Second-order self-force calculations will be critical for modeling extreme-mass-ratio inspirals, and they are now known to have high accuracy even for binaries with mass ratios $\sim 1:10$. Many of the challenges facing these calculations are related to slow convergence of spherical-harmonic (or spheroidal harmonic) mode sums in a region containing the small companion. In this paper, we begin to develop a multidomain framework that can evade those problems. Building on recent work by Osburn and Nishimura, in the problematic region of spacetime, we use a puncture scheme and decompose the punctured field equations into a basis of Fourier and azimuthal $m$ modes, avoiding a harmonic decomposition in the $\theta$ direction. Outside the problematic region, we allow for a complete spherical- or spheroidal-harmonic decomposition. As a demonstration, we implement this framework in the simple context of a scalar charge in circular orbit around a Schwarzschild black hole. Our implementation utilizes several recent advances: a spectral method in each region, hyperboloidal compactification, and an extremely high-order puncture.

Most self-force calculations rely, in one way or another, on representations of a particle’s Detweiler-Whiting singular field. We present a simple method of calculating the singular field to high order in a local expansion in powers of distance from the particle. As a demonstration, we compute the singular field to 14th order in distance, 10 orders beyond the previous state of the art, in the simple case of a scalar charge in circular orbit around a Schwarzschild black hole. We provide the result in both a four-dimensional form and a decomposed form suitable for use in an $m$-mode puncture scheme. Our method should have applications in overcoming bottlenecks in current self-force calculations at both first and second orders in perturbation theory.

We analyze, by rigorous renormalization group methods, a Fermi model for weak forces with a single family of leptons, one massless and the other with mass $m=M{e}^{-\beta }$, with $M$ the gauge boson mass, a quartic nonlocal interaction with coupling ${\lambda }^2$, and a momentum cutoff $\mathrm{\Lambda }$. The magnetic moment is written as a series in ${\lambda }^2$, with $n$-th coefficients bounded by $C^n(\frac{m^2}{M^2}){\beta }^{2n}(\frac{{\mathrm{\Lambda }}^2}{M^2}{)}^{(1+0^{+})(n-1)}$ if $C$ is a constant; this implies convergence and provides nonperturbative bounds on the higher order contributions. The fact that the magnetic moment is associated with a dimensionally irrelevant quantity requires the implementation of cancellations in the multiscale analysis.

Models are developed for the motion of charge-2 Abelian Higgs vortices through the 2-vortex moduli space $\mathcal{M}$, with the vortices excited by their shape mode oscillations. The models simplify to the well-known geodesic flow on $\mathcal{M}$, modified by a potential, when the mode oscillations are fast relative to the moduli space motion and their amplitudes are small. When the lowest-frequency mode is excited with a large amplitude, the geodesic flow is not a correct description. Instead, a chaotic, or even fractal, multibounce structure in vortex-vortex collisions is predicted.

Asymptotic safety is a powerful mechanism for obtaining a consistent and predictive quantum field theory beyond the realm of perturbation theory. It hinges on an interacting fixed point of the Wilsonian renormalization group flow which controls the microscopic dynamics. Connecting the fixed point to observations requires constructing the set of effective actions compatible with this microscopic dynamics. Technically, this information is stored in the UV-critical surface of the fixed point. In this work, we describe a novel approach for extracting this information based on analytical and pseudospectral methods. Our construction is illustrated at the level of the three-dimensional Ising model and easily generalizes to any asymptotically safe quantum field theory. It also constitutes an important step toward setting up a well-founded swampland program within the gravitational asymptotic safety program.

Recently, Bonanno et al. [Dust collapse in asymptotic safety: A path to regular black holes, Phys. Rev. Lett. 132, 031401 (2024)] presented an explicit metric describing the exterior of a collapsing dust ball within the framework of asymptotically safe gravity. Based on this metric, we investigate in detail the properties of the quasinormal mode (QNM) spectra for test massless scalar, vector, and Dirac fields. We find accurate values for the fundamental QNM frequency and the first overtones, demonstrating the appearance of a peculiar spiral-like behavior of the overtones compared to the fundamental modes. Additionally, we study black hole shadows and show that they align with Enstein Horizon Telescope observations. Finally, we study the gray-body factors and provide explicit lower bound estimates.

We propose a high order discontinuous Galerkin (DG) scheme with subcell finite volume (FV) limiter to solve a monolithic first-order hyperbolic Baumgarte-Shapiro-Shibata-Nakamura-Oohara-Kojima (BSSNOK) formulation of the coupled Einstein-Euler equations. The numerical scheme runs with adaptive mesh refinement (AMR) in three space dimensions, is endowed with time-accurate local time stepping (LTS) and is able to deal with both conservative and nonconservative hyperbolic systems. The system of governing partial differential equations was shown to be strongly hyperbolic and is solved in a monolithic fashion with one numerical framework that can be simultaneously applied to both the conservative matter subsystem as well as the nonconservative subsystem for the spacetime. Since high order unlimited DG schemes are well known to produce spurious oscillations in the presence of discontinuities and singularities, our subcell finite volume limiter is crucial for the robust discretization of shock waves arising in the matter as well as for the stable treatment of puncture black holes. We test the new method on a set of classical test problems of numerical general relativity, showing good agreement with available exact or numerical reference solutions. In particular, we perform the first long term evolution of the inspiralling merger of two puncture black holes with a high order Arbitrary high order schemes using derivatives (ADER-DG) scheme.

We perform Monte Carlo simulations of stationary planar accretion of a collisionless gas onto a moving Schwarzschild black hole. In this work—a sequel to our previous paper on the Monte Carlo method for stationary general-relativistic Vlasov systems—we demonstrate that our approach can be extended beyond the simplifying assumptions of the spherical symmetry or axial symmetry in the planar case. Our method of computing observable quantities, such as the particle current density, can be regarded as a rigorous coarse graining scheme, adapted to a numerical grid. Main difficulties are related to an appropriate parametrization of particle trajectories and a selection of parameters consistent with assumed requirements on the distribution function.

We revisit the path-integral approach to the wave function of the Universe by utilizing Lefschetz thimble analyses and resurgence theory. The traditional Euclidean path integral of gravity has the notorious ambiguity of the direction of Wick rotation. In contrast, the Lorentzian method can be formulated concretely with the Picard-Lefschetz theory. Yet, a challenge remains: the physical parameter space lies on a Stokes line, meaning that the Lefschetz-thimble structure is still unclear. Through complex deformations, we resolve this issue by uniquely identifying the thimble structure. This leads to the tunneling wave function, as opposed to the no-boundary wave function, offering a more rigorous proof of the previous results. Further exploring the parameter space, we discover rich structures: the ambiguity of the Borel resummation of perturbative series around the tunneling saddle points is exactly canceled by the ambiguity of the contributions from no-boundary saddle points. This indicates that resurgence also works in quantum cosmology, particularly in the minisuperspace model.

Neutrino masses and quantum gravity are strong reasons to extend the standard model of particle physics. A large extra dimension can be motivated by quantum gravity and can explain the small neutrino masses with new singlet states that propagate in the bulk. In such a case, a Kaluza-Klein tower of sterile neutrinos emerges. We revisit constraints on towers of sterile neutrinos that come from cosmological observables such as the effective number of noninteracting relativistic species and the dark matter density. These limits generically rule out micron-sized extra dimensions. We explore the weakening of these constraints to accommodate an extra dimension close to the micron size by assuming that the Universe is reheated after inflation to a low temperature. We discuss how such a possibility can be distinguished in the event of a positive signal in a cosmological observable.

The LIGO-Virgo-Kagra collaboration has observed gravitational waves consistent with the mergers of a black hole and a neutron star, namely GW200105 and GW200115, providing evidence for such cataclysmic events. Although no electromagnetic counterpart was reported for either of these two events, under certain conditions black hole-neutron star mergers are expected to form a significant accretion disk and to produce both a short gamma ray burst and a kilonova, much as observed in the binary neutron star merger GW170817. Here, we extend our publicly available code mhduet to study numerically the merger of a magnetized neutron star with a black hole. mhduet employs large eddy simulation (LES) techniques to help capture the magnetic field amplification resulting from turbulence and other subgrid scale dynamics in the postmerger stage. In particular, we simulate a merger with parameters favorable to producing an accretion disk, focusing on the formation and dynamics of the turbulent disk and the resulting magnetic field amplification. Following the tidal disruption and during the formation of the accretion disk, the magnetic field undergoes significant amplification driven by the Kelvin-Helmholtz instability, reaching strengths of more than ${10}^{14}\mathrm{G}$ from a realistic initial strength of ${10}^{11}\mathrm{G}$ in short timescales of approximately 20 ms. Despite employing LES techniques with a finest resolution of 120 m that is among the highest in black hole-neutron star mergers, it is still insufficient to demonstrate convergence of the magnetic field growth. Although the effects of the LES are here rather modest, we expect them to be more significant at higher resolution, as observed in binary neutron star merger simulations.

We present the results of two searches for gravitational waves from the postmerger remnants of the binary neutron star coalescence events GW170817 and GW190425. The searches are fully coherent over 1800 s of data from the second (for GW170817) and third (for GW190425) observing runs of the LIGO and Virgo observatories. The searches compute the matched filter $\mathcal{F}$-statistic, and use a piecewise model of the rapidly changing frequency evolution appropriate for young neutron stars. No detection is claimed. The peak root-sum-squared strain upper limit at 50% detection probability ($h_{\mathrm{rss}}^{50\%}$) of both searches occurs at 1700 Hz and is estimated at $1.64\times {10}^{-22}{\mathrm{Hz}}^{-1/2}$ for GW170817, and $1.0\times {10}^{-22}{\mathrm{Hz}}^{-1/2}$ for GW190425. This is the first gravitational wave search for a neutron star remnant of GW190425.

We apply current analytical knowledge on the characteristic mass and linear evolution of miniclusters down to redshift $z=0$ to the hypothetical minicluster distribution of the Milky Way. Using the mass-radius relation and a core-halo relation for stable soliton solutions composed of axionlike particles (ALPs), we connect the galactic minicluster mass distribution to that of their ALP star cores. We consider different temperature evolutions of the ALP field with masses in the range ${10}^{-12}\mathrm{eV}\le m_a\le {10}^{-3}\mathrm{eV}$ and infer the abundance and properties of quantum chromodynamics (QCD) axion- and ALP stars in our galaxy. We reevaluate detection prospects for collisions of neutron stars with both ALP stars and miniclusters as well as relativistic ALP bursts, so-called Bosenovae. Our analysis shows that the collision rates between miniclusters and neutron stars can become as large as $\sim {10}^5{\mathrm{yr}}^{-1}{\mathrm{galaxy}}^{-1}$, but that the fraction of encounters that can lead to resonance between ALP mass and magnetosphere plasma frequency is generally well below $\sim 1{\mathrm{yr}}^{-1}{\mathrm{galaxy}}^{-1}$, depending on the ALP model. We confirm previous results that merger rates of ALP stars are extremely small $<{10}^{-12}{\mathrm{yr}}^{-1}$ ${\mathrm{galaxy}}^{-1}$, while their host miniclusters can merge much more frequently, up to $\sim {10}^3{\mathrm{yr}}^{-1}{\mathrm{galaxy}}^{-1}$ for the QCD axion. We find that Bosenovae and parametric resonance are much more likely to lead to observable signatures than neutron star encounters. We also suggest that a combination of accretion and parametric resonance can lead to observable radio lines for a wide range of ALP masses $m_a$ and photon-couplings $g_{a\gamma \gamma }$.

We study the thermodynamics of the Polyakov-Nambu-Jona-Lasinio model considering the effects of an effective chiral chemical potential. We offer a new parametrization of the Polyakov-loop potential depending on temperature and the chiral chemical potential which, when used together with a proper regularization scheme of vacuum contributions, predicts results consistent with those from lattice simulations.

This work investigates the phase structure of the nonrenormalizable ($3+1$)-dimensional Nambu–Jona-Lasinio (NJL) model with particular focus on inhomogeneous phases (IPs), where the chiral condensate is nonuniform in space, and the closely related moat regimes, where mesonic dispersion relations favor nonvanishing momenta. We use the mean-field approximation and consider five different regularization schemes including three lattice discretizations. The results within the different regularization schemes are systematically analyzed in order to study the dependence of the IP on the choice of regularization scheme and regulator value. The IP exhibits a drastic dependence on the chosen regularization scheme rendering any physical interpretation of results on inhomogeneous phases in this model doubtful. In contrast, we find only a mild scheme dependence of the moat regime suggesting that its existence is a consequence of the action of the NJL model and its symmetries and, thus, that it might also exist in QCD.

We study the transverse momentum ($q_T$) spectrum of the Higgs boson produced via the annihilation of massive quarks ($s$, $c$, $b$) in proton-proton collisions. Using soft-collinear effective theory (SCET) and working in the five-flavor scheme, we provide predictions at three-loop order in resummed perturbation theory (${\mathrm{N}}^3\mathrm{L}{\mathrm{L}}^{\prime }$). We match the resummed calculation to full fixed-order results at next-to-next-to-leading order (NNLO), and introduce a decorrelation method to enable a consistent matching to an approximate ${\mathrm{N}}^3\mathrm{LO}$ (${\mathrm{aN}}^3\mathrm{LO}$) result. Since the $b$-quark initiated process exhibits large nonsingular corrections, it requires special care in the matching procedure and estimation of associated theoretical uncertainties, which we discuss in detail. Our results constitute the most accurate predictions to date for these processes in the small $q_T$ region and could be used to improve the determination of Higgs Yukawa couplings from the shape of the measured Higgs $q_T$ spectrum.

The Future Circular Collider (FCC)—in its first incarnation as a lepton collider—will produce, according to the proposed design, more than 100 billion pairs of $\tau$ leptons after working for four years at the energy of the $Z$-boson resonance. The $\tau$ lepton is special because its relatively long lifetime makes it possible to reconstruct the momenta of neutrinos emitted in the single pion decay mode. The resulting large number of events is an ideal source for a full quantum tomography of the process that will test quantum entanglement and the violation of Bell inequality with unprecedented precision. In addition, the study of polarizations and spin correlations can provide a competitive determination of the Weinberg angle ${\theta }_W$ and constrain possible anomalous couplings in the neutral electroweak current. We utilize analytic results and Monte Carlo simulations to explore to what extent these goals might be accomplished.

Using an analytical result for the eigensystem of the linearized collision term for a classical system of massless scalar particles with quartic self-interactions, we show that the shear-stress linear response function possesses a branch-cut singularity that covers the whole positive imaginary semiaxis. This is demonstrated in two ways: (1) by truncating the exact, infinite system of linear equations for the rank-two tensor modes, which reveals the cut touching the origin; and (2) by employing the Trotterization techniques to invert the linear response problem. The former shows that the first pole tends toward the origin and the average separation between consecutive poles tends toward zero as power laws in the dimension of the basis. The latter allows one to obtain the response function in closed form in terms of Tricomi hypergeometrical functions, which possess a branch-cut on the above-mentioned semiaxis. This suggests that the presence of a cut along the imaginary frequency axis of the shear stress correlator, inferred from previous numerical analyses of weakly coupled scalar $\lambda {\phi }^4$ theories, does not arise due to quantum statistics but instead emerges from the fundamental properties of this system’s interactions.