The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Mokhtar Hassaine - One of the best experts on this subject based on the ideXlab platform.
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Regular black holes and gravitational particle-like solutions in generic DHOST theories
2021Co-Authors: Olaf Baake, Mokhtar Hassaine, Christos Charmousis, Miguel SanAbstract:We construct regular, asymptotically flat black holes of higher order scalar tensor (DHOST) theories, which are obtained by making use of a generalized Kerr-Schild solution generating method. The solutions depend on a mass Integration Constant, admit a smooth core of chosen regularity, and generically have an inner and outer event horizon. In particular, below a certain mass threshold, we find massive, horizonless, particle-like solutions. We scan through possible observational signatures ranging from weak to strong gravity and study the thermodynamics of our regular solutions, comparing them, when possible, to General Relativity black holes and their thermodynamic laws.
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Thermodynamics of charged Lifshitz black holes with quadratic corrections
Physical Review D, 2015Co-Authors: Moisés Bravo-gaete, Mokhtar HassaineAbstract:In arbitrary dimension, we consider the Einstein-Maxwell Lagrangian supplemented by the more general quadratic-curvature corrections. For this model, we derive four classes of charged Lifshitz black hole solutions for which the metric function is shown to depend on a unique Integration Constant. The masses of these solutions are computed using the quasilocal formalism based on the relation established between the off-shell ADT and Noether potentials. Among these four solutions, three of them are interpreted as extremal in the sense that their mass vanishes identically. For the last family of solutions, the quasilocal mass and the electric charge both are shown to depend on the Integration Constant. Finally, we verify that the first law of thermodynamics holds for each solution and a Smarr formula is also established for the four solutions.
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Black holes in new massive gravity dressed by a (non)minimally coupled scalar field
Physical Review D, 2014Co-Authors: Francisco Correa, Mokhtar Hassaine, Julio OlivaAbstract:We consider a self-interacting, massive scalar field (non)minimally coupled to new massive gravity in three dimensions. For this model, we first derive a family of black hole solutions depending on a unique Integration Constant and parameterized in terms of the nonminimal coupling parameter. Imposing the absence of naked singularities restricts the parameters in such a way that the field vanishes at infinity and fixes the metric to be asymptotically AdS. Within this family of solutions it is possible to find a black hole supported by a minimally coupled scalar field and therefore the existence of these solutions is not inherent to the presence of the nonminimal coupling. The Wald formula for the entropy, being proportional to the lapse function evaluated at the horizon, yields a zero entropy in spite of the fact that the solution has a non zero temperature. As a consequence, the unique Integration Constant may be interpreted as a sort of gravitational hair. As in the source free case, we show that the same field equations admit as well asymptotically Lifshitz black hole solutions in a different region of the space of parameters. These Lifshitz solutions are divided in three families for which all the parameters entering in the action may be expressed in term of the dynamical exponent.
Dimitrios Tsimpis - One of the best experts on this subject based on the ideXlab platform.
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Non-singular deformations of singular compactifications, the cosmological Constant and the hierarchy problem
Classical and Quantum Gravity, 2000Co-Authors: Alan Chodos, Erich Poppitz, Dimitrios TsimpisAbstract:We consider deformations of the singular `global cosmic string' compactifications, known to naturally generate exponentially large scales. The deformations are obtained by allowing a Constant-curvature metric on the brane and correspond to a choice of Integration Constant. We show that there exists a unique value of the Integration Constant that gives rise to a non-singular solution. The metric on the brane is dS4 with an exponentially small value of the expansion parameter. We derive an upper bound on the brane cosmological Constant. We find and investigate more general singular solutions - `dilatonic global string' compactifications - and show that they can have non-singular deformations. We give an embedding of these solutions in type IIB supergravity. There is only one class of supersymmetry-preserving singular dilatonic solutions. We show that they do not have non-singular deformations of the type considered here.
Konstantinos N Moutsopoulos - One of the best experts on this subject based on the ideXlab platform.
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exact and approximate analytical solutions for unsteady fully developed turbulent flow in porous media and fractures for time dependent boundary conditions
Journal of Hydrology, 2009Co-Authors: Konstantinos N MoutsopoulosAbstract:Summary The problem of recharge of water to an initially dry, semi-infinite aquifer is investigated, where the occurrence of turbulent flow is considered. By applying a similarity transform an analytical solution is obtained by the Adomian’s decomposition method. The Integration Constant of the power series is determined by examining the mathematical structure of the solution at the downstream part of the front. It is demonstrated that for two specific cases the Adomian’s series are reduced to exact solutions. The analytical solutions above, derived on the basis of fully developed turbulent flow regime are compared to the water table profile computed on the basis of the Forchheimer equation. Four specific cases in real world coordinated are investigated: (a) the propagation of a linear traveling wave, (b) injection of fluid at Constant flow-rate in a fracture or aquifer, (c) flow induced by a sudden raise of the piezometric head, (d) redistribution of a finite quantity of water in a porous medium. Potential applications of the above cited results are water body–aquifers interaction, and exploitation of hot dry rocks.
R. Hilfer - One of the best experts on this subject based on the ideXlab platform.
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Traveling Wave Solutions in a Generalized Theory for Macroscopic Capillarity
Transport in Porous Media, 2013Co-Authors: O. Hönig, F. Doster, R. HilferAbstract:One-dimensional traveling wave solutions for imbibition processes into a homogeneous porous medium are found within a recent generalized theory of macroscopic capillarity. The generalized theory is based on the hydrodynamic differences between percolating and nonpercolating fluid parts. The traveling wave solutions are obtained using a dynamical systems approach. An exhaustive study of all smooth traveling wave solutions for primary and secondary imbibition processes is reported here. It is made possible by introducing two novel methods of reduced graphical representation. In the first method the Integration Constant of the dynamical system is related graphically to the boundary data and the wave velocity. In the second representation the wave velocity is plotted as a function of the boundary data. Each of these two graphical representations provides an exhaustive overview over all one-dimensional and smooth solutions of traveling wave type, that can arise in primary and secondary imbibition. Analogous representations are possible for other systems, solution classes, and processes.
Alan Chodos - One of the best experts on this subject based on the ideXlab platform.
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Non-singular deformations of singular compactifications, the cosmological Constant and the hierarchy problem
Classical and Quantum Gravity, 2000Co-Authors: Alan Chodos, Erich Poppitz, Dimitrios TsimpisAbstract:We consider deformations of the singular `global cosmic string' compactifications, known to naturally generate exponentially large scales. The deformations are obtained by allowing a Constant-curvature metric on the brane and correspond to a choice of Integration Constant. We show that there exists a unique value of the Integration Constant that gives rise to a non-singular solution. The metric on the brane is dS4 with an exponentially small value of the expansion parameter. We derive an upper bound on the brane cosmological Constant. We find and investigate more general singular solutions - `dilatonic global string' compactifications - and show that they can have non-singular deformations. We give an embedding of these solutions in type IIB supergravity. There is only one class of supersymmetry-preserving singular dilatonic solutions. We show that they do not have non-singular deformations of the type considered here.