We present a Bayesian framework that enhances the identification of strongly lensed gravitational waves (GWs) by incorporating an astrophysically informed spatial constraint from the Euclid galaxy lens catalog. The core of our method is a two-step positional weighting scheme: first, GW parameter estimation is performed under a uniform sky prior to obtain the GW sky localization posterior; this posterior then reweights Euclid candidate lens galaxies, yielding an astrophysically informed multimessenger spatial constraint. This constraint refines a second round of GW parameter estimation by adjusting only lens position plausibility (not intrinsic GW parameters) and isolates lens-consistent contributions in lensing Bayes factor calculation. Comparing this Euclid-constrained spatial constraint against a uniform sky constraint within our framework reveals distinct behaviors. While the posterior estimates of the intrinsic waveform parameters show little sensitivity to this constraint change, the Bayes factor for lensing identification exhibits significant dependence on the spatial constraint. Crucially, for truly lensed event pairs, the Bayes factor systematically increases, whereas for unlensed pairs it decreases. This dual effect is vital for robust discrimination. Our analysis demonstrates that this multimessenger approach significantly improves the confidence of lensing searches. For lensed pairs, the method boosts the Bayes factor by an average factor of $\sim 10$, while effectively suppressing false positives for unlensed coincidences. This underscores the critical importance of spatial constraint specification and showcases the substantial gains achievable by synergizing gravitational-wave data with electromagnetic survey information.

While no gravitational-wave detection of subsolar mass black holes has been confirmed to date, a number of candidate detections invite us to speculate on the origin of such black holes should a detection be confirmed. It is generally assumed that the observation of a black hole with subsolar mass $M_{\mathrm{obs}}$ would provide strong evidence for primordial black holes (PBHs). The mass $M_{\mathrm{PBH}}$ of the PBH, however, does not necessarily have to be equal to $M_{\mathrm{obs}}$, as it would in what we term a “direct PBH scenario.” Instead, a black hole of mass $M_{\mathrm{obs}}$ may form in a capture of a much smaller primordial black hole, $M_{\mathrm{PBH}}\ll M_{\mathrm{obs}}$, by a dwarf star of mass $M_{*}\simeq M_{\mathrm{obs}}$, followed by the total consumption of the star by the PBH. We provide some rough estimates and demonstrate that such an “indirect PBH scenario” may also lead to significant populations of black holes with mass $M_{\mathrm{obs}}$, especially in dwarf galaxies, and may be able to explain rare subsolar mass events.

The discovery of massive, high redshift galaxies with the James Webb Space Telescope (JWST) has been argued to challenge $\mathrm{\Lambda }\mathrm{CDM}$ (cold dark matter): such systems would require extremely rare halos and baryon-to-stellar-mass conversion efficiencies unphysically approaching—or exceeding—100%. If confirmed at galaxy-formation–forbidden efficiencies, these galaxies could signal new physics beyond standard cosmological structure formation. We develop a galaxy model framework that ties the linear power spectrum to the inferred efficiencies of galaxy growth while incorporating multiple sources of uncertainties in order to test the structure formation models. The sources of error include (i) observational sample variance, (ii) asymmetric scatter induced by the steepness of the high-mass halo tail, and (iii) systematic uncertainties in stellar mass estimates. We find that the inferred star-formation efficiency is largely controlled by systematic uncertainties in the stellar mass estimates derived from spectral energy distribution modeling of JWST-detected galaxies. Because of the inherent Eddington-like bias, systematic uncertainties amplify the asymmetry of the scatter, in some cases by orders of magnitude, thereby bringing the inferred efficiencies into closer agreement with expectations from early galaxy formation models. We also present how these uncertainties can be can be applied to the inferred UV luminosity function. Our framework can be used to test $\mathrm{\Lambda }\mathrm{CDM}$ as errors are reduced and further detections are made.

Comparing population-synthesis models to the results of hierarchical Bayesian inference in gravitational-wave astronomy requires a careful understanding of the domain of validity of the models fitted to data. This comparison is usually done using the inferred astrophysical distribution: from the data that were collected, one deconvolves selection effects to reconstruct the generating population distribution. In this paper, we demonstrate the benefits of instead comparing observable populations directly. In this approach, the domain of validity of the models is trivially respected, such that only the relevant parameter space regions as predicted by the astrophysical models of interest contribute to the comparison. With this in mind, it can be useful to fit the observed population directly, rather than effectively deconvolving the selection effects only to fold them back in when reconstructing the observable population. We clarify that unbiased inference of the observable compact-binary population is indeed possible. Crucially, this approach still requires incorporating selection effects, but in a manner that differs from the standard implementation. We apply our observable-space reconstruction to LIGO-Virgo-KAGRA data from their third observing run and illustrate its potential by comparing the results to the predictions of a fiducial population-synthesis model.

We have studied how the thermoelectric properties of the quark-gluon plasma (QGP) are affected by a weak-momentum anisotropy arising from the asymptotic expansion of matter in the initial stages of ultrarelativistic heavy-ion collisions. The highly energetic medium produced in such collisions exhibits a notable temperature difference between its central and peripheral regions. This temperature gradient induces an electric field whose magnitude per unit temperature gradient, in the limit of vanishing electric current, defines the Seebeck coefficient of the medium. We have calculated the Seebeck coefficients for both individual quark flavors and the entire QGP medium in the presence of expansion-induced anisotropy by solving the relativistic Boltzmann transport equation in the relaxation time approximation within the kinetic theory framework. The partonic interactions are incorporated through their effective thermal masses within the quasiparticle model for an anisotropic QGP medium. We have observed that the magnitude of the Seebeck coefficient for each quark flavor as well as for the entire QGP medium increases in the presence of expansion-induced anisotropy, indicating a stronger induced electric field in the anisotropic medium compared to the isotropic case. Given that an increase in the Seebeck coefficient may lead to observable signatures such as charge asymmetries in particle distributions and to modifications in the transport behavior of the QGP, these results may provide useful input for future phenomenological studies investigating the internal structure and phase properties of the QGP in heavy-ion collisions.

We discuss physics-informed renormalization group flows (PIRGs) for general operators. We show that operator PIRGs provide comprehensive access to all correlation functions of the quantum field theory under investigation. The operator PIRGs can be seen as a completion of the PIRG approach, whose qualitative computational simplification and structural insights are now fully accessible for general applications. The potential of this setup is assessed within a simple analytic example of the zero-dimensional ${\varphi }^4$-theory, for which the generating functions of the fundamental field are computed within a vertex expansion, using the one- to ten-point functions.

Neutral triple gauge couplings (nTGCs) first arise from the dimension-8 operators of the Standard Model effective field theory (SMEFT), rather than the dimension-4 SM Lagrangian and dimension-6 SMEFT operators, opening up a unique window for probing new physics at the dimension-8 level. In this work, we formulate the nTGC form factors of $ZZ{V}^{*}$ ($V=Z$, $\gamma$) that are compatible with the spontaneous breaking of the $\mathrm{SU}(2)\otimes \mathrm{U}(1)$ electroweak gauge symmetry and consistently match the dimension-8 nTGC operators in the broken phase. We study the sensitivities for probing both the $ZZ{V}^{*}$ form factors and the corresponding new physics scales through $ZZ$ production (with visible/invisible fermionic $Z$ decays) at high energy $e^{+}{e}^{-}$ colliders including CEPC, FCC-ee, LCF, ILC, and CLIC. In particular, we identify the dimension-8 operator that contributes to the pure triple $Z$ boson coupling $ZZ{Z}^{*}$ alone, but not the mixed $ZZ{\gamma }^{*}$ coupling. We further study the correlations between probes of the $ZZ{Z}^{*}$ and $ZZ{\gamma }^{*}$ couplings. Using machine learning, we show that angular distributions of the final-state fermions can play key roles in suppressing the SM backgrounds. The sensitivities can be further improved by using polarized $e^{\mp }$ beams, and we find that the optimal sensitivity bounds on the nTGC correlations are given by the mixed setting including both the unpolarized operation and the follow-up polarized operation. We demonstrate that machine learning is advantageous for handling the 4-body final states from $ZZ$ decays and improves significantly the sensitivity reaches of probes of nTGCs in $e^{+}{e}^{-}$ collisions. We find that nTGC new physics scales can be probed up to the multi-TeV scale at the proposed $e^{+}{e}^{-}$ colliders.

Lepton number violating meson decays, such as $M_1^{-}\to M_2^{+}{\ell }_1^{-}{\ell }_2^{-}$, provide constraints on $d=9$ $\mathrm{\Delta }L=2$ operators. Renormalization group equation (RGE)-improved bounds on the Wilson coefficients of these operators have been presented in the literature, taking into account perturbative quantum chromodynamics (QCD) one-loop corrections and the corresponding operator mixing. Here, we present for the first time the contribution of connected diagrams to the hadronic matrix elements $⟨M_2|{\mathcal{O}}_h|M_1⟩$. These diagrams, usually overlooked under the assumption that $⟨M_2|{\mathcal{O}}_h|M_1⟩\sim ⟨M_2|J_{q_3{q}_4}|0⟩\times ⟨0|J_{q_1{q}_2}|M_1⟩\gg ⟨M_2|J_{q_3{q}_2}\times J_{q_1{q}_4}|M_1⟩$, can give indeed a significant contribution to the matrix element. Including these connected diagrams is but the first step toward a full nonperturbative computation of the long-range QCD effects in these operators, that should be performed using lattice field theory techniques. However, connected diagrams represent the leading order in the $1/N_c$ expansion of the QCD nonperturbative effects and thus our work can be understood as a realistic, first approximation to a complete calculation of the long-range part of the matrix elements.

We investigate the temperature dependence of the shear viscosity ($\eta$) and bulk viscosity ($\zeta$) of the gluon plasma using lattice QCD over the range $0.76-2.25T_c$, extending from below the transition temperature $T_c$ across the transition region and into the deconfined phase. At each temperature, we employ three large, fine lattices, which enables controlled continuum extrapolations of the energy-momentum tensor correlators. Using gradient flow together with a recently developed blocking technique, we achieve percent-level precision for these correlators, providing strong constraints for a model-based spectral analysis. Since the inversion to real-time information is intrinsically ill posed, we extract viscosities by fitting spectral functions whose ultraviolet behavior is matched to the best available perturbative result, while the infrared region is described by a Lorentzian transport peak. The dominant modeling uncertainty associated with the transport peak width is bracketed by varying it over a physically motivated range set by thermal scales. We find that the shear-viscosity-to-entropy-density ratio, $\eta /s$, exhibits a minimum near the transition temperature $T_c$ and increases for $T>T_c$, whereas the bulk-viscosity-to-entropy-density ratio, $\zeta /s$, decreases monotonically over the entire temperature range studied.

We report on the existence of a hydrodynamic attractor in the Mueller-Israel-Stewart framework of a fluid living in the novel geometry discovered recently by Grozdanov [arXiv:2510.10769]. This geometry, corresponding to a hyperbolic slicing of ${\text{dS}}_3\times \mathbb{R}$, complements previous analyses of attractors in Bjorken (flat slicing) and Gubser (spherical slicing) flows. The fluid behaves like a sharply localized droplet propagating rapidly along the light cone. Typical solutions approach the hydrodynamic attractor rapidly at late times despite a Knudsen number exceeding unity, suggesting that the inverse Reynolds number captures hydrodynamization more faithfully since the shear stress vanishes at late times. This is in stark contrast to Gubser flow, which has both the Knudsen and inverse Reynolds number becoming small for intermediate times. We close with a comparison to Weyl-transformed Bjorken flow and discuss possible phenomenological applications.

We develop a new technique and calculate conformal (Gegenbauer) moments of the two-loop coefficient functions in deeply virtual Compton scattering. These results are necessary for the extraction of the generalized parton distributions from the experimental data to the next-to-next-to leading order accuracy within the Mellin-Barnes approach.

The gravity-mediated entanglement experiments employ concepts from quantum information to argue that if entanglement due to gravitational interaction is observed, then gravity cannot be described by a classical system. However, the proposed experiments remain beyond our current technological capability, with optimistic projections placing the experiment outside of the short-term future. Here we argue that current matter-wave interferometers are sufficient to indirectly prove that gravitational interaction creates entanglement between two systems. Specifically, we prove that if we experimentally verify the Schrödinger equation for a single delocalized system interacting gravitationally with an external mass, then, under one of two reasonable assumptions, the time evolution of two delocalized systems will lead to gravity-mediated entanglement.

Adiabatic vacua play a central role in quantum fields in cosmological spacetimes, where they serve as distinguished initial conditions and as reference states for the renormalization of observables. In this paper, we introduce new methods based on linear complex structures, which provide a powerful tool for determining adiabatic vacua. The new methods generalize both the standard WKB approach and the Lewis-Riesenfeld invariants, and allow us to study the problem of many coupled bosonic degrees of freedom with a general quadratic time-dependent Hamiltonian. We show that the adiabatic number operator and the adiabatic vacuum of finite order can be expressed in terms of the adiabatic complex structure of the same order. We compare our results with standard techniques, which apply only to a single degree of freedom, and comment on their applicability to problems in quantum fields in cosmological spacetimes, many-body systems, and quantum thermodynamics, where the Hamiltonian is time dependent with slowly changing parameters.

We provide a framework and explicit construction for the regularized measurement of a large class of spacetime-localized observables in bosonic quantum field theory. The measurements fully satisfy relativistic causality and causal transparency, i.e., avoid unphysical superluminal signaling. We show explicitly how the measurement of time-extended observables backreacts on itself and induces correlations between other measurements in its causal future. Our framework is fully compositional in spacetime and extends previous results on the measurement of instantaneous observables.

We investigate the phenomenon of mass inflation in the interior of regular black holes arising in quasitopological gravity. These geometries are characterized by a bounded curvature core and the presence of an inner (Cauchy) horizon located near the fundamental scale $\ell$. To examine whether mass inflation persists in this setting, we model the interaction of ingoing and outgoing perturbations by considering the collision of two spherical null shells inside the black hole. Using the Dray–’t Hooft–Barrabes–Israel junction condition, we derive conditions under which the metric function and curvature invariants may experience significant amplification near the inner horizon. Our analysis shows that, unlike in classical Reissner-Nordström or Kerr geometries, significant mass inflation requires shell intersection at radii very close to the horizon, with radial separations from it of the order $r-r_{*}\lesssim \ell (\ell /r_{\mathrm{g}}{)}^{2n(D-3)}$, where $r_{\mathrm{g}}$ is the gravitational radius of the black hole, $D$ is the number of spacetime dimensions, and $n\ge 1$ is a parameter depending on a concrete quasitopological gravity model. For macroscopic black holes with $r_{\mathrm{g}}\gg \ell$, this distance is much smaller than the fundamental scale $\ell$. We discuss possible consequences of this effect.

We calculate the high-frequency limit of the Halilsoy and Chandrasekhar standing gravitational wave solutions. We show that the backreaction effect is the same for these classes of solutions and we analyze the causal structure of the effective spacetime. In addition, we rederive both classes of solutions without referring to the Ernst equation and generation techniques.

To date, many exotic predictions of Einstein’s equations have been corroborated, with one exception: wormholes (WHs). In this work, we analyze a new exact solution combination to the Einstein-Maxwell-dilaton or phantom equations, which represent rotating WHs with magnetic and electric fields. The solution contains a ring singularity that, like other solutions, satisfies wormhole cosmic censorship; that is, the singularity is causally disconnected by the WH throat. We show that this WH is traversable through regions close to the poles, where the tidal forces and magnetic field are reasonably small. We satisfy the energy conditions for the dilatonlike solution. We argue that if dilatonlike interactions can exist in nature, for example, if extra dimensions exist as in superstring theory, WHs are a natural realistic prediction of Einstein’s equations, and we should be able to observe them somehow, probably as black hole mimics. We present several examples of realistic WHs that may occur in nature, and we also introduce a new exact black hole solution.

We revisit an inflationary scenario in which primordial inhomogeneities arise from a quantum collapse, a stochastic mechanism described in the context of quantum collapse theories in its continuous version and within semiclassical gravity. The predictions of the model in Cañate, Pearle, and Sudarsky [Phys. Rev. D 87, 104024 (2013).] and Lechuga and Sudarsky [J. Cosmol. Astropart. Phys. 01 (2024) 038.] show a nonconventional scalar spectrum governed by two new parameters in the collapse rate, whose aim is twofold: on one side, to account for the primordial cosmic structure, and on the other to explain the suppression amplitude associated with long-wavelength modes, thereby eliminating the occurrence of eternal inflation. Furthermore, this model can contribute to accounting for the lack of power anomaly in the low $l$ angular power spectra of the cosmic microwave background. Using the latest data from the Planck (2018) Collaboration, we establish observational constraints on the model parameters, which produce a characteristic low-$\ell$ suppression in the cosmic microwave background spectrum. We conclude that the Planck data support the solution presented in Lechuga and Sudarsky [J. Cosmol. Astropart. Phys. 01 (2024) 038.], in other words, that the model allows us to solve simultaneously the emergence of the cosmic structure and, at the same time, avoid the eternal inflation scenario.

Binary neutron star merger (BNSM) ejecta are considered a primary repository of $r$-process nucleosynthesis and a source of the observed heavy-element abundances. We implement composition mixing into ray-by-ray radiation-hydrodynamic simulations of BNSM ejecta, coupled with an online nuclear network (NN). We model mixing via a gradient-based mixing approximation that evolves simultaneously with the hydrodynamics. We find that mixing occurs in regions where the electron fraction changes rapidly. While mixing smooths composition gradients in transition regions, it has a negligible impact on the heavy-element yields. This is because the primary $r$-process site (the equatorial ejecta) is initially homogeneous in free neutrons, leaving no strong gradients for mixing to act upon. In each angular ray, the abundances of the most produced elements are robust under mixing, while the less abundant ones are more affected. The total global abundances change only slightly from mixing, since each angular ray contributes its most abundant elements. Furthermore, the predicted kilonova light curves show only minor reddening, with differences below the detectability of state-of-the-art telescopes. In general, we do not observe significant effects from mixing in the time span of the $r$-process. Consequently, mixing only leads to minor variations in abundances and light curves in ray-by-ray simulations.

We explore the prospects of probing the complex singlet extension of the Standard Model (CxSM) with gravitational waves from the electroweak phase transition. The study establishes a connection of the scalar potential parameters, the thermodynamic properties of the phase transition, with the directly measured stochastic gravitational-wave background in the presence of astrophysical background and foreground. Considering the space-based gravitational-wave detector Taiji, we construct a frequency-domain likelihood that incorporates instrumental and astrophysical noises, and we perform both Fisher-matrix forecasts and Bayesian nested sampling analysis. The comparison of these two approaches demonstrates consistent parameter recovery and highlights the sensitivity of Taiji to millihertz gravitational-wave signals. We further propagate the inferred constraints on the gravitational-wave spectrum back to the underlying CxSM parameters, obtaining meaningful limits on the Higgs self-couplings. The results emphasize the complementarity between gravitational-wave observations and collider measurements, showing that future missions such as Taiji can serve as a powerful probe of electroweak-scale new physics and the dynamical origin of the Higgs sector.