In the present work, we have considered tachyonic field, phantom field and scalar field in both interacting and non-interacting situations and investigated the validity of the generalized second law of thermodynamics in a flat FRW universe. We found that in all cases, excepting the phantom field dominated universe, the derivative of the entropy is remaining at negative level and is increasing with the decrease in the redshift.
In this letter, we have considered the universe is filled with the mixture of tachyonic field and scalar or phantom field. If the tachyonic field interacts with scalar or phantom field, the interaction term decays with time and the energy for scalar field is transferred to tachyonic field or the energy for phantom field is transferred to tachyonic field. The tachyonic field and scalar field potentials always decrease, but phantom field potential always increases.
In this work, we have analyzed two scenarios namely, "intermediate" and "logamadiate" scenarios for closed, open and flat anisotropic universe in presence of phantom field, normal tachyonic field and phantom tachyonic field. We have assumed that there is no interaction between the above mentioned dark energy and dark matter. In these two types of the scenarios of the universe, the nature of the scalar fields and corresponding potentials have been investigated. In intermediate scenario, (i) the potential for normal tachyonic field decreases, (ii) the potentials for phantom tachyonic field and p…
Tachyonic scalar field-driven late universe with dust matter content is considered. The cosmic expansion is modeled with power-law and phantom power-law expansion at late time, i.e. $z \lesssim 0.45$. WMAP7 and its combined data are used to constraint the model. The forms of potential and the field solution are different for quintessence and tachyonic cases. Power-law cosmology model (driven by either quintessence or tachyonic field) predicts unmatched equation of state parameter to the observational value, hence the power-law model is excluded for both quintessence and tachyonic field. In the…
In this work, I have considered that the universe is filled with normal matter and phantom field (or tachyonic field). If the universe is filled with scalar field, Ellis et al have shown that emergent scenario is possible only for $k=+1$ i.e. for closed universe and here I have shown that the emergent scenario is possible for closed universe if the universe contains normal tachyonic field. But for phantom field (or tachyonic field), the negative kinetic term can generate the emergent scenario for all values of $k ~(=0,\pm 1)$. From recently developed statefinder parameters, the behaviour of di…
In this paper we discuss the laws of thermodynamics for interacting tachyonic scalar field. The components of the tachyonic scalar field in the universe are taken to exist in the state of non-equilibrium initially, but due to interaction they undergo a transition towards the equilibrium state. We show that the zeroth law of thermodynamics demands interaction among the components of cosmic field. The second law of thermodynamics is governing dynamics in transfer of energy among the three components of the proposed field with local violation of conservation of energy for individual components.
In this work we have investigated the emergent scenario of the universe described by Loop quantum cosmology model, DGP brane model and Kaluza-Klein cosmology. Scalar field along with barotropic fluid as normal matter is considered as the matter content of the universe. In Loop quantum cosmology it is found that the emergent scenario is realized with the imposition of some conditions on the value of the density of normal matter in case of normal and phantom scalar field. This is a surprising result indeed considering the fact that scalar field is the dominating matter component. In case of Tach…
We present a nonparametric form-invariance transformation through which we establish a link between phantom and tachyonic models in flat Friedmann-Robertson-Walker cosmologies.
In this paper, we investigate the phantom energy accretion onto 3D black hole formulated in Einstein-Power-Maxwell theory. We have presented the conditions for critical accretion of phantom energy onto black hole. Further, we discuss the thermodynamics of phantom energy accreting onto black hole and found that first law of thermodynamics is easily satisfied while second law and generalized second law of thermodynamics remain invalid and conditionally valid, respectively. The results for BTZ black hole can be recovered by taking Maxwellian contribution equal to zero.
It was confirmed that the negative modes of the Euclidean section for asymptotically flat black holes reveal the thermodynamic instability of these black holes in the grand canonical ensemble (GCE). These include Schwarzschild, Reissner-Nordström, Kerr, and Kerr-Newman black holes. In this work, we develop the relation between thermodynamic instability in the GCE and tachyonic instability for asymptotically flat black holes, where the latter is the onset for obtaining black holes with scalar hair. This implies that the tachyonic instability of black holes when introducing scalar coupling to th…
The accretion of a phantom fluid with non-zero chemical potential by black holes is discussed with basis on the Generalized Second Law of thermodynamics. For phantom fluids with positive temperature and negative chemical potential we demonstrate that the accretion process is possible, and that the condition guaranteeing the positiveness of the phantom fluid entropy coincides with the one required by Generalized Second Law. In particular, this result provides a complementary confirmation that cosmological phantom fluids do not need to have negative temperatures.
We discuss the thermodynamic properties of the Friedmann-Robertson-Walker universe with dark energy fluids labelled by $ω=p/ρ<-1/3$. Using the integrability condition, we show that the phantom phase of $w<-1$ can still be thermodynamically allowed even when the temperature takes on negative values because in that case, there exists at least a condition of keeping physical values for $p$ and $ρ$
In this paper we are interested to consider mathematical ways to obtain different phenomenological fluids from two-component Tachyonic scalar fields. We consider interaction between components and investigate problem numerically. Statefinder diagnostics and validity of the generalized second law of thermodynamics performed and checked. We suppose that our Universe bounded by Hubble horizon.
The thermodynamic properties of dark energy-dominated universe in the presence of a black hole are investigated in the general case of a varying equation-of-state-parameter $w(a)$. We show that all the thermodynamics quantities are regular at the phantom divide crossing, and particularly the temperature and the entropy of the dark fluid are always positive definite. We also study the accretion process of a phantom fluid by black holes and the conditions required for the validity of the generalized second law of thermodynamics. As a results we obtain a strictly negative chemical potential and a…
In this work we present an analysis of the phantom zone in a causal viscous cosmology from a thermodynamic point of view. In this description we consider a chemical potential and the approach of irreversible processes. We assume a flat universe filled with a single dissipative fluid described by a barotropic equation of state, $p = ωρ$. This model allows to construct a negative chemical potential for the phantom regime but also this construction allows us to have positive definite temperature and entropy.
In this paper, we have studied the accretion of phantom energy on a (2+1)-dimensional stationary Banados-Teitelboim-Zanelli (BTZ) black hole. It has already been shown by Babichev et al that for the accretion of phantom energy onto a Schwarzschild black hole, the mass of black hole would decrease and the rate of change of mass would be dependent on the mass of the black hole. However, in the case of (2+1)-dimensional BTZ black hole, the mass evolution due to phantom accretion is independent of the mass of the black hole and is dependent only on the pressure and density of the phantom energy. W…
We derive an exact wormhole spacetime supported by a phantom scalar field in the context of $f({\sf R})$ gravity. Without specifying the form of the $f({\sf R})$ function, the scalar field self-interacts with a mass term potential that is derived from the scalar equation and the resulting $f({\sf R})$ model is purely supported by the scalar field and it is free of ghosts and avoids the tachyonic instability.
We apply the holographic principle to a flat dark energy dominated Friedmann-Robertson-Walker spacetime filled with a tachyon scalar field with constant equation of state $w=p/ρ$, both for $w>-1$ and $w<-1$. By using a geometrical covariant procedure, which allows the construction of holographic hypersurfaces, we have obtained for each case the position of the preferred screen and have then compared these with those obtained by using the holographic dark energy model with the future event horizon as the infrared cutoff. In the phantom scenario, one of the two obtained holographic screens is pl…
Motivated by some earlier works \cite{pavon,sadjadi} dealing with the study of generalized second law (GSL) of thermodynamics for a system comprising of a Schwarzschild black accreting a test non-self-gravitating fluid namely phantom energy in FRW universe, we extend them when the entropy of horizons of black hole and the cosmological undergo quantum corrections. Two types of such corrections are relevant here including logarithmic and power-law, while both are motivated from different theoretical backgrounds. We obtain general mathematical conditions for the validity of GSL in each case. Furt…
Usually considered highly speculative, tachyons can be treated via straightforward Einsteinian dynamics. Kinetic theory and thermodynamics for a gas of ``dark'' tachyons are readily constructed. Such a gas exhibits density and pressure which, for the dominant constituent of a suitable Friedmann-Robertson-Walker spacetime, can drive cosmic evolution with features both similar to and distinct from those of a standard dark-energy/dark-matter model. Hence, tachyons might bear further consideration as a cosmic dark-matter candidate.
We review recent work and present new examples about the character of singularities in globally and regularly hyperbolic, isotropic universes. These include recent singular relativistic models, tachyonic and phantom universes as well as inflationary cosmologies.
We reconstruct the field potentials in case of (non)phantom fields for different models resulting from parametrization of q(t), a(t) or H(t). In addition we carry out similar procedure for tachyonic field. We also discuss specific form of parametrization for reconstruction of scalar field potential.
Thermodynamic constraints and future singularities in Unimodular Gravity driven by phantom and non-phantom fluids
Universidad de Santiago de Chile（圣地亚哥智利大学）；Center for Inter-disciplinary Research in Astrophysics and Space Exploration (CIRAS), Universidad de Santiago de Chile（圣地亚哥智利大学天体物理与空间探索跨学科研究中心）；Pontificia Universidad Católica de Valparaíso（瓦尔帕莱索天主教大学）；Universidad Veracruzana（韦拉克鲁斯大学）
Teleparallel gravity is an equivalent formulation of general relativity in which instead of the Ricci scalar $R$, one uses the torsion scalar $T$ for the Lagrangian density. Recently teleparallel dark energy has been proposed by Geng et al. in (Geng et al., 2011). They have added quintessence scalar field, allowing also a non-minimal coupling with gravity in the Lagrangian of teleparallel gravity and found that such a non-minimally coupled quintessence theory has a richer structure than the same one in the frame work of general relativity. In the present work we are interested in tachyonic tel…
The thermodynamic properties of dark energy fluids described by an equation of state parameter $ω=p/ρ$ are rediscussed in the context of FRW type geometries. Contrarily to previous claims, it is argued here that the phantom regime $ω<-1$ is not physically possible since that both the temperature and the entropy of every physical fluids must be always positive definite. This means that one cannot appeal to negative temperature in order to save the phantom dark energy hypothesis as has been recently done in the literature. Such a result remains true as long as the chemical potential is zero. How…
We study thermodynamics of the apparent horizon in $F(R)$ gravity. In particular, we demonstrate that a $F(R)$ gravity model with realizing a crossing of the phantom divide can satisfy the second law of thermodynamics in the effective phantom phase as well as non-phantom one.
A non-equilibrium picture of thermodynamics is discussed at the apparent horizon of FRW universe in $f(R,T)$ gravity, where $R$ is the Ricci scalar and $T$ is the trace of the energy-momentum tensor. We take two forms of the energy-momentum tensor of dark components and demonstrate that equilibrium description of thermodynamics is not achievable in both cases. We check the validity of the first and second law of thermodynamics in this scenario. It is shown that the Friedmann equations can be expressed in the form of first law of thermodynamics $T_hdS'_h+T_hd_{\jmath}S'=-dE'+W'dV$, where $d_{\j…
In this paper we show that, analogously to as it occurs for black holes, there exist three well-defined laws for Lorentzian wormhole thermodynamics and that these laws are related with a thermal phantom-like radiation process coming from the wormhole throat. It is argued that the existence of wormholes could be manifested by means such a radiation. These results are obtained by analyzing the Hayward formalism of spherically symmetric solutions containing trapping horizons, the phenomenon of phantom accretion onto wormholes and the development of phantom thermodynamics.
A thermodynamic analysis of the black hole solutions coming from the Einstein-Maxwell-Dilaton theory (EMD) in 4D is done. By consider the canonical and grand-canonical ensemble, we apply standard method as well as a recent method known as Geometrothermodynamics (GTD). We are particularly interested in the characteristics of the so called phantom black hole solutions. We will analyze the thermodynamics of these solutions, the points of phase transition and their extremal limit. Also the thermodynamic stability is analyzed. We obtain a mismatch of the between the results of the GTD method when c…
In the present work we investigated the validity of the generalized second law (GSL) of thermo- dynamics in presence of interaction between DBI-essence and other four candidates of dark energy namely modified Chaplygin gas, hessence, tachyonic field and new agegraphic dark energy. It has been observed that the GSL breaks down in presence of the interactions. However, the event horizon remains to be an increasing function of time.
We use the Legendre invariant formalism of geometrothermodynamics to investigate the geometric properties of the equilibrium space of a spherically symmetric phantom black hole with electric charge and dilaton. We find that at certain points of the equilibrium space, the thermodynamic curvature is characterized by the presence of singularities that are interpreted as phase transitions. We also investigate the phase transition structure by using the standard approach of black hole thermodynamics based upon the analysis of the heat capacity and response functions. We show compatibility between t…
Phantom fields with negative kinetic energy are often plagued by the vacuum quantum instability in the ultraviolet region. We present a Lorentz-violating dark energy model free from this problem and show that the crossing of the cosmological constant boundary w=-1 to the phantom equation of state is realized before reaching a de Sitter attractor. Another interesting feature is a peculiar time-dependence of the effective Newton's constant; the magnitude of this effect is naturally small but may be close to experimental limits. We also derive momentum scales of instabilities at which tachyons or…
In this work, we have considered the power law correction of entropy on the horizon. If the flat FRW Universe is filled with the n components fluid with interactions, the GSL of thermodynamics for apparent and event horizons have been investigated for equilibrium and non-equilibrium cases. If we consider a small perturbation around the de Sitter space-time, the general conditions of the validity of GSL have been found. Also if a phantom dominated Universe has a polelike type scale factor, the validity of GSL has also been analyzed. Further we have obtained constraints on the power-law paramete…
We discuss the generalized second law of thermodynamics in three different systems by taking quantum corrections (logarithmic and power law) to cosmological horizon entropy as well as black hole entropy. Firstly, we consider phantom energy accretion onto the Schwarzschild black hole in the closed FRW universe and investigate validity of the generalized second law of thermodynamics on the apparent and event horizons. In another scenario, we evaluate the critical mass of the Schwarzschild black hole with upper and lower bounds under accretion process due to phantom-like modified generalized chap…
This paper is committed to calculations near a type of future singularity driven by phantom energy. At the singularities considered, the scale factor remains finite but its derivative diverges. The general behavior of barotropic phantom energy producing this singularity is calculated under the assumption that near the singularity such fluid is the dominant contributor. We use the semiclassical formula for renormalized stress tensors of conformally invariant fields in conformally flat spacetimes and analyze the softening/enhancing of the singularity due to quantum vacuum contributions. This dyn…
The main goal of this work is investigation of NADE in the cyclic universe scenario. Since, cyclic universe is explained by a phantom phase ($ω<-1$), it is shown when there is no interaction between matter and dark energy, ADE and NADE do not produce a phantom phase, then can not describe cyclic universe. Therefore, we study interacting models of ADE and NADE in the modified Friedmann equation. We find out that, in the high energy regime, which it is a necessary part of cyclic universe evolution, only NADE can describe this phantom phase era for cyclic universe. Considering deceleration parame…
We study the Vaidya black hole surrounded by the exotic quintessence-like, phantom-like and cosmological constant-like fields by means of entropic considerations. Explicitly, we show that for this thermodynamical system, the requirement for the identification of D-bound and Bekenstein entropy bound can be considered as a thermodynamical criterion by which one can rule out the quintessence-like and phantom-like fields, and prefer the cosmological constant as a viþable cosmological field.
We obtain a new solution of the Einstein-anti-Maxwell theory with cosmological constant, called anti-Reissner-Nordstrom-(A)de Sitter (anti-RN-(A)dS) solution. The basic properties of this solution is reviewed. Its thermodynamics is consistently established, with the extreme cases and phase transitions, where the analysis is performed through two methods, the usual one and that of Geometrothermodynamics . The Geometrothermodynamics analysis does not provide a result in agreement with the usual method or by the specific heat. We establish local and global thermodynamic stabilities of anti-RN-AdS…
We show that to investigate the thermodynamic properties of charged phantom spherically symmetric anti-de-Sitter black holes, it is necessary to consider the cosmological constant as a thermodynamic variable so that the corresponding fundamental equation is a homogeneous function defined on an extended equilibrium space. We explore all the thermodynamic properties of this class of black holes by using the classical physical approach, based upon the analysis of the fundamental equation, and the alternative mathematical approach as proposed in geometrothermodynamics. We show that both approaches…
In standard cosmology, with the evolution of the universe, the matter density and thermodynamic pressure gradually decreases. Also in course of evolution, the matter in the universe obeys (or violates) some restrictions or energy conditions. If the matter distribution obeys strong energy condition (SEC), the universe is in a decelerating phase while violation of SEC indicates an accelerated expansion of the universe. In the period of accelerated expansion the matter may be either of quintessence nature or of phantom nature depending on the fulfilment of the weak energy condition (WEC) or viola…
We consider a non-minimal coupling of a perfect fluid matter system with geometry, which the coupling function is taken to be an arbitrary function of the Ricci scalar. Due to such a coupling, the matter stress tensor is no longer conserved and there is an energy transfer between the two components. By solving the conservation equation and applying the second law of thermodynamics, we show that direction of the energy transfer depends on the equation of state of the matter fluid. In particular, a phantom fluid should loose energy with expansion of the universe. This energy reduction can avoid …
This paper is devoted to some simple approach based on general physics tools to describe the physical properties of a hypothetical particle which can be the source of dark energy in the Universe known as phantom. Phantom is characterized by the fact that it possesses negative momentum and kinetic energy and that it gives large negative pressure which acts as antigravity. We consider phantom harmonic oscillator in comparison to a standard harmonic oscillator. By using the first law of thermodynamics we explain why the energy density of the Universe grows when it is filled with phantom. We also …
In this work we extend previous work on the evolution of a Primordial Black Hole (PBH) to address the presence of a dark energy component with a super-negative equation of state as a background, investigating the competition between the radiation accretion, the Hawking evaporation and the phantom accretion, the latter two causing a decrease on black hole mass. It is found that there is an instant during the matter-dominated era after which the radiation accretion becomes negligible compared to the phantom accretion. The Hawking evaporation may become important again depending on a mass thresho…
The generalized Chaplygin gas, characterized by the equation of state $p=-\mathcal{A}/ρ^α$, has been considered as a model for dark energy due its dark-energy-like evolution at late times. When dissipative processes are taken account, within the framework of the standard Eckart theory of relativistic irreversible thermodynamics, cosmological analytical solutions are found. Using the truncated causal version of the Israel-Stewart formalism, a suitable model was constructed which cross the $w=-1$ barrier. The future-singularities encounter in both approaches are of a new type, not included in th…
