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In this paper we have analysed Tsallis holographic dark energy in a flat Friedmann-Robertson-Walker model under the framework of f ( R , T ) gravity. The effects of this model in a non interactive universe are studied by taking different IR cut-offs that include particle horizon, event horizon, conformal age of the universe and GO (Granda-Oliveros) horizon. The cosmic evolution is studied by determining the conventional cosmological tools including the density parameter Ω D E , equation of state parameter ω D E and the deceleration parameter q . We have analysed the impact of these parameters by assuming different values for the matter-curvature coupling constant λ and the Tsallis parameter δ . We observe that all our four models exhibit appropriate behavior for the system parameters and support the accelerated expansion mode described by phantom-like scenario. Stability was only achieved for event horizon (partially) based on the speed of sound v s 2 . Furthermore we examined the behavior of our model by using various diagnostic mechanisms such as ω D E − ω D E ′ analysis, statefinder pair ( r , s ) , O m diagnostic and statefinder hierarchy S 3 ( 1 ) and S 4 ( 1 ) . The trajectories of the ω D E − ω D E ′ show a transition from freezing to thawing region, whereas r − s plane corresponds to a phase shift between Chaplygin gas model and quintessence model for particle and event horizon and solely Chaplygin gas model for conformal age and quintessence for GO-horizon. O m parameter also supports the quintessence era while statefinder hierarchy distinguishes our model effectively from the Λ CDM model and demonstrates the distinctive nature of all our models.

The holographic principle is applied to a description of the Universe in the early stage of its evolution. As an example, we examine a cosmological model with a bounce with subsequent transition to the early stage of inflation. We investigate cosmological models based on a viscous liquid with a generalized equation of state in terms of the holographic cutoff proposed by Nojiri and Odintsov. Within the framework of these models, we have calculated the infrared radius in terms of the particle horizon or the event horizon. Energy conservation laws are obtained from the holographic point of view. The viscous liquid describing the bounce and the early Universe is presented as a generalization of holographic energy.

In the formalism of generalized holographic dark energy (HDE), the holographic cut-off is generalized to depend upon $L_\mathrm{IR} = L_\mathrm{IR} \left( L_\mathrm{p}, \dot L_\mathrm{p}, \ddot L_\mathrm{p}, \cdots, L_\mathrm{f}, \dot L_\mathrm{f}, \cdots, a\right)$ with $L_\mathrm{p}$ and $L_\mathrm{f}$ are the particle horizon and the future horizon, respectively (moreover $a$ is the scale factor of the universe). Based on such formalism, in the present paper, we show that a wide class of dark energy (DE) models can be regarded as different candidates of the generalized HDE family, with respective cut-offs. This can be thought as a symmetry between the generalized HDE and different DE models. In this regard, we consider several entropic dark energy models - like Tsallis entropic DE, the R\'{e}nyi entropic DE, and the Sharma-Mittal entropic DE - and showed that they are indeed equivalent with the generalized HDE. Such equivalence between the entropic DE and the generalized HDE is extended to the scenario where the respective exponents of the entropy functions are allowed to vary with the expansion of the universe. Besides the entropic DE models, the correspondence with the generalized HDE is also established for the Quintessence and for the Ricci DE models. In all the above cases, the effective equation of state (EoS) parameter corresponds to the holographic energy density are determined, by which the equivalence of various DE models with the respective generalized HDE models are further confirmed. The equivalent holographic cut-offs are determined by two ways: (1) in terms of the particle horizon and its derivatives, (2) in terms of the future horizon horizon and its derivatives., Comment: To appear in Symmetry

We study transition rates and cross sections from first principles in a spatially flat radiation dominated cosmology. We consider a model of scalar particles to study scattering and heavy particle production from pair annihilation, drawing more general conclusions. The S-matrix formulation is ill suited to study these ubiquitous processes in a rapidly expanding cosmology. We introduce a physically motivated adiabatic expansion that relies on wavelengths much smaller than the particle horizon at a given time. The leading order in this expansion dominates the transition rates and cross sections. Several important and general results are direct consequences of the cosmological redshift and a finite particle horizon: i) a violation of local Lorentz invariance, ii) freeze-out of the production cross section at a finite time, iii) sub-threshold production of heavier particles as a consequence of the uncertainty in the local energy from a finite particle horizon, a manifestation of the \emph{antizeno} effect. If heavy dark matter is produced via annihilation of a lighter species, sub-threshold production yields an enhanced abundance. We discuss several possible consequences of these effects., Comment: more discussions

In this paper, we suggest that the early universe starts from a high-energetic state with a two dimensional description and the state recovers to be four dimensional when the universe evolves into the radiation dominated phase. This scenario is consistent with the recent viewpoint that quantum gravity should be effectively two dimensional in the ultraviolet and recovers to be four dimensional in the infrared. A relationship has been established between the running of effective dimension and that of the entropy inside particle horizon of the universe, i.e., as the effective dimension runs from two to four, the corresponding entropy runs from the holographic entropy to the normal entropy appropriate to radiation. These results can be generalized to higher dimensional cases., Comment: 6 pages, no figures

In this work, we analyzed the effect of different prescriptions of the IR cutoffs, namely the Hubble horizon cutoff, particle horizon cutoff, Granda and Oliveros horizon cut off, and the Ricci horizon cutoff on the growth rate of clustering for the Tsallis holographic dark energy (THDE) model in an FRW universe devoid of any interactions between the dark Universe. Furthermore, we used the concept of configurational entropy to derive constraints (qualitatively) on the model parameters for the THDE model in each IR cutoff prescription from the fact that the rate of change of configurational entropy hits a minimum at a particular scale factor $$a_{DE}$$ a DE which indicate precisely the epoch of dark energy domination predicted by the relevant cosmological model as a function of the model parameter(s). By using the current observational constraints on the redshift of transition from a decelerated to an accelerated Universe, we derived constraints on the model parameters appearing in each IR cutoff definition and on the non-additivity parameter $$\delta $$ δ characterizing the THDE model and report the existence of simple linear dependency between $$\delta $$ δ and $$a_{DE}$$ a DE in each IR cutoff setup.

In the present paper, we use the holographic approach to describe the early-time acceleration and the late-time acceleration eras of our Universe in a unified manner. Such “holographic unification” is found to have a correspondence with various higher curvature cosmological models with or without matter fields. The corresponding holographic cutoffs are determined in terms of the particle horizon and its derivatives, or the future horizon and its derivatives. As a result, the holographic energy density we propose is able to merge various cosmological epochs of the Universe from a holographic point of view. We find the holographic correspondence of several F(R) gravity models, including axion-F(R) gravity models, of several Gauss-Bonnet F(G) models and finally of F(T) models, and in each case we demonstrate that it is possible to describe in a unified way inflation and late-time acceleration in the context of the same holographic model., This work is partially supported by the JSPS Grant-inAid for Scientific Research (C) No. 18K03615 (S. N.), and by MINECO (Spain), FIS2016-76363-P (S. D. O)

The evolution of the wave function in quantum mechanics is deterministic like that of classical waves. Only when we bring in observers the fundamentally different quantum reality emerges. Similarly the introduction of observers changes the nature of spacetime by causing a split between past and future, concepts that are not well defined in the observer-free world. The induced temporal boundary leads to a resonance condition for the oscillatory vacuum solutions of the metric in Euclidean time. It corresponds to an exponential de Sitter evolution in real time, which can be represented by a cosmological constant Lambda = 2 pi(2)/r(u)(2), where r(u) is the radius of the particle horizon at the epoch when the observer exists. For the present epoch we get a value of Lambda that agrees with the observed value within 2 sigma of the observational errors. This explanation resolves the cosmic coincidence problem. Our epoch in cosmic history does not herald the onset of an inflationary phase driven by some dark energy. We show that the observed accelerated expansion that is deduced from the redshifts is an 'edge effect' due to the observer-induced boundary and not representative of the intrinsic evolution. The new theory satisfies the BBN (Big Bang nucleosynthesis) and CMB (cosmic microwave background) observational constraints equally well as the concordance model of standard cosmology. There is no link between the dark energy and dark matter problems. Previous conclusions that dark matter is mainly non-baryonic are not affected., Journal of Physics Communications, 4 (10), ISSN:2399-6528

This paper explains thermodynamic irreversibility by applying the expansion of the Universe to thermodynamic systems. The effect of metric expansion is immeasurably small on shorter scales than intergalactic distances. Multi-particle systems, however, are chaotic, and amplify any small disturbance exponentially. Metric expansion gives rise to time-asymmetric behaviour in thermodynamic systems in a short time (few nanoseconds in air, few ten picoseconds in water). In contrast to existing publications, this paper explains without any additional assumptions the rise of thermodynamic irreversibility from the underlying reversible mechanics of particles. Calculations for the special case which assumes FLRW metric, slow motions ( v ≪ c ) and approximates space locally by Euclidean space show that metric expansion causes entropy increase in isolated systems. The rise of time-asymmetry, however, is not affected by these assumptions. Any influence of the expansion of the Universe on the local metric causes a coupling between local mechanics and evolution of the Universe.

The invariance of physical law between a prior to a present universe is brought up, as a continuation of analyzing entropy in today’s universe, and the relationship of entropy to information content in a prior universe. If or not there is enough information to preserve the amount of physical law also may play a role as to if or not additional dimensions for cosmological dynamics are necessary.

In present article we consider an axion F(R) gravity model and described with the help of holographic principle the cosmological models of viscous dark fluid coupled with axion matter in a spatially flat Friedmann-Robertson-Walker (FRW) universe. This description based on generalized infrared-cutoff holographic dark energy, proposed by Nojiri and Odintsov. We explored the Little Rip, the Pseudo Rip, and the power-law bounce cosmological models in terms of the parameters of the inhomogeneous equation of the state of viscous dark fluid and calculated the infrared cutoffs analytically. We represented the energy conservation equation for the dark fluid from a holographic point of view and showed a correspondence between the cosmology of a viscous fluid and holographic cosmology. We analyzed the autonomous dynamic system. In the absence of interaction between fluids, solutions are obtained corresponding to two cases. In the first case, dark energy is missing and the extension describes the component of dark matter. The second case corresponds to cosmological models with an extension due to dark energy. The solutions obtained are investigated for stability. For a cosmological model with the interaction of a special type, the stability of solutions of the dynamic system is also investigated., Comment: 13 pages, 2 figures, to appear in International Journal of Geometric Methods in Modern Physics

We find the probability density distribution of torque orientations in the Universe for the entire period of its evolution. It is shown that in the early Universe the orientation of its spin is random, and the cosmological principle is satisfied. This result is naturally consistent with the CMBisotropy. In the modern Universe the rotation axis direction becomes anisotropic, and the cosmological principle, strictly speaking, is not satisfied. This is confirmed by the large-scale anisotropy in the distribution of space objects and by the torque alignment direction. But since the value of the angular velocity of our Universe is $$\omega_{U_{n}}\sim10^{-19}\;\text{Hz}$$ , finding of such rotation and its influence on the natural processes is extremely difficult. So today dominates the view that the Universe is isotropic, and the cosmological principle is satisfied in it.

In this work we study wormholes solutions based on fractional action cosmology. We discuss cosmic dynamics of the universe in the presence of wormhole and wormhole wave function in closed Friedmann–Robertson–Walker (FRW) universe. We have observed that cosmic acceleration with traversable wormhole may be realized without the need of exotic matter like dark and phantom energy unless the scale factor of the universe obeys a power law dominated by a negative fractional parameter, which is constrained from type Ia supernovae data. Besides, we have derived wormholes wave function in a closed FRW universe and we have found that a wormhole can survive in the presence of quantum effects only if the expansion of the universe is accelerated with time.

In this paper, it is proposed that the size of the classical electron, which is a stable elemental particle with the smallest concentration of matter in Nature, can be used to explain the very big size of the Universe. In order to reach that objective, the apparent size of heavenly bodies as seemed each other at very big distances in space, is used as a fundamental concept. Also, it is proved that the size, shape, mass, and future of the Universe are ruled by the speed of light, and the range of gravitational interactions.

This note questions the validity of the Expanding Universe Theory with simple mathematics and shows Static Universe is still consistent with Hubble’s Law without assumption of expansion of the space (or the universe). If we had an explosion of a huge cel...

This work briefly reviews and extends the author’s three previous works (2015), Journal of Modern Physics, 6, 78-87, and 1360-1370; (2016), 7, 1829-1844 that propose as an alternative to the accelerating ΛCDM universe, the decelerating Einstein de Sitter (EdS) universe, in which dark energy is a different phase of dark matter located only in intergalactic space (IGS), and that instead of a negative pressure, it has an index of refraction n≈1.50, and hence a reduced speed of light c / n through it. This allows the EdS universe to expand the extra distance necessary to obtain the diminished brightness of the Type Ia supernovae. In view of the recent suggestion that the universe is not accelerating, but possibly expanding uniformly, a table is given comparing both the accelerating and uniformly expanding universes with the EdS universe supplemented by the reduced speed of light. It is shown that fitting the uniformly expanding universe leads to a smaller value of n, and hence too short an age for the EdS universe, unlike the case with fitting the accelerating universe. The main result is that the proposed reduced speed of light in the IGS predicts discordant redshifts. It is shown that the current explanation of “accidental superposition,” is most likely insufficient to explain the number of observations, and that the present proposal could make up the difference. It can be tested astronomically, as illustrated in a figure.

We formulate the idea of a Universe crossing different evolving phases where in each phase one can define a basic field at lattice structure (Uk) increasing in mass (Universe-lattice). The mass creation in Uk has a double consequence for the equivalence “mass-space”: Increasing gravity (with varying metric) and increasing space (expansion). We demonstrate that each phase is at variable metric beginning by open metric and to follow a flat metric and after closed. Then we define the lattice-field of intersection between two lattice fields of base into universe and we analyse the universe in the Nucleo-synthesis phase (intersection-lattice ) and in the that of recombination (intersection-lattice ). We show that the phase is built on the intersection of the lattices of the proton (Up) and electron (Ue) or . We show UH to be at variable metric (open in the past, flat in the present and closed in the future). Then, we explain some fundamental aspects of this universe UH: Hubble’s law by creating the mass-space in it, its age (13.82 million of Years) as time for reaching the flat metric phase and the value of critic density. In last we talk about dark universe lattice , having hadronic nature, and calculating its spatial step and its density in present phase of .

The wave function for the spin the early universe is obtained through the adaption of the quantum formalism to one solution of the Wheeler-DeWitt’s equation [1], associated with the wave function of the universe. In addition, some observations performed by Stephen Hawking in relation to the vorticity of the universe [2] are used. This wave function for the spin could be used for indirectly to demonstrate the presence of dark matter in the universe.

We hypothesize a closed Universe belonging to the oscillatory class. More precisely, we postulate a Universe that evolves following a simple harmonic motion whose pulsation is equal to the ratio between the speed of light and the mean radius of curvature. The existence of at least a further spatial dimension is contemplated. Although the space we are allowed to perceive is curved, since it is identifiable with a hypersphere whose radius depends on our state of motion, the Universe in its entirety, herein assimilated to a four-dimensional ball, is to be considered as being flat. All the points are replaced by straight line segments: In other terms, what we perceive as being a point is actually a straight line segment crossing the center of the above mentioned four-dimensional ball. In the light of these hypotheses, we can easily obtain the identity that represents the so called relativistic energy. In this paper we discuss, more thoroughly than elsewhere, the deduction of the so called mass-energy equivalence. Moreover, by carrying out a simple comparison with the way in which we perceive a bi-dimensional surface, the noteworthy concept of dimensional thickness is introduced.

We discuss the particle horizon problem in the framework of spatially homogeneous and isotropic scalar cosmologies. To this purpose we consider a Friedmann&ndash, Lema&icirc, tre&ndash, Robertson&ndash, Walker (FLRW) spacetime with possibly non-zero spatial sectional curvature (and arbitrary dimension), and assume that the content of the universe is a family of perfect fluids, plus a scalar field that can be a quintessence or a phantom (depending on the sign of the kinetic part in its action functional). We show that the occurrence of a particle horizon is unavoidable if the field is a quintessence, the spatial curvature is non-positive and the usual energy conditions are fulfilled by the perfect fluids. As a partial converse, we present three solvable models where a phantom is present in addition to a perfect fluid, and no particle horizon appears.

Contrary to the common approach of the general relativity, the author uses his invariant integral of physical mesomechanics to model and study the universe at the large scale of about 100 MPc in the Euclidian space. The flatness of the universe proven by numerous probes of the WMAP and PLANCK satellite missions necessitates this approach. From the invariant integral of cosmology, the interaction force of two point masses in the cosmic-gravitational field is derived. This force is proven to be a sum of two terms, the one being the Newtonian gravity and the other the repulsion force caused by the cosmological constant. Both terms make up the right-hand part of the evolution equation of the dynamic universe. Qualitatively in agreement with the FLRW and ACDM models, and WMAP and PLANCK mission data, the exact solution of this equation has provided the history of the early decelerating universe and the asymptotic description of the Big Bang, the expansion at an almost constant rate in the middle age, and the current stage of the accelerated expansion of the universe. The age of the universe is found to be equal to 12.3 billion years. It is shown that neutron stars become stable Black Holes when their masses are greater than 6.7Msun. Then, it is assumed that the universe not only expands but also revolves, and the evolution equations of the revolving and expanding universe are advanced, with the cosmological constant being defined in terms of the angular velocity of the universe. A singular solution of these evolution equations has described the history of the revolving and expanding universe, at least, up to the age of about ten billion years. Orbital velocities of stars in the Milky Way are calculated to be about 250 km/s independent of the distance of stars from the galaxy center. Using the equation of the fractal dimension of the universe as a power-law fractal, the thickness of a disk-shaped universe is found. The graviton of minimum frequency is hypothesized to be the smallest elementary particle and the building block of everything.

In this paper, we analyse the effect of the expansion of the universe on the clustering of galaxies. We evaluate the configurational integral for interacting system of galaxies in an expanding universe by including effects produced by the cosmological constant. The gravitational partition function is obtained using this configuration integral. Thermodynamic quantities, specifically, Helmholtz free energy, entropy, internal energy, pressure and chemical potential are also derived for this system. It is observed that they depend on the modified clustering parameter for this system of galaxies. It is also demonstrated that these thermodynamical quantities get corrected because of the cosmological constant., Comment: 6 pages, 1 figure, Published in MNRAS

In this paper, we investigate the Ghost Dark Energy (GDE) and the Generalized Ghost Dark Energy (GGDE) in a cyclic universe in which the high-energy regime is modified by the effects of quantum gravity, causing a turnaround (and a bounce) of the universe. First, we study the non-interacting cases for both of these models. We find that, in the absence of interaction in a cyclic universe, the deceleration parameter becomes a constant; as a result, the universe cannot move from an accelerated expansion phase to a deceleration phase and so cannot reach turnaround point and starts to contract. Then, we extend our study to the interacting GDE and GGDE models. We obtain the evolution of the dark energy density, the deceleration and the equation of state parameters for these models in a cyclic universe. In this case, the transition from an accelerated expansion phase to the deceleration phase in the future (near the turnaround point) can be achieved in a cyclic universe. © 2016, Shiraz University., Research Institute for Astronomy and Astrophysics of Maragha

The prominence of 8π in cosmological solutions regarding the structure of space might be accommodated by factors other than the presence of mass. When the total set is considered a LC (inductance-capacitance) circuit, the “time constant” differs from Planck’s time by a factor of 8π which satisfies the numbers of turns (N) within the geometry of a universal solenoid. The calculated separation between two concentric spherical Casimir boundaries whose energies and pressures define the current universe is ~54 μm. If the volume of the universe was held constant the linear distance of this extraordinarily flat space would require the hypothetical entanglement velocity (~1023 m·s-1) continuing until the final epoch (~1018 s) of the universe to be integrated into a singular entity. We suggest that 8π may be a reflection of the temporal properties of an implicit solenoid-like spatial structure that will ultimately be manifested quite differently as the temporal boundary of the universe is approached. Two perspectives emerge. The first reflects the topological properties of a line that become the second derivative of the surface of a sphere. The second is the shape would be extraordinarily flat.

A step-by-step foundation for the differential character of the Universe’s rotation is presented. First, invoking the concept of spacetime foam with spin, it is reasonable to assume that the very early Universe can be described by the Dirac equation. Second, it is shown using the Ehrenfest theorem that, from a classical point of view, the early Universe can be described by the Papapetrou equations. Third, it is stressed that our Universe can perform only rotational motion. It is shown based on the spin part of the Papapetrou equations that the Universe’s rotation depends appreciably on the physical properties of a specific cosmological epoch. The rotational angular velocity is calculated for three basic cosmological epochs: the matter-dominated epoch, the transition period (from domination of matter to domination of vacuum), and the vacuum-dominated epoch.

In a flat Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) geometry, we consider the expansion of the universe powered by the gravitationally induced `adiabatic' matter creation. To demonstrate how matter creation works well with the expanding universe, we have considered a general creation rate and analyzed this rate in the framework of dynamical analysis. The dynamical analysis hints the presence of a non-singular universe (without the big bang singularity) with two successive accelerated phases, one at the very early phase of the universe (i.e. inflation), and the other one describes the current accelerating universe, where this early, late accelerated phases are associated with an unstable fixed point (i.e. repeller) and a stable fixed (attractor) points, respectively. We have described this phenomena by analytic solutions of the Hubble function and the scale factor of the FLRW universe. Using Jacobi Last multiplier method, we have found a Lagrangian for this matter creation rate describing this scenario of the universe. To match with our early physics results, we introduce an equivalent dynamics driven by a single scalar field and discussed the associated observable parameters compared them with the latest PLANCK data sets. Finally, introducing the teleparallel modified gravity, we have established an equivalent gravitational theory in the framework of matter creation., Comment: 15 pages (two column format), 3 figures, Some typos corrected, Published version in MNRAS

The solution of the Friedmann cosmological equations for the scale factor in a model of the Universe containing matter having the equation of state of dust and dark energy is considered. The equation-of-state parameter of the dark energy is taken to be an arbitrary constant w = −1.006 ± 0.045, whose value is constrained by the current observational limits. An exact solution for the scale factor as a function of physical time and conformal time is obtained. Approximate solutions have been found for the entire admissible conformal time interval with an accuracy better than 1%, which exceeds the accuracy of the determined global parameters of our Universe. This is the first time an exact solution for the scale factor describing the evolution of the Universe in a unified way, beginning with the matter-dominated epoch and ending with the infinitely remote future, has been obtained.

A hydro-dynamical model for gravity by using an analogy with the attraction of spherical sources in incompressible fluids is proposed. Information regarding a photon-like particle called graviton is taken using an author's previous paper (6). The substance and radiation interaction due to emission of gravitons takes place via an energy field made of the emitted gravitons and filling the entire universe. The energy distribution is considered uniform at the universe scale. A consequence of the proposed model is the increasing of the universal "constant" of gravity, as a function of the age of universe.

We consider the model of evolution of the Universe where the Big Bang is regarded as an explosion of a photon superstar. The inflationary epoch is not necessary in the model. The model describes the fundamental phenomena observed: the Universe is expanding at an increasing rate, it is homogeneous and isotropic and contains no antimatter, and its metrics is almost flat.

The Current Standard Model of the Universe asserts that the universe is generated from a single Big Bang event followed by inflation. There is no center to this universe, hence, no preferential reference frame to describe the motions of celestial objects. We propose a new, Shell Model of the Universe, which contends that the universe is created from multiple, concentric big bangs. Accordingly, that origin presents itself as a unique, preferential reference frame, which furnishes the simplest description of the motions of galaxies in the cosmos. This is similar in manner to how planetary motion is more straightforwardly described via a sun-centered Solar System rather than an earth-centered one. The appeal of the Shell Model of the Universe lies in its simplistic ability to resolve the paradox of quasars, explain the variability in Hubble’s Constant, and solve the problematic accelerated expansion of the universe.

We initially look at a non singular universe representation as given by Rovelli and Vidotto, in terms of a quantum bounce, via minimum mass quark stars, as a start of how to estimate of entropy and also of the number of operations of an expanding universe. The bench mark used is, to after considering a quark star, to look at the mass of a universe, estimated, and from there, we can obtain the entropy if we look at the Schwartzshield radii of a universe, and then the radii of the universe about 380,000 years after the big bang. In the latter, we show how to get the number of operations as akin to the reasoning used by Seth Lloyd, in 2001, and also from there close with a few comments as to the “naturalness” of heavy Gravity from this formulation of entropy, which is based upon a start of considering what is a Planck star, as far as minimum quantum effects in Black hole physics, and by extension early universe cosmology.