In this letter, we propose a novel cosmological model-independent method to determine 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 <math><mi>H</mi><mo>(</mo><mi>z</mi><mo>)</mo></math> 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 (<math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>K</mi></mrow></msub></math>) 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 <math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>K</mi></mrow></msub><mo>=</mo><mo>−</mo><msubsup><mrow><mn>0.096</mn></mrow><mrow><mo>−</mo><mn>0.195</mn></mrow><mrow><mo>+</mo><mn>0.190</mn></mrow></msubsup></math> with 1σ observational uncertainty. Although the measured <math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>K</mi></mrow></msub></math> is in good agreement with zero cosmic curvature within 1σ confidence level, our result revels the fact of a closed universe. More importantly, our results show that the obtained <math><msub><mrow><mi>Ω</mi></mrow><mrow><mi>K</mi></mrow></msub></math> 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.

China

Xiaolong Gong

Yifei Xu

Tonghua Liu

Shuo Cao

Jianyong Jiang

Yalong Nan

Ruobin Ding

Jieci Wang

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

As an exact result required by the Etherington reciprocity theorem, the cosmic distance duality relation (CDDR), <math><mi>η</mi><mo>(</mo><mi>z</mi><mo>)</mo><mo>=</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>L</mi></mrow></msub><mo>(</mo><mi>z</mi><mo>)</mo><msup><mrow><mo>(</mo><mn>1</mn><mo>+</mo><mi>z</mi><mo>)</mo></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup><mo>/</mo><msub><mrow><mi>D</mi></mrow><mrow><mi>A</mi></mrow></msub><mo>(</mo><mi>z</mi><mo>)</mo><mo>=</mo><mn>1</mn></math> plays an essential part in modern cosmology. In this paper, we present a new method (<math><mi>η</mi><mo>(</mo><msub><mrow><mi>z</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>)</mo><mo>/</mo><mi>η</mi><mo>(</mo><msub><mrow><mi>z</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>)</mo></math>) to use the measurements of ultra-compact structure in radio quasars (QSO) and the latest observations of type Ia supernova (SN Ia) to test CDDR. By taking the observations directly from SN Ia and QSOs, one can completely eliminate the uncertainty caused by the calibration of the absolute magnitudes of standard candles (<math><msub><mrow><mi>M</mi></mrow><mrow><mi>B</mi></mrow></msub></math>) and the linear sizes of standard rulers (<math><msub><mrow><mi>l</mi></mrow><mrow><mi>m</mi></mrow></msub></math>). Benefit from the absence of nuisance parameters involved in other currently available methods, our analysis demonstrates no evidence for the deviation and redshift evolution of CDDR up to <math><mi>z</mi><mo>=</mo><mn>2.3</mn></math>. The combination of our methodology and the machine learning Artificial Neural Network (ANN) would produce <math><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></math> level constraints on the violation parameter at high redshifts. Our results indicate perfect agreement between observations and predictions, supporting the persisting claims that the Etherington reciprocity theorem could still be the best description of our universe.

Shuai Ma

Yuting Liu

Chenfa Zheng

What are recent observations telling us in light of improved tests of distance duality relation?

In this paper, we use the latest observations of quasars covering the redshift range of  $$0.04&lt;z&lt;5.1$$  <math> <mrow> <mn>0.04</mn> <mo>&lt;</mo> <mi>z</mi> <mo>&lt;</mo> <mn>5.1</mn> </mrow> </math>   to investigate a series of Chaplygin gas models as candidates for unified dark matter and dark energy. Based on different combinations of available standard candle and standard ruler data, we put constraints on the generalized Chaplygin gas (GCG), modified Chaplygin gas (MCG), new generalized Chaplygin gas (NGCG) and viscous generalized Chaplygin gas (VGCG) models. Moreover, we apply Jensen–Shannon divergence (JSD), statefinder diagnostics, and the deviance information criterion (DIC) to distinguish these CG models, based on the statistical results derived from Markov chain Monte Carlo method. The results show that (1) The standard ruler data could provide more stringent constraints on the cosmological parameters of different CG models considered in this analysis. Interestingly, the matter density parameter  $$\varOmega _{m}$$  <math> <msub> <mi>Ω</mi> <mi>m</mi> </msub> </math>   and Hubble constant  $$H_{0}$$  <math> <msub> <mi>H</mi> <mn>0</mn> </msub> </math>   derived from the available data are well consistent with those from the Planck 2018 results; (2) Based on the statistical criteria JSD, our findings demonstrate the well consistency between Chaplygin gas and the concordance  $$\varLambda $$  <math> <mi>Λ</mi> </math>  CDM model. However, in the framework of statefinder diagnostics, the GCG and NGCG models cannot be distinguished from  $$\varLambda $$  <math> <mi>Λ</mi> </math>  CDM, while MCG and VGCG models show significant deviation from  $$\varLambda $$  <math> <mi>Λ</mi> </math>  CDM in the present epoch; (3) According to the the statistical criteria DIC, we show that the MCG and VGCG models have substantial observational support from high-redshift quasars, whereas the GCG and NGCG models miss out on the less observational support category but can not be ruled out.

Jie Zheng

Yujie Lian

Zong-Hong Zhu

Revisiting Chaplygin gas cosmologies with the recent observations of high-redshift quasars

In this work, we consider the burst signal of the dark photon, the hypothetical vector boson of the <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mi>B</mi></msub></math> or <math><mi>U</mi><mo>(</mo><mn>1</mn><msub><mo>)</mo><mrow><mi>B</mi><mo>−</mo><mi>L</mi></mrow></msub></math> gauge group, generated by a compact binary star system. The absence of the signal in the laser interferometer puts bounds on the coupling constant <math><mi>ε</mi></math> to the ordinary matter. It turns out that if the dark photon is massless, <math><msup><mi>ε</mi><mn>2</mn></msup></math> is on the order of <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>37</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>33</mn></mrow></msup></mrow></math> at most; in the massive case, the upper bound of <math><msup><mi>ε</mi><mn>2</mn></msup></math> is about <math><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>38</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>31</mn></mrow></msup></mrow></math> in the mass range from <math><msup><mn>10</mn><mrow><mo>−</mo><mn>19</mn></mrow></msup></math> to <math><msup><mn>10</mn><mrow><mo>−</mo><mn>11</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math>. These are the first bounds derived from the interferometer observations independent of the assumption of dark photons being dark matter.

Shaoqi Hou

Shuxun Tian

Dark photon bursts from compact binary systems and constraints

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  $$z\sim 2.3$$  <math> <mrow> <mi>z</mi> <mo>∼</mo> <mn>2.3</mn> </mrow> </math>  . 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  $$1\sigma $$  <math> <mrow> <mn>1</mn> <mi>σ</mi> </mrow> </math>   based on the reconstructed distances through GP in the overlapping redshift domain. Moreover, we find that ultra-compact radio quasars could provide  $$10^{-3}$$  <math> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>3</mn> </mrow> </msup> </math>  -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  $$10^{-2}$$  <math> <msup> <mn>10</mn> <mrow> <mo>-</mo> <mn>2</mn> </mrow> </msup> </math>  , with the validity of such distance duality relation within  $$2\sigma $$  <math> <mrow> <mn>2</mn> <mi>σ</mi> </mrow> </math>   confidence level.

Japan

Sixuan Zhang

Wuzheng Guo

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

It is well known that de Sitter(dS) black holes generally have a black hole horizon and a cosmological horizon, both of which have Hawking radiation. But the radiation temperature of the two horizons is generally different, so dS black holes do not meet the requirements of thermal equilibrium stability, which brings certain difficulties to the study of the thermodynamic characteristics of black holes. In this paper, dS black hole is regarded as a thermodynamic system, and the effective thermodynamic quantities of the system are obtained. The influence of various state parameters on the effective thermodynamic quantities in the massive gravity space-time is discussed. The condition of the phase transition of the de Sitter black hole in massive gravity space-time is given. We consider that the total entropy of the dS black hole is the sum of the corresponding entropy of the two horizons plus an extra term from the correlation of the two horizons. By comparing the entropic force of interaction between black hole horizon and the cosmological horizon with Lennard-Jones force between two particles, we find that the change rule of entropic force between the two system is surprisingly the same. The research will help us to explore the real reason of accelerating expansion of the universe.

Yubo Ma

Yang Zhang

Lichun Zhang

Liang Wu

Ying Gao

Yu Pan

Phase transition and entropic force of de Sitter black hole in massive gravity

In order to estimate cosmic curvature from cosmological probes like standard candles, one has to measure the luminosity distance  $$D_L(z)$$  <math> <mrow> <msub> <mi>D</mi> <mi>L</mi> </msub> <mrow> <mo>(</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> </math>  , its derivative with respect to redshift  $$D'_L(z)$$  <math> <mrow> <msubsup> <mi>D</mi> <mi>L</mi> <mo>′</mo> </msubsup> <mrow> <mo>(</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> </math>   and the expansion rate H(z) at the same redshift. In this paper, we study how such idea could be implemented with future generation of space-based DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO), in combination with cosmic chronometers providing cosmology-independent H(z) data. Our results show that for the Hubble diagram of simulated DECIGO data acting as a new type of standard siren, it would be able to constrain cosmic curvature with the precision of  $$\varDelta \varOmega _k= 0.09$$  <math> <mrow> <mi>Δ</mi> <msub> <mi>Ω</mi> <mi>k</mi> </msub> <mo>=</mo> <mn>0.09</mn> </mrow> </math>   with the currently available sample of 31 measurements of Hubble parameters. In the framework of the third generation ground-based gravitational wave detectors, the spatial curvature is constrained to be  $$\varDelta \varOmega _k= 0.13$$  <math> <mrow> <mi>Δ</mi> <msub> <mi>Ω</mi> <mi>k</mi> </msub> <mo>=</mo> <mn>0.13</mn> </mrow> </math>   for Einstein Telescope (ET). More interestingly, compared to other approaches aiming for model-independent estimations of spatial curvature, our analysis also achieve the reconstruction of the evolution of  $$\varOmega _k(z)$$  <math> <mrow> <msub> <mi>Ω</mi> <mi>k</mi> </msub> <mrow> <mo>(</mo> <mi>z</mi> <mo>)</mo> </mrow> </mrow> </math>  , in the framework of a model-independent method of Gaussian processes (GP) without assuming a specific form. Therefore, one can expect that the newly emerged gravitational wave astronomy can become useful in local measurements of cosmic curvature using distant sources.

Xiaogang Zheng

Poland

Marek Biesiada

Shuaibo Geng

Model-independent constraints on cosmic curvature: implication from the future space gravitational-wave antenna DECIGO

The gas depletion factor $$\gamma (z)$$ <math><mrow><mi>γ</mi><mo>(</mo><mi>z</mi><mo>)</mo></mrow></math> , i.e., the average ratio of the gas mass fraction to the cosmic mean baryon fraction of galaxy clusters, plays a very important role in the cosmological application of the gas mass fraction measurements. In this paper, using the newest catalog of 182 galaxy clusters detected by the Atacama Cosmology Telescope (ACT) Polarization experiment, we investigate the possible redshift evolution of $$\gamma (z)$$ <math><mrow><mi>γ</mi><mo>(</mo><mi>z</mi><mo>)</mo></mrow></math>  through a new cosmology-independent method. The method is based on non-parametric reconstruction using the measurements of Hubble parameters from cosmic chronometers. Unlike hydrodynamical simulations suggesting constant depletion factor, our results reveal the trend of $$\gamma (z)$$ <math><mrow><mi>γ</mi><mo>(</mo><mi>z</mi><mo>)</mo></mrow></math>  decreasing with redshift. This result is supported by a parametric model fit as well as by calculations on the reduced ACTPol sample and on the alternative sample of 91 SZ clusters reported earlier in ACT compilation. Discussion of possible systematic effects leaves an open question about validity of the empirical relation $$M_{tot}$$ <math><msub><mi>M</mi><mrow><mi>tot</mi></mrow></msub></math> –$$f_{gas}$$ <math><msub><mi>f</mi><mrow><mi>gas</mi></mrow></msub></math>  obtained on very close clusters. These results might pave the way to explore the hot gas fraction within large radii of galaxy clusters as well as its possible evolution with redshift, which should be studied further on larger galaxy cluster samples in the upcoming X-ray/SZ cluster surveys.

Jing-Zhao Qi

Sylwia Miernik

The gas depletion factor in galaxy clusters: implication from Atacama Cosmology Telescope Polarization experiment measurements

In this paper, we assemble a well-defined sample of early-type gravitational lenses extracted from a large collection of 158 systems, and use the redshift distribution of galactic-scale lenses to test the standard cosmological model ($$\varLambda $$ <math><mi>Λ</mi></math> CDM) and the modified gravity theory (DGP). Two additional sub-samples are also included to account for possible selection effect introduced by the detectability of lens galaxies. Our results show that independent measurement of the matter density parameter ($$\varOmega _m$$ <math><msub><mi>Ω</mi><mi>m</mi></msub></math> ) could be expected from such strong lensing statistics. Based on future measurements of strong lensing systems from the forthcoming LSST survey, one can expect $$\varOmega _m$$ <math><msub><mi>Ω</mi><mi>m</mi></msub></math>  to be estimated at the precision of $$\varDelta \varOmega _m\sim 0.006$$ <math><mrow><mi>Δ</mi><msub><mi>Ω</mi><mi>m</mi></msub><mo>∼</mo><mn>0.006</mn></mrow></math> , which provides a better constraint on $$\varOmega _m$$ <math><msub><mi>Ω</mi><mi>m</mi></msub></math>  than Planck 2015 results. Moreover, use the lens redshift test is also used to constrain the characteristic velocity dispersion of the lensing galaxies, which is well consistent with that derived from the optical spectroscopic observations. A parameter $$f_E$$ <math><msub><mi>f</mi><mi>E</mi></msub></math>  is adopted to quantify the relation between the lensing-based velocity dispersion and the corresponding stellar value. Finally, the accumulation of detectable galactic lenses from future LSST survey would lead to more stringent fits of $$\varDelta f_E\sim 10^{-3}$$ <math><mrow><mi>Δ</mi><msub><mi>f</mi><mi>E</mi></msub><mo>∼</mo><msup><mn>10</mn><mrow><mo>-</mo><mn>3</mn></mrow></msup></mrow></math> , which encourages us to test the global properties of early-type galaxies at much higher accuracy.

Yu-Bo Ma

Jia Zhang

Implications of the lens redshift distribution of strong lensing systems: cosmological parameters and the global properties of early-type galaxies

In this paper, we discuss the effective thermodynamic quantities of higher dimensional electrically charged hairy black holes in de Sitter spacetime, considering the correlation between the black hole horizon and the cosmological horizon. Our results show that, the interaction term determined by the position of the two horizons could significantly contribute to the total entropy of de Sitter spacetime. Moreover, different from the case in AdS spacetime, we find both zero-order and second-order phase transitions under certain conditions, with the absence of first-order phase transition in the electrically charged hairy black holes. These results are strongly supported by the classification of phase transition in Ehrenfest’s equations. More interestingly, our analysis demonstrates the validity of the Ehrenfest equations at the critical point, and futhermore indicates the similarity of Prigogine–Defay (PD) ratio between ECBH spacetime and AdS spacetime.

Li-Chun Zhang

Entropy of the electrically charged hairy black holes