Order Formalism Research Articles

Is pQCD energy loss in trouble?

Current pQCD calculations for the energy loss of a hard parton moving through a medium of thermalized static scattering centres are inapplicable to the small colliding systems (such as p/d + A) that have, in recent years, hinted at the presence of tiny droplets of QGP through the presence of collective behaviour, strangeness enhancement and quarkonium suppression. The well-known DGLV, ASW, BDMPS-Z, AMY and HT calculations all exploit both the large separation distance (between scattering centre and radiation) and the large system approximations. We relax the large system assumption and recompute the energy loss in the DGLV formalism in order to address the glaring lack of theoretical control over small-system energy loss. Alarmingly, we find that the correction terms dominate at large energies, resulting in ∼ 100% negative correction, calling into question the validity of the large formation time assumption used in all pQCD-based energy loss calculations. Our results demand a complete overhaul of energy-loss calculations for all system sizes.

Holography in Lovelock Chern-Simons AdS gravity

We analyse holographic field theory dual to Lovelock Chern-Simons AdS Gravity in higher dimensions using first order formalism. We first find asymptotic symmetries in the AdS sector showing that they consist of local translations, local Lorentz rotations, dilatations and non-Abelian gauge transformations. Then, we compute $1$-point functions of energy-momentum and spin currents in a dual conformal field theory and write Ward identities. We find that the holographic theory possesses Weyl anomaly and also breaks non-Abelian gauge symmetry at the quantum level.

Laser Diode to Single-Mode Circular Core Parabolic Index Fiber Coupling via Upside-Down Tapered Hyperbolic Microlens on the Tip of the Fiber: Prediction of Coupling Optics by ABCD Matrix Formalism

Abstract We employ ABCD matrix formalism in order to investigate the coupling optics involving laser diode to single-mode circular core parabolic index fiber excitation via upside-down tapered hyperbolic microlens on the fiber tip. Analytic expressions for coupling efficiencies both in absence and in presence of transverse and angular mismatches are formulated. The concerned investigations are made for two practical wavelengths namely 1.3 µm and 1.5 µm. The execution of the prescribed formulations involves little computation. It has been found that the wavelength 1.5 µm is more efficient in respect of coupling. It is also seen that the present coupling device at both the wavelengths shows more tolerance with respect to angular mismatch. As regards tolerance with respect to transverse mismatch, the result is poor at both the wavelengths used. Consequently, it is desirable that designers should not to exceed transverse mismatch beyond 1 μm.

Büttiker Probe-Based Modeling of TDDB: Application to Dielectric Breakdown in MTJs and MOS Devices

Dielectric layers are gradually being downscaled in different electronic devices like MOSFETs and magnetic tunnel junctions (MTJ) with shrinking device sizes. As a result, time dependent dielectric breakdown has become a major issue in such devices. In this paper we propose a generalized way of modeling the stress-induced leakage current (SILC) and postbreakdown current (PBC) due to time dependent wear-out of the dielectric layer. We model the traps formed in dielectric layer using Buttiker probe and incorporate the Buttiker probe self-energies in standard self-consistent nonequilibrium Green’s function formalism in order to determine SILC and PBC. In addition, we have shown the impact of breakdown in the dielectric layer on the spin current and spin filtering characteristics of an MTJ. The proposed model is generic in nature. It can be extended from MTJs and conventional CMOS technology to any other devices with any type of single and multiple layers of dielectric material(s).

The simplest non-minimal matter\u2013geometry coupling in the f(R,\xa0T) cosmology

f(R, T) gravity is an extended theory of gravity in which the gravitational action contains general terms of both the Ricci scalar R and the trace of the energy-momentum tensor T. In this way, f(R, T) models are capable of describing a non-minimal coupling between geometry (through terms in R) and matter (through terms in T). In this article we construct a cosmological model from the simplest non-minimal matter–geometry coupling within the f(R, T) gravity formalism, by means of an effective energy-momentum tensor, given by the sum of the usual matter energy-momentum tensor with a dark energy contribution, with the latter coming from the matter–geometry coupling terms. We apply the energy conditions to our solutions in order to obtain a range of values for the free parameters of the model which yield a healthy and well-behaved scenario. For some values of the free parameters which are submissive to the energy conditions application, it is possible to predict a transition from a decelerated period of the expansion of the universe to a period of acceleration (dark energy era). We also propose further applications of this particular case of the f(R, T) formalism in order to check its reliability in other fields, rather than cosmology.

Phantom solution in a non-linear Israel–Stewart theory

In this paper we present a phantom solution with a big rip singularity in a non-linear regime of the Israel–Stewart formalism. In this framework it is possible to extend this causal formalism in order to describe accelerated expansion, where assumption of near equilibrium is no longer valid. We assume a flat universe filled with a single viscous fluid ruled by a barotropic EoS, p=ωρ, which can represent a late time accelerated phase of the cosmic evolution. The solution allows to cross the phantom divide without evoking an exotic matter fluid and the effective EoS parameter is always lesser than −1 and constant in time.

Binary cluster model calculations for 20Ne and 44Ti nuclei

The elastic scattering data of [Formula: see text] and [Formula: see text] systems at [Formula: see text] = 32.2–146 MeV and [Formula: see text] = 24.1–49.5 MeV energies have been analyzed with double-folding (DF) potential in optical model formalism in order to investigate the cluster structures of [Formula: see text]Ne and [Formula: see text]Ti nuclei. The deduced DF potentials between [Formula: see text] and [Formula: see text]O as well as [Formula: see text] and [Formula: see text]Ca have been used for obtaining the excitation energies and [Formula: see text]-decay widths of [Formula: see text]Ne and [Formula: see text]Ti in Gamow code, but the reasonable results could not be obtained. Thus, the real parts of DF potentials which are in the best agreement with experimental data have been fitted with the squared-Woods–Saxon (WS2) potential parameters to calculate the [Formula: see text]-decay widths of [Formula: see text]Ne and [Formula: see text]Ti with Wentzel–Kramers–Brillouin (WKB) approach. The nuclear potential sets obtained in WKB calculations are also used for Gamow code calculations. We take into account the deformation and orientation of [Formula: see text]Ca nucleus to examine their influence on both the excitation energies and decay widths of [Formula: see text]Ti. Besides, by using the binary cluster model the rotational band energies and electromagnetic transition probabilities (BE2)s according to angles are also reproduced for both nuclei. The obtained results showed that the binary cluster model is very useful to understand the observables of [Formula: see text]Ne and [Formula: see text]Ti nuclei. Although only spherical calculations are made for [Formula: see text]Ne ([Formula: see text] + [Formula: see text]O), the deformation in [Formula: see text]Ca would be important for the understanding of [Formula: see text]Ti ([Formula: see text] + [Formula: see text]Ca) cluster structure. The mechanism presented here would also be applied to understand the cluster structures in heavy nuclei.

From SL(5, ℝ) Yang–Mills theory to induced gravity

From pure Yang–Mills action for the [Formula: see text] group in four Euclidean dimensions we obtain a gravity theory in the first order formalism. Besides the Einstein–Hilbert term, the effective gravity has a cosmological constant term, a curvature squared term, a torsion squared term and a matter sector. To obtain such geometrodynamical theory, asymptotic freedom and the Gribov parameter (soft BRST symmetry breaking) are crucial. Particularly, Newton and cosmological constant are related to these parameters and they also run as functions of the energy scale. One-loop computations are performed and the results are interpreted.

Noncommutative cosmological model in the presence of a phantom fluid

We study noncommutative classical Friedmann-Robertson-Walker cosmological models. The constant curvature of the spatial sections can be positive ($k=1$), negative ($k=-1$) or zero ($k=0$). The matter is represented by a perfect fluid with negative pressure, phantom fluid, which satisfies the equation of state $p =\alpha \rho$ , with $\alpha < - 1$, where $p$ is the pressure and $\rho$ is the energy density. We use Schutz's formalism in order to write the perfect fluid Hamiltonian. The noncommutativity is introduced by nontrivial Poisson brackets between few variables of the models. In order to recover a description in terms of commutative variables, we introduce variables transformations that depend on a noncommutative parameter ($\gamma$). The main motivation for the introduction of the noncommutativity is trying to explain the present accelerated expansion of the universe. We obtain the dynamical equations for these models and solve them. The solutions have four constants: $\gamma$, a parameter associated with the fluid energy $C$, $k$, $\alpha$ and the initial conditions of the models variables. For each value of $\alpha$, we obtain different equations of motion. Then, we compare the evolution of the universe between the present noncommutative models and the corresponding commutative ones ($\gamma \to 0$). The results show that $\gamma$ is very useful for describing an accelerating universe. We estimate the value of $\gamma$, for the present conditions of the Universe. Then, using that value of $\gamma$, in one of the noncommutative cosmological models, we compute the amount of time this universe would take to reach the {\it big rip}.

Curvature dependence of relativistic epicyclic frequencies in static, axially symmetric spacetimes

The sum of squared epicyclic frequencies of nearly circular motion ($\omega_r^2+\omega_\theta^2$) in axially symmetric configurations of Newtonian gravity is known to depend both on the matter density and on the angular velocity profile of circular orbits. It was recently found that this sum goes to zero at the photon orbits of Schwarzschild and Kerr spacetimes. However, these are the only relativistic configurations for which such result exists in the literature. Here, we extend the above formalism in order to describe the analogous relation for geodesic motion in arbitrary static, axially symmetric, asymptotically flat solutions of general relativity. The sum of squared epicyclic frequencies is found to vanish at photon radii of vacuum solutions. In the presence of matter, we obtain that $\omega_r^2+\omega_\theta^2>0$ for perturbed timelike circular geodesics on the equatorial plane if the strong energy condition holds for the matter-energy fluid of spacetime; in vacuum, the allowed region for timelike circular geodesic motion is characterized by the inequality above. The results presented here may be of use to shed light on general issues concerning the stability of circular orbits once they approach photon radii, mainly the ones corresponding to stable photon motion.

A combined theory for magnetohydrodynamic equilibria with anisotropic pressure and magnetic shear

We present a new approach to the theory of magnetohydrodynamic equilibria with anisotropic pressure, magnetic shear and translational/rotational invariance. This approach involves combining two existing formalisms in order to eliminate their individual weaknesses. The theoretical aspects of the method are explored in detail along with numerical solutions which make use of the method. Eventually, this method could be applied to model various plasma systems, such as planetary magnetospheres.

Weyl gravity revisited

The on shell equivalence of first order and second order formalisms for the Einstein-Hilbert action does not hold for those actions quadratic in curvature. It would seem that by considering the connection and the metric as independent dynamical variables, there are no quartic propagators for any dynamical variable. This suggests that it is possible to get both renormalizability and unitarity along these lines. We have studied a particular instance of those theories, namely Weyl gravity. In this first paper we show that it is not possible to implement this program with the Weyl connection alone.

Bateman–Feshbach Tikochinsky and Caldirola–Kanai Oscillators with New Fractional Differentiation

In this work, the study of the fractional behavior of the Bateman–Feshbach–Tikochinsky and Caldirola–Kanai oscillators by using different fractional derivatives is presented. We obtained the Euler–Lagrange and the Hamiltonian formalisms in order to represent the dynamic models based on the Liouville–Caputo, Caputo–Fabrizio–Caputo and the new fractional derivative based on the Mittag–Leffler kernel with arbitrary order α. Simulation results are presented in order to show the fractional behavior of the oscillators, and the classical behavior is recovered when α is equal to 1.

Analysis of Thermoluminescence Glow Curves using Derivatives of different Orders.

The suitability of the second derivative method for locating component peaks in complex thermoluminescence (TL) glow curves has been investigated in this work by considering both numerically simulated and experimental TL peaks. This technique is useful to acquire knowledge of the number of component peaks in a complex TL curve which in turn serves as a basic information before applying the deconvolution technique to the glow curve. To check the consistency of the results so obtained, we have also applied the first derivative technique to TL glow curves. It is well-known that kinetic order formalism fails for saturated TL peaks with heavy retrapping. Such peaks are usually broad and, to the best of our knowledge, have not yet been observed experimentally. The present derivative technique has been used to detect whether such broad peaks are truly single or not by considering a number of numerically simulated saturated glow curves with heavy retrapping where the conventional peak shape method fails. In all the cases considered here, the second derivative technique proves to be a potential candidate for estimating the number of peaks and their respective locations in a complex TL glow curve.

Dimensionally Compactified Chern-Simon Theory in 5D as a Gravitation Theory in 4D

We propose a gravitation theory in 4 dimensional space-time obtained by compacting to 4 dimensions the five dimensional topological Chern-Simons theory with the gauge group SO(1,5) or SO(2,4) – the de Sitter or anti-de Sitter group of 5-dimensional space-time. In the resulting theory, torsion, which is solution of the field equations as in any gravitation theory in the first order formalism, is not necessarily zero. However, a cosmological solution with zero torsion exists, which reproduces the Lambda-CDM cosmological solution of General Relativity. A realistic solution with spherical symmetry is also obtained.

Effect of grain size on electric transport and magnetic behavior of strontium hexaferrite (SrFe12O19)

Polycrystalline M-type hexagonal strontium hexaferrite (SrFe12O19) was prepared by conventional ceramic route (LG SrM) and auto combustion (SG SrM) method. The single-phase pattern and well grain growth was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average crystalline size is found to be 41.35 nm in LG SrM, while that of SG SrM is 36.87 nm. In this report, the electric transport behavior of LG SrM and SG SrM (SrFe12O19) was successfully investigated and the analysis is done in the frequency range 100 Hz to 1 MHz at temperature 30–200 °C. The relaxation behavior was examined by considering the impedance and modulus formalism in order to investigate the grain and grain boundary and surface polarization conduction process. The magnetic properties such as saturation magnetization, remanence, coercivity and anisotropy field are calculated from the hysteresis loop measurement. It was found that the saturation magnetization gets increased in LG SrM as compared to SG SrM system while the coercivity of SG SrM is greater than that of LG SrM.

5D Lovelock gravity: New exact solutions with torsion

We investigate Lovelock gravity in five dimensions in first order formalism. We construct a new class of solutions: BTZ black ring with(out) torsion. We show that our solution with torsion exists in the different sector of the Lovelock gravity compared to Lovelock Chern-Simons and the sector investigated by Canfora et al. We compute conserved charges of the solutions by using Nester's formula, and confirm the results by canonical method. We show that the theory linearized around the background with torsion possesses additional degrees of freedom compared to general relativity.

ENGLISH

We obtain axionic charged primordial black holes on a vacuum created gravitational pair of (3¯ by the Kalb-Ramond field on a D4-brane in presence of a background open string metric. The new geometries on an emergent pair of (3¯ universe is shown to be influenced by the non-perturbative quantum effects underlying a geometric torsion in a second order formalism. The presence of small extra dimensions transverse to the pair in the formalism ensures dynamical � ¯

SO(4) group structure for a motivated QCD Hamiltonian: Analytic and Tamm–Dancoff solutions

Starting from the QCD Hamiltonian written in the canonical Coulomb gauge formalism, we developed a mapping onto an SO(4) representation which is suitable for the description of the QCD spectra at low energies. The mapping does not break the flavor symmetry and it preserves the singlet-colorless structure of the states. We present and discuss the structure of integer and half-integer-spin states with masses below 2 GeV. Finally, we extend the formalism in order to include particle–hole-like correlations in building excitations.

Numerical analysis of transmission coefficient, LDOS, and DOS in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$ Al x Ga 1 - x N/GaN resonant tunneling MODFETs

Numerical analysis of the transmission coefficient, local density of states, and density of states in superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$AlxGa1-xN/GaN resonant tunneling modulation-doped field-effect transistors (MODFETs) using $$\hbox {next}{} \mathbf{nano}^{3}$$nextnano3 software and the contact block reduction method is presented. This method is a variant of non-equilibrium Green's function formalism, which has been integrated into the $$\hbox {next}\mathbf{nano}^{3}$$nextnano3 software package. Using this formalism in order to model any quantum devices and estimate their charge profiles by computing transmission coefficient, local density of states (LDOS) and density of states (DOS). This formalism can also be used to describe the quantum transport limit in ballistic devices very efficiently. In particular, we investigated the influences of the aluminum mole fraction and the thickness and width of the cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N}$$AlxGa1-xN on the transmission coefficient. The results of this work show that, for narrow width of 5 nm and low Al mole fraction of $$x = 20\,\%$$x=20% of barrier layers, cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$AlxGa1-xN/GaN superlattice nanostructures with very high density of states of 407 $$\hbox {eV}^{-1}$$eV-1 at the resonance energy are preferred to achieve the maximum transmission coefficient. We also calculated the local density of states of superlattice nanostructures of cubic $$\hbox {Al}_{x}\hbox {Ga}_{1-x}\hbox {N/GaN}$$AlxGa1-xN/GaN to resolve the apparent contradiction between the structure and manufacturability of new-generation resonant tunneling MODFET devices for terahertz and high-power applications.