scholarly journals Possible Explanation of the Dynamics of the Universe Expansion without Dark Energy and without New Gravitational Degrees of Freedom

2021 ◽  
Vol 11 (01) ◽  
pp. 1-7
Author(s):  
Eugene Oks
Keyword(s):  
Dark Energy ◽  
Degrees Of Freedom ◽  
Universe Expansion ◽  
The Universe

scholarly journals The Constant of the Universe Expansion Acceleration ΓH, the Einstein Variation of c and Parameters VH, Ω, Ʌ and ɣ

2020 ◽  
Vol 12 (3) ◽  
pp. 28
Author(s):  
J. G. Lartigue
Keyword(s):  
Dark Energy ◽  
Gravitational Field ◽  
Additional Condition ◽  
Expansion Velocity ◽  
Gravitational Acceleration ◽  
Universe Expansion ◽  
Physical Universe ◽  
C Value ◽  
Space Expansion ◽  
The Universe

The Hubble-Lemaitre equation v=H∙r  (cm∙s-1) represented a linear function of the radial Space expansion velocity, if H would be a constant. Sometimes it has been assumed as H = 1/t, which sends back to the classical v = r/t. However, the later discovered acceleration required the additional condition for H to be, also, a function of time; or, opposed, the existence of a not yet defined dark energy. In a previous paper [1] it had been proposed a provisional expression for a constant Universe expansion acceleration as function of distance: Γ= H2( cm∙s-2). Now, the substitution of r as a function of time, takes to five new equations of H, the Hubble velocity vH , the Hubble acceleration ΓH and the positive Hubble potential VH of the Space. So the proposed Hubble functions for the Space: H, rH , vH, ΓH and VH result higher than those in a gravitational field. All of these Hubble functions act in the total Space expansion though, into the Physical Universe, ΓH is not perceived as it does, continuously, the opposed gravitational acceleration g. Otherwise, a revision is made of the Einstein equation for the c value as function of the gravitational potential φ. Additional proposals are made about the horizons definitions and parameters Ω, Ʌ and ɣ.

scholarly journals The Energy Conservation in Our Universe and the Pressureless Dark Energy

2015 ◽  
Vol 2015 ◽  
pp. 1-4
Author(s):  
Man Ho Chan
Keyword(s):  
Dark Energy ◽  
Energy Conservation ◽  
Total Energy ◽  
Dark Energy Model ◽  
Vacuum Energy ◽  
Energy Model ◽  
Universe Expansion ◽  
The Law ◽  
The Universe

Recent observations confirm that a certain amount of unknown dark energy exists in our universe so that the current expansion of our universe is accelerating. It is commonly believed that the pressure of the dark energy is negative and the density of the dark energy is almost a constant throughout the universe expansion. In this paper, we show that the law of energy conservation in our universe has to be modified because more vacuum energy is gained due to the universe expansion. As a result, the pressure of dark energy would be zero if the total energy of our universe is increasing. This pressureless dark energy model basically agrees with the current observational results.

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 Holographic dark energy and the universe expansion acceleration

2006 ◽  
Vol 636 (2) ◽  
pp. 75-79 ◽  
Author(s):  
J.P. Beltrán Almeida ◽  
J.G. Pereira
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Universe Expansion ◽  
The Universe

scholarly journals A note on the relations between thermodynamics, energy definitions and Friedmann equations

2017 ◽  
Vol 32 (13) ◽  
pp. 1750078 ◽  
Author(s):  
H. Moradpour ◽  
Rafael C. Nunes ◽  
Everton M. C. Abreu ◽  
Jorge Ananias Neto
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Perfect Fluid ◽  
Observational Constraints ◽  
Pressure Equation ◽  
Universe Expansion ◽  
Friedmann Equations ◽  
Suitable Solution ◽  
Thermodynamic Pressure ◽  
The Universe

We investigate the relation between the Friedmann and thermodynamic pressure equations, through solving the Friedmann and thermodynamic pressure equations simultaneously. Our investigation shows that a perfect fluid, as a suitable solution for the Friedmann equations leading to the standard modeling of the universe expansion history, cannot simultaneously satisfy the thermodynamic pressure equation and those of Friedmann. Moreover, we consider various energy definitions, such as the Komar mass, and solve the Friedmann and thermodynamic pressure equations simultaneously to get some models for dark energy fluids. The cosmological consequences of obtained solutions are also addressed. Our results indicate that some of obtained solutions may unify the dominated fluid in both the primary inflationary and current accelerating eras into one model. In addition, by taking into account a cosmic fluid of a known equation of state (EoS), and combining it with the Friedmann and thermodynamic pressure equations, we obtain the corresponding energy of these cosmic fluids and face their limitations. Finally, we point out the cosmological features of this cosmic fluid and also study its observational constraints.

scholarly journals Stringy-running-vacuum-model inflation: from primordial gravitational waves and stiff axion matter to dynamical dark energy

2021 ◽  
Author(s):  
Nick E. Mavromatos ◽  
Joan Solà Peracaula
Keyword(s):  
Dark Energy ◽  
Degrees Of Freedom ◽  
Domain Walls ◽  
Basic Structure ◽  
Vacuum Model ◽  
Living Fossils ◽  
Primordial Gravitational Waves ◽  
The Universe ◽  
Dynamical Dark Energy ◽  
Effective Description

AbstractIn previous works, we have derived a Running Vacuum Model (RVM) for a string Universe, which provides an effective description of the evolution of 4-dimensional string-inspired cosmologies from inflation till the present epoch. In the context of this “stringy RVM” version, it is assumed that the early Universe is characterised by purely gravitational degrees of freedom, from the massless gravitational string multiplet, including the antisymmetric tensor field. The latter plays an important role, since its dual gives rise to a ‘stiff’ gravitational axion “matter”, which in turn couples to the gravitational anomaly terms, assumed to be non-trivial at early epochs. In the presence of primordial gravitational wave (GW) perturbations, such anomalous couplings lead to an RVM-like dynamical inflation, without external inflatons. We review here this framework and discuss potential scenarios for the generation of such primordial GW, among which the formation of unstable domain walls, which eventually collapse in a non-spherical-symmetric manner, giving rise to GW. We also remark that the same type of “stiff” axionic matter could provide, upon the generation of appropriate potentials during the post-inflationary eras, (part of) the Dark Matter (DM) in the Universe, which could well be ultralight, depending on the parameters of the string-inspired model. All in all, the new (stringy) mechanism for RVM inflation preserves the basic structure of the original (and more phenomenological) RVM, as well as its main advantages: namely, a mechanism for graceful exit and for generating a huge amount of entropy capable of explaining the horizon problem. It also predicts axionic DM and the existence of mild dynamical Dark Energy (DE) of quintessence type in the present universe, both being “living fossils” of the inflationary stages of the cosmic evolution. Altogether the modern RVM appears to be a theoretically sound (string-based) approach to cosmology with a variety of phenomenologically testable consequences.

scholarly journals Cosmological Model with Interconnection between Dark Energy and Matter

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 412
Author(s):  
Gennady S. Bisnovatyi-Kogan
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Density Ratio ◽  
Hubble Constant ◽  
Variable Component ◽  
Time Interval ◽  
Universe Expansion ◽  
The Difference ◽  
Cmb Fluctuations ◽  
The Universe

It is accepted in the present cosmology model that the scalar field, which is responsible for the inflation stage in the early universe, transforms completely into matter, and the accelerated universe expansion is presently governed by dark energy (DE), whose origin is not connected with the inflationary scalar field. We suppose here that dark matter (DM) has a common origin with a small variable component of dark energy (DEV). We suggest that DE may presently have two components, one of which is the Einstein constant Λ, and another, smaller component DEV (ΛV) comes from the remnants of the scalar field responsible for inflation, which gave birth to the origin of presently existing matter. In this note we consider only the stages of the universe expansion after recombination, z≃1100, when DM was the most abundant component of the matter, therefore we suggest for simplicity that a connection exists between DM and DEV so that the ratio of their densities remains constant over all the stages after recombination, ρDM=αρDEV, with a constant α. One of the problems revealed recently in cosmology is a so-called Hubble tension (HT), which is the difference between values of the present Hubble constant, measured by observation of the universe at redshift z≲1, and by observations of a distant universe with CMB fluctuations originated at z∼1100. In this paper we suggest that this discrepancy may be explained by deviation of the cosmological expansion from a standard Lambda-CDM model of a flat universe, due to the action of an additional variable component DEV. Taking into account the influence of DEV on the universe’s expansion, we find the value of α that could remove the HT problem. In order to maintain the almost constant DEV/DM energy density ratio during the time interval at z<1100, we suggest the existence of a wide mass DM particle distribution.

scholarly journals DARK ENERGY: THE ABSOLUTE ELECTRIC POTENTIAL OF THE UNIVERSE

2009 ◽  
Vol 18 (14) ◽  
pp. 2243-2248 ◽  
Author(s):  
JOSE BELTRÁN JIMÉNEZ ◽  
ANTONIO L. MAROTO
Keyword(s):  
Electromagnetic Field ◽  
Dark Energy ◽  
Electric Potential ◽  
Invariant Theory ◽  
Degrees Of Freedom ◽  
Polarization State ◽  
Accelerated Expansion ◽  
Gauge Invariant ◽  
Expansion Of The Universe ◽  
The Universe

Is there an absolute cosmic electric potential? The recent discovery of the accelerated expansion of the universe could be indicating that this is certainly the case. In this essay we show that the consistency of the covariant and gauge-invariant theory of electromagnetism is truly questionable when considered on cosmological scales. Out of the four components of the electromagnetic field, Maxwell's theory contains only two physical degrees of freedom. However, in the presence of gravity, one of the "unphysical" states cannot be consistently eliminated, thus becoming real. This third polarization state is completely decoupled from charged matter, but can be excited gravitationally, thus breaking gauge invariance. On large scales the new state can be seen as a homogeneous cosmic electric potential, whose energy density behaves as a cosmological constant.

scholarly journals Thermodynamic behavior and stability of Polytropic gas

2016 ◽  
Vol 25 (01) ◽  
pp. 1650014 ◽  
Author(s):  
H. Moradpour ◽  
A. Abri ◽  
H. Ebadi
Keyword(s):  
Dark Energy ◽  
High Temperature ◽  
Small Volume ◽  
Initial Conditions ◽  
Polytropic Gas ◽  
Universe Expansion ◽  
Thermodynamic Behavior ◽  
And Behavior ◽  
The Universe

We focus on the thermodynamic behavior of Polytropic gas as a candidate for dark energy (DE). We use the general arguments of thermodynamics to investigate its properties and behavior. We find that a Polytropic gas can exhibit the DE-like behavior. It also may be used to simulate a fluid with zero pressure at the small volume and high temperature limits. Briefly, our study shows that this gas may be used to describe the universe expansion history from the matter dominated era to the current accelerating era. By applying some initial conditions to the system, we can establish a relation between the Polytropic gas parameters and the initial conditions. Relationships with related works have also been addressed.

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