Gravity Metrics Research Articles

Heavy quark potential and jet quenching parameter in a rotating D-instanton background

We obtain the dual gravity metric of rotating nuclear matter by performing a standard Lorentz transformation on the static metric in the D-instanton background. We then study the effects of the angular velocity, instanton density, and temperature on the heavy quark potential. The results show that the angular velocity and the temperature promote dissociation of the quark–antiquark pair, and the instanton density suppresses dissociation. Similarly, according to the results for the jet quenching parameter, we find that the parameter increases with the increase in angular velocity, instanton density, and temperature, and the jet quenching parameter in the rotating D-instanton background is larger than that of N=4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {N} =4$$\\end{document} supersymmetric Yang–Mills (SYM) theory.

Comparative Analysis of Different Accessibility to Transportation Stations Gap Indices

In this paper, an analytical methodology is presented for computing the accessibility of transportation stations gap (ATSG) using differences between the accessibility indices for the public and private stations within a certain travel time thresholds in the city of Mashhad, Iran. Analyzing the conceptual differences among current modal accessibility methods of transportation stations can help to evaluate ATSG more accurately and minimizes the number of gaps between the private and public transportation stations. To address this need, we conducted a comparative analysis of the different accessibility methods and developed a novel approach based on spatio-temporal analysis. Three accessibility models were analyzed—contour (cumulative) (CN), potential access (PA), and gravity metric (GM)—considering three spatial factors (land use, transportation infrastructure, and population densities). Temporal factors including three travel time thresholds (3, 15, and 60 min) and three peak time periods (morning, noon, and afternoon) were analyzed to calculate the ATSG values for the private and public modes. Resulted ATSG values indicated superior accessibility for private cars in all three time thresholds applying three methods. However, our subsequent in-depth analysis of results determined that the ATSG values fluctuated as the time thresholds changed in the CN and PA methods. In the GM method, these values systematically increased as the time thresholds increased. The consequences of the GM method were more in line with reality and showed higher accuracy compared with others.

Null geodesic structure for the Barriola–Vilenkin spacetime via k-essence

Based on the work of Chandrasekhar [The Mathematical Theory of Black Holes, Chap. 3, Sec. 20 (Oxford University Press, 1992)], we investigate the null geodesic structure of the emergent Barriola–Vilenkin (BV) spacetime in the context of k-essence theory. For k-essence, the emergent gravity metric is a one-to-one correspondence with the BV metric connected to the Schwarzschild background, where the global monopole charge is replaced by the dark energy density. This equivalence holds specifically for a certain class of k-essence scalar fields that have been constructed by Gangopadhyay and Manna [Eur. Phys. Lett. 100, 49001 (2012)]. We have traced out different trajectories for null geodesic in the presence of dark energy for the k-essence emergent BV spacetime. It is demonstrated that the outcomes deviate from the typical Schwarzschild spacetime owing to the fundamental configuration with a constant dark energy density.

Liouville quantum gravity metrics are not doubling

Liouville quantum gravity metrics are not doubling

Universality: Random Matrices, Random Geometry and SPDEs

The postulate that large random systems can be described by limiting objects whose characteristic do not depend on the exact details of the models one started from is central in probability theory, under the name of universality. This workshop was aimed at uncovering the latest developments of this concept in the various topics where it is relevant, namely statistical physics, stochastic partial differential equations, random geometries and random matrices. It was in particular the occasion to feature some important recently introduced universal objects like the stochastic quantization of the Yang-Mills measure in dimensions 2 and 3, the KPZ fixed point, Liouville quantum gravity metrics and other objects connected to the Gaussian free field.

Collapsing scenario for the k-essence emergent generalized Vaidya spacetime in the context of massive gravity's rainbow

In this study, we investigate the collapsing scenario for the k-essence emergent Vaidya spacetime in the context of massive gravity's rainbow. For this study, we consider that the background metric is Vaidya spacetime in massive gravity's rainbow. We show that the k-essence emergent gravity metric closely resembles the new type of generalized Vaidya massive gravity metric with the rainbow deformations for null fluid collapse, where we consider the k-essence scalar field as a function solely of the advanced or the retarded time. The k-essence emergent Vaidya massive gravity rainbow mass function is also different. This new type k-essence emergent Vaidya massive gravity rainbow metric satisfies the required energy conditions. The existence of a locally naked central singularity and the strength and strongness of the singularities for the rainbow deformations of the k-essence emergent Vaidya massive gravity metric are the interesting outcomes of the present work.

Quantum Spin Coupled Entanglement and Space of Gravitational Degrees of Freedom

It is argued, based on indications from recent studies,as reported, that the degree of entanglement in vortex fields represented by spin orbit coupling is related to gravitational degree of freedom on vector vortex fields traversing spatial distances. Therefore the spin coupled quantum entanglement entropy can be understood as a gravity measurement in local inertial frames. The space of gravitational degrees of freedom has connections to quantum entanglement of spin coupled vortex flows. This relates quantum spin coupled entanglement with space time geometry. A gravity metric can have correspondence with quantum spin coupled entanglement.

Time-like geodesic structure for the emergent Barriola–Vilenkin type spacetime

For a particular type of k-essence scalar field, the k-essence emergent gravity metric is exactly mapped on to the Barriola–Vilenkin (BV) type metric for Schwarzschild background established by Gangopadhyay and Manna. Based on the Chandrasekhar, we report the exciting features of the time-like geodesic structure in the presence of dark energy in an emergent gravity scenario for this Barriola–Vilenkin type metric. We trace the different kinds of trajectories for time-like geodesic in the presence of dark energy for the k-essence emergent Barriola–Vilenkin spacetime, which is same as the Schwarzchild spacetime in view of the basic orientation, but the allowed ranges of the aphelion and perihelion distances are much more different. The bound and unbound orbits are plotted for a fixed value of the dark energy density.

Generalized Gibbons-Hawking-York term for f(R) gravity

A derivation of the Gibbons-Hawking-York boundary term for modified gravity metric is presented. The GHY term is generalized for the case of f(R) modified gravity. It is shown that a stable set of field equations can be formed with aid of the new GHY term for the case of f(R) gravity action. It is proven that the new term demands no particular value of δga or ∂Lδga on the boundary. Finally, the surface terms are shown to vanish in the derivation of the new equations.

The Hawking temperature in the context of dark energy for Kerr\u2013Newman and Kerr\u2013Newman\u2013AdS backgrounds

We show that the Hawking temperature is modified in the presence of dark energy in an emergent gravity scenario for Kerr–Newman(KN) and Kerr–Newman–AdS(KNAdS) background metrics. The emergent gravity metric is not conformally equivalent to the gravitational metric. We calculate the Hawking temperatures for these emergent gravity metrics along theta =0. Also we show that the emergent black hole metrics are satisfying Einstein’s equations for large r and theta =0. Our analysis is done in the context of dark energy in an emergent gravity scenario having k-essence scalar fields phi with a Dirac–Born–Infeld type Lagrangian. In KN and KNAdS background, the scalar field phi (r,t)=phi _{1}(r)+phi _{2}(t) satisfies the emergent gravity equations of motion at rrightarrow infty for theta =0.

The Hawking temperature in the context of dark energy for Reissner–Nordstrom and Kerr background

For emergent gravity metrics, presence of dark energy modifies the Hawking temperature. We show that for the spherically symmetric Reissner-Nordstrom (RN) background metric, the emergent metric can be mapped into a Robinson-Trautman blackhole. Allowed values of the dark energy density follow from rather general conditions. For some allowed value of the dark energy density this blackhole can have zero Hawking temperature i.e. the blackhole does not radiate. For a Kerr background along $\theta=0$, the emergent blackhole metric satisfies Einstein's equations for large $r$ and always radiates. Our analysis is done in the context of emergent gravity metrics having $k-$essence scalar fields $\phi$ with a Born-Infeld type lagrangian. In both cases the scalar field $\phi(r,t)=\phi_{1}(r)+\phi_{2}(t)$ also satisfies the emergent gravity equations of motion for $r\rightarrow\infty$ and $\theta=0$. \keywords{dark energy, k-essence, Reissner-Nordstrom and Kerr blackholes} \pacs{98.80.-k ;95.36.+x}

Bimetric structure formation: Non-Gaussian predictions

The minimal bimetric theory employing a disformal transformation between matter and gravity metrics is known to produce exactly scale-invariant fluctuations. It has a purely equilateral non-Gaussian signal, with an amplitude smaller than that of DBI inflation (with opposite sign) but larger than standard inflation. We consider non-minimal bimetric models, where the coupling $B$ appearing in the disformal transformation ${\hat g}_{\mn}= g_{\mn} -B\partial_\mu\phi\partial_\nu\phi$ can run with $\phi$. For power-law $B(\phi)$ these models predict tilted spectra. For each value of the spectral index, a distinctive distortion to the equilateral property can be found. The constraint between this distortion and the spectral index can be seen as a "consistency relation" for non-minimal bimetric models.

A GENERALIZED METRIC OF GRAVITATION

Useful expressions relating the metric components grr and gtt of the static isotropic space–time, and the scalar curvature R, with the general Lagrangian are obtained. A generalized metric of gravity is introduced, which is essentially nonsingular, and reducible to cosmological and hence Schwarzschild geometries by imposing a weak-field constraint.

Particle-like solution for SO(3) gauge field coupled to strong gravity

The classical equations for the SO(3) gauge field coupled with the strong gravity metric are considered in the f-g theory of Salam et al. The asymptotics of the regular static spherically symmetric solutions are obtained.