Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation o... more Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation of state. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension λ of the RS-II model. It is interesting to see that upto a certain value of energy density ρ satisfying ρ/λ < 1, weak energy condition is violated and universe super-accelerates. But as ρ increases more, only strong energy condition is violated and universe accelerates.
International Journal of Modern Physics D, Nov 1, 2019
In the present work, we compare the thermodynamical viability of two types of noncanonical scalar... more In the present work, we compare the thermodynamical viability of two types of noncanonical scalar field models with kinetic corrections: the square kinetic and square root kinetic corrections. In modern cosmology, the generalised second law of thermodynamics (GSLT) plays an important role in deciding thermodynamical compliance of a model as one cannot consider a model to be viable if it fails to respect GSLT. Hence, for comparing thermodynamical viability, we examine the validity of GSLT for these two models. For this purpose, by employing the Unified first law (UFL), we calculate the total entropy of these two models in apparent and event horizons. The validity of GSLT is then examined from the autonomous systems as the original expressions of total entropy are very complicated. Although, at the background level, both models give interesting cosmological dynamics, however, thermodynamically we found that the square kinetic correction is more realistic as compared to the square root kinetic correction. More precisely, the GSLT holds for the square kinetic correction throughout the evolutionary history except only during the radiation epoch where the scalar field may not represent a true description of the matter content. On the other hand, the square root kinetic model fails to satisfy the GSLT in major cosmological eras.
In recent past, Hawking temperature has been modified for the validity of thermodynamical laws at... more In recent past, Hawking temperature has been modified for the validity of thermodynamical laws at the event horizon in general relativity context. This lead to the introduction of modified Hawking temperature and it has been found that the modified Hawking temperature is more realistic on the event horizon. With this motivation, here we investigate the thermodynamical consistency of scalar-tensor gravity based models by examining the validity of the generalized second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) at the event horizon. In order to attain our goal, we consider a spatially flat Friedman-Robertson-Walker Universe filled with ordinary matter and the boundary of the Universe bounded by the event horizon that is in thermal equilibrium with modified Hawking temperature. Next, we calculate the general expressions for the GSLT and TE using modified Hawking temperature in the context of the more general action of scalar-tensor gravity where there is a nonminimally coupling between the scalar field and matter Lagrangian (as the chameleon field). From the general expression of GSLT, we find that the null energy condition must hold for a viable scalar-tensor model of the Universe dominated by a perfect fluid. Furthermore, in order to better understand these complicated general expressions of GSLT and TE, we explore the validity of the GSLT and TE for two viable models of scalar-tensor gravity namely Brans-Dicke gravity with a self-interacting potential and Chameleon gravity at the event horizon using special cosmological solutions. Finally, some graphical representation of the GSLT and TE have been presented. From the graphical analysis, we found that the power-law forms of the scale factor and scalar field is much favourable for the study of universal thermodynamics as compared to other choices of the scalar field and the analytic function. Keywords Scalar-tensor gravity • Generalized second law of thermodynamics • Thermodynamical equilibrium • Modified Hawking temperature • Event horizon B Jibitesh Dutta
International Journal of Theoretical Physics, May 25, 2016
The present work deals with four alternative formulation of Bekenstein system on event horizon in... more The present work deals with four alternative formulation of Bekenstein system on event horizon in f (R) gravity. While thermodynamical laws holds in universe bounded by apparent horizon, these laws break down on event horizon. With alternative formulation of thermodynamical parameters (temperature and entropy), thermodynamical laws hold on event horizon in Einstein Gravity. With this motivation, we extend the idea of generalised Hawking temperature and modified Bekenstein entropy in homogeneous and isotropic model of universe on event horizon and examine whether thermodynamical laws hold in f(R) gravity. Specifically, we examine and compare validity of generalised second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) in four alternative modified Bekenstein scenarios. As Dark energy is a possible dominant candidate for matter in the univerese and Holographic Dark Energy (HDE) can give effective description of f(R) gravity, so matter in the universe is taken as in the form interacting HDE. In order to understand the complicated expressions, finally the above laws are examined from graphical representation using three Planck data sets and it is found that generalised/modified Hawking temperature has a crucial role in making perfect thermodynamical system.
Here we formulate scenario of emergent universe from particle creation mechanism in spatially fla... more Here we formulate scenario of emergent universe from particle creation mechanism in spatially flat braneworld models. We consider an isotropic and homogeneous universe in Braneworld cosmology and universe is considered as a non-equilibrium thermodynamical system with dissipation due to particle creation mechanism. Assuming the particle creation rate as a function of the Hubble parameter , we formulate emergent scenario in RS2 and DGP models of Braneworld.
We apply the formalism of dynamical system analysis to investigate the evolution of interacting d... more We apply the formalism of dynamical system analysis to investigate the evolution of interacting dark energy scenarios at the background and perturbation levels in a unified way. Since the resulting dynamical system contains the extra perturbation variable related to the matter overdensity, the critical points of the background analysis split, corresponding to different behavior of matter perturbations, and hence to stability properties. From the combined analysis, we find critical points that describe the non-accelerating matter-dominated epoch with the correct growth of matter structure, and the fact that they are saddle provides the natural exit from this phase. Furthermore, we find stable attractors at late times corresponding to a dark energy-dominated accelerated solution with constant matter perturbations, as required by observations. Thus, interacting cosmology can describe the matter and dark energy epochs correctly, both at the background and perturbation levels, which reveals the capabilities of the interaction.
International Journal of Modern Physics D, May 1, 2009
Here, cosmology of the late and future universe is obtained from f (R)− gravity with non-linear c... more Here, cosmology of the late and future universe is obtained from f (R)− gravity with non-linear curvature terms R 2 and R 3 (R being the Ricci scalar curvature). It is different from f (R)−dark energy models [6] where non-linear curvature terms are taken as gravitational alternative of dark energy. In the present model, neither linear nor non-linear curvature terms are taken as dark energy. Rather, dark energy terms are induced by curvature terms in the Friedmann equation derived from f (R)−gravitational equations. It has advantage over f (R)−dark energy models in the sense that the present model satisfies WMAP results and expands as ∼ t 2/3 during matter dominance. So, it does not have problems due to which f (R)−dark energy models are criticised in [7]. Curvature-induced dark energy, obtained here, mimics phantom. Different phases of this model, including acceleration and deceleration during phantom phase, are investigated here. It is found 1 2 S.K.SRIVASTAVA that expansion of the universe will stop at the age (3.87t 0 + 694.4)kyr (t 0 being the present age of the universe) and, after this epoch, it will contract and collapse by the time (336.87t 0 + 694.4)kyr. Further, it is shown that universe will escape predicted collapse (obtained using classical mechanics) on making quantum gravity corrections relevant near collapse time due to extremely high energy density and large curvature analogous to the state of very early universe. Interestingly, cosmological constant is also induced here, which is extremely small in classical domain, but very high in the quantum domain.
In the evolution of late universe, the main source of matter are Dark energy and Dark matter. The... more In the evolution of late universe, the main source of matter are Dark energy and Dark matter. They are indirectly detected only through their gravitational manifestations. So the possibility of interaction with each other without violating observational restrictions is not ruled out. With this motivation, we investigate the dynamics of DGP braneworld where source of dark energy is a scalar field and it interacts with matter source. Since observation favours phantom case more, we have also studied the dynamics of interacting phantom scalar field. In non interacting DGP braneworld there are no late time accelerated scaling attractors and hence cannot alleviate Coincidence problem. In this paper, we shall show that it is possible to get late time accelerated scaling solutions. The phase space is studied by taking two categories of potentials (Exponential and Non exponential functions). The stability of critical points are examined by taking two specific interactions. The first interaction gives late time accelerated scaling solution for phantom field only under exponential potential, while for second interaction we do not get any scaling solution. Furthermore, we have shown that this scaling solution is also classically stable.
International Journal of Modern Physics D, Feb 1, 2009
Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation o... more Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation of state. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension λ of the RS-II model. It is interesting to see that upto a certain value of energy density ρ satisfying ρ/λ < 1, weak energy condition is violated and universe super-accelerates. But as ρ increases more, only strong energy condition is violated and universe accelerates.
We extend the investigation of cosmological dynamics of the general non-canonical scalar field mo... more We extend the investigation of cosmological dynamics of the general non-canonical scalar field models by dynamical system techniques for a broad class of potentials and coupling functions. In other words, we do not restrict the analysis to exponential or power-law potentials and coupling functions. This type of investigation helps in understanding the general properties of a class of cosmological models. In order to better understand the phase space of the models, we investigate the various special cases and discuss the stability and viability issues. Performing a detailed stability analysis, we show that it is possible to describe the cosmic history of the universe at the background level namely the early radiation dominated era, intermediate matter dominated era and the late time dark energy domination. Moreover, we find that we can identify a broad class of potentials and coupling functions for which it is possible to get an appealing unified description of dark matter and dark energy. The results obtained here, therefore, enlarge the previous analyses wherein only a specific potential and coupling functions describe the unification of dark sectors. Further, we also observe that a specific scenario can also possibly explain the phenomenon of slow-roll inflationary exit.
In this work we present the cosmological dynamics of interacting dark energy models in the framew... more In this work we present the cosmological dynamics of interacting dark energy models in the framework of particle creation mechanism. The particle creation mechanism presented here describes the true non equilibrium thermodynamics of the universe. In spatially flat Friedmann-Lemaître-Robertson-Walker universe considered here, the dissipative bulk viscous pressure is due to the non conservation of particle number. For simplicity, we assume that the creation of perfect fluid particles to be isentropic (adiabatic) and consequently the viscous pressure obeys a linear relationship with particle creation rate. Due to complicated nature of the Einstein's field equations, dynamical systems analysis has been performed to understand deeply about the cosmological dynamics. We have found some interesting cosmological scenarios like late-time evolution of universe dominated by dark energy which could mimic quintessence, cosmological constant or phantom field through a dark matter dominated era. We also obtained a possibility of crossing the phantom divide line which is favored by observations.
Rastall gravity theory shows notable features consistent with physical observations in comparison... more Rastall gravity theory shows notable features consistent with physical observations in comparison to the standard Einstein theory. Recently, there has been a debate about the equivalence of Rastall gravity and general relativity. Motivated by this open issue, in the present work, we attempt to shed some light on this debate by analyzing the evolution of the Rastall based cosmological model at the background as well as perturbation level. Employing the dynamical system techniques, we found that at late times, the dynamics of the model resembles the ΛCDM model at the background level irrespective of the choice of Rastall's parameter. However, at the perturbation level, we found that the evolution of the growth index heavily depends on the Rastall's parameter and displays a significant deviation from the ΛCDM model.
The present work deals with the dynamical system investigation of interacting dark energy models ... more The present work deals with the dynamical system investigation of interacting dark energy models (quintessence and phantom) in the framework of Loop Quantum Cosmology by taking into account a broad class of self-interacting scalar field potentials. The main reason for studying potentials beyond the exponential type is to obtain additional critical points which can yield more interesting cosmological solutions. The stability of critical points and the asymptotic behavior of the phase space are analyzed using dynamical system tools and numerical techniques. We study two class of interacting dark energy models and consider two specific potentials as examples: the hyperbolic potential and the inverse power-law potential. We found a rich and interesting phenomenology including the avoidance of big rip singularities due to loop quantum effects, smooth and non-linear transitions from matter domination to dark energy domination and finite periods of phantom domination with dynamical crossing of the phantom barrier.
Journal of Cosmology and Astroparticle Physics, Jan 22, 2018
We consider scalar field models of dark energy interacting with dark matter through a coupling pr... more We consider scalar field models of dark energy interacting with dark matter through a coupling proportional to the contraction of the four-derivative of the scalar field with the four-velocity of the dark matter fluid. The coupling is realized at the Lagrangian level employing the formalism of Scalar-Fluid theories, which use a consistent Lagrangian approach for relativistic fluid to describe dark matter. This framework produces fully covariant field equations, from which we can derive unequivocal cosmological equations at both background and linear perturbations levels. The background evolution is analyzed in detail applying dynamical systems techniques, which allow us to find the complete asymptotic behavior of the universe given any set of model parameters and initial conditions. Furthermore we study linear cosmological perturbations investigating the growth of cosmic structures within the quasi-static approximation. We find that these interacting dark energy models give rise to interesting phenomenological dynamics, including late-time transitions from dark matter to dark energy domination, matter and accelerated scaling solutions and dynamical crossing of the phantom barrier. Moreover we obtain possible deviations from standard ΛCDM behavior at the linear perturbations level, which have an impact on the dynamics of structure formation and might provide characteristic observational signatures.
We expand the dynamical systems investigation of cosmological scalar fields characterised by kine... more We expand the dynamical systems investigation of cosmological scalar fields characterised by kinetic corrections presented in [N. Tamanini, Phys. Rev. D 89 (2014) 083521]. In particular we do not restrict the analysis to exponential potentials only, but we consider arbitrary scalar field potentials and derive general results regarding the corresponding cosmological dynamics. Two specific potentials are then used as examples to show how these models can be employed not only to describe dark energy, but also to achieve dynamical crossing of the phantom barrier at late times. Stability and viability issues at the classical level are also discussed.
Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation o... more Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation of state. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension λ of the RS-II model. It is interesting to see that upto a certain value of energy density ρ satisfying ρ/λ < 1, weak energy condition is violated and universe super-accelerates. But as ρ increases more, only strong energy condition is violated and universe accelerates.
International Journal of Modern Physics D, Nov 1, 2019
In the present work, we compare the thermodynamical viability of two types of noncanonical scalar... more In the present work, we compare the thermodynamical viability of two types of noncanonical scalar field models with kinetic corrections: the square kinetic and square root kinetic corrections. In modern cosmology, the generalised second law of thermodynamics (GSLT) plays an important role in deciding thermodynamical compliance of a model as one cannot consider a model to be viable if it fails to respect GSLT. Hence, for comparing thermodynamical viability, we examine the validity of GSLT for these two models. For this purpose, by employing the Unified first law (UFL), we calculate the total entropy of these two models in apparent and event horizons. The validity of GSLT is then examined from the autonomous systems as the original expressions of total entropy are very complicated. Although, at the background level, both models give interesting cosmological dynamics, however, thermodynamically we found that the square kinetic correction is more realistic as compared to the square root kinetic correction. More precisely, the GSLT holds for the square kinetic correction throughout the evolutionary history except only during the radiation epoch where the scalar field may not represent a true description of the matter content. On the other hand, the square root kinetic model fails to satisfy the GSLT in major cosmological eras.
In recent past, Hawking temperature has been modified for the validity of thermodynamical laws at... more In recent past, Hawking temperature has been modified for the validity of thermodynamical laws at the event horizon in general relativity context. This lead to the introduction of modified Hawking temperature and it has been found that the modified Hawking temperature is more realistic on the event horizon. With this motivation, here we investigate the thermodynamical consistency of scalar-tensor gravity based models by examining the validity of the generalized second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) at the event horizon. In order to attain our goal, we consider a spatially flat Friedman-Robertson-Walker Universe filled with ordinary matter and the boundary of the Universe bounded by the event horizon that is in thermal equilibrium with modified Hawking temperature. Next, we calculate the general expressions for the GSLT and TE using modified Hawking temperature in the context of the more general action of scalar-tensor gravity where there is a nonminimally coupling between the scalar field and matter Lagrangian (as the chameleon field). From the general expression of GSLT, we find that the null energy condition must hold for a viable scalar-tensor model of the Universe dominated by a perfect fluid. Furthermore, in order to better understand these complicated general expressions of GSLT and TE, we explore the validity of the GSLT and TE for two viable models of scalar-tensor gravity namely Brans-Dicke gravity with a self-interacting potential and Chameleon gravity at the event horizon using special cosmological solutions. Finally, some graphical representation of the GSLT and TE have been presented. From the graphical analysis, we found that the power-law forms of the scale factor and scalar field is much favourable for the study of universal thermodynamics as compared to other choices of the scalar field and the analytic function. Keywords Scalar-tensor gravity • Generalized second law of thermodynamics • Thermodynamical equilibrium • Modified Hawking temperature • Event horizon B Jibitesh Dutta
International Journal of Theoretical Physics, May 25, 2016
The present work deals with four alternative formulation of Bekenstein system on event horizon in... more The present work deals with four alternative formulation of Bekenstein system on event horizon in f (R) gravity. While thermodynamical laws holds in universe bounded by apparent horizon, these laws break down on event horizon. With alternative formulation of thermodynamical parameters (temperature and entropy), thermodynamical laws hold on event horizon in Einstein Gravity. With this motivation, we extend the idea of generalised Hawking temperature and modified Bekenstein entropy in homogeneous and isotropic model of universe on event horizon and examine whether thermodynamical laws hold in f(R) gravity. Specifically, we examine and compare validity of generalised second law of thermodynamics (GSLT) and thermodynamical equilibrium (TE) in four alternative modified Bekenstein scenarios. As Dark energy is a possible dominant candidate for matter in the univerese and Holographic Dark Energy (HDE) can give effective description of f(R) gravity, so matter in the universe is taken as in the form interacting HDE. In order to understand the complicated expressions, finally the above laws are examined from graphical representation using three Planck data sets and it is found that generalised/modified Hawking temperature has a crucial role in making perfect thermodynamical system.
Here we formulate scenario of emergent universe from particle creation mechanism in spatially fla... more Here we formulate scenario of emergent universe from particle creation mechanism in spatially flat braneworld models. We consider an isotropic and homogeneous universe in Braneworld cosmology and universe is considered as a non-equilibrium thermodynamical system with dissipation due to particle creation mechanism. Assuming the particle creation rate as a function of the Hubble parameter , we formulate emergent scenario in RS2 and DGP models of Braneworld.
We apply the formalism of dynamical system analysis to investigate the evolution of interacting d... more We apply the formalism of dynamical system analysis to investigate the evolution of interacting dark energy scenarios at the background and perturbation levels in a unified way. Since the resulting dynamical system contains the extra perturbation variable related to the matter overdensity, the critical points of the background analysis split, corresponding to different behavior of matter perturbations, and hence to stability properties. From the combined analysis, we find critical points that describe the non-accelerating matter-dominated epoch with the correct growth of matter structure, and the fact that they are saddle provides the natural exit from this phase. Furthermore, we find stable attractors at late times corresponding to a dark energy-dominated accelerated solution with constant matter perturbations, as required by observations. Thus, interacting cosmology can describe the matter and dark energy epochs correctly, both at the background and perturbation levels, which reveals the capabilities of the interaction.
International Journal of Modern Physics D, May 1, 2009
Here, cosmology of the late and future universe is obtained from f (R)− gravity with non-linear c... more Here, cosmology of the late and future universe is obtained from f (R)− gravity with non-linear curvature terms R 2 and R 3 (R being the Ricci scalar curvature). It is different from f (R)−dark energy models [6] where non-linear curvature terms are taken as gravitational alternative of dark energy. In the present model, neither linear nor non-linear curvature terms are taken as dark energy. Rather, dark energy terms are induced by curvature terms in the Friedmann equation derived from f (R)−gravitational equations. It has advantage over f (R)−dark energy models in the sense that the present model satisfies WMAP results and expands as ∼ t 2/3 during matter dominance. So, it does not have problems due to which f (R)−dark energy models are criticised in [7]. Curvature-induced dark energy, obtained here, mimics phantom. Different phases of this model, including acceleration and deceleration during phantom phase, are investigated here. It is found 1 2 S.K.SRIVASTAVA that expansion of the universe will stop at the age (3.87t 0 + 694.4)kyr (t 0 being the present age of the universe) and, after this epoch, it will contract and collapse by the time (336.87t 0 + 694.4)kyr. Further, it is shown that universe will escape predicted collapse (obtained using classical mechanics) on making quantum gravity corrections relevant near collapse time due to extremely high energy density and large curvature analogous to the state of very early universe. Interestingly, cosmological constant is also induced here, which is extremely small in classical domain, but very high in the quantum domain.
In the evolution of late universe, the main source of matter are Dark energy and Dark matter. The... more In the evolution of late universe, the main source of matter are Dark energy and Dark matter. They are indirectly detected only through their gravitational manifestations. So the possibility of interaction with each other without violating observational restrictions is not ruled out. With this motivation, we investigate the dynamics of DGP braneworld where source of dark energy is a scalar field and it interacts with matter source. Since observation favours phantom case more, we have also studied the dynamics of interacting phantom scalar field. In non interacting DGP braneworld there are no late time accelerated scaling attractors and hence cannot alleviate Coincidence problem. In this paper, we shall show that it is possible to get late time accelerated scaling solutions. The phase space is studied by taking two categories of potentials (Exponential and Non exponential functions). The stability of critical points are examined by taking two specific interactions. The first interaction gives late time accelerated scaling solution for phantom field only under exponential potential, while for second interaction we do not get any scaling solution. Furthermore, we have shown that this scaling solution is also classically stable.
International Journal of Modern Physics D, Feb 1, 2009
Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation o... more Here, RS-II model of brane-gravity is considered for phantom universe using non-linear equation of state. Phantom fluid is known to violate the weak energy condition. In this paper, it is found that this characteristic of phantom energy is affected drastically by the negative brane-tension λ of the RS-II model. It is interesting to see that upto a certain value of energy density ρ satisfying ρ/λ < 1, weak energy condition is violated and universe super-accelerates. But as ρ increases more, only strong energy condition is violated and universe accelerates.
We extend the investigation of cosmological dynamics of the general non-canonical scalar field mo... more We extend the investigation of cosmological dynamics of the general non-canonical scalar field models by dynamical system techniques for a broad class of potentials and coupling functions. In other words, we do not restrict the analysis to exponential or power-law potentials and coupling functions. This type of investigation helps in understanding the general properties of a class of cosmological models. In order to better understand the phase space of the models, we investigate the various special cases and discuss the stability and viability issues. Performing a detailed stability analysis, we show that it is possible to describe the cosmic history of the universe at the background level namely the early radiation dominated era, intermediate matter dominated era and the late time dark energy domination. Moreover, we find that we can identify a broad class of potentials and coupling functions for which it is possible to get an appealing unified description of dark matter and dark energy. The results obtained here, therefore, enlarge the previous analyses wherein only a specific potential and coupling functions describe the unification of dark sectors. Further, we also observe that a specific scenario can also possibly explain the phenomenon of slow-roll inflationary exit.
In this work we present the cosmological dynamics of interacting dark energy models in the framew... more In this work we present the cosmological dynamics of interacting dark energy models in the framework of particle creation mechanism. The particle creation mechanism presented here describes the true non equilibrium thermodynamics of the universe. In spatially flat Friedmann-Lemaître-Robertson-Walker universe considered here, the dissipative bulk viscous pressure is due to the non conservation of particle number. For simplicity, we assume that the creation of perfect fluid particles to be isentropic (adiabatic) and consequently the viscous pressure obeys a linear relationship with particle creation rate. Due to complicated nature of the Einstein's field equations, dynamical systems analysis has been performed to understand deeply about the cosmological dynamics. We have found some interesting cosmological scenarios like late-time evolution of universe dominated by dark energy which could mimic quintessence, cosmological constant or phantom field through a dark matter dominated era. We also obtained a possibility of crossing the phantom divide line which is favored by observations.
Rastall gravity theory shows notable features consistent with physical observations in comparison... more Rastall gravity theory shows notable features consistent with physical observations in comparison to the standard Einstein theory. Recently, there has been a debate about the equivalence of Rastall gravity and general relativity. Motivated by this open issue, in the present work, we attempt to shed some light on this debate by analyzing the evolution of the Rastall based cosmological model at the background as well as perturbation level. Employing the dynamical system techniques, we found that at late times, the dynamics of the model resembles the ΛCDM model at the background level irrespective of the choice of Rastall's parameter. However, at the perturbation level, we found that the evolution of the growth index heavily depends on the Rastall's parameter and displays a significant deviation from the ΛCDM model.
The present work deals with the dynamical system investigation of interacting dark energy models ... more The present work deals with the dynamical system investigation of interacting dark energy models (quintessence and phantom) in the framework of Loop Quantum Cosmology by taking into account a broad class of self-interacting scalar field potentials. The main reason for studying potentials beyond the exponential type is to obtain additional critical points which can yield more interesting cosmological solutions. The stability of critical points and the asymptotic behavior of the phase space are analyzed using dynamical system tools and numerical techniques. We study two class of interacting dark energy models and consider two specific potentials as examples: the hyperbolic potential and the inverse power-law potential. We found a rich and interesting phenomenology including the avoidance of big rip singularities due to loop quantum effects, smooth and non-linear transitions from matter domination to dark energy domination and finite periods of phantom domination with dynamical crossing of the phantom barrier.
Journal of Cosmology and Astroparticle Physics, Jan 22, 2018
We consider scalar field models of dark energy interacting with dark matter through a coupling pr... more We consider scalar field models of dark energy interacting with dark matter through a coupling proportional to the contraction of the four-derivative of the scalar field with the four-velocity of the dark matter fluid. The coupling is realized at the Lagrangian level employing the formalism of Scalar-Fluid theories, which use a consistent Lagrangian approach for relativistic fluid to describe dark matter. This framework produces fully covariant field equations, from which we can derive unequivocal cosmological equations at both background and linear perturbations levels. The background evolution is analyzed in detail applying dynamical systems techniques, which allow us to find the complete asymptotic behavior of the universe given any set of model parameters and initial conditions. Furthermore we study linear cosmological perturbations investigating the growth of cosmic structures within the quasi-static approximation. We find that these interacting dark energy models give rise to interesting phenomenological dynamics, including late-time transitions from dark matter to dark energy domination, matter and accelerated scaling solutions and dynamical crossing of the phantom barrier. Moreover we obtain possible deviations from standard ΛCDM behavior at the linear perturbations level, which have an impact on the dynamics of structure formation and might provide characteristic observational signatures.
We expand the dynamical systems investigation of cosmological scalar fields characterised by kine... more We expand the dynamical systems investigation of cosmological scalar fields characterised by kinetic corrections presented in [N. Tamanini, Phys. Rev. D 89 (2014) 083521]. In particular we do not restrict the analysis to exponential potentials only, but we consider arbitrary scalar field potentials and derive general results regarding the corresponding cosmological dynamics. Two specific potentials are then used as examples to show how these models can be employed not only to describe dark energy, but also to achieve dynamical crossing of the phantom barrier at late times. Stability and viability issues at the classical level are also discussed.
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Papers by JIbitesh Dutta