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John D. Barrow - One of the best experts on this subject based on the ideXlab platform.
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dynamics of einstein aether Scalar Field cosmology
European Physical Journal C, 2019Co-Authors: Andronikos Paliathanasis, G Papagiannopoulos, Spyros Basilakos, John D. BarrowAbstract:We study the cosmological evolution of the Field equations in the context of Einstein–Aether cosmology by including a Scalar Field in a spatially flat Friedmann–Lemaitre–Robertson–Walker spacetime. Our analysis is separated into two separate where a pressureless fluid source is included or absent. In particular, we determine the critical points of the Field equations and we study the stability of the specific solutions. The limit of general relativity is fully recovered, while the dynamical system admits de Sitter solutions which can describe the past inflationary era and the future late-time attractor. Results for generic Scalar Field potentials are presented while some numerical behaviours are given for specific potential forms.
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dynamical analysis in Scalar Field cosmology
Physical Review D, 2015Co-Authors: Andronikos Paliathanasis, Spyros Basilakos, Michael Tsamparlis, John D. BarrowAbstract:We give a general method to find exact cosmological solutions for Scalar-Field dark energy in the presence of perfect fluids. We use the existence of invariant transformations for the Wheeler De Witt (WdW) equation. We show that the existence of a point transformation under which the WdW equation is invariant is equivalent to the existence of conservation laws for the Field equations, which indicates the existence of analytical solutions. We extend previous work by providing exact solutions for the Hubble parameter and the effective dark-energy equation of state parameter for cosmologies containing a combination of perfect fluid and a Scalar Field whose self-interaction potential is a power of hyperbolic functions. We find solutions explicity when the perfect fluid is radiation or cold dark matter and determine the effects of non-zero spatial curvature. Using the Planck 2015 data, we determine the evolution of the effective equation of state of the dark energy. Finally, we study the global dynamics using dimensionless variables. We find that if the current cosmological model is Liouville integrable (admits conservation laws) then there is a unique stable point which describes the de-Sitter phase of the universe.
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n body simulations for coupled Scalar Field cosmology
Physical Review D, 2011Co-Authors: John D. BarrowAbstract:We describe in detail the general methodology and numerical implementation of consistent N-body simulations for coupled-Scalar-Field models, including background cosmology and the generation of initial conditions (with the different couplings to different matter species taken into account). We perform fully consistent simulations for a class of coupled-Scalar-Field models with an inverse power-law potential and negative coupling constant, for which the chameleon mechanism does not work. We find that in such cosmological models the Scalar-Field potential plays a negligible role except in the background expansion, and the fifth force that is produced is proportional to gravity in magnitude, justifying the use of a rescaled gravitational constant G in some earlier N-body simulation works for similar models. We then study the effects of the Scalar coupling on the nonlinear matter power spectra and compare with linear perturbation calculations to see the agreement and places where the nonlinear treatment deviates from the linear approximation. We also propose an algorithm to identify gravitationally virialized matter halos, trying to take account of the fact that the virialization itself is also modified by the Scalar-Field coupling. We use the algorithm to measure the mass function and study the properties of dark-matter halos. We find that the more » net effect of the Scalar coupling helps produce more heavy halos in our simulation boxes and suppresses the inner (but not the outer) density profile of halos compared with the {Lambda}CDM prediction, while the suppression weakens as the coupling between the Scalar Field and dark-matter particles increases in strength. « less
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Scalar Field cosmologies
Classical and Quantum Gravity, 1993Co-Authors: John D. Barrow, Paul SaichAbstract:The authors present a class of exact isotropic cosmological models containing perfect fluids and Scalar Fields with nonzero potentials and discuss the conditions under which inflation can occur and when the Scalar Field source dominates the late stages of the expansion of the universe.
Cristian Martinez - One of the best experts on this subject based on the ideXlab platform.
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topological black holes dressed with a conformally coupled Scalar Field and electric charge
Physical Review D, 2006Co-Authors: Cristian Martinez, Ricardo Troncoso, Juan Pablo StaforelliAbstract:Electrically charged solutions for gravity with a conformally coupled Scalar Field are found in four dimensions in the presence of a cosmological constant. If a quartic self-interaction term for the Scalar Field is considered, there is a solution describing an asymptotically locally AdS charged black hole dressed with a Scalar Field that is regular on and outside the event horizon, which is a surface of negative constant curvature. This black hole can have negative mass, which is bounded from below for the extremal case, and its causal structure shows that the solution describes a ``black hole inside a black hole''. The thermodynamics of the nonextremal black hole is analyzed in the grand canonical ensemble. The entropy does not follow the area law, and there is an effective Newton constant which depends on the value of the Scalar Field at the horizon. If the base manifold is locally flat, the solution has no electric charge, and the Scalar Field has a vanishing stress-energy tensor so that it dresses a locally AdS spacetime with a nut at the origin. In the case of vanishing self interaction, the solutions also dress locally AdS spacetimes, and if the base manifold is of negative constant curvature a massless electrically charged hairy black hole is obtained. The thermodynamics of this black hole is also analyzed. It is found that the bounds for the black holes parameters in the conformal frame obtained from requiring the entropy to be positive are mapped into the ones that guarantee cosmic censorship in the Einstein frame.
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exact black hole solution with a minimally coupled Scalar Field
Physical Review D, 2004Co-Authors: Cristian Martinez, Ricardo Troncoso, Jorge ZanelliAbstract:An exact four-dimensional black hole solution of gravity with a minimally coupled self-interacting Scalar Field is reported. The event horizon is a surface of negative constant curvature enclosing the curvature singularity at the origin, and the Scalar Field is regular everywhere outside the origin. This solution is an asymptotically locally anti-deSitter spacetime. The strong energy condition is satisfied on and outside the event horizon. The thermodynamical analysis shows the existence of a critical temperature, below which a black hole in vacuum undergoes a spontaneous dressing up with a nontrivial Scalar Field in a process reminiscent of ferromagnetism.
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Black holes and asymptotics of 2 + 1 gravity coupled to a Scalar Field
Physical Review D, 2002Co-Authors: Marc Henneaux, Cristian Martinez, Ricardo Troncoso, Jorge ZanelliAbstract:We consider $2+1$ gravity minimally coupled to a self-interacting Scalar Field. The case in which the fall-off of the Fields at infinity is slower than that of a localized distribution of matter is analyzed. It is found that the asymptotic symmetry group remains the same as in pure gravity (i.e., the conformal group). The generators of the asymptotic symmetries, however, acquire a contribution from the Scalar Field, but the algebra of the canonical generators possesses the standard central extension. In this context, new massive black hole solutions with a regular Scalar Field are found for a one-parameter family of potentials. These black holes are continuously connected to the standard zero mass black hole.
Jorge Zanelli - One of the best experts on this subject based on the ideXlab platform.
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exact black hole solution with a minimally coupled Scalar Field
Physical Review D, 2004Co-Authors: Cristian Martinez, Ricardo Troncoso, Jorge ZanelliAbstract:An exact four-dimensional black hole solution of gravity with a minimally coupled self-interacting Scalar Field is reported. The event horizon is a surface of negative constant curvature enclosing the curvature singularity at the origin, and the Scalar Field is regular everywhere outside the origin. This solution is an asymptotically locally anti-deSitter spacetime. The strong energy condition is satisfied on and outside the event horizon. The thermodynamical analysis shows the existence of a critical temperature, below which a black hole in vacuum undergoes a spontaneous dressing up with a nontrivial Scalar Field in a process reminiscent of ferromagnetism.
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Black holes and asymptotics of 2 + 1 gravity coupled to a Scalar Field
Physical Review D, 2002Co-Authors: Marc Henneaux, Cristian Martinez, Ricardo Troncoso, Jorge ZanelliAbstract:We consider $2+1$ gravity minimally coupled to a self-interacting Scalar Field. The case in which the fall-off of the Fields at infinity is slower than that of a localized distribution of matter is analyzed. It is found that the asymptotic symmetry group remains the same as in pure gravity (i.e., the conformal group). The generators of the asymptotic symmetries, however, acquire a contribution from the Scalar Field, but the algebra of the canonical generators possesses the standard central extension. In this context, new massive black hole solutions with a regular Scalar Field are found for a one-parameter family of potentials. These black holes are continuously connected to the standard zero mass black hole.
Jiming Chen - One of the best experts on this subject based on the ideXlab platform.
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cooperative and active sensing in mobile sensor networks for Scalar Field mapping
Systems Man and Cybernetics, 2015Co-Authors: Weihua Sheng, Jiming ChenAbstract:Scalar Field mapping has many applications including environmental monitoring, search and rescue, etc. In such applications, there is a need to achieve a certain level of confidence regarding the estimates of the Scalar Field. In this paper, a cooperative and active sensing framework is developed to enable Scalar Field mapping using multiple mobile sensor nodes. The cooperative and active controller is designed via the real-time feedback of the sensing performance to steer the mobile sensors to new locations in order to improve the sensing quality. During the movement of the mobile sensors, the measurements from each sensor node and its neighbors are fused with the corresponding confidences using distributed consensus filters. As a result, an online map of the Scalar Field is built while achieving a certain level of confidence of the estimates. We conducted computer simulations to validate and evaluate our proposed algorithms.
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cooperative and active sensing in mobile sensor networks for Scalar Field mapping
Conference on Automation Science and Engineering, 2013Co-Authors: Weihua Sheng, Jiming ChenAbstract:Scalar Field mapping has many applications including environmental monitoring, search and rescue, etc. In such applications there is a need to achieve a certain level of confidence regarding the estimates at each location. In this paper, a cooperative and active sensing framework is developed to enable Scalar Field mapping using multiple mobile sensor nodes. The cooperative and active controller is designed via the real-time feedback of the sensing performance to steer the mobile sensors to new locations in order to improve the sensing quality. During the movement of the mobile sensors, the measurements from each sensor node and its neighbors are taken and fused with the corresponding confidences using distributed consensus filters. As a result an online map of the Scalar Field is built with a certain level of confidence of the estimates. We conducted computer simulations to validate and evaluate our proposed algorithms.
Darío Núñez - One of the best experts on this subject based on the ideXlab platform.
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The Scalar Field Dark Matter Model: A Braneworld Connection
Lecture Notes in Physics, 2004Co-Authors: Tonatiuh Matos, F. Siddhartha Guzman, L. Arturo Ureña-lópez, Miguel Alcubierre, Ricardo Becerril, Darío NúñezAbstract:This work is a review for the progress of the Scalar Field dark matter (SFDM) hypothesis. Here we outline a possible brane world model justifying the hypothesis of the Scalar Field origin for the dark matter (DM). This model contains two branes, on one of the branes lives the matter of the standard model of particles but on the other one, only spin-0 fundamental interactions are present. In this model these spin-0 Fields are the DM and maybe the dark energy (DE). Thus, DM and DE interact only through the gravitational force with the matter brane. Starting with this hypothesis, we write a Lagrangian where the dark matter is of Scalar origin with a cosh Scalar Field potential. The Scalar Field with a cosh potential behaves exactly in the same way as dust at cosmological scales. In this sense the Scalar Field mimics very well cold dark matter (CDM). The free parameters of the Lagrangian can be fixed using cosmological observations. After fixing all the free parameters of the model, we found that a Scalar Field fluctuation collapses forming objects with a preferred mass of ∼ 10 12 M� . Nevertheless, at galactic scales there exist some strong differences with the CDM paradigm. The Scalar Field contains an effective pression which avoids the collapse of a Scalar Field fluctuation, implying that Scalar Field objects like galaxies contain a flat density profile in the center. This implies that the SFDM paradigm could resolve the cusp density profile problem of galaxies.
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Scalar Field Dark Matter
Exact Solutions and Scalar Fields in Gravity, 1Co-Authors: Tonatiuh Matos, F. Siddhartha Guzman, L. Arturo Ureña-lópez, Darío NúñezAbstract:The main goal of this work is to put the last results of the Scalar Field Dark Matter model of the Universe at cosmological and at galactic level in a work together. We present the complete solution to the 95% Scalar Field cosmological model in which the dark matter is modeled by a Scalar Field Φ with the Scalar potential \( V(\Phi ) = V_o [\cosh (\lambda \sqrt {k_o } \Phi ) - 1] \) and the dark energy is modeled by a Scalar Field Ψ, endowed with the Scalar potential \( \tilde V(\Psi ) = \tilde V_o [\sinh (\alpha \sqrt {k_o } \Psi )]^\beta\). This model has only two free parameters, λ and the equation of state ωψ. The results of the model are: 1) the fine tuning and the cosmic coincidence problems are ameliorated for both dark matter and dark energy and the models agrees with astronomical observations. 2) The model predicts a suppression of the Mass Power Spectrum for small scales having a wave number k>k min,φ, where k min,φ ≃4.5h Mpc −1 for λ≃20.3. This last fact could help to explain the dearth of dwarf galaxies and the smoothness of galaxy core halos. 3) From this, all parameters of the Scalar dark matter potential are completely determined. 4) The dark matter consists of an ultra-light particle, whose mass is m φ ≃1.1×10 −23 eV and all the success of the standard cold dark matter model is recovered. 5) If the scale of renormalization of the model is of order of the Planck Mass, then the Scalar Field Φ can be a reliable model for dark matter in galaxies. 6) The predicted scattering cross section fits the value required for self-interacting dark matter. 7) Studying a spherically symmetric fluctuation of the Scalar Field Φ in cosmos we show that it could be the halo dark matter in galaxies. 8) The local space-time of the fluctuation of the Scalar Field Φ contains a three dimensional space-like hypersurface with surplus of angle. 9) We also present a model for the dark matter in the halos of spiral galaxies, we obtain that 10) the effective energy density goes like 1/(r 2 +K 2) and 11) the resulting circular velocity profile of tests particles is in good agreement with the observed one in spiral galaxies. This implies that a Scalar Field could also be a good candidate as the dark matter of the Universe
