The millihertz gravitational-wave band offers a new view of compact objects and black holes across cosmic history. TianQin, a planned space-based observatory, will explore this band through long-duration observations. In this talk, I will discuss its astrophysical prospects, from Galactic double white dwarfs and stellar-mass black hole binaries to massive black hole mergers and...
Cosmological tensions are one of the central topics of modern cosmology. The most prominent is the Hubble tension in which the measured expansion rate of the Universe from distance ladder is more than $5 \sigma$ larger than that predicted by $\Lambda$CDM based on CMB. Recently, BAO observation from DESI also reports a $2 - 3 \sigma$ tension with $\Lambda$CDM which might point to evolving dark...
In this work, we address a foundational challenge in quantum field theory on curved spacetime by developing a consistent framework in spherically symmetric loop quantum gravity. We introduce a methodology for defining meaningful superpositions of quantum geometry and matter states near the semiclassical apparent horizon. This is achieved by identifying a restricted subspace of the...
Space-based gravitational wave detection (e.g., LISA, Taiji, and TianQin) relies on ultra-high-precision inter-satellite laser interferometry. However, clock noise is approximately two orders of magnitude higher than the detector noise floor, which severely limits the overall detection sensitivity and becomes a critical constraint for space-based gravitational wave observatories. To address...
Quantum-gravity models often provide effective background dynamics, while cosmological observables depend on the dynamics of inhomogeneous perturbations. I will discuss a Hamiltonian framework for bridging this gap. Requiring consistent local evolution strongly constrains how a modified homogeneous or symmetric dynamics can be completed into a spatial theory. The resulting Hamiltonian...
3-form dark energy shows a similar behavior to but distinguishable one from that of a scalar field in an expanding universe, and its tensorial structure allows for unique couplings that cannot be experienced by canonical scalars.
We here explore the possibility that 3-form dark energy can explain the cosmic birefringence angle β~0.3°, as suggested by observations of the CMB polarization.
We...
The discrepancy between early- and late-Universe determinations of the Hubble constant may point to physics beyond ΛCDM or to unaccounted-for systematics. Numerous late-time modifications to the expansion history have been proposed to alleviate this discrepancy, with limited success. Recent works have shown that, when the sound-horizon and supernova calibrations are held fixed,any purely...
The motion of black-hole systems can leave distinctive imprints on gravitational-wave signals, offering a unique window into both their surrounding environments and merger dynamics. In this talk, I will discuss two representative effects associated with black-hole motion across different stages of binary evolution. First, I will consider stellar-mass binary black holes orbiting a supermassive...
We study the dynamics of the Bianchi I universe in modified loop quantum cosmology (mLQC-I) and uncover a robust mechanism for isotropization: the shear is dynamically suppressed after the bounce and decays rapidly in the quantum postbounce regime, independently of the equation of state of standard matter sources. This naturally drives the Universe toward a homogeneous and isotropic expanding...
Developing covariant effective descriptions of quantum-corrected black holes is an important challenge in loop quantum gravity (LQG). In this talk, I will present an LQG-inspired effective action in spherical symmetry that admits the quantum Oppenheimer–Snyder (q-OS) black hole as a vacuum solution. Starting from a two-dimensional dilaton gravity framework obtained by integrating out the...
The ringdown signal following a binary black hole merger offers a crucial avenue for investigating black hole properties and testing General Relativity in strong-field regimes. Beyond linear quasinormal modes, General Relativity predicts the existence of second-order quasinormal modes arising from the nonlinear coupling of gravitational waves. This talk presents an analysis of the ringdown...
The nearly scale-invariant primordial power spectrum provides the standard initial conditions for cosmological perturbations. However, the largest observable scales remain only weakly constrained by current CMB measurements, leaving open the possibility of deviations from scale invariance, such as an infrared (IR) cutoff in the primordial spectrum. This possibility is further motivated by the...
Uncovering the origins of binary black holes through gravitational-wave detections provides a powerful probe of the evolution, interactions, and environments of massive stars. Stellar theory predicts a forbidden range of black-hole masses between 50-130Msun due to pair-instability supernovae. In this talk, I will present our latest observational evidence of the pair-instability gap in the...
Observations of the cosmic microwave background (CMB) and radio wavelengths can probe multiple evolutionary stages spanning the early to late Universe, which feature large-scale structures and long-timescale processes. These observations are therefore of fundamental importance for investigating core physical problems concerning dark matter, dark energy, and gravitational waves. Future CMB...
The detection of GW170817 and its electromagnetic counterpart placed a stringent bound on the difference between the speeds of gravitational waves and light, severely restricting viable scalar-tensor models of dark energy. In particular, large parts of Horndeski and beyond Horndeski theories appeared to be ruled out as a description of late-time cosmic acceleration. In this talk we revisit...
We study the scalarization of the entire Bardeen spacetime which is constructed from a nonlinear magnetic monopole. For the pure Bardeen model, it is well known that there exist not only the general horizonless, nonsingular Bardeen spacetime solutions but also regular black hole (BH) solutions. When considering the Bardeen model coupled to a scalar field, we find that under the premise of...
Every rapidly spinning neutron star with slight asymmetry would broadcast a continuous hum of gravitational waves (GW). None of these signals has been detected yet, but the silence itself is measurable: searches now set upper limits on the GW amplitude of dozens of known pulsars, and for a growing subset those limits dig below the energy budget available from the stars’ own spin-down. We ask...
In modern cosmological research, using cosmological numerical simulations to study the evolution of the large-scale structure of the Universe has proven to be a highly effective technique. However, cosmological numerical simulations beyond the standard cosmological model require numerous modifications to existing cosmological simulation frameworks. They are technically complex and have a high...
This is a work about the complex conformal Kähler structure and the related duality symmetry of Plebański-Demiański class, a kind of type-D spacetime. We reviewed the complex metric and complex Kähler structure of complex spacetimes, which has the complex valued metric and almost complex structure as well as the related potential function. We find a SO(2, C) duality transformation of...
I shall present the Discovering Sky at the Longest wavelength (DSL) mission, also known as the Hongmeng mission in Chinese, which aims to unveil the sky at this low frequency band by using an array of microsatellites flying in formation on an orbit around the Moon. The mission will make highly precise 21cm global spectrum measurement in the 0.1-30 MHz band and in the 30-120 MHz band, without...
Dark matter may leave observable signatures in gravitational-wave detectors through a remarkably broad range of physical mechanisms. In this talk, I will discuss recent searches using data from the fourth observing run of the LIGO–Virgo–KAGRA detector network. First, I will present a direct search for ultralight dark matter, in which coherently oscillating scalar, vector, and tensor fields can...
We use neural ODEs and state-of-the-art lattice QCD thermodynamics to calibrate a holographic Einstein-Maxwell-Dilaton model with Gauss-Bonnet corrections. The model quantitatively reproduces the equation of state at zero and finite baryon chemical potential and predicts the phase structure in the T-mu_B plane, a temperature-dependent ratio of shear viscosity over entropy, and a peaked ratio...
The axion solution to the strong CP problem is only as robust as the Peccei-Quinn symmetry it relies on, and quantum gravity is expected to break it. We quantify the resulting axion quality problem using principled measures of fine-tuning, and show that the cost is severe. For the QCD axion to account for the observed dark matter, Planck-suppressed symmetry-breaking operators must be absent up...
We investigate the timelike entanglement first law in holographic conformal field theories whose bulk dual is Lovelock gravity. Using the double Wick rotation formulation of timelike entanglement entropy together with the Jacobson-Myers entropy functional, we compute the linear variation of holographic timelike entanglement entropy for hyperbolic subregions. For cubic Lovelock gravity, we...
The 21-cm signal from the cosmic Dark Ages is a powerful probe of cosmology and
inflation, but its science potential depends critically on the design of the lunar
far-side interferometer that will observe it. We derive closed-form relations
connecting the array design to the two goals this epoch offers: measuring a chosen
small scale, and extracting the largest possible cosmological...
I will discuss a new mechanism for generating primordial large-scale curvature perturbations and gravitational wave (GW) anisotropies via a first-order phase transition modulated by a light spectator field. The spectator acquires fluctuations during inflation, which come into play at a post-inflation phase transition by modulating the bubble nucleation rate. Such a modulation induces spatial...
Entanglement harvesting transfers quantum field correlations to localized probes, yet whether these correlations can alter stable strategic behavior has remained unclear. We formulate a quantum-input game in which two Unruh–DeWitt detectors harvest vacuum entanglement from a free massless scalar field in $(3+1)$-dimensional Minkowski spacetime. A referee converts this state into payoffs using...
RadioSkySim: A Flexible and Scalable Python Framework for Radio-Astronomical Sky Simulation
RadioSkySim is a Python-based sky simulation framework developed within the BINGO Collaboration to support the modeling, analysis, and validation of radio-astronomical observations. Designed with an emphasis on modularity, extensibility, and computational efficiency, it provides a flexible...
We present a holographic calculation of the semileptonic decays $B\to D$ and $B_s\to D_s$ within the AdS/QCD Softwall Model. Heavy-light mesons are described by normalizable bulk modes, while the flavor-changing current $J_\text{EW}^\mu=\bar{c}\,\gamma^\mu\,b$ is associated with a massless bulk vector field, motivated by the UV scaling dimension $\Delta=3$ of the QCD current. An effective...
We describe a bounded search for local and global anomaly-free six-dimensional $(1,0)$ models with tensor number $T=1$ and gauge group containing a diagonal abelian factor $U(1)_{R+}$. The abelian factor is the diagonal combination of the usual gauged $U(1)_R$ and a $U(1)\subset Sp(n_H)$ acting on hypermultiplets. We have searched for locally and globally anomaly-free $G_1\times U(1)_{R+}$ and...
The geometric distances of active galactic nuclei (AGNs) are challenging to measure because of their exceptionally compact structure, yet vast cosmic distances. A combination of spectroastrometry and reverberation mapping (SARM) of broad-line regions (BLRs) constitutes a novel means to probe the geometric distance of AGNs, which has recently become practically feasible owing to successful...
Cosmological correlators are calculated through the in-in formalism in (quasi-)de Sitter background. Their effective description is best represented by a reduced density matrix. In this talk, I will first review the differences between the usual EFT used in scattering amplitude calculations and the Schwinger-Keldysh EFT for correlators. I will then discuss the reduced density matrix for a...
Higher-derivative and nonlocal gravity models arise in various approaches to quantum gravity, either as candidates for renormalizable theories of gravity or as effective low-energy descriptions. In this talk, we present several recent results on classical solutions in higher-derivative gravity, focusing on the possibility of resolving the black-hole singularity present in solutions of general...
A thermal medium modifies the propagation of gauge fields, producing collective excitations with a plasmon gap. Does it affect primordial gravitational waves in the same way? For gravity, the thermal soft scale coincides with the Hubble rate, making cosmic expansion essential to answering this question. In this talk, I compute the linear response of thermal radiation, modeled by a conformal...
JWST's little red dots (LRDs) are unexpectedly non-variable. We present a semi-analytic framework for variability in super-Eddington slim disks with winds, combining photon trapping, photospheric averaging, and diffusion filtering, calibrated on ordinary quasars. Forward-modeling the TWINKLE non-detections of 18 LRDs, we derive a lower limit ṁ ≳ 60 (95% confidence) for 10⁷ M⊙ black holes,...
Primordial black holes (PBHs) provide a unique probe of the early Universe. Their cosmological evolution is governed by the competition between mass accretion and Hawking evaporation. In this paper we look into the details impact of accretion. Most of the earlier analysis relied on non-relativistic accretion models. In this work, we reinvestigate this in a fully relativistic framework for Kerr...
Primordial gravitational waves generate radiation density perturbations at second order, providing a possible connection between small-scale tensor power and primordial black hole (PBH) formation. In this talk, we revisit this connection using a finite-time semianalytic solution for arbitrary source momenta. The solution retains the regular homogeneous contribution fixed by the initial spatial...
Beyond general relativity, regular black-hole geometries and modified cosmologies are often constructed independently, raising the question of whether black holes, gravitational collapse, and cosmology can still arise as different regimes of a common gravitational dynamics. We answer this question by showing that, within the covariant spherically symmetric effective Hamiltonian framework, the...
We consider Bianchi IX dynamics of a Universe filled with a massless phantom field. Such an exotic matter source enables regimes impossible in vacuum or with a standard scalar field. In particular, two Kasner indices of BKL oscillations can be simultaneously negative, and the absolute value of a negative index can be large. We describe the consequences of these features and explain the nature...
暗物质（DM）是宇宙的基本组成成分，因此有必要研究其对黑洞（BH）阴影的影响，尤其是事件视界望远镜（EHT）观测所证实的旋转黑洞。本文利用 Newman–Janis 算法（NJA），将暗物质环绕的施瓦西黑洞解推广为轴对称的克尔黑洞解，并研究其事件视界与能层结构。通过分析零测地线，我们考察了暗物质质量（(\Delta M)）对黑洞阴影半径、形变及相关能量发射率的影响。结果表明，当暗物质质量低于某一临界值时，其影响可以忽略；一旦超过该阈值，黑洞的各类结构均显著扩张。此外，即使黑洞具有较高自旋，暗物质仍有助于其阴影保持近圆形轮廓。较大暗物质质量引起的显著结构扩张可能超出当前观测约束。这表明，为与天体物理观测保持一致，黑洞紧邻区域内应不存在暗物质，或其中的局域暗物质质量必须低于该临界值。
Chiral gravitational wave backgrounds are predicted in many well-motivated mechanisms. We investigate the detection of Chiral GWBs using a network of detectors under arbitrary configurations. We also propose a dipole pulsar timing array, which demonstrates sensitivity to Chiral gravitational wave backgrounds from the nanohertz to microhertz regime.
Recent PTA analyses reporting evidence for a nanohertz common-spectrum process motivate targeted tests of whether any anisotropic component of the stochastic gravitational-wave background (SGWB) is correlated with the nearby large-scale structure (LSS), as anticipated for an astrophysical background dominated by supermassive black hole binaries. We present the first Bayesian PTA likelihood...
Can the geometry hidden behind a black hole's event horizon be reconstructed from its exterior quasinormal-mode spectrum? In this talk, I will explore how high-overtone quasinormal modes encode information about black hole interiors. We show that distinct power-law corrections to the spectrum, obtained through angular-momentum and scalar-mass responses, allow the temporal and angular Kasner...
The intrinsic spin of fermions generates torsion in spacetime. This gives rise to a parity-violating, nonuniversal four-fermion interaction, which is expected to become significant in dense matter, such as in early-universe cosmology or in neutron stars. We calculate the effect of the interaction term in a gravitationally collapsing gas of fermions with an isotropic spin distribution. We use...
I will introduce a neat mathematical framework that can be utilized to study, in a unified manner, different aspects of $f(R),\,f(T),\,f(G)$ or $f(Q)$ gravity. As an example of the application of this framework, I will show its applicability for a comparative analysis between $f(R)$ gravity and the trivial FLRW connection branch of $f(Q)$ gravity, with respect to the two following questions:...
Possible existence of antimatter at astrophysical and cosmological scales is considered. It is shown that the model of primordial black hole of 1993 may lead to a noticeable populations of our Galaxy with diferent forms of
antimatter and observational manifestations of the latter are presented.
We establish a general no-inner horizon theorem for a wide class of static anisotropic black holes in Einstein gravity. As an application, we demonstrate that a large variety of black holes which possess homogeneous but anisotropic three-dimensional horizons can not have inner horizons. Our theorem is consistent with some previously known results, implying an underlying mechanism that certain...
The Kerr–Bertotti–Robinson (Kerr–BR) spacetime is a recently constructed exact Einstein–Maxwell solution describing a rotating black hole immersed in a homogeneous Bertotti–Robinson electromagnetic universe. Unlike the familiar Melvin-type magnetized Kerr families, its asymptotics are AdS₂ × S², the external field explicitly deforms the horizon and extremality condition, and its Maxwell and...
Although the standard model of Big Bang nucleosynthesis successfully describes the formation of light elements, it faces a well-known challenge: the observed abundance of lithium-7 is approximately three times lower than the theoretically predicted value. This work proposes a mechanism to resolve this primordial lithium deficit through the emission of baryons by evaporating primordial black...
Gravity from entropy proposes quantum relative entropy between the spacetime metric and the metric induced by geometry and matter fields as the fundamental action for gravity. The resulting modified Einstein equations reduce to general relativity in the weak-coupling, low-curvature limit, while departing from it at high curvature. In this talk, I derive the Friedmann-equation analogues of GfE...
Black hole is an interesting physical object which is both a thermodynamical system and nest of chaos. In this talk, I will firstly introduce the conformal anomaly corrections on the black hole geometry in 4d spherical symmetric spacetime. After introducing the black hole solution, I will discuss the thermodynamics and chaotic properties of this black hole. We investigate the phase transition...
We investigate dark matter admixed neutron stars in which the neutron star coexists with an anisotropic dark matter halo described by the Einasto density profile, a model recently shown to produce regular, singularity-free black hole solutions~[Phys. Rev. D \textbf{113}, 043011 (2026)].
Solving the modified Tolman--Oppenheimer--Volkoff equations with two different equations of state (BSk19...
The Big Bang singularity marks a fundamental breakdown of General Relativity, yet all proposed quantum gravitational remedies invoke microphysical assumptions beyond the observational reach. We show that a minimal, purely classical modification of the gravitational potential --- preserving the inverse-square law where tested, but free to depart at unmeasured scales --- is sufficient to produce...
I will review known results on scalar-tensor theories, including their disformal transformations, stability and degeneracy.
Next, will present recent results on scalar-vector-tensor theories with second order equations of motion.
Finally, I will show a new class of degenerate SVT theories, that was obtained via disformal transformation.
During last decade and a half many results are obtained that show when (i) particle collisions in a strong gravitational field lead to an unbounded energy in the center of mass E_{c.m.} of two colliding particles, (ii) when the process leads also to significant energy extraction measured at infinity. The set of possible scenarios can be divided to three main cases: (i) collisions near black...
We study the late-time expansion history of the Universe within the VCDM model, a Type-II MMG realization that preserves the successes of General Relativity while extending beyond constant vacuum energy through a minimal Hamiltonian modification, generating a time-dependent vacuum sector without introducing additional degrees of freedom. We investigate this framework within a cosmographic...
We investigate a Schwarzschild-like black hole embedded in a combined environment consisting of a Dehnen-type dark matter halo and a cloud of strings. We first construct the corresponding composite spacetime metric and examine its geometric properties, including the horizon structure, curvature invariants, and the validity of the classical energy conditions. Subsequently, we explore the...
Ultralight bosons could trigger superradiant instabilities in rapidly spinning black holes, forming oscillating clouds while extracting rotational energy.
We consider an extended, superradiance-informed spin distribution model that characterizes possible environment-induced spin variations and compare its predictions with the observed population of merging black hole binaries in the...
