Pulsar Timing Arrays (PTAs) offer an independent method for searching for ultralight dark matter (ULDM), whose wavelike nature induces periodic oscillations in the arrival times of radio pulses. In addition to this gravitational effect, the direct coupling between ULDM and ordinary matter results in pulsar spin fluctuations and reference clock shifts, leading to observable effects in PTAs. The second data release from the European PTA (EPTA) indicates that ULDM cannot account for all dark matter in the mass range $m_{\varphi }\in [{10}^{-24.0}-{10}^{-23.3}]\mathrm{eV}$ based solely on gravitational effects. In this work, we derive constraints on the coupling coefficients by considering both gravitational and coupling effects. Our results demonstrate that for ULDM with lighter masses, i.e., approximately $m_{\varphi }\le {10}^{-22}\mathrm{eV}$, EPTA provides stronger constraints on these couplings than previous PTA experiments and establishes comparable or even tighter constraints than other precise experiments, such as the atomic clock measurements.

Shock breakout emission is likely the first electromagnetic signal from a wide variety of astrophysical explosive phenomena, including supernovae and neutron star (NS) mergers; as exemplified by GRB 170817A, this signal can be the dominant component in low-luminosity short $\gamma$-ray bursts. In this work, we investigate the cocoon shock breakout emission in NS mergers and how its signal depends on the outermost layers of the ejecta profile, which we derive from general-relativistic radiation hydrodynamic simulations. To explore the influence of the outermost layers of the ejecta on the breakout emission, we model the ejecta profile as either having a sharp cutoff or an extended smooth tail. We find that the shock breakout emission is strongly influenced by the shape of the outermost layers of the ejecta, with breakouts from extended density profiles yielding emission consistent with the observed properties of GRB 170817A; on the contrary, breakouts from ejecta with a sharp cutoff tend to overestimate the radiated energy. Using a Bayesian analysis, we estimate the best-fit parameters for the central engine, considering both accreting black hole (BH) and magnetized NS scenarios. Our findings indicate a slight preference for scenarios in which the remnant suffers an early collapse to a BH. Our work probes the nature of neutron star mergers and highlights the importance of carefully treating the shape of the ejecta outermost layers in modeling early electromagnetic counterparts from these events.

The relativistic inverse stellar structure problem determines the equation of state of the stellar matter given a knowledge of suitable macroscopic observable properties (e.g. their masses and radii) of the stars composed of that material. This study determines how accurately this equation of state can be determined using noisy mass and radius observations. The relationship between the size of the observational errors and the accuracy of the inferred equation of state is evaluated, and the optimal number of adjustable equation of state parameters needed to achieve the highest accuracy is determined.

Different from the previous treatment in a two-body framework, we introduce the dimeson distribution amplitudes (DAs) to describe the strong dynamics between the S-wave resonances $a_0(980,1450)$ and the $K\overline{K}(\pi \eta )$ pair, where the Gegenbauer coefficient required is determined from the experimental data on the timelike form factors involved. The branching ratios and direct $CP$ asymmetries of the decays $B\to a_0^{(\prime )}h\to K\overline{K}(\pi \eta )h$, with $a_0=a_0(980)$, $a_0^{\prime }=a_0(1450)$ and $h$ referring to a pion or a kaon, are then calculated in the perturbative QCD (PQCD) approach. We find that the branching ratios of the corresponding quasi-two-body decays $B\to a_0^{(\prime )}K$ obtained with the narrow width approximation are closer to those predicted in the QCD factorization (QCDF) approach compared to the previous PQCD calculations, no matter a three-body or a two-body framework is assumed. Furthermore, all our predictions for these $B\to a_0^{(\prime )}K$ decays are below the current experimental upper limits except for those of decays $B^0\to a_0^{(\prime )-}{K}^{+}$, which are (slightly) larger than the upper limits. Under the narrow width approximation, the branching ratios of the decays $B^{+}\to a_0^{(\prime )+}{\pi }^0$, $B^0\to a_0^{(\prime )+}{\pi }^{-}$, and $B^0\to a_0^{(\prime )0}{\pi }^0$ are comparable to or agree well with the previous PQCD and the QCDF calculations. While for the decays $B^{+}\to a_0^{(\prime )0}{\pi }^{+}$ and $B^0\to a_0^{(\prime )-}{\pi }^{+}$, their branching ratios are predicted to be unexpectedly large, for example, the obtained branching ratio of decay $B^{+}\to a_0^0{\pi }^{+}$ is even higher than the current experimental upper limit. For the decays $B^0\to a_0^{(\prime )-}{K}^{+},a_0^{(\prime )0}{\pi }^0,a_0^{(\prime )+}{\pi }^{-}$, where the tree and the penguin amplitudes are comparable in magnitude, the direct $CP$ asymmetries are sensitive to the strong phases, which are very different obtained by other theoretical predictions for some channels. Therefore, it is very important to accurately determine the strong phases of these decays, which are crucial to precisely predict the direct $CP$ asymmetries and further clarify the inner structures of the resonances $a_0(980)$ and $a_0(1450)$.

The prospected sensitivity in ${\alpha }_{\mathrm{S}}$ determination using an event shape observable and ratio of energy correlators at future electron-positron colliders is presented. The study focuses on the collinear region which has suffered from large theoretical and hadronization uncertainty in the past. The ratio effectively reduces the impacts of the uncertainties. With the amount of data that future electron-positron colliders could produce in 1 minute ($40{\mathrm{pb}}^{-1}$), a 1–2% precision of ${\alpha }_{\mathrm{S}}$ could be reached depending on the hadronization uncertainty considered.

We extend the so-called hyperchargeless Higgs triplet model to include a weak triplet of Dirac fermions and a Dirac fermion $X$ transforming trivially under the Standard Model gauge group. We are motivated in part by a collection of anomalies that can be interpreted as a new scalar state with a mass of approximately 152 GeV coupling to $W$ but not $Z$ bosons, which may be consistent with the electrically neutral triplet scalar in this model (provided that it mixes very slightly with the Standard Model Higgs boson). Meanwhile, the lightest neutral fermion in the model is stable and can be thermal dark matter with the correct relic abundance if it mixes lightly with the neutral triplet fermion, such that the dark matter is composed mostly of $X$. Because $X$ couples to the Standard Model only through a Yukawa-like interaction with the pair of triplets, this model falls into the frustrated dark matter paradigm. Finally, the spectrum of exotic fermions in this model can exhibit the strong compression favored by the current excess in the monojet channel, and it evades multijet constraints in the region favored by monojets. In this work, we explore this model’s phenomenology and compare the parameter space regions best suited to each of the aforementioned excesses and constraints.

Accessing a full picture of the internal structure of hadrons would be a key topic of hadron physics, with the main motivation to study the strong interaction binding the visible matter. Furthermore, the underlying structure of known exotic states remains an unresolved fundamental issue in hadron physics, which is currently being addressed by hadron physics community. It is well known that electromagnetic characteristics can serve as a distinguishing feature for states whose internal structures are complex and not yet fully understood. The aim of this study is to determine the magnetic moments of vector hidden-charm tetraquark states by making use of QCD light-cone sum rules. In order to achieve this objective, the states mentioned above are considered in terms of the diquark-antidiquark structure. Subsequently, a comprehensive examination is conducted, with four distinct interpolating currents being given particular consideration, as these have the potential to couple with the aforementioned states. It has been observed that there are considerable discrepancies between the magnetic moment results extracted employing different diquark-antidiquark structures. Such a prediction may be interpreted as the possibility of more than one tetraquark with the identical quantum numbers and similar quark constituents but with different magnetic moments. The numerical predictions yielded have led to the conclusion that the magnetic moments of the vector hidden-charm tetraquark states are capable of projecting the inner structure of these states, which may then be used to determine their quark-gluon structure and quantum numbers. In order to provide a comprehensive analysis, the individual quark contributions to the magnetic moments are also examined. As a byproduct, the quadrupole moments of these states are also extracted, and the obtained values differ from zero, which indicates that the charge distribution of these states is not spherical.

Exclusive production of a ${\chi }_{c1}$ axial vector quarkonia in photon-proton scattering at high energies requires a $C$-odd $t$-channel exchange. In the limit of vanishing momentum transfer this occurs either via the exchange of a photon, the Primakoff process, where the spin of the proton does not change. For axial-vector meson production, as a consequence of the Landau-Yang theorem, the Primakoff cross section is finite as $t\to 0$. Alternatively, a $C$-odd spin dependent Odderon can be exchanged, which involves a spin flip of the proton. The resulting cross section is related to the square of the collinear trigluon correlator or the $k_{\perp }$-moment of the gluon Sivers function. Using two models for the gluon Sivers function from the literature we compute the ratio of Sivers to Primakoff cross sections and the angular coefficient ${\lambda }_{\theta }$ governing the angular distribution of the ${\chi }_{c1}\to J/\psi +\gamma$ decay as functions of $x$. We point out that these observables constrain the magnitude of the gluon Sivers function at small $x$ which could be accessed in electron-proton scattering and ultraperipheral proton-proton and nucleus-proton collisions.

The BESIII Collaboration recently reported the observation of two new resonances, $X(1910)$ and $X(2300)$, which have sparked our interest in studying the light hadron family with $J^{PC}=1^{+-}$. In this work, we investigate the mass spectra and Okubo-Zweig-Iizuka (OZI)-allowed two-body strong decays of $b_1$, $h_1$, and $h_1^{\prime }$ using the modified Godfrey-Isgur (MGI) quark model and quark-pair creation (QPC) model with newly fitted parameters. We also explore the possibility of identifying $X(1910)$ and $X(2300)$ as $h_1$ or $h_1^{\prime }$ states. Our numerical results suggest that $X(1910)$ could be a promising candidate for the $h_1^{\prime }(2^1{P}_1)$ state with quark content $s\overline{s}$, while the structure of $X(2300)$ remains uncertain.

By viewing black hole solutions as topological defects in thermodynamic parameter space, we unveil a novel topological class and two new topological subclasses, respectively, denoted as $W^{0-\leftrightarrow 1+}$, ${\overline{W}}^{1+}$, and ${\widehat{W}}^{1+}$, that extend beyond the four established categories proposed by Wei et al. [Phys. Rev. D 110, L081501 (2024)]. Within the newly identified class and these two novel subclasses, the innermost small black hole states exhibit a distinct sequence of unstable, stable, and stable behaviors, while the outermost large black hole states display a uniform pattern of stable behaviors. These classifications indicate thermodynamic properties both in the low and high Hawking temperature regimes that are strikingly different from the previously known four topological classes. In particular, we demonstrate that the static charged anti–de Sitter black holes in gauged supergravity exhibit an intricate thermodynamic evolution that is notably distinct from that of the Reissner-Nordström anti–de Sitter black hole. From a topological perspective, we emphasize the advantages and potential of investigating thermodynamic phase transitions in these black hole spacetimes, an area that has been rarely explored in the previous research. Our findings not only enrich and sharpen the framework of topological classifications in black hole thermodynamics but also represent a significant stride toward unraveling the fundamental nature of black holes and gravity.

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: ${\varphi }_c={3.7}_{-0.5}^{+0.3}{M}_{\mathrm{P}}$, ${\log }_{10}{\omega }_L={7.1}_{-0.3}^{+0.6}$, and ${\log }_{10}\sigma =-{8.3}_{-0.6}^{+0.3}$ 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.

We analyze the stability properties of a simple holographic model for a confining field theory. The gravity dual consists of an Abelian gauge field, with nontrivial magnetic flux, coupled to six-dimensional gravity with a negative cosmological constant. We construct a one-parameter family of regular solitonic solutions, where the gauge field carries flux along a compact circle that smoothly shrinks. The free energy of these solitonic backgrounds is compared to that of domain-wall solutions. This reveals a zero-temperature first-order phase transition in the dual field theory, separating confining and conformal phases. We compute the spectrum of bound states by analyzing field fluctuations in the gravity background, after dimensional reduction on the circle. A tachyonic instability emerges near a turning point in the free energy. The phase transition prevents the realization of this instability. Near the phase transition and beyond, in metastable and unstable regions, we find evidence that the lightest scalar may be interpreted as an approximate dilaton.

We systematically study spin precession of neutral particles freely moving in spacetime. We first derive the formula describing spin precession within a general stationary and axisymmetric spacetime. We then apply our formula to study spin precession of neutral spinning particles moving within various spacetimes that are among the most ubiquitous ones found in the literature. Our results are then used to extract the helicity flip probability for neutrinos propagating in each one of those selected spacetimes. It is found that low-energy neutrinos acquire a spin-flip probability that is as large as unity in all the spacetimes considered here. The remarkable result, however, is that while spin-flip probability for high-energy neutrinos remains insignificant in most of these spacetimes, some of them do allow spin-flip probability to reach unity even for high-energy neutrinos.

We discuss the decoherence in a quantum system induced by interaction with gravitational degrees of freedom that are part of a higher derivative theory. The deformation of a mass distribution due to gravitational waves acquires naturally a mass quadrupole moment. This adds higher derivative dynamics of the quadrupole moment to the unitary evolution of the system, where the quadrupole moment oscillates with the gravitational frequencies following a higher derivative theory. The consequence of higher derivatives in the dynamics is that four canonical variables describe the system. This departure from the usual particle position and momentum operators gives an entirely different interpretation of the decoherence basis. This model focuses on the open dynamics of the quadrupole moment, rather than on individual particles. As such, a short example is given to utilize quadrupole measurements to probe gravitational decoherence and noise. We first derive a Langevin equation for a lower derivative model and show how higher derivatives naturally emerge on the boundary. A quantum master equation is derived for the emerging quadrupole moment, considering that the environment is a higher derivative theory of gravity.

Our research aims to probe the anisotropic matter field around black holes using black hole perturbation theory. Black holes in the Universe are usually surrounded by matter or fields, and it is important to study the perturbation and the characteristic modes of a black hole that coexists with such a matter field. In this study, we focus on a family of black hole solutions to Einstein’s equations that extend the Reissner-Nordström spacetime to include an anisotropic matter field. In addition to mass and charge, this type of black hole possesses additional hair due to the negative radial pressure of the anisotropic matter. We investigate the perturbations of the massless scalar and electromagnetic fields and calculate the quasinormal modes (QNMs). We also study the critical orbits around the black hole and their properties to investigate the connection between the eikonal QNMs, black hole shadow radius, and Lyapunov exponent. Additionally, we analyze the graybody factors and scattering coefficients using the perturbation results. Our findings indicate that the presence of anisotropic matter fields leads to a splitting in the QNM frequencies compared to the Schwarzschild case. This splitting feature is also reflected in the shadow radius, Lyapunov exponent, and graybody factors.

In this paper, we present an enhanced semianalytic method for calculating quasinormal excitation factors in the eikonal regime, specifically for Schwarzschild black holes. To achieve improved accuracy in our quasinormal mode computations, we extend the Dolan and Ottewill inverse multipolar expansion technique and incorporate higher-order corrections from the Wentzel–Kramers–Brillouin method of Iyer and Will. Our approach is carried out to a higher order than previous methods, thereby reducing the relative error, particularly for lower multipolar numbers. We validate our results by comparing them with those obtained using the Mano, Suzuki, and Takasugi method, demonstrating excellent agreement. A key advantage of our method is its ability to extract quasinormal excitation factors, which are crucial for accurately modeling gravitational wave signals from binary black hole mergers. This advancement provides a useful tool for future gravitational wave studies, enabling better quantification of quasinormal mode excitations and more precise identification of individual modes during black hole ringdowns.

New physics and systematic errors can lead to deviations between the models used to analyze gravitational wave data and the actual signal. Such deviations will generally be correlated between detectors and manifest differently across the gravitational wave source parameter space. The previously introduced SCoRe framework uses these features to distinguish these deviations from noise and extract physical information from their source-dependent variation. In this work, we further analyze the hierarchical component of the method—we include the expected dependence of the deviations on the source parameters into the inference process, obtaining more physically informative results. As a specific example, we study a deviation that scales as a power law of the mass scale of black hole binaries—as, for example, in the effective field theory of gravity. We show how the signal-to-noise ratio of the cross-correlated residual power can be used to recover the power-law index. We demonstrate how both the distribution in source and deviation strength determine which region of source parameter space influences the inference most. Finally, we forecast the constraint on the power law index for a network of two Cosmic Explorer-like detectors with a year of observation period.

Gravitational microlensing of gravitational waves (GWs) opens up the exciting possibility of studying the spacetime geometry around the lens. In this work, we investigate the prospects of constraining the charged hair of a charged gravitating object from the observation of a GW signal microlensed by the same. The charge can have electromagnetic or modified gravity origin. We compute the analytic form of the lensing potential with charge and construct the lensed waveforms for a range of mass and charge of the charged object, assuming them to be non spinning. Using an approximate likelihood function, we explore how future observations of microlensed GWs can constrain the charge of the lens. We conclude that lensing observations are unlikely to be able to constrain the electromagnetic charge of black holes. However, we might be able to put modest constraints on certain modified gravity models (e.g., the braneworld scenario) or the possibility of the lenses being exotic objects (e.g., naked singularities).

Using low redshift data on astrophysical reionization, we derive a new Lyman-$\alpha$ limit on axion-like particles (ALP) as cold dark matter in an ALP mass range of $m_a\sim 30–1000\mathrm{eV}$. Compared to Leo T and soft x-ray bounds, we show that this limit is so far the most stringent in the ALP mass range of $m_a\sim 375–425\mathrm{eV}$ and complementary in the ALP mass range otherwise. In light of these bounds, we show new exclusion limits on $m_a$ for the ALP dark matter from either misalignment or a freeze-in mechanism, depending on parameter $\beta$ and reheating temperature $T_{\mathrm{reh}}$, respectively.

We explore linear and nonlinear dimensionality reduction techniques for statistical inference of parameters in cosmology. Given the importance of compressing the increasingly complex data vectors used in cosmology, we address questions that impact the constraining power achieved, such as: Are currently used methods effectively lossless? Under what conditions do nonlinear methods, typically based on neural nets, outperform linear methods? Through theoretical analysis and experiments with simulated weak lensing data vectors we compare three standard linear methods and neural network based methods. We also propose two linear methods inspired by information theory: a variation of the MOPED algorithm we call e-MOPED and an adaptation of canonical correlation analysis (CCA), which is a method uncommon in cosmology but well known in statistics. Both e-MOPED and CCA utilize simulations spanning the full parameter space, and rely on the sensitivity of the data vector to the parameters of interest. In the context of our experiments, the two linear methods we propose consistently outperform the rest. The gains are significant compared to compression methods used in the literature: up to 30% in the figure of merit for ${\mathrm{\Omega }}_m$ and $S_8$ in a realistic simulation based inference analysis that includes statistical and systematic errors. We also recommend two modifications that improve the performance of all methods: First, include components in the compressed data vector that may not target the key parameters but still enhance the constraints on due to their correlations. The gain is significant, above 20% in the figure of merit. Second, compress Gaussian and non-Gaussian statistics separately—we include two summary statistics of each type in our analysis.