Complex Langevin simulations are an attempt to solve the sign (or complex-action) problem encountered in various physical systems of interest. The method is based on a complexification of the underlying degrees of freedom and an evolution in an auxiliary time dimension. The complexification, however, does not come without drawbacks, the most severe of which is the infamous “wrong convergence” problem, stating that complex Langevin simulations sometimes fail to produce correct answers despite their apparent convergence. It has long been realized that wrong convergence may—in principle—be fixed by the introduction of a suitable kernel into the complex Langevin equation, such that the conventional correctness criteria are met. However, as we discuss in this work, complex Langevin results may—especially in the presence of a kernel—still be affected by unwanted so-called integration cycles of the theory spoiling them. Indeed, we confirm numerically that in the absence of boundary terms the complex Langevin results are given by a linear combination of such integration cycles, as put forward by Salcedo and Seiler [L. L. Salcedo and E. Seiler, J. Phys. A 52, 035201 (2019)]. In particular, we shed light on the way different choices of kernel affect which integration cycles are being sampled in a simulation and how this knowledge can be used to ensure correct convergence in simple toy models.

We provide new global parametrizations of $\pi \pi \to \pi \pi$ scattering for the S2, P, D, F, and G partial waves up to at least 1.8 GeV, easy to implement for phenomenological use. With earlier S0-wave parametrizations, slightly updated here, they reproduce previous partial wave dispersion analyses up to the $\pi \omega$ threshold. In addition, these new parametrizations have improved their description of recent P-wave data, the inelasticity in various waves, and their fulfillment of Roy-like and forward dispersion relations. The latter now test very high partial waves and have an improved matching with the Regge regime, extending those with P-wave contributions up to 1.6 GeV. Above 1.6 GeV and up to 1.8 GeV, or sometimes somewhat beyond, the parametrizations are simple unconstrained fits to data.

We investigate ${\varphi }^{2n+1}$ deformations of the generalized free theory in the $\epsilon$ expansion, where the canonical kinetic term is generalized to a higher-derivative version. For $n=1$, we use the conformal multiplet recombination method to determine the leading anomalous dimensions of the fundamental scalar operator $\varphi$ and the bilinear composite operators $\mathcal{J}$. Then, we extend the $n=1$ analysis to the Potts model with $S_{N+1}$ symmetry and its higher-derivative generalization, in which $\varphi$ is promoted to an $N$-component field. We further examine the Chew-Frautschi plots and their $N$ dependence. However, for each integer $n>1$, the leading anomalous dimensions of $\varphi$ and $\mathcal{J}$ are not fully determined and contain one unconstrained constant, which in the canonical cases can be fixed by the results from the diagrammatic method. In all cases, we verify that the multiplet-recombination results are consistent with crossing symmetry using the analytic bootstrap methods.

We analyze the interaction between two quantum systems in spacetime, and we compare two possible models to describe it: (1) a fully quantum field theoretical (QFT) description of the coupling of two quantum systems mediated by a quantum field, and (2) a quantum-controlled model (qc-model), which is an effectively relativistic direct coupling in which the interaction of two quantum systems is not mediated by a field with local quantum degrees of freedom. We show that while there are regimes where the qc-model can approximate QFT arbitrarily well, it can suffer from retrocausal effects. We discuss in what regimes those retrocausal predictions of the qc-model are non-negligible and whether they can be used to argue that gravity induced entanglement experiments can reveal genuinely quantum aspects of the gravitational interaction or not.

We generalize earlier solutions of gravitational shocks sourced by distributional null stress-energy, and analyze their observable effects. A systematic method is proposed to demonstrate consistency between the gravitational effects of a null perfect fluid, i.e., a photon gas, and a collection of gravitational shock waves from point null particles. The anisotropy and time dependence of observable gravitational shifts produced by individual null shocks on a spherically arranged system of clocks relative to a central observer are derived. Shock solutions are used to characterize the angular and temporal spectra of gravitational fluctuations from a photon gas, inherited from the micro structure of the individual null particles. Angular and temporal frequency spectra and correlation functions of gravitational redshift are computed as functions of the ratio of particle impact parameter and transverse size to the size of the measuring sphere. Spectra and correlations of the transient, pure-phase component of anisotropy are computed from differential gravitational time shifts. It is argued some of their symmetries may be preserved in gravitational vacuum fluctuations.

We study the evolution of eccentric, equatorial extreme-mass-ratio inspirals (EMRIs) immersed in the accretion disks of active galactic nuclei. We find that single gravitational-wave observations from these systems could provide measurements with $\sim 10\%$ relative precision of, simultaneously, the disk viscosity and mass accretion rate of the central supermassive black hole. This is possible when the EMRI transitions, within the observation time, from supersonic to subsonic motion relative to the disk gas, for eccentricities $e\gtrsim 0.025–0.1$. The estimate of the accretion rate would assist in the identification of the EMRI’s host galaxy, or the observation of a direct electromagnetic counterpart, improving the chances of using these sources as cosmological sirens. Our work highlights the rich phenomenology of binary evolution in astrophysical environments and the need to improve the modeling and analysis of these systems for future gravitational-wave astronomy.

Recently Hollands et al. proposed a new formula for the entropy of a dynamical black hole for an arbitrary theory of gravity obtained from a diffeomorphism covariant Lagrangian via the Noether charge method [Phys. Rev. D 110, 024070 (2024)]. We present an alternative, pedagogical derivation of the dynamical black hole entropy for $f(R)$ gravity as well as canonical scalar-tensor theory by means of conformal transformations. First, in general relativity we generalize Visser and Yan’s pedagogical proof of the nonstationary physical process first law to black holes that may not be in vacuum, and give a pedagogical derivation of the second-order behavior of the dynamical black hole entropy for vacuum perturbations by considering the second-order variation of the Raychaudhuri equation. Second, we apply the derivation for general relativity to theories in the Einstein frames, and then recast the conclusions in their original frames. We show that the dynamical black hole entropy formulas of these theories satisfy both the nonstationary physical process first law and the nonstationary comparison first law via the Einstein frame. We further study the second-order behavior of the dynamical black hole entropy for vacuum perturbations, and observe that the second law is obeyed at second order in those theories. Using the Einstein frame, we also determine the relationship between the dynamical black hole entropy and the Wald entropy of the generalized apparent horizon in the original frame.

We present analytical expressions for the fluxes of energy and angular momentum from a point mass on an inclined spherical orbit about a Kerr black hole. The expressions are obtained using the method of Mano, Suzuki, and Takasugi to construct analytical solutions of the Teukolsky equation, and are given as post-Newtonian expansions valid through 12 post-Newtonian (PN) orders, with arbitrary values for the inclination parameter $x$ and black hole spin $a$. We characterize the structure of the PN expansions in terms of their dependence on $x$ and $a$, and we validate our results against numerical calculations.

The width of a resonance in a nearly integrable system, i.e., in a nonintegrable system where chaotic motion is still not prominent, can tell us how a perturbation parameter is driving the system away from integrability. Although the tool that we are presenting here can be used, is quite generic, and can be used in a variety of systems, our particular interest lies in binary compact object systems known as extreme mass ratio inspirals (EMRIs). In an EMRI, a lighter compact object, like a black hole or a neutron star, inspirals into a supermassive black hole due to gravitational radiation reaction. During this inspiral, the lighter object crosses resonances, which are still not very well modeled. Measuring the width of resonances in EMRI models allows us to estimate the importance of each perturbation parameter able to drive the system away from resonances and decide whether its impact should be included in EMRI waveform modeling or not. To tackle this issue in our study, we show first that recurrence quantifiers of orbits carry imprints of resonant behavior, regardless of the system’s dimensionality. As a next step, we apply a long short-term memory machine learning architecture to automate the resonance detection procedure. Our analysis is developed on a simple standard map and gradually we extend it to more complicated systems, until finally we employ it in a generic deformed Kerr spacetime known in the literature as the Johannsen-Psaltis spacetime.

The most precise determination of the sum of neutrino masses from cosmological data, derived from analysis of the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO) from the Dark Energy Spectroscopic Instrument (DESI), favors a value below the minimum inferred from neutrino flavor oscillation experiments. We explore which data are most responsible for this puzzling aspect of the current constraints on neutrino mass and whether they are related to other anomalies in cosmology. We demonstrate conclusively that the preference for negative neutrino masses is a consequence of larger-than-expected lensing of the CMB in both the two- and four-point lensing statistics. Furthermore, we show that this preference is robust to changes in the likelihoods of the BAO and CMB optical depth analyses given the available data. We then show that this excess clustering is not easily explained by changes to the expansion history and is likely distinct from the preference for dynamical dark energy in DESI BAO data. Finally, we discuss how future data may impact these results, including an analysis of Planck CMB with mock DESI five-year data. We conclude that the negative neutrino mass preference is likely to persist even as more cosmological data are collected in the near future.

The recent results on the baryon acoustic oscillations measurements from the DESI collaboration have shown tantalizing hints for a time-evolving dark energy equation of state parameter $w(z)$, with a statistically significant deviation from the cosmological constant and cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) model. One of the simplest and theoretically well-motivated plausible candidates to explain the observed behavior of $w(z)$, is scalar-field quintessence. Here, we consider a class of models known as $\alpha$-attractor, which describe in a single framework both inflation and the late-time acceleration of the Universe. Using the recent DESI data, in conjunction with other cosmological observations, we place stringent constraints on $\alpha$-attractor models and compare them to the $\mathrm{\Lambda }\mathrm{CDM}$ model. We find the $\alpha$ parameter of the theory, which is physically motivated from supergravity and supersymmetry theories to have the values $3\alpha \in \{1,2,3,4,5,6,7\}$, is constrained to be $\alpha \simeq 1.89_{-0.35}^{+0.40}$. In addition, we find that the rest of the cosmological parameters of the model agree with the corresponding values of $\mathrm{\Lambda }\mathrm{CDM}$, while a Bayesian analysis finds strong support in favor of the $\alpha$-attractor model. We also highlight an interesting connection between the $\alpha$-attractor models and the stochastic gravitational wave background, where a contribution to the latter could derive from an enhancement of inflationary gravitational waves at high frequencies due to an early kination phase, thus providing an interesting alternative way to constrain the theory.

In this paper, we investigate the impact of scalar fluctuations ($\chi$) nonminimally coupled to gravity, $\xi {\chi }^{2}R$, as a potential source of secondary gravitational waves (SGWs). Our study reveals that when reheating EoS $w_{\varphi }<1/3$ and $\xi \lesssim 1/6$ or $w_{\varphi }>1/3$ and $\xi \gtrsim 1/6$, the superhorizon modes of scalar field experience a tachyonic instability during the reheating phase. Such instability causes a substantial growth in the scalar field amplitude leading to pronounced production of SGWs in the low and intermediate-frequency ranges that are strong enough to be detected by Planck and future gravitational wave detectors. Such growth in superhorizon modes of the scalar field and associated GW production may have a significant effect on the strength of the tensor fluctuation at the cosmic microwave background (CMB) scales (parametrized by $r$) and the number of relativistic degrees of freedom (parametrized by $\mathrm{\Delta }{N}_{\mathrm{eff}}$) at the time of CMB decoupling. To prevent such overproduction, the Planck constraints on tensor-to-scalar ratio $r\le 0.036$ and $\mathrm{\Delta }{N}_{\mathrm{eff}}\le 0.284$ yield a strong lower bound on $\xi$ for $w_{\varphi }<1/3$, and upper bound on the value of $\xi$ for $w_{\varphi }>1/3$. Taking into account all the observational constraints we found the value of $\xi$ should be $\gtrsim 0.02$ for $w_{\varphi }=0$, and $\lesssim 4.0$ for $w_{\varphi }\ge 1/2$ for a wide range of reheating temperature within ${10}^{-2}\lesssim T_{\mathrm{re}}\lesssim {10}^{14}\mathrm{GeV}$, and for a wide range of inflationary energy scales. Further, as one approaches $w_{\varphi }$ toward $1/3$, the value of $\xi$ remains unconstrained. Finally, we identify the parameter regions in the $(T_{\mathrm{re}},\xi )$ plane, which can be probed by the upcoming GW experiments namely BBO, DECIGO, LISA, and ET.

We explore the impact of the backreaction of evaporation on the quantum state of primordial black holes (PBHs), known as “memory burden,” on the baryon asymmetry production in the Universe through high-scale leptogenesis. Focusing on PBH masses ranging from 1 to 1000 g, we investigate the interplay between the nonthermal production of heavy sterile neutrinos and the entropy injection within this nonstandard cosmological framework. By assuming appropriate values for the memory-burden parameters, $q=1/2$ and $k=1$, we derive mutual exclusion limits between PBHs and thermal leptogenesis in the mixed parameter space. Our analysis reveals that the primary contribution of PBHs to baryon asymmetry stems from entropy injection. Indeed, we find that, different from earlier studies based on the semiclassical Hawking evaporation, the memory-burden effect suppresses the nonthermal source term in the PBH mass range explored. This has significant implications for understanding baryogenesis in such alternative cosmological scenarios.

Ultrahigh-energy neutrinos ($\mathrm{UHE}\nu$s) can be used as a valuable probe of superheavy dark matter above $\sim {10}^9\mathrm{GeV}$, the latter being difficult to probe with collider and direct detection experiments due to the feebly interacting nature. Searching for radio emissions originating from the interaction of $\mathrm{UHE}\nu$s with the lunar regolith enables us to explore energies beyond ${10}^{12}\mathrm{GeV}$, which astrophysical accelerators cannot achieve. Taking into account the interaction of $\mathrm{UHE}\nu$s with the cosmic neutrino background and resulting standard neutrino cascades to calculate the neutrino flux on Earth, for the first time, we investigate sensitivities of such lunar radio observations to very heavy dark matter. We also examine the impacts of cosmogenic neutrinos that have the astrophysical origin. We show that the proposed ultralong wavelength lunar radio telescope, as well as the existing low-frequency array, can provide the most stringent constraints on decaying or annihilating superheavy dark matter with masses at $\gtrsim {10}^{12}\mathrm{GeV}$. The limits are complementary to or even stronger than those from other $\mathrm{UHE}\nu$ detectors, such as the IceCube-Gen2 radio array and the Giant Radio Array for Neutrino Detection.

The energy-momentum tensor form factors are studied in ${\mathrm{\Phi }}^4$ theory to one-loop order with particular focus on the $D$-term, a particle property which has attracted a lot of attention in the recent literature. It is shown that the free Klein-Gordon theory value of the $D$-term $D_{\mathrm{free}}=-1$ is reduced to $D_{\text{one-loop}}=-\frac{1}{3}$ even if the ${\mathrm{\Phi }}^4$ interaction is infinitesimally small. A companion work in ${\mathrm{\Phi }}^3$ theory confirms this result which may indicate that it is independent of the type of interaction as long as the scalar theory is renormalizable. Dispersion relations are studied. Various definitions of mean square radii including the mechanical radius are investigated. The findings contribute to a better understanding of the energy momentum tensor properties of particles and their interpretation.

We explore the potential of studying sterile neutrinos at a future high-energy muon collider, where these particles can generate small active neutrino masses via the seesaw mechanism and exhibit long-lived particle signatures. A Dirac sterile neutrino model with ${\mathrm{U}(1)}_{L_{\mu }-L_{\tau }}$ symmetry is introduced, where the heavy right-handed neutrino ($N_R$) produces tiny active neutrino masses, and the light left-handed neutrino ($N_L$) naturally behaves as a long-lived particle. The ${\mathrm{U}(1)}_{L_{\mu }-L_{\tau }}$ gauge symmetry also enhances sterile neutrino pair production at a future high-energy muon collider. Using the displaced vertex method, the muon collider can search for heavy sterile neutrino, especially for $m_L>m_W$. We find that a muon collider with $\sqrt{s}=3(10)\mathrm{TeV}$ and luminosity $\mathcal{L}=1(10){\mathrm{ab}}^{-1}$ can probe $N_L$ masses of $m_L\in [100,1500(5000)]\mathrm{GeV}$ and mixing angles ${\theta }_{\nu L}\in [{10}^{-13},{10}^{-6}]$.

We propose gauge covariant neural networks along with a specialized training algorithm for lattice QCD, designed to handle realistic quarks and gluons in four-dimensional space-time. We show that the smearing procedure can be interpreted as an extended version of residual neural networks with fixed parameters. To demonstrate the applicability of our neural networks, we develop a self-learning hybrid Monte Carlo algorithm in the context of two-color QCD, yielding outcomes consistent with those from the conventional hybrid Monte Carlo approach.

Recent experiments have found spin alignment of $J/\psi$ with respect to the event plane in heavy ion collisions, suggesting a medium effect that is spin dependent. We propose a possible mechanism with polarized dissociation from the motion of $J/\psi$ with respect to the medium. We calculate the polarized dissociation rate for a quarkonium spin triplet state from spin chromomagnetic coupling in the potential nonrelativistic QCD framework. This is done for the leading order gluo-dissociation process and the next to leading order inelastic Coulomb scattering process. The polarized dissociation rate is expressed as a function of relative velocity between quarkonium and quark-gluon plasma and the quantization axis. Applying the polarized dissociation rate to quarkonium evolution with a dissociation effect only in a Bjorken flow, we find the spin 0 state to dissociate less than the other spin states, leading to positive ${\rho }_{00}-1/3$. The regeneration contribution is expected to give a contribution with the opposite sign.

In this work we compare the SuSAv2 model, based on the superscaling phenomenon and the relativistic mean field theory, with charged-current inclusive neutrino cross sections from the NOvA and MicroBooNE experiments, whose targets are composed primarily by ${}^{12}\mathrm{C}$ and ${}^{40}\mathrm{Ar}$, respectively. The neutrino energy in these experiments covers a kinematic range from tens of MeV to roughly 20 GeV. Thus, we consider the different reaction mechanisms that contribute significantly to these kinematics, namely quasielastic, two-particle two-hole meson exchange currents, resonances, and deep inelastic scattering contributions.

This work presents the first prediction of tetralepton resonant states containing muons, extending beyond the simplest tetralepton system, dipositronium (${\mathrm{Ps}}_2$). With the rapid advancements in experimental facilities, the production and study of these intriguing states may be within reach. We perform a comprehensive analysis of $S$-wave trilepton and tetralepton systems within the framework of a QED Coulomb potential. We employ the Gaussian expansion method to solve the three- or four-body Schrödinger equation and utilize the complex scaling method to identify resonant states. We uncover a series of bound and resonant states in the trilepton systems $e^{+}{e}^{+}{e}^{-}$, ${\mu }^{+}{\mu }^{+}{\mu }^{-}$, $e^{+}{e}^{+}{\mu }^{-}$, and ${\mu }^{+}{\mu }^{+}{e}^{-}$, as well as the tetralepton systems $e^{+}{e}^{+}{e}^{-}{e}^{-}$, ${\mu }^{+}{\mu }^{+}{\mu }^{-}{\mu }^{-}$, and ${\mu }^{+}{\mu }^{+}{e}^{-}{e}^{-}$. The energies of these states range from $-30\mathrm{eV}$ to $-1\mathrm{eV}$ below the total mass of three or four leptons, with their widths varying from less than 0.01 eV to approximately 0.07 eV. Additionally, we calculate the spin configurations and root mean square radii of these states, providing insight into their spatial structures. No bound or resonant states are found in the trilepton $e^{+}{\mu }^{+}{e}^{-}$, ${\mu }^{+}{e}^{+}{\mu }^{-}$ systems, nor in the tetralepton ${\mu }^{+}{e}^{+}{\mu }^{-}{e}^{-}$ system. A comparison with fully heavy tetraquark systems reveals that the additional color degree of freedom in QCD results in the absence of low-energy bound and resonant states. However, this extra degree of freedom allows for a broader range of $J^{PC}$ quantum numbers to produce resonant states, highlighting the rich complexity of QCD systems.