We study the dominant signatures that arise in Higgs physics at colliders when extending the Standard Model (SM) with a Yukawa interaction to heavy neutral leptons, while suppressing their mixing to active neutrinos. We focus on the production of heavy neutral leptons from Higgs bosons that subsequently decay via the Higgs to SM fermions to determine the experimental reach at the LHC detectors and far detectors such as FASER and MATHUSLA. We also determine the impact of precision Higgs constraints on beyond-SM parameters in this scenario.

The juxtaposition of the precision of lepton flavor measurements and the limited energy range of the Large Hadron Collider (LHC) to discover dynamical degrees of freedom linked to the generation of the observed lepton mass patterns naively suggests only a limited relevance of the LHC’s high luminosity phase. This, potentially, extends to future colliders. Using the concrete example of the type-II seesaw model and its effective field theory extension, we show that blind directions create a rich phenomenological interplay of muon precision measurements and electroweak resonance searches at present and future colliders, with testable implications for the HL-LHC phase.

Axion rotations can simultaneously explain the dark matter abundance and the baryon asymmetry of the Universe by kinetic misalignment and axiogenesis. We consider a scenario in which the Peccei-Quinn symmetry breaking field is as large as the Planck scale during inflation and the axion rotation is initiated by the inflaton-induced potential immediately after the end of inflation. This is a realization of the cogenesis scenario that is free of problems with domain walls and isocurvature perturbations thanks to large explicit Peccei-Quinn symmetry breaking at the Planck scale during inflation. The baryon asymmetry can be more efficiently produced by leptoaxiogenesis, in which case the axion mass is predicted to be larger than $\mathcal{O}(0.1)\mathrm{meV}$. We also discuss a UV complete model in supersymmetric theories.

The SU(3) gauge theory with $N_f=8$ nearly massless Dirac fermions has long been of theoretical and phenomenological interest due to the near-conformality arising from its proximity to the conformal window. One particularly interesting feature is the emergence of a relatively light, stable flavor-singlet scalar meson $\sigma (J^{PC}=0^{++})$ in contrast to the $N_f=2$ theory QCD. In this work, we study the finite-volume dependence of the $\sigma$ meson correlation function computed in lattice gauge theory and determine the $\sigma$ meson mass and decay constant extrapolated to the infinite-volume limit. We also determine the infinite-volume mass and decay constant of the flavor-nonsinglet scalar meson $a_0$.

We present a phenomenological study of the $\gamma {\gamma }^{*}\to K{\overline{K}}^{*}(892)$ process by including the $s$-channel production of the $\eta (1475)$ and $f_1(1420)$ resonances. The nonresonant channel via $K$- and $K^{*}$-exchanges is investigated carefully by performing the Lorentz tensor decomposition and is constructed to yield a correct high-energy Regge behavior. The transition form factor of $f_1(1420)$ is adjusted to achieve a reasonable description of the existing L3 data in the $f_1(1420)$ resonance region. This model is intended to serve as a Monte Carlo generator for the analysis currently being performed by the BESIII Collaboration. We also estimate the polarized $\gamma {\gamma }^{*}\to K{\overline{K}}^{*}(892)$ cross sections and demonstrate how to extract the transition form factors of $f_1(1420)$ from the polarized cross sections.

We employ a dispersion relation that allows us to recover the phase of the electromagnetic form factor of the pion from its absolute value above threshold. Compared to alternative approaches building on the phase, this approach builds on experimental input directly accessible at colliders. Employing the precise datasets from the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}$ reaction, we obtain the phase of the electromagnetic form factor up to 2.5 GeV, well beyond standard dispersive approaches. In addition, we separate the isovector and isoscalar components, that allows us to extract the $P$-wave $\pi \pi$ phase shift. We also provide relevant results, including the radius of the form factor and bounds in the spacelike region. Last, but not least, the study assess potential systematic uncertainties from the interpolation method and potential zeros of the form factor.

We analyze the resonance contributions to the generalized Baldin sum rule, namely the sum of the generalized electric and magnetic nucleon polarizabilities ${\alpha }_E(Q^2)$ and ${\beta }_M(Q^2)$, within the holographic QCD model by Witten, Sakai, and Sugimoto (WSS). In particular, we account for the contributions from the first low-lying nucleon resonances with spin-$1/2$ and spin-$3/2$ and both parities. After having extrapolated the WSS model parameters to fit experimental data on baryonic observables, we compare our findings with alternative predictions in literature, finding a qualitative agreement with all of them. Moreover, at least for the proton case, where data are available, our results are in qualitative accordance with resonance contributions extracted from experimental nucleon-resonance helicity amplitudes.

We study the linearized gravity theory in the Newman-Unti gauge in the near horizon region of the de Sitter spacetime. The linearized Einstein equation involves the cosmological constant. The near horizon symmetry consists of near horizon supertranslation and near horizon superrotation. We compute the near horizon supertranslation charge and find the proper near horizon falloff conditions that uncover a soft graviton theorem from the Ward identity of the near horizon supertranslation.

We propose relativistic Luttinger fermions as a new ingredient for the construction of fundamental quantum field theories. We construct the corresponding Clifford algebra and the spin metric for relativistic invariance of the action using the spin-base invariant formalism. The corresponding minimal spinor has 32 complex components, matching with the degrees of freedom of a standard-model generation including a right-handed neutrino. The resulting fermion fields exhibit a canonical scaling different from Dirac fermions and thus support the construction of novel relativistic and perturbatively renormalizable, interacting quantum field theories. In particular, new asymptotically free self-interacting field theories can be constructed, representing first examples of high-energy complete quantum field theories based on pure matter degrees of freedom. Gauge theories with relativistic Luttinger fermions exhibit a strong paramagnetic dominance, requiring large non-Abelian gauge groups to maintain asymptotic freedom. We comment on the possibility to use Luttinger fermions for particle physics model building and the expected naturalness properties of such models.

The gravitational capture of a stellar-mass object by a supermassive black hole represents a unique probe of warped spacetime. The small object, typically a stellar-mass black hole, describes a very large number of cycles before crossing the event horizon. Because of the mass difference, we call these captures extreme-mass-ratio inspirals (EMRIs). Their merger event rate at the Galactic Center is negligible, but the amount of time spent in the early inspiral is not. Early EMRIs (E-EMRIs) spend hundreds of thousands of years in band during this phase. At very early stages, the peak of the frequency will not change during an observational time. At later stages in the evolution, it will change a bit and finally the EMRI explores a wide range of them when it is close to merger. We distinguish between “monocromatic” E-EMRIs, which do not change their (peak) frequency, oligochromatic E-EMRIs, which explore a short range and polychromatic ones, and the EMRIs which have been discussed so far in the literature. We derive the number of E-EMRIs at the Galactic Center, and we also calculate their signal-to-noise ratios (SNR) and perform a study of parameter extraction. We show that parameters such as the spin and the mass can be extracted with an error which can be as small as ${10}^{-11}$ and ${10}^{-5}{M}_{\odot }$. There are between hundreds and thousands of E-EMRIs in their monochromatic stage at the Galactic Centre (GC), and tens in their oligochromatic phase. The SNR ranges from a minimum of 10 (larger likelihood) to a maximum of ${10}^6$ (smaller likelihood). Moreover, we derive the contribution signal corresponding to the incoherent sum of continuous sources of oligochromatic E-EMRIs with two representatives masses, $10M_{\odot }$ and $40M_{\odot }$, and show that their curves will cover a significant part of Laser Interferometer Space Antennas (LISAs) sensitivity curve. Depending on their level of circularization, they might be detected as individual sources or form a foreground population.

We study trajectories of test particles around a luminous, static, spherically symmetric neutron star, under the combined influence of gravity and radiation. In general relativity, for Schwarzschild spacetime, an equilibrium sphere (the Eddington capture sphere) is formed for near-Eddington luminosities. We generalize these results to a broad class of static, spherical spacetimes. We also study the dynamics of particles in a strong radiation field in spherical spacetimes. The results are illustrated for two cases, Reissner-Nordström spacetime of a charged spherical object in general relativity and Kehagias-Sfetsos spacetime, arising from the Hořava-Lifshitz gravity theory. Our findings apply to neutron stars under gravitational field equations different from the vacuum Einstein field equations of general relativity, such as in modified theories of gravity, the only requirement being that test particles follow geodesics in the absence of the radiation field. The effects that we describe are, in principle, measurable through observations of x-ray bursts of neutron stars. Hence, detailed future studies could use such observations to test gravity theories in the strong-field regime, provided that the impact of the spacetime geometry can be disentangled from the astrophysical uncertainties.

In this paper, we derive the generic solution of the Newman-Penrose equations in the Newman-Unti gauge with vanishing curvature tensor. The obtained solutions are the vacua of the gravitational theory which are connected to the derivations in metric formalism from exponentiating the infinitesimal BMS generators in the Bondi-Metzner-Sachs (BMS) gauge in Compère and Long [J. High Energy Phys. 07 (2016) 137 and Classical Quantum Gravity 33, 195001 (2016)] by a radial transformation. The coordinate transformations in the Newman-Unti gauge connecting each vacuum are also obtained. We confirm that the supertranslation charge of the gravitational vacua with respect to global considerations vanishes exactly not only in the Einstein theory but also when including the Holst, Pontryagin, and Gauss-Bonnet terms, which verifies that the gravitational vacua are not affected by those trivial or boundary terms.

We investigate in detail the weak-field gravitational lensing of a relativistic neutral massive particle induced by a regular black-bounce-Schwarzschild black hole proposed by Simpson and Visser. Starting with the calculation of the gravitational deflection of the massive particle up to the third post-Minkowskian order, the Virbhadra-Ellis lens equation is solved perturbatively beyond the weak-deflection limit to achieve the expressions for the lensing observables of the primary and secondary images of a pointlike particle source. The main observables contain not only the positions, the flux magnifications, and the gravitational time delays of the individual images, but also the positional relations, the magnification relations (including the total magnification), the magnification centroid, and the differential time delay. We then discuss the velocity-induced effects originated from the deviation of the particle’s initial velocity from the speed of light on the black-bounce-Schwarzschild lensing observables of the images of a pointlike light source and the effects induced by the bounce parameter of the spacetime on the measurable image properties of Schwarzschild lensing of the massive particle. As an application of the results, we model the supermassive black hole in the Galactic Center (i.e., Sgr ${\mathrm{A}}^{*}$) as the lens and focus on evaluating the possibilities to detect the new velocity- and bounce-induced effects on the practical lensing observables and analyzing the dependence of these effects on the parameters.

In this paper, we focus on massive Einstein-dilaton gravity including the coupling of dilaton scalar field to massive graviton terms, and then derive static and spherically symmetric solutions of charged dilatonic black holes in four dimensional spacetime. We find that the dilatonic black hole could possess different horizon structures for some suitably parameters. Then, we also investigate the thermodynamic properties of charged dilatonic black holes where $f(r)$ approaches $+\infty$ and $-\infty$, respectively.

Recently, Cui et al. [Nature (London) 621, 711 (2023)] reported that the jet nozzle of M87* exhibits a precession with a period of approximately 11 years. This finding strongly suggests that the supermassive black hole in the core of M87 galaxy is a spinning black hole with a tilted accretion disk. In this paper, our aim is to utilize these observations to preliminarily constrain the parameters of the black hole by using the characteristics of the geodesic motion. Firstly, we investigate the properties of the spherical orbits and the innermost stable spherical orbits with constant radius. The corresponding angular momentum, energy, and Carter constant for both prograde and retrograde orbits are calculated. We find that, compared to equatorial circular orbits, these quantities exhibit significant differences for fixed tilt angles. Moreover, the Carter constant takes positive values for nonvanishing tilt angles. Notably, the presence of misalignment of the orbit angular momentum and black hole spin leads to a precession effect in these spherical orbits. We then make use of these spherical orbits to model the warp radius of the tilted accretion disk, which allows us to determine the corresponding precession period through the motion of massive particles. Further comparing with the observation of M87*, the relationship between the black hole spin and the warp radius is given, through which if one of them is tested, the other one will be effectively determined. Additionally, our study establishes an upper bound on the warp radius of the accretion disk. These findings demonstrate that the precession of the jet nozzle offers a promising approach for testing the physics of strong gravitational regions near supermassive black holes.

We compute the purely local-in-time (scale-free and logarithm-free) part of the conservative dynamics of gravitationally interacting two-body systems at the fourth post-Minkowskian order, and at the thirtieth order in velocity. The gauge-invariant content of this fourth post-Minkowskian local dynamics is given in two ways: (i) its contribution to the on-shell action (for both hyperboliclike and ellipticlike motions); and (ii) its contribution to the effective one-body Hamiltonian (in energy gauge). Our computation capitalizes on the tutti frutti approach [D. Bini et al., Novel approach to binary dynamics: Application to the fifth post-Newtonian level, Phys. Rev. Lett. 123, 231104 (2019)] and on recent post-Minkowskian advances [Z. Bern et al., Scattering amplitudes, the tail effect, and conservative binary dynamics at O(G4), Phys. Rev. Lett. 128, 161103 (2022); C. Dlapa et al., Conservative dynamics of binary systems at fourth post-Minkowskian order in the large-eccentricity expansion, Phys. Rev. Lett. 128, 161104 (2022); C. Dlapa et al., Local in time conservative binary dynamics at fourth post-Minkowskian order, 132, 221401 (2024)].

The recently computed post-Newtonian (PN) gravitational-wave phasing up to 4.5PN order accounts for several novel physical effects in compact binary dynamics such as the tail of the memory, tails of tails of tails, and tails of mass hexadecapole and current octupole moments. Therefore, it is instructive to assess the ability of current-generation (2G) detectors such as LIGO and Virgo; next-generation (XG) ground-based gravitational wave detectors such as the Cosmic Explorer and Einstein Telescope; and space-based detectors like LISA to test the predictions of PN theory at these orders. Employing the Fisher information matrix, we find that the projected bounds on the deviations from the logarithmic PN phasing coefficient at 4PN are $\mathcal{O}({10}^{-2})$ and $\mathcal{O}({10}^{-1})$ for XG and 2G detectors, respectively. Similarly, the projected bounds on the other three PN coefficients that appear at 4PN and 4.5PN are $\mathcal{O}({10}^{-1}–{10}^{-2})$ for XG and $\mathcal{O}(1)$ for 2G detectors. LISA observations of supermassive BHs could provide the tightest constraints on these four parameters in the range $\mathcal{O}({10}^{-4}–{10}^{-2})$. The variation in these bounds is studied as a function of total mass and the mass ratio of the binaries in quasicircular orbits. These new tests are unique probes of higher order nonlinear interactions in compact binary dynamics and their consistency with the predictions of general relativity.

We investigate quantum characteristics around Schwarzschild black hole, exploring various quantum resources and their interplay in curved space-time. Our analysis reveals intriguing behaviors of quantum coherence, global and genuine multipartite entanglement, first-order coherence, and mutual information in different scenarios. Initially, we consider three particles shared among Alice, Bob, and Charlie in a Minkowski space far from the event horizon, where these particles are correlated via Greenberger-Horne-Zeilinger-type correlation. While Alice’s particle remains in Minkowski space, Bob and Charlie accelerate towards the event horizon, experiencing black hole evaporation and generating antiparticles correlated via the Hawking effect. We employ the Kruskal basis formulation to derive a pentapartite pure state shared among particles inside and outside the event horizon. Investigating different scenarios among particles both inside and outside the event horizon, we observe how quantum resources evolve and distribute among consideration of different particles with Hawking temperature and mode frequency. The trade-off relationship between first-order coherence and concurrence fill persists, indicating the intricate interplay between coherence and entanglement. Notably, the mutual information between external observers and particles inside the black hole becomes nonzero, deepening our understanding of quantum effects in curved space-time and shedding light on the quantum nature of the black hole. We believe that these findings will pave the way for future investigations into the fundamental quantum mechanical aspects of gravity under extreme environments.

The cosmological constant term can be seen as a constant potential for a (scalar) field. In this viewpoint, at late times, the field is stopped rolling and behaves as a cosmological constant ($w=-1$). While at the early Universe, its kinetic term can be dominant and behaves as a stiff fluid ($w=+1$). This new phase lowers the cosmological sound horizon by increasing the Hubble parameter for very high redshifts. Consequently, the lower cosmological sound horizon results in the higher Hubble constant at the present time. This early phase ends before the photon decoupling, so we do not expect any new physics after the last scattering surface. We checked this model in the presence of (reduced) CMB, BAOs, SNs, and $H_0$ datasets and could show the Hubble tension is fully relieved.

Axion dark matter can form stable, self-gravitating, and coherent configurations known as axion stars, which are rendered unstable above a critical mass by the Chern-Simons coupling to electromagnetism. We study, using numerical relativity, the merger and subsequent decay of compact axion stars. We show that two subcritical stars can merge, and form a more massive, excited, and critical star, which survives for a finite period before rapidly decaying via electromagnetic radiation. We find a rich multimessenger signal, composed of gravitational waves, electromagnetic radiation, and axion radiation. The gravitational wave signal is broken into two parts: a weak and broad signal from the merger, followed by a much stronger signal of almost fixed frequency from the decay. The electromagnetic radiation follows only the gravitational waves from the decay, while the axion signal is continuous throughout the process. We briefly discuss the detectability of such a signal.