We discuss the properties of the two-flavor quark-meson diquark (QMD) model as a renormalizable low-energy model for quantum chromodynamics (QCD) in the 2SC phase of QCD. The effective degrees of freedom are the mesons (sigma and pions), quarks, and diquarks. Some of the parameters of the model can be determined by expressing them in terms of the vacuum meson masses and the pion decay constant using the on-shell renormalization scheme. The remaining parameters are considered free, although they in principle can be calculated from QCD. The thermodynamic potential is calculated in a mean-field approximation taking only quark loops into account. In this approximation, we derive a set of renormalization group equations for the running masses and couplings. The solutions to these equations are used to improve the thermodynamic potential $\mathrm{\Omega }$ and thereby thermodynamic quantities. Four parameter sets are chosen and the phase diagram in the $\overline{\mu }\text{−}T$ plane is obtained (with $\overline{\mu }=\frac{1}{3}{\mu }_B$). We also calculate the speed of sound $c_s$ as a function of $\overline{\mu }$ at vanishing temperature. For large values of $\overline{\mu }$, the speed of sound approaches the conformal limit $c_s=\frac{1}{\sqrt{3}}$ from above, in disagreement with perturbative calculations, but in agreement with hard-dense-loop resummed perturbation theory.

This study presents a quantum chromodynamics (QCD) analysis of fragmentation functions (FFs) for neutral pions (${\pi }^0$), neutral kaons ($K_S^0$), and eta mesons ($\eta$), utilizing world data of single-inclusive hadron production in $e^{+}{e}^{-}$ annihilation involving the most recent BESIII data with low collision energy, to test the operational region of QCD collinear factorization for single-inclusive hadron production. We found that the QCD-based analysis at next-to-next-to-leading order in perturbative QCD with parametrized higher-twist effects can explain both existing high-energy world data and the BESIII new measurements, while the latter cannot be explained with existing FFs extracted with high-energy data. To investigate the higher-twist contributions to this discrepancy, a direct functional approach is employed, providing a testing framework for characterizing the experimental results over a wide range of energy scales, from low to high, thus extending the classical theoretical models to the BESIII domain.

We propose novel superfluids induced by the parity-doubled baryons. The parity-doubled baryons, i.e., a nucleon $N(940)$ with mass 940 MeV and spin-parity $J^P=1/2^{+}$ and an excited nucleon $N^{*}(1535)$ with mass 1535 MeV and spin-parity $J^P=1/2^{-}$ in vacuum, become degenerate at sufficiently high density where the chiral symmetry is restored. In this study, we extend the conventional U(1) chiral symmetry to the higher dimensional symmetries, dubbed emergent chiral symmetries, including the naive and mirror assignments as their subgroups. Starting with the Lagrangian up to four-point interactions among the neutron $n$ and its chiral partner $n^{*}$, neutral components in $N$ and $N^{*}$, in pure neutron matter, we investigate the properties of the ground state with a pairing gap generated by the $n$ and $n^{*}$ in the mean-field approximation. We find vector-type condensates that induce the dynamical breaking of a new class of internal symmetries, emergent chiral symmetries, as well as the baryon number and the rotational symmetries of the real space, indicating the appearance of massless Nambu-Goldstone bosons consisting of six quarks: emergent pions, superfluid phonons, and magnons, respectively. We also study the fermionic excitation modes at low-energy scales and show that they exhibit a spatial anisotropy of the propagation at the Dirac cone in momentum space. Some phenomenological implications are advocated, shedding new light on the properties of neutron stars.

A top quark and an antitop quark produced together at colliders have correlated spins. These spins constitute a quantum state that can exhibit entanglement and violate Bell’s inequality. In realistic collider experiments, most analyses allow the axes, as well the Lorentz frame, to vary event by event, thus introducing a dependence on the choice of event-dependent basis leading us to adopt “fictitious states,” rather than genuine quantum states. The basis dependence of fictitious states allows for an optimization procedure, which makes the usage of fictitious states advantageous in measuring entanglement and Bell inequality violation. In this work, we show analytically that the basis that diagonalizes the spin-spin correlations is optimal for maximizing spin correlations, entanglement, and Bell inequality violation. We show that the optimal basis is approximately the same as the fixed beam basis (or the rotated beam basis) near the $t\overline{t}$ production threshold, while it approaches the helicity basis far above threshold. Using this basis, we present the sensitivity for entanglement and Bell inequality violation in $t\overline{t}$ events at the Large Hadron Collider (LHC) and a future $e^{+}{e}^{-}$ collider. Since observing Bell inequality violation appears to be quite challenging experimentally, and requires a large dataset in collider experiments, choosing the optimal basis is crucially important to observe Bell inequality violation. Our method and general approach are equally applicable to other systems beyond $t\overline{t}$, including interactions beyond the Standard Model.

Recent neutrino-nucleus cross-section measurements of observables characterizing kinematic imbalance from the T2K, MicroBooNE, and MINERvA experiments are used to benchmark predictions from widely used neutrino interaction event generators. Given the different neutrino energy spectra and nuclear targets employed by the three experiments, comparisons of model predictions to their measurements breaks degeneracies that would be present in any single measurement. In particular, the comparison of T2K and MINERvA measurements offers a probe of energy dependence, while a comparison of T2K and MicroBooNE investigates scaling with nuclear target. In order to isolate the impact of individual nuclear effects, model comparisons are made following systematic alterations to the nuclear ground state, final-state interactions, and multinucleon interaction strength. The measurements are further compared to the generators used as an input to DUNE/SBN and T2K/Hyper-K analyses. While no model is able to quantitatively describe all of the measurements, evidence is found for mismodeling of A-scaling in multinucleon interactions and it is found that tight control over how energy is distributed among hadrons following final-state interactions is likely to be crucial to achieving improved agreement. Overall, this work provides a novel characterization of neutrino interactions while offering guidance for refining existing generator predictions.

The path integral approach to a quantum theory of gravity is widely regarded as an indispensable strategy. However, determining what additional elements, beyond black hole or anti–de Sitter (AdS) spacetime, should be incorporated into the path integral remains crucial yet perplexing. We argue that the spacetime with a conical singularity in its Euclidean counterpart should be the most important ingredient to append to the path integral. Therefore, physical quantities should be ensemble averaged over all geometries since they are described by the same Lorentzian metric. When the ensemble average is introduced, the Hawking-Page transition for the Schwarzschild-AdS black hole and the small-large black hole transition for the Reissner-Nordström-AdS black hole naturally arise as semiclassical approximations, when the size of the black hole system is much larger than the Planck length. Away from the semiclassical limit, the system is a superposition of different geometries, and the averaged quantities would deviate from the black hole thermodynamics. Expanding around the classical saddles, the subleading order of the Newton constant contributions can be derived, which are half of the Hawking temperature both for the Schwarzschild and Reissner-Nordström black holes. The result may imply a universal structure. The subsubleading terms and more intriguing physics that diverge from black hole thermodynamics are revealed. The ensemble-averaged theory provides a new way of studying subleading effects and extending the traditional AdS/CFT correspondence.

In the context of holographic conformal field theories (CFTs), a system of linear partial differential equations was recently proposed to be the higher-dimensional analog of the null-state equations in $d=2$ CFTs at large central charge. Solving these equations in a near-light-cone expansion yields solutions that match the minimal-twist multistress tensor contributions to a heavy-light four-point correlator (or a thermal two-point correlator) computed using holography, the conformal bootstrap, and other methods. This paper explores the exact solutions to these equations. We begin by observing that, in an expansion in terms of the ratio between the heavy operator’s dimension and the central charge, the $d=2$ correlator involving the level-two degenerate scalars at each order can be represented as a Bessel function; the resummation yields the Virasoro vacuum block. We next observe a relation between the $d=2$ correlator and the $d=4$ near-light-cone correlator involving light scalars with the same conformal dimension. The resummed $d=4$ correlator takes a simple form in the complex frequency domain. Unlike the Virasoro vacuum block, the resummation in $d=4$ leads to essential singularities. Similar expressions are also obtained when the light scalar’s dimension takes other finite values. These CFT results correspond to a holographic computation with a spherical black hole. In addition, using the differential equations, we demonstrate that the correlators can be reconstructed via certain modes. In $d=2$, these modes are related to the Virasoro algebra.

In this paper, we consider a Carroll magnetic limit of a one-loop scalar effective action. We work on general static backgrounds and compute both divergent and finite parts of the effective action in this limit. We show that the divergent part can be removed by adding local counterterms. The finite part is related to an effective action in a lower dimensional theory which however does not coincide in general with the one obtained by a Carroll limit in the classical counterpart.

Recently, Arkani-Hamed et al. proposed the existence of zeros in scattering amplitudes in certain quantum field theories including the cubic adjoint scalar theory $\mathrm{Tr}({\varphi }^3)$, the $SU(N)$ nonlinear sigma model and Yang-Mills theory. These hidden zeros are special kinematic points where the amplitude vanishes and factorizes into a product of lower-point amplitudes, similar to factorization near poles. In this paper, we show a close connection between the existence of such zeros and the double-copy map. In fact, compatibility with the Bern-Carrasco-Johansson relations requires the presence of these zeros. We also show that these zeros extend via the Kawai-Lewellen-Tye relations to special Galileon amplitudes and their corrections, evincing that these hidden zeros are also present in permutation-invariant amplitudes.

The inhomogeneous Abelian Higgs model with a magnetic impurity in the Bogomolny-Prasad-Sommerfield (BPS) limit is studied for both relativistic and nonrelativistic regimes. Though the symmetry of spatial translation is broken by inhomogeneity, extension to an $\mathcal{N}=1$ supersymmetric theory is admitted. The quartic scalar potential has a minimum value depending on strength of the impurity but possesses a broken phase at a spatial asymptote. The vacuum configuration of a broken phase can be neither a constant nor the minimum of the scalar potential but is found as a nontrivial solution of the Bogomolny equations. While its energy density and magnetic field are given by the function of spatial coordinates, the energy and magnetic flux remain zero. The sign of the magnetic impurity term allows either a BPS sector or anti-BPS sector but not both. Thus, the obtained solution is identified as the new inhomogeneous broken vacuum of minimum zero energy. In the presence of rotationally symmetric Gaussian type inhomogeneity, topological vortex solutions are also obtained, and the effects of the impurity to the vortex are numerically analyzed.

We formulate fermionic versions, for any number of spatial dimensions, of the van der Waals and Casimir-Polder interactions and study their properties. In both cases, the systems we introduce contain localized “atoms”: two-level systems, coupled to a vacuum Dirac field. This Dirac field plays here a role akin to the electromagnetic field in the van der Waals case. In this context, bag model conditions for the Dirac field serve as the analog of the “mirror” in the Casimir-Polder effect. We found that, in this case, the resulting interaction is repulsive.

We present and investigate two issues within the measurement scheme for QFT presented by Polo-Gómez et al. [Phys. Rev. D 105, 065003 (2022)]. We point out some discrepancies that arise when the measurement scheme is applied to contextual field states and show that $n$-point function assignments based on local processing regions sometimes lead to inconsistencies. To solve these issues, we modify the measurement scheme to use nonrelativistic detectors to induce an update rule for algebraic states in the Haag-Kastler formulation of quantum field theory. In this way, $n$-point functions can be consistently evaluated across any region having a definite causal relation with measurements.

Massive higher-spin states/fields appear in the effective description of various systems from hadrons and nuclei to black holes, whenever the point-particle approximation is justified, as well as in the bottom-up approaches to the quantum gravity problem. In four dimensions the actions for massive higher-spin fields utilize either the Singh-Hagen/Zinoviev set of auxiliary fields or a single chiral field, which is an $sl(2,\mathbb{C})$ spin-tensor of type $(2s,0)$, generalizing the Chalmers-Siegel approach. We show that these two actions are on the opposite ends of a discrete family of actions where the physical field is a spin-tensor of type $(s+k,s-k)$. The $(2s-1,1)$- and $(2s-2,2)$-cases generalize the Proca and the Fierz-Pauli actions, respectively, to all spins. A similar family of second-order actions exists for fermionic higher-spin fields.

We investigate the open dynamics of quantum particles in relativistic scattering. Specifically, we consider the scattering process of quantum particles coupled to an environment initially in a vacuum state. Tracing out the environment and using the unitarity of an S operator, we find the Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) generator that describes the evolution of the particles. The GKSL generator is exemplified by focusing on the concrete processes: one is the decay of scalar particle ($\varphi \to \chi \chi$), and the others are the pair annihilation and the $2\to 2$ scattering of scalar particles ($\varphi \varphi \to \chi \chi$ and $\varphi \varphi \to \varphi \varphi$). The GKSL generator for $\varphi \to \chi \chi$ has a parameter with the coupling between $\varphi$ and $\chi$ and the masses of the fields. The GKSL generator associated with $\varphi \varphi \to \chi \chi$ is characterized by a Lorentz-invariant function of initial momenta. Notably, in the pair annihilation process, we show that the probability of pair annihilation varies depending on the superposition state of incident scalar $\varphi$ particles. Furthermore, we observe that the GKSL generators derived in this paper have Poincaré symmetry. This means that GKSL generators with Poincaré symmetry provide an effective description of the asymptotic behavior of open quantum dynamics in the long-term processes considered here.

We perform an extensive bootstrap study of Hermitian and non-Hermitian theories based on the novel analytic continuation of $⟨{\varphi }^n⟩$ or $⟨(i\varphi {)}^n⟩$ in $n$. We first use the quantum harmonic oscillator to illustrate various aspects of the ${\varphi }^n$ trajectory bootstrap method, such as the large $n$ expansion, matching conditions, exact quantization condition, and high energy asymptotic behavior. Then we derive highly accurate solutions for the anharmonic oscillators with the parity invariant potential $V(\varphi )={\varphi }^2+{\varphi }^m$ and the $\mathcal{P}\mathcal{T}$ invariant potential $V(\varphi )=-(i\varphi {)}^m$ for a large range of integral $m$, showing the high efficiency and general applicability of this new bootstrap approach. For the Hermitian quartic and non-Hermitian cubic oscillators, we further verify that the noninteger $n$ results for $⟨{\varphi }^n⟩$ or $⟨(i\varphi {)}^n⟩$ are consistent with those from the wave function approach. In the $\mathcal{P}\mathcal{T}$ invariant case, the existence of $⟨(i\varphi {)}^n⟩$ with noninteger $n$ allows us to bootstrap the non-Hermitian theories with noninteger powers, such as fractional and irrational $m$.

It is known that the $U(2)$ Wess-Zumino-Witten model is dual to the free fermion theory in two dimensions via non-Abelian bosonization. While it is decomposed into the $SU(2)$ Wess-Zumino-Witten model and a free compact boson, the former is believed to be equivalent to the $O(3)$ nonlinear sigma model with the theta term at $\theta =\pi$. In this work, we reexamine this duality through the lens of nonperturbative renormalization group (RG) flow. We analyze the RG flow structure of the $O(3)$ nonlinear sigma model with the theta term in two dimensions using the functional renormalization group. Our results reveal a nontrivial fixed point with a nonzero value of the topological coupling. The scaling dimensions (critical exponents) at this fixed point suggest the realization of a duality between the $O(3)$ nonlinear sigma model with the theta term and the free fermion theory, indicating that these models belong to the same universality class.

The gravitational-wave (GW) memory effect is a strong-field relativistic phenomenon that is associated with a persistent change in the GW strain after the passage of a GW. The nonlinear effect arises from interactions of GWs themselves in the wave zone and is an observable effect connected to the infrared properties of general relativity. The detection of the GW memory effect is possible with LIGO and Virgo in a population of binary-black-hole (BBH) mergers or from individual events with next-generation ground- and space-based GW detectors or pulsar timing arrays. Matched-filtering-based searches for the GW memory require accurate, and preferably rapid-to-evaluate waveform models of the memory effect’s GW signal. One important element of such a waveform model is a model for the final memory offset—namely, the net change in strain between early and late times. In this paper, we construct a model for the final memory offset from the merger of nonspinning BBH systems in quasicircular orbits. A novel ingredient of this model is that we first compute the memory signal for extreme mass-ratio inspirals using a high post-Newtonian-order analytic calculation, and we use this analytical result to fix the coefficient in the fit which is linear in the mass-ratio. The resulting memory-offset fit could be used for detecting the GW memory for binaries that merge on a timescale that is short relative to the inverse of the low-frequency cutoff of a GW detector. Additionally, this fit will be useful for analytic waveform models of the GW memory signals in the time and frequency domains.

We derive a Weyl-invariant equation for gravity by gauging the global Weyl invariance of vacuum Einstein equations. The equation is linear in the curvature and a natural generalization of Einstein equations to Weyl geometry. The system has five physical polarizations, two tensor modes, two vectors modes, and one scalar, associated to the cosmological constant. An exact black hole solution is found. We study the dynamics on Friedman backgrounds and the evolution of cosmological perturbations. It is shown that cosmological vector modes do not decay in this model.

Black holes are extreme outcomes of general relativity, and can form through a variety of ways, including gravitational collapse of massive stars, or quantum fluctuations in the early Universe. Here, we ask the question of whether they can form via focusing of radiation by compact binaries or intense lasers, or via trapping at the light ring of black holes. We provide evidence that gravitational lensing of radiation from a small, finite number of sources is not a viable mechanism to form black holes.

Third-generation gravitational-wave detectors will observe up to millions of merging binary black holes. With such a vast dataset, stacking events into population analyses will arguably be more important than analyzing single sources. We present the first application of population-level Fisher-matrix forecasts tailored to third-generation gravitational-wave interferometers. We implement the formalism first derived by Gair et al. [Mon. Not. R. Astron. Soc. 519, 2736 (2023)] and explore how future experiments such as Einstein Telescope and Cosmic Explorer will constrain the distributions of black-hole masses, spins, and redshift. Third-generation detectors will be transformative, improving constraints on the population hyperparameters by several orders of magnitude compared to current data. At the same time, we highlight that a single third-generation observatory and a network of detectors will deliver qualitatively similar performances. Obtaining precise measurements of some population features (e.g., peaks in the mass spectrum) will require only a few months of observations while others (e.g., the fraction of binaries with aligned spins) will instead require years if not decades. We argue population forecasts of this kind should be featured in white papers and feasibility studies aimed at developing the science case of future gravitational-wave interferometers.