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We study some aspects of a class of non-AdS holography where the 3d bulk gravity is given by Generalized Minimal Massive Gravity (GMMG). We consider the spacelike warped $AdS_3$ ($WAdS_3$) black hole solution of this model where the 2d dual boundary theory is the warped conformal field theory (WFCT). The charge algebra of the isometries in the bulk and the charge algebra of the vacuum symmetries at the boundary are compatible and this is an evidence for the duality conjecture. Further evidence for this duality is the equality of entanglement entropy and modular Hamiltonian on both sides of the duality. So we consider the modular Hamiltonian for the single interval at the boundary in associated to the modular flow generators of the vacuum. We calculate the gravitational charge in associated to the asymptotic Killing vectors that preserve the metric boundary conditions. Assuming the first law of the entanglement entropy to be true, we introduce the matching conditions between the variables in two side of the duality and we find equality of the modular Hamiltonian variations and the gravitational charge variations in two sides of the duality. According to the results of the present paper we can say with more sure that the dual theory of the warped $AdS3$ black hole solution of GMMG is a Warped CFT., 23 pages. Accepted for publication in EPJC

In this paper, we study a constant-roll inflationary model in the context of brane-world cosmology caused by a quintessence scalar field for warm inflation with a constant dissipative parameter [Formula: see text]. We determine the analytical solution for the Friedmann equation coupled to the equation of motion of the scalar field. The evolution of the primordial scalar and tensor perturbations is also studied using the modified Langevin equation. To check the viability of the model, we use numerical approaches and plot some figures. Our results for the scalar spectral index and the tensor-to-scalar ratio show good consistency with observations.

In this work, we investigate the near horizon and asymptotic symmetries of static and rotating hairy$-$AdS black hole in the framework of general minimal massive gravity. We obtain energy, angular momentum and entropy of the solutions. Then we show that our results for these quantities are consistent with the first law of black hole thermodynamics. By considering the near horizon geometry of black hole, we find near horizon conserved charges and their algebra. By writing the algebra of conserved charges in terms of Fourier modes we have obtained the conserved charges in terms of zero modes., Comment: 14 pages. V2: 18 pages, matches the published version

We study the generalized minimal massive gravity (GMMG) in Compere, Song and Strominger boundary conditions employing a semi-product of a Virasoro and a $\hat{u}(1)$ Kac-Moody current algebras as the asymptotic symmetry algebra. We calculate the entropy of BTZ black holes via the degeneracy of states belonging to a Warped-CFT. We compute the linearized energy excitations by using the representations of the algebra $\hat{u}(1) \times SL(2,R)_R$ and show that energies of excitations are non-negative at (two) chiral points in the parameter space. At these special points, the charge algebra is described by either Virasoro algebra or Kac-Moody algebra. We also consider some special limits of the GMMG theory which correspond to $2+1$-dimensional massive gravity theories such as new massive and minimal massive gravity theories., Comment: 10 pages, references added, published in Phys. Rev. D

We study a single field inflationary model modified by a non-minimal coupling term between the Ricci scalar $R$ and the scalar field $\varphi$ in the context of constant-roll inflation. The first-order formalism is used to analyse the constant-roll inflation instead of the standard methods used in the literature. In principle, the formalism considers two functions of the scalar field, $W=W(\varphi)$ and $Z=Z(\varphi)$, which lead to the reduction of the equations of motion to first-order differential equations. The approach can be applied to a wide range of cosmological situations since it directly relates the function $W$ with Hubble parameter $H$. We perform the inflationary analysis for power-law and exponential couplings, separately. Then, we investigate the features of constant-roll potentials as inflationary potentials. Finally, we compare the inflationary parameters of the models with the observations of CMB anisotropies in view of realize a physically motivated model., Comment: 15 pages, 6 figures, Accepted for publication in Int. J. Mod. Phys. D

By applying entropic barriers, we present a rod separation mechanism that induces the movement of rods of different sizes in the opposite directions. This mechanism is based on the combination of the saw-tooth channel, a static force, and an oscillating driving force. The asymmetric shape of the channel and the elongated shape of the rod causesa complicated interaction effect between the rods and the channel walls which reduces the accessible configuration space for the rods and leads to entropic free-energy effects.

In this paper we present the generalization of Chern-Simons-like theories of gravity (CSLTG) to spin-3. We propose a Lagrangian describing the spin-3 fields coupled to Chern-Simons-like theories of gravity. Then we obtain conserved charges of these theories by using a quasi-local formalism. We find a general formula for entropy of black holes solutions of Spin-3 CSLTG. As an example, we apply our formalism to the spin-3 Generalized minimal massive gravity (GMMG) model. We analysis this model at linearized level and show that this model propagate two massive spin-2 modes and two massive spin-3 modes. We find no-ghost and no-tachyon conditions, which can be satisfy in the parameter space of the model. Then we find energy, angular momentum and entropy of a special black hole solution of this model.

We study the nonlinearity for the zigzag graphene nanoribbons (ZGNRs) with zigzag triangular holes (ZTHs). We show that in the presence of an external uniform magnetic field, a two-dimensional f-deformed Dirac oscillator can be used to describe the dynamics of the electrons in the ZGNRs with ZTHs. It is shown for the first time that the magnetic field direction has effect on the chirality of charge carriers in the ZGNRs punched with triangular holes. We also obtain the Landau-level spectrum in the weak and strong magnetic field regimes. Additionally, we compare Landau-level spectrum of this graphene-based device in the f-deformed scenario and original one. Our results provide a general viewpoint for the development of the zigzag graphene nanoribbons.

We apply the new fall of conditions presented in the paper \cite{10} on asymptotically flat spacetime solutions of Chern-Simons-like theories of gravity. We show that the considered fall of conditions asymptotically solve equations of motion of generalized minimal massive gravity. We demonstrate that there exist two type of solutions, one of those is trivial and the others are non-trivial. By looking at non-trivial solutions, for asymptotically flat spacetimes in the generalized minimal massive gravity, in contrast to Einstein gravity, cosmological parameter can be non-zero. We obtain the conserved charges of the asymptotically flat spacetimes in generalized minimal massive gravity, and by introducing Fourier modes we show that the asymptotic symmetry algebra is a semidirect product of a $BMS_{3}$ algebra and two $U(1)$ current algebras. Also we verify that the $BMS_{3}$ algebra can be obtained by a contraction of the AdS$_3$ asymptotic symmetry algebra when the AdS$_3$ radius tends to infinity in the flat-space limit. Finally we find energy, angular momentum and entropy for a particular case and deduce that these quantities satisfy the first law of flat space cosmologies., 16 pages. arXiv admin note: text overlap with arXiv:1701.00209

In this work, the Klein tunneling of semi-Dirac-like fermions confined in a single-layer graphene under uniaxial strain is studied. We consider the universal Hamiltonian to obtain the analytical solution for the transmission probability through a two-dimensional electrostatic barrier in the strongly strained graphene at the so-called merging point. In this regard, the numerical results of the transmission probability for several values of the merging parameter are presented. We demonstrate that the barrier would be completely transparent on the normal incidence for all values of the merging parameter. Finally, we turn our attention to obtain the exact solution of the transmission probability for a potential step to better illustrate it.

This article is devoted to static spherically symmetric black hole solutions of dRGT (de Rham–Gabadadze–Tolley) massive gravity in the presence of cosmological constant. The unitary and non-unitary gauges are used to find the solutions in three, four and five dimensions. We show that there are two general classes of solutions. In one of them, the effect of massive potential is appeared as the effective cosmological constant. By investigating these solutions in different dimensions, we find an expression for effective cosmological constant in arbitrary dimensions.

We present approximate analytical solutions of the Klein–Gordon equation with arbitrary l state for the Manning–Rosen potential using the Nikiforov–Uvarov method and adopting the approximation scheme for the centrifugal term. We provide the bound state energy spectrum and the wave function in terms of the hypergeometric functions.

We have studied constant-roll inflation using the q-de Sitter scale factor. Both the cold and warm inflation have been considered, and the scalar potential and inflaton field have been determined. Also tensor to scalar ratio and the spectral index are obtained. In the cold inflation case, the perturbations have been investigated using Mukhanov–Sasaki equation, and the results determined for the spectral index and tensor to scalar ration are consistent with observations. In the warm inflation two cases of constant damping ([Formula: see text]) and the field dependent damping ([Formula: see text]) have been studied. In both cases the power spectrum and the tensor to scalar ratio are determined as a function of the inflaton field. It has been shown that in both cases the spectral index is independent of the inflaton field. In the case of constant damping the obtained value for the spectral index is inconsistent with observations but for the case of field dependent damping the parameter [Formula: see text] can be chosen such that the value obtained for all the physical quantities including the spectral index be consistent with present cosmological observations.

Flat Space Cosmology (FSC) spacetimes are exact solutions of 3D gravity theories. In this work, we study phase transition between FSC spacetimes and Hot Flat Spacetimes (HFS) in general minimal massive gravity and exotic general massive gravity. We show that similar to topological massive gravity the tunneling occurs between two spacetimes by comparing their free energies. We also obtain the corrections to the Bekenstein-Hawking entropy, and its effect on the phase transition is studied., 13 pages, typos corrected, main results and conclusion unchanged, reference and paragraph added

In the present work, we consider the non-minimal coupling inflationary model in the context of the constant-roll idea which is investigated by the first-order formalism. We attempt to find the hidden symmetries behind the model by the Lie symmetry method. We supply this aim by using the symmetry features of the Heun function instead of Killing vector approach. We show that the hidden symmetries of the non-minimal constant-roll inflation in the cases of power-law and exponential couplings are characterized as a generalized form of s l ( 2 , R ) and s u ( 1 , 1 ) algebra

Tunneling and the Goos–Hänchen-like (GHL) shifts of quasiparticles through double rectangular potential barriers in mono-layer graphene under uniaxial strain were considered. Expressions for the transmission coefficient and the lateral shift of the transferred beam were obtained by considering the boundary conditions and the stationary phase method, respectively. Moreover, the numerical results of the transmission probability and the lateral shifts for three values of the merging parameter, δ were presented. It was observed, for two values of δ, very large shifts could be obtained and we found the demeanor of the GHL shift is adjustable by changing parameters and is influenced strongly by δ. Finally, our calculations were examined by the limit condition in accordance with the results obtained for a single barrier in presence of the strong uniaxial strain.

The explicit form of the field equations has been obtained by varying the action of the four-dimensional Einstein-dilaton gravity in the presence of the scalar-coupled exponential nonlinear electrodynamics. The exact black hole solutions of the field equations have been obtained in an energy-dependent spherically symmetric geometry. It has been found that the solution of the scalar field equation can be obtained by combining two Liouville potentials. We have introduced three types of exponentially charged dilatonic black holes and their thermodynamic properties have been studied noting the effects of rainbow functions. The impacts of rainbow functions on the conserved and thermodynamic quantities of the new black hole solutions have been explored. Through the Smarr mass formula, it has been demonstrated that the first law of black hole thermodynamics remains valid for either of the new rainbow black hole solutions. The quantum gravitational effects on the thermodynamic phase transition or thermal stability of the black holes have been studied by use of the canonical ensemble method. By calculating the black hole heat capacity, the type-1 and type-2 phase transition points and the conditions under which the exponentially charged rainbow black holes are locally stable have been identified.

In this paper we obtain the Hamiltonian of Dirac oscillator in an external magnetic field in terms of q-deformed creation and annihilation operators in 2 + 1 dimensions. For this system, we find coordinate representations of q-deformed creation and annihilation operators, eigenvalues and eigenfunctions. We also construct the lowest Landau levels exactly by applying the q-deformed Dirac annihilation operator to the vacuum state. This system may be considered for the study of graphene in the q-deformed version.

In this paper we obtain conserved charges of spin-3 topologically massive gravity by using a quasi-local formalism. We find a general formula to calculate conserved charge of the spin-3 topologically massive gravity which corresponds to a Killing vector field $\xi$. We show that this general formula reduces to the previous one for the ordinary spin-3 gravity presented in \cite{31} when we take into account only transformation under diffeomorphism, without considering generalized Lorentz gauge transformation (i.e. $\lambda _{\xi} =0$), and by taking $\frac{1}{\mu}\rightarrow 0$. Then we obtain a general formula for the entropy of black hole solutions of the spin-3 topologically massive gravity. Finally we apply our formalism to calculate energy, angular momentum and entropy of a special black hole solution and we find that obtained results are consistent with previous results in the limiting cases. Moreover our result for energy, angular momentum and entropy are consistent with the first law of black hole mechanics., Comment: 24 pages

The Chern–Simons-like theories of gravity (CSLTG) are formulated at first order formalism. In this formalism, the derivation of the entropy of a black hole on bifurcation surface, as a quasi-local conserved charge is problematic. In this paper we overcome these problems by considering the concept of total variation and the Lorentz–Lie derivative. We firstly find an expression for the ADT conserved current in the context of the CSLTG which is based on the concept of the Killing vector fields. Then, we generalize it to be conserved for all diffeomorphism generators. Thus, we can extract an off-shell conserved charge for any vector field which generates a diffeomorphism. The formalism presented here is based on the concept of quasi-local conserved charges which are off-shell. The charges can be calculated on any codimension two space-like surface surrounding a black hole and the results are independent of the chosen surface. By using the off-shell quasi-local conserved charge, we investigate the Virasoro algebra and find a formula to calculate the central extension term. We apply the formalism to the BTZ black hole solution in the context of the Einstein gravity and the Generalized massive gravity, then we find the eigenvalues of their Virasoro generators as well as the corresponding central charges. Eventually, we calculate the entropy of the BTZ black hole by the Cardy formula and we show that the result exactly matches the one obtained by the concept of the off-shell conserved charges.

We investigate the Casimir force for a system composed of two thick slabs as substrates within three different homogeneous layers. We use the scattering approach along with the Matsubara formalism in order to calculate the Casimir force at finite temperature. First, we focus on constructing the reflection matrices and then we calculate the Casimir force for a water–lipid system. According to the conventional use of silicon as a substrate, we apply the formalism to calculate the Casimir force for layers of Au, VO2, mica, KCl and foam rubber on the thick slabs of silicon. Afterwards, introducing an increasing factor, we compare our results with Lifshitz force in the vacuum between two semispaces of silicon in order to illustrate the influence of the layers on intensifying the Casimir force. We also calculate the Casimir force between two slabs of the forementioned materials with finite thicknesses to indicate the substrate's role in increasing the obtained Casimir force. Our simple calculation is interesting since one can extend it along with the Rigorous Coupled Wave Analysis to systems containing inhomogeneous layers as good candidates for designing nanomechanical devices.

The dwell time corresponding to the Klein tunneling of Dirac fermions confined in single-layer graphene in the presence of uniaxial strain was investigated. The numerical results of the tunneling time and the transmission probability for several values of the merging parameter were presented. The effect of barrier's height/length, energy, incident angle and merging parameter on the traversal time was considered. Results showed that the merging parameter and the angle of the incidence were important characters in the existence of the Hartman effect, and therefore Hartman effect was not observed at tunneling of Dirac fermions with different values of merging parameter for δ = 0 and δ 0 for normal incident. In the case of δ > 0 are equivalent to the gapped graphene under uniaxial strain at the merging point, tunneling time was independent on the barrier thickness.

Recently it has been speculated that a set of infinitesimal [Formula: see text] diffeomorphisms exist which act nontrivially on the horizon of some black holes such as Kerr and Kerr–Newman black holes.[Formula: see text] Having applied this symmetry in covariant phase space formalism, one can obtain Virasoro charges as surface integrals on the horizon. Kerr–Bolt space–time is well known for its asymptotically topology and has been studied widely in recent years. In this work, we are interested to find conserved charge associated to the Virasoro symmetry of Kerr–Bolt geometry using covariant phase space formalism. We will show right and left central charge are [Formula: see text], respectively. Our results also show good agreement with Kerr space–time in the limiting behavior.

Starting from an engineered periodic optical structure formed by waveguide arrays comprised of two interleaved lattices, we simulate a deformed Dirac equation. We show that the system also simulate graphene nano ribbons under strain. This optical analogue allows us to study the phenomenon of Zitterbewegung for the modified Dirac equation. Our results show that the amplitude of Zitterbewegung oscillations changes as the deformation parameter is changed.

In this work, explicit expressions for the transition rates of an isotropic quantum charged harmonic oscillator in the vicinity of a perfectly conducting half-space under the influence of an external classical source are obtained. In the absence of external sources, it is shown that the decay rate of an initially exited state of the oscillator is a periodic function in terms of the normalized distance to the plate. The modified transition rates in the presence of external classical sources are obtained in the large-time limit indicating a contribution proportional to the squared module of the Fourier transform of the external source. In the absence of the conducting plate and external sources, the results are in agreement with the free space case. The problem is generalized to the case of a real conducting half-space.

In this paper, we obtain the effect of backreaction on the scale factor of the Friedmann–Lemaître–Robertson–Walker (FLRW) and de Sitter spaces. We consider a non-minimally coupled massive scalar field to the curvature scalar. For our purpose, we use the results of vacuum expectation values of energy–momentum tensor, which have been obtained previously. By substituting the quantum energy density into the Friedmann equation, we obtain the linear order perturbation of the scale factor. So, the effect of backreaction leads to the new scale factor.

In this paper, we study the problem of massless particle creation in a flat, homogeneous and isotropic universe in the framework of $f(G)$ gravity. The Bogolyubov coefficients are calculated for the accelerating power-law solutions of the model in a matter dominated universe, from which the total number of created particle per unit volume of space can be obtained. It is proved that the total particle density always has a finite value. Therefore, the Bogolyubov transformations are well-defined and the Hilbert spaces spanned by the vacuum states at different times are unitarily equivalent. We find that the particles with small values of the mode $k$ are produced in the past and particles with large values of $k$ are produced only in the future. The negative pressure resulting from the gravitational particle creation is also determined. It is then argued that this pressure even in the presence of energy density and thermal pressure may affect significantly the cosmic expansion.

We address the exact relations for the energy spectrum of massive Dirac fermions of graphene for a class of position-dependent magnetic field profiles, which could be created under inhomogeneous strain fields, with possibility of inducing a Dirac gap. We then show that in the linear regime our results correspond well to the earlier approaches for the massless case. We also prove that our approach for obtaining the relativistic Landau levels of Dirac fermions created by a constant magnetic field together with a spatially varying normal pseudo-magnetic profile, which varies as $ 1/x^2$ , recovers well the earlier results in this regard. It turns out that, in this case, the associated Landau energy levels are obtained by considering two shape-invariant potentials which belong to the family of isotonic oscillators with a set of equally spaced energy levels.

Recently, the theory of Topologically massive gravity non-minimally coupled to a scalar field has been proposed which comes from Lorentz-Chern-Simons theory \cite{1}. That theory is a torsion free one. We extend that theory by adding an extra term which makes torsion to be non-zero. The extended theory can be regarded as an extension of Minimal massive gravity such that it is non-minimally coupled to a scalar field. We obtain equations of motion of extended theory such that they are expressed in terms of usual torsion free spin-connection. We show that BTZ spacetime is a solution of this theory when scalar field is constant. We define quasi-local conserved charge by the concept of generalized off-shell ADT current which both are conserved for any asymptotically Killing vector field as well as a Killing vector field which is admitted by spacetime everywhere. Also we find general formula for entropy of stationary black hole solution in the context of considered theory. We apply the obtained formulas on BTZ black hole solution, to calculate energy, angular momentum and entropy of this soultion. We obtain the central extension term, the central charges and the eigenvalues of the Virasoro algebra generators for the BTZ black hole solution. We calculate energy and angular momentum of BTZ black hole using the eigenvalues of the Virasoro algebra generators. Also we calculate the entropy of BTZ black hole by using the Cardy formula. We find that obtained results using two different ways are exactly matched as we expected., Comment: 22 pages, no figure

In the first order formalism of gravity theories, there are some theories which are not Lorentz-diffeomorphism covariant. In the framework of such theories we cannot apply the method of conserved charge calculation used in Lorentz-diffeomorphism covariant theories. In this paper we firstly introduce the total variation of a quantity due to an infinitesimal Lorentz-diffeomorphism transformation. Secondly, in order to obtain the conserved charges of Lorentz-diffeomorphism non-covariant theories, we extend the Tachikawa method \cite{3}. This extension includes not only Lorentz gauge transformation but also the diffeomorphism. We apply this method to the Chern-Simons-like theories of gravity (CSLTG) and obtain a general formula for the entropy of black holes in those theories. Finally, some examples on CSLTG are provided and the entropy of the BTZ black hole is calculated in the context of the examples., 13 pages, we have improved language of the paper

In this paper we study the Generalized Minimal Massive Gravity (GMMG) in asymptotically $AdS_3$ background. The generalized minimal massive gravity theory is realized by adding the CS deformation term, the higher derivative deformation term, and an extra term to pure Einstein gravity with a negative cosmological constant. We study the linearized excitations around the $AdS_3$ background and find that at special point (tricritical) in parameter space the two massive graviton solutions become massless and they are replaced by two solutions with logarithmic and logarithmic-squared boundary behavior. So it is natural to proposed that GMMG model could also provide a holographic description for a $3-$rank Logarithmic Conformal Field Theory (LCFT). We calculate the energy of the linearized gravitons in $AdS_3$ background, and show that the theory is free of negative-energy bulk modes. Then we obtain the central charges of the CFT dual explicitly and show GMMG also avoids the aforementioned "bulk-boundary unitarity clash". After that we show that General Zwei-Dreibein Gravity (GZDG) model can reduce to GMMG model. Finally by a Hamiltonian analysis we show that the GMMG model has no Boulware-Deser ghosts and this model propagate only two physical modes., 23 pages, new sections added

In this paper, we examine the validity of the first law of inner mechanics of black holes in Generalized Minimal Massive Gravity. We consider BTZ and spacelike warped black holes and show that the first law of inner mechanics is valid for given black holes in Generalized Minimal Massive Gravity. As we expect, due to the presence of the Lorentz Chern–Simons term in Lagrangian of considered model, the product of the entropies of the inner and outer horizons depends on the mass as it happens in Topologically Massive Gravity.

Einstein-Maxwell theory is not only covariant under diffeomorphisms but also is under $U(1)$ gauge transformations. We introduce a combined transformation constructed out of diffeomorphism and $U(1)$ gauge transformation. We show that symplectic potential, which is defined in covariant phase space method, is not invariant under combined transformations. In order to deal with that problem, following Donnelly and Freidel proposal \cite{1}, we introduce new fields. In this way, phase space and consequently symplectic potential will be extended. We show that new fields produce edge modes. We consider surface-preserving symmetries and we show that the group of surface-preserving symmetries is semi-direct sum of 2-dimensional diffeomorphism group on a spacelike codimension two surface with $SL(2,\mathbb{R})$ and $U(1)$. Eventually, we deduce that the Casimir of $SL(2,\mathbb{R})$ is the area element, similar to the pure gravity case \cite{1}., Comment: 18 pages

We calculate the transmission coefficient for a particle crossing a potential barrier in monolayer graphene with Rashba spin-orbit coupling and in bilayer graphene. We show that in both the cases one can go from Klein tunneling regime, characterized by perfect normal transmission, to anti-Klein tunneling regime, with perfect normal reflection, by tuning the Rashba spin-orbit coupling for a monolayer or the interplane coupling for a bilayer graphene. We show that the intermediate regime is characterized by a non-monotonic behavior with oscillations and resonances in the normal transmission amplitude as a function of the coupling and of the potential parameters., Comment: 9 pages, 5 figures

The brane inflationary model inspired by a polytropic inflationary idea is studied. In the slow-roll approximation and high energy limit, for a chaotic potential, the model is developed, and its characteristics are discussed. We obtain explicit expressions for the scalar power spectrum, the tensor-scalar ratio, the scalar spectral index and its running in terms of the polytropic parameters. We find a new constraint on the energy scale of the inflation and the brane tension using the WMAP9 data.

In this paper, we derive a f-deformed Hamiltonian for the anti-Jaynes-Cummings (AJC) model, using a trapped ion technology. We show that f-deformed Dirac oscillator is a mathematical description of the anti-Jaynes-Cummings model in a nonlinear Kerr-like medium. We prove that one can simulate the Zitterbewegung effect in the f-deformed version of the anti-Jaynes-Cummings model. We also study the non-relativistic limit of the f-deformed Dirac oscillator and interpret the Zitterbewegung effect in this limit with quantum optic interferometers.

The exact solution of the Schrodinger equation for the four quasi-exactly solvable potentials is presented using the functional Bethe ansatz method. It is shown that all models give rise to the same basic differential equation which is quasi-exactly solvable. The eigenvalues, eigenfunctions and the allowed potential parameters are given for each of the four models in terms of the roots of a set of algebraic Bethe ansatz equations.

In the first part of the present work, the correction to photon emission rate of an oscillating two-level atom in the presence of electromagnetic quantum vacuum field has been investigated for two different configurations: (i) Atom is trapped in the vicinity of a perfect conductor (ii) Atom is trapped between two perfect conductors. In the second part, the correction to the decay rate of an initially excited oscillating two-level atom due to the presence of a perfect conducting surface is found., 18 pages, 6 figures

We study the warm-tachyon inflationary universe model with viscous pressure in high-dissipation regime. General conditions which are required for this model to be realizable are derived in the slow-roll approximation. We present analytic expressions for density perturbation and amplitude of tensor perturbation in longitudinal gauge. Expressions of tensor-to-scalar ratio, scalar spectral index and its running are obtained. We develop our model by using exponential potential, the characteristics of this model are calculated for two specific cases in great details: 1- Dissipative parameter $\Gamma$ and bulk viscous parameter $\zeta$ are constant parameters. 2- Dissipative parameter is a function of tachyon field $\phi$ and bulk viscous parameter is a function of matter-radiation mixture energy density $\rho$. The parameters of the model are restricted by recent observational data from the nine-year Wilkinson microwave anisotropy probe (WMAP9), Planck and BICEP2 data., Comment: 19 pages, 3 figures, accepted for publication in PLB (2014). arXiv admin note: substantial text overlap with arXiv:1302.0493, arXiv:1312.2832

Recently, various observational data predict a possibility that inflation may naturally occur in a warm region. In this scenario, radiation is produced during the inflation epoch and reheating is avoided. The main question arises that what is the origin of warm inflation in 4D universe? We answer to this question in brane-antibrane system. We propose a model that allows all cosmological parameters like the scale factor a, the Hubble parameter H and phantom energy density depend on the equation of state parameter in transverse dimension between two branes. Thus, an enhancement in these parameters can be a signature of some evolutions in extra dimension. In our model, the expansion of 4D universe is controlled by the separation distance between branes and evolves from non-phantom phase to phantom one. Consequently, phantom-dominated era of the universe accelerates and ends up in big-rip singularity. Also, we show that as the tachyon potential increases, the effect of interaction between branes on the 4D universe expansion becomes systematically more effective, because at higher energies there exists more channels for flowing energy from extra dimension to other four dimensions. Finally, we test our model against WMAP and Planck data and obtain the ripping time. According to experimental data, $N\simeq 50$ case leads to $n_{s}\simeq 0.96$, where \emph{N} and $n_{s}$ are the number e-folds and the spectral index respectively. This standard case may be found in $0.01 < R_{Tensor-scalar } < 0.22$, where $R_{Tensor-scalar }$ is the tensor-scalar ratio. At this point, the finite time that Big Rip singularity occurs is $t_{rip}=33(Gyr)$., 16 pages, 3 figures, Accepted in Phys. Lett. B. arXiv admin note: text overlap with arXiv:0708.3233 by other authors

In this paper we introduce the "warm vector inflation" scenario. In warm inflation scenario radiation is produced during the inflation epoch and reheating is avoided. Slow-roll and perturbation parameters of this model are presented. We develop our model using intermediate inflation model. In this case, the model is compatible with observational data. We also study the model using another exact cosmological solution, named logamediate scenario. We present slow-roll and Hubble parameters, power spectrum and tensor-scalar ratio in terms of inflaton. The model is compatible with WMAP7 and Planck observational data., 23 pages, 8 figures. Accepted for publication in PLB (2013)

The general Bianchi type I with dark energy in the form of standard and modified Chaplygin gas with variable G and Λ and bulk viscosity have been investigated. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. Moreover, for the general exponential solutions, from which the de Sitter and power-law solutions may be obtained, we obtain models that reproduce the early universe, assumed as the inflation, and the late time accelerated expanding universe, that which yields a constant value for the deceleration parameter. We reconstruct bulk viscosity, ξ, gravitational parameter, G, cosmological term, Λ, density parameter, Ω, cosmological constant density parameter, ΩΛ, and deceleration parameter, q, for different equations of state. In the large time limit the model describes an accelerating universe wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

The ordinary and entropy-corrected versions of the holographic dark energy models in the spatially flat Friedmann–Robertson–Walker universe are considered. Then the F(G) modified gravity models as a candidates of dark energy are reconstructed according to the ordinary and entropy-corrected versions of the holographic dark energy models. The EoS parameters corresponding to the F(G) gravity models are obtained. The validity phantom or quintessence models in this framework of the modified gravity are investigated.

We study particle production in a flat Friedmann–Robertson–Walker universe in the framework of f(T) gravity. An exact power-law solution is obtained by solving the Friedmann equations and assuming that matter is minimally coupled with gravitation. The torsion scalar, T, appears to plays the same role as the curvature (Ricci scalar) in general relativity (GR) and its modified theories, f(R). Particularly, in the phantom phase, we observe that the vacuum state corresponds to a vanishing torsion scalar and particle production becomes important as the torsion scalar diverges. This aspect not only provides the equivalence between teleparallel gravity and GR, but also between their respective modified versions, f(T) and f(R), in the view of massless particle production phenomenon when matter is minimally coupled with gravity. However, when the gravitational and scalar fields are not minimally coupled, it appears that this similarity between the teleparallel gravity and GR may break down, because the torsion scalar no longer has the same time-dependent expression as the Ricci scalar.

This paper deals with the problem of defining off-shell conserved charges in a set of theories known as the Chern-Simons-like theories of gravity. The method is derived in a general way, which may find applications in a wide set of theories, and then specified to the case of generalized minimal massive gravity, where known results of the central charge and black hole entropy are reproduced. The results for the charges are useful to the community and can be applied to all three-dimensional gravity theories within the class of Chern-Simons-like theories of gravity which includes almost all of them. The given specific examples show a consistency check of the more general method.

In this paper we show that warped AdS$_{3}$ black hole spacetime is a solution of the generalized minimal massive gravity (GMMG) and introduce suitable boundary conditions for asymptotically warped AdS$_{3}$ spacetimes. Then we find the Killing vector fields such that transformations generated by them preserve the considered boundary conditions. We calculate the conserved charges which correspond to the obtained Killing vector fields and show that the algebra of the asymptotic conserved charges is given as the semi direct product of the Virasoro algebra with $U(1)$ current algebra. We use a particular Sugawara construction to reconstruct the conformal algebra. Thus, we are allowed to use the Cardy formula to calculate the entropy of the warped black hole. We demonstrate that the gravitational entropy of the warped black hole exactly coincide with what we obtain via Cardy's formula. As we expect the warped Cardy formula also give us exactly the same result which we obtain from usual Cardy's formula. We calculate mass and angular momentum of the warped black and then check that obtained mass, angular momentum and entropy satisfy first law of the black hole mechanics. According to the results of this paper we belief that the dual theory of the warped AdS$_{3}$ black hole solution of GMMG is a Warped CFT., Comment: 24 pages, accepted for publication in Class. Quant. Grav. (2017)

We give a detailed review of construction of conserved quantities in extended theories of gravity for asymptotically maximally symmetric spacetimes and carry out explicit computations for various solutions. Our construction is based on the Killing charge method, and a proper discussion of the conserved charges of extended gravity theories with this method requires studying the corresponding charges in Einstein's theory with or without a cosmological constant. Hence we study the ADM charges (in the asymptotically flat case but in generic viable coordinates), the AD charges (in generic Einstein spaces, including the anti-de Sitter spacetimes) and the ADT charges in anti-de Sitter spacetimes. We also discuss the conformal properties and the behavior of these charges under large gauge transformations as well as the linearization instability issue which explains the vanishing charge problem for some particular extended theories. We devote a long discussion to the quasi-local and off-shell generalization of conserved charges in the 2+1 dimensional Chern-Simons like theories and suggest their possible relevance to the entropy of black holes., Comment: 116 pages, 1 figure, a review, references added, matches the version to appear in Physics Reports