arXiv subjects

Jianbo Lu

Publications and source records attributed to Jianbo Lu.

At least 37 records · Page 2Linked to original sources

arXiv2024

Lorentz group in gravity theories

In this paper, it is argued that in gravity theories the local Lorentz group can not be considered as a gauge group in the sense of Yang-Mills theories, the Lorentz connection is not a gauge potential but an artificial force, the inertial force. A genuine gravity theory should be a translation gauge theory, though a unnormal gauge theory. All the three theories of the Geometrical Trinity of Gravity are translation gauge theories. A real gravity theory should get rid of "gauging" Lorentz group. The covariantization of the teleparallel gravity is not necessary physically.

gr-qc↗

arXiv2024

Investigating the Physical Properties of Traversable Wormholes in the Modified $f(R,T)$ Gravity

In the paper, we analyze some physical properties of static traversable WH within the framework of $f(R,T)$ modified gravitational theory. Firstly, we explore the validity of the null, weak, dominant and strong energy conditions for wormhole matter for the considered $f(R,T)=R+αR^2+λT$ model. Research shows that it is possible to obtain traversable WH geometry without bring in exotic matter that violates the null energy condition in the $f(R,T)$ theory. The violation of the dominant energy condition in this model may be related to quantum fluctuations or indicates the existence of special matter that violates this EC within the wormhole. Moreover, it is found that in the $f(R,T)=R+αR^2+λT$ model, relative to the GR, the introduction of the geometric term $αR^2$ has no remarkable impact on the wormhole matter components and their properties, while the appearance of the matter-geometry coupling term $λT$ can resolve the question that WH matter violates the null, weak and strong energy condition in GR. Additionally, we investigate dependency of the valid NEC on model parameters and quantify the matter components within the wormhole using the ``volume integral quantifier". Lastly, based on the modified Tolman-Oppenheimer-Volkov equation, we find that the traversable WH in this theory is stable. On the other hand, we use the classical reconstruction technique to derive wormhole solution in $f(R,T)$ theory and discuss the corresponding ECs of matter. It is found that all four ECs (NEC, WEC, SEC and DEC) of matter in the traversable wormholes are valid in this reconstructed $f(R,T)$ model, i.e we provide a wormhole solution without introducing the exotic matter and special matter in $f(R,T)$ theory.

gr-qc↗

arXiv2024

Validity of energy conditions of matter in traversable wormholes under the $f(Q)$ modified gravity theory

In the framework of the theory of general relativity, in order to obtain stable traversable wormholes, matter needs to violate the null energy condition. It is well known that the violation of the energy condition (EC) of matter leads to various physical problems. To address this issue, researchers have turned their attention to exploring modified theories of gravity, aiming to avoid the violation of ECs by introducing geometric terms. In this paper, within the framework of the $f(Q)$ modified gravitational theory, we investigate the effectiveness of ECs for matter in traversable wormholes. We examine the compliance of four types of energy conditions (weak energy condition, null energy condition, dominant energy condition, and strong energy condition) in the model by selecting a power-law model for $f(Q)$ and considering different shape functions $b(r)$. Our study reveals that for traversable wormholes realized through the $f(Q)$ modified gravity theory using the power-law model $f(Q)=a(-Q)^n$, all four types of ECs for matter can be satisfied. There is no need to introduce exotic matter (violating the null energy condition) or special matter (violating other energy conditions) artificially in the physics of wormholes.

gr-qc↗

arXiv2024

Fermionic steering is not nonlocal in the background of dilaton black hole

We study the redistribution of the fermionic steering and the relation among fermionic Bell nonlocality, steering, and entanglement in the background of the Garfinkle-Horowitz-Strominger dilaton black hole. We analyze the meaning of the fermionic steering in terms of the Bell inequality in curved spacetime. We find that the fermionic steering, which is previously found to survive in the extreme dilaton black hole, cannot be considered to be nonlocal. We also find that the dilaton gravity can redistribute the fermionic steering, but cannot redistribute Bell nonlocality, which means that the physically inaccessible steering is also not nonlocal. Unlike the inaccessible entanglement, the inaccessible steering may increase non-monotonically with the dilaton. Furthermore, we obtain some monogamy relations between the fermionic steering and entanglement in dilaton spacetime. In addition, we show the difference between the fermionic and bosonic steering in curved spacetime.

quant-ph↗

arXiv2022

Equality scale-based and sound horizon-based analysis of the Hubble tension

The Hubble horizon at matter-radiation equality ($k^{-1}_{\rm{eq}}$) and the sound horizon at the last scattering surface ($r_s(z_*)$) provides interesting consistency check for the $Λ$CDM model and its extensions. It is well known that the reduction of $r_s$ can be compensated by the increase of $H_0$, while the same is true for the standard rulers $k_{\rm{eq}}$. Adding extra radiational component to the early universe can reduce $k_{\rm{eq}}$. The addition of early dark energy (EDE), however, tends to increase $k_{\rm{eq}}$. We perform $k_{\rm{eq}}$- and $r_s$-based analyses in both the EDE model and the Wess-Zumino Dark Radiation (WZDR) model. In the latter case we find $ΔH_0 = 0.4$ between the $r_s$- and $k_{\rm{eq}}$-based datasets, while in the former case we find $ΔH_0 = 1.2$. This result suggests that the dark radiation scenario is more consistent in the fit of the two standard rulers ($k_{\rm{eq}}$ and $r_s$). As a forecast analyses, we fit the two models with a mock $k_{\rm{eq}}$ prior derived from \emph{Planck} best-fit $Λ$CDM model. Compared with the best-fit $H_0$ in baseline $Λ$CDM model, we find $ΔH_0 = 1.1$ for WZDR model and $ΔH_0 = - 2.4$ for EDE model.

astro-ph.CO↗

arXiv2021

From GR to STG -- Inheritance and development of Einstein's heritages

A review of General Relativity, Teleparallel Gravity, and Symmetric Teleparallel gravity is given in this paper. By comparing these theories some conclusions are obtained. It is argued that the essence of gravity is the translation connection. The gauge group associated with gravity is merely the translation group. Lorentz group is relevant with only inertial effects and has nothing to do with gravity. The Lorentz connection represents a inertial force rather than a gauge potential, which leads to the equivalent principle. Neither curvature nor torsion belongs to spacetime but certain transformation group and their connections. The statement "gravity is equivalent to curved spacetime" is a misunderstanding, not Einstein's real intention. Not curvature but torsion i.e. the anholonomy of the tetrad represents gravity. Einstein's great genius is choosing metric as the fundamental variable to describe gravity. Some conceptual issues, for example, general covariance, Lorentz covariance, reference system dependence, gravitational energy-momentum are discussed.

gr-qc↗

arXiv2021

Dynamical dark energy after Planck CMB final release and $H_0$ tension

In this article we compare a variety of well known dynamical dark energy models using the cosmic microwave background measurements from the 2018 Planck legacy and 2015 Planck data releases, the baryon acoustic oscillations measurements and the local measurements of $H_0$ obtained by the SH0ES (Supernovae, $H_0$, for the Equation of State of Dark energy) collaboration analysing the Hubble Space Telescope data. We discuss the alleviation of $H_0$ tension, that is obtained at the price of a phantom-like dark energy equation of state. We perform a Bayesian evidence analysis to quantify the improvement of the fit, finding that all the dark energy models considered in this work are preferred against the $Λ$CDM scenario. Finally, among all the possibilities analyzed, the CPL model is the best one in fitting the data and solving the $H_0$ tension at the same time. However, unfortunately, this dynamical dark energy solution is not supported by the baryon acoustic oscillations (BAO) data, and the tension is restored when BAO data are included for all the models.

astro-ph.CO↗

arXiv2020

Salient Bundle Adjustment for Visual SLAM

Recently, the philosophy of visual saliency and attention has started to gain popularity in the robotics community. Therefore, this paper aims to mimic this mechanism in SLAM framework by using saliency prediction model. Comparing with traditional SLAM that treated all feature points as equal important in optimization process, we think that the salient feature points should play more important role in optimization process. Therefore, we proposed a saliency model to predict the saliency map, which can capture both scene semantic and geometric information. Then, we proposed Salient Bundle Adjustment by using the value of saliency map as the weight of the feature points in traditional Bundle Adjustment approach. Exhaustive experiments conducted with the state-of-the-art algorithm in KITTI and EuRoc datasets show that our proposed algorithm outperforms existing algorithms in both indoor and outdoor environments. Finally, we will make our saliency dataset and relevant source code open-source for enabling future research.

cs.RO↗

arXiv2020

Linearized physics and gravitational-waves polarizations in the Palatini formalism of GBD theory

A generalized Brans-Dicke (GBD) theory in the framework of Palatini formalism are proposed in this paper. We derive the field equations by using the variational approach and obtain the linearized equations by using the weak-field approximation method. We show various properties of the geometrical scalar field in the Palatini-formalism of GBD theory: it is massless and source-free, which are different from the results given in the metric-formalism of GBD theory. Also, we investigate the polarization modes of gravitational waves (GWs) by using the the geodesic deviation method and the Newman-Penrose method in the Palatini-GBD theory. It is observed that there are three polarizations modes and four oscillation in the Palatini-GBD theory. Concretely, they are the two transverse tensor ($+$) and ($\times$) standard polarization modes, and one breathing mode (with two oscillation). The results of GWs polarization in the Palatini-GBD theory are different from that in the metric-GBD theory, where there are four polarizations modes: the two standard tensorial modes ($+$ and $\times$), a scalar breathing mode, and a massive scalar mode that is a mix of the longitudinal and the breathing polarization. Comparing with the Palatini-$f(\tilde{R})$ theory and the General Relativity, we can see that the extra breathing mode of GWs polarization can be found in the Palatini-GBD theory. At last, the expression of the parameterized post Newton (PPN) parameter is derived, which could pass through the experimental test.

gr-qc↗

arXiv2019

Challenging bulk viscous unified scenarios with cosmological observations

In a spatially flat Friedmann-Lemaître-Robertson-Walker universe, we investigate a unified cosmic fluid scenario endowed with bulk viscosity in which the coefficient of the bulk viscosity has a power law evolution. The power law in the bulk viscous coefficient is a general case in this study which naturally includes several choices as special cases. Considering such a general bulk viscous scenario, in the present work we have extracted the observational constraints using the latest cosmological datasets and examine their behaviour at the level of both background and perturbations. From the observational analyses, we find that a non-zero bulk viscous coefficient is always favored and some of the models in this series are able to weaken the current tension on $H_0$ for some dataset. However, from the Bayesian evidence analysis, $Λ$CDM is favored over the bulk viscous model.

astro-ph.CO↗

arXiv2019

The generalized Brans-Dicke theory and its cosmology

A generalized Brans-Dicke (GBD) theory is proposed and studied in this paper. The interesting property has been found in the GBD theory, for example it can naturally solve the problem of γvalue emerging in f(R) modified gravity without introducing the so-called chameleon mechanism. In addition, it can be found that the GBD theory could solve some problems existing in other theories. (1) The $f(R)$ theory is equivalent to the BD theory with a potential (abbreviated as BDV) for taking a specific value of the BD parameter ω=0, where the specific choice: ω=0 is quite exceptional, and it is hard to understand the corresponding absence of the kinetic-energy term for the field. However, fields in the GBD own the non-disappeared dynamical effect. (2) In the double scalar-fields quintom model, it is required to include both the canonical quintessence field and the non-canonical phantom field in order to make the state parameter to cross over w=-1, while several fundamental problems are associated with phantom field, such as the problem of negative kinetic term and the fine-tuning problem, etc. While, in the GBD model, the state parameter of geometrical dark energy can cross over the phantom boundary as achieved in the quintom model, without bearing the problems existing in the quintom model. (3) The GBD theory tends to investigate the physics from the viewpoint of geometry, while the BDV or the two scalar-fields quintom model tends to solve physical problems from the viewpoint of matter. It is possible that several special characteristics of scalar fields could be revealed through studies of geometrical gravity in the GBD. As an example, we investigate the potential V of the BD scalar field, and an effective form of V could be given by studying on the GBD theory. And, it seems that a viable condition for the BD theory could be found.

gr-qc↗

arXiv2019

Cosmology in symmetric teleparallel gravity and its dynamical system

We explore an extension of the symmetric teleparallel gravity denoted the $f(Q)$ theory, by considering a function of the nonmetricity invariant $Q$ as the gravitational Lagrangian. Some interesting properties could be found in the $f(Q)$ theory by comparing with the $f(R)$ and $f(T)$ theories. The field equations are derived in the $f(Q)$ theory. The cosmological application is investigated. In this theory the accelerating expansion is an intrinsic property of the universe geometry without need of either exotic dark energy or extra fields. And the state equation of the geometrical dark energy can cross over the phantom divide line in the $f(Q)$ theory. In addition, the dynamical system method are investigated. It is shown that there are five critical points in the STG model for taking $f(Q)=Q+αQ^2$. The critical points $P_{4}$ and $P_{5}$ are stable. $P_{4}$ corresponds to the geometrical dark energy dominated de Sitter universe ($w_{tot}^{eff}$=-1), while $P_{5}$ corresponds to the matter dominated universe ($w_{tot}^{eff}$=0). Given that $P_{4}$ represents an attractor, the cosmological constant problems, such as the fine tuning problem, could be solved in the STG model.

gr-qc↗

arXiv2019

Linearized modified gravity theories and gravitational waves physics in the GBD theory

The generalized Brans-Dicke (abbreviated as GBD) theory is obtained by replacing the Ricci scalar $R$ in the original Brans-Dicke (BD) action with an arbitrary function $f(R)$. Comparing with other theories, some interesting properties have been found or some problems existing in other theories could be solved in the GBD theory. For example, (1) the state parameter of geometrical dark energy in the GBD model can cross over the phantom boundary $w=-1$, without bearing the problems existing in the quintom model (e.g. the problem of negative kinetic term and the fine-tuning problem, etc); (2) $f(R)$ theory is equivalent to the BD theory with a potential (BDV) with the couple parameter $ω=0$, where the kinetic term of field in the equivalent BDV theory is absent. While the scalar fields in the GBD own the non-disappeared kinetic term, when one compares the GBD theory with the $f(R)$ theory. In this paper, we continue to investigate the GBD theory. Using the method of the weak-field approximation, we explore the linearized physics in the GBD theory. The linearized equations of the gravitational field and two scalar fields are given. We investigate their solutions in the linearized theory for a point mass. It is shown that the problem of the $γ$ (parametrized post-Newtonian parameter) value in the $f(R)$ theory could be solved in the GBD theory, where the theoretical $γ$ value in the GBD theory can be consistent with the observational results. At last, we study the gravitational waves physics in the vacuum for the GBD theory. It is found that the gravitational radiation in the GBD theory has new freedoms beyond the two standard modes in the general relativity theory.

gr-qc↗

arXiv2017

Test of the Weak Equivalence Principle using LIGO observations of GW150914 and Fermi observations of GBM transient 150914

About 0.4s after the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected a transient gravitational-wave (GW) signal GW150914, the Fermi Gamma-ray Burst Monitor (GBM) also found a weak electromagnetic transient (GBM transient 150914). Time and location coincidences favor a possible association between GW150904 and GBM transient 150914. Under this possible association, we adopt Fermi's electromagnetic (EM) localization and derive constraints on possible violations of the Weak Equivalence Principle (WEP) from the observations of two events. Our calculations are based on four comparisons: (1)The first is the comparison of the initial GWs detected at the two LIGO sites. From the different polarizations of these initial GWs, we obtain a limit on any difference in the parametrized post-Newtonian (PPN) parameter $Δγ\lesssim 10^{-10}$. (2) The second is a comparison of GWs and possible EM waves. Using a traditional super-Eddington accretion model for GBM transient 150914, we again obtain an upper limit $Δγ\lesssim 10^{-10}$. Compared with previous results for photons and neutrinos, our limits are five orders of magnitude stronger than those from PeV neutrinos in blazar flares, and seven orders stronger than those from MeV neutrinos in SN1987A. (3) The third is a comparison of GWs with different frequencies in the range [35 Hz, 250 Hz]. (4) The fourth is a comparison of EM waves with different energies in the range [1 keV, 10 MeV]. These last two comparisons lead to an even stronger limit, $Δγ\lesssim 10^{-8}$. Our results highlight the potential of multi-messenger signals exploiting different emission channels to strengthen existing tests of the WEP.

gr-qc↗

arXiv2017

H-infinity Filtering for Cloud-Aided Semi-active Suspension with Delayed Information

This chapter presents an H-infinity filtering framework for cloud-aided semiactive suspension system with time-varying delays. In this system, road profile information is downloaded from a cloud database to facilitate onboard estimation of suspension states. Time-varying data transmission delays are considered and assumed to be bounded. A quarter-car linear suspension model is used and an H-infinity filter is designed with both onboard sensor measurements and delayed road profile information from the cloud. The filter design procedure is designed based on linear matrix inequalities (LMIs). Numerical simulation results are reported that illustrates the fusion of cloud-based and on-board information that can be achieved in Vehicleto- Cloud-to-Vehicle (V2C2V) implementation.

eess.SY↗

arXiv2016

Cosmic constraint on massive neutrinos in viable f(R) gravity with producing LCDM background expansion

Tensions between several cosmic observations were found recently, such as the inconsistent values of $H_{0}$ (or $σ_{8}$) were indicated by the different cosmic observations. Introducing the massive neutrinos in $Λ$CDM could potentially solve the tensions. Viable $f(R)$ gravity producing $Λ$CDM background expansion with massive neutrinos is investigated in this paper. We fit the current observational data: Planck-2015 CMB, RSD, BAO and SNIa to constrain the mass of neutrinos in viable $f(R)$ theory. The constraint results at 95\% confidence level are: $Σm_ν<0.202$ eV for the active neutrino case, $m_{ν, sterile}^{eff}<0.757$ eV with $N_{eff}<3.22$ for the sterile neutrino case. For the effects by the mass of neutrinos, the constraint results on model parameter at 95\% confidence level become $f_{R0}\times 10^{-6}> -1.89$ and $f_{R0}\times 10^{-6}> -2.02$ for two cases, respectively. It is also shown that the fitting values of several parameters much depend on the neutrino properties, such as the cold dark matter density, the cosmological quantities at matter-radiation equality, the neutrino density and the fraction of baryonic mass in helium. At last, the constraint result shows that the tension between direct and CMB measurements of $H_0$ gets slightly weaker in the viable $f(R)$ model than that in the base $Λ$CDM model.

astro-ph.CO↗

arXiv2016

Cosmological constraints on coupled dark energy

The coupled dark energy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as $\bar{Q}=3Hξ_x\barρ_x$, which is related to the interaction rate and energy density of dark energy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, $fσ_8(z)$ data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us there is no evidence of interaction at 2$σ$ level, it is very hard to distinguish different coupled models from other ones.

astro-ph.CO↗

arXiv2016

Cosmology in Poincare gauge gravity with a pseudoscalar torsion

A cosmology of Poincare gauge theory is developed, where several properties of universe corresponding to the cosmological equations with the pseudoscalar torsion function are investigated. The cosmological constant is found to be the intrinsic torsion and curvature of the vacuum universe and is derived from the theory naturally rather than added artificially, i.e. the dark energy originates from geometry and includes the cosmological constant but differs from it. The cosmological constant puzzle, the coincidence and fine tuning problem are relieved naturally at the same time. By solving the cosmological equations, the analytic cosmological solution is obtained and can be compared with the LCDM model. In addition, the expressions of density parameters of the matter and the geometric dark energy are derived, and it is shown that the evolution of state equations for the geometric dark energy agrees with the current observational data. At last, the full equations of linear cosmological perturbations and the solutions are obtained.

gr-qc↗