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The exploration of the surrounding world and the universe is an important theme in the legacy of humankind. The detection of gravitational waves is adding a new dimension to this grand effort. What are the fundamental physical laws governing the dynamics of the universe? What is the fundamental composition of the universe? How has the universe evolved in the past and how will it evolve in the future? These are the basic questions that press for answers. The space-based gravitational wave detector TianQin will tune in to gravitational waves in the millihertz frequency range ($10^{-4} \sim 1$ Hz, to be specific), opening a new gravitational wave spectrum window to explore many of the previously hidden sectors of the universe. TianQin will discover many astrophysical systems, populating the universe at different redshifts: some will be of new types that have never been detected before, some will have very high signal-to-noise ratios, and some will have very high parameter estimation precision. The plethora of information collected will bring us to new fronts on which to search for the breaking points of general relativity, the possible violation of established physical laws, the signature of possible new gravitational physics and new fundamental fields, and to improve our knowledge on the expansion history of the universe. In this white paper, we highlight the advances that TianQin can bring to fundamental physics and cosmology., Comment: 113 pages

Recently, a $\sim3.9\sigma$ preference for dynamical dark energy from the Dark Energy Spectroscopic Instrument (DESI) collaboration inspired hot debates on new physics or systematics. In this letter, we reveal this significant preference is dominated by an external low-redshift supernova (low-$z$ SN) sample that combines with the Dark Energy Survey SN program (DES-SN) in their Year 5 data release (DESY5). Further implementing the $a_B$ (the intercept of the SN magnitude-redshift relation) diagnosis between low-$z$ and DES-SN samples, we find large dispersions in the low-$z$ SN sample with a $\sim0.043$ magnitude discrepancy in $-5a_B$ from the high-$z$ DES-SN sample, suggesting potential systematics in DESY5. Correcting for this low-$z$ systematics or directly ignoring the low-$z$ sample can largely reduce the preference for dynamical DE to be $<2\sigma$ or even $<1\sigma$ if further eliminating the data interference from the cosmic microwave background. Therefore, the DESI preference for dynamical DE might be a mirage of unknown systematics in low-$z$ SNe with a mismatch intercept., Comment: v1, 5 pages + references, 3 figures, 1 table; v2, references added, a new figure is added without CMB

Spin-2 ultralight dark matter (ULDM) is a viable dark matter candidate and it can be constrained using gravitational wave (GW) observations. In this paper, we investigate the detectability of spin-2 ULDM by space-based GW interferometers. By considering a direct coupling between spin-2 ULDM and ordinary matter, we derive the corresponding response functions and sensitivity curves for various time-delay interferometry channels and calculate the optimal sensitivity curves for future millihertz GW detectors. Our results demonstrate that the space-based detectors can place stringent constraints on the coupling constant of spin-2 ULDM, reaching $\alpha \sim 10^{-10}$ around a mass of $m \sim 10^{-17} \rm eV$, surpassing current limits from ground-based detectors and pulsar timing arrays. Thus, the space-based GW detectors can serve as powerful tools not only for detecting GWs but also for probing fundamental properties of ultralight dark matter., Comment: 12 pages, 6 figures

The mergers of galaxies and supermassive black holes (SMBHs) are key drivers of galaxy evolution, contributing to the growth of both galaxies and their central black holes. Current projects like Pulsar Timing Arrays (PTAs) and upcoming missions such as the Laser Interferometer Space Antenna (LISA), Taiji, and Tianqin are designed to detect gravitational waves (GWs) emitted by SMBH binaries during their inspiral and merger phases. We investigate the capability to probe the merger rates of SMBHs and their host galaxies by combining current PTA detections and mock GW data for LISA-like detectors, while incorporating observational constraints from the $M_{\bullet}-M_*$ relationship and galaxy stellar mass functions. Our findings highlight the critical role of GW detections with LISA-like detectors in exploring the merger rates of galaxies and SMBHs and the timescale of SMBH mergers. Additionally, incorporating PTA constraints on the stochastic gravitational wave background further refines model parameters and reduces uncertainties. Gravitational wave detections offer an independent method for estimating galaxy merger rates, providing a valuable consistency check against rates derived from galaxy pair observations and cosmological simulations. Furthermore, comparing SMBH mass assembly through mergers with growth via accretion provides key insights into the evolutionary history of SMBHs, with the timescale of SMBH binary mergers playing a significant role in shaping their merger rates and merger mass assembly., Comment: 10 pages, 8 figures

We investigate the pseudospectrum of the Kerr black hole, which indicates the instability of the spectrum of QNMs of the Kerr black hole. Methodologically, we use the hyperboloidal framework to cast the quasinormal mode (QNM) problem into a two-dimensional eigenvalue problem associated with a non-self-adjoint operator, and then the spectrum and pseudospectrum are solved by imposing the two-dimensional Chebyshev collocation method. The (energy) norm is constructed by using the conserved current method for the spin $s=0$ case. In order to study the convergence issues, an extra $H^k$-norm term is added into the original energy norm. For the finite rank approximation of the operator, it is found that as $k$ increases, the pseudospectrum becomes sharp when the complex number $\omega$ is close to the QNM spectra. In contrast, when $\omega$ moves away from the QNM spectra, the pseudospectrum becomes mild. Furthermore, we discussed the convergence of pseudospectra with different $H^k$-norms. As $k$ increases, the convergence of the pseudospectrum improves. However, at the same time, an increase in the imaginary part of $\omega$ can deteriorate the convergence of the pseudospectrum under the condition of the same norms., Comment: 17 pages, 6 figures

Early detection and localization of gravitational waves (GWs) are crucial for identifying and capturing their electromagnetic (EM) counterparts, playing a significant role in multi-messenger astronomy. For second-generation (2G) detectors such as LIGO, Virgo, and KAGRA, the typical duration of GW signals ranges from $\mathcal{O}(0.1)$ seconds to several tens of seconds due to their optimal sensitivities only at higher frequencies. This limited duration is insufficient to provide adequate early warning and localization for potential GWs and their associated EM counterparts. In this paper, we investigate whether eccentricity-induced higher harmonic modes, which enter the detector band much earlier than the dominant mode, can aid early detection and localization of GW sources using the 2G ground-based detector network. We select two typical events, a GW170817-like BNS and a GW150914-like BBH, as illustrative examples. For a GW170817-like BNS, we find that the eccentric case with $e_0=0.4$ at 10 Hz can achieve an SNR of 4 and the threshold SNR of 8 approximately 12 minutes and 5 minutes before merger, representing 4.5- and 1.5-minute improvements in time-to-merger compared to the circular case, respectively. Additionally, with $e_0=0.4$, it can achieve a localization of $1000 \, (100)\, \rm deg^2$ at 5 (1) minutes before the merger, reflecting improvements of 2 minutes (15 seconds) compared to the circular case. For a typical GW150914-like BBH, due to the much shorter signal duration, the time-to-merger gained from higher modes for achieving the same SNR and localization is limited to $\mathcal{O}(0.1)-\mathcal{O}(1)$ seconds. Our results demonstrate the usefulness of eccentricity-induced higher harmonic modes in improving early warning and localization of GW and EM counterparts, particularly for BNS systems., Comment: 8 pages, 2 figures

The growing ``Hubble tension'' has prompted the need for precise measurements of cosmological distances. This paper demonstrates a purely geometric approach for determining the distance to extragalactic binaries through a joint analysis of spectroastrometry (SA), radial velocity (RV), and light curve (LC) observations. A parameterized model for the binary system is outlined, and simulated SA, RV, and LC data are computed to infer the probability distribution of model parameters based on the mock data. The impact of data quality and binary parameters on distance uncertainties is comprehensively analyzed, showcasing the method's potential for high-precision distance measurements. For a typical eclipsing binary in the Large Magellanic Cloud (LMC), the distance uncertainty is approximately 6% under reasonable observational conditions. Within a specific range of data quality and input parameters, the distance measurement precision of individual binary star systems is generally better than 10%. As a geometric method based on the simplest dynamics, it is independent of empirical calibration and the systematics caused by model selections can be tested using nearby binaries with known distances. By measuring multiple binary star systems or monitoring one binary system repeatedly, geometric distance measurements of nearby galaxies can be achieved, providing valuable insights into the Hubble tension and advancing our understanding of the universe's structure and evolution., Comment: 16 pages, 9 figures, accepted by ApJ

We investigate density fluctuations and scalar-induced gravitational waves (GWs) arising from the production of long-lived solitons and oscillons, which can dominate the early Universe and drive reheating prior to the standard radiation-dominated era. Curvature perturbations are generated not only by the Poisson distribution of these solitons/oscillons but are also amplified during the early matter-dominated phase when the solitons/oscillons dominate. Scalar-induced GWs with characteristic energy spectra emerge from these amplified curvature perturbations, particularly at the sudden transition from matter domination to radiation domination. We analyze this scenario and its GW predictions in detail, focusing on the impact of the initial energy fraction, the lifetime, and the average separation of these solitons/oscillons. This provides a wealth of potential observational targets for various GW detectors. Furthermore, for inflation and preheating models that produce oscillons with large separations, we derive new constraints on these models based on the upper bounds on the effective number of relativistic degrees of freedom, as anticipated from future cosmic microwave background and large-scale structure observations., Comment: 13 pages, 8 figures

In recent years, the long-term effects of non-linear perturbations were found to be important for the evolution of the hierarchical triple system, which, for the central third body of a larger mass, can significantly suppress the occurrences of orbital flip that changes the sign of angular momentum of inner binary. However, as the third-body mass increases significantly, the ambient dark matter spike becomes much more dense, rendering the effect of dynamical friction non-negligible. In this work, we take the dynamical friction into account for the first time in the hierarchical triple system up to the octupole order and find that the suppressed occurrences of orbital flip could be recovered, making the detection of orbital flip a potential probe of the dark matter via observations of either electromagnetic waves or gravitational waves., Comment: 21 pages, 3 figures, 1 table

In this study, we investigate the stability of the greybody factor of Hayward black holes by adding a small bump to the effective potential. Since the greybody factor depends on frequency, we introduce the $\mathcal{G}$-factor and $\mathcal{H}$-factor to quantitatively characterize its stability. We study the stability of the greybody factor within the equal amplitude method and the equal energy method, respectively. Here, the equal amplitude method can be directly imposed by fixing the amplitude of the bump, while the equal energy method requires a physical definition of the energy of the bump with the assistance of hyperboloidal framework. For both methods, when the location of the bump is close to the event horizon of the black hole, and the closer it is to the peak of the original potential, the larger are $\mathcal{G}$-factor and $\mathcal{H}$-factor, and they are bounded by the magnitude of the amplitude or the energy. More importantly, for the equal amplitude method, two factors tend to a specific value as the location of the bump increases. In contrast, for the equal energy method, two factors converge to zero as the location of the bump increases. Notably, the $\mathcal{G}$-factor and the $\mathcal{H}$-factor are insensitive to the regular parameter of Hayward black hole. Therefore, our results indicate that the greybody factor is stable under specific perturbations., Comment: 17 pages, 10 figures and 1 table. Typos are corrected, discussion is improved. This manuscript has been accepted for publication as a regular article in PRD

Scaling laws for critical phenomena take pivotal status in almost all branches of physics. However, as scaling laws are commonly guaranteed by the renormalization group theory, systems that violate them have rarely been found. In this letter, we demonstrate that gravitational system can break scaling laws. We derive this result through investigating phase transition and critical phenomenon in a gravitational system with quantum anomaly. For the first time, we outline the key conditions to violate the scaling laws in generic gravitational system viewed from the equation of state $P=P(T,V)$. Our results indicate that quantum effects can magnify the distinctiveness of gravity, which may be significant to understand the microscopic structure of spacetime., Comment: 7 pages, 3 figures

Recent reports of stochastic gravitational wave background from four independent pulsar-timing-array collaborations have renewed the interest in the cosmological gravitational wave background (CGWB), which is expected to open a new window into the early Universe. Although the early Universe is supposed to be extremely flat from an inflationary point of view, the cosmic microwave background (CMB) data alone from the Planck satellite measurement prefers an enhanced lensing amplitude that can be explained by a closed Universe. In this paper, we propose an independent method to constrain the early-universe flatness from the anisotropies of CGWB. Using the generalized harmonic decompositions in the non-flat spacetime, we find CGWBs from different physical mechanisms such as cosmic inflation and phase transitions share the same integrated Sachs-Wolfe (ISW) term but possess different SW terms, which would exhibit different behaviors when including the spatial curvature since the ISW effect is more sensitive to the spatial curvature than the SW effect. Furthermore, we provide the cross-correlations between CGWB and CMB, implying a positive or negative correlation between their SW effect terms depending on the GW mechanisms, which may hint at the sign of $f_{\mathrm{NL}}$ when considering non-Gaussianity contributions to anisotropies., Comment: 29 pages, 7 figures. Published version in JCAP. We have added a new section to analyze the SNR and made our code available at the acknowledgment

Gravitational waves (GWs) offer a new observational window into the universe, providing insights into compact objects and cosmic structures. Gravitational lensing, commonly studied in electromagnetic waves, also affects GWs, introducing magnification, time delays, and multiple images. While existing studies focus on static lenses, many astrophysical lenses are dynamic, with time-varying mass distributions such as moving stars or orbiting binaries. We develop a general theoretical framework to describe non-static lenses and demonstrate how they modulate GW signals, inducing unique time-varying amplitude modulations and spectral broadening. By examining uniformly moving and orbiting binary lenses, we show that these modulations provide new observational signatures, enhancing our understanding of lensing objects and the dynamics of the universe. Our findings have important implications for GW astronomy, offering novel ways to probe lens dynamics and improve the interpretations of GW signals., Comment: 20 pages, 8 figures

The decade-persistent Hubble tension has become a $5\sigma$ crisis of modern cosmology between the early-Universe extrapolation from globally fitting the standard $\Lambda$CDM to Planck-CMB measurements and the late-Universe measurement from the three-rung distance ladder with SH0ES calibration. Regarding the current dilemma of theoretical resolutions, recent focus has shifted to systematics inspection. Here we find an associated $5\sigma$ tension in the intercept of the supernova magnitude-redshift relation between the second-rung and third-rung supernovae from the PantheonPlus compilation independent of calibrations in use. As required by the consistency of the distance-ladder method, we propose a method to eliminate the intercept tension, directly constraining $H_0=73.4\pm1.0\;\mathrm{km/s/Mpc}$ from the first two-rung distance ladder alone without referring to the third-rung supernovae but still consistent with both SH0ES typical three-rung and first two-rung constraints, which not only supports our method to rebuild the intercept consistency but also rules out third-rung supernova systematics including the late-time transition in supernova absolute magnitude. Further crosschecking with the Carnegie Supernova Project revealed that different calibrators alone still consistently prefer our results. Therefore, the original Hubble tension between the Planck-CMB measurements and SH0ES three-rung distance ladder can be narrowed down to a tension between the Planck-CMB and the first two-rung measurements., Comment: v2, two columns, 13 pages, 2 tables, 6 figures, minor improvement for CSP SNe calibrated by TRGB

Thermodynamics of black holes offers a promising avenue for exploring the quantum nature of black holes and quantum gravity. In this Letter, we investigate the thermodynamic properties of dyonic black holes in the five-dimensional Einstein-Maxwell-Chern-Simons theory, obtained from IIB supergravity. We demonstrate that the standard form of the first law of thermodynamics is inconsistent with the quantum statistical relation widely adopted in black hole physics. By employing the on-shell variation of the Euclidean action and the Iyer-Wald formalism, we resolve this discrepancy and derive both the standard form of the first law and Smarr formula for the dyonic black holes. Furthermore, our findings are corroborated by numerical tests and are consistent with general hydrodynamic expectations., Comment: 5 pages, 2 figures, and supplementary information

In the early universe, the first-order phase transition may occur in the background of magnetic fields, leading to baryon number asymmetry through chiral anomaly. We have numerically simulated the first-order electroweak phase transition in the background of a magnetic field in a three-dimensional lattice, discovered the phenomenon of Higgs condensation, and for the first time given the relationship between baryon number asymmetry and magnetic field strength. The magnetic field strength required to achieve the matter-antimatter asymmetry by the evolution of magnetohydrodynamics is about $10^{-17}\sim10^{-14}$ Gauss at present depending on the correlation length of the helical magnetic field. Our research provides a strong basis for explaining the baryon number asymmetry with cosmic magnetic fields., Comment: 7+12 pages, 19 figures, comments welcome!

We investigate the internal dynamics of hairy black holes in the Einstein-Maxwell-vector theory. The development of the charged vector hair necessarily removes the inner Cauchy horizon and results in an anisotropic black hole ending at a spacelike singularity. The far interior evolution is characterized by the chaotic alternations among different Kasner epochs. We show that those late interior time dynamics of bounces and epochs can be captured analytically. In particular, we obtain three distinct types of transformation laws for the alternation of Kasner epochs analytically, including the Kasner inversion, Kasner transition, and Kasner reflection. Our analytical approach is corroborated by numerical solutions to the full equations of motion. Moreover, we provide a clear explanation of the alternation of Kasner epochs found numerically in the literature., Comment: 24 pages, 3 figures

We investigate the evolution of cosmological scalar perturbations in the case that the background radiation is weakly coupled to a light scalar field $\phi$. The light scalar $\phi$ is a homogeneous background field with a large initial value. In the radiation-dominated Universe, the coupling term introduces an effective mass to $\phi$ and the background ultra-relativistic particles. The oscillations of $\phi$ result in the periodic change of the equation of state parameter and the sound speed, which provides a novel mechanism to amplify subhorizon scalar perturbations through parametric resonance. The amplification of scalar perturbations leads to a stochastic gravitational-waves background~(SGWB) expected to be observed by multiband gravitational wave observers. The observation of the SGWB helps to determine the initial value of $\phi$ and the coupling strength of the interaction. This mechanism is generally applicable to the interactions that introduce an effective mass, and we take the interaction between $\phi$ and electrons as a concrete example to illustrate the result. We find that under the condition that the coupling coefficient $\lambda=10^{-16}$ and the initial value $\phi_i=10^{18}$ GeV, the resulting SGWB spectrum is expected to be observed by the future observers including LISA, $Taiji$, DECIGO and BBO., Comment: 13 pages, 4 figures

The QCD phase diagram is crucial for understanding strongly interacting matter under extreme conditions, with major implications for cosmology, neutron stars, and heavy-ion collisions. We present a novel holographic QCD model utilizing neural ordinary differential equations (ODEs) to map the QCD phase diagram under magnetic field $B$, baryon chemical potential $\mu_B$, and temperature $T$. By solving the inverse problem of constructing the gravitational theory from Lattice QCD data, we reveal an unprecedentedly rich phase structure at finite $B$, including discovering multiple critical endpoints (CEPs) under strong magnetic fields. Specifically, for {$B = 1.618 \, \mathrm{GeV}^2=2.592 \times 10^{19}$ Gauss}, we identify two distinct CEPs at $(T_C = 87.3 \, \mathrm{MeV}, \, \mu_C = 115.9 \, \mathrm{MeV})$ and $(T_C = 78.9 \, \mathrm{MeV}, \, \mu_C = 244.0 \, \mathrm{MeV})$. Notably, the critical exponents vary depending on the CEP's location. These findings significantly advance our understanding of the QCD phase structure and provide concrete predictions for experimental validation at upcoming facilities such as FAIR, JPARC-HI, and NICA., Comment: 12 pages, 13 figures

Primordial black holes (PBHs) may form before cosmological first-order phase transitions, leading to inevitable collisions between PBHs and bubble walls. In this Letter, we have simulated for the first time the co-evolution of an expanding scalar wall passing through a black hole with full numerical relativity. This black hole-bubble wall collision yields multiple far-reaching phenomena including the PBH mass growth, gravitational wave radiations, and momentum recoil that endows PBHs with additional velocities, approximately doubling the formation rate for PBH binaries and hence strengthening the observational constraints on the PBH abundances., Comment: v1, 5 pages + supplemental material; v2, 5-page main text (peak frequency estimation for GWs from PBH-bubble collisions is added) + 8-page largely extended supplemental material with details in numerical simulations (including numerical methods, initial data, convergence tests, and long-term evolutions)

First-order primordial curvature perturbations are known to induce gravitational waves at the second-order, which can in turn probe the small-scale curvature perturbations near the end of the inflation. In this work, we extend the previous analysis in the Gaussian case into the non-Gaussian case, with particular efforts to obtain some thumb rules of sandwiching the associated peaks in gravitational waves induced from multiple peaks of non-Gaussian curvature perturbations., Comment: 22 pages, 6 figures, published in JCAP

Recently, much attention has been focused on the false vacuum islands that are flooded by an expanding ocean of true-vacuum bubbles slightly later than most of the other parts of the world. These delayed decay regions will accumulate locally larger vacuum energy density by staying in the false vacuum longer than those already transited into the true vacuum. A false vacuum island with thus acquired density contrast of a super-horizon size will evolve locally from radiation dominance to vacuum dominance, creating a local baby Universe that can be regarded effectively as a local closed Universe. If such density contrasts of super-horizon sizes can ever grow large enough to exceed the threshold of gravitational collapse, primordial black holes will form similar to those collapsing curvature perturbations on super-horizon scales induced by small-scale enhancements during inflation. If not, such density contrasts can still induce curvature perturbations potentially observable today. In this paper, we revisit and elaborate on the generations of primordial black holes and curvature perturbations from delayed-decayed false vacuum islands during asynchronous first-order phase transitions with fitting formulas convenient for future model-independent studies., Comment: v1, two columns, 16 pages, 8 figures; v2, 17 pages, 8 figures, minor revision, version accepted for publication in Sci. China Phys. Mech. Astron. (SCPMA); v3, to match the published version

The pulsar timings are sensitive to both the nanohertz gravitational-wave background and the oscillation of ultralight dark matter. The Hellings-Downs angular correlation curve provides a criterion to search for stochastic gravitational-wave backgrounds at nanohertz via pulsar timing arrays. We study the angular correlation of the timing residuals induced by the spin-2 ultralight dark matter, which is different from the usual Hellings-Downs correlation. At a typical frequency, we show that the spin-2 ultralight dark matter can give rise to the deformation of the Hellings-Downs correlation curve induced by the stochastic gravitational wave background., Comment: 7 pages, 4 figures

We first show that the master equations for massless perturbations of accelerating rotating black holes can be transformed into the Heun's equation. The quasinormal modes of the black holes can be easily calculated in the framework of the Heun's equation. We identify three modes for the tensor perturbations: the photon sphere modes, which reduce to the quasinormal modes of Kerr black holes when the acceleration parameter vanishes; the near-extremal modes, which branch from the first set and become dominant when the spin is near extremal; and the acceleration modes, which are closely related to the acceleration horizon. We calculate the frequency spectrum of the QNMs in various spin and acceleration parameters. We choose an angular boundary condition that keeps the angular function regular at $ \theta = 0 $ and $\pi$, which is consistent with the boundary condition of the Kerr black hole. The conical singularity caused by the acceleration influences this boundary condition. We find that the $m_0 = 1$ modes have an anomalous behavior at particular accelerations., Comment: 16 pages, 10 figures; updated version, added references and some details, accepted for publication in PRD

Industrial anomaly detection is generally addressed as an unsupervised task that aims at locating defects with only normal training samples. Recently, numerous 2D anomaly detection methods have been proposed and have achieved promising results, however, using only the 2D RGB data as input is not sufficient to identify imperceptible geometric surface anomalies. Hence, in this work, we focus on multi-modal anomaly detection. Specifically, we investigate early multi-modal approaches that attempted to utilize models pre-trained on large-scale visual datasets, i.e., ImageNet, to construct feature databases. And we empirically find that directly using these pre-trained models is not optimal, it can either fail to detect subtle defects or mistake abnormal features as normal ones. This may be attributed to the domain gap between target industrial data and source data.Towards this problem, we propose a Local-to-global Self-supervised Feature Adaptation (LSFA) method to finetune the adaptors and learn task-oriented representation toward anomaly detection.Both intra-modal adaptation and cross-modal alignment are optimized from a local-to-global perspective in LSFA to ensure the representation quality and consistency in the inference stage.Extensive experiments demonstrate that our method not only brings a significant performance boost to feature embedding based approaches, but also outperforms previous State-of-The-Art (SoTA) methods prominently on both MVTec-3D AD and Eyecandies datasets, e.g., LSFA achieves 97.1% I-AUROC on MVTec-3D, surpass previous SoTA by +3.4%.

Recent detections of a low-frequency gravitational wave background (GWB) from various pulsar-timing-array (PTA) observations have renewed the interest in the inspiraling supermassive black hole binaries (SMBHBs), whose population is believed to be the most promising candidate with possible generalizations from including either orbital eccentricity or dark matter (DM) spike. In this paper, we show that the inclusion of both can further display distinctive features detectable in future PTA observations. With a typical initial eccentricity $e_0\sim\mathcal{O}(0.1)$ for the inspiraling SMBHBs, even a shallow DM spike can easily drive the orbital eccentricity close to $1$, leaving behind a large turnover eccentricity when GWs begin to dominate the orbital circularization. In particular, the DM spike index $\gamma_\mathrm{sp}$ universally manifests itself in the characteristic strain by $h_c\sim f^{7/6-\gamma_\mathrm{sp}/3}$ in the far infrared and features a novel oscillation structure at low frequencies. Future PTA detection of such characteristics would be the smoking gun for the DM spike and even reveal the nature of DM., Comment: v5, 22 pages, 8 figures, accepted version for publication in JCAP

The study of the interior of hairy black holes has received significant attention recently. This paper builds upon our recent analytical approach to investigate the internal dynamics of charged black holes with scalar hair in general spacetime dimensions. The geometries of these hairy balck holes end at a spacelike singularity. We investigate the alternation of Kasner epoch at later interior times and obtain the analytic expression for two kinds of transformation, namely Kasner inversion and Kasner transition. Moreover, we classify three different types of Kasner alternations for a large class of Einstein-Maxwell-scalar theory. Our analytical results are corroborated by numerical solutions to the full equations of motion, including a top-down model from supergravity. For general interactions, more complicated behaviors beyond our analytical description are also found and discussed, including the presence of non-Kasner epochs and the random change of the amplitude of the Kasner exponent at late interior times., Comment: Published version

We simultaneously study gravitational waves (GWs) and free axions emitted from axionic string-wall networks in the early universe using advanced 3D lattice simulations. Our simulations start before the Peccei-Quinn phase transition and end with the destruction of string-wall networks below the QCD scale. The axion dark matter (DM) relic abundance radiated from string-wall networks are updated and refined for the scenarios of $N_{\rm DW}>1$. In this scenario, we observe that the GW spectrum is almost independent of the bias term and $N_{\rm DW}$, and $\Omega_{\rm GW}h^2\propto f^{1.29}(f^{-0.43})$ in the IR and middle-frequency regions. After considering the constraints from DM relic abundance, we found that the QCD axion model predicts undetectable GW emissions, and the axion-like particles model allows for a detectable GW signal in the nano-Hertz to the milli-Hertz frequency range corresponding to axion masses range from KeV to TeV. For $N_{\rm DW}=1$, the GW energy density appears undetectable for QCD axions and axion-like particles., Comment: 7+13 pages; cosmic simulations on axion dark matter are added

The early and precise localization of gravitational waves (GWs) is pivotal in detecting their electromagnetic (EM) counterparts, especially for binary neutron stars (BNS) and neutron star-black hole binaries (NSBH). In this letter, we pioneer the exploration of utilizing the higher harmonic modes induced by the eccentricity of compact binaries to localize GWs with ground-based detectors even before the quadrupole baseline $\ell=2$ mode enters the detector band. Our theoretical analysis marks a first in proposing a strategy for gaining the earliest possible warning and maximizing preparation time for observing pre- and/or post-merger EM counterparts. We simulate three typical binaries from GWTC-3 with eccentricities ranging from 0.05 to 0.4. Our results reveal that the third-generation (3G) detectors (low frequency cut-off $f_0=5$ Hz) can accumulate sufficient signal-to-noise ratios through higher modes before the onset of the baseline $\ell=2$ mode entry into the band. Notably, relying solely on the higher modes, the 3G detector network ET+2CE achieves an average localization on the order of $1-10^2~\rm deg^2$ around 1-1.8 hours before the merger of a GW170817-like BNS, and $10-10^3~\rm deg^2$ approximately 18-30 minutes prior to the merger of a GW200115-like NSBH. A $100~\rm deg^2$ localization is attainable even 2-4 hours prior to a BNS merger. Moreover, in the near face-on orientations which are generally more favorable for EM counterpart detection, the localization can be further improved., Comment: 8 pages, 2 figures, published in PRD

The space-based laser interferometers, LISA, Taiji and TianQin, are targeting to observe milliHz gravitational waves (GWs) in the 2030s. The joint observations from multiple space-based detectors yield significant advantages. In this work, we recap the studies and investigations for the joint space-based GW detector networks to highlight: 1) the high precision of sky localization for the massive binary black hole (BBH) coalescences and the GW sirens in the cosmological implication, 2) the effectiveness to test the parity violation in the stochastic GW background observations, 3) the efficiency of subtracting galactic foreground, 4) the improvement in stellar-mass BBH observations. We inspect alternative networks by trading off massive BBH observations and stochastic GW background observation., Comment: 32 pages, 14 figures, reviews on recent studies about space-borne GW networks, comments and feedbacks are welcome

The celebrated anti-de Sitter/conformal field theory (AdS/CFT) correspondence1-3, also known as the gravity/gauge duality, posits a dual relationship between the quantum gravity in an AdS spacetime and the CFT defined on its lower-dimensional boundary. This correspondence not only offers profound insights into the enigmatic nature of quantum gravity but also shows mighty power in addressing strongly-correlated systems. However, despite its importance in contemporary physics, the AdS/CFT correspondence remains a conjecture, and further experimental investigation is highly sought after. Here, we present the first experimental exploration of this conjecture by testing its core corollary: the leading-order effects of a strongly-coupled CFT can be exactly described by a weakly-coupled classical field in a higher-dimensional AdS spacetime. Through measuring the bulk entanglement entropy (BEE) and boundary-boundary correlation function (BBCF) of scalar fields in both conventional type-I and previously overlooked type-II hyperbolic lattices, serving as the discretized regularizations of spatial geometries of pure AdS2+1 spacetime and AdS2+1 black hole, respectively, we experimentally confirm that BEE exhibits a logarithmic scaling with the subsystem size, following the Ryu-Takayanagi (RT) formula, while BBCF showcases an exponential law dependence on the boundary separation, the scaling dimension of which conforms to the Klebanov-Witten (KW) relation, both of which align remarkably well with the established CFT outcomes. This heuristic experimental effort opens a new avenue for in-depth investigations on the gravity/gauge duality and extensive exploration of quantum-gravity-inspired phenomena in classical systems.