arXiv subjects

Xiaolong Gong

Publications and source records attributed to Xiaolong Gong.

7 recordsLinked to original sources

arXiv2026

Nonlocal correlations of fermionic entanglement in the spacetime of Einstein-Gauss-Bonnet black hole

The investigation of nonclassical correlations in curved spacetimes offers key insights into the intersection of quantum information theory and gravitational physics. This paper studies two nonlocal correlation measures, non local advantage of quantum coherence (NAQC) and Bell nonlocality (BN) in a $d$-dimensional spherically symmetric Einstein-Gauss-Bonnet (EGB) black hole spacetime. We consider two observers (Alice and Rob) initially sharing a maximally entangled Bell state: Alice freely falls into the black hole (inertial Kruskal frame), while Rob accelerates outside the horizon (non-inertial Schwarzschild-like frame). The Unruh-Hawking effect modifies Rob's field modes, requiring Bogoliubov transformations to relate the two frames. We derive the mixed bipartite density matrix for fermionic fields and analytical expressions for NAQC and BN, which depend on Hawking temperature (itself governed by $α$, $d$, and $r_h$). Our results show both correlations degrade monotonically with increasing Hawking temperature, confirm the NAQC-BN hierarchical relationship persists in EGB spacetime, and highlighting the impact of high curvature corrections on quantum resources.

gr-qc↗

arXiv2024

Multiple measurements on the cosmic curvature using Gaussian process regression without calibration and a cosmological model

In this letter, we propose an improved cosmological model-independent method to measure cosmic curvature, combining the recent measurements of transverse and line-of-sight directions in the baryon acoustic oscillations (BAO) with cosmic chronometers (CC) datasets. Considering that the CC dataset is discrete and includes only 32 $H(z)$ measurements, we apply Gaussian process (GP) regression to fit the CC dataset and reconstruct them. Our methodology, which does not need the calibration or selection of any cosmological model, provide multiple measurements of spatial curvature ($Ω_K$) at different redshifts (depending on the redshift coverage of BAO dataset). For combination of all BAO data, we find that the constraint result on cosmic curvature is $Ω_K=-0.096^{+0.190}_{-0.195}$ with $1σ$ observational uncertainty. Although the measured $Ω_K$ is in good agreement with zero cosmic curvature within 1$σ$ confidence level, our result revels the fact of a closed universe. More importantly, our results show that the obtained $Ω_K$ measurements are almost unaffected by different priors of the Hubble constant. This could help solve the issue of the Hubble tension that may be caused by inconsistencies in the spatial curvature between the early and late universes.

astro-ph.CO↗

arXiv2023

Modes mismatch induced variation of quantum coherence for two-mode localized Gaussian states in accelerated frame

Quantum coherence is the basic concept of superposition of quantum states and plays an important role in quantum metrology. We show how a pair of uniformly accelerated observers with a local two-mode Gaussian quantum state affects the Gaussian quantum coherence. We find that the quantum coherence decreases with increasing acceleration, which is due to the Unruh effect that destroys the quantum resource. Essentially, the variation of quantum coherence is caused by the modes mismatch between the input and output mode. Through 2000 randomly generated states, we demonstrate that such mismatch is dominated by the acceleration effect and mildly affected by the waveform parameters. Moreover, the squeezing parameter acted as a suppressor of the reduced coherence, but it tended to be invalid in the high squeezing. In addition, the squeezing parameter can act as a suppressor of the reduced coherence, but the effect of the squeezing parameter tends to be ineffective under high squeezing conditions.

quant-ph↗

arXiv2021

Revisiting the cosmic distance duality relation with machine learning reconstruction methods: the combination of HII galaxies and ultra-compact radio quasars

In this paper, we carry out an assessment of cosmic distance duality relation (CDDR) based on the latest observations of HII galaxies acting as standard candles and ultra-compact structure in radio quasars acting as standard rulers. Particularly, two machine learning reconstruction methods (Gaussian Process (GP) and Artificial Neural Network (ANN)) are applied to reconstruct the Hubble diagrams from observational data. We show that both approaches are capable of reconstructing the current constraints on possible deviations from the CDDR in the redshift range $z\sim 2.3$. Considering four different parametric methods of CDDR, which quantify deviations from the CDDR and the standard cosmological model, we compare the results of the two different machine learning approaches. It is observed that the validity of CDDR is in well agreement with the current observational data within $1σ$ based on the reconstructed distances through GP in the overlapping redshift domain. Moreover, we find that ultra-compact radio quasars could provide $10^{-3}$-level constraints on the violation parameter at high redshifts, when combined with the observations of HII galaxies. In the framework of ANN, one could derive robust constraints on the violation parameter at a precision of $10^{-2}$, with the validity of such distance duality relation within $2σ$ confidence level.

astro-ph.CO↗

arXiv2012

A Disc-Corona Model for a Rotating Black Hole

We propose a disc-corona model in which a geometrically thin, optically thick disc surrounds a Kerr black hole, and magnetic fields exert a time-steady torque on the inner edge of the accretion disc. The analytical expression of the total gravitational power is derived from the thin-disc dynamics equations by using this new boundary condition. It is shown that the magnetic torque can considerably enhance the amount of energy released in the disc-corona system. Furthermore, the global solutions of this disc-corona system are obtained numerically. We find that the fraction of the power dissipated into the corona in the total for such disc-corona system increases with the increasing dimensionless black hole spin parameter $a_\ast $, but is insensitive on the $Δ\varepsilon $ which is the additional radiative efficiency parameter relevant to magnetic torque, for $Δ\varepsilon > 1$. In addition, the emerged spectra from this disc-corona system are simulated by using Monte-Carlo method, and the effect of the different parameters on the output spectra is discussed.

astro-ph.HE↗

arXiv2012

Observational constraints on unified dark matter including Hubble parameter data

We constrain a unified dark matter (UDM) model from the latest observational data. This model assumes that the dark sector is degenerate. Dark energy and dark matter are the same component. It can be described by an affine equation of state $P_X= p_0 +αρ_X$. Our data set contains the newly revised $H(z)$ data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the results in a flat universe: $Ω_Λ$=$0.719_{-0.0305}^{+0.0264}(1σ)_{-0.0458}^{+0.0380}(2σ)$, $α$=$1.72_{-4.79}^{+3.92}(1σ)_{-7.30}^{+5.47}(2σ)(\times10^{-3})$, $Ω_bh^2$=$0.0226_{-0.0011}^{+0.0011}(1σ)_{-0.0015}^{+0.0016}(2σ)$. Moreover, when considering a non-flat universe, $Ω_Λ$=$0.722_{-0.0447}^{+0.0362}(1σ)_{-0.0634}^{+0.0479}(2σ)$, $α$=$0.242_{-0.775}^{+0.787}(1σ)_{-1.03}^{+1.10}(2σ)(\times10^{-2})$, $Ω_bh^2$=$0.0227_{-0.0014}^{+0.0015}(1σ)_{-0.0018}^{+0.0021}(2σ)$, $Ω_k$=$-0.194_{-1.85}^{+2.02}(1σ)_{-2.57}^{+2.75}(2σ)(\times10^{-2})$. These give a more stringent results than before. We also give the results from other combinations of these data for comparison. The observational Hubble parameter data can give a more stringent constraint than SNe Ia. From the constraint results, we can see the parameters $α$ and $Ω_k$ are very close to zero, which means a flat universe is strongly supported and the speed of sound of the dark sector seems to be zero.

astro-ph.CO↗

arXiv2012

Jet magnetically accelerated from disk-corona around a rotating black hole

A jet acceleration model for extracting energy from disk-corona surrounding a rotating black hole is proposed. In the disk-corona scenario, we obtain the ratio of the power dissipated in the corona to the total for such disk-corona system by solving the disk dynamics equations. The analytical expression of the jet power is derived based on the electronic circuit theory of the magnetosphere. It is shown that jet power increases with the increasing black hole (BH) spin, and concentrates in the inner region of the disk-corona. In addition, we use a sample consisting of 37 radio loud quasars to explore their jet production mechanism, and show that our jet formation mechanism can simulate almost all sources with high power jet, that fail to be explained by the Blandford-Znajek (BZ) process.

astro-ph.HE↗