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Zeitschriftenartikel zum Thema „I vialed the universe“

Autor: Grafiati

Veröffentlicht am 4. Juni 2021

Zuletzt aktualisiert am 29. Juli 2025

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1

Singh, Kangujam Priyokumar, and Mahbubur Rahman Mollah. "Could the Lyra manifold be the hidden source of the dark energy?" International Journal of Geometric Methods in Modern Physics 14, no. 04 (2017): 1750063. http://dx.doi.org/10.1142/s0219887817500633.

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In the course of investigation of our present universe by considering the five-dimensional locally rotationally symmetric (LRS) Bianchi type-I universe with time-dependent deceleration parameters in Lyra manifold, it is excitingly found that the geometry itself of Lyra manifold behaves and consistent with present observational findings for accelerating universe. The behavior of the universes and their contribution to the process of evolution are examined. While studying their physical, dynamical and kinematical properties for different cases, it is found that this model is a new and viable for

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Trafimow, David, Tonghui Wang, and Cong Wang. "A Viable Approach to Mitigating Irreproducibility." Stats 4, no. 1 (2021): 205–15. http://dx.doi.org/10.3390/stats4010015.

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In a recent article, Trafimow suggested the usefulness of imagining an ideal universe where the only difference between original and replication experiments is the operation of randomness. This contrasts with replication in the real universe where systematicity, as well as randomness, creates differences between original and replication experiments. Although Trafimow showed (a) that the probability of replication in the ideal universe places an upper bound on the probability of replication in the real universe, and (b) how to calculate the probability of replication in the ideal universe, the

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Trivedi, Oem, and Maxim Khlopov. "Impossibility of rips and cosmological singularities in a universe merging with baby universes." Journal of Cosmology and Astroparticle Physics 2024, no. 09 (2024): 040. http://dx.doi.org/10.1088/1475-7516/2024/09/040.

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Abstract Understanding the late-time acceleration of the universe and its subtleties is one of the biggest mysteries in cosmology. A lot of different approaches have been put forward to deal with this, ranging from the conventional cosmological constant to various models of dark energy and beyond. Recently one very interesting approach to explaining the late time acceleration has been put forward, where the expansion of the universe is driven by mergers with other “baby” universes and has been shown to be quite viable as well from the point of view of recent observational data. So in this work

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Kleidis, Kostas, and Nikolaos K. Spyrou. "Dark Energy as a Natural Property of Cosmic Polytropes—A Tutorial." Dynamics 3, no. 1 (2023): 71–95. http://dx.doi.org/10.3390/dynamics3010006.

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A conventional approach to the dark energy (DE) concept is reviewed and discussed. According to it, there is absolutely no need for a novel DE component in the universe, provided that its matter–energy content is represented by a perfect fluid whose volume elements perform polytropic flows. When the (thermodynamic) energy of the associated internal motions is taken into account as an additional source of the universal gravitational field, it compensates the DE needed to compromise spatial flatness in an accelerating universe. The unified model which is driven by a polytropic fluid not only int

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Kim, Choong Sun. "Can stabilization and symmetry breakings give rise to life in the process of the universe evolution?" International Journal of Astrobiology 18, no. 4 (2018): 311–15. http://dx.doi.org/10.1017/s1473550418000071.

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AbstractBiogenesis can be understood as the final process of the Universe's evolution, from Planck scale down to nuclear scale to atomic scale to molecular scale, then finally to bioscale, with the breaking of relevant symmetries at every step. By assuming the simplest definition of life, that life is just a molecular system which can reproduce itself (auto-reproducing molecular system – ARMS) and has such kinetic ability (kineto-molecular system), at least for its microscopic level, as to respond actively to its surrounding environments, we tried to explain the origin of life, taking the fina

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CLAVELLI, L., and GARY R. GOLDSTEIN. "AN ALTERNATIVE STRING LANDSCAPE COSMOLOGY: ELIMINATING BIZARRENESS." International Journal of Modern Physics A 28, no. 29 (2013): 1350148. http://dx.doi.org/10.1142/s0217751x13501480.

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In what has become a standard eternal inflation picture of the string landscape there are many problematic consequences and a difficulty defining probabilities for the occurrence of each type of universe. One feature in particular that might be philosophically disconcerting is the infinite cloning of each individual and each civilization in infinite numbers of separated regions of the multiverse. Even if this is not ruled out due to causal separation one should ask whether the infinite cloning is a universal prediction of string landscape models or whether there are scenarios in which it is av

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Mukherjee, Dipayan, H. K. Jassal, and Kinjalk Lochan. "f(R) dual theories of quintessence: expansion-collapse duality." Journal of Cosmology and Astroparticle Physics 2021, no. 12 (2021): 016. http://dx.doi.org/10.1088/1475-7516/2021/12/016.

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Abstract The accelerated expansion of the universe demands presence of an exotic matter, namely the dark energy. Though the cosmological constant fits this role very well, a scalar field minimally coupled to gravity, or quintessence, can also be considered as a viable alternative for the cosmological constant. We study f(R) gravity models which can lead to an effective description of dark energy implemented by quintessence fields in Einstein gravity, using the Einstein frame-Jordan frame duality. For a family of viable quintessence models, the reconstruction of the f(R) function in the Jordan

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Sharif, M., and H. Ismat Fatima. "Built-in inflation in f(G) gravity." International Journal of Modern Physics D 25, no. 01 (2016): 1650011. http://dx.doi.org/10.1142/s0218271816500115.

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In this paper, we study the role of Gauss–Bonnet term for the early and late time accelerating phases of the universe with the help of two viable [Formula: see text] models in the background of flat FRW universe model. These models show inflationary behavior as well as the present accelerating expansion of the universe. The contribution of Gauss–Bonnet term in pressure and energy density is used to calculate equation of state (EoS) parameter for the modified fluid which behaves like cosmological constant with [Formula: see text]. We discuss early inflation and late accelerating expansion of th

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Habe, A., C. Hanyu, and S. Yachi. "Clusters of Galaxies in a Flat CHDM Universe." Symposium - International Astronomical Union 188 (1998): 299. http://dx.doi.org/10.1017/s0074180900115232.

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Cold and hot dark matter (CHDM) model is one of viable models which can reproduce the large scale structure of the universe. HDM may affect structure of clusters of galaxies in CHDM universe. Bryan et al. (1994) gave numerical results of CHDM model that explain some statistical features of X-ray clusters of galaxies, e.g. X-ray luminosiry-temperature realtion, L ∝~ T3.5, without considering radiative processes. However their numerical resolution is insufficient to resolve the cores of X-ray clusters. So, we simulate the formation of clusters in CHDM universe more carefully.

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Impey, Chris. "What We Don’t Know About the Universe." International Astronomical Union Colloquium 171 (1999): 393–400. http://dx.doi.org/10.1017/s0252921100054610.

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AbstractDespite progress on many fronts in cosmology, outstanding questions remain. What is the nature of the dark matter? Is the inflationary big bang model viable? Must we accept a non-zero cosmological constant? Do we know the true population of galaxies? What is the range of star formation histories in the universe? Can gravity alone explain the large scale structure we observe? Studies of the low surface brightness universe may provide the answers to many of these questions.

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Keskin, A. I. "Cosmic accelerated expansion of the Universe with phantom fluid." Canadian Journal of Physics 97, no. 11 (2019): 1221–24. http://dx.doi.org/10.1139/cjp-2018-0765.

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The phantom behavior of the Universe is discussed in an extended version of Gauss–Bonnet gravity. Following the method proposed by the author (Int. J. Mod. Phys. D, 27, 1850078. 2018. doi: 10.1142/S0218271818500785 ), we obtain a viable cosmological model for the phantom phase of the Universe. We find a condition for m in the model ∼Gm, which shows phantom expansion of the Universe. On the other hand, using a phantom source term ∼T2n in the model we observe that the term ∼Gn, with n > 3/4, gives a phantomic space–time expansion. This form (Gn + T2n) obtained for the phantom phase of the Uni

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Ketov, Sergei V. "Supergravity as the Dark Side of the Universe." International Journal of Modern Physics A 35, no. 02n03 (2020): 2040038. http://dx.doi.org/10.1142/s0217751x20400382.

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The Dark Side of the Universe, which includes the cosmological inflation in the early Universe, the current dark energy and dark matter, can be theoretically described by supergravity, though it is non-trivial. We recall the arguments pro and contra supersymmetry and supergravity, and define the viable supergravity models describing the Dark Side of the Universe in agreement with all current observations. Our approach to inflation is based on the Starobinsky model, the dark energy is identified with the positive cosmological constant (de Sitter vacuum), and the dark matter particle is given by

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Nandi, Debottam. "Stability of a Viable Non-Minimal Bounce." Universe 7, no. 3 (2021): 62. http://dx.doi.org/10.3390/universe7030062.

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The main difficulties in constructing a viable early Universe bouncing model are: to bypass the observational and theoretical no-go theorem, to construct a stable non-singular bouncing phase, and perhaps, the major concern of it is to construct a stable attractor solution which can evade the Belinsky–Khalatnikov–Lifshitz (BKL) instability as well. In this article, in the homogeneous and isotropic background, we extensively study the stability analysis of the recently proposed viable non-minimal bouncing theory in the presence of an additional barotropic fluid and show that, the bouncing soluti

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Fabris, Júlio C., Felipe T. Falciano, Luiz F. Guimarães, and Nelson Pinto-Neto. "On the Possibility of a Static Universe." Universe 10, no. 2 (2024): 92. http://dx.doi.org/10.3390/universe10020092.

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After a century of cosmological observations, we have a solid standard model of cosmology. However, from a theoretical viewpoint, it is a compelling question if the cosmological data inevitably require an expanding universe independently of the theoretical framework. The possibility of obtaining a viable cosmological model with a constant scale-factor is discussed in the context of the Brans–Dicke class of scalar–tensor theories. It is shown that a flat spatial section requires the presence of a stiff matter fluid. However, some kinematical properties of the standard cosmological model can be

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Adak, Debabrata, and Amna Ali. "Bounce and collapse in the slotheonic universe." International Journal of Modern Physics D 26, no. 09 (2017): 1750089. http://dx.doi.org/10.1142/s0218271817500894.

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In this paper, we examine the cosmological dynamics of a slotheon field in a linear potential. The slotheon correction term [Formula: see text] respects the galileon symmetry in curved spacetime. We demonstrate the future evolution of universe in this model. We show that in this scenario, the universe ends with the Big Crunch singularity like the standard case. The difference being that the time at which the singularity occurs is delayed in the slotheon gravity. The delay crucially depends upon the strength of slotheon correction. We use observational data from Type Ia Supernovae, Baryon Acous

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de Haro, Jaume, and Llibert Aresté Saló. "A Review of Quintessential Inflation." Galaxies 9, no. 4 (2021): 73. http://dx.doi.org/10.3390/galaxies9040073.

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Some of the most important quintessential inflation scenarios, such as the Peebles–Vilenkin model, are described in detail. These models are able to explain the early- and late-time accelerated expansions of our universe, and the phase transition from the end of inflation to the beginning of kination where the adiabatic evolution of the universe was broken in order to produce enough particles to reheat the universe with a viable temperature, thereby aligning with the Hot Big Bang universe. In addition, while considering the reheating to be due to the gravitational production of superheavy part

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Bhatti, M. Zaeem-ul-Haq, and Z. Yousaf. "Dynamical variables and evolution of the universe." International Journal of Modern Physics D 26, no. 04 (2017): 1750029. http://dx.doi.org/10.1142/s0218271817500298.

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One of the striking feature of inhomogeneous matter distribution under the effects of fourth-order gravity and electromagnetic field have been discussed in this manuscript. We have considered a compact spherical celestial star undergoing expansion due to the presence of higher curvature invariants of [Formula: see text] gravity and imperfect fluid. We have explored the dynamical equations and field equations in [Formula: see text] gravity. An explicit expression have been found for Weyl tensor and material variables under the dark dynamical effects. Using a viable [Formula: see text] model, so

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Kumar, Suresh. "Probing the matter and dark energy sources in a viable Big Rip model of the Universe." Modern Physics Letters A 29, no. 25 (2014): 1450119. http://dx.doi.org/10.1142/s0217732314501193.

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Chevallier–Polarski–Linder (CPL) parametrization for the equation of state (EoS) of dark energy in terms of cosmic redshift or scale factor have been frequently studied in the literature. In this study, we consider cosmic time-based CPL parametrization for the EoS parameter of the effective cosmic fluid that fills the fabric of spatially flat and homogeneous Robertson–Walker (RW) spacetime in General Relativity. The model exhibits two worthy features: (i) It fits the observational data from the latest H(z) and Union 2.1 SN Ia compilations matching the success of ΛCDM model. (ii) It describes t

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Lorenz-Petzold, D. "Is the Stephani-Krasiński solution a viable model of the Universe?" Journal of Astrophysics and Astronomy 7, no. 3 (1986): 155–70. http://dx.doi.org/10.1007/bf02714208.

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Katore, S. D., S. P. Hatkar, and S. V. Gore. "Cosmology of string bulk viscosity in f(G) theory of gravitation." International Journal of Geometric Methods in Modern Physics 15, no. 07 (2018): 1850116. http://dx.doi.org/10.1142/s0219887818501165.

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LRS Bianchi type I space time is considered to explore bulk viscous string model in modified [Formula: see text] gravity. Field equations are solved with some physically viable condition. It is observed that the string phase of the universe disappears. The Gauss–Bonnet invariant significantly effects on galactic fluid. The universe is expanding and isotropic at large time. Some physical parameters are also discussed in detail.

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Fischer, Arthur E. "Friedmann’s equation and the creation of the universe." International Journal of Modern Physics D 27, no. 14 (2018): 1847013. http://dx.doi.org/10.1142/s0218271818470132.

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In this paper, we present mathematical evidence that the beginning of the universe did not occur at the big bang at [Formula: see text] with the universe in a state of infinite density, but occurred at [Formula: see text] with the universe in a state of infinite dilution. We show the essential importance played by the native quadratic structure of a generic Friedmann’s equation [Formula: see text] in the time derivative [Formula: see text] in arriving at this conclusion and show how this quadratic structure together with the accompanying time-reversal symmetry of Friedmann’s equation has profo

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Pozdnyakov, N. A. "Accretion in very early Universe and charge asymmetry." Journal of Cosmology and Astroparticle Physics 2025, no. 05 (2025): 068. https://doi.org/10.1088/1475-7516/2025/05/068.

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Abstract Additional elementary species and primordial black holes are common candidates for dark matter. Their co-existence in the early Universe leads to accretion if particles are heavy. We solve equation of motion affected by expansion which enhances black hole growth rates. They depend upon particles freeze-out time rather than their mass. Taking into account friction we study recently suggested baryogenesis mechanism operating via scattering cross-section difference between particles and antiparticles on relativistic symmetric plasma. We find that asymmetry is accumulated in a narrow rang

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Sharif, M., and Ayesha Sarwar. "Thermodynamics of anisotropic emergent universe in nonlinear electrodynamics." Modern Physics Letters A 31, no. 22 (2016): 1650129. http://dx.doi.org/10.1142/s0217732316501297.

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In this paper, we study the emergent universe (EU) with interacting fluids in the background of Bianchi type I (BI) universe model. For this purpose, we consider polytropic equation of state (EoS) which constitutes three non-interacting fluids. In order to check the viability of the cosmological models, we take a two-fluid model interacting with dust fluid and a three-fluid model in which each fluid has nonlinear EoS interacting at [Formula: see text]. It turns out that both models are realistic cosmological viable. We also check the validity of the generalized second law of thermodynamics (GS

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Mishra, B., Sankarsan Tarai, and S. K. Tripathy. "Dynamics of an Anisotropic Universe inf(R,T)Theory." Advances in High Energy Physics 2016 (2016): 1–8. http://dx.doi.org/10.1155/2016/8543560.

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Dynamics of an anisotropic universe is studied inf(R,T)gravity using a rescaled functionalf(R,T), whereRis the Ricci Scalar andTis the trace of energy-momentum tensor. Three models have been constructed assuming a power law expansion of the universe. Physical features of the models are discussed. The model parameters are constrained from a dimensional analysis. It is found from the work that the anisotropic Bianchi typeVIh(BVIh) model in the modified gravity generally favours a quintessence phase when the parameterhis either-1or0. We may not get viable models in conformity with the present day

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Montani, Giovanni, Nakia Carlevaro, and Mariaveronica De Angelis. "Modified Gravity in the Presence of Matter Creation: Scenario for the Late Universe." Entropy 26, no. 8 (2024): 662. http://dx.doi.org/10.3390/e26080662.

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We consider a dynamic scenario for characterizing the late Universe evolution, aiming to mitigate the Hubble tension. Specifically, we consider a metric f(R) gravity in the Jordan frame which is implemented to the dynamics of a flat isotropic Universe. This cosmological model incorporates a matter creation process, due to the time variation of the cosmological gravitational field. We model particle creation by representing the isotropic Universe (specifically, a given fiducial volume) as an open thermodynamic system. The resulting dynamical model involves four unknowns: the Hubble parameter, t

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Das, Saurya. "Bose–Einstein condensation as an alternative to inflation." International Journal of Modern Physics D 24, no. 12 (2015): 1544001. http://dx.doi.org/10.1142/s0218271815440010.

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It was recently shown that gravitons with a very small mass should have formed a Bose–Einstein condensate (BEC) in the very early universe, whose density and quantum potential can account for the dark matter (DM) and dark energy (DE) in the universe respectively. Here, we show that the condensation can also naturally explain the observed large scale homogeneity and isotropy of the universe. Furthermore, gravitons continue to fall into their ground state within the condensate at every epoch, accounting for the observed flatness of space at cosmological distance scales. Finally, we argue that th

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Piratova Moreno, Eduard Fernando, and Luz Ángela García. "LATE ACCELERATED EXPANSION OF THE UNIVERSE IN DIFFUSIVE SCENARIOS." Revista Mexicana de Astronomía y Astrofísica 59, no. 2 (2023): 389–99. http://dx.doi.org/10.22201/ia.01851101p.2023.59.02.15.

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We present a diffusion model in a cosmological framework to describe the accelerated expansion of the Universe at late times. We first introduce a scalar field in Einstein's field equations to account for the effect of diffusion as the driver of today's expansion. We also study a second option for the diffusion source: a perfect fluid with a barotropic equation of state. We establish the equations that relate the fluid evolution with the cosmic budget and find analytical solutions of the field equations with different diffusion coeffcients: constant, redshift-dependent, and σ proportional to t

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FELIPE, RICARDO GONZÁLEZ. "NEUTRINOS AND THE MATTER-ANTIMATTER ASYMMETRY IN THE UNIVERSE." International Journal of Modern Physics E 20, supp01 (2011): 56–64. http://dx.doi.org/10.1142/s0218301311040074.

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The discovery of neutrino oscillations provides a solid evidence for nonzero neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny constitutes a puzzling problem in particle physics. From the theoretical viewpoint, the smallness of neutrino masses can be elegantly explained through the seesaw mechanism. Another challenging issue for particle physics and cosmology is the explanation of the matter-antimatter asymmetry observed in Nature. Among the viable mechanisms, leptogenesis is a simple and well-motivated framework. In this paper we briefly review these aspects, maki

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Ashmita, Kinjal Banerjee, and Prasanta Kumar Das. "Constructing viable interacting dark matter and dark energy models: a dynamical systems approach." Journal of Cosmology and Astroparticle Physics 2024, no. 11 (2024): 034. http://dx.doi.org/10.1088/1475-7516/2024/11/034.

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Abstract We study the evolution of k = -1 FLRW cosmological models for two interacting Dark Matter-Dark Energy Models using dynamical system analysis. Since we are interested in late time evolution, the sign of the interaction term is chosen such that it facilitates the transfer of energy from dark matter to dark energy. We also explore the k = 0 invariant subspace of these models. We find that both these models have sectors which have a stable fixed point where we can recover an accelerating universe with a negative equation of state. This indicates these can be viable models for our universe

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Singh, S. Surendra. "Interaction of anisotropic dark energy fluid with perfect fluid in the presence of cosmological term Λ". Modern Physics Letters A 33, № 15 (2018): 1850084. http://dx.doi.org/10.1142/s0217732318500840.

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Considering the locally rotationally symmetric (LRS) Bianchi type-I metric with cosmological constant [Formula: see text], Einstein’s field equations are discussed based on the background of anisotropic fluid. We assumed the condition A = B[Formula: see text] for the metric potentials A and B, where m is a positive constant to obtain the viable model of the Universe. It is found that [Formula: see text] is positive and inversely proportional to time. The values of matter-energy density [Formula: see text], dark energy density [Formula: see text] and deceleration parameter q are found to be con

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Zimin, I. N., and V. M. Kartvelishvili. "A Viable University: Foresight, Logframe, Lifestyle and Risks." Vestnik of the Plekhanov Russian University of Economics, no. 5 (October 20, 2021): 12–32. http://dx.doi.org/10.21686/2413-2829-2021-5-12-32.

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The study continues the study of the fundamental characteristics of models of viable systems conducted by the authors. The current issues of construction, reorganization and preservation of the life-incapable structure of a higher educational institution - university U, representing a recursive active subsystem of the educational environment, which is part of the universe-society, are considered. The formalized definitions of an absolutely viable, viable, conditionally viable and non-viable system are given, allowing from a mathematical point of view to assess the optimality of the structure a

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Sá, Paulo M. "Unified Description of Dark Energy and Dark Matter within the Generalized Hybrid Metric-Palatini Theory of Gravity." Universe 6, no. 6 (2020): 78. http://dx.doi.org/10.3390/universe6060078.

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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 repro

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WILTSHIRE, DAVID L. "FROM TIME TO TIMESCAPE — EINSTEIN'S UNFINISHED REVOLUTION." International Journal of Modern Physics D 18, no. 14 (2009): 2121–34. http://dx.doi.org/10.1142/s0218271809016193.

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I argue that Einstein overlooked an important aspect of the relativity of time in never quite realizing his quest to embody Mach's principle in his theory of gravity. As a step towards that goal, I broaden the strong equivalence principle to a new principle of physics, the cosmological equivalence principle, to account for the role of the evolving average regional density of the universe in the synchronisation of clocks and the relative calibration of inertial frames. In a universe dominated by voids of the size observed in large-scale structure surveys, the density contrasts of expanding regi

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V., B. Raut, and A. Salve S. "Plane Symmetric Magnetized Dark Energy Cosmological Model in f(R,T) Gravity." International Journal of Advance and Applied Research S6, no. 18 (2025): 505–15. https://doi.org/10.5281/zenodo.15260307.

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<em>In this study, we investigate a plane-symmetric cosmological model within the framework of </em><em> gravity, incorporating a magnetized dark energy component. The motivation behind this work stems from the growing interest in modified theories of gravity as viable alternatives to General Relativity (GR) in explaining the accelerated expansion of the universe. Our model considers a time-dependent deceleration parameter; the influence of magnetized dark energy is analyzed in detail, particularly in relation to its impact on the anisotropic behaviour of the universe. The behaviour of ke

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RODRIGUES, M. E., I. G. SALAKO, M. J. S. HOUNDJO, and J. TOSSA. "LOCALLY ROTATIONALLY SYMMETRIC BIANCHI TYPE-I COSMOLOGICAL MODEL IN f(T) GRAVITY: FROM EARLY TO DARK ENERGY DOMINATED UNIVERSE." International Journal of Modern Physics D 23, no. 01 (2014): 1450004. http://dx.doi.org/10.1142/s0218271814500047.

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We study the locally rotational symmetry Bianchi type-I dark energy model in the framework of f(T) theory of gravity, where T denotes the torsion scalar. A viable cosmological model is undertaken and the isotropization of this latter is checked, yielding a result that reflects the real evolution of our universe. Moreover, still in the anisotropic optic, a more complicated f(T) model is obtained from the cosmological reconstruction scheme and the analysis shows that the universe is more anisotropic at the beginning if the terms of higher order in T are not considered. This means that the nonlin

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Chichiri, Carlos, Graciela B. Gelmini, Philip Lu, and Volodymyr Takhistov. "Cosmological dependence of sterile neutrino dark matter with self-interacting neutrinos." Journal of Cosmology and Astroparticle Physics 2022, no. 09 (2022): 036. http://dx.doi.org/10.1088/1475-7516/2022/09/036.

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Abstract Unexplored interactions of neutrinos could be the key to understanding the nature of the dark matter (DM). In particular, active neutrinos with new self-interactions can produce keV-mass sterile neutrinos that account for the whole of the DM through the Dodelson-Widrow mechanism for a large range of active-sterile mixing values. This production typically occurs before Big-Bang Nucleosynthesis (BBN) in a yet uncharted era of the Universe. We assess how the mixing range for keV-mass sterile neutrino DM is affected by the uncertainty in the early Universe pre-BBN cosmology. This is parti

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Arora, Simran, Sanjay Mandal, Saikat Chakraborty, Genly Leon, and P. K. Sahoo. "Can f(R) gravity isotropise a pre-bounce contracting universe?" Journal of Cosmology and Astroparticle Physics 2022, no. 09 (2022): 042. http://dx.doi.org/10.1088/1475-7516/2022/09/042.

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Abstract We address the important issue of isotropisation of a pre-bounce contracting phase in f(R) gravity, which would be relevant to constructing any viable nonsingular bouncing scenario in f(R) gravity. The main motivation behind this work is to investigate whether the f(R) gravity, by itself, can isotropise a contracting universe starting initially with small anisotropy without incorporating a super-stiff or non-ideal fluid, impossible in general relativity. Considering Bianchi I cosmology and employing a dynamical system analysis, we see that this is not possible for R n (n > 1) and R

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Pereira, David S., João Ferraz, Francisco S. N. Lobo, and José P. Mimoso. "Baryogenesis: A Symmetry Breaking in the Primordial Universe Revisited." Symmetry 16, no. 1 (2023): 13. http://dx.doi.org/10.3390/sym16010013.

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In this review article, we revisit the topic of baryogenesis, which is the physical process that generated the observed baryon asymmetry during the first stages of the primordial Universe. A viable theoretical explanation to understand and investigate the mechanisms underlying baryogenesis must always ensure that the Sakharov criteria are fulfilled. These essentially state the following: (i) baryon number violation; (ii) the violation of both C (charge conjugation symmetry) and CP (the composition of parity and C); (iii) and the departure from equilibrium. Throughout the years, various mechani

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Demianski, M., E. Piedipalumbo, C. Rubano, and C. Tortora. "Two viable quintessence models of the Universe: Confrontation of theoretical predictions with observational data." Astronomy & Astrophysics 431, no. 1 (2005): 27–43. http://dx.doi.org/10.1051/0004-6361:20041508.

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Hara, Tetsuya, Shoji Morioka, and Shigeru Miyoshi. "On the Large-Scale Structures Formed by Wakes of Open Cosmic Strings." International Astronomical Union Colloquium 124 (1990): 677–81. http://dx.doi.org/10.1017/s0252921100005819.

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Large-scale structures of the universe have been variously described as sheetlike, filamentary, cellular, bubbles or spongelike. Recently cosmic strings become one of viable candidates for galaxy formation scenario, and some of the large-scale structures seem to be simply explained by the open cosmic strings).

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CAPOZZIELLO, S., V. F. CARDONE, G. LAMBIASE, and A. TROISI. "A FLUID OF STRINGS AS A VIABLE CANDIDATE FOR THE DARK SIDE OF THE UNIVERSE." International Journal of Modern Physics D 15, no. 01 (2006): 69–94. http://dx.doi.org/10.1142/s021827180600764x.

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We investigate the possibility that part of the dark matter is not made out of the usual cold dark matter (CDM) dust-like particles, but is in the form of a fluid of strings with barotropic factor ws= -1/3 of cosmic origin. To this aim, we split the dark matter density parameter into two terms and investigate the dynamics of a spatially flat universe filled with baryons, CDM, a fluid of strings and dark energy, modeling the latter as a cosmological constant or a negative pressure fluid with a constant equation of state w < 0. To test the viability of the models and to constrain their parame

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Biswas, Sujay Kr, and Subenoy Chakraborty. "Interacting dark energy in f(T) cosmology: A dynamical system analysis." International Journal of Modern Physics D 24, no. 07 (2015): 1550046. http://dx.doi.org/10.1142/s0218271815500467.

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This paper deals with an interacting dark energy (DE) model in the framework of f(T) cosmology. A cosmologically viable form of f(T) is chosen (T is the torsion scalar in teleparallelism) in the background of flat homogeneous and isotropic Friedmann–Robertson–Walker (FRW) spacetime model of the universe. The matter content of the universe is chosen as dust interacting with minimally coupled scalar field. The evolution equations are reduced to an autonomous system of ordinary differential equations by suitable transformation of variables. The nature of critical points is analyzed by evaluating

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Raut, S. V., and A. K. Dabre. "Modified Holographic Dark Energy in LRS Bianchi Type-I Space-time with f(R,T) Gravity: An Analytical Approach to the Cosmological Constant Problem." Journal of Neonatal Surgery 14, no. 6S (2025): 553–61. https://doi.org/10.52783/jns.v14.2274.

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In this study, we explore the implications of Modified Holographic Dark Energy (MHDE) in the context of Locally Rotationally Symmetric (LRS) Bianchi Type-I space-time under the framework of f(R,T) gravity. The investigation aims to provide an analytical perspective on the longstanding cosmological constant problem by incorporating a functional dependence of the Ricci scalar R and the trace of the energy-momentum tensor T. The dynamical behavior of the universe is examined through the evolution of key cosmological parameters such as the deceleration parameter, the equation of state parameter, a

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Duschl, Wolfgang J., and Peter A. Strittmatter. "The Formation and Feeding of Massive Black Holes in the Early Universe." International Astronomical Union Colloquium 184 (2002): 343–49. http://dx.doi.org/10.1017/s0252921100030992.

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AbstractIt is still an open question whether the super-massive black holes thought to be present in quasars are of primordial nature, or whether there is a viable way of forming them in the very short time scale (less than a billion years) permitted by the observational data. In this contribution, we present a way in which a galaxy-galaxy merger can provide not only the “fuel” for quasar activity, but can also build a super-massive black hole, i.e., “the engine”, in the first place.

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Ghoderao, Pulkit S., and Arttu Rajantie. "Curvature perturbations from preheating with scale dependence." Journal of Cosmology and Astroparticle Physics 2024, no. 05 (2024): 106. http://dx.doi.org/10.1088/1475-7516/2024/05/106.

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Abstract We extend the formalism to calculate non-Gaussianity of primordial curvature perturbations produced by preheating in the presence of a light scalar field. The calculation is carried out in the separate universe approximation using the non-perturbative delta N formalism and lattice field theory simulations. Initial conditions for simulations are drawn from a statistical ensemble determined by modes that left the horizon during inflation, with the time-dependence of Hubble rate during inflation taken into account. Our results show that cosmic variance, i.e., the contribution from modes

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Keskin, A. I. "Coexistence of early-time inflation and late-time acceleration with scalar fields in theory of F(G,T) gravity." International Journal of Modern Physics D 27, no. 08 (2018): 1850078. http://dx.doi.org/10.1142/s0218271818500785.

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In this study, we discuss coexistence of the early-time inflation and the late-time acceleration of the universe in the context of the theory of [Formula: see text] gravity with scalar field which is minimally coupled with the gravity, where [Formula: see text] is the gauss bonnet invariant and [Formula: see text] is the trace of energy–momentum tensor (EMT). We reconstruct the Friedmann equation (FE) and then search for the real value of a particular model [Formula: see text], where [Formula: see text] and [Formula: see text] are real constants. A Gauss–Bonnet system (GBS) for viable cosmolog

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Lohakare, Santosh V., and B. Mishra. "Stability of f(Q, B) Gravity via Dynamical System Approach: A Comprehensive Bayesian Statistical Analysis." Astrophysical Journal 978, no. 1 (2024): 26. https://doi.org/10.3847/1538-4357/ad9602.

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Abstract In this work, we explore the cosmological stability of f(Q, B) gravity using a dynamical system approach, where Q denotes the nonmetricity scalar and B represents the boundary term. We determine the model parameters of f(Q, B) through Bayesian statistical analysis, employing Markov Chain Monte Carlo techniques. This analysis incorporates numerical solutions and observational data from cosmic chronometers, the extended Pantheon+ data set, and baryonic acoustic oscillation measurements. Our findings reveal a stable critical point within the dynamical system of the model, corresponding t

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Pereira, Thiago S., та Davincy T. Pabon. "Extending the ΛCDM model through shear-free anisotropies". Modern Physics Letters A 31, № 21 (2016): 1640009. http://dx.doi.org/10.1142/s0217732316400095.

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If the spacetime metric has anisotropic spatial curvature, one can still expand the universe as if it were isotropic, provided that the energy–momentum tensor satisfies a certain constraint. This leads to the so-called shear-free (SF) metrics, which have the interesting property of violating the cosmological principle while still preserving the isotropy of the cosmic microwave background (CMB) radiation. In this work, we show that SF cosmologies correspond to an attractor solution in the space of models with anisotropic spatial curvature. Through a rigorous definition of linear perturbation th

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Ho, Shu-Yu, Pyungwon Ko, and Dibyendu Nanda. "Light thermal self-interacting dark matter in the shadow of non-standard cosmology." Journal of Cosmology and Astroparticle Physics 2024, no. 04 (2024): 055. http://dx.doi.org/10.1088/1475-7516/2024/04/055.

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Abstract In this paper, we construct a viable model for a GeV scale self-interacting dark matter (DM), where the DM was thermally produced in the early universe. Here, a new vector-like fermion with a dark charge under the U(1)_D gauge symmetry serves as a secluded WIMP DM and it can dominantly annihilate into the light dark gauge boson and singlet scalar through the dark gauge interaction. Also, the self-interaction of DM is induced by the light dark gauge boson via the same gauge interaction. In addition to these particles, we further introduce two Weyl fermions and a doublet scalar, by whic

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Yanar, Hilmi, Mustafa Salti, Oktay Aydogdu, Irfan Acikgoz, and Erol Yasar. "Galactic entropy in extended Kaluza–Klein cosmology." Modern Physics Letters A 31, no. 06 (2016): 1650038. http://dx.doi.org/10.1142/s0217732316500383.

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We use a Kaluza–Klein model with variable cosmological and gravitational terms to discuss the nature of galactic entropy function. For this purpose, we assume a universe filled with dark fluid and consider five-dimensional (5D) field equations using the Gamma law equation. We mainly discuss the validity of the first and generalized second laws of galactic thermodynamics for viable Kaluza–Klein models.

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