Holographic Energy Research Articles

Generalized cutoff for late time acceleration and inflation: The cosmology of holographic fluid

Motivated by the work of Nojiri et al. [Phys. Lett. B 797 (2019) 134829], we utilize the holographic principle in the early universe to realize the holographic origin through inflation. A similar argument can be made for its well-researched late-time application, and the early-time horizon contraction naturally boosts holographic energy density at inflationary scales. After accounting for the IR cutoff adjustment and using holographic Ricci dark energy as the inflationary fluid, we have shown the significance of [Formula: see text] in the inflation realization. For holographic Ricci dark fluid’s potential to realize inflation, several restrictions were derived. The e-folding number was used to discuss inflationary observables and determine the slow-roll parameters. The study covered the effects of reconstructing the IR cutoff and the potential for inflation to be realized after taking into account holographic Ricci dark energy as a special instance of the most generalized Nojiri–Odintsov holographic dark energy [S. Nojiri and S. D. Odintsov, Gen. Relativ. Gravit. 38 (2006) 1285–1304]. Additionally, some time intervals for the potential of inflation have been calculated, and the behavior of the equation of state parameter has also been discussed.

Holographic energy loss near critical temperature in an anisotropic background

We study the energy loss of a quark moving in a strongly coupled quark gluon plasma under the influence of anisotropy. The heavy quark drag force, diffusion coefficient, and jet quenching parameter are calculated using the Einstein–Maxwell-dilaton model, where the anisotropic background is characterized by an arbitrary dynamical parameter A. Our findings indicate that as the anisotropic factor A increases, the drag force and jet quenching parameter both increase, while the diffusion coefficient decreases. Additionally, we observe that the energy loss becomes more significant when the quark moves perpendicular to the anisotropy direction in the transverse plane. The enhancement of the rescaled jet quenching parameters near critical temperature T c , as well as drag forces for a fast-moving heavy quark is observed, which presents one of the typical features of quantum chromodynamics phase transition.

Holographic energy density, dark energy sound speed, and tensions in cosmological parameters: H0 and S8

Interesting discrepancies in cosmological parameters are challenging the success of the ΛCDM model. Direct measurements of the Hubble constant H 0 using Cepheid variables and supernovae turn out to be higher than inferred from the Cosmic Microwave Background (CMB). Weak galaxy lensing surveys consistently report values of the strength of matter clustering σ 8 lower than values derived from the CMB in the context of ΛCDM. In this paper we address these discrepancies in cosmological parameters by considering Dark Energy (DE) as a fluid with evolving equation of state w de(z), constant sound speed squared ĉ s 2, and vanishing anisotropic stress σ. Our w de(z) is derived from the Holographic Principle and can consecutively exhibit radiation-like, matter-like, and DE-like behaviour, thus affecting the sound horizon and the comoving angular diameter distance, hence H 0. Here we show DE sound speed plays a part in the matter clustering behaviour through its effect on the evolution of the gravitational potential. We compute cosmological constraints using several data set combinations including primary CMB, CMB lensing, redshift-space-distortions, local distance-ladder, supernovae, and baryon acoustic oscillations. In our analysis we marginalise over ĉ s 2 and find ĉ s 2 = 1 is excluded at ≳ 3σ. For our baseline result including the whole data set we found H 0 and σ 8 in good agreement (within ≈ 2σ) with low redshift probes. Our constraint for the baryon energy density ω b is however in ≈ 3σ tension with BBN constraints. We conclude evolving DE also having non-standard clustering properties [e.g., ĉ s 2(z,k)] might be relevant for the solution of current discrepancies in cosmological parameters.

Scalar Field Models of Barrow Holographic Dark Energy in f(R,T) Gravity

This research study investigates Barrow holographic dark energy with an energy density of ρΛ=CH2−Δ by considering the Hubble horizon as the IR cut-off in the f(R,T) gravity framework. We employ Barrow holographic dark energy to obtain the equation of the state for the Barrow holographic energy density in a flat FLRW Universe. Concretely, we study the correspondence between quintessence, k-essence, and dilation scalar field models with the Barrow holographic dark energy in a flat f(R,T) Universe. Furthermore, we reconstruct the dynamics and potential for all these models for different values of the Barrow parameter: Δ. Via this study, we can show that for Barrow holographic quintessence, k-essence, and dilation scalar field models, if the corresponding model parameters satisfy some limitations, the accelerated expansion can be achieved.

Thermal correlation functions in CFT and factorization

We study 2-point and 3-point functions in CFT at finite temperature for large dimension operators using holography. The 2-point function leads to a universal formula for the holographic free energy in d dimensions in terms of the c-anomaly coefficient. By including α′ corrections to the black brane background, we reproduce the leading correction at strong coupling. In turn, 3-point functions have a very intricate structure, exhibiting a number of interesting properties. In simple cases, we find an analytic formula. When the dimensions satisfy ∆i = ∆j + ∆k, the thermal 3-point function satisfies a factorization property. We argue that in d > 2 factorization is a reflection of the semiclassical regime.

Different Faces of Generalized Holographic Dark Energy

In the formalism of generalized holographic dark energy (HDE), the holographic cut-off is generalized to depend upon LIR=LIRLp,L˙p,L¨p,⋯,Lf,L˙f,⋯,a with Lp and Lf being the particle horizon and the future horizon, respectively (moreover, a is the scale factor of the Universe). Based on such formalism, in the present paper, we show that a wide class of dark energy (DE) models can be regarded as different candidates for the generalized HDE family, with respective cut-offs. This can be thought as a symmetry between the generalized HDE and different DE models. In this regard, we considered several entropic dark energy models—such as the Tsallis entropic DE, the Rényi entropic DE, and the Sharma–Mittal entropic DE—and found that they are indeed equivalent with the generalized HDE. Such equivalence between the entropic DE and the generalized HDE is extended to the scenario where the respective exponents of the entropy functions are allowed to vary with the expansion of the Universe. Besides the entropic DE models, the correspondence with the generalized HDE was also established for the quintessence and for the Ricci DE model. In all the above cases, the effective equation of state (EoS) parameter corresponding to the holographic energy density was determined, by which the equivalence of various DE models with the respective generalized HDE models was further confirmed. The equivalent holographic cut-offs were determined by two ways: (1) in terms of the particle horizon and its derivatives, (2) in terms of the future horizon horizon and its derivatives.

On the holographic phase transitions at finite topological charge

Exploring the significant impacts of topological charge on the holographic phase transitions and conductivity we start from an Einstein–Maxwell system coupled with a charged scalar field in Anti-de Sitter spacetime. In our set up, the corresponding black hole (BH) is chosen to be the topological AdS one where the pressure is identified with the cosmological constant (Kubiznak and Mann in JHEP 7:33, 2012), then the AdS BH undergoes the phase transition from small to large BHs, which is totally similar to the transition from gas to liquid in the van der Waals theory. Our numerical computation shows that the process of condensation is favored at finite topological charge, in particular, the phase transition from small to large BHs in the bulk generates a mechanism for changing the order of phase transition in the boundary: the second order phase transitions occur at pressures higher than the critical pressure of the phase transition from small to large BHs while they become first order at lower pressures. This property is confirmed with the aid of holographic free energy. Finally, the frequency dependent conductivity exhibits an energy gap when the phase transition is second order and when the phase transition becomes first order this gap is either reduced or totally lost.

Holographic energy loss of a rotating heavy quark at finite chemical potential

We study the energy lost by a rotating heavy point particle along a circle of radius l with angular velocity ω in N=4 super Yang-Mills (SYM) theory with chemical potential from holography. We compute the energy loss both from the drag force channel and radiation channel, respectively. It is shown that for both cases the inclusion of chemical potential tends to increase the energy loss, consistently with the findings of the energy loss of a linearly moving quark.

Holographic Description of the Early Universe

The holographic principle is applied to a description of the Universe in the early stage of its evolution. As an example, we examine a cosmological model with a bounce with subsequent transition to the early stage of inflation. We investigate cosmological models based on a viscous liquid with a generalized equation of state in terms of the holographic cutoff proposed by Nojiri and Odintsov. Within the framework of these models, we have calculated the infrared radius in terms of the particle horizon or the event horizon. Energy conservation laws are obtained from the holographic point of view. The viscous liquid describing the bounce and the early Universe is presented as a generalization of holographic energy.

Unifying holographic inflation with holographic dark energy: A covariant approach

In the present paper, we use the holographic approach to describe the early-time acceleration and the late-time acceleration eras of our Universe in a unified manner. Such ``holographic unification'' is found to have a correspondence with various higher curvature cosmological models with or without matter fields. The corresponding holographic cut-offs are determined in terms of the particle horizon and its derivatives, or the future horizon and its derivatives. As a result, the holographic energy density we propose is able to merge various cosmological epochs of the Universe from a holographic point of view. We find the holographic correspondence of several $F(R)$ gravity models, including axion-$F(R)$ gravity models, of several Gauss-Bonnet $F(G)$ models and finally of $F(T)$ models, and in each case we demonstrate that it is possible to describe in a unified way inflation and late-time acceleration in the context of the same holographic model.

Holographic description of M-branes via AdS2

We study AdS2× S4× S2× Σ2 solutions in type IIB string theory arising from D1-D3-NS5 brane intersections. These backgrounds enjoy sixteen supercharges and the corresponding internal geometry is non-compact due to the specific form of the warping w.r.t. the Riemann surface Σ2. Even though a direct computation of the holographic free energy of the would-be dual CFT1 yields a divergent behaviour, it reveals the typical N3 scaling of a 6d theory upon introducing a hard cut-off. We claim that such geometries may be interpreted as the gravity duals of M(atrix) models describing an IR phase of the (2, 0) theory of M5 branes, in presence of momentum and NUT charges. We discuss parallel AdS2 geometries describing longitudinal M2 branes in the UV, where the counting of the number of degrees of freedom correctly reproduces the expected N3/2 behaviour of the dual field theory. These geometries provide explicit examples where deconstructed extra dimensions yield well-defined UV descriptions in terms of higher-dimensional CFTs.

Modified holographic energy density-driven inflation and some cosmological outcomes

Motivated by the work of Nojiri et al. [S. Nojiri, S. D. Odintsov and E. N. Saridakis, Holographic inflation, Phys. Lett. B 797 (2019) 134829], this study reports a model of inflation under the consideration that the inflationary regime is originated by a type of holographic energy density. The infrared cutoff has been selected based on the modified holographic model that is a particular case of Nojiri–Odintsov holographic dark energy [S. Nojiri and S. D. Odintsov, Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38 (2006) 1285] that unifies phantom inflation with the acceleration of the universe on late time. On getting an analytical solution for Hubble parameter we considered the presence of bulk viscosity and the effective equation of state parameter appeared to be consistent with inflationary scenario with some constraints. It has also being observed that in the inflationary scenario the contribution of bulk viscosity is not of much significance and its influence is increasing with the evolution of the universe. Inflationary observables have been computed for the model and the slow-roll parameters have been computed. Finally, it has been observed that the trajectories in [Formula: see text] are compatible with the observational bound found by Planck. It has been concluded that the tensor to scalar ratio for this model can explain the primordial fluctuation in the early universe as well.

Голографическое описание ранней Вселенной

The holographic principle is applied to the description of the Universe at an early stage of its evolution. As an example, we study a cosmological model with a bounce followed by a transition to the early stage of inflation. We study cosmological models of a viscous fluid with a generalized equation of state in terms of holographic cutoff proposed by Nojiri and Odintsov. Within these models, the infrared radius is calculated in terms of the particle horizon or event horizon. The laws of energy conservation are obtained from a holographic point of view. A viscous fluid describing bounce and early inflation is presented as generalized holographic energy

Some models of holographic dark energy on the Randall–Sundrum brane and observational data

Some models of holographic dark energy for Randall–Sundrum brane are considered. For the first class of dark energy models, we take energy density in the form [Formula: see text], where [Formula: see text] is size of event horizon in universe and [Formula: see text] is parameter (Tsallis holographic energy). Analysis of observational data allows to define upper limit on value of [Formula: see text] ([Formula: see text] is current energy density in the universe and [Formula: see text] is brane tension). Then we investigate models for which dark energy density has the form [Formula: see text] where [Formula: see text] is Hubble parameter.

Inflation driven by a holographic energy density

In this letter we study a model of inflation in which the inflationary regimen comes from a type of holographic energy density. In particular, we consider the Granda-Oliveros proposal for the holographic energy density, which contains two free dimensionless parameters, α and β. This holographic energy density is associated to the so-called Granda-Oliveros infrared cutoff (G-O cutoff). Additionally, since in the inflationary regimen the energy scales are very high, it is necessary to modify the G-O cutoff taking into account a correction due to the ultraviolet cutoff. In this way, we obtain an algebraic equation which implicitly includes the Hubble parameter (as a function of the e-folding number, N) and from this, we calculate the Hubble slow-roll parameters and the values of the inflationary observables: the scalar spectral index of the curvature perturbations and its running, the tensor spectral index and the tensor-to-scalar ratio. Finally, since the values for these inflationary observables are known (Planck 2018 observations), we present constraints on the parameters α and β to make this a viable model.

Holographic bounce

We investigate the bounce realization arising from the application of the holographic principle in the early universe, inspired by its well-studied late-time application. We first consider as Infrared cutoffs the particle and future event horizons, and we show that the decrease of the horizons at early times naturally increases holographic energy density at bouncing scales, while we additionally obtain the necessary null energy condition violation. Furthermore, adding a simple correction to the horizons due to the Ultraviolet cutoff we analytically obtain improved nonsingular bouncing solutions, in which the value of the minimum scale factor is controlled by the UV correction. Finally, we construct generalized scenarios, arisen from the use of extended Infrared cutoffs, and as specific examples we consider cutoffs that can reproduce F(R) gravity, and the bounce realization within it.

Holographic inflation

We apply the holographic principle at the early universe, obtaining an inflation realization of holographic origin. Such a consideration has equal footing with its well-studied late-time application, and moreover the decrease of the horizons at early times naturally increases holographic energy density at inflationary scales. Taking as Infrared cutoff the particle or future event horizons, and adding a simple correction due to the Ultraviolet cutoff, whose role is non-negligible at the high energy scales of inflation, we result in a holographic inflation scenario that is very efficient in incorporating inflationary requirements and predictions. We first extract analytically the solution of the Hubble function in an implicit form, which gives a scale factor evolution of the desired e-foldings. Furthermore, we analytically calculate the Hubble slow-roll parameters and then the inflation-related observables, such as the scalar spectral index and its running, the tensor-to-scalar ratio, and the tensor spectral index. Confronting the predictions with Planck 2018 observations we show that the agreement is perfect and in particular deep inside the 1σ region.

Perturbative solutions of mathcal{N}={1}^{ast } holography on S4

We apply the recently proposed perturbative technique to solve the supergravity BPS equations of mathcal{N}={1}^{ast } theories put on S4. In particular, we have calculated the coefficients of the leading quartic terms exactly, in the expression of the universal part for the holographic free energy as a function of the mass parameters. We also report on the coefficients of higher order terms up to 10th order, which are computed numerically.

Solving mass-deformed holography perturbatively

We study supergravity BPS equations which correspond to mass-deformation of some representative AdS/CFT examples. The field theory of interest are mathcal{N} = 4, D = 4 super Yang-Mills, the ABJM model in D = 3, and the Brandhuber-Oz fixed point in D = 5. For these gauge theories the free energy with mass terms for matter multiplets is calculable in large-N limit using supersymmetric localization technique. We suggest a perturbative method to solve the supergravity equations. For the dual of mass-deformed ABJM model we reproduce the known exact solutions. For the mass-deformed Brandhuber-Oz theory our method gives the holographic free energy in analytic form. For mathcal{N} = 2* theory our result is in good agreement with the localization result.

Mass deformations of the ABJM theory: the holographic free energy

We find a class of new supersymmetric Euclidean solutions in four-dimensional maximal gauged supergravity. The holographic dual description of these backgrounds is given by a mass-deformation of the ABJM theory with general values for the R-charges. We calculate the S3 free energy for the supergravity backgrounds and find agreement with the supersymmetric localization calculation of the free energy in the large N limit.