arXiv subjects

Chen Yuan

Publications and source records attributed to Chen Yuan.

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

GW231123 Mass Gap Event and the Primordial Black Hole Scenario

We investigate the possibility that the recently reported GW231123 event, with component masses $M_1=137^{+22}_{-17}\,M_\odot$, $M_2=103^{+20}_{-52}\,M_\odot$ and a local merger rate $R_{\mathrm{local}}=0.08^{+0.19}_{-0.07}\,\mathrm{Gpc^{-3}\,yr^{-1}}$, originates from primordial black holes (PBHs) formed during an early matter-dominated era. We compute the PBH mass function, abundance, spin distribution and the merger rate density and find a set of choices for the parameters to reproduce the key properties of GW231123. While PBHs formed in such a scenario can acquire large spins through sustained tidal torques, the spin distribution remains uncertain and additional accretion might lead to extreme spin values inferred in GW231123. We also show that the resulting PBH abundance, $f_{\mathrm{pbh}}=1.64^{+5.00}_{-1.59}\times10^{-1}$, lies close to the exclusion bounds from CMB accretion limits and other probes, highlighting a potential tension with current constraints. Finally, we estimate the scalar-induced gravitational waves (SIGWs) that are inevitably generated during PBH formation. PBHs that interpret GW231123 are accompanied by negligible SIGWs in the nano-hertz band, indicating no conflict with current pulsar timing arrays data.

astro-ph.CO↗

arXiv2025

Whispers from the Early Universe: The Ringdown of Primordial Black Holes

We investigate the stochastic gravitational wave background (SGWB) generated by the ringdown phase of primordial black holes (PBHs) formed in the early universe. As the ringdown signal is independent of the PBH formation mechanism, the resulting SGWB offers a model-independent probe of PBHs. We numerically compute the ringdown waveform and derive the corresponding SGWB. We show that such a signal could be detected by future pulsar timing arrays (PTAs) for PBHs heavier than the solar mass. Additionally, we evaluate the SGWB from binary PBH mergers and demonstrate that it lies within the sensitivity bands of next-generation ground-based interferometers such as Cosmic Explorer and Einstein Telescope, suggesting a multi-band observational strategy for probing the PBH dark matter scenario.

astro-ph.CO↗

arXiv2025

On the Gauge Invariance of Secondary Gravitational Waves

Second-order tensor perturbations induced by primordial fluctuations play a crucial role in probing small-scale physics, but gauge dependence of their energy density has remained a fundamental challenge in cosmological perturbation theory. We address this issue by introducing a boundary condition-based filtering method that extracts physical radiation through the Sommerfeld criterion. We demonstrate that after filtering non-physical modes, the energy density of secondary gravitational waves becomes gauge-invariant and exhibits physically consistent behavior in the sub-horizon limit. This approach provides a unified framework for both adiabatic and isocurvature perturbations, enhancing theoretical predictions and observational signatures of early universe physics.

astro-ph.CO↗

arXiv2025

Gauge Dependence of Gravitational Waves Induced by Primordial Isocurvature Fluctuations

Primordial isocurvature perturbations, which can arise from various sources in the early Universe, have the potential to leave observable imprints on the gravitational-wave background and provide insights into the nature of primordial fluctuations. In this study, we investigate the gauge dependence of induced gravitational waves (IGWs) sourced by these isocurvature perturbations during radiation dominated era and the kination period in the early universe. We analyze the energy density spectra of IGWs in three different gauges: synchronous, Newtonian, and uniform curvature gauges. To facilitate this analysis, we derive analytical solutions for the perturbations that contribute to the IGW spectra and a general gauge transformation from Newtonian gauge to an arbitrary gauge. Our results reveal significant differences in the energy spectra across these gauges. We find that the energy density of IGWs during radiation domination increases with conformal time as $η^8$ and $η^4$ for synchronous and uniform curvature gauges, respectively, while it converges in the Newtonian gauge. These findings highlight the importance of gauge choice in calculating IGWs and have implications for the interpretation of future observations of the gravitational-wave background.

gr-qc↗

arXiv2025

Gravitational Waves Induced by Scalar Perturbations with a Broken Power-law Peak

We give an analytical approximation for the energy spectrum of the scalar-induced gravitational waves (SIGWs) generated by a broken power-law power spectrum, and find that both the asymptotic power-law tails and the intermediate peak contribute distinct features to the SIGW spectrum. Moreover, the broken power-law power spectrum has abundant near-peak features and our results can be used as a near-peak approximation that covers a wide range of models. Our analytical approximation is useful in the rapid generation of the SIGW energy spectrum, which is beneficial for gravitational wave data analysis.

gr-qc↗

arXiv2025

Gravitational Waves from Accretion Disks: Turbulence, Mode Excitation and Prospects for Future Detectors

We study gravitational-wave emission by turbulent flows in accretion disks around spinning black holes or neutron stars. We aim to understand how turbulence can stochastically excite black hole quasinormal ringing and contribute to a stochastic gravitational-wave background from accretion disks around compact objects. We employ general relativistic magnetohydrodynamic simulations and feed them as the source of the Teukolsky master equation to evaluate the gravitational wave energy spectrum of a single source. The stochastic gravitational wave background from accretion disks generated by the population of stellar-mass compact objects is far below the sensitivity of third-generation ground-based detectors. In contrast, the supermassive black hole population, in particular those actively accreting, could lead to $Ω_{\mathrm{GW}}\sim 10^{-15}$ in the microHertz. This signal remains well below the sensitivities of pulsar-timing-arrays and LISA, making direct observation infeasible.

gr-qc↗

arXiv2024

Constraints on the Primordial Black Hole Abundance through Scalar-Induced Gravitational Waves from Advanced LIGO and Virgo's First Three Observing Runs

As a promising dark matter candidate, primordial black holes (PBHs) lighter than $\sim10^{-18}M_{\odot}$ are supposed to have evaporated by today through Hawking radiation. This scenario is challenged by the memory burden effect, which suggests that the evaporation of black holes may slow down significantly after they have emitted about half of their initial mass. We explore the astrophysical implications of the memory burden effect on the PBH abundance by today and the possibility for PBHs lighter than $\sim10^{-18}M_{\odot}$ to persist as dark matter. Our analysis utilizes current LIGO-Virgo-KAGRA data to constrain the primordial power spectrum and infer the PBH abundance. We find a null detection of scalar-induced gravitational waves that accompanied the formation of the PBHs. Then we find that PBHs are ruled out within the mass range $\sim[10^{-24},10^{-19}]M_{\odot}$. Furthermore, we expect that next-generation gravitational wave detectors, such as the Einstein Telescope and the Cosmic Explorer, will provide even more stringent constraints. Our results indicate that future detectors can reach sensitivities that could rule out PBH as dark matter within $\sim[10^{-29}M_{\odot},10^{-16}M_{\odot}]$ in the null detection of scalar-induced gravitational waves.

astro-ph.CO↗

arXiv2024

Primordial Black Hole Interpretation in Subsolar Mass Gravitational Wave Candidate SSM200308

In the recent second part of the third observation run by the LIGO-Virgo-KAGRA collaboration, a candidate with sub-solar mass components was reported, which we labelled as SSM200308. This study investigates the premise that primordial black holes (PBHs), arising from Gaussian perturbation collapses, could explain SSM200308. Through Bayesian analysis, we obtain the primordial curvature power spectrum that leads to the merger rate of PBHs aligning with observational data as long as they constitute {$f_{\mathrm{PBH}}=5.66^{+58.68}_{-5.44}\times 10^{-2}$ } of the dark matter. However, while the gravitational wave (GW) background from binary PBH mergers is within current observational limits, the scalar-induced GWs associated with PBH formation exceed the constraints imposed by pulsar timing arrays, challenging the Gaussian perturbation collapse PBH model as the source of SSM200308.

astro-ph.CO↗

arXiv2024

GW230529_181500: A Potential Primordial Binary Black Hole Merger in the Mass Gap

During the fourth observing run of the LIGO-Virgo-KAGRA detector network, the LIGO Livingston observatory detected a coalescing compact binary, GW230529_181500, with component masses of $2.5-4.5\, M_\odot$ and $1.2-2.0\, M_\odot$ at the $90\%$ credible level. The gravitational-wave data alone is insufficient to determine whether the components are neutron stars or black holes. In this paper, we propose that GW230529_181500 originated from the merger of two primordial black holes (PBHs). We estimate a merger rate of $5.0^{+47.0}_{-4.9} \mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$ for compact binary coalescences with properties similar to GW230529_181500. Assuming the source is a PBH-PBH merger, GW230529-like events lead to approximately $1.7^{+36.2}_{-1.5} \times 10^{-3}$ of the dark matter in the form of PBHs. The required abundance of PBHs to explain this event is consistent with existing upper limits derived from microlensing, cosmic microwave background observations and the null detection of gravitational wave background by LIGO-Virgo-KAGRA.

gr-qc↗

arXiv2024

Randomness-Efficient Constructions of Capacity-Achieving List-Decodable Codes

We wish to generate list-decodable codes over small alphabets using as little randomness as possible. Specifically, we hope to generate codes achieving what we term the Elias bound, which means that they are $(ρ,L)$-list-decodable with rate $R \geq 1-h(ρ)-O(1/L)$. A long line of work shows that uniformly random linear codes (RLCs) achieve the Elias bound: hence, we know $O(n^2)$ random bits suffice. Prior works demonstrate that just $O(Ln)$ random bits suffice, via puncturing of low-bias codes. These recent constructions are combinatorial. We provide two new constructions, which are algebraic. Compared to prior works, our constructions are simpler and more direct. Furthermore, our codes are designed in such a way that their duals are also quite easy to analyze. Our first construction -- which can be seen as a generalization of the Wozencraft ensemble -- achieves the Elias bound and consumes $Ln$ random bits. Additionally, its dual code achieves the GV-bound with high probability, and both the primal and dual admit quasilinear-time encoding algorithms. The second construction consumes $2nL$ random bits and yields a code where both it and its dual achieve the Elias bound. As we discuss, properties of a dual code are often crucial for applications in cryptography. In all of the above cases -- including the prior works achieving randomness complexity $O(Ln)$ -- the codes are designed to "approximate" RLCs. Namely, for a given locality parameter $L$ we construct codes achieving the same $L$-local properties as RLCs. This allows one to appeal to known list-decodability results for RLCs and thereby conclude that the code approximating an RLC also achieves the Elias bound. As a final contribution, we indicate that such a proof strategy is inherently unable to generate list-decodable codes of rate $R$ over $\mathbb F_q$ with less than $L(1-R)n\log_2(q)$ bits of randomness.

cs.IT↗

arXiv2024

Full analysis of the scalar-induced gravitational waves for the curvature perturbation with local-type non-Gaussianities

Primordial black holes (PBHs) are supposed to form through the gravitational collapse of regions with large density fluctuations. The formation of PBHs inevitably leads to the emission of scalar-induced gravitational wave (SIGW) signals, offering a unique opportunity to test the hypothesis of PBHs as a constituent of dark matter (DM). Previous studies have calculated the energy spectrum of SIGWs in local-type non-Gaussian models, primarily considering the contributions from the $F_{\mathrm{NL}}$-order or the $G_{\mathrm{NL}}$-order while neglecting connected diagrams. In this study, we extend the previous work by (i) considering the full contribution of non-Gaussian diagrams up to the $G_{\mathrm{NL}}$-order; (ii) deriving the generic scaling of the SIGW energy spectrum in the infrared region. We derive semi-analytical results applicable to arbitrary primordial power spectra and numerically evaluate the energy spectrum of SIGWs for a log-normal power spectrum.

astro-ph.CO↗

arXiv2023

Secure and Accurate Summation of Many Floating-Point Numbers

Motivated by the importance of floating-point computations, we study the problem of securely and accurately summing many floating-point numbers. Prior work has focused on security absent accuracy or accuracy absent security, whereas our approach achieves both of them. Specifically, we show how to implement floating-point superaccumulators using secure multi-party computation techniques, so that a number of participants holding secret shares of floating-point numbers can accurately compute their sum while keeping the individual values private.

cs.CR↗

arXiv2023

Tight Bounds on List-Decodable and List-Recoverable Zero-Rate Codes

In this work, we consider the list-decodability and list-recoverability of codes in the zero-rate regime. Briefly, a code $\mathcal{C} \subseteq [q]^n$ is $(p,\ell,L)$-list-recoverable if for all tuples of input lists $(Y_1,\dots,Y_n)$ with each $Y_i \subseteq [q]$ and $|Y_i|=\ell$ the number of codewords $c \in \mathcal{C}$ such that $c_i \notin Y_i$ for at most $pn$ choices of $i \in [n]$ is less than $L$; list-decoding is the special case of $\ell=1$. In recent work by Resch, Yuan and Zhang~(ICALP~2023) the zero-rate threshold for list-recovery was determined for all parameters: that is, the work explicitly computes $p_*:=p_*(q,\ell,L)$ with the property that for all $ε>0$ (a) there exist infinite families positive-rate $(p_*-ε,\ell,L)$-list-recoverable codes, and (b) any $(p_*+ε,\ell,L)$-list-recoverable code has rate $0$. In fact, in the latter case the code has constant size, independent on $n$. However, the constant size in their work is quite large in $1/ε$, at least $|\mathcal{C}|\geq (\frac{1}ε)^{O(q^L)}$. Our contribution in this work is to show that for all choices of $q,\ell$ and $L$ with $q \geq 3$, any $(p_*+ε,\ell,L)$-list-recoverable code must have size $O_{q,\ell,L}(1/ε)$, and furthermore this upper bound is complemented by a matching lower bound $Ω_{q,\ell,L}(1/ε)$. This greatly generalizes work by Alon, Bukh and Polyanskiy~(IEEE Trans.\ Inf.\ Theory~2018) which focused only on the case of binary alphabet (and thus necessarily only list-decoding). We remark that we can in fact recover the same result for $q=2$ and even $L$, as obtained by Alon, Bukh and Polyanskiy: we thus strictly generalize their work.

cs.IT↗

arXiv2023

Constructions of $k$-uniform states in heterogeneous systems

A pure quantum state of $n$ parties associated with the Hilbert space $\CC^{d_1}\otimes \CC^{d_2}\otimes\cdots\otimes \CC^{d_n}$ is called $k$-uniform if all the reductions to $k$-parties are maximally mixed. The $n$ partite system is called homogenous if the local dimension $d_1=d_2=\cdots=d_n$, while it is called heterogeneous if the local dimension are not all equal. $k$-uniform sates play an important role in quantum information theory. There are many progress in characterizing and constructing $k$-uniform states in homogeneous systems. However, the study of entanglement for heterogeneous systems is much more challenging than that for the homogeneous case. There are very few results known for the $k$-uniform states in heterogeneous systems for $k>3$. We present two general methods to construct $k$-uniform states in the heterogeneous systems for general $k$. The first construction is derived from the error correcting codes by establishing a connection between irredundant mixed orthogonal arrays and error correcting codes. We can produce many new $k$-uniform states such that the local dimension of each subsystem can be a prime power. The second construction is derived from a matrix $H$ meeting the condition that $H_{A\times \bar{A}}+H^T_{\bar{A}\times A}$ has full rank for any row index set $A$ of size $k$. These matrix construction can provide more flexible choices for the local dimensions, i.e., the local dimensions can be any integer (not necessarily prime power) subject to some constraints. Our constructions imply that for any positive integer $k$, one can construct $k$-uniform states of a heterogeneous system in many different Hilbert spaces.

quant-ph↗

arXiv2023

Beating the probabilistic lower bound on $q$-perfect hashing

For an integer $q\ge 2$, a perfect $q$-hash code $C$ is a block code over $[q]:=\{1,\ldots,q\}$ of length $n$ in which every subset $\{\mathbf{c}_1,\mathbf{c}_2,\dots,\mathbf{c}_q\}$ of $q$ elements is separated, i.e., there exists $i\in[n]$ such that $\{\mathrm{proj}_i(\mathbf{c}_1),\dots,\mathrm{proj}_i(\mathbf{c}_q)\}=[q]$, where $\mathrm{proj}_i(\mathbf{c}_j)$ denotes the $i$th position of $\mathbf{c}_j$. Finding the maximum size $M(n,q)$ of perfect $q$-hash codes of length $n$, for given $q$ and $n$, is a fundamental problem in combinatorics, information theory, and computer science. In this paper, we are interested in asymptotic behavior of this problem. Precisely speaking, we will focus on the quantity $R_q:=\limsup_{n\rightarrow\infty}\frac{\log_2 M(n,q)}n$. A well-known probabilistic argument shows an existence lower bound on $R_q$, namely $R_q\ge\frac1{q-1}\log_2\left(\frac1{1-q!/q^q}\right)$ \cite{FK,K86}. This is still the best-known lower bound till now except for the case $q=3$ \cite{KM}. The improved lower bound of $R_3$ was discovered in 1988 and there has been no progress on the lower bound of $R_q$ for more than $30$ years. In this paper we show that this probabilistic lower bound can be improved for $q$ from $4$ to $15$ and all odd integers between $17$ and $25$, and \emph{all sufficiently large} $q$.

cs.IT↗

arXiv2023

Primordial black holes generated by the non-minimal spectator field

In this paper, we propose a model in which a spectator field non-minimally couples to an inflaton field and the power spectrum of the perturbation of the spectator field at small scales is dramatically enhanced by the sharp feature in the form of non-minimal coupling. At or after the end of inflation, the perturbation of the spectator field is converted into curvature perturbation and leads to the formation of primordial black holes (PBHs). Furthermore, for example, we consider three phenomenological models for generating PBHs with mass function peaked at $\sim10^{-12}M_\odot$ and representing all the cold dark matter in our Universe and find that the scalar induced gravitational waves generated by the curvature perturbation can be detected by the future space-borne gravitational-wave detectors such as Taiji, TianQin and LISA.

astro-ph.CO↗

arXiv2023

On the Interaction between Ultralight Bosons and Quantum-Corrected Black Holes

Both ultralight dark matter and exploring the quantum nature of black holes are all topics of great interest in gravitational wave astronomy at present. The superradiant instability allows an exotic compact object (ECO) to be surrounded by an ultralight boson cloud, which leads to the emission of gravitational waves and further triggers rich dynamical effects. In this paper, we study the gravitational effects of superradiant instabilities by calculating the energy fluxes of gravitational waves emitted from ultralight scalar dark matter fields by solving the Teukolsky equation in the background of a massive ECO phenomenologically described by a Kerr geometry with a reflective boundary condition at its physical boundary. We find that both the amplitude and phase of the reflectivity will either suppress or enhance the energy flux of GWs by several orders of magnitude if $Mμ\gtrsim 0.5$ where $M$ and $μ$ are the mass of ECO and boson, respectively. However, the modifications to energy flux are negligible if $M μ\lesssim 0.5$. Our results suggest that reflectivity will play a significant role in the near-horizon physics of ECO.

gr-qc↗