The potential hadron-to-quark phase transition in neutron stars has not been fully understood as the property of cold, dense, and strongly interacting matter cannot be theoretically described by the first-principle perturbative calculations, nor have they been systematically measured through terrestrial low-to-intermediate energy heavy-ion experiments. Given the Tolman-Oppenheimer-Volkoff (TOV) equations, the equation of state (EoS) of the neutron star (NS) matter can be constrained by the observations of NS mass, radius, and tidal deformability. However, large observational uncertainties and the limited number of observations currently make it challenging to strictly reconstruct the EoS, especially to identify interesting features such as a strong first-order phase transition. In this work, we study the dependency of reconstruction quality of the phase transition on the number of NS observations of mass and radius as well as their uncertainty, based on a fiducial EoS. We conquer this challenging problem by constructing a neural network, which allows one to parametrize the EoS with minimum model-dependency, and by devising an algorithm of parameter optimization based on the analytical linear response analysis of the TOV equations. This work may pave the way for the understanding of the phase transition features in NSs using future x-ray and gravitational wave measurements.

By analyzing $7.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data collected at the center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we report the observation of the semimuonic decays of $D^{+}\to {\overline{K}}_1(1270{)}^0{\mu }^{+}{\nu }_{\mu }$ and $D^0\to K_1(1270{)}^{-}{\mu }^{+}{\nu }_{\mu }$ with statistical significances of $12.5\sigma$ and $6.0\sigma$, respectively. Their decay branching fractions are determined to be $\mathcal{B}[D^{+}\to {\overline{K}}_1(1270{)}^0{\mu }^{+}{\nu }_{\mu }]=(2.36\pm 0.20_{-0.27}^{+0.18}\pm 0.48)\times {10}^{-3}$ and $\mathcal{B}[D^0\to K_1(1270{)}^{-}{\mu }^{+}{\nu }_{\mu }]=(0.78\pm 0.11_{-0.09}^{+0.05}\pm 0.15)\times {10}^{-3}$, where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of ${\overline{K}}_1(1270{)}^0\to K^{-}{\pi }^{+}{\pi }^0$ or $K_1(1270{)}^{-}\to K^{-}{\pi }^{+}{\pi }^{-}$. Combining our branching fractions with the previous measurements of $\mathcal{B}[D^{+}\to {\overline{K}}_1(1270{)}^0{e}^{+}{\nu }_e]$ and $\mathcal{B}[D^0\to K_1(1270{)}^{-}{e}^{+}{\nu }_e]$, we determine the branching fraction ratios to be $\mathcal{B}[D^{+}\to {\overline{K}}_1(1270{)}^0{\mu }^{+}{\nu }_{\mu }]/\mathcal{B}[D^{+}\to {\overline{K}}_1(1270{)}^0{e}^{+}{\nu }_e]=1.03\pm {0.14}_{-0.15}^{+0.11}$ and $\mathcal{B}[D^0\to K_1(1270{)}^{-}{\mu }^{+}{\nu }_{\mu }]/\mathcal{B}[D^0\to K_1(1270{)}^{-}{e}^{+}{\nu }_e]=0.74\pm {0.13}_{-0.13}^{+0.08}$. Using the branching fractions measured in this work and the world-average lifetimes of the $D^{+}$ and $D^0$ mesons, we determine the semimuonic partial decay width ratio to be $\mathrm{\Gamma }[D^{+}\to {\overline{K}}_1(1270{)}^0{\mu }^{+}{\nu }_{\mu }]/\mathrm{\Gamma }[D^0\to K_1(1270{)}^{-}{\mu }^{+}{\nu }_{\mu }]=1.22\pm {0.10}_{-0.09}^{+0.06}$, which is consistent with unity as predicted by isospin conservation.

It is known that the scalar fields can be trapped on branes of different types, and the $U(1)$ gauge vector fields can be localized on the thick de Sitter brane, or the thick Minkowski brane via coupling with gravity. The Kalb-Ramond fields can be localized on the Minkowski brane and the thick de-Sitter brane, with certain couplings. In this paper, with considering a coupling mechanism between the kinetic term of the $q$-form fields and the background spacetime, we investigate the localization of Kaluza-Klein modes for the $q$-form fields in $D$-dimensional spacetime. Concrete $q$-form fields are discussed within five-dimensional brane models with typical spacetime geometries: Minkowski, de Sitter, and anti–de Sitter. In the Minkowski brane case, the zero modes of various $q$-form fields can be localized on the brane. In the de Sitter brane case, the zero mode of the $U(1)$ gauge vector fields can be localized on the brane. Lastly in the anti–de Sitter brane case, the zero mode of the Kalb-Ramond fields can be localized on the brane. For the massive Kaluza-Klein modes of these $q$-form fields, they could be localized or quasi-localized on the brane of different types. Besides, subtle and detailed behaviors of the Kaluza-Klein modes for $q$-form fields are observed: the zero modes could be localized on both sides of the brane, and the massive modes could be localized or quasilocalized at the brane position.

The measurement of spin precession and orbital eccentricity in gravitational-wave (GW) signals is a key priority in GW astronomy, as these effects not only provide unique insights into the astrophysical formation and evolution of compact binaries, but also, if neglected in waveform models, could introduce significant biases in parameter estimation, searches, and tests of general relativity. Despite the growing potential of upcoming LIGO-Virgo-KAGRA observing runs and future detectors to measure eccentric-precessing signals, accurately and efficiently modeling them remains a significant challenge. In this work, we present pyefpe, a frequency-domain post-Newtonian (PN) waveform model for the inspiral of precessing-eccentric compact binaries. pyefpe improves upon previous models by introducing analytical expressions for the Fourier mode amplitudes, enhancing the numerical stability of the multiple scale analysis framework, and adding recently derived PN corrections, critical to accurately describe signals in GW detectors. Additionally, we simplify the numerical implementation and introduce a scheme to interpolate the polarization amplitudes, achieving a speedup of up to $\sim \mathcal{O}(15)$ in the waveform computations, making the model practical for data analysis applications. We thoroughly validate pyefpe by comparing it to other waveform models in the quasicircular and eccentric-spin-aligned limits, finding good agreement. Additionally, we demonstrate pyefpe ’s capability to analyze simulated GW events, accurately recovering the parameters of signals described by both pyefpe and imrphenomxp. While pyefpe still lacks important physical effects, such as higher-order PN corrections, higher-order modes, mode asymmetries, tidal interactions, or the merger-ringdown phase, it represents a significant step toward more complete waveform models, offering a flexible and efficient framework that can be extended in future work to incorporate these effects.

Motivated by a recently discovered connection between the greybody factors of black holes and the ringdown signal, we investigate the greybody factors of ultracompact horizonless objects, also elucidating their connection to echoes. The greybody factor of ultracompact objects features both low-frequency resonances and high-frequency quasireflectionless scattering modes, which become purely reflectionless in the presence of symmetric cavity potentials, as might be the case for a wormhole. We show these high-frequency (quasi)reflectionless scattering modes, rather than low-frequency resonances, to be directly responsible for the echoes in the time-domain response of ultracompact objects or of black holes surrounded by matter fields localized at large distances.

As gravitational wave (GW) detector networks continue to improve in sensitivity, the demand on the accuracy of waveform models which predict the GW signals from compact binary coalescences is becoming more stringent. At high signal-to-noise ratios (SNRs) discrepancies between waveform models and the true solutions of Einstein’s equations can introduce significant systematic biases in parameter estimation (PE). These biases affect the inferred astrophysical properties, including matter effects, and can also lead to erroneous claims of deviations from general relativity, impacting the interpretation of astrophysical populations and cosmological parameters. While efforts to address these biases have focused on developing more precise models, we explore an alternative strategy to account for uncertainties in waveform models, particularly from calibrating an effective-one-body (EOB) model against numerical relativity (NR) data. We introduce an efficient method for modeling and marginalizing over waveform uncertainty in the SEOBNRv4 model, which captures the dominant (2, 2) mode for nonprecessing quasicircular binary black holes (BBHs). Our approach uses Gaussian process regression (GPR) to model amplitude and phase deviations in the Fourier domain. This method mitigates systematic biases in PE and increases posterior variance by incorporating a broader distribution of waveforms, consistent with previous findings. This study emphasizes the importance of incorporating waveform uncertainties in GW data analysis and presents a novel, practical framework to include these uncertainties in Bayesian PE for EOB models, with broad applicability.

Effective field theory methods allow us to modify general relativity through higher-curvature corrections to the Einstein-Hilbert action, while preserving Lorentz invariance and the number of gravitational degrees of freedom. We here construct an approximate inspiral-merger-ringdown waveform model within the cubic, parity-preserving class of effective-field-theory extensions to Einstein’s theory for the gravitational waves emitted by quasicircular binary black holes with aligned/antialigned spins. Using this waveform model, we first explore the detectability of non-Einsteinian effective-field-theory effects through an extended version of effective cycles to illustrate the need to include non-Einsteinian amplitude corrections. We then use this model to analyze the GW170608 event in a full Bayesian framework, and we place new improved and more robust constraints on the coupling constants of the effective field theory. Our Bayesian model selection study disfavors the non-Einsteinian theory with a (log) Bayes factor of $\log {\mathcal{B}}_{\mathrm{GR}}^{\mathrm{EFT}}=-2.81$. Our Bayesian parameter estimation study places the constraints ${\overline{\alpha }}_1=0.87_{-1.03}^{+1.95}$ and ${\overline{\alpha }}_2=-0.35_{-2.92}^{+4.12}$ at 90% confidence on the coupling parameters of the effective-field theory. These constraints are 3.5 stronger than previous constraints, informative relative to the prior, and independent of the choice of prior on the coupling parameters of the modified theory.

As the first step to explore the nonlinear dynamics of an extra dimension in the Kaluza-Klein (KK) spacetime with black objects through numerical relativity, we generate time-symmetric initial data of a black string and/or a KK bubble with space-dependent compactification radius. The initial data developed in this paper are classified into three types. First, we present analytic initial data with SO(3) symmetry whose three-dimensional section is spherically symmetric. These initial data include a black string without a KK bubble, a black string trapping a KK bubble, and a naked KK bubble. Second, we present analytic initial data for multiple black strings with varying compactification radius, which is a natural generalization of the Brill-Lindquist initial data for four-dimensional general relativity. Finally, we develop a numerical method for generating the initial data with a black string and a KK bubble located at different positions, which would be useful in simulating what happens when an expanding KK bubble meets black objects in dynamical context.

Detecting a compact subsolar object would have profound implications in physics, the reach of which depends on the nature of the object. Here, we explore such consequences for a putative subsolar-mass gravitational wave event detected by the LIGO-Virgo-KAGRA Collaboration. We forecast that the nature of a subsolar binary (made of light neutron stars, primordial black holes, or more exotic compact objects) can be inferred with a great statistical confidence level already during the ongoing fourth observing run, based on the large tidal deformability effects on the signal. The detection of a primordial black hole would have implications for cosmology and dark matter scenarios, while the measurement of the tidal deformability of a subsolar neutron star could rule out or confirm the existence of strange stars made of quarks.

Finding the best parametrization for cosmological models in the absence of first-principle theories is an open question. We propose a data-driven parametrization of cosmological models given by the disentangled “latent” representation of a variational autoencoder (VAE) trained to compress cosmic microwave background (CMB) temperature power spectra. We consider a broad range of $\mathrm{\Lambda }$-cold-dark-matter ($\lambda \mathrm{CDM}$) and beyond-$\mathrm{\Lambda }\mathrm{CDM}$ cosmologies with an additional early dark energy (EDE) component. We show that these spectra can be compressed into five ($\mathrm{\Lambda }\mathrm{CDM}$) or eight (EDE) independent latent parameters, as expected when using temperature power spectra alone, and which reconstruct spectra at an accuracy well within the Planck errors. These latent parameters have a physical interpretation in terms of well-known features of the CMB temperature spectrum: these include the position, height and even-odd modulation of the acoustic peaks, as well as the gravitational lensing effect. The VAE also discovers one latent parameter which entirely isolates the EDE effects from those related to $\mathrm{\Lambda }\mathrm{CDM}$ parameters, thus revealing a previously unknown degree of freedom in the CMB temperature power spectrum. We further showcase how to place constraints on the latent parameters using Planck data as typically done for cosmological parameters, obtaining latent values consistent with previous $\mathrm{\Lambda }\mathrm{CDM}$ and EDE cosmological constraints. Our work demonstrates the potential of a data-driven reformulation of current beyond-$\mathrm{\Lambda }\mathrm{CDM}$ phenomenological models into the independent degrees of freedom to which the data observables are sensitive.

Gravitational wave (GW) searches using pulsar timing arrays (PTAs) are commonly assumed to be limited to a GW frequency of $\lesssim 4\times {10}^{-7}\mathrm{Hz}$ given by the Nyquist rate associated with the average observational cadence of 2 weeks for a single pulsar. However, by taking advantage of asynchronous observations of multiple pulsars, a PTA can detect GW signals at higher frequencies. This allows a sufficiently large PTA to detect and characterize the ringdown signals emitted following the merger of supermassive binary black holes (SMBBHs), leading to stringent tests of the no-hair theorem in the mass range of such systems. Such large-scale PTAs are imminent with the advent of the FAST telescope and the upcoming era of the Square Kilometer Array (SKA). To scope out the data analysis challenges involved in such a search, we propose a likelihood-based method coupled with particle swarm optimization and apply it to a simulated large-scale PTA comprised of 100 pulsars, each having a timing residual noise standard deviation of 100 nsec, with randomized observation times. Focusing on the dominant (2, 2) mode of the ringdown signal, we show that it is possible to achieve a 99% detection probability with a false alarm probability below 0.2% for an optimal signal-to-noise ratio (SNR) $>10$. This corresponds, for example, to an equal-mass nonspinning SMBBH with an observer frame chirp mass $M_c=9.52\times {10}^9{M}_{\odot }$ at a luminosity distance of $D_L=420\mathrm{Mpc}$.

In this work, we show that, if axionlike particles (ALPs) from core-collapse supernovae (SNe) couple to protons, they would produce very characteristic signatures in neutrino water Cherenkov detectors through their scattering off free protons via $ap\to p\gamma$ interactions. Specifically, sub-MeV ALPs would generate photons with energies $\sim 30\mathrm{MeV}$, which could be observed by Super-Kamiokande and Hyper-Kamiokande as a delayed signal after a future detection of SN neutrinos. We apply this to a hypothetical neighboring SN (at a maximum distance of 100 kpc) and demonstrate that the region in the parameter space with ALP masses between ${10}^{-4}$ and 1 MeV and ALP-proton couplings in the range $3\times {10}^{-6}–4\times {10}^{-5}$ could be probed. We argue that this new signature, combined with the one expected at $\sim 7\mathrm{MeV}$ from oxygen deexcitation, would allow us to disentangle ALP-neutron and ALP-proton couplings.

Even in the absence of neutrino masses, a neutrino gas can exhibit a homogeneous flavor instability that leads to a periodic motion known as the fast flavor pendulum. A well-known necessary condition is a crossing of the angular flavor lepton distribution. In an earlier work, some of us showed that homogeneous flavor instabilities also obey a Nyquist criterion, inspired by plasma physics. This condition, while more restrictive than the angular crossing, is only sufficient if the unstable branch of the dispersion relation is bounded by critical points that both lie under the light cone (points with subluminal phase velocity). While the lepton-number angle distribution, assumed to be axially symmetric, easily allows one to determine the real-valued branch of the dispersion relation and to recognize if instead superluminal critical points exist, this graphical method does not translate into a simple instability condition. We discuss the homogeneous mode in the more general context of the dispersion relation for modes with arbitrary wave number and stress that it plays no special role on this continuum, except for its regular but fragile long-term behavior, owed to its many symmetries.

In quantum field theories, field redefinitions are often employed to remove redundant operators in the Lagrangian, making calculations simpler and physics more evident. This technique requires some care regarding, among other things, the choice of observables, the range of applicability, and the appearance and disappearance of solutions of the equations of motion (EOM). Many of these issues can already be studied at the classical level, which is the focus of this work. We highlight the importance of selecting appropriate observables and initial/boundary conditions to ensure the physical invariance of solutions. A classical analog to the Lehmann-Symanzik-Zimmermann (LSZ) formula is presented, confirming that some observables remain independent of field variables without tracking redefinitions. Additionally, we address, with an example, the limitations of noninvertible field redefinitions, particularly with nonperturbative objects like solitons, and discuss their implications for classical and quantum field theories.

The order of the chiral phase transition in two-color and two-flavor ${\mathrm{QC}}_2\mathrm{D}$ is investigated using the functional renormalization group (FRG) technique in an effective model setting. We calculate the $\beta$ function of all couplings in the dimensionally reduced Ginzburg-Landau free energy functional with Pauli-Gürsey SU(4) symmetry. We compare results of the perturbative $\epsilon$ expansion approach with those obtained via the FRG, evaluated directly in $d=3$ dimensions. The perturbative results suggest that the fixed-point structure is more intricate than that of three-color QCD, a conclusion further supported by the FRG analysis. Both methods display an infrared stable $O(6)$ fixed point at infinite axial anomaly; however, the FRG approach also reveals the existence of $U_A(1)$ anomaly-free fixed points, which can become infrared stable if the anomaly in the underlying theory vanishes at the critical temperature. These findings imply that the phase transition can be of second order, consistent with earlier findings for three colors.

The vortex state properties of a pair of scalar particles produced in a strong circularly polarized electromagnetic standing wave field are investigated under the dipole approximation in the multiphoton regime. We find that vortex orientation is related to the intrinsic orbital angular momentum of created particles associating with the helicity of absorbed photons, while the magnitude of the orbital angular momentum, i.e., the topology charge, is determined by the number of absorbed photons. Moreover, the properties of particle creation and vortices formation can be understood by analyzing the pair production process in quasiparticle representation. This study provides new insights into the angular momentum transfer from field to particle in the scalar pair production process in vacuum. It is expected that there are similar findings about vortex features for different spin alignment in electron-positron pair production in strong fields via the topology charge as a new freedom.

Spectroscopic parameters and decays of the exotic tensor meson $T$ with content $bc\overline{b}\overline{c}$ are explored in the context of the diquark-antidiquark model. We treat it as a state built of axial-vector diquark $b^{T}C{\gamma }_{\mu }c$ and antidiquark $\overline{b}{\gamma }_{\nu }C{\overline{c}}^T$, where $C$ is the charge conjugation matrix. The mass $m$ and current coupling $\mathrm{\Lambda }$ of this tetraquark are extracted from two-point sum rules. Our result for $m=(12.70\pm 0.09)\mathrm{GeV}$ proves that $T$ is unstable against strong dissociations to two-meson final states. Its dominant decay channels are processes $T\to J/\psi \mathrm{\Upsilon }$, ${\eta }_b{\eta }_c$, and $B_c^{(*)+}{B}_c^{(*)-}$. Kinematically allowed transformations of $T$ include also decays $T\to D^{(*)+}{D}^{(*)-}$ and $D^{(*)0}{\overline{D}}^{(*)0}$, which are generated by $b\overline{b}$ annihilation inside of $T$. The full width of $T$ is estimated by considering all of these channels. Their partial widths are calculated by invoking methods of three-point sum rule approach, which are required to evaluate strong couplings at corresponding tetraquark-meson-meson vertices. Our predictions for the mass and width ${\mathrm{\Gamma }}_T=(117.4\pm 15.9)\mathrm{MeV}$ of the tensor state $T$ provide useful information for experimental studies of fully heavy four-quark exotic structures.

We investigate nucleon tensor form factors in the large-$N_c$ limit. In this picture, the nucleon emerges as a state of the $N_c$ valence quarks, which were bound by pion mean fields that were created by the presence of the valence quarks self-consistently. We find that the tensor charge ($g_T^{u-d}=0.99$) and the anomalous tensor magnetic moment (${\kappa }_T^{u+d}=7.61$) are dominated by valence quarks, while the tensor quadrupole moment ($Q_T^{u-d}=-7.02$) shows significant sea quark effects. We examine how these quantities vary as the average size of the pion mean field is changed, showing interpolation between nonrelativistic quark and Skyrme limits. We also observe that $g_T^{u-d}$ and ${\kappa }_T^{u+d}$ depend weakly on the pion mass. In contrast, $Q_T^{u-d}$ exhibits strong enhancement near the chiral limit. The numerical results are in good agreement with available lattice quantum chromodynamics (QCD) data and provide predictions for unmeasured quantities.

We construct an effective chiral theory for the nucleon, based on the low-energy effect quantum chromodynamics (QCD) partition function from the QCD instanton vacuum. We fully consider the momentum-dependent dynamical quark mass whose value at the zero virtuality of the quark is determined by the gap equation from the instanton vacuum, $M_0=359\mathrm{MeV}$. The nucleon emerges as a state of $N_c$ valence quarks bound by the pion mean field, which was created self-consistently by the $N_c$ valence quarks. In the large Euclidean time, the classical nucleon mass is evaluated by minimizing the sum of the $N_c$ discrete-level energies and the Dirac-continuum energy: $M_{\mathrm{cl}}=1.2680\mathrm{GeV}$. The pion mean-field solution turns out broader than the local chiral quark-soliton model. The zero-mode quantization furnishes the nucleon with proper quantum numbers such as the spin and isospin. We compute the moment of inertia $I=1.3853\mathrm{fm}$ by using the self-consistent mean-field solution, which yields the $\mathrm{\Delta }-N$ mass splitting $M_{\mathrm{\Delta }-N}=213.67\mathrm{MeV}$. In the same manner, singly heavy baryons can be described as a bound state of the $N_c-1$ valence quarks with the corresponding pion mean field, with the heavy quark regarded as a static color source. The mass splitting of the singly heavy baryons is obtained to be $M_{{\mathrm{\Sigma }}_Q-{\mathrm{\Lambda }}_Q}=206.20\mathrm{MeV}$, which are in good agreement with the experimental data. The effective chiral theory developed in the present work will provide a solid theoretical framework to investigate gluonic observables of both the light and singly heavy baryons.

Using publicly available numerical relativity (NR) simulations for nonspinning eccentric binary black hole (BBH) mergers, [Tousif Islam, Straightforward mode hierarchy in eccentric binary black hole mergers and associated waveform model, arXiv:2403.15506.] demonstrated that the eccentricity-induced modulations in the amplitudes and frequencies of different spherical harmonic modes are mutually consistent and can be modeled using a single time series modulation. We extend the validity of the results to all nonprecessing binaries by using 83 NR simulations from the SXS, RIT, and MAYA catalogs for aligned-spin eccentric BBH mergers with mass ratios ranging from $1:1$ to $1:4$. Based on these phenomenological relations, we provide a framework named gwnrxhme to compute multimodal eccentric nonprecessing waveforms using two inputs: quadrupolar eccentric waveforms, and the corresponding multimodal quasicircular nonprecessing waveforms. Furthermore, we compute an overall degree of departure in SXS, RIT, and MAYA NR data from these relations and find that SXS NR simulations generally adhere to these relations more strictly than RIT and MAYA data. We also show that these relations can offer a cost-effective way to filter out noisy higher-order spherical harmonic modes extracted from NR data. Our framework is publicly available through the gwmodels package.