The proposed Large Hadron electron Collider (LHeC), with a center-of-mass energy of $\sqrt{s}\approx 1.3\mathrm{TeV}$, provides a clean and sensitive environment to probe the top quark’s neutral current interactions with the $Z$ boson via $e^{-}p\to e^{-}t\overline{t}$. We investigate the precision with which the Standard Model (SM) $t\overline{t}Z$ couplings—the vector and axial-vector components ($\mathrm{\Delta }{C}_{1V},\mathrm{\Delta }{C}_{1A}$) can be measured, along with possible new physics effects parametrized by higher-dimensional operators inducing weak electric and magnetic dipolelike interactions ($C_{2V},C_{2A}$). Focusing on the semileptonic decay channel, where either the top quark decays leptonically to a positively charged lepton (${\ell }^{+}=e^{+},{\mu }^{+}$) and the antitop hadronically, or vice versa, we utilize the azimuthal angle difference $\mathrm{\Delta }{\varphi }_{e^{-}{\ell }^{\pm }}$ between the scattered electron and the charged lepton ${\ell }^{\pm }$ as the key observable to derive projected constraints. Using a one-parameter multibin ${\chi }^2$ analysis of the differential $\mathrm{\Delta }{\varphi }_{e^{-}{\ell }^{\pm }}$ distribution, the constraints on $\mathrm{\Delta }{C}_{1A}$ improve from $\mathcal{O}({10}^{-1})$ at $50{\mathrm{fb}}^{-1}$ to $\mathcal{O}({10}^{-2})$ at $1000{\mathrm{fb}}^{-1}$, while the improvement for $\mathrm{\Delta }{C}_{1V}$ remains within the same order of magnitude, $\mathcal{O}({10}^{-1})$. These results correspond to average relative precisions of approximately 8% and 68%, respectively, with respect to their SM values. The anomalous tensor couplings $C_{2V}$ and $C_{2A}$ are constrained at the $\mathcal{O}({10}^{-1})$ level even at low luminosity and improve moderately with increasing luminosity. While the two-parameter analysis broadens the allowed regions due to parameter correlations, it maintains competitive sensitivity, particularly for the SM-like couplings. Throughout, we assume a systematic uncertainty of ${\delta }_s=5\%$ in all analyses, and all results are quoted at the 95% confidence level. These results demonstrate the LHeC’s potential to provide complementary and competitive sensitivity to top-$Z$ couplings compared to current and future hadron and lepton collider capabilities.

We present a novel procedure for analyzing the lattice QCD spectrum via the finite-volume formalism to obtain constraints on multihadron scattering amplitudes at both real and complex energies. This approach combines a Bayesian reconstruction of the scattering amplitude on the real axis with Nevanlinna interpolation for analytic continuation to complex-valued energies. The method is nonparametric, inherently accounting for parametrization dependence within the uncertainty. We demonstrate the applicability of this approach using both toy data and real lattice QCD data in resonant systems from the Hadron Spectrum and the Baryon Scattering collaborations.

Karsten-Wilczek (KW) fermions are a popular variant of minimally doubled fermions. We construct Symanzik effective action for KW fermions, which is known to break the hypercubic symmetry of the lattice action. In this work we make the two fermionic modes, called tastes, explicit using the point-splitting proposal of Creutz and Misumi and write the KW action in terms of the taste fields We identify the symmetries of the point-split action and write down the Symanzik effective action up to dimension-5, including the divergent dimension-3, operators for both free and interacting KW fermions.

We present the first numerical relativity simulations of the gravitational scattering of two neutron stars. Constraint-satisfying initial data for two equal-mass nonspinning sequences are constructed at fixed energy and various initial angular momenta (impact parameter) and evolved with Einstein equations through the scattering process. The strong-field scattering dynamics are explored up to scattering angles of 220° and the threshold of dynamical captures. The transition to bound orbits is aided by significant mass ejecta up to baryon mass $\sim 0.1M_{\odot }$. A quantitative comparison with predictions of the scattering angle from state-of-the-art effective-one-body and post-Minkowskian calculations indicates quantitative agreement for large initial angular momenta, although significant discrepancies in the tidal contribution emerge toward the capture threshold. Gravitational waveforms and radiated energy are in qualitative agreement with the analogous black hole problem and state-of-the-art effective-one-body predictions. Toward the capture threshold, waveforms from scattering dynamics carry a strong imprint of matter effects, including the stars’ $f$-mode excitations during the close encounter. Overall, our simulations open a new avenue to study tidal interactions in the relativistic two-body problem.

We develop a systematic method for analyzing the causal structure at vertices in ($2+1$)-dimensional Lorentzian simplicial gravity. By examining the intersection patterns of light ones emanating from a vertex with its simplicial neighborhood, we identify 13 distinct causal types of Lorentzian tetrahedra—excluding configurations with null faces. This classification forms the basis for a topological characterization of the local causal structure in terms of the number of connected regions on the triangulated 2-sphere that are spacelike and timelike separated from a bulk vertex. These local causal data allow us to identify regular causal configurations and new types of irregular causal configurations, generalizing well-known ($1+1$)-dimensional topologies, such as “Trousers” and “Yarmulkes,” to higher dimensions. We further investigate the dynamical implications of vertex causality by analyzing the behavior of deficit angles and the Regge action in explicit configurations. Transitions in “vertex causality” coincide with discontinuities in the curvature, suggesting discrete topology change. Causally irregular hinges correspond to discrete conical singularities, while vertex causal irregularities manifest as pointlike singularities. Interestingly, we find that vertex and hinge causality are generally independent. These results have direct implications for discrete quantum gravity approaches where the emergence of semiclassical spacetime depends on how causal structures are encoded within the triangulation.

We elaborate on the nonlinear realization approach to spontaneously broken supergravity in three dimensions presented by Kuzenko and Stirling [Proc. R. Soc. A 479, 20230350 (2023)]. Using this approach, we provide a novel derivation of $\mathcal{N}$-extended supergravity, with and without a cosmological term. It corresponds to a Stückelberg-type extension of the following theories: (i) the $(p,q)$ anti–de Sitter (AdS) supergravity theories with $p+q=\mathcal{N}$, $p\ge q\ge 0$ proposed by Achúcarro and Townsend and (ii) the $\mathcal{N}$-extended Poincaré supergravity of Marcus and Schwarz. We also apply the approach to obtain a Stückelberg reformulation of the supersymmetric Lorentz Chern-Simons action for arbitrary $\mathcal{N}$. In our construction, the pure supergravity actions (Poincaré and AdS) share the invariance under two different local $\mathcal{N}$-extended supersymmetries. One of them acts on the Goldstini, while the other supersymmetry leaves the Goldstini inert. The $\mathcal{N}$-extended supersymmetric Lorentz Chern-Simons action proposed in our setting shares the former supersymmetry, but differs in the one that leaves the Goldstini inert. The supersymmetry that acts on the Goldstini can be used to gauge them away, and then the resulting actions coincide with that given in the literature.

The phenomenon of particle production for quantum field theories in curved spacetimes is crucial to understand the large-scale structure of the universe from an inflationary epoch. In contrast to the free and fixed-background case, the production of particles with strong interactions and backreaction is not completely understood, especially in situations that require going beyond perturbation theory. In this work, we present advances in this direction by focusing on a self-interacting field theory of Dirac fermions in an expanding Friedmann-Robertson-Walker universe. By using a Hamiltonian lattice regularization with continuous conformal time and rescaled fields, this model becomes amenable to either a cold-atom analog-gravity quantum simulation, or a dynamical variational approach. Leveraging a family of variational fermionic Gaussian states, we investigate how dynamical mass generation and the formation of fermion condensates associated to certain broken symmetries modify some well-known results of the free field theory. In particular, we study how the nonperturbative condensates arise and, more importantly, how their real-time evolution has an impact on particle production. Depending on the Hubble expansion rate, we find an interesting interplay of interactions and particle production, including a nontrivial backreaction on the condensates and a parity-breaking spectrum of produced particles.

We study large-$N_c$ scalar ${\mathrm{QCD}}_2$, a $1+1$-dimensional confining gauge theory with fundamental scalar quarks, whose meson spectrum is governed by a Bethe-Salpeter equation structurally parallel to the ’t Hooft equation. Exploiting this structural analogy, we develop a nonperturbative analytic framework, based on integrability and inspired by the Fateev-Lukyanov-Zamolodchikov (FLZ) method, originally devised for the ’t Hooft model and later extended in our previous works. Notably, the same Bethe-Salpeter equation also arises in the description of interchain mesons in the doubled Ising model coupled via a spin-spin interaction term. Within the FLZ approach, we find spectral sums and derive a systematic large-$n$ WKB expansion for the meson spectrum. The analytic results reproduce the expected behavior in key asymptotic regimes, such as the near-critical limit $m\to g/\sqrt{\pi }$ and the heavy-quark regime $m\gg g$, and are in good agreement with numerical data. Finally, by analytically continuing the mass parameter into the complex plane, we uncover two infinite families of singularities where individual mesons become massless, suggesting a hidden connection to nontrivial conformal field theories.

We propose an efficient regularization method for functional determinants of radial operators using heat kernel coefficients. Our key finding is a systematic way to identify heat kernel coefficients in the angular momentum space. We explicitly obtain the formulas up to sixth order in the heat kernel expansion, which suffice to regularize up to 13-dimensional functional determinants. We find that the heat kernel coefficients accurately approximate the large angular momentum dependence of functional determinants, and make numerical computations more efficient. In the limit of a large angular momentum, our formulas reduce to the Wentzel-Kramers-Brillouin formulas in previous studies, but are extended to higher orders. All the results are available in both the zeta function regularization and the dimensional regularization.

Models with classically degenerate vacua often support quasiclassical configurations of nontrivial topology. In ($0+1$)-dimensional quantum mechanics with a double-well potential, for example, instantons induce mixing between the two perturbative ground states in the purely bosonic case, while in the supersymmetric version, the tunneling amplitude is suppressed. In this work, we investigate ($1+1$)-dimensional models featuring classically Bogomol’nyi-Prasad-Sommerfield saturated kinks with degenerate masses and identical topology. Recent studies suggest that such kinks may undergo mixing mediated by scalar-field instantons. We analyze this phenomenon in a supersymmetric framework and demonstrate that, whereas mixing indeed occurs in the bosonic theory, the presence of fermionic zero modes in the supersymmetric case leads to the vanishing of the transition amplitude. To illustrate these results, we examine two examples featuring Wess-Zumino models with two and four supercharges. The latter example is motivated by the Affleck-Dine-Seiberg superpotential. We also present a number of developments of instanton calculus in the case of instantons in kink backgrounds.

We present a comprehensive analysis of the quasinormal modes (QNMs) of a massive scalar field in Schwarzschild spacetime using two complementary numerical techniques: the Hill-determinant method and Leaver’s continued-fraction method. Our study systematically compares the performance, convergence, and consistency of the two approaches across a wide range of field masses and angular momenta. We identify three critical mass thresholds, $m_{\lim }$, $m_{\max }$, and $m_{zd}$, which govern qualitative changes in the QNM spectrum. In particular, long-lived modes emerge at $m_{zd}$, where the imaginary part of the frequency vanishes and the mode becomes essentially nondecaying. This phenomenon is robust across multipoles and may have important implications for the phenomenology of massive fields around black holes. Our results provide a detailed numerical characterization of massive scalar QNMs and highlight the complementary strengths of the Hill-determinant and continued-fraction methods, paving the way for future studies of rotating or charged black holes and quasibound states.

Starobinsky’s $R+\alpha R^2$ inflation provides a compelling one-parameter inflationary model that is supported by current cosmological observations. However, at the same order in spacetime derivatives as the $R^2$ term, an effective theory of spacetime geometry must also include the Weyl-squared curvature invariant $W^2$. In this paper, we study the inflationary predictions of the gravitational theory with action of the form $R+\alpha R^2-\beta W^2$, where the coupling constant $\alpha$ sets the scale of inflation, and corrections due to the $W^2$ term are treated self-consistently via reduction of order in an expansion in the coupling constant $\beta$, at the linear order in $\beta /\alpha$. Cosmological perturbations are found to be described by an effective action with a nontrivial speed of sound $c_{\mathrm{s}}$ for scalar and $c_{\mathrm{t}}$ for tensor modes, satisfying the relation $c_{\mathrm{t}}/c_{\mathrm{s}}\simeq 1+\frac{\beta }{6\alpha }$ during the inflationary phase. Within this self-consistent framework, we compute several primordial observables up to the next-to-next-to-next-to leading order (N3LO). We find the tensor-to-scalar ratio $r\simeq 3(1-\frac{\beta }{6\alpha })(n_{\mathrm{s}}-1{)}^2$, the tensor tilt $n_{\mathrm{t}}\simeq -\frac{r}{8}$, and the running of the scalar tilt ${\mathfrak{a}}_{\mathrm{s}}\simeq -\frac{1}{2}(n_{\mathrm{s}}-1{)}^2$, all expressed in terms of the observed scalar tilt $n_{\mathrm{s}}$. We also provide the corresponding corrections up to N3LO, $\mathcal{O}((n_{\mathrm{s}}-1{)}^3)$.

Strong gravitational lensing creates multiple images of a gravitational wave transient. The current state-of-the-art method for identifying such lensing events is a computationally expensive full Bayesian analysis. In this paper, we investigate the feasibility and efficiency of using the overlap of sky localization probability maps (skymaps) to quickly filter potentially lensed gravitational wave signal pairs. We introduce three overlap statistics and test their performance using 200 simulated lensed pairs of gravitational-wave signals across five sets of signal-to-noise ratios. By setting a threshold with a false positive rate of $\mathrm{FPR}={10}^{-2}$ for the three overlap statistics, we find that we can filter out over 99% of nonlensed events while retaining all lensed events. The statistics for each event pair can be computed instantly, and can be used in practice to quickly analyze existing events using the skymaps from the low-latency localization pipelines when results from the full parameter estimation are not available.

Eccentric compact binary coalescences (CBCs) are expected to be observed in current and future gravitational-wave (GW) detector networks. Such detections are especially valuable as they can provide insights on the environments that nurture CBCs. However, it has been recently pointed out that a number of other physical and beyond-GR effects could imitate, or be mimicked by, eccentric CBCs. The standard approach to ascertain that a detected CBC is eccentric is to employ Bayesian model selection, where the eccentric CBC hypothesis is compared against other hypotheses. Such an approach is not only computationally intensive and time-consuming, but could also be misleading if none of the models under consideration represent the true model. In this work, we propose a conceptually simple but powerful method to directly confirm or reject the eccentric hypothesis, without needing to compare the hypothesis with the plethora of other possible hypotheses. The key idea is that while spurious nonzero values of eccentricity, at some reference frequency, could be acquired when a noneccentric CBC with additional physical/beyond-GR effects is recovered with an eccentric CBC waveform model, the evolution of eccentricity with frequency will in general not be mimicked. We accordingly formulate an eccentricity evolution consistency test (EECT). The method compares the eccentricity recovered at some low frequency value (e.g., 10 Hz), evolved to higher frequencies assuming GR, with eccentricities recovered at those same higher frequencies. Discrepancy between the two eccentricities at any reference frequency would violate EECT and indicate the presence of a mimicker. As a proof of concept, assuming a few eccentric CBC systems, quasicircular CBCs with additional physics mimicking eccentricity, and an O4-like three-detector-network configuration, we demonstrate that our proposed method is indeed able to reject mimickers at $\ge 68\%$ confidence, while ensuring that truly eccentric CBCs satisfy EECT.

We study the properties of remnants formed in prompt-collapse binary neutron star mergers. We consider nonspinning neutron star binaries over a range of total masses and mass ratios across a set of 22 equations of state, totaling 107 numerical relativity simulations. We report the final mass and spin of the systems (including the accretion disk and ejecta) to be constrained in a narrow range—$0.98\lesssim M_f/M\lesssim 0.99$ for the mass and $0.85\lesssim a_f\lesssim 0.95$ for the dimensionless spin—regardless of the binary configuration and matter effects. This sets them apart from binary black hole merger remnants. We assess the detectability of the postmerger signal in a future 40 km Cosmic Explorer observatory and find that the signal-to-noise ratio in the postmerger of an optimally located and oriented binary at a distance of 100 Mpc can range from $<1$ to 8, depending on the binary configuration and equation of state, with a majority of them greater than 4 in the set of simulations that we consider. We also consider the distinguishability between prompt-collapse binary neutron star and binary black hole mergers with the same masses and spins. We find that Cosmic Explorer will be able to distinguish such systems primarily via the measurement of tidal effects in the late inspiral. Neutron star binaries with reduced tidal deformability $\tilde{\mathrm{\Lambda }}$ as small as $\sim 3.5$ can be identified up to a distance of 100 Mpc, while neutron star binaries with $\tilde{\mathrm{\Lambda }}\sim 22$ can be identified to distances greater than 250 Mpc. This is larger than the distance up to which the postmerger will be visible. Finally, we discuss the possible implications of our findings for the equation of state of neutron stars from the gravitational wave event GW230529.

We explore the evolution of vortex light in the presence of gravitational waves (GWs) and demonstrate that the quantized orbital angular momentum (OAM) states can make transitions to other states due to the GWs. The interaction is calculated based on the framework of the wave propagation in linearized gravity theory and canonical quantization of the light field in curved spacetime. It is found that when a photon possessing OAM of $l$ interacts with GWs, the OAM modes of $l\pm 1$ and $l\pm 2$ may be excited with probabilities of $P_{l\pm 1}\sim {10}^{-17}$ and $P_{l\pm 2}\sim {10}^{-20}$, respectively. Higher probabilities of the transitions can be achieved when the photon radial wave vector or the propagation distance is increased, or when the photons encounter GWs with stronger amplitudes or smaller frequencies. Thus, a new GW detection technique is proposed, which may exhibit good performance in a wide range of GW frequencies. Furthermore, the detector is insensitive to seismic noise and is more advantageous for determining the distance of the source compared to current interferometer detectors.

Next-generation detectors are expected to be sensitive to postmerger signals from binary neutron star coalescences and, thus, to directly probe the remnant dynamics. We investigate the scientific potential of postmerger observations with the Einstein Telescope using full Bayesian analyses with the state of the art waveform model NRPMw. We show that postmerger signals with $\mathrm{SNR}\sim 7$ can be confidently detected with a Bayes’ factor of $\log \mathcal{B}\simeq 5$ ($\mathrm{e}$-folded); the posterior distributions report informative measurements already at $\mathrm{SNR}\sim 6$ for some noise realizations. The postmerger peak frequency $f_2$ can be confidently identified at SNR 7 with errors of $O(1\mathrm{kHz})$, that decrease below $O(100\mathrm{Hz})$ for SNR 10. The remnant’s time of collapse to black hole can be constrained to $O(20\mathrm{ms})$ at SNR 10. However, the inference can be biased by noise fluctuations if the latter exceed the signal’s amplitude before collapse. Violations of the equation of state (EOS)-insensitive relations for $f_2$ can be detected at $\mathrm{SNR}\gtrsim 8$ if the frequency shifts are $\gtrsim 500\mathrm{Hz}$. They can be smoking guns for EOS softening effects at extreme densities. However, the $f_2$ measurement can be significantly biased by subdominant frequency components for short-lived remnants. In these cases, an EOS softening might be better inferred from the remnant’s earlier collapse.

We present a renormalization-free framework for modeling galaxy bias based on unified Lagrangian perturbation theory (ULPT). In this approach, the galaxy density field is constructed entirely from Galileon-type operators, which also characterize the intrinsic nonlinear evolution of dark matter. This formulation ensures that the bias expansion is well defined at the field level, automatically satisfies the statistical conditions of vanishing ensemble and volume averages, and eliminates the need for any ad hoc renormalization procedures. We derive analytic expressions for the one-loop galaxy-galaxy and galaxy-matter power spectra and implement an efficient numerical algorithm using fftlog and fast-pt, enabling rapid and accurate evaluation of the full power spectrum. The resulting model requires only a minimal set of bias parameters, comprising three for correlation functions and four for power spectra. To assess its predictive accuracy, we perform joint fits to the halo-halo auto- and halo-matter cross-power spectra obtained from the dark emulator, considering nine combinations of redshift and halo mass, with 100 cosmological models sampled for each combination. We find that a single set of bias parameters successfully and simultaneously reproduces both spectra with better than $\sim 1\%$ accuracy up to $k\simeq 0.3h{\mathrm{Mpc}}^{-1}$ for typical linear bias values in the range $b_1\sim 0.8$ to 2. For more strongly biased tracers with $b_1\sim 3$, the agreement remains within $\sim 1\%$ up to $k\simeq 0.2h{\mathrm{Mpc}}^{-1}$. We further confirm that the same bias parameters consistently describe the two-point correlation functions in configuration space down to $r\simeq 15h^{-1}\mathrm{Mpc}$ with comparable accuracy. Moreover, ULPT predicts the theoretical relation $b_{K^2}^{\mathrm{E}}=-\frac{3}{4}{b}_2^{\mathrm{E}}$ between second-order Eulerian local and tidal bias parameters, which is validated through comparison with empirical fitting formulas calibrated on $N$-body simulations. These findings demonstrate that the ULPT framework offers a physically interpretable, statistically consistent, and computationally efficient model for nonlinear galaxy bias, with promising applicability to other observables such as redshift-space distortions, bispectra, and density-field reconstruction. The numerical implementation developed in this work is publicly released as the open-source python package ulptkit (https://github.com/naonori/ulptkit).

The James Webb Space Telescope (JWST) has unveiled unexpectedly massive galaxy candidates at high redshifts, challenging standard Lambda cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) cosmological predictions. In this work, we study the predictions of more realistic dark matter halo models combined with modified matter power spectra for interpreting JWST observations of high-redshift galaxies. We employ three halo mass functions: the conventional Sheth-Tormen (ST) model and two physically motivated alternatives introduced by Del Popolo (DP1 and DP2) that incorporate angular momentum, dynamical friction, and cosmological constant effects. These are coupled with parametrically modified power spectra featuring small-scale enhancements characterized by spectral indices and characteristic scales, motivated by cosmological scenarios. Our analysis of cumulative stellar mass densities at $z\simeq 8–10$ reveals that the standard ST mass function systematically underpredicts JWST observations, achieving marginal consistency only with high star formation efficiencies. The DP1 and DP2 models show improved agreement within standard $\mathrm{\Lambda }\mathrm{CDM}$, with DP2 consistent with JWST measurements at the $1\sigma$ level for moderate star formation efficiencies. While modified power spectra can further alleviate residual tensions, the statistical support for these extended models requires further investigation. In cases where DP2 predictions deviate from JWST observations by more than $2\sigma$, which often occurs at excessively high star formation efficiencies, the applied corrections fail to completely eliminate the tension. Our results demonstrate that incorporating realistic halo collapse physics, often neglected in standard analyses, can substantially alleviate apparent tensions between JWST observations and $\mathrm{\Lambda }\mathrm{CDM}$ predictions, highlighting the critical importance of small-scale structure formation physics in early cosmic epochs.

Recent measurements of the galaxy four-point correlation function (4PCF) from the Sloan Digital Sky Survey Baryon Oscillation Spectroscopic Survey indicate potential statistical evidence for parity violation. If this signal is of genuine physical origin, it must stem from beyond-Standard Model physics, most likely during the very early Universe, prior to decoupling ($z\sim 1020$). Since the baryon acoustic oscillation (BAO) features imprint at decoupling, they are expected in the parity-odd galaxy 4PCF. Thus detecting them would be an additional piece of evidence that the signal is genuine. We demonstrate, using a toy parity-violating model, how the BAO imprint on the parity-odd 4PCF. We then show how to do a model-independent search for BAO in the odd 4PCF. This is desirable since, if the signal is real, we may not know for some time what model of e.g. inflation produces it. If BAO are detected in the parity-odd sector, they can be used as a standard ruler as is already done in the two-point correlation function and three-point correlation function. We derive a simple formula relating the expected precision on the BAO scale to the overall parity-odd detection significance. Searching for the BAO in the odd 4PCF of redshift surveys such as DESI, Euclid, Spherex, and Roman will be a valuable additional avenue to determine if parity violation in the distribution of galaxies is real.