosmological constant problem in which conventional calculation of vacuum (or dark) energy density using quantum mechanics leads to a value ~10114 J/m3 which is ~10123 times more than the vacuum energy (5.3×10-10 J/m3) estimated from astronomical observations of expanding universe. Similarly, cosmic coincidence problem questions why the matter energy density (ordinary plus dark matter) is of the same order as the vacuum energy density at present time. Finally, the mechanism responsible for spatial flatness and expansion of the universe are not clearly understood. In this paper, by taking the vacuum as a finite and closed quantum oscillator, we solve all of the above-mentioned problems. At first, by using purely quantum mechanical approach, we predict that the dark energy density is c4/(GR2) = 5.27×10-10 J/m3 (where R is radius of 3-sphere of universe) and matter energy density is c4/(2GR2) = 2.6×10-10 J/m3 which match well with astronomical observations. We also prove that the dark energy has always been ~66.7% and matter energy has been ~33.3% of total energy and hence, the so called cosmic coincidence problem doesn’t exist. Next, we show how flatness of space could be maintained since the early stage of universe. Finally, using our model, we derive the expression for age and radius of universe which match well with the astronomical data.

scholarly journals Minimum Length Uncertainty Relations in the Presence of Dark Energy

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 11 ◽  
Author(s):  
Matthew J. Lake
Keyword(s):  
Dark Energy ◽  
High Energy ◽  
Electron Neutrino ◽  
Minimum Length ◽  
Uncertainty Relations ◽  
Electron Mass ◽  
De Sitter ◽  
Order Of Magnitude ◽  
Near Future ◽  
The Universe

We introduce a dark energy-modified minimum length uncertainty relation (DE-MLUR) or dark energy uncertainty principle (DE-UP) for short. The new relation is structurally similar to the MLUR introduced by Károlyházy (1968), and reproduced by Ng and van Dam (1994) using alternative arguments, but with a number of important differences. These include a dependence on the de Sitter horizon, which may be expressed in terms of the cosmological constant as l dS ∼ 1 / Λ . Applying the DE-UP to both charged and neutral particles, we obtain estimates of two limiting mass scales, expressed in terms of the fundamental constants G , c , ℏ , Λ , e . Evaluated numerically, the charged particle limit corresponds to the order of magnitude value of the electron mass ( m e ), while the neutral particle limit is consistent with current experimental bounds on the mass of the electron neutrino ( m ν e ). Possible cosmological consequences of the DE-UP are considered and we note that these lead naturally to a holographic relation between the bulk and the boundary of the Universe. Low and high energy regimes in which dark energy effects may dominate canonical quantum behaviour are identified and the possibility of testing the model using near-future experiments is briefly discussed.

A Clifford-gravity-based cosmology, dark matter and dark energy

2015 ◽  
Vol 12 (03) ◽  
pp. 1550037 ◽  
Author(s):  
Carlos Castro
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Degrees Of Freedom ◽  
Vacuum Energy ◽  
Vacuum Energy Density ◽  
De Sitter ◽  
Four Dimensions ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

A Clifford-gravity-based model is exploited to build a generalized action (beyond the current ones used in the literature) and arrive at relevant numerical results which are consistent with the presently-observed de Sitter accelerating expansion of the universe driven by a very small vacuum energy density ρ obs ~ 10-120(MP)4 (MP is the Planck mass) and provide promising dark energy/matter candidates in terms of the 16 scalars corresponding to the degrees of freedom associated with a Cl (3, 1)-algebra-valued scalar field Φ in four dimensions.

scholarly journals Modified cosmology through Kaniadakis horizon entropy

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Andreas Lymperis ◽  
Spyros Basilakos ◽  
Emmanuel N. Saridakis
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Equation ◽  
State Parameter ◽  
De Sitter ◽  
Single Model ◽  
Dark Energy Density ◽  
Horizon Entropy ◽  
Analytical Expressions ◽  
The Universe

AbstractWe apply the gravity-thermodynamics conjecture, namely the first law of thermodynamics on the Universe horizon, but using the generalized Kaniadakis entropy instead of the standard Bekenstein–Hawking one. The former is a one-parameter generalization of the classical Boltzmann–Gibbs–Shannon entropy, arising from a coherent and self-consistent relativistic statistical theory. We obtain new modified cosmological scenarios, namely modified Friedmann equations, which contain new extra terms that constitute an effective dark energy sector depending on the single model Kaniadakis parameter K. We investigate the cosmological evolution, by extracting analytical expressions for the dark energy density and equation-of-state parameters and we show that the Universe exhibits the usual thermal history, with a transition redshift from deceleration to acceleration at around 0.6. Furthermore, depending on the value of K, the dark energy equation-of-state parameter deviates from $$\Lambda $$ Λ CDM cosmology at small redshifts, while lying always in the phantom regime, and at asymptotically large times the Universe always results in a dark-energy dominated, de Sitter phase. Finally, even in the case where we do not consider an explicit cosmological constant the resulting cosmology is very interesting and in agreement with the observed behavior.

CASTING LIGHT ON THE GHOST

2011 ◽  
Vol 26 (34) ◽  
pp. 2533-2547
Author(s):  
FEDERICO R. URBAN
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Magnetic Fields ◽  
Vacuum Energy ◽  
Time Dependent ◽  
Correct Order ◽  
Dark Energy Density ◽  
Long Range Interactions ◽  
Order Of Magnitude ◽  
The Impact

The infrared sector of QCD contains all the necessary ingredients, once laid onto a time-dependent, curved background, to cater for the much needed cosmological vacuum energy. This is achieved through the fields that describe the impact of the long-range interactions of QCD, the Veneziano ghost and its dipolar partner. Although technically extremely challenging, the physics is well understood and the estimated dark energy density is of the correct order of magnitude. In this brief review I will retrace the steps leading to two new cosmological applications of this model, namely the possibility of the generation of cosmic magnetic fields, and the unification of several observed polarization anomalies under the same roof.

scholarly journals On The Symmetry of The Universe

2020 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Thermodynamic Equilibrium ◽  
Vacuum Energy ◽  
Quantum Mechanical ◽  
Baryonic Matter ◽  
Time Uncertainty ◽  
Matter Effect ◽  
Mechanical Interpretation ◽  
The Universe

It is shown that the Lambda component in the cosmological Lambda-CDM model can be conceived as vacuum energy, consisting of gravitational particles subject to Heisenberg’s energy-time uncertainty. These particles can be modelled as elementary polarisable Dirac-type dipoles (“darks”) in a fluidal space at thermodynamic equilibrium, with spins that are subject to the Bekenstein-Hawking entropy. Around the baryonic kernels, uniformly distributed in the universe, the spins are polarized, thereby invoking an increase of the effective gravitational strength of the kernels. It explains the dark matter effect to the extent that the numerical value of Milgrom’s acceleration constant can be assessed by theory. Non-polarized vacuum particles beyond the baryonic kernels compose the dark energy. The result is a quantum mechanical interpretation of gravity in terms of quantitatively established shares in baryonic matter, dark matter and dark energy, which correspond with the values of the Lambda-CDM model..

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 Generalized emergent dark energy: observational Hubble data constraints and stability analysis

2020 ◽  
Vol 497 (2) ◽  
pp. 1590-1602
Author(s):  
A Hernández-Almada ◽  
Genly Leon ◽  
Juan Magaña ◽  
Miguel A García-Aspeitia ◽  
V Motta
Keyword(s):  
Dark Energy ◽  
Stability Analysis ◽  
Degree Of Freedom ◽  
Dark Energy Density ◽  
Homogeneous Sample ◽  
The Standard Model ◽  
Yield Values ◽  
Data Constraints ◽  
The Universe ◽  
Universe Evolution

ABSTRACT Recently, a phenomenologically emergent dark energy (PEDE) model was presented with a dark energy density evolving as $\widetilde{\Omega }_{\rm {DE}}(z) = \Omega _{\rm {DE,0}}[ 1 - {\rm {tanh}}({\log }_{10}(1+z))]$, i.e. with no degree of freedom. Later on, a generalized model was proposed by adding one degree of freedom to the PEDE model, encoded in the parameter Δ. Motivated by these proposals, we constrain the parameter space ($h,\Omega _m^{(0)}$) and ($h,\Omega _m^{(0)}, \Delta$) for PEDE and generalized emergent dark energy (GEDE), respectively, by employing the most recent observational (non-)homogeneous and differential age Hubble data. Additionally, we reconstruct the deceleration and jerk parameters and estimate yield values at z = 0 of $q_0 = -0.784^{+0.028}_{-0.027}$ and $j_0 = 1.241^{+0.164}_{-0.149}$ for PEDE and $q_0 = -0.730^{+0.059}_{-0.067}$ and $j_0 = 1.293^{+0.194}_{-0.187}$ for GEDE using the homogeneous sample. We report values on the deceleration–acceleration transition redshift with those reported in the literature within 2σ CL. Furthermore, we perform a stability analysis of the PEDE and GEDE models to study the global evolution of the Universe around their critical points. Although the PEDE and GEDE dynamics are similar to the standard model, our stability analysis indicates that in both models there is an accelerated phase at early epochs of the Universe evolution.

scholarly journals The dark sector cosmology

2020 ◽  
Vol 29 (14) ◽  
pp. 2030014
Author(s):  
Elcio Abdalla ◽  
Alessandro Marins
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Acoustic Oscillations ◽  
Dark Sector ◽  
Fundamental Physics ◽  
Observational Techniques ◽  
Distance Indicators ◽  
The Universe ◽  
Theoretical Developments

The most important problem in fundamental physics is the description of the contents of the Universe. Today, we know that 95% thereof is totally unknown. Two thirds of that amount is the mysterious Dark Energy described in an interesting and important review [E. J. Copeland, M. Sami and S. Tsujikawa, Int. J. Mod. Phys. D 15 (2006) 1753]. We briefly extend here the ideas contained in that review including the more general Dark Sector, that is, Dark Matter and Dark Energy, eventually composing a new physical Sector. Understanding the Dark Sector with precision is paramount for us to be able to understand all the other cosmological parameters comprehensively as modifications of the modeling could lead to potential biases of inferred parameters of the model, such as measurements of the Hubble constant and distance indicators such as the Baryon Acoustic Oscillations. We discuss several modern methods of observation that can disentangle the different possible descriptions of the Dark Sector. The possible applications of some theoretical developments are also included in this paper as well as a more thorough evaluation of new observational techniques at lower frequencies and gravitational waves.

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