Binary neutron stars (BNSs) and neutron star–black hole (NSBH) binaries are two of the most promising gravitational wave (GW) sources to probe matter effects. Upcoming observing runs of LIGO-Virgo-KAGRA detectors and future third generation detectors like Einstein Telescope and Cosmic Explorer will allow the extraction of detailed information on these matter effects from the GW signature of BNS and NSBH systems. One subtle effect which may be helpful to extract more information from the detection of compact binary systems is the nonlinear memory. In this work, we investigate the observational consequences of gravitational wave nonlinear memory in the presence of matter effects. We start by quantifying the impact of nonlinear memory on distinguishing BNS mergers from binary black holes (BBHs) or NSBH mergers. We find that for the third generation detectors, the addition of nonlinear memory to the GW signal model expands the parameter space where BNS signals become distinguishable from the BBH and NSBH signals. Using numerical relativity simulations, we also study the nonlinear memory generated from the postmerger phase of BNS systems. We find that it does not show a strong dependence on the equation of state of the NS. However, the amplitude of nonlinear memory from the BNS postmerger phase is much lower than the one from BBH systems of the same masses. Furthermore, we compute the detection prospects of nonlinear memory from the postmerger phase of NS systems by accumulating signal strength from a population of BNS mergers for the current and future detectors. Finally, we discuss the impact of possible linear memory from the dynamical ejecta of BNS and NSBH systems and its signal strength relative to the nonlinear memory. We find that linear memory almost always has a much weaker effect than nonlinear memory.

Considering ten well-known relativistic mean field models, we invoke feeble interaction between hadronic matter and fermionic dark matter (DM) $\chi$ via new physics scalar ($\varphi$) and vector ($\xi$) mediators in neutron star core, thereby forming DM admixed neutron stars (DMANSs). The chosen masses of the DM fermion ($m_{\chi }$) and the mediators ($m_{\varphi }$ and $m_{\xi }$) are consistent with the self-interaction constraint from bullet cluster while their respective couplings ($y_{\varphi }$ and $y_{\xi }$) are also constrained by the present day relic abundance. Assuming that both $\varphi$ and $\xi$ contribute equally to the relic abundance, we compute the equation of state of the DMANSs and consequently their structural properties. We found that for a particular (constant) DM density, the presence of lighter DM results in more massive DMANSs with larger radius. In the light of the various recent constraints like those from the massive pulsar PSR $\mathrm{J}0740+6620$, the gravitational wave (GW170817) data and the results of NICER experiments for PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$, we provide a bound on $m_{\chi }$ within the framework of the present work as $m_{\chi }\approx (0.1-30)\mathrm{GeV}$ for a wide range of fixed DM Fermi momenta $k_F^{\chi }=(0.01-0.06)\mathrm{GeV}$. In the case of the hadronic models that yield larger radii corresponding to the low mass neutron stars in the no-DM scenario, interaction with comparatively heavier DM fermion is necessary in order to ensure that the DMANSs obtained with such models satisfy the radius constraints from both GW170817 and NICER data for PSR $\mathrm{J}0030+0451$.

Most gravitational wave (GW) events observed so far by the LIGO and Virgo detectors are consistent with mergers of binary black holes (BBHs) on quasicircular orbits. However, some events, such as GW190521, are also consistent with having nonzero orbital eccentricity at detection, which can indicate that the binary formed via dynamical interactions. Active GW search pipelines employing quasicircular waveform templates are inefficient for detecting eccentric mergers. Additionally, analysis of GW signals from eccentric BBH with waveform models neglecting eccentricity can lead to biases in the recovered parameters. Here, we explore the detectability and characterization of eccentric signals when searches and analyses rely on quasicircular waveform models. We find that for a reference eccentric population, the fraction of events having fitting factor (FF) $<0.95$ can be up to $\approx 2.2\%$ compared to $\approx 0.4\%$ for the baseline population. This results in the loss in signal recovery fraction for up to 6% for the region in parameter space with non-negligible eccentricity ($e_{10}>0.01$) and high mass ratio ($q>3$). We perform parameter estimation (PE) for nonspinning and aligned-spin eccentric injections of GWs from binaries of total mass $M=35M_{\odot }$, based on numerical relativity simulations and an effective one-body (EOB) based inspiral merger-ringdown model (teobresums), and recover them using both quasicircular and eccentric waveform models. For $e_{20}\sim 0.1$, analyses using quasicircular waveform models are unable to recover the injected chirp mass within the 90% credible interval. Further, for these low-mass injections, spin-induced precession does not mimic eccentricity, with PE correctly ruling out high values of effective precession parameter ${\chi }_p$. For injections of $e_{20}\sim 0.1$, PE conducted with an inspiral-only eccentric waveform model correctly characterizes the injected signal to within 90% confidence, and recovers the injected eccentricities, suggesting that such models are sufficient for characterization of low-mass eccentric BBH.

The decay or annihilation of dark matter particles may produce a steady flux of very-high-energy gamma rays detectable above the diffuse background. Nearby clusters of galaxies provide excellent targets to search for the signatures of particle dark matter interactions. In particular, the Virgo cluster spans several degrees across the sky and can be efficiently probed with a wide field-of-view instrument. The High Altitude Water Cherenkov (HAWC) observatory, due to its wide field of view and sensitivity to gamma rays at an energy scale of 300 GeV–100 TeV is well-suited for this search. Using 2141 days of data, we search for $\gamma$-ray emission from the Virgo cluster, assuming well-motivated dark matter substructure models. Our results provide some of the strongest constraints on the decay lifetime of dark matter for masses above 10 TeV.

Neutron star (NS) binaries can be potentially intriguing gravitational wave sources, with both high- and low-frequency radiation from the possibly aspherical individual stars and the binary orbit, respectively. The successful detection of such a dual-line source could provide fresh insights into binary geometry and NS physics. In the absence of electromagnetic observations, we develop a strategy for inferring the spin-orbit misalignment angle using the tight dual-line double NS system under the spin-orbit coupling. Based on the four-year joint detection of a typical dual-line system with the Laser Interferometer Space Antenna and Cosmic Explorer, we find that the misalignment angle and the NS moment of inertia can be measured with subpercentage and 5% accuracy, respectively.

We systematically study hidden charm pentaquark states in the constituent quark model with a general Hamiltonian for multiquark systems, considering the coupling between the ${\mathrm{\Sigma }}_c^{(*)}{\overline{D}}^{(*)}$ molecular states and the $q^{3}c\overline{c}$ compact pentaquark states by the one-gluon exchange hyperfine interaction. The ground state hidden-charm pentaquark mass spectra and the strong decay widths are calculated. This work suggests that $P_c(4312)$, $P_c(4457)$, and $P_c(4380)$ resonances might be mainly ${\mathrm{\Sigma }}_c\overline{D}$, ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$, and ${\mathrm{\Sigma }}_c^{*}\overline{D}$ hadronic molecules respectively, and $P_c(4440)$ might include sizable pentaquark components.

The Electron-Ion Collider in China (EicC) has been proposed to study the inner structure of matter and fundamental laws of strong interactions. In this paper, we will present a conceptual design of the tracking system based on the state-of-art silicon detector and micropattern gaseous detector at the EicC and demonstrate that it will enable us to reconstruct charm hadron with good significance, hence study gluonic parton distribution functions in nucleons and nuclei, as well as gluon helicity distributions. The impact study using reweighting techniques shows that the impact of the EicC will be mainly in the large $x$ region. It complements similar physics programs at the Electron-Ion Collider at Brookhaven National Laboratory.

We propose a method to calculate the $q\overline{q}$ light front wave functions (LFWFs) of photons at low virtuality, i.e., the light front amplitude of ${\gamma }^{*}\to q\overline{q}$ at low $Q^2$, based on a light front projection approach. We exemplify this method using a contact interaction model within Dyson-Schwinger equations formalism and obtain the nonperturbative photon $q\overline{q}$ LFWFs. In this case, we find the nonperturbative effects are encoded in the enhanced quark mass and a dressing function of covariant quark-photon vertex, as compared to the leading order quantum electrodynamics photon $q\overline{q}$ LFWFs. We then use nonperturbative-effect modified photon $q\overline{q}$ LFWFs to study the inclusive deep inelastic scattering HERA data in the framework of the color dipole model. The results demonstrate that the theoretical description of data at low $Q^2$ can be significantly improved once the nonperturbative corrections are included in the photon LFWFs.

We study the freeze-out parameters in a QCD-assisted effective theory that accurately captures the quantum and in-medium effects of QCD at low energies. The functional renormalization group approach is implemented in our work to incorporate the nonperturbative quantum, thermal, and density fluctuations. By analyzing the calculated baryon number susceptibility ratios ${\chi }_2^B/{\chi }_1^B$ and ${\chi }_3^B/{\chi }_2^B$, we determine the chemical freeze-out temperatures and baryon chemical potentials in cases of hard thermal or dense loop improved $\mu$-dependent gluon potential and $\mu$-independent gluon potential. We calculate the ${\chi }_4^B/{\chi }_2^B(\kappa {\sigma }^2)$ and ${\chi }_6^B/{\chi }_2^B$ along the freeze-out line for both cases. It is found that $\kappa {\sigma }^2$ exhibits a nonmonotonic behavior in a low collision energy region and approaches one for lower collision energy. ${\chi }_6^B/{\chi }_2^B$ shows a similar complicated behavior in our calculation.

We point out that an unnatural hierarchy between certain higher-dimensional operator coefficients in a low-energy effective field theory (EFT) would automatically imply that the Higgs’ vacuum expectation value is hierarchically smaller than the EFT cutoff, assuming the EFT emerged from a unitary, causal and local UV completion. Future colliders may have the sensitivity to infer such a pattern of coefficients for a little hierarchy with an EFT cutoff up to $\mathcal{O}(10)\mathrm{TeV}$.

We determine the adiabatic tidal contributions to the radiation reacted momentum impulse $\mathrm{\Delta }{p}_i^{\mu }$ and scattering angle $\theta$ between two scattered massive bodies (neutron stars) at next-to-next-to-leading post-Minkowskian order. The state-of-the-art three-loop (fourth post-Mikowskian order) worldline quantum field theory toolkit using dimensional regularization is employed to establish the classical observables. We encounter divergent terms in the gravitoelectric and gravitomagnetic quadrupolar sectors necessitating the addition of postadiabatic counterterms in this classical theory. This leads us to include also the leading postadiabatic tidal contributions to the observables. The resulting renormalization group flow of the associated postadiabatic Love numbers is established and shown to agree with a recent gravitoelectric third post-Newtonian analysis in the nonrelativistic limit.

We study spherical collapse of a scalar cloud in scalar-Gauss-Bonnet gravity—a theory in which black holes can develop scalar hair if they are in a certain mass range. We show that an additional quadratic coupling of the scalar field to the Ricci scalar can mitigate loss of hyperbolicity problems that have plagued previous numerical collapse studies and instead lead to well-posed evolution. This suggests that including specific additional interactions can be a successful strategy for tackling well-posedness problems in effective field theories of gravity with nonminimally coupled scalars. Our simulations also show that spherical collapse leads to black holes with scalar hair when their mass is below a mass threshold and above a minimum mass bound and that above the mass threshold, the collapse leads to black holes without hair, in line with results in the static case and perturbative analyses. For masses below the minimum mass bound, we find that the scalar cloud smoothly dissipates, leaving behind flat space.

We describe a novel search strategy for axions (or hadronically coupled axionlike particles) in the mass range of $m_a\lesssim 350\mathrm{MeV}$. The search relies on kaon decay at rest, which produces a monoenergetic signal in a large volume detector (e.g., a tank of liquid scintillator) from axion decays $a\to \gamma \gamma$ or $a\to e^{+}{e}^{-}$. The decay modes $K^{+}\to {\pi }^{+}a$ and $a\to \gamma \gamma$ are induced by the axion’s coupling to gluons, which is generic to any model which addresses the strong $CP$ problem. We recast a recent search from MicroBooNE for $e^{+}{e}^{-}$ pairs and study prospects at ${\mathrm{JSNS}}^2$ and other near-term facilities. We find that ${\mathrm{JSNS}}^2$ will have world-leading sensitivity to hadronically coupled axions in the mass range of $40\mathrm{MeV}\lesssim m_a\lesssim 350\mathrm{MeV}$.

Causality and stability are fundamental requirements for the differential equations describing predictable relativistic many-body systems. In this work, we investigate the stability and causality criteria in linear mode analysis. We discuss the updated stability criterion in $3+1$-dimensional systems and introduce the improved sufficient criterion for causality. Our findings clearly demonstrate that stability implies causality in linear mode analysis. Furthermore, based on the theorems present in this work, we conclude that if updated stability criterion and improved causality criterion are fulfilled in one inertial frame of reference (IFR), they hold for all IFR.

Parisi’s hypercube model describes a charged particle hopping on a $d$-dimensional hypercube with disordered background fluxes in the large $d$ limit. It was noted previously [Jia and Verbaarschot, J. High Energy Phys. 11 (2020) 154] that the hypercube model at leading order in $1/d$ has the same spectral density as the double-scaled Sachdev-Ye-Kitaev (DS-SYK) model. In this work we identify the set of observables that have the same correlation functions as the DS-SYK model, demonstrating that the hypercube model is an equally good microscopic model for $\mathrm{near}\text{−}{\mathrm{AdS}}_2/\mathrm{near}\text{−}{\mathrm{CFT}}_1$ holography. Unlike the SYK model, the hypercube model is not $p$-local. Rather, we note that the shared feature between the two models is that they both have a large amount of disordered but uniform fluxes on their Fock-space graphs, and we propose this is a broader characterization of $\mathrm{near}\text{−}{\mathrm{CFT}}_1$ microscopics. Moreover, we suggest that the hypercube model can be viewed as the operator growth model of the DS-SYK model. We explain some universality in subleading corrections and relate them to bulk vertices. Finally, we revise a claim made in the aforementioned reference about the existence of a spectral gap.

Analytic continuations of integer-valued parameters can lead to profound insights, such as angular momentum in Regge theory, the number of replicas in spin glasses, the number of internal degrees of freedom, the spacetime dimension in dimensional regularization, and Wilson’s renormalization group. In this work, we consider a new kind of analytic continuation of correlation functions, inspired by two recent approaches to underdetermined Dyson-Schwinger equations in $D$-dimensional spacetime. If the Green’s functions $G_n=⟨{\varphi }^n⟩$ admit analytic continuation to complex values of $n$, the two different approaches are unified by a novel principle for self-consistent problems: Singularities in the complex plane should be minimal. This principle manifests as the merging of different branches of Green’s functions in the quartic theories. For $D=0$, we obtain the closed-form solutions of the general $g{\varphi }^m$ theories, including the cases with complex coupling constant $g$ or noninteger power $m$. For $D=1$, we derive rapidly convergent results for the Hermitian quartic and non-Hermitian cubic theories by minimizing the complexity of the singularity at $n=\infty$.

We investigate the spherically symmetric gravitational collapse of a massless scalar field in the framework of a type-II minimally modified gravity theory called VCDM (where V replaces $\mathrm{\Lambda }$ in the $\mathrm{\Lambda }$CDM abbreviation). This theory propagates only two local physical degrees of freedom (DoF) supplemented by the so-called instantaneous (or shadowy) mode. Imposing asymptotically flat spacetime in the standard Minkowski time slicing, one can integrate out the instantaneous mode. Consequently, the equations of motion reduce to those in general relativity (GR) with the maximal slicing. Unlike GR, however, VCDM lacks 4D diffeomorphism invariance, and thus one cannot change the time slicing that is preferred by the theory. We then numerically evolve the system to see if and how a black hole forms. For small amplitudes of the initial scalar profile, we find that its collapse does not generate any black hole, singularity or breakdown of the time slicing. For sufficiently large amplitudes, however, the collapse does indeed result in the formation of an apparent horizon in a finite time. After that, the solution outside the horizon is described by a static configuration, i.e., the Schwarzschild geometry with a finite and time-independent lapse function. Inside the horizon, on the other hand, the numerical results indicate that the lapse function keeps decreasing toward zero so that the central singularity is never reached. This implies the necessity for a UV completion of the theory to describe physics inside the horizon. Still, we can conclude that VCDM is able to fully describe the entire time evolution of the Universe outside the black hole horizon without knowledge about such a UV completion.

Even if globally neutral, in various scenarios compact objects can have a nonvanishing dipole moment. Examples include neutron stars with magnetic dipoles, black-hole microstates in the string-theory fuzzball scenario, and classical black holes in modified theories of gravity with spin-induced scalarization or Lorentz-violating terms. A fundamental dipole moment would give rise to rich phenomenology, for example, to intrinsic precession and extra emission channels in binary systems. We show that extreme mass-ratio inspirals (EMRIs) detectable by future gravitational-wave interferometers allow us to study a fundamental dipole on the secondary object in a model-agnostic fashion. By developing a general model for a fundamental scalar dipole, we compute the extra flux associated with it. This effect is suppressed by the square of the mass ratio relative to the case of fundamental charges, making its detection with EMRIs very challenging for the typical dipole moments predicted in various models. On the other hand, for the same reason, the impact of an extra dipole for constraints on extra fundamental charges is likely negligible, making the latter constraints more robust.

LIGO-Aundha (A1), the Indian gravitational wave detector, is expected to join the International Gravitational-Wave Observatory Network (IGWN) and begin operations in the early 2030s. We study the impact of this additional detector on the accuracy of determining the direction of incoming transient signals from coalescing binary neutron star (BNS) sources with moderately high signal-to-noise ratios. It is conceivable that A1’s sensitivity, effective bandwidth, and duty cycle will improve incrementally through multiple detector commissioning rounds to achieve the desired ‘LIGO-A+’ design sensitivity. For this purpose, we examine A1 under two distinct noise power spectral densities. One mirrors the conditions during the fourth science run (O4) of the LIGO Hanford and Livingston detectors, simulating an early commissioning stage, while the other represents the $\mathrm{A}+\text{design sensitivity}$. We consider various duty cycles of A1 at the sensitivities mentioned above for a comprehensive analysis. We show that even at the O4 sensitivity with a modest 20% duty cycle, A1’s addition to the IGWN leads to a 15% reduction in median sky-localization errors ($\mathrm{\Delta }{\mathrm{\Omega }}_{90\%}$) to 5.6 sq. deg. At its design sensitivity and 80% duty cycle, this error shrinks further to 2.4 sq. deg, with 84% sources localized within a nominal error box of 10 sq. deg. This remarkable level of accuracy in pinpointing sources will have a positive impact on Gravitational Wave (GW) astronomy and cosmology. Even in the worst-case scenario, where signals are subthreshold in A1, we demonstrate its critical role in reducing the localization uncertainties of the BNS source. Our results are obtained from a large Bayesian parameter estimation study using simulated signals injected in a heterogeneous network of detectors using the recently developed meshfree approximation aided rapid Bayesian inference pipeline. We consider a seismic cut-off frequency of 10 Hz for all the detectors. We also present hypothetical improvements in sky localization for a few Gravitational-Wave Transient Catalog-like events injected in real data after including a hypothetical A1 detector to the subnetwork in which such events were originally detected. We also demonstrate that A1’s inclusion could resolve the degeneracy between the luminosity distance and inclination angle parameters, even in scenarios where A1 does not directly contribute to improving the network signal-to-noise ratio for the event.

The formalism of hypersurface data is a framework to study hypersurfaces of any causal character abstractly (i.e., without the need of viewing them as embedded in an ambient space). In this paper we exploit this formalism to study the problem of matching two spacetimes in a fully abstract manner, as this turns out to be advantageous over other approaches in several respects. We then concentrate on the case when the boundaries are null and prove that the whole matching is determined by a diffeomorphism $\phi$ on the abstract dataset. By exploiting the gauge structure of the formalism we find explicit expressions for the gravitational/matter-energy content of any null thin shell. The results hold for arbitrary topology. A particular case of interest is when more than one matching is allowed. Assuming that one of the matchings has already been solved, we provide explicit expressions for the gravitational/matter-energy content of any other shell in terms of the known one. This situation covers, in particular, all cut-and-paste constructions, where one can simply take as known matching the trivial reattachment of the two regions. We include, as an example, the most general matching of two regions of the (anti-)de Sitter or Minkowski spacetime across a totally geodesic null hypersurface.