Post-Newtonian parameter <Emphasis Type="Italic">γ</Emphasis> in generalized non-local gravity

We investigate the post-Newtonian parameter γ and derive its formalism in generalized non-local (GNL) gravity, which is the modified theory of general relativity (GR) obtained by adding a term m ^2n?2 R?^?n R to the Einstein-Hilbert action. Concretely, based on parametrizing the generalized non-local action in which gravity is described by a series of dynamical scalar fields ? ⁱ in addition to the metric tensor g _μν, the post-Newtonian limit is computed, and the effective gravitational constant as well as the post-Newtonian parameters are directly obtained from the generalized non-local gravity. Moreover, by discussing the values of the parametrized post-Newtonian parameters γ, we can compare our expressions and results with those in Hohmann and Järv et al. (2016), as well as current observational constraints on the values of γ in Will (2006). Hence, we draw restrictions on the nonminimal coupling terms F? around their background values.     

One-loop effective action for non-local modified Gauss–Bonnet gravity in de Sitter space

We discuss the classical and quantum properties of non-local modified Gauss–Bonnet gravity in de Sitter space, using its equivalent representation via string-inspired local scalar-Gauss–Bonnet gravity with a scalar potential. A classical, multiple de Sitter universe solution is found where one of the de Sitter phases corresponds to the primordial inflationary epoch, while the other de Sitter space solution—the one with the smallest Hubble rate—describes the late-time acceleration of our universe. A Chameleon scenario for the theory under investigation is developed, and it is successfully used to show that the theory complies with gravitational tests. An explicit expression for the one-loop effective action for this non-local modified Gauss–Bonnet gravity in the de Sitter space is obtained. It is argued that this effective action might be an important step towards the solution of the cosmological constant problem.     

The symmetry energy γ parameter of relativistic mean-field models

The relativistic mean-field models tested in previous works against nuclear matter experimental values,critical parameters and macroscopic stellar properties are revisited and used in the evaluation of the symmetry energyγ parameter obtained in three different ways. We have checked that, independent of the choice made to calculate theγ values, a trend of linear correlation is observed between γ and the symmetry energy(S_0) and a more clear linear relationship is established between γ and the slope of the symmetry energy(L_0). These results directly contribute to the arising of other linear correlations between γ and the neutron star radii of R_(1.0) and R_(1.4), in agreement with recent findings. Finally, we have found that short-range correlations induce two specific parametrizations, namely,IU-FSU and DD-MEδ, simultaneously compatible with the neutron star mass constraint of 1.93≤M_(max)/M_☉≤2.05 and with the overlap band for the L_0 ×S_0 region, to present γ in the range of γ=0.25±0.05.     

Local and non-local conserved quantities for generalized non-linear Schrödinger equations

It is shown how to construct infinitely many conserved quantities for the classical non-linear Schrödinger equation associated with an arbitrary Hermitian symmetric spaceG/K. These quantities are non-local in general, but include a series of local quantities as a special case. Their Poisson bracket algebra is studied, and is found to be a realization of the half Kac-Moody algebrak _R [], consisting of polynomials in positive powers of a complex parameter which have coefficients in the compact real form ofk (the Lie algebra ofK).     

Critical gravity in the Chern–Simons modified gravity

We perform the perturbation analysis of the Chern–Simons modified gravity around the AdS₄ spacetime (its curvature radius ℓ) to obtain the critical gravity. In general, we could not obtain an explicit form of perturbed Einstein equation which shows a massive graviton propagation clearly, but for the Kerr–Schild perturbation and Chern–Simons coupling θ=kx/y, we find the AdS wave as a single massive solution to the perturbed Einstein equation. Its mass squared is given by M ²=[−9+(2ℓ ²/k−1)²]/4ℓ ². At the critical point of M ²=0 (k=ℓ ²/2), the solution takes the log-form and the linearized excitation energies vanish.     

New bounds for Tsallis parameter in a noncommutative phase–space entropic gravity and nonextensive Friedmann equations

In this paper, we have analyzed the nonextensive Tsallis statistical mechanics in the light of Verlinde’s formalism. We have obtained, with the aid of a noncommutative phase–space entropic gravity, a new bound for Tsallis nonextensive (NE) parameter (TNP) that is clearly different from the ones present in the current literature. We derived the Friedmann equations in a NE scenario. We also obtained here a relation between the gravitational constant and the TNP.     

Reconstruction method of computational ghost imaging based on non-local generalized total variation北大核心CSCD

鬼成像是一种能够透过大雾等恶劣环境的成像技术。针对传统鬼成像重建图像存在噪声较多、图像对比度较低等问题,将非局部广义全变分方法用于鬼成像的图像重建之中,提出基于非局部广义全变分的计算鬼成像重建方法。所提方法构造了一种非局部相关性权重设计梯度算子,将其代入全变分重建算法中,使得重建的图像能有效去除噪声的同时实现细节较好的还原。首先在不同条件下进行仿真模拟,得到所提方法的峰值信噪比相对其他方法提升1 dB左右,且具有更好的主观视觉效果,进而设计并搭建实验平台对算法的有效性进行验证,实验结果证明了所提方法在去除噪声和细节重建等方面的优越性。     

Einstein–Cartan gravity,Asymptotic Safety,and the running Immirzi parameter

In this paper we analyze the functional renormalization group flow of quantum gravity on the Einstein–Cartan theory space. The latter consists of all action functionals depending on the spin connection and the vielbein field (co-frame) which are invariant under both spacetime diffeomorphisms and local frame rotations. In the first part of the paper we develop a general methodology and corresponding calculational tools which can be used to analyze the flow equation for the pertinent effective average action for any truncation of this theory space. In the second part we apply it to a specific three-dimensional truncated theory space which is parametrized by Newton’s constant, the cosmological constant, and the Immirzi parameter. A comprehensive analysis of their scale dependences is performed, and the possibility of defining an asymptotically safe theory on this hitherto unexplored theory space is investigated. In principle Asymptotic Safety of metric gravity (at least at the level of the effective average action) is neither necessary nor sufficient for Asymptotic Safety on the Einstein–Cartan theory space which might accommodate different “universality classes” of microscopic quantum gravity theories. Nevertheless, we do find evidence for the existence of at least one non-Gaussian renormalization group fixed point which seems suitable for the Asymptotic Safety construction in a setting where the spin connection and the vielbein are the fundamental field variables.     

Stars in five-dimensional Kaluza–Klein gravity

The European Physical Journal C - We study the effect of ρ 0–γ mixing in e + e −→π + π − and its relevance for the comparison of the square modulus of...     

Gravastars in modified Gauss–Bonnet gravity

This paper aims to discuss the viable and analytic solution of the spherically symmetric gravastar model under the influence of modification of Gauss–Bonnet gravity, i.e., f(G) gravity, where G is the Gauss–Bonnet curvature term. For this purpose, we evaluate the field equations in corresponding theory and conservation equation with the help of an effective energy–momentum tensor. A mathematical formalism of the gravastar’s three regions, i.e., interior de-Sitter region, thin shell, and the exterior Schwarzschild vacuum region have been discussed. We, then analyze different realistic features, in particular energy, entropy, and length of the shell. The viability of these physical features is then examined through the graphical representations separately. Within the framework of an alternative theory, we have obtained the exact and singularity free model of gravastar.     

Stars in five-dimensional Kaluza–Klein gravity

In the five-dimensional Kaluza–Klein (KK) theory there is a well known class of static and electromagnetic-free KK-equations characterized by a naked singularity behavior, namely the Generalized Schwarzschild solution (GSS). We present here a set of interior solutions of five-dimensional KK-equations. These equations have been numerically integrated to match the GSS in the vacuum. The solutions are candidates to describe the possible interior perfect fluid source of the exterior GSS metric and thus they can be models for stars for static, neutral astrophysical objects in the ordinary (four-dimensional) spacetime.     

Classical and quantum algebras of non-local charges in σ models

We investigate the algebras of the non-local charges and their generating functionals (the monodromy matrices) in classical and quantum non-linear models. In the case of the classical chiral models it turns out that there exists no definition of the Poisson bracket of two monodromy matrices satisfying antisymmetry and the Jacobi identity. Thus, the classical non-local charges do not generate a Lie algebra. In the case of the quantum O(N) non-linear model, we explicitly determine the conserved quantum monodromy operator from a factorization principle together withP,T, and O(N) invariance. We give closed expressions for its matrix elements between asymptotic states in terms of the known two-particleS-matrix. The quantumR-matrix of the model is found. The quantum non-local charges obey a quadratic Lie algebra governed by a Yang-Baxter equation.Laboratoire associé au CNRS No. LA 280     

Quark–hadron phase transition in massive gravity

We study the quark–hadron phase transition in the framework of massive gravity. We show that the modification of the FRW cosmological equations leads to the quark–hadron phase transition in the early massive Universe. Using numerical analysis, we consider that a phase transition based on the chiral symmetry breaking after the electroweak transition, occurred at approximately 10 μs after the Big Bang to convert a plasma of free quarks and gluons into hadrons.     

Comparison of the lattice Λ parameter with the continuum Λ parameter in massless QCD

The ratio of the scale parameter Λ in massless QCD defined on a lattice to the one in the continuum theory is determined by performing one-loop renormalization of the coupling constant. Our calculation method on a lattice directly relates Λ^lattice to the continuum one in the minimal subtraction scheme. The effect of incorporation of massless quarks depends on a parameter λ which is introduced to avoid trouble with fermions on a lattice. For λ=1, which is Wilson's value, the ratio previously calculated by Hasenfratz in the pure gauge theory is changed as follows:

$\text{Δ}{}_{\mathrm{\alpha =1}}{}^{\mathrm{MOM}}\text{Δ}{}^{\mathrm{lattice}}\text{=83.5}\text{for pure SU(3) gauge theory;}$

$\text{Δ}{}_{\mathrm{\alpha =1}}{}^{\mathrm{MOM}}\text{Δ}{}^{\mathrm{lattice}}\text{=105.7}\text{for QCD with 3 flavors;}$

$\text{Δ}{}_{\mathrm{\alpha =1}}{}^{\mathrm{MOM}}\text{Δ}{}^{\mathrm{lattice}}\text{=105.7}\text{117.0 for QCD with 4 flavors.}$

Critical properties of the lattice QCD will also be discussed briefly.     

Duality in Yang’s theory of gravity

The historical route and the current status of a curvature-squared model of gravity, in the affine form proposed by Yang, is briefly reviewed. Due to its inherent scale invariance, it enjoys some advantage for quantization, similarly as internal Yang-Mills fields. However, the exact vacuum solutions with double duality properties exhibit a vacuum degeneracy. By modifying the duality via a scale breaking term, we demonstrate that only the Einstein equations with induced cosmological constant emerge for the classical background, even when coupled to matter sources.     

The rotating black hole in renormalizable quantum gravity: The three-dimensional Hořava gravity case

Recently Ho?ava proposed a renormalizable quantum gravity, without the ghost problem, by abandoning Einstein?s equal-footing treatment of space and time through the anisotropic scaling dimensions. Since then various interesting aspects, including the exact black hole solutions have been studied but no rotating   black hole solutions have been found yet, except some limiting cases. In order to fill the gap, I consider a simpler three-dimensional set-up with z=2$z=2$ and obtain the exact rotating black hole solution. This solution has a ring curvature singularity inside the outer horizon, like the four-dimensional Kerr black hole in Einstein gravity, as well as a curvature singularity at the origin. The usual mass bound works also here but in a modified form. Moreover, it is shown that the conventional first law of thermodynamics with the usual Hawking temperature and chemical potential does not work, which seems to be the genuine effect of Lorentz-violating gravity due to lack of the absolute horizon.