Properties Of Spacetime Research Articles

Quasiclassical model of inhomogeneous cosmology

Fluctuation terms and higher moments of a quantum state imply corrections to the classical equations of motion that may have implications in early-Universe cosmology, for instance in the state-dependent form of effective potentials. In addition, space-time properties are relevant in cosmology, in particular when combined with quantum corrections required to maintain general covariance in a consistent way. Here, an extension of previous investigations of static quasiclassical space-time models to dynamical ones is presented, describing the evolution of one-dimensional space as in the classical Lemaitre–Tolman–Bondi models. The corresponding spatial metric has two independent components, both of which are in general subject to quantum fluctuations. The main result is that individual moments from both components are indeed required for general covariance to be maintained at a semiclassical level, while quantum correlations between the components are less relevant.

Statistical Formulation of Background Independence in Manifestly-Covariant Quantum Gravity Theory

The notion of background independence is a distinguished feature that should characterize the conceptual foundation of any physically-acceptable theory of quantum gravity. It states that the structure of the space-time continuum described by classical General Relativity should possess an emergent character, namely, that it should arise from the quantum-dynamical gravitational field. In this paper, the above issue is addressed in the framework of manifestly-covariant quantum gravity theory. Accordingly, a statistical formulation of background independence is provided, consistent with the principle of manifest covariance. In particular, it is shown that the classical background metric tensor determining the geometric properties of space-time can be expressed consistently in terms of a suitable statistical average of the stochastic quantum gravitational field tensor. As an application, a particular realization of background independence is shown to hold for analytical Gaussian solutions of the quantum probability density function.

Tutorial for Space-Time ICI Parallel Cancellation Techniques for OFDM Systems

Orthogonal frequency division multiplexing (OFDM) expects the subcarriers to be orthogonal. However, the factors, such as residual carrier frequency, offset time variations due to Doppler shift or phase noise leads to a loss in the orthogonality between subcarriers and results in inter-carrier interference (ICI). Further developing the parallel cancellation (PC) scheme to mitigate the ICI of OFDM systems, the authors expand this OFDM symbol-based PC scheme into a space-time (ST) coded system. This simple space-time parallel cancellation (STPC) scheme is a technique that combines the useful properties of ST and PC schemes together. Computer simulations indicate that OFDM systems using the STPC scheme outperform the regular PC and ST systems in slow and fast frequency selective fading channels, specifically at a high signal-noise ratio (SNR). Furthermore, the error floor of the STPC-OFDM system is significantly lower than that of the regular ST systems without increasing computational load.

Retraced Lucid Multi-dimensional Chinese Logic System behind Chinese Medicine

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Some error has occurred while processing your request. Please try after some time. Export to End Note Procite Reference Manager Save my selection Research ArticleRetraced Lucid Multi-dimensional Chinese Logic System behind Chinese MedicineYu, Edwin CL Author Information Honorary Professor, School of Chinese Medicine, Hong Kong Baptist University, Hong Kong. Adjunct Professor, Hong Kong Institute of Integrative Medicine, the Chinese University of Hong Kong, Hong Kong. Director, InteMed Hong Kong This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal. Chinese Medicine and Culture ():10.1097/MC9.0000000000000054, March 24, 2023. | DOI: 10.1097/MC9.0000000000000054 Open PAP Metrics Abstract Chinese Logic system is not universally accepted. However, the ancient tacit knowledge behind the logic system permeated the culture and promoted numerous impactful inventions throughout the history. Traditional Chinese medicine with its effectiveness should also have stemmed out from such logic system. This paper aims to rearticulate the underlying lucid multi-dimensional logic system, which faded in obscurity only because of time-out loss of the mid-right concept. Retracing this past tacit but important concept could uncover a multi-dimensional system over a point relating to all matters while capturing the central core of the matter. The seemingly unmanageable multi-dimensional logic was strengthened by verification processes which affirmed its further extensions, and made up the language of the people, the concepts of Yin-Yang, and the development of extensions of Ba Gua derivatives, which furthered the interpretation of the space-time properties and Chinese medicine. Copyright © 2023 Shanghai University of Traditional Chinese Medicine. Source Retraced Lucid Multi-dimensional Chinese Logic System behind Chinese Medicine Chinese Medicine and Culture : March 24, 2023 Full-Size Email + Favorites Export View in Gallery Email to Colleague Colleague's E-mail is Invalid Your Name: Colleague's Email: Separate multiple e-mails with a (;). Message: Thought you might appreciate this item(s) I saw in Chinese Medicine and Culture. Your message has been successfully sent to your colleague. Some error has occurred while processing your request. Please try after some time. Export All Images to PowerPoint File Add to My Favorites Email to Colleague Colleague's E-mail is Invalid Your Name: Colleague's Email: Separate multiple e-mails with a (;). Message: Thought you might appreciate this item(s) I saw in Chinese Medicine and Culture. Your message has been successfully sent to your colleague. Some error has occurred while processing your request. Please try after some time. Export to End Note Procite Reference Manager Save my selection Article Level Metrics Article Keywords Keyword Highlighting Highlight selected keywords in the article text. Multi-dimensional logic system Traditional Chinese medicine Yin Yang Search for Similar Articles You may search for similar articles that contain these same keywords or you may modify the keyword list to augment your search. 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Phase transitions and stability of Eguchi-Hanson-AdS solitons

The Eguchi-Hanson-AdS5 family of spacetimes are a class of static, geodesically complete asymptotically locally AdS5 soliton solutions of the vacuum Einstein equations with negative cosmological constant. They have negative mass and are parameterized by an integer p ≥ 3 with a conformal boundary with spatial topology L(p, 1). We investigate mode solutions of the scalar wave equation on this background and show that, similar to AdS5, the geometry admits a normal mode spectrum (i.e. solutions that neither grow or decay in time). In addition, we also discuss other geometric properties of these soliton spacetimes, including the behaviour of causal geodesics and their thermodynamic properties. We also point out a surprising connection with the AdS soliton.

Renormalization group flow to effective quantum mechanics in the IR in an emergent dual holographic description for spontaneous chiral symmetry breaking

Implementing the Wilsonian renormalization group (RG) transformation in a nonperturbative way, we construct an effective holographic dual description with an emergent extradimension identified with an RG scale. Taking the large$-N$ limit, we obtain an equation of motion of an order-parameter field, here the chiral condensate for our explicit demonstration. In particular, an intertwined structure manifests between the first-order RG flow equations of renormalized coupling functions and the second-order differential equation of the order-parameter field, thus referred to as a nonperturbative RG-improved mean-field theory. Assuming translational symmetry as a vacuum state, we solve these nonlinear coupled mean-field equations based on a matching method between UV- and IR-regional solutions. As a result, we find an RG flow from a weakly-coupled chiral-symmetric UV fixed point to a strongly-correlated chiral-symmetry broken IR fixed point, where the renormalized velocity of Dirac fermions vanishes most rapidly and effective quantum mechanics appears at IR. Furthermore, we translate these RG flows of coupling functions into those of emergent metric tensors and extract out geometrical properties of the emergent holographic spacetime constructed from the UV- and IR-regional solutions. Surprisingly, we obtain the volume law of entanglement entropy in the Ryu-Takayanagi formula, which implies appearance of a black hole type solution in the limit of infinite cutoff even at zero temperature. We critically discuss our field theoretic interpretation for this solution in terms of potentially gapless multi-particle excitation spectra.

Space-Time Properties of Extreme RN Black Holes in Static Triangular Distribution

We studied the space-time properties of the triangular symmetric black hole in the case of extreme RN black hole. Because the neutral test particle is only affected by space-time in the curved space-time, we chose the triangular symmetric black hole as the model with which to study the motion of the test particle in this case. The curvature tensor and curvature scalar were calculated by giving the metric and the Christoffel Symbol, and then the kinematics equation of the test particle was obtained and analyzed by using these quantities. Then we analyzed the relationship between the coordinate distance and the inherent distance, the relationship between the coordinate time and the inherent time, the inherent velocity and the coordinate velocity of light, and then verified the correctness of general relativity. Next, the one-dimensional effective potential and two-dimensional effective potential of the system under different separation distances were analyzed. Finally, we analyzed and explored the innermost stable circular orbit, calculated all the Lagrange points under this model, and expounded some applications of circular orbit in astrophysics.

Noncommutative-Geometry Wormholes Based on the Casimir Effect

While wormholes are as good a prediction of Einstein’s theory as black holes, they are subject to severe restrictions from quantum field theory. In particular, holding a wormhole open requires a violation of the null energy condition, calling for the existence of exotic matter. The Casimir effect has shown that this physical requirement can be met on a small scale, thereby solving a key conceptual problem. The Casimir effect does not, however, guarantee that the small-scale violation is sufficient for supporting a macroscopic wormhole. The purpose of this paper is to connect the Casimir effect to noncommutative geometry, which also aims to accommodate small-scale effects, the difference being that these can now be viewed as intrinsic properties of spacetime. As a result, the noncommutative effects can be implemented by modifying only the energy momentum tensor in the Einstein field equations, while leaving the Einstein tensor unchanged. The wormhole can therefore be macroscopic in spite of the small Casimir effect.

Echoes of charged black-bounce spacetimes

In present work, the evolution of scalar field and electromagnetic field under the background of the charged black-bounce spacetimes are investigated, and we obtain an obvious echoes signal which appropriately reports the properties of the charged black-bounce spacetimes and disclose the physical reasons behind such phenomena. Furthermore, by studying the quasinormal ringdown, we analyze the three states of the charged black-bounce spacetimes in detail, our results show that the echoes signal only appears when (|{Q}|le m) and (|{l}|> m+ sqrt{m ^{2}-Q^{2} }) in this spacetime, while when the parameters demand (|{Q}|>m), the echoes signal will be transformed into a quasinormal ringdown of the two-way traversable wormhole, and the charged black-bounce is a regular black hole with normal horizons by requiring (|{Q}|le m) and (|{l}|< m-sqrt{m ^{2}-Q^{2} }).

Toward a New Generation of Compact Transportable Yb+ Optical Clocks

Optical atomic clocks are currently one of the most sensitive tools making it possible to precisely test the fundamental symmetry properties of spacetime and Einstein’s theory of relativity. At the same time, the extremely high stability and accuracy of compact transportable optical clocks open new perspectives in important fields, such as satellite navigation, relativistic geodesy, and the global time and frequency network. Our project aimed to develop a compact transportable optical clock based on a single ytterbium ion. We present the first prototype of the Yb+ clock (298 kg in 1 m3) and present several solutions aimed to improve the clock’s robustness to approach the demands of a space-qualified system. We present spectroscopic studies of a 435.5 nm quadrupole clock transition with Fourier-limited spectra of 25 Hz. The estimated instability of the output frequency at 1 GHz, which was down-converted with an optical frequency comb (OFC), is at the level of 9×10−15/τ, and the long-term instability and inaccuracy are at the level of 5×10−16. As the next steps, we present a new design for the clock laser and the OFC.

All-optical spatio-temporal metrology for isolated attosecond pulses

Characterizing an isolated attosecond pulse (IAP) is essential for its potential applications. A complete characterization of an IAP ultimately requires the determination of its electric field in both time and space domains. However, previous methods, like the widely-used RABBITT and attosecond streaking, only measure the temporal profile of the attosecond pulse. Here we demonstrate an all-optical method for the measurement of the space-time properties of an IAP. By introducing a non-collinear perturbing pulse to the driving field, the process of IAP generation is modified both spatially and temporally, manifesting as a spatial and a frequency modulation in the harmonic spectrum. By using a FROG-like retrieval method, the spatio-spectral phases of the harmonic spectrum are faithfully extracted from the induced spatio-spectral modulations, which allows a thorough characterization of the IAP in both time and space. With this method, the spatio-temporal structures of the IAP generated in a two-color driving field in both the near- and far-field are fully reconstructed, from which a weak spatio-temporal coupling in the IAP generation is revealed. Our approach overcomes the limitation in the temporal measurement in conventional in situ scheme, providing a reliable and holistic metrology for IAP characterization.

Strongest Atomic Physics Bounds on Noncommutative Quantum Gravity Models.

Investigations of possible violations of the Pauli exclusion principle represent critical tests of the microscopic space-time structure and properties. Space-time noncommutativity provides a class of universality for several quantum gravity models. In this context the VIP-2 lead experiment sets the strongest bounds, searching for the Pauli exclusion principle violating atomic transitions in lead, excluding the θ-Poincaré noncommutative quantum gravity models far above the Planck scale for nonvanishing θ_{μν} electriclike components, and up to 6.9×10^{-2} Planck scales if θ_{0i}=0.

Photon regions, shadow observables, and constraints from M87* of a charged rotating black hole

Inspired by the observations of supermassive black hole M87* in \emph{Event Horizon Telescope }(EHT) experiment, a remarkable surge in black hole physics is to use the black hole shadow's observables to distinguish general relativity (GR) and modified theories of gravity (MoG), which could also help to disclose the astrophysical nature of the center black hole in EHT observation. In this paper, we shall extensively carry out the study of a charged rotating black hole in conformal gravity, in which the term related with the charge has different falloffs from the usual Kerr-Newman (KN) black hole. We investigate the spacetime properties including the horizons, ergospheres and the photon regions; afterward, we show the boundary of black hole shadow and investigate its characterized observables. The features closely depend on the spin and charge parameters, which are compared with those in Kerr and KN black holes. Then presupposing the M87* a charged rotating black hole in conformal gravity, we also constrain the black hole parameters via the observation constraints from EHT experiment. We find that the constraints on the inferred circularity deviation, $\Delta C \lesssim 0.1$, and on the shadow axial ratio, $1< D_x \lesssim 4/3$, for the M87* black hole are satisfied for the entire parameter space of the charged rotating black hole in conformal gravity. However, the shadow angular diameter $\theta_d = 42 \pm 3 \mu as$ will give upper bound on the parameter space. Our findings indicate that the current charged rotating black hole in conformal gravity could be a candidate for astrophysical black holes. Moreover, the EHT observation on the axial ratio $D_x$ may help us to distinguish Kerr black hole and the current charged rotating black hole in conformal gravity in some parameter space.

Electromagnetic Fields around Black Holes in Einstein Æther Gravity

Axial symmetry and stationary properties of spacetime allow to find exact analytical solutions of differential equations describing fields and particles in a gravitational background. The present work is mainly devoted to derivation of exact solutions of Maxwell’s equations for magnetic fields generated by current loops around static black holes (BHs) in Einstein-aether gravity based on the spacetime symmetries in both regions: (i) interior and (ii) exterior to the current loop for a proper observer. The spacetime symmetries are applied in separating variables to solve the second order ordinary differential equation for vector potential of electromagnetic field and the equations of motion of test particles around the aether BH. We also study effects of the aether field on innermost stable circular orbits (ISCOs) of the test particles assuming the current loop position is placed there. It is obtained that the ISCO radius, as well as dipole magnetic moment of the current loop decrease with the increase of the aether parameter c14. Moreover, the performed analysis indicates that the aether field causes a decrease in the magnetic field inside and outside the current loop due to the change of its position.

Deterministic Terahertz Wave Control in Scattering Media.

Scattering-assisted synthesis of broadband optical pulses is recognized to have a cross-disciplinary fundamental and application importance. Achieving full-waveform synthesis generally requires means for assessing the instantaneous electric field, i.e., the absolute electromagnetic phase. These are generally not accessible to established methodologies for scattering-assisted pulse envelope and phase shaping. The lack of field sensitivity also results in complex indirect approaches to evaluate the scattering space–time properties. The terahertz frequency domain potentially offers some distinctive new possibilities, thanks to the availability of methods to perform absolute measurements of the scattered electric field, as opposed to optical intensity-based diagnostics. An interesting conceptual question is whether this additional degree of freedom can lead to different types of methodologies toward wave shaping and direct field-waveform control. In this work, we theoretically investigate a deterministic scheme to achieve broadband, spatiotemporal waveform control of terahertz fields mediated by a scattering medium. Direct field access via time-domain spectroscopy enables a process in which the field and scattering matrix of the medium are assessed with minimal experimental efforts. Then, illumination conditions for an arbitrary targeted output field waveform are deterministically retrieved through numerical inversion. In addition, complete field knowledge enables reconstructing field distributions with complex phase profiles, as in the case of phase-only masks and optical vortices, a significantly challenging task for traditional implementations at optical frequencies based on intensity measurements aided with interferometric techniques.

Anisotropic noncommutative Schwarzschild metamaterial

The propagation of light through the metamaterial analogue to the Noncommutative Schwarzschild spacetime is studied. NonCommutative (NC) spacetime properties have been considered in several high energy theories which in the context of gravitation, those may be considered as effective theories of quantum gravity. Following the approach established in [6], we found the properties related to the metamaterial corresponding to the NC-Schwarzschild spacetime. The main effects observed in the simulations are a deviation in the light path and a difference in the electric field norm of the beam compared to the propagation in the standard Schwarzschild metamaterial. These measurable effects are useful to determine the existence of noncommutativity. Also, metamaterial simulations offer a novel way to explore possible observable consequences of modified theories of General Relativity.

Stabilizing spherical energy shells with angular momentum in gravitational backgrounds

Spherical energy shells in General Relativity tend to collapse due to gravitational effects and/or due to tension effects. Shell stabilization may be achieved by modifying the gravitational properties of the background spacetime. Thus, gravastars consist of stiff matter shells with an interior deSitter space and an exterior Schwarzshild spacetime whose attractive gravity balances the interior repulsive gravity of the interior deSitter spacetime leading to a stable stiff matter shell. Similar stabilization effects may be achieved by considering rotating shells. Here we study the stability of slowly rotating fluid shells. We show that the angular velocity of the shell has stabilizing properties analogous to the repulsive deSitter gravity of the interior of a gravastar. We thus use the Israel junction conditions [W. Israel, Nuovo Cim. B 44S10 (1966) 1, Erratum: Nuovo Cim. B 48 (1967) 463; N. Deruelle, M. Sasaki and Y. Sendouda, Prog. Theor. Phys. 119 (2008) 237, arXiv:0711.1150 [gr-qc]] and the fluid equation of state of the rotating shell to construct the dynamical equations that determine the evolution of the rotating shell radius. These dynamical equations depend on the parameters of the background spacetime and on the angular velocity of the shell. Assuming a rotating interior and a Schwarzschild exterior spacetime we show that the angular velocity of the shell has interesting stabilizing properties on the evolution of its radius R. Thus, rotating matter (or vacuum) shells can imitate black holes while avoiding the presence of a singularity and without the presence of an interior deSitter space.

TsT, black holes, and Toverline{T} + Joverline{T} + Toverline{J}

We generate a class of string backgrounds by a sequence of TsT transformations of the NS1-NS5 system that we argue are holographically dual to states in a single-trace Toverline{T} + Joverline{T} + Toverline{J} -deformed CFT2. The new string backgrounds include general rotating black hole solutions with two U(1) charges as well as a smooth solution without a horizon that is interpreted as the ground state. As evidence for the correspondence we (i) derive the long string spectrum and relate it to the spectrum of the dual field theory; (ii) show that the black hole thermodynamics can be reproduced from single-trace Toverline{T} + Joverline{T} + Toverline{J} -deformed CFTs; and (iii) show that the energy of the ground state matches the energy of the vacuum in the dual theory. We also study geometric properties of these new spacetimes and find that for some choices of the parameters the three-dimensional Ricci scalar in the Einstein frame can become positive in a region outside the horizon before reaching closed timelike curves and singularities.

Quasiperiodic oscillations from noncommutative inspired black holes

We investigate the dynamics of test particles in the spacetime of noncommutative inspired black holes (NCi BHs). In this context, we first analyse spacetime properties of the NCi BHs together with innermost stable circular orbits (ISCOs) for the particles. It is observed that whereas the ISCO radius does not depend on the NC parameter, the frequencies of the Keplerian orbits and harmonic oscillations are NC parameter dependent. As an application, we consider quasiperiodic oscillations (QPOs) to test effects of the NC gravity around the BHs using twin-peak QPOs frequencies. It is found that the frequency changes even in the presence of the critical NC parameter are smaller than the error in the frequency measurements. The method developed for testing gravity using data from twin peak QPOs may also be applied to other alternate theories of gravity to obtain restrictions on the central BH parameters. We show that the orbits of QPOs lie near ISCO. This assumption may be helpful in solving the ISCO measurement problems in astrophysical observations. In addition, we determine the mass of the central BH in microquasar GRS 1915-105 and the QPO orbit in both the relativistic precession and warped disk models. It is shown that these parameters do not depend on the quantum corrections in the NC gravity. Lastly, we investigate the gravitational capture cross-section for photons and show that the effect of the NC parameter is also less than the error in shadow measurements of the supermassive BH (SMBH) Messier 87 (M87).

Searching new particles at neutrino telescopes with quantum-gravitational decoherence

We discuss the interplay of wave packet decoherence and decoherence induced by quantum gravity via interactions with spacetime foam for high-energy astrophysical neutrinos. In this context, we point out a compelling consequence of the expectation that quantum gravity should break global symmetries, namely that quantum-gravity induced decoherence may not only be the most sensitive probe for quantum properties of spacetime but also can provide both a powerful tool for the search for new particles, including totally decoupled backgrounds interacting only gravitationally, and at the same time a window into the intricacies of black hole information processing.