scholarly journals Late time transition in the evolution of the Universe

2021 ◽  
Author(s):  
EKREM AYDINER ◽  
Isil Oz ◽  
Tekin Dereli ◽  
Mustafa Sarisaman
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Power Law ◽  
Numerical Solutions ◽  
Scale Factor ◽  
Late Time ◽  
Transition Problem ◽  
Exponential Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Abstract The late time crossover from a power-law to an exponential expansion of the Universe evolution is the major problem in today’s physical cosmology. Unless this critical transition problem is solved, it is not possible to reach a holistic theory of cosmology. In this study, we propose a simple model in the FLRW framework, where dark matter and dark energy interact through a potential. We analytically solve this model and obtain scale factor a(t) from the presented model. Mainly, employing numerical solutions we show that the scale parameter has a hybrid form which includes power and exponential terms. The numerical results clearly show that there is a time crossover tc in the scale factor a(t) curve, which indicates the transition from the power-law to the exponential expansion of the Universe. We fit these unscaled curves and obtain that scale factor behaves as a(t) ∝ t 2/3 below t ≤ tc, and as a(t) ∝ exp(H0t) with H0 = 0.4 and H0 = 0.3 for the relatively weak and strong interactions above t > tc, respectively. It is the first time that we explicitly obtain a hybrid scale factor incorporating the power and exponential terms as a(t) ∝ t 2/3 e H0t . We conclude that the presented model can solve the late time transition problem of the Universe based on dark matter and dark energy interaction. Additionally, we numerically obtain other kinematic parameters depending upon the scale factor. We discuss the limit behaviors of all relevant cosmological parameters. Our results are completely in good agreement with observational data. Finally, we state that this work makes essential steps towards solving a critical outstanding problem of the cosmology, and has a potential to creates a paradigm for future studies in this field.

scholarly journals Late time transition in the evolution of the Universe

2021 ◽  
Author(s):  
Ekrem Aydiner ◽  
Isil Basaran Oz ◽  
Tekin Dereli ◽  
Mustafa Sarisaman
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Power Law ◽  
Numerical Solutions ◽  
Scale Factor ◽  
Late Time ◽  
Transition Problem ◽  
Exponential Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Abstract The late time crossover from a power-law to an exponential expansion of the Universe evolution is the major problem in today’s physical cosmology. Unless this critical transition problem is solved, it is not possible to reach a holistic theory of cosmology. In this study, we propose a simple model in the FLRW framework, where dark matter and dark energy interact through a potential. We analytically solve this model and obtain scale factor a(t) from the presented model. Mainly, employing numerical solutions we show that the scale parameter has a hybrid form which includes power and exponential terms. The numerical results clearly show that there is a time crossover tc in the scale factor a(t) curve, which indicates the transition from the power-law to the exponential expansion of the Universe. We fit these unscaled curves and obtain that scale factor behaves as a(t) ∝ t2/3 below t ≤ tc, and as a(t) ∝ exp(H0t) with H0 = 0.4 and H0 = 0.3 for the relatively weak and strong interactions above t > tc, respectively. It is the first time that we explicitly obtain a hybrid scale factor incorporating the power and exponential terms as a(t) ∝ t2/3eH0t . We conclude that the presented model can solve the late time transition problem of the Universe based on dark matter and dark energy interaction. Additionally, we numerically obtain other kinematic parameters depending upon the scale factor. We discuss the limit behaviors of all relevant cosmological parameters. Our results are completely in good agreement with observational data. Finally, we state that this work makes essential steps towards solving a critical outstanding problem of the cosmology, and has a potential to creates a paradigm for future studies in this field.

scholarly journals The hybrid scale factor, the transition from the matter dominated era to the dark energy dominated era and time evolution of the Universe

2021 ◽  
Author(s):  
Ekrem Aydiner ◽  
Isil Basaran-Oz ◽  
Tekin Dereli ◽  
Mustafa Sarisaman
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Power Law ◽  
Hubble Parameter ◽  
Scale Factor ◽  
Late Time ◽  
Critical Transition ◽  
Evolution Of The Universe ◽  
Exponential Expansion ◽  
The Universe

Abstract The late time crossover from matter dominated era (represented power-law evolution) to the dark energy dominated era (represented exponential evolution) of the Universe evolution is the major problem in today’s physical cosmology. Unless this critical transition problem is solved, it is not possible to reach a holistic theory of cosmology. To explain this critical transition we propose a new model where the dark matter and dark energy interacting through a potential. Based on the FLRW framework we analytically solve this model and obtain the scale factor a(t). In addition, we numerically compute all cosmological quantities. We find more significant results to enlightening the physical mechanism of the critical transition. Firstly, we show that the scale factor a(t) has a hybrid form as a(t) = a0(t/t0) α e ht/t0 . This is main and important result in the presented work, which clearly indicates that the transition from the power-law to the exponential expansion of the Universe. The numerical results clearly provide that there is a time crossover tc in the scale factor a curve, which indicates the transition from the power-law to the exponential expansion of the Universe. Below t/t0 ≤ tc, matter era dominated hence time evolution of the Universe is given by a(t) ∝ (t/t0) α , on the other hand, above t/t0 > tc, the evolution is represented by a(t) ∝ exp(ht/t0). It is first time, the hybrid result for scale factor is exactly obtained from the presented model without use any approximation. Secondly, we fit the scale factor below and above tc. Surprisingly, we find that the scale factor behaves as a(t) ∝ (t/t0) 2/3 below t/t0 ≤ tc, and as a(t) ∝ exp(ht/t0) which indicates that the Hubble parameter takes the value in the interval of the around H0 = 69.5 and H0 = 73.5 km s−1Mpc−1 depend on the weak and strong interactions between dark components above t/t0 > tc, respectively. These are remarkable that α = 2/3 is completely consistent exact solution of the FLRW and re-scaled Hubble parameter H0 is the observable intervals given by Planck, CMB and SNIa data (or other combinations) for chosen interaction values are purely consistent with cosmological observations. Thirdly, we find from the model the transition point from matter dominated era to the dark energy dominated era in the cosmic time is the t0 = 9.8 Gyear which is consistent with the theoretical solution and observations. Additionally, we numerically obtain and analyse other cosmological quantities such as dimensionless Hubble parameter h, deceleration parameter q, jerk parameter j and EoS parameter w. We show that all cosmological quantities of this model are consistent observational results for the matter and dark energy dominated eras. As a result, we consider late time crossover of the Universe, we propose an interacting dark matter and dark energy model, we show that this model can explain the late time crossover phenomena of the Universe and our solutions are very good consistent with theoretical and observational results. Finally, we state that this work makes essential steps towards solving a critical outstanding problem of the cosmology, and has a potential to creates a paradigm for future studies in this field. Furthermore, the model also sheds light on the interaction mechanism of dark matter and dark energy in the Universe.

scholarly journals Unified Description of Dark Energy and Dark Matter within the Generalized Hybrid Metric-Palatini Theory of Gravity

Universe ◽  
2020 ◽  
Vol 6 (6) ◽  
pp. 78 ◽  
Author(s):  
Paulo M. Sá
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Fields ◽  
Accelerated Expansion ◽  
Late Time ◽  
Intermediate Phases ◽  
Expansion Of The Universe ◽  
Theory Of Gravity ◽  
The Universe ◽  
Unified Description

The generalized hybrid metric-Palatini theory of gravity admits a scalar-tensor representation in terms of two interacting scalar fields. We show that, upon an appropriate choice of the interaction potential, one of the scalar fields behaves like dark energy, inducing a late-time accelerated expansion of the universe, while the other scalar field behaves like pressureless dark matter that, together with ordinary baryonic matter, dominates the intermediate phases of cosmic evolution. This unified description of dark energy and dark matter gives rise to viable cosmological solutions, which reproduce the main features of the evolution of the universe.

scholarly journals Late time transition of Universe and the hybrid scale factor

2022 ◽  
Vol 82 (1) ◽  
Author(s):  
E. Aydiner ◽  
I. Basaran-Öz ◽  
T. Dereli ◽  
M. Sarisaman
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Time Evolution ◽  
Hubble Parameter ◽  
Energy Condition ◽  
Scalar Fields ◽  
Scale Factor ◽  
Late Time ◽  
Eos Parameter ◽  
The Universe

AbstractIn this study, we propose an interacting model to explain the physical mechanism of the late time transition from matter-dominated era to the dark energy-dominated era of the Universe evolution and to obtain a scale factor a(t) representing two eras together. In the present model, we consider a minimal coupling of two scalar fields which correspond to the dark matter and dark energy interacting through a potential based on the FLRW framework. Analytical solution of this model leads to a new scale factor a(t) in the hybrid form $$a(t)=a_{0} (t/t_{0})^{\alpha } e^{ht/t_{0}}$$ a ( t ) = a 0 ( t / t 0 ) α e h t / t 0 . This peculiar result reveals that the scale factor behaving as $$a (t) \propto (t/t_{0})^{\alpha }$$ a ( t ) ∝ ( t / t 0 ) α in the range $$t/t_{0}\le t_{c}$$ t / t 0 ≤ t c corresponds to the matter-dominated era while $$a(t) \propto \exp (ht/t_{0})$$ a ( t ) ∝ exp ( h t / t 0 ) in the range $$t/t_{0}>t_{c}$$ t / t 0 > t c accounts for the dark energy-dominated era, respectively. Surprisingly, we explore that the transition from the power-law to the exponential expansion appears at the crossover time $$t_{0} \approx 9.8$$ t 0 ≈ 9.8 Gyear. We attain that the presented model leads to precisely correct results so that the crossover time $$t_{0}$$ t 0 and $$\alpha $$ α are completely consistent with the exact solution of the FLRW and re-scaled Hubble parameter $$H_{0}$$ H 0 lies within the observed limits given by Planck, CMB and SNIa data (or other combinations), which lead to consistent cosmological quantities such as the dimensionless Hubble parameter h, deceleration parameter q, jerk parameter j and EoS parameter w. We also discuss time dependent behavior of the dark energy and dark matter to show their roles on the time evolution of the universe. Additionally, we observe that all main results completely depend on the structure of the interaction potential when the parameter values are tuned to satisfy the zero energy condition. Finally, we conclude that interactions in the dark sector may play an important role on the time evolution and provides a mechanism to explain the late time transition of the Universe.

Anisotropic models with generalized hybrid expansion in Brans–Dicke theory of gravity

2021 ◽  
pp. 2150141
Author(s):  
S. Surendra Singh ◽  
Yohenba Soibam
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Power Law ◽  
Bianchi Type ◽  
Scale Factor ◽  
Late Time ◽  
Type I ◽  
Coincidence Problem ◽  
Bianchi Type I ◽  
Average Scale Factor

The hybrid expansion law (HEL) for average scale factor that yields power-law and exponential-law cosmologies is considered in spatially homogenous and anisotropic Bianchi type-I model in the context of Brans–Dicke (BD) Theory of gravitation. The solutions of the field equations have been calculated by assuming the power-law expression between the average scale factor [Formula: see text] and scalar field ([Formula: see text]). We studied both interacting and non-interacting forms of dark energy and dark matter and obtained respective solutions. The energy density [Formula: see text] decreases with time while energy densities [Formula: see text] increases with time. In both the cases, the physical acceptability and stability of the models are also studied. The coincidence problem in [Formula: see text]CDM model can be ruled out with proper choice of coupling between dark matter (DM) and dark energy (DE). We also discussed the physical behaviors of the derived models with the current observations applied to late-time acceleration and beginning of the universe. In this model, it is observed that our HEL Bianchi type I universe is highly anisotropic in the beginning of universe and becomes isotropic and overlaps with flat [Formula: see text]CDM model at late times.

Interacting new holographic dark energy model with varying G in nonflat universe

2013 ◽  
Vol 91 (12) ◽  
pp. 1090-1092
Author(s):  
V. Fayaz ◽  
F. Felegary ◽  
H. Hossienkhani
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Energy Model ◽  
Accelerated Expansion ◽  
Late Time ◽  
Holographic Dark Energy Model ◽  
Expansion Of The Universe ◽  
The Universe

Motivated by the work of Karami and Fehri (Phys. Lett. B, 684, 61 (2010)). We generalize their work with varying G. We investigate the new holographic dark energy model with varying G. We consider a spatially nonflat universe containing interacting new holographic dark energy with pressureless dark matter. We obtain the equation of state and the deceleration parameters. Also we reconstruct ωA for a = a0tn and H = [β/(α − 1)](1/t) in the late time universe. We also obtain q for a = a0tn and H = [β/(α − 1)](1/t) in the present time universe, which describes accelerated expansion of the universe.

The accelerating universe and dark energy

2014 ◽  
Vol 23 (06) ◽  
pp. 1430012 ◽  
Author(s):  
Charles Baltay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Parameters ◽  
Accelerating Universe ◽  
Heavy Particles ◽  
Familiar World ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Present Understanding

The recent discovery by Riess et al.1 and Perlmutter et al.2 that the expansion of the universe is accelerating is one of the most significant discoveries in cosmology in the last few decades. To explain this acceleration a mysterious new component of the universe, dark energy, was hypothesized. Using general relativity (GR), the measured rate of acceleration translates to the present understanding that the baryonic matter, of which the familiar world is made of, is a mere 4% of the total mass-energy of the universe, with nonbaryonic dark matter making up 24% and dark energy making up the majority 72%. Dark matter, by definition, has attractive gravity, and even though we presently do not know what it is, it could be made of the next heavy particles discovered by particle physicists. Dark energy, however, is much more mysterious, in that even though we do not know what it is, it must have some kind of repulsive gravity and negative pressure, very unusual properties that are not part of the present understanding of physics. Investigating the nature of dark energy is therefore one of the most important areas of cosmology. In this review, the cosmology of an expanding universe, based on GR, is discussed. The methods of studying the acceleration of the universe, and the nature of dark energy, are presented. A large amount of experimentation on this topic has taken place in the decade since the discovery of the acceleration. These are discussed and the present state of knowledge of the cosmological parameters is summarized in Table 7 below. A vigorous program to further these studies is under way. These are presented and the expected results are summarized in Table 10 below. The hope is that at the end of this program, it would be possible to tell whether dark energy is due to Einstein's cosmological constant or is some other new constituent of the universe, or alternately the apparent acceleration is due to some modification of GR.

Power law expansion of the early universe for a V (a) = kan potential

2018 ◽  
Vol 33 (01) ◽  
pp. 1850005
Author(s):  
Augusto S. Freitas
Keyword(s):  
Early Universe ◽  
Power Law ◽  
Analytical Solutions ◽  
Scale Factor ◽  
Rigorous Proof ◽  
Exponential Expansion ◽  
True Vacuum ◽  
Classical Potential ◽  
The Universe

In a recent paper, He, Gao and Cai [Phys. Rev. D 89, 083510 (2014)], found a rigorous proof, based on analytical solutions of the Wheeler–DeWitt (WDWE) equation, of the spontaneous creation of the universe from nothing. The solutions were obtained from a classical potential [Formula: see text], where [Formula: see text] is the scale factor. In this paper, we present a complementary (to that of He, Gao and Cai) solution to the WDWE equation with [Formula: see text]. I have found an exponential expansion of the true vacuum bubble for all scenarios. In all scenarios, we found a power law behavior of the scale factor result which is in agreement with another studies.

scholarly journals CAN BRANS–DICKE SCALAR FIELD ACCOUNT FOR DARK ENERGY AND DARK MATTER?

2006 ◽  
Vol 21 (15) ◽  
pp. 1241-1248 ◽  
Author(s):  
M. ARIK ◽  
M. C. ÇALIK
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Late Time ◽  
Energy Contribution ◽  
Time Solution ◽  
The Universe

By using a linearized non-vacuum late time solution in Brans–Dicke cosmology, we account for the 75% dark energy contribution but not for approximately 23% dark matter contribution to the present day energy density of the universe.

scholarly journals DO RECENT SUPERNOVAE Ia OBSERVATIONS TEND TO RULE OUT ALL THE COSMOLOGIES?

2007 ◽  
Vol 16 (10) ◽  
pp. 1641-1651 ◽  
Author(s):  
RAM GOPAL VISHWAKARMA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Gravitational Lensing ◽  
Weakly Interacting Massive Particles ◽  
Cosmological Models ◽  
Accelerated Expansion ◽  
Standard Candle ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Rule Out

Dark energy and the accelerated expansion of the universe have been the direct predictions of the distant supernovae Ia observations which are also supported, indirectly, by the observations of the CMB anisotropies, gravitational lensing and the studies of galaxy clusters. Today these results are accommodated in what has become the concordance cosmology: a universe with flat spatial sections t = constant with about 70% of its energy in the form of Einstein's cosmological constant Λ and about 25% in the form of dark matter (made of perhaps weakly-interacting massive particles). Though the composition is weird, the theory has shown remarkable successes at many fronts. However, we find that as more and more supernovae Ia are observed, more accurately and towards higher redshift, the probability that the data are well-explained by the cosmological models decreases alarmingly, finally ruling out the concordance model at more than 95% confidence level. This raises doubts against the "standard candle"-hypothesis of the supernovae Ia and their use in constraining the cosmological models. We need a better understanding of the entire SN Ia phenomenon in order to extract cosmological consequences from them.

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