IR Cutoff Research Articles

Thermal stability of Tsallis holographic dark energy in nonflat universe

We consider a nonflat Friedmann–Robertson–Walker universe filled by a pressureless dark matter and Tsallis holographic dark energy (THDE) whose IR cutoff is the apparent horizon. We also consider both noninteracting and interacting cases in which a mutual interaction between the two dark sectors of cosmos is taken into account. For the noninteracting case, the density, equation of state (EoS) and the deceleration parameters show a satisfactory behavior by themselves, and the phantom line is not crossed. In this manner, unlike the flat case for THDE (Tavayef et al. in Phys Lett B 781:195, 2018), where the squared of sound speed is always negative, the squared of sound speed is negative and approaches zero at future. In the interacting case, the phantom line is crossed by EoS parameter, the squared of the sound speed is always negative and the density and deceleration parameters have acceptable behavior. Finally, by studying the thermodynamic parameters, namely the heat capacities and the compressibility criterions, the thermal stability of both cases are discussed which reveals that both models are thermodynamically unstable.

Towards the generalized gravitational entropy for spacetimes with non-Lorentz invariant duals

Based on the Lewkowycz-Maldacena prescription and the fine structure analysis of holographic entanglement proposed in [1], we explicitly calculate the holographic entanglement entropy for warped CFT that duals to AdS3 with a Dirichlet-Neumann type of boundary conditions. We find that certain type of null geodesics emanating from the entangling surface ∂ mathcal{A} relate the field theory UV cutoff and the gravity IR cutoff. Inspired by the construction, we furthermore propose an intrinsic prescription to calculate the generalized gravitational entropy for general spacetimes with non-Lorentz invariant duals. Compared with the RT formula, there are two main differences. Firstly, instead of requiring that the bulk extremal surface ℰ should be anchored on ∂ mathcal{A} , we require the consistency between the boundary and bulk causal structures to determine the corresponding ℰ. Secondly we use the null geodesics (or hypersurfaces) emanating from ∂ mathcal{A} and normal to ℰ to regulate ℰ in the bulk. We apply this prescription to flat space in three dimensions and get the entanglement entropies straightforwardly.

Tsallis holographic dark energy in the brane cosmology

We study some cosmological features of Tsallis holographic dark energy (THDE) in Cyclic, DGP and RS II braneworlds. In our setup, a flat FRW universe is considered filled by a pressureless source and THDE with the Hubble radius as the IR cutoff, while there is no interaction between them. Our result shows that although suitable behavior can be obtained for the system parameters such as the deceleration parameter, the models are not always stable during the cosmic evolution at the classical level.

Thermodynamic approach to holographic dark energy and the R\xe9nyi entropy

Using the first law of thermodynamics, we propose a relation between the system entropy (S) and its IR (L) and UV (Lambda ) cutoffs. In addition, applying this relation to the apparent horizon of flat FRW universe, whose entropy meets the Rényi entropy, a new holographic dark energy model is addressed. Thereinafter, the evolution of the flat FRW universe, filled by a pressureless source and the obtained dark energy candidate, is studied. In our model, there is no mutual interaction between the cosmos sectors. We find out that the obtained model is theoretically powerful to explain the current accelerated phase of the universe. This result emphasizes that the generalized entropy formalism is suitable for describing systems including the long-range interactions such as gravity.

Can holographic dark energy models fit the observational data?

In this work we investigate the holographic dark energy models with slowly time-varying model parameter defined based on the current Hubble horizon length scale. While the previous studies on the three popular holographic dark energy models defined based on the future event horizon, Ricci scale and Granda-Oliveros IR cutoffs showed that these models cannot fit the observational data [I. A. Akhlaghi, M. Malekjani, S. Basilakos, and H. Haghi, Mon. Not. R. Astron. Soc. 477, 3659 (2018)], in this work we show that the holographic dark energy models with time-varying model parameter defined on the current Hubble radius are well favored by observations. Using the standard ${\ensuremath{\chi}}^{2}$ minimization in the context of Markov Chain Monte Carlo method, we compare the ability of holographic dark energy models with time-varying ${c}^{2}$ parameter constructed on the current Hubble length scale against different sets of observational data namely expansion data, growth rate data, and $\mathrm{expansion}+\mathrm{growth}$ rate data, respectively. Based on the values of Akaike and Bayesian information criteria, we find that these types of holographic dark energy models are well fitted to both expansion and growth rate observations as equal to $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ cosmology. We also put constraints on the cosmological parameters and show that the transition epoch form early decelerated to current accelerated expansion calculated in holographic dark energy models with time-varying model parameter defined on the Hubble length is consistent with observations.

Holographic dark energy model in the DGP braneworld with time varying holographic parameter

We study the cosmological dynamics of holographic dark energy in a DGP braneworld in which the holographic parameter c2 is slowly varying with time. In our model, two famous IR cutoffs including the Hubble radius and the Granda–Oliveros cutoffs are considered. Our study shows that, for both cutoffs, there is a transition from a deceleration phase to an accelerated one for the universe which is in agreement with recent observations. It has been obtained that, even in the absence of an interaction between the dark sectors of cosmos, the equation of state parameter of the model with the Hubble radius as IR cutoffs can cross the phantom line, namely ωD<−1.

Tsallis holographic dark energy in the Brans\u2013Dicke cosmology

Using the Tsallis generalized entropy, holographic hypothesis and also considering the Hubble horizon as the IR cutoff, we build a holographic model for dark energy and study its cosmological consequences in the Brans–Dicke framework. At first, we focus on a non-interacting universe, and thereinafter, we study the results of considering a sign-changeable interaction between the dark sectors of the cosmos. Our investigations show that, compared with the flat case, the power and freedom of the model in describing the cosmic evolution is significantly increased in the presence of the curvature. The stability analysis also indicates that, independent of the universe curvature, both the interacting and non-interacting cases are classically unstable. In fact, both the classical stability criterion and an acceptable behavior for the cosmos quantities, including the deceleration and density parameters as well as the equation of state, are not simultaneously obtainable.

Model selection and constraints from holographic dark energy scenarios

In this study we combine the expansion and the growth data in order to investigate the ability of the three most popular holographic dark energy models, namely event future horizon, Ricci scale and Granda-Oliveros IR cutoffs, to fit the data. Using a standard $\chi^2$ minimization method we place tight constraints on the free parameters of the models. Based on the values of the Akaike and Bayesian information criteria we find that two out of three holographic dark energy models are disfavored by the data, because they predict a non-negligible amount of dark energy density at early enough times. Although the growth rate data are relatively consistent with the holographic dark energy models which are based on Ricci scale and Granda-Oliveros IR cutoffs, the combined analysis provides strong indications against these models. Finally, we find that the model for which the holographic dark energy is related with the future horizon is consistent with the combined observational data.

Einstein static universe, GUP, and natural IR and UV cut-offs

We study the Einstein static universe (ESU) in the framework of Generalized Uncertainty Principle (GUP) constructed by the Snyder non-commutative space. It is shown that the deformation parameter can induce an effective energy density subject to GUP which obeys the holographic principle (HP) and plays the role of a cosmological constant. Using the holographic feature of this effective energy density, we introduce natural IR and UV cut-offs which depend on the GUP-based effective equation of state. Moreover, we propose a solution to the cosmological constant problem (CCP). This solution is based on the result that the Einstein equations just couple to the tiny holographic-based surface energy density (cosmological constant) induced by the deformation parameter, rather than the large quantum gravitational-based volume energy density (vacuum energy) having contributions of order [Formula: see text].

Generalized entropy formalism and a new holographic dark energy model

Recently, the Rényi and Tsallis generalized entropies have extensively been used in order to study various cosmological and gravitational setups. Here, using a special type of generalized entropy, a generalization of both the Rényi and Tsallis entropy, together with holographic principle, we build a new model for holographic dark energy. Thereinafter, considering a flat FRW universe, filled by a pressureless component and the new obtained dark energy model, the evolution of cosmos has been investigated showing satisfactory results and behavior. In our model, the Hubble horizon plays the role of IR cutoff, and there is no mutual interaction between the cosmos components. Our results indicate that the generalized entropy formalism may open a new window to become more familiar with the nature of spacetime and its properties.

Nucleon form factors in the nuclear medium

By using the AdS/CFT correspondence, we investigate various form factors between nucleons and mesons in a nuclear medium. In order to describe a nuclear medium holographically, we take into account the thermal charged AdS geometry with an appropriate IR cutoff. After introducing an anomalous dimension as a free parameter, we investigate how the nucleon’s mass is affected by the change of the anomalous dimension. Moreover, we study how the form factors of nucleons rely on the properties of the nuclear medium. We show that in a nuclear medium with different numbers of proton and neutron, the degenerated nucleon form factor in the vacuum is split into four different values depending on the isospin charges of nucleon and meson.

The Hubble IR cutoff in holographic ellipsoidal cosmologies

It is well known that for spatially flat FRW cosmologies, the holographic dark energy disfavors the Hubble parameter as a candidate for the IR cutoff. For overcoming this problem, we explore the use of this cutoff in holographic ellipsoidal cosmological models, and derive the general ellipsoidal metric induced by a such holographic energy density. Despite the drawbacks that this cutoff presents in homogeneous and isotropic universes, based on this general metric, we developed a suitable ellipsoidal holographic cosmological model, filled with a dark matter and a dark energy components. At late time stages, the cosmic evolution is dominated by a holographic anisotropic dark energy with barotropic equations of state. The cosmologies expand in all directions in accelerated manner. Since the ellipsoidal cosmologies given here are not asymptotically FRW, the deviation from homogeneity and isotropy of the universe on large cosmological scales remains constant during all cosmic evolution. This feature allows the studied holographic ellipsoidal cosmologies to be ruled by an equation of state omega =p/rho , whose range belongs to quintessence or even phantom matter.

Boundary conformal anomalies on hyperbolic spaces and Euclidean balls

We compute conformal anomalies for conformal field theories with free conformal scalars and massless spin 1/2 fields in hyperbolic space ℍd and in the ball {mathbb{B}}^d , for 2≤d≤7. These spaces are related by a conformal transformation. In even dimensional spaces, the conformal anomalies on ℍ2n and {mathbb{B}}^{2n} are shown to be identical. In odd dimensional spaces, the conformal anomaly on {mathbb{B}}^{2n+1} comes from a boundary contribution, which exactly coincides with that of ℍ2n + 1 provided one identifies the UV short-distance cutoff on {mathbb{B}}^{2n+1} with the inverse large distance IR cutoff on ℍ2n + 1, just as prescribed by the conformal map. As an application, we determine, for the first time, the conformal anomaly coefficients multiplying the Euler characteristic of the boundary for scalars and half-spin fields with various boundary conditions in d = 5 and d = 7.

Event activity-dependence of jet production in p–Pb collisions at [formula omitted] measured with semi-inclusive hadron+jet correlations by ALICE

We report measurement of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (pT) hadron trigger, for p–Pb collisions at sNN=5.02 TeV, in p–Pb classified by event activity. This observable has been measured in pp and Pb–Pb collisions at the LHC, providing a new probe to measure quenching. Jets are reconstructed from charged particle tracks using anti-kt with R=0.4 and low IR cutoff of jet constituents (pT,track>0.15 GeV/c). The complex uncorrelated jet background is corrected by a data-driven approach. Recoil jet distributions are reported for 15<pT,jetch<50 GeV/c. Events are classified by signal in the ALICE V0A detector, which measures forward multiplicity, and ZNA, which measures the number of neutrons at zero degrees. This self-normalized observable does not require scaling of reference distributions by 〈TpA〉, thereby avoiding the need for geometric modeling. We compare the trigger-normalized recoil jet yield for p–Pb collisions with different event activity to measure the effects of jet quenching in small systems at the LHC.

Subtracting infrared renormalons from Wilson coefficients: Uniqueness and power dependences on ΛQCD

In the context of OPE and using the large-$\beta_0$ approximation, we propose a method to define Wilson coefficients free from uncertainties due to IR renormalons. We first introduce a general observable $X(Q^2)$ with an explicit IR cutoff, and then we extract a genuine UV contribution $X_\mathrm{UV}$ as a cutoff-independent part. $X_\mathrm{UV}$ includes power corrections $\sim (\Lambda_\mathrm{QCD}^2/Q^2)^n$ which are independent of renormalons. Using the integration-by-regions method, we observe that $X_\mathrm{UV}$ coincides with the leading Wilson coefficient in OPE and also clarify that the power corrections originate from UV region. We examine scheme dependence of $X_\mathrm{UV}$ and single out a specific scheme favorable in terms of analytical properties. Our method would be optimal with respect to systematicity, analyticity and stability. We test our formulation with the examples of the Adler function, QCD force between $Q \bar{Q}$, and $R$-ratio in $e^{+} e^{-}$ collision.

A Note on Holographic Dark Energy with Varying c 2 Term

We reconsider the holographic dark energy (HDE) model with a slowly time varying $ c^2(z)$ parameter in the energy density, namely $\rho_D=3M_p^2 c^2(z)/L^2$, where $L$ is the IR cutoff and $z$ is the redshift parameter. As the system's IR cutoff we choose the Hubble radius and the Granda-Oliveros (GO) cutoffs. The latter inspired by the Ricci scalar curvature. We derive the evolution of the cosmological parameters such as the equation of state and the deceleration parameters as the explicit functions of the redshift parameter $z$. Then, we plot the evolutions of these cosmological parameters in terms of the redshift parameter during the history of the universe. Interestingly enough, we observe that by choosing $L=H^{-1}$ as the IR cutoff for the HDE with time varying $ c ^2(z) $ term, the present acceleration of the universe expansion can be achieved, even in the absence of interaction between dark energy and dark matter. This is in contrast to the usual HDE model with constant $c^2$ term, which leads to a wrong equation of state, namely that for dust $w_D=0$, when the IR cutoff is chosen the Hubble radius.

Emergent gravity on covariant quantum spaces in the IKKT model

We study perturbations of 4-dimensional fuzzy spheres as backgrounds in the IKKT or IIB matrix model. Gauge fields and metric fluctuations are identified among the excitation modes with lowest spin, supplemented by a tower of higher-spin fields. They arise from an internal structure which can be viewed as a twisted bundle over $S^4$, leading to a covariant noncommutative geometry. The linearized 4-dimensional Einstein equations are obtained from the classical matrix model action under certain conditions, modified by an IR cutoff. Some one-loop contributions to the effective action are computed using the formalism of string states.

Production of electricity from ethanol and ammonium based wastewater via photo-electrochemical process

A PEC cell is tested with two types of electrolyte (e.g., electrolyte pollutant and alcohols) under irradiation with a Xenon lamp through an IR cutoff filter (IRA-25S). The main objective of this study is to optimize the production of electricity from wastewater containing ethanol and ammonium using a photo-electrochemical (PEC) process. DOE statistical analysis was used to optimize the parameters that influenced the process, namely the active area of photoanode and the concentration of electrolyte. The significance level of the active area of a photo-anode was found to be within 0.5–1.0 cm2, the electrolyte concentrations were found to be 5–20% by volume and the types of electrolytes used included ammonia and an ethanol aqueous solution. For the optimization process, the response surface method (RSM) using central composite design (CCD) was applied to generate a map of the response. The results were statistically analyzed using an analysis of variance (ANOVA) to identify the factors that influence the production of the current density from a PEC cell. An electrolyte containing ethanol was found to produce higher currents than electrolyte containing ammonium. The optimum parameters that produced the maximum current density of 0.77 mA/cm2 were achieved using an ethanol electrolyte with an active area of 0.73 cm2 and a concentration of 20% by volume. Confirmation experiment showed that the current density is about 97% similar to the expected value that is 0.75 mA/cm2.

Properties of infrared extrapolations in a harmonic oscillator basis

The success and utility of effective field theory (EFT) in explaining the structure and reactions of few-nucleon systems has prompted the initiation of EFT-inspired extrapolations to larger model spaces in ab initio methods such as the no-core shell model (NCSM). In this contribution, we review and continue our studies of infrared (ir) and ultraviolet (uv) regulators of NCSM calculations in which the input is phenomenological [Formula: see text] and [Formula: see text] interactions fitted to data. We extend our previous findings that an extrapolation in the ir cutoff with the uv cutoff above the intrinsic uv scale of the interaction is quite successful, not only for the eigenstates of the Hamiltonian but also for expectation values of operators, such as [Formula: see text], considered long range. The latter results are obtained with Hamiltonians transformed by the similarity renormalization group (SRG) evolution. On the other hand, a possible extrapolation of ground state energies in the uv cutoff when the ir cutoff is below the intrinsic ir scale is not robust and does not agree with the ir extrapolation of the same data or with independent calculations using other methods.

Holographic Nambu–Jona-Lasinio interactions

NJL interactions are introduced into the D3/ probe D7 system using Witten's double trace operator prescription which includes the operator as a classical term in the effective potential. In the supersymmetric system they do not induce chiral symmetry breaking which we attribute to the flat effective potential with quark mass in the supersymmetric theory. If additional supersymmetry breaking is introduced then standard NJL behaviour is realized. In examples where chiral symmetry breaking is not preferred such as with a B field plus an IR cut off chiral condensation is triggered by the NJL interaction at a second order transition after a finite critical coupling. If the model already contains chiral symmetry breaking, for example in the B field case with no IR cut off, then the NJL interaction enhances the quark mass at all values of the NJL coupling. We also consider the system at finite temperature: the temperature discourages condensation but when combined with a magnetic field we find regions of parameter space where the NJL interaction triggers a first order chiral transition above a critical coupling.