Infrared Cutoff Research Articles

Fractional holographic dark energy

Holographic dark energy theories present a fascinating interface to probe late-time cosmology, as guided by contemporary ideas about quantum gravity. In this work, we present a new holographic dark energy scenario designated “Fractional Holographic Dark Energy” (FHDE). This model extends the conventional framework of HDEs by incorporating specific features from fractional calculus and fractional Wheeler-De Witt equation recently applied, e.g., in cosmological settings. In this manner, we retrieve a novel form of HDE energy density. We then show how FHDE can provide a consistent picture of the evolution of the late-time universe even with the simple choice of the Hubble horizon as the IR (infrared) cutoff. We provide detailed descriptions of the cosmological evolution, showing how the fractional calculus ingredients can alleviate quite a few issues associated with the conventional HDE scenario. Concretely, we compute and plot diagrams using the Hubble horizon cutoff for HDE. The density parameters for DE and dark matter (DM), the deceleration parameter, and the DE EoS parameter indicate how the universe may evolve within our “FHDE” model, fitting within an appropriate scenario of late-time cosmology.

Fitting the DESI BAO data with dark energy driven by the Cohen-Kaplan-Nelson bound

Gravity constrains the range of validity of quantum field theory. As has been pointed out by Cohen, Kaplan, and Nelson (CKN), such effects lead to interdependent ultraviolet (UV) and infrared (IR) cutoffs that may stabilize the dark energy of the universe against quantum corrections, if the IR cutoff is set by the Hubble horizon. As a consequence of the cosmic expansion, this argument implies a time-dependent dark energy density. In this paper we confront this idea with recent data from DESI BAO, Hubble and supernova measurements. We find that the CKN model provides a better fit to the data than the ΛCDM model and can compete with other models of time-dependent dark energy that have been studied so far.

Localized modes in the IR phase of QCD

Infrared (IR) dimension function dIR(λ) characterizes the space effectively utilized by QCD quarks at Dirac scale λ, and indirectly the space occupied by glue fields. It was proposed that its nonanalytic behavior in thermal reflects the separation of QCD system into an IR component and an independent bulk. Here we study the “plateau modes” in the IR component, whose dimensional properties were puzzling. Indeed, in the recent scenario of transition to IR phase, this low-dimensional plateau connects the Anderson-like mobility edge λIR=0 in Dirac spectrum with mobility edges ±λA. For this structure to be truly Anderson-like, plateau modes have to be exponentially localized, implying that both the effective distances Leff∝Lγ and the effective volumes Veff∝LdIR in these modes grow slower than any positive power of IR cutoff L. Although γ=0 was confirmed in the plateau, it was found that dIR≈1. Here we apply the recently proposed technique to the problem. We conclude that a plateau mode of pure-glue QCD at UV cutoff a=0.085 fm occupies a subvolume of IR dimension zero with probability at least 0.9999, substantiating this aspect of metal-to-critical scenario to a respective degree. Published by the American Physical Society 2024

Rb8Nb10Ge6O41: a new niobium-germanate crystal featuring unique one-dimensional [Nb7O30]∞ chains and wide mid-IR transparency.

Germanate oxides have garnered considerable interest owing to their diverse structural configuration and intriguing properties. Herein, we present a novel niobium germanate crystal, Rb8Nb10Ge6O41, extracted through the process of spontaneous crystallization. It showcases a unique three-dimensional (3D) structural framework composed of one-dimensional (1D) twisted [Nb7O30]∞ chains and isolated [Ge3O9] rings, arising from the divergent polymerized manifestations of [NbO6] and [GeO4] basic building blocks, respectively, marking the first instance of such a topography in germanate materials. Notably, the title compound exhibits exceptional thermal stability up to 1250 °C with a good congruent melting nature. Moreover, it achieves a short ultraviolet edge at 306 nm and a favorable infrared edge cutoff exceeding 6.2 μm, thus indicating a wide transparency window. Additionally, this study elucidates the microscopic birefringence of Rb8Nb10Ge6O41 and clarifies the intricate relationship between its structure and properties. Our findings suggest that the polymerization of distinct structural motifs within a single compound is an effective strategy for exploring novel inorganic materials.

Examining the physical viability of the f(R) gravity via observational constraints

f(R) gravity is an extension of Einstein's General Relativity derived from relaxing the hypothesis that the Hilbert-Einstein action for the gravitational field is strictly linear in the Ricci curvature scalar R and explains the late-time cosmic acceleration of the Universe. We investigate the spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) line element filled with two fluids, with the first being pressureless matter and the second being the Renyi holographic dark energy (RHDE) in this study. In this scenario, the Hubble horizon H acts as an Infrared (IR) cutoff. In this regard, the effects of IR cutoff with the Hubble horizon on the traits of RHDE models have been researched. The volumetric power law expansion and the two models of f(R) i.e. f(R)=R+bRm and f(R)=R−μ4R are taken into consideration for the solution of the field equations. The estimated model parameter values that would best fit and work with current observational datasets. This estimation uses 1048 points from the Pantheon supernovae datasets and 30 points from the Hubble datasets. The likelihood function and Bayesian analysis are integrated with the Markov Chain Monte Carlo (MCMC) method at the 1 σ and 2 σ confidence levels. It is crucial to remember that f(R) is a rising function ofR, demonstrating the model's plausibility. For both models, the equation of state (EoS) value is close to a Quintessence zone. The model behaves in a ΛCDM (ΛCold Dark Matter) like manner, as shown by the fact that the statefinder diagnostic pair falls to(r=1,s=0). The Om(z) parameter shows a discrète behaviour.

Dynamical dark energy and infinite statistics

In the [Formula: see text]CDM model, dark energy is viewed as a constant vacuum energy density, the cosmological constant in the Einstein–Hilbert action. This assumption can be relaxed in various models that introduce a dynamical dark energy. In this paper, we argue that the mixing between infrared (IR) and ultraviolet (UV) degrees of freedom in quantum gravity leads to infinite statistics, the unique statistics consistent with Lorentz invariance in the presence of nonlocality, and yields a fine structure for dark energy. Introducing IR and UV cutoffs into the quantum gravity action, we deduce the form of [Formula: see text] as a function of redshift and translate this to the behavior of the Hubble parameter.

A dynamical system approach to the holographic dark energy in a modified theory of gravity

In this paper, we carry a dynamical system analysis of a holographic dark energy model of a modified theory of gravity based on braneworld scenario. The infra-red cutoff of the holographic dark energy is considered to be the Hubble scale in a first approach and the Ricci scalar curvature scale in a second approach. We present a detailed analysis of the critical points, their stability and the late-time cosmological viability of the solutions in the phase space. For both holographic dark energy models, we investigate the case of a noninteracting braneworld and extend our analysis to the interacting case between dark energy and cold dark matter by considering some specific forms of interaction.

Infrared problem in the Faddeev-Popov ghost propagator in perturbative quantum gravity in de Sitter spacetime

The propagators for the Faddeev-Popov (FP) ghosts in Yang-Mills theory and perturbative gravity in the covariant gauge are infrared (IR) divergent in de Sitter spacetime. An IR cutoff in the momentum space to regularize these divergences breaks the de Sitter invariance. These IR divergences are due to the spatially constant modes in the Yang-Mills case and the modes proportional to the Killing vectors in the case of perturbative gravity. It has been proposed that these IR divergences can be removed, with the de Sitter invariance preserved, by first regularizing them with an additional mass term for the FP ghosts and then taking the massless limit. In the Yang-Mills case, this procedure has been shown to correspond to requiring that the physical states, and the vacuum state in particular, be annihilated by some conserved charges in the Landau gauge. In this paper we show that there are similar conserved charges in perturbative gravity in the covariant Landau gauge in de Sitter spacetime and that the IR-regularization procedure described above also correspond to requiring that the vacuum state be annihilated by these charges with a natural definition of the interacting vacuum state.

Removal of infrared divergences in the Beliaev-Dyson equation for Bose-Einstein-condensed systems

We present a renormalized theory which is free of the infrared (IR) divergences for Bose-Einstein-condensed systems. It is shown that the Beliaev-Dyson equation can be made regular in the IR limit by expressing the Green functions in the form of a series starting from the Bogiliubov approximation. In the resulting equations for Green's functions, all IR divergences are removed completely due to the appearance of natural IR cutoff factors. Our theory is applied to a low-density Bose gas, where we calculate the first three terms in the series expansion of the ground-state energy and chemical potential.

Quantum cosmology of a dynamical Lambda

By allowing torsion into the gravitational dynamics one can promote the cosmological constant, $\Lambda$, to a dynamical variable in a class of quasi-topological theories. In this paper we perform a mini-superspace quantization of these theories in the connection representation. If $\Lambda$ is kept fixed, the solution is a delta-normalizable version of the Chern-Simons (CS) state, which is the dual of the Hartle and Hawking and Vilenkin wave-functions. We find that the CS state solves the Wheeler-DeWitt equation also if $\Lambda$ is rendered dynamical by an Euler quasi-topological invariant, {\it in the parity-even branch of the theory}. In the absence of an infra-red (IR) cut-off, the CS state suggests the marginal probability $P(\Lambda)=\delta(\Lambda)$. Should there be an IR cutoff (for whatever reason) the probability is sharply peaked at the cut off. In the parity-odd branch, however, we can still find the CS state as a particular (but not most general) solution, but further work is needed to sharpen the predictions. For the theory based on the Pontryagin invariant (which only has a parity-odd branch) the CS wave function no longer is a solution to the constraints. We find the most general solution in this case, which again leaves room for a range of predictions for $\Lambda$.

The soft mathcal{S} -matrix in gravity

The gravitational mathcal{S} -matrix defined with an infrared (IR) cutoff factorizes into hard and soft factors. The soft factor is universal and contains all the IR and collinear divergences. Here we show, in a momentum space basis, that the intricate expression for the soft factor is fully reproduced by two boundary currents, which live on the celestial sphere. The first of these is the supertranslation current, which generates spacetime supertranslations. The second is its symplectic partner, the Goldstone current for spontaneously broken supertranslations. The current algebra has an off-diagonal level structure involving the gravitational cusp anomalous dimension and the logarithm of the IR cutoff. It is further shown that the gravitational memory effect is contained as an IR safe observable within the soft mathcal{S} -matrix.

A dynamical system analysis of Tsallis holographic dark energy

In this paper we deal with the Tsallis holographic dark energy from a dynamical system approach. Here we assume the Hubble horizon as an infra red cutoff. We consider the cosmic evolution of the model in noninteracting, linearly, sign changeable and nonlinearly interacting cases. The analysis includes an autonomous system of equations and then we analyze the related phase spaces. We find that for a consistent picture of cosmic evolution in all cases we should take $\delta >1$ . However in the linear interaction case there exists a chance for $\delta <1$ but the necessity of a decelerating matter dominated epoch leads to a restriction on the coupling constant $b$ . This restriction rejects the chance of the $\delta <1$ in the latter case. Then we find that an observationally consistent description of the cosmic evolution for THDE in the presence of the discussed interaction terms is possible for $\delta >1$ . In the linearly interacting case of interaction we also find the restriction $b^{2}<\frac{1}{3}$ for a consistent picture of cosmic evolution. Beside we study the squared sound speed analysis and find chances of stability for suitable choices of free parameters. We also discuss the impacts of the interaction terms on the age of the universe.

Single Sensor Multi-Spectral Imaging

This dissertation presents the benefits of using a multispectral Single Sensor Camera (SSC) that, simultaneously acquire images in the visible and near-infrared (NIR) bands. The principal benefits while addressing problems related to image bands in the spectral range of 400 to 1100 nanometers, there are cost reductions in the hardware setup because only one SSC is needed instead of two; moreover, the cameras’ calibration and images alignment are not required anymore. Concerning to the NIR spectrum, even though this band is close to the visible band and shares many properties, the sensor sensitivity is material dependent due to different behavior of absorption/reflectance capturing a given scene compared to visible channels. Many works in literature have proven the benefits of working with NIR to enhance RGB images (e.g., image enhancement, dehazing, etc.). In spite of the advantage of using SSC (e.g., low latency), there are some drawbacks to be solved. One of these drawbacks corresponds to the nature of the silicon-based sensor, which in addition to capturing the RGB image when the infrared cut off filter is not installed it also acquires NIR information into the visible image. This phenomenon is called RGB and NIR crosstalking. This thesis firstly faces this problem in challenging images and then it shows the benefit of using multispectral images in the edge detection task.Then, three methods based on CNN have been proposed for edge detection. While the first one is based on the most used model, holistically-nested edge detection (HED) termed as multispectral HED (MS-HED), the other two have been proposed observing the drawbacks of MS-HED. These two novel architectures have been designed from scratch; after the first architecture is validated in the visible domain a slight redesign is proposed to tackle the multispectral domain. A dataset is collected to face this problem with SSCs. Even though edge detection is confronted in the multispectral domain, its qualitative and quantitative evaluation demonstrates the generalization in other datasets used for edge detection, improving state-of-the-art results. One of the main properties of this proposal is to show that the edge detection problem can be tackled by just training the proposed architecture one-time while validating it in other datasets.

Effects of anisotropy on the sign-changeable interacting Tsallis holographic dark energy

We consider a spatially homogeneous and anisotropic Bianchi type-I universe which is filled by pressureless dark matter (DM) and Tsallis holographic dark energy (THDE). We assume the two dark components of the universe are interacting with each other throughout a sign-changeable mutual interaction term. Various infra-red (IR) cutoffs are studied, and it is obtained that all models display classical instability by themselves at the future [Formula: see text]. Moreover, we find out that some models can cross the phantom line. In order to have a more comprehensive study, the statefinder diagnostic and the [Formula: see text] plane are also investigated showing that the model parameters significantly affect the evolution trajectories in the [Formula: see text] and [Formula: see text] planes.

Tsallis agegraphic dark energy model

Using the non-extensive Tsallis entropy and the holographic hypothesis, we propose a new dark energy (DE) model with timescale as infrared (IR) cutoff. Considering the age of the Universe as well as the conformal time as IR cutoffs, we investigate the cosmological consequences of the proposed DE models and study the evolution of the Universe filled by a pressureless matter and the obtained DE candidates. We find that although this model can describe the late time acceleration and the density, deceleration and the equation of state parameters show satisfactory behavior by themselves, these models are classically unstable unless the interaction between the two dark sectors of the Universe is taken into account. In addition, the results of the existence of a mutual interaction between the cosmos sectors are also addressed. We find out that the interacting models are stable at the classical level which is in contrast to the original interacting agegraphic dark energy models which are classically unstable [K. Y. Kim, H. W. Lee and Y. S. Myung, Phys. Lett. B 660, 118 (2008)].

The role of an invariant IR cutoff in late time cosmological dynamics

We study the role of an invariant infra-red cutoff in the late time cosmological dynamics. This low energy cutoff originates from the existence of a minimal measurable uncertainty as a result of the curvature of background manifold, and can be encoded in an extended uncertainty relation. Inspired by black hole entropy-area relation, we extend the analysis to the thermodynamics of apparent horizon of the universe. By treating both the Newtonian and general relativistic cosmologies, we show that the contribution of infra-red cutoff in the equations of dynamics can be interpreted as an effective fluid which is capable of explaining late time cosmic speed up and even transition to a phantom phase of expansion. We use the latest observational data from PLANCK2018 to constrain the parameter of an extended uncertainty relation.

Note on Tsallis holographic dark energy

We explore the effects of considering various infrared (IR) cutoffs, including the particle horizon, the Ricci horizon and the Granda–Oliveros (GO) cutoffs, on the properties of Tsallis holographic dark energy (THDE) model, proposed inspired by Tsallis generalized entropy formalism (Tavayef et al. in Phys Lett B 781:195, 2018). Interestingly enough, we find that for the particle horizon as IR cutoff, the obtained THDE model can describe the late time accelerated universe. This is in contrast to the usual HDE model which cannot lead to an accelerated universe, if one considers the particle horizon as the IR cutoff. We also investigate the cosmological consequences of THDE under the assumption of a mutual interaction between the dark sectors of the Universe. It is shown that the evolution history of the Universe can be described by these IR cutoffs and thus the current cosmic acceleration can also be realized. The sound instability of the THDE models for each cutoff are also explored, separately.

Revisiting holographic dark energy in cyclic cosmology

Considering the holographic dark energy (HDE) with two different infrared (IR) cutoffs, we study the evolution of a cyclic universe, which avoids the Big-Rip singularity. Our results show that, even in the absence of a mutual interaction between the cosmos sectors, the HDE model with the Hubble radius as IR cutoff can mimic a cosmological constant in the framework of a cyclic cosmology. In addition, we find that both the interacting and non-interacting universes may enter into a cycle of sequential contraction and expansion, if the Granda–Oliveros cutoff is chosen as the IR cutoff in the energy density of the HDE. We also investigate the instability of the model against perturbations and find the ranges of the parameters in which the model is stable.

Holographic dark energy with the sign-changeable interaction term

We use three infrared (IR) cutoffs, including the future event horizon, the Hubble and Granda–Oliveros (GO) cutoffs, to construct three holographic models of dark energy (DE). Additionally, we consider a Friedmann–Robertson–Walker (FRW) universe filled by a dark matter (DM) and a DE that interact with each other through a mutual sign-changeable interaction with positive coupling constant. Thereinafter, we address the evolution of the some cosmological parameters, such as the equation of state (EoS) and dimensionless density parameters of DE as well as the deceleration parameter, during the cosmic evolution from the matter-dominated era until the late-time acceleration. We observe that a holographic dark energy (HDE) model with Hubble cutoff interacting with DM cannot be in line with the current universe. Our study shows that models with the future event horizon as the IR cutoff or the GO cutoff are in good agreement with the observational data. In fact, we find out that these two recent models can predict the universe transition from a deceleration phase to the acceleration one in a compatible way with observations. The three obtained models may also allow the EoS parameter to cross the phantom line, a result which depends on the values of the system’s constants such as the value of the interaction coupling constant.

Two-layer anti-reflection coating with mullite and polyimide foam for large-diameter cryogenic infrared filters.

We have developed a novel two-layer anti-reflection (AR) coating method for large-diameter infrared (IR) filters made of alumina, for use at cryogenic temperatures in millimeter wave measurements. Thermally sprayed mullite and polyimide foam (Skybond Foam) are used as the AR material. An advantage of the Skybond Foam is that the index of refraction is chosen between 1.1 and 1.7 by changing the filling factor. Combination with mullite is suitable for wide-band millimeter wave measurements with sufficient IR cutoff capability. We present the material properties, fabrication of a large-diameter IR filter made of alumina with this AR coating method, and characterizations at cryogenic temperatures. This technology can be applied to a low-temperature receiver system with a large-diameter focal plane for next-generation cosmic microwave background polarization measurements, such as POLARBEAR-2 (PB-2).