arXiv subjects

Puxun Wu

Publications and source records attributed to Puxun Wu.

At least 37 records · Page 2Linked to original sources

arXiv2025

Gravitational wave cosmology

Gravitational waves (GWs) originating from cosmological sources offer direct insights into the physics of the primordial Universe, the fundamental nature of gravity, and the cosmic expansion of the Universe. In this review paper, we present a comprehensive overview of our recent advances in GW cosmology, supported by the national key research and development program of China, focusing on cosmological GW sources and their implications for fundamental physics and cosmology. We first discuss the generation mechanisms and characteristics of stochastic gravitational wave backgrounds generated by physical processes occurred in the early Universe, including those from inflation, phase transitions, and topological defects, and summarize current and possible future constraints from pulsar timing array and space-based detectors. Next, we explore the formation and observational prospects of primordial black holes as GW sources and their potential connection to dark matter. We then analyze how GWs are affected by large-scale structure, cosmological perturbations, and possible modifications of gravity on GW propagation, and how these effects can be used to test fundamental symmetry of gravity. Finally, we discuss the application of GW standard sirens in measuring the Hubble constant, the expansion history, and dark energy parameters, including their combination with electromagnetic observations. These topics together show how GW observations, especially with upcoming space-based detectors, such as LISA, Taiji, and Tianqin, can provide new information about the physics of the early Universe, cosmological evolution, and the nature of gravity.

gr-qc↗

arXiv2025

Search for possible signals of space-time non-commutativity from ACT DR6

The non-commutative geometry offers an effective framework for describing physics at the Planck scale, incorporating generic quantum-gravitational effects through an intrinsic minimal length and the $κ$-deformed space-time stands out as a particularly well-developed model based on a Lie-algebraic type non-commutative space-time structure. We investigate the inflationary paradigm and the associated primordial perturbations within the framework of $κ$-deformed non-commutative space-time. By constructing a scalar field theory invariant under the $κ$-Poincaré algebra, we derive the deformed oscillator algebra for the field modes of the primordial perturbations resulting in the non-trivial scale dependent modification of both the scalar and tensor power spectra. Further, we compute the corresponding $κ$-deformed corrections to the scalar spectral index and its running, finding that the $κ$-deformation naturally provides a higher value for spectral index which offers a potential resolution to the discrepancy between the values reported by PLANCK and ACT. Finally we perform a comprehensive Bayesian analysis using the latest ACT DR6 data, constraining the $κ$-deformed non-commutative length scale to $λ=2.17^{+2.33}_{-1.53}\times 10^{-30}m$ at the $1σ$ confidence level, suggesting the precision cosmology as a powerful probe of quantum gravity phenomenology.

hep-th↗

arXiv2025

Probability density function for dispersion measure of fast radio burst from extragalactic medium

Fast Radio Bursts (FRBs) have emerged as powerful probes in cosmology. An optimized method was recently proposed to extract the cosmic baryon density from localized FRBs by maximizing the joint likelihood function of the extragalactic dispersion measure ($\mathrm{DM}_{\mathrm{ext}}$). In this paper, we identify a crucial factor that was omitted in the probability density function (PDF) for $\mathrm{DM}_{\mathrm{ext}}$ in that method. Using simulated FRB data, we demonstrate that neglecting this factor leads to a systematic bias in the inferred cosmic baryon density, with deviations exceeding the $1σ$ confidence level. This highlights the necessity of including the missing factor for reliable cosmological applications of FRBs. Furthermore, applying our corrected PDF to a sample of 88 real localized FRBs, we find that the baryon density inferred with the original PDF is inconsistent with the Planck 2018 CMB results, whereas our corrected PDF yields excellent agreement.

astro-ph.CO↗

arXiv2025

Revisiting cosmic acceleration with DESI BAO

We revisit the evolution of cosmic acceleration in a spatially flat $w_0w_a$CDM universe, in which the equation of state of dark energy takes the CPL parametrization, using the latest baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI), in combination with Planck cosmic microwave background (CMB) data and several type Ia supernova datasets, including PantheonPlus, Union3, and DESY5. We analyze the deceleration parameter $q(z)$ and the jerk parameter $j(z)$ and further validate our results using the $Om(z)$ diagnostic. Our findings indicate significant deviations from the predictions of the $Λ$CDM model. Specifically, DESI BAO, DESI BAO + CMB, DESI BAO + CMB + Union3, and DESI BAO + CMB + DESY5 all provide strong evidence for a slowing down of cosmic acceleration at late times, as indicated by $j(0) < 0$ at more than 1$σ$ confidence level, within the framework of $w_0w_a$CDM model. These results suggest that in the $w_0w_a$CDM universe cosmic acceleration has already peaked and is now in a phase of decline.

astro-ph.CO↗

arXiv2025

Gamma-Ray Bursts Calibrated by Using Artificial Neural Networks from the Pantheon+ Sample

In this paper, we calibrate the luminosity relation of gamma-ray bursts (GRBs) by Artificial Neural Networks (ANN) which is employed to analyze the Pantheon+ sample of type Ia supernovae (SNe Ia) in a manner independent of cosmological assumptions. The A219 GRB dataset are used to calibrate the Amati relation ($E_{\rm p}$-$E_{\rm iso}$) at low redshift with the ANN framework, facilitating the construction of the Hubble diagram at higher redshifts. Cosmological models are constrained with GRBs at high-redshift and the latest observational Hubble data (OHD) via a Markov Chain Monte Carlo numerical approach. For the Chevallier-Polarski-Linder (CPL) model within a flat universe, we obtain $Ω_{\rm m} = 0.321^{+0.078}_{-0.069}$, $h = 0.654^{+0.053}_{-0.071}$, $w_0 = -1.02^{+0.67}_{-0.50}$, and $w_a = -0.98^{+0.58}_{-0.58}$ at the 1-$σ$ confidence level, which indicating a preference for dark energy with potential redshift evolution ($w_a \neq 0$). These findings by using ANN align closely with those derived from GRBs calibrated by using Gaussian Processes.

astro-ph.CO↗

arXiv2025

Testing redshift variation of the X-ray and ultraviolet luminosity relations of quasars

Quasars serve as important cosmological probes and constructing accurate luminosity relations for them is essential for their use in cosmology. If the coefficients of quasar's luminosity relation vary with redshift, it could introduce biases into cosmological constraints derived from quasars. In this paper, we conduct a detailed analysis of the redshift variation in the X-ray luminosity and ultraviolet (UV) luminosity ($L_\mathrm{X}$-$L_\mathrm{UV}$) relations of quasars. For the standard $L_\mathrm{X}$-$L_\mathrm{UV}$ relation, we find that the relation coefficients exhibit a strong and linear correlation with redshift, which is not attributable to the selection effect. Additionally, we examine two three-dimensional, redshift-evolving $L_\mathrm{X}$-$L_\mathrm{UV}$ relations and find that the inclusion of a redshift-dependent term does not eliminate the impact of redshift evolution, as the relation coefficients continue to evolve with redshift. Finally, we construct a new $L_\mathrm{X}$-$L_\mathrm{UV}$ relation in which the redshift evolution of the relation coefficients is nearly eliminated. Calibrating the luminosity relations using Hubble parameter measurements, we demonstrate that quasars utilizing our new relation yield effective constraints on cosmological parameters that are consistent with results from Planck CMB data, unlike constraints derived from the standard relation.

astro-ph.CO↗

arXiv2025

Entropic force and bouncing behaviour in $κ$-Minkowski space-time

We generalise the entropic force description of gravity into $κ$-Minkowski space-time and derive the $κ$-deformed corrections to the Newton's gravitational force. Using this we show the appearance of logarithmic correction as the first order $κ$-deformed correction term to Bekenstein-Hawking entropy. Further we also derive the $κ$-deformed Friedmann equations and study the evolution of scale factor in $κ$-deformed space-time. Finally we show that the $κ$-deformation parameter avoids the initial singularity in early universe by providing a bounce behaviour for the case of spatially flat and closed universe.

gr-qc↗

arXiv2025

Constraining inflation with nonminimal derivative coupling with the Parkes Pulsar Timing Array third data release

We study an inflation model with nonminimal derivative coupling that features a coupling between the derivative of the inflaton field and the Einstein tensor. This model naturally amplifies curvature perturbations at small scales via gravitationally enhanced friction, a mechanism critical for the formation of primordial black holes and the associated production of potentially detectable scalar-induced gravitational waves. We derive analytical expressions for the primordial power spectrum, enabling efficient exploration of the model parameter space without requiring computationally intensive numerical solutions of the Mukhanov-Sasaki equation. Using the third data release of the Parkes Pulsar Timing Array (PPTA DR3), we constrain the model parameters characterizing the coupling function: $ϕ_c = 3.7^{+0.3}_{-0.5} M_\mathrm{P}$, $\log_{10} ω_L = 7.1^{+0.6}_{-0.3}$, and $\log_{10} σ= -8.3^{+0.3}_{-0.6}$ at 90\% confidence level. Our results demonstrate the growing capability of pulsar timing arrays to probe early Universe physics, complementing traditional cosmic microwave background observations by providing unique constraints on inflationary dynamics at small scales.

gr-qc↗

arXiv2025

Model-independent Gamma-Ray Bursts Constraints on Cosmological Models Using Machine Learning

In this paper, we calibrate the luminosity relation of gamma-ray bursts (GRBs) with the machine learning (ML) algorithms from the Pantheon+ sample of type Ia supernovae in a cosmology-independent way. By using K-Nearest Neighbors (KNN) and Random Forest (RF) selected with the best performance in the ML algorithms, we calibrate the Amati relation (\unboldmath{$E_{\rm p}$-$E_{\rm iso}$}) relation with the A219 sample to construct the Hubble diagram of GRBs. Via the Markov Chain Monte Carlo numerical method with GRBs at high redshift and latest observational Hubble data, we find the results of constraints on cosmological models by using KNN and RF algorithms are consistent with those obtained from GRBs calibrated by using the Gaussian Process.

astro-ph.CO↗

arXiv2025

Infrared Behavior of Induced Gravitational Waves from Isocurvature Perturbations

Induced gravitational waves provide a powerful probe of primordial perturbations in the early universe through their distinctive spectral properties. We analyze the spectral energy density $Ω_{\text{GW}}$ of gravitational waves induced by isocurvature scalar perturbations. In the infrared regime, we find that the spectral slope $n_{\text{GW}} \equiv \text{d} \lnΩ_\mathrm{GW}/\text{d}\ln k$ takes the log-dependent form $3-4/ \ln (\tilde{k}_*^2 / 6k^2)$, where $\tilde{k}_*$ represents the effective peak scale of the primordial scalar power spectrum. This characteristic behavior differs markedly from that of adiabatic-induced gravitational waves, establishing a robust observational discriminant between isocurvature and adiabatic primordial perturbation modes.

gr-qc↗

arXiv2024

Probing Cosmic Background Dynamics with a Cosmological-model-independent Method

The Hubble constant $H_0$ tension has emerged as the most serious crisis in modern cosmology, potentially indicating that the $Λ$CDM model may not describe our universe accurately. In this paper, we establish a new, cosmological-model-independent method to study the cosmic background dynamics. Using the latest Pantheon+ Type Ia supernova (SN Ia) sample and the model-independent SN Ia sample (P+1690), we derive values for the luminosity distance, the Hubble parameter, and the deceleration parameter at five different redshift points ranging from 0.12 to 0.52. Our analysis shows that results obtained from the Pantheon+ sample align with the predictions of the $Λ$CDM model within 2$σ$ confidence level (CL), while those obtained from the P+1690 sample exhibit deviations of about $2\sim3σ$ CL. Furthermore, we explore the equation of state (EoS) of dark energy and find that while the EoS values from the Pantheon+ sample remain consistent with $-1$ within 2$σ$ CL, the P+1690 sample does not conform to this standard. These findings remain unchanged after the inclusion of the Hubble parameter measurements in our analysis. Our results indicate that the $Λ$CDM model remains compatible with the Pantheon+ SN Ia and the Hubble parameter measurements at 2$σ$ CL.

astro-ph.CO↗

arXiv2024

Alleviating the Hubble-constant tension and the growth tension via a transition of absolute magnitude favored by the Pantheon+ sample

We establish a cosmological-model-independent method to extract the apparent magnitude and its derivative at different redshifts from the Pantheon+ type Ia supernova sample, and find that the obtained values deviate clearly from the prediction of the $Λ$CDM model at the lowest redshift. This deviation can be explained as a result of a transition of the absolute magnitude $M$ in the low redshift region. The observations seem to favor this transition since the minimum values of $χ^2$ for two ansatzes of a varying $M$ are less than that of a constant $M$. The Hubble constant tension is alleviated from larger than $5σ$ to be about $1$ to $2σ$ for a varying $M$, and the growth tension can be resolved after attributing the variation of $M$ to a modification of the effective Newton's constant.

astro-ph.CO↗

arXiv2024

Constraints on Cosmological Models from Quasars Calibrated with Type Ia Supernova by a Gaussian Process

In this paper, we use quasars calibrated from type Ia supernova (SN Ia) to constrain cosmological models. We consider three different X-ray luminosity ($L_{X}$) - ultraviolet luminosity ($L_{UV}$) relations of quasars, i.e., the standard $L_{X}$-$L_{UV}$ relation and two redshift-evolutionary relations (Type I and Type II) respectively constructed from copula and considering a redshift correction to the luminosity of quasars. Only in the case of the Type I relation, quasars can always provide effective constraints on the $Λ$CDM model. Furthermore, we show that, when the observational Hubble data (OHD) are added, the constraints on the absolute magnitude $M$ of SN Ia and the Hubble constant $H_0$ can be obtained. In the $Λ$CDM model, the OHD measurements plus quasars with the Type I relation yields $M$ =$-19.321^{+0.085}_{-0.076}$, which is in good agreement with the measurement from SH0ES ($M=-19.253\pm{0.027}$), and $H_0$ = $70.80\pm3.6~\mathrm{km~s^{-1}Mpc^{-1}}$, falling between the measurements from SH0ES and the Planck cosmic microwave background radiation data.

astro-ph.CO↗

arXiv2024

Resonant amplification of curvature perturbations in inflation model with periodical derivative coupling

In this paper, we introduce a weak, transient and periodical derivative coupling between the inflaton field and gravity, and find that the square of the sound speed of the curvature perturbations becomes a periodic function, which results in that the equation of the curvature perturbations can be transformed into the form of the Mathieu equation in the sub-horizon limit. Thus, the parametric resonance will amplify the curvature perturbations so as to generate a formation of abundant primordial black holes (PBHs). We show that the generated PBHs can make up most of dark matter. Associated with the generation of PBHs, the large scalar perturbations will give rise to the scalar induced gravitational waves which may be detected by future gravitational wave projects.

gr-qc↗

arXiv2024

NANOGrav hints for first-order confinement-deconfinement phase transition in different QCD-matter scenarios

Recent observations from several pulsar timing array (PTA) collaborations have unveiled compelling evidence for a stochastic signal in the nanohertz band. This signal aligns remarkably with a gravitational wave (GW) background, potentially originating from the first-order color charge confinement phase transition. Distinct quantum chromodynamics (QCD) matters, such as quarks or gluons, and diverse phase transition processes thereof can yield disparate GW energy density spectra. In this paper, employing the Bayesian analysis on the NANOGrav 15-year data set, we explore the compatibility with the observed PTA signal of the GW from phase transitions of various QCD matter scenarios in the framework of the holographic QCD. We find that the PTA signal can be effectively explained by the GW from the confinement-deconfinement phase transition of pure quark systems in a hard wall model of the holographic QCD where the bubble dynamics, one important source of the GWs, is of the Jouguet detonations. Notably, our analysis decisively rules out the plausibility of the pure gluon QCD-matter scenario and the non-runaway bubble dynamics model for the phase transition in explaining the observed PTA signal.

astro-ph.CO↗

arXiv2024

Power spectrum with $k^6$ growth for primordial black holes

The decrease of both the rolling speed of the inflaton and the sound speed of the curvature perturbations can amplify the curvature perturbations during inflation so as to generate a sizable amount of primordial black holes. In the ultraslow-roll inflation scenario, it has been found that the power spectrum of curvature perturbations has a $k^4$ growth. In this paper, we find that when the speed of sound decreases suddenly, the curvature perturbations becomes scale dependent in the infrared limit and the power spectrum of the curvature perturbation only has a $k^2$ growth. Furthermore, by studying the evolution of the power spectrum in the inflation model, in which both the sound speed of the curvature perturbations and the rolling speed of the inflaton are reduced, we find that the power spectrum is nearly scale invariant at the large scales to satisfy the constraint from the cosmic microwave background radiation observations, and at the same time can be enhanced at the small scales to result in an abundant formation of primordial black holes. In the cases of the simultaneous changes of the sound speed and the slow-roll parameter $η$ and the change of the sound speed preceding that of the slow-roll parameter $η$, the power spectrum can possess a $k^6$ growth under certain conditions, which is the steepest growth of the power spectrum reported so far.

gr-qc↗

arXiv2024

Observations favor the redshift-evolutionary $L_X$-$L_{UV}$ relation of quasars from copula

We compare, with data from the quasars, the Hubble parameter measurements, and the Pantheon+ type Ia supernova, three different relations between X-ray luminosity ($L_X$) and ultraviolet luminosity ($L_{UV}$) of quasars. These three relations consist of the standard and two redshift-evolutionary $L_X$-$L_{UV}$ relations which are constructed respectively by considering a redshift dependent correction to the luminosities of quasars and using the statistical tool called copula. By employing the PAge approximation for a cosmological-model-independent description of the cosmic background evolution and dividing the quasar data into the low-redshift and high-redshift parts, we find that the constraints on the PAge parameters from the low-redshift and high-redshift data, which are obtained with the redshift-evolutionary relations, are consistent with each other, while they are not when the standard relation is considered. If the data are used to constrain the coefficients of the relations and the PAge parameters simultaneously, then the observations support the redshift-evolutionary relations at more than $3σ$. The Akaike and Bayes information criteria indicate that there is strong evidence against the standard relation and mild evidence against the redshift-evolutionary relation constructed by considering a redshift dependent correction to the luminosities of quasars. This suggests that the redshift-evolutionary $L_X$-$L_{UV}$ relation of quasars constructed from copula is favored by the observations.

astro-ph.CO↗

arXiv2023

Cosmological-model-independent determination of Hubble constant from fast radio bursts and Hubble parameter measurements

We establish a cosmological-model-independent method to determine the Hubble constant $H_0$ from the localized fast radio bursts (FRBs) and the Hubble parameter measurements from cosmic chronometers and obtain a first such determination $H_0=71\pm 3~\mathrm{km/s/Mpc}$, with an uncertainty of 4\%, from the eighteen localized FRBs and nineteen Hubble parameter measurements in the redshift range $0<z\leq0.66$. This value, which is independent of the cosmological model, is consistent with the results from the nearby type Ia supernovae (SN Ia) data calibrated by Cepheids and the Planck cosmic microwave background radiation observations at the $1σ$ and 2$σ$ confidence level, respectively. Simulations show that the uncertainty of $H_0$ can be decreased to the level of that from the nearby SN Ia when mock data from 500 localized FRBs with 50 Hubble parameter measurements in the redshift range of $0<z\leq1$ are used. Since localized FRBs are expected to be detected in large quantities, our method will be able to give a reliable and more precise determination of $H_0$ in the very near future, which will help us to figure out the possible origin of the Hubble constant disagreement.

astro-ph.CO↗