The existence of a new spin-zero particle with a mass below the electroweak scale is predicted by several theoretical models. Searches for resonant production of photon pairs at the LHC are able to probe these models. We present a search for a narrow resonance produced through gluon fusion that decays into a pair of photons with an invariant mass between 10 and 70 GeV, using a proton-proton collision dataset from the CMS experiment. This dataset, corresponding to an integrated luminosity of $54.4{\mathrm{fb}}^{-1}$, was recorded in 2018 at a center-of-mass energy of 13 TeV using a newly introduced diphoton trigger that enabled exploration of the low-mass diphoton spectrum. No significant excess above the expected background is observed. Upper limits are set on the product of the gluon fusion production cross section and the branching fraction of the diphoton decay of a narrow resonance. An interpretation of these limits within an effective field theory framework for axionlike particles is also provided.

We investigate operator growth in a Brownian spin Sachdev-Ye-Kitaev (SYK) model with random all-to-all interactions, focusing on the full operator-size distribution. For Hamiltonians containing $q$-body interactions, we derive a closed master equation for the Pauli-string expansion coefficients and recast their dynamics into a generating-function formulation suitable for the large-$N$ limit. This approach allows us to diagonalize the leading-order evolution operator explicitly and obtain exact solutions for arbitrary initial operator distributions, including the effects of decoherence. Going beyond leading order, we develop a systematic $1/N$ expansion that captures higher-order corrections to the operator-size dynamics and the late-time behavior. Our results demonstrate that higher-order effects play a crucial role in operator scrambling and that the full operator-size distribution provides a more refined probe of quantum chaos in Brownian and open quantum systems.

We study Euclidean wineglass wormholes, which mediate the nucleation of inflationary spacetimes from an existing spacetime with asymptotically flat or anti–de Sitter regions. These wormholes are distinguished by the presence of a local maximum of the scale factor, which allows the analytically continued Lorentzian spacetime to expand after materialization. We present explicit numerical wormhole solutions supported either by an axionic field or a magnetic gauge field, in both cases in conjunction with a self-interacting scalar field. More exotic solutions, with multiple extrema of the scale factor, are also described. As we discovered recently, in the limit of small axionic or magnetic charge, wineglass wormhole solutions split into two separate geometries, one being the background spacetime and the other a disconnected no-boundary instanton. We study the associated topology changing transition in detail and provide an extensive discussion of both the properties and puzzles exhibited by this common family of wineglass/no-boundary instantons.

We derive a novel two-field four-dimensional integrable field theory (IFT) from 6D holomorphic Chern-Simons theory on twistor space. The four-dimensional IFT depends on a skew-symmetric linear operator acting on a Lie algebra, and when this operator is specialized to a solution of the modified classical Yang-Baxter equation, the IFT develops a semilocal symmetry associated with this solution. The resulting 4D analog of the Yang-Baxter sigma model is related by symmetry reduction to the well-known 2D Yang-Baxter sigma model. An important implication that we find is the embedding of the equations of motion of the 2D Yang-Baxter sigma model in the anti-self-dual Yang-Mills equations. The 6D Chern-Simons theory on twistor space can alternatively be symmetry reduced to a 4D Chern-Simons theory configuration with disorder surface defects. The latter realizes the Yang-Baxter sigma model, implying a “diamond” for the Yang-Baxter sigma model obtained from twistor space. We also show that the homogeneous 2D Yang-Baxter sigma model can be derived from a limit of our setup.

We continue the study of non-Abelian vortex string in 4D $\mathcal{N}=2$ supersymmetric QCD (SQCD) as critical superstring, and extend this analysis to $U(N)$ gauge theory with arbitrary even $N$ and $N_f=2N$ number of quarks. We introduce a special mass deformation and show that the SQCD hadron spectrum is still given by the string spectrum on the 2D $\mathcal{N}=2$ supersymmetric black hole. We perform a cross-check by computing the multiplicity of hadronic states of the high-energy part of the spectrum both from string and field theory pictures. We also clarify the spontaneous breaking of the global flavor symmetry by the vacuum expectation value of the massless baryon. We finally claim that phase diagram of $\mathcal{N}=2$ SQCD with $N_f=2N$ consists of the Higgs phase at weak coupling and string/hadronic phase at strong coupling, separated by phase transition, and is seen as a conifold transition from the string theory point of view.

We investigate the Lamb shift of centripetally accelerated atoms coupled to electromagnetic vacuum fluctuations. Focusing on a very small orbital radius (so that the tangential speed remains nonrelativistic and the proper centripetal acceleration can be extremely small), we show that the resulting level shift is intrinsically anisotropic and depends sensitively on the atomic polarization direction. For atoms polarizable along the rotation axis, the leading noninertial contribution enters only at second order in the orbital radius and can slightly increase the energy-level spacing. For atoms polarizable perpendicular to the rotation axis, the noninertial contribution appears already at zeroth order in the radius and always increases the energy-level spacing. Remarkably, when the angular velocity greatly exceeds the transition frequency, the rotation-induced correction can become comparable in magnitude to the inertial Lamb shift, indicating that circular motion can significantly modify the Lamb shift even in the regime of very small centripetal accelerations.

We have investigated the geometric phase acquired by a uniformly accelerated Unruh-DeWitt detector coupled to vacuum fluctuations of a massless conformal scalar field in anti–de Sitter (AdS) spacetime. Using the open-quantum-system formalism, we calculate the phase under three boundary conditions (Dirichlet, transparent, and Neumann) imposed on the field at the AdS boundary. Our findings reveal a sharp distinction between subcritical and supercritical accelerations. For subcritical accelerations, the detector evolves effectively as an isolated system, and the geometric phase is independent of both the AdS radius and the acceleration. For supercritical accelerations, however, topology-acceleration-induced phase corrections emerge and display pronounced boundary-condition dependence. When the AdS radius is smaller than the detector’s proper wavelength, the magnitude of the correction at large accelerations follows the ordering Neumann $>$ transparent $>$ Dirichlet. Moreover, over a finite interval of the detector’s weight parameter, both Dirichlet and Neumann boundary conditions produce a richer peak structure in the phase correction than the transparent case, with the detailed pattern governed by the competition between the acceleration and the detector’s energy gap. Finally, for transparent boundary conditions in the supercritical regime, the AdS phase correction closely resembles its de Sitter counterpart.

Leveraging the computational framework presented in Brunello and De Angelis [J. High Energy Phys. 07 (2024) 062], we evaluate the analytic scattering waveform in general relativity to second order, $G^3{M}^3/r{b}^2$ and to all orders in velocity. This new representation of the next-to-leading order waveform is well suited for numerical evaluation. Integrating the (modulus square of the) waveform over the angles on the celestial sphere, we also compute the power spectrum of the radiation to order $G^4$ numerically.

We investigate the decoherence of a quantum spatial superposition of a static particle in Schwarzschild and Reissner-Nordström black holes. By treating the particle as a localized classical source coupled to a quantum scalar field, we reformulate the decoherence process in the Danielson-Satishchandran-Wald gedankenexperiment through coherent state generation and derive the local expression for the decoherence functional in terms of the Wightman function. In the long-time limit, the decoherence rate is shown to be characterized by the low-frequency behavior of the Wightman function. We then employ the asymptotic matching method to calculate the analytical expressions of the Wightman functions in the Boulware, Unruh, and Hartle-Hawking vacua. We show that the decoherence behavior depends on the quantum state of the environmental field. While the Boulware vacuum gives vanishing decoherence for a static superposition, the thermal effects associated with Hawking radiation in the Unruh and Hartle-Hawking vacua can induce nonvanishing decoherence.

We investigate the systematic biases in measuring orbital eccentricity for binary black hole (BBH) mergers that arise when higher-order modes (HOMs) of gravitational waves are neglected in waveform modeling. Using Bayesian inference with the state-of-the-art eccentric, spin-aligned, higher-mode effective-one-body model seobnrv5ehm, we reanalyze six previously suggested eccentric gravitational-wave events—GW190521, GW190620, GW190701, GW191109, GW200129, and GW200208_222617. Comparing results with its dominant-mode-only counterpart seobnrv5e, we find no statistically significant HOM-induced bias in eccentricity for any of these events, including GW190521, whose eccentricity has been debated in the literature. To explore representative parameter regimes vulnerable to HOM omission, we perform a broad zero-noise injection campaign varying detector-frame total mass, mass ratio, eccentricity, inclination, and network SNR. We find that significant systematic biases (${\mathrm{\Delta }}_e/\sigma >1$) arise predominantly in systems with relatively high total mass ($M^{\det }\gtrsim 120M_{\odot }$), highly asymmetric mass ratios ($q\gtrsim 4$), large inclinations (${\theta }_{\mathrm{JN}}\gtrsim 30°$), and high SNRs (${\rho }_{\mathrm{mf}}^N\approx 50$). Notably, for quasicircular BBHs with approximately $M^{\det }\gtrsim 140M_{\odot }$, our results suggest that neglecting HOMs may lead to strong false-positive evidence for nonzero eccentricity. By contrast, for lower-mass systems ($M^{\det }\sim 100M_{\odot }$), HOM exclusion produces negligible eccentricity biases. Our results demonstrate that although current eccentric candidates are not impacted by HOM omission, future eccentricity measurements—particularly for relatively massive, asymmetric, or edge-on systems—require HOM-inclusive waveforms to avoid substantial systematic errors.

Exploiting the correspondence between Kerr–Newman–(A)dS black hole solutions in general relativity and their constant-curvature counterparts in $f(R)$ gravity, we employ a unified framework to investigate the horizon structure and extremal configurations of these black holes, focusing primarily on the anti–de Sitter case. By solving the extremality conditions with respect to the squared rotation parameter $a^2$ and the inverse curvature scale $l^{-2}$, we obtain closed analytic relations that provide a transparent parametrization of the extremal branch in the $(a^2,l^{-2})$ parameter space. We determine the physically admissible domain of the rotating extremal branch and derive the corresponding critical charge, $q_{\max }=M/2$, at which the metric becomes singular and the branch reaches its critical rotation limit. For vanishing electric charge, the rotation parameter decreases monotonically along the extremal branch and remains bounded from below, implying the existence of a minimal rotation, $a_{\min }=3\sqrt{3}M/8$. The rotating extremal branch also exhibits a distinguished internal point at which the normalized rotational and curvature scales coincide. The inclusion of electric charge introduces an additional competing scale, broadening the rotating extremal branch while lowering the corresponding minimal rotation to $a_{\min }=M/4$ at the critical charge $q_{\max }=M/2$. Comparing these results with the corresponding de Sitter case, we show that extremality in AdS is constrained by a geometric end point, whereas the dS branch exhibits a considerably richer structure characterized by an ultraextremal maximum and a subsequent decay toward the nonrotating limit. Finally, we demonstrate that the algebraic mass constraint associated with the quartic horizon equation completely removes the real-root structure, yielding a class of solutions without physical horizons.

Born-Infeld new massive gravity completes new massive gravity to all orders in curvature through the determinant of the metric shifted by the Einstein tensor. We recast it with an independent auxiliary metric $q_{\mu \nu }$, whose algebraic equation of motion $q_{\mu \nu }=g_{\mu \nu }+\frac{\sigma }{m^2}{G}_{\mu \nu }(g)$ recovers the determinant action exactly on the regular branch and resums the infinite curvature series into a single relation. In the desensitized variable $P^{\mu \nu }=\sqrt{-q}{q}^{\mu \nu }$, the three-dimensional action is polynomial, with all derivative dependence carried by the coupling $P^{\mu \nu }{G}_{\mu \nu }(g)$. The formulation makes known properties follow with substantially less algebra: the unique vacuum follows in one line, and the quadratic action yields a single Pauli-Fierz massive spin-2 field with the Fierz-Pauli tuning generated rather than imposed. On locally anti–de Sitter backgrounds, the conserved charges, Bañados–Teitelboim–Zanelli mass and angular momentum, central charge, and entropy reduce to the Einstein results times a common factor. The formulation also isolates the nonlinear degree-of-freedom problem in the right variables, leaving the full Dirac count to separate work.

We demonstrate the uniqueness of the spacetimes recently found by us [Phys. Rev. D 112, 064076 (2025)]. First, we prove that the conformal-to-Carter metric ansatz we used therein is the only one possible for stationary axisymmetric geometries that are of Weyl type D, with geodesic and shear-free principal null directions which are orthogonal to polar directions, and whose specific 1-form $\theta$ is closed. Because this result is general, without employing any field equations, such conformal-to-Carter metric may find interesting applications also in various alternative theories of gravity. Then, we show that in the Einstein-Maxwell theory the only nontrivial electrovacuum solution for the conformal-to-Carter metric with the fully nonaligned and non-null electromagnetic field is the Ovcharenko-Podolský class found in 2025. Complementarily, the only solution with the double-aligned and non-null electromagnetic field is the Plebański-Demiański class found in 1976.

We present a quantization of unimodular gravity in the connection representation for a homogeneous, isotropic, and spatially flat cosmological model without matter. In this model, the wave function is governed by a Schrödinger-type equation derived from a reduced phase space approach. Our analysis suggests that, within this minimal setting, the regularity of the operators and the self-adjointness of the Hamiltonian operator are incompatible with a negative cosmological constant. For a positive cosmological constant, the wave functions vanish at zero spatial volume. This behavior emerges as a consequence of enforcing the unimodular condition at the quantum level. Semiclassical fluctuations of the geometry are evaluated and discussed in relation to the cosmological constant problem.

We investigate the pole structure of Kerr black-hole perturbations in the frequency domain, focusing on the building blocks of the Green’s function for the radial Teukolsky equation: the homogeneous radial solutions, the connection coefficients, and the Green’s function itself. We show that the homogeneous solutions and the local connection coefficients develop simple poles at the Matsubara frequencies, thereby establishing the Matsubara pole structure explicitly within the Teukolsky formalism for asymptotically flat Kerr black holes. At the level of the local fixed-sector connection formula, the explicit Matsubara-pole factors cancel in the ratio of connection coefficients entering a decomposed Green’s function contribution. We also identify higher-order zero-frequency singularities in the decomposed Green’s function contributions, which scale as ${\omega }^{-2l-1}$ and cancel collectively in the total radial Green’s function. These results clarify how Matsubara poles and sectoral zero-frequency singularities arise in the Teukolsky formalism and provide a frequency-domain foundation for understanding prompt response in time-domain ringdown waveforms in Kerr spacetime.

We study the formation of asteroid-mass primordial black holes (PBHs) as a dark matter candidate in supersymmetric extensions of the Standard Model. We show that the presence of heavy particles predicted in the minimal supersymmetric Standard Model (MSSM) can lead to a transient softening of the equation of state of the Universe during their nonrelativistic transition, enhancing PBH formation. We compute the effective equation of state for different realizations of the MSSM mass spectrum, parametrized by three characteristic mass scales. Assuming a broad and approximately scale-invariant primordial curvature power spectrum, we evaluate the resulting PBH mass functions and compare them with current observational constraints. We find that, for supersymmetric masses above $\sim {10}^5\mathrm{GeV}$, the PBH mass function is significantly enhanced in the asteroid-mass window, allowing PBHs to account for the total dark matter abundance without violating existing bounds. In contrast, within the Standard Model the same configurations lead to PBH mass functions that are observationally excluded. For lighter supersymmetric mass spectra, PBH production is shifted toward masses above $\sim {10}^{22}\mathrm{g}$, which are strongly constrained by microlensing searches, thereby reducing their allowed contribution to the dark matter density.

We propose a new nonminimally coupled quintessence model to account for the late-time dark energy dynamics indicated by recent dark energy spectroscopic instrument measurements. Within this framework, the quintessence density begins to decrease only when it starts to dominate the Universe, which naturally accounts for the late-time onset of dark energy weakening. The coupling also induces a sign change in the effective energy transfer between dark matter and dark energy during cosmic evolution. While the scalar field itself remains canonical and never crosses the phantom divide, the modified evolution of the dark matter density gives rise to an effective crossing behavior in the observationally inferred dark energy sector. Compared with both $\mathrm{\Lambda }\mathrm{CDM}$ and $w_0{w}_a\mathrm{CDM}$ models, our model is favored more strongly by current cosmological data. This work may provide a promising avenue for understanding the observational late-time weakening of dark energy and the origin of its dynamics.

Classically scale-invariant (and perturbative) theories provide a way to understand large hierarchies, as scales are generated through dimensional transmutation. They always lead to first-order phase transitions, since symmetries are radiatively broken, and they generically feature quasiflat potentials, which are suitable for inflation. We construct a simple but fully realistic model of this kind that accounts for all observational evidence of new physics and is remarkably compatible with the most recent constraints on inflationary observables from both the Planck/BICEP/Keck and the Atacama Cosmology Telescope Collaborations. This model illustrates how classical scale invariance generically leads to a nonstandard cosmology in which inflation occurs in two stages: a slow-roll stage and a thermal stage, separated by a radiation-dominated era.

We present a cosmological reassessment of light sterile-neutrino scenarios, examining whether current observations exclude sterile neutrinos as a class or primarily constrain the fully thermalized case. We consider three distinct realizations; (i) a fully thermalized sterile (FTS) species, (ii) a different-temperature sterile-neutrino thermal relic (DTS) relative to the active neutrino background and (iii) a Dodelson-Widrow-like (DW) sterile neutrino with reduced phase-space normalization. Constraints are derived within both $\mathrm{\Lambda }\mathrm{CDM}$ and the CPL dynamical dark-energy framework using combinations of Planck-Cosmic Microwave Background data, DESI DR2 BAO measurements, and the PantheonPlus and Union3 Type Ia supernova samples. For baseline data combinations without a local $H_0$ prior, the FTS scenario is strongly disfavored in both cosmological models. Adding the local $H_0^{\mathrm{DN}}$ prior allows $\mathrm{\Lambda }\mathrm{CDM}+\mathrm{FTS}$ to accommodate the high local $H_0$ value and become statistically competitive with standard $\mathrm{\Lambda }\mathrm{CDM}$ once SNIa data are included, although the sterile-neutrino mass remains consistent with zero. By contrast, partially populated sterile-neutrino scenarios remain viable: the DW realization is broadly compatible with current observations, while the DTS scenario yields the least cosmological pressure among the cases considered. Overall, cosmological data mainly require a strongly suppressed effective sterile abundance, leading to tight constraints on $m_s^{\mathrm{eff}}$ while allowing substantially weaker bounds on the physical sterile mass. We conclude that current observations do not generically exclude sterile neutrinos, but rather place strong pressure on fully thermalized or highly populated scenarios, highlighting the importance of production history and phase-space distribution when interpreting cosmological constraints.

Primordial non-Gaussianity (PNG) is a common prediction of a wide class of inflationary models. Equilateral-type PNG, generically predicted by single-field inflationary models with higher-derivative interactions, imprints subtle but measurable signatures on the large-scale distribution of matter. An important parameter of these imprints is the PNG-induced bias coefficient $b_{\psi }$, which quantifies how the abundance and clustering of dark matter halos and galaxies respond to mode coupling in the initial conditions. Measuring $b_{\psi }$ is important for constraining equilateral PNG, yet it is notoriously challenging due to its degeneracy with Gaussian scale-dependent bias contributions. In this work, we present the first precision measurements of equilateral $b_{\psi }$ for dark matter halos using effective field theory at the field level. We show that this approach disentangles PNG effects from those of the Gaussian bias by virtue of noise variance cancellation. We compare our results with the phenomenological predictions based on the peak-background split model, finding some agreement at the qualitative level on the redshift and mass dependence, but poor agreement at the quantitative level. We present a fitting formula for $b_{\psi }$ as a function of the linear bias, which can be used to set priors in PNG searches with ongoing and future galaxy surveys.