We extend the arguments of Maldacena and Núñez to include higher codimension brane setups and derive a new no-go theorem. Specifically, we show that, under reasonable assumptions on the energy-momentum conservation and the bulk curvature, codimension-two branes fail to support stable de Sitter solutions. For codimensions higher than two embedded in a compact internal space, we show that negative tension sources would be required. This result places strong constraints on the viability of higher-dimensional braneworld models as a means to obtain de Sitter space within string theory.

The axion quark nugget (AQN) model is an emerging candidate for cold dark matter, and proposes that dark matter consists of (anti)quarks in a color superconducting state enclosed by an axion domain wall. We performed the first dedicated AQN experiment using an axion haloscope, based on the scenario that antimatter AQNs could annihilate with Earth matter and release relativistic axions. This experiment employed a high-temperature superconducting microwave cavity that achieved a quality factor exceeding one million in a strong magnetic field, alongside a quantum-noise-limited Josephson parametric amplifier. Combined with an additional experiment using a large-volume copper cavity, our investigation focused on the range of axion rest mass between $1.9\mathrm{\mu }\mathrm{eV}$ and $9.3\mathrm{\mu }\mathrm{eV}$, and attempted to detect the daily modulation of the signal predicted by the model. While no definitive signals were detected, this study establishes the initial groundwork for exploring broader parameter spaces in future experiments.

We establish for the first time the conditions that must be imposed on the action for a magnetic universe in a theory of nonlinear electrodynamics in order to have an asymptotically de Sitter initial state followed by a slow roll inflationary phase. We show that models so far proposed in the literature do not allow for a prolonged inflationary phase consistent with observations. We construct a Lagrangian that reduces to the Maxwell one in weak field; this is the only class of models that satisfies the required conditions for slow roll in the early Universe.

We propose a new collider signature for the composite origin of the electroweak symmetry breaking of the standard model. The Higgs sector consists of new fundamental fermions (hyperquarks), which confine at a hadronization scale ${\mathrm{\Lambda }}_{\mathrm{HC}}\sim \mathrm{few}$ TeV. At energies above ${\mathrm{\Lambda }}_{\mathrm{HC}}$, the Drell-Yan production of the hyperquarks leads to the production of a few electroweak bosons, in analogy with hadron production in QCD at $e^{+}{e}^{-}\to q\overline{q}$ around a few GeV. We show that this regime can be probed at future colliders, namely the proposed 100 TeV hadron collider (FCC-hh) and a 10 TeV muon collider. Together with the direct discovery of electroweak resonances, the multi-electroweak boson signature provides a smoking gun for Higgs compositeness.

Harmonizing classical and quantum worlds is a major challenge for modern physics. A significant portion of the scientific community supports the notion that classical mechanics is an effective theory that arises from quantum mechanics. Recently, the present authors have argued that this should not be the case, as quantum mechanics is not trustworthy for describing the center of mass of systems with masses $m$ much larger than the Planck mass $M_{\mathrm{P}}$. In this vein, a simple gravitational self-decoherence model was proposed, describing how the center of mass of quantum systems would classicalize for $m\sim M_{\mathrm{P}}$ [G. H. S. Aguiar and G. E. A. Matsas, Phys. Rev. D 112, 046004 (2025)]. Here, we show that our model does not prevent macroscopic systems (with classical centers of mass) from harboring quantum internal vibrations (as has been observed in the laboratory).

We study a large class of domain wall solutions with $Mk{w}_3\times {\mathrm{\Sigma }}^2$ and $Mk{w}_2\times {\mathrm{\Sigma }}^3$ slices from maximal gauged supergravity in six dimensions. ${\mathrm{\Sigma }}^2$ and ${\mathrm{\Sigma }}^3$ are given by a Riemann surface and a three-manifold with constant curvature while $Mk{w}_{3,2}$ denotes three-/two-dimensional Minkowski space. We consider the maximal gauged supergravity with $CSO(p,q,5-p-q)$ and $CSO(p,q,4-p-q)⋉{\mathbb{R}}^4$ gauge groups arising from an $S^1$ reduction of seven-dimensional maximal gauged supergravity with $CSO(p,q,5-p-q)$ and $CSO(p,q,4-p-q)$ gauge groups. The two types of gauge group can be embedded in type IIA theory via consistent truncations on $H^{p,q}\times {\mathbb{R}}^{5-p-q}$ and $H^{p,q}\times {\mathbb{R}}^{4-p-q}\times S^1$, respectively. By performing topological twists on ${\mathrm{\Sigma }}^2$ and ${\mathrm{\Sigma }}^3$, we find a number of solutions interpolating between locally flat domain walls in the UV and curved domain walls with $Mk{w}_3\times {\mathrm{\Sigma }}^2$ and $Mk{w}_2\times {\mathrm{\Sigma }}^3$ slices in the IR. Many solutions admit physical IR singularities and can be interpreted as holographic renormalization group (RG) flows across dimensions from five-dimensional field theories to three- and two-dimensional nonconformal field theories in the IR. Upon being uplifted to type IIA theory, we expect the solutions to describe brane configurations involving D4-branes wrapped on ${\mathrm{\Sigma }}^2$ and ${\mathrm{\Sigma }}^3$.

In scalar-tensor theories, compact objects may experience spontaneous scalarization. Recently, it was shown that matter-induced spontaneous scalarization of neutron stars is predominantly associated with a first-order phase transition. Here we consider matter-induced spontaneous scalarization of boson stars. Employing a repulsive quartic potential for the bosonic matter, we find only first-order phase transitions.

Next-generation gravitational wave (GW) experiments will explore higher frequencies where wavelengths become comparable to the dimensions of the detector. In this regime, GWs may be detected not only through mechanical deformations from tidal forces, but also via induced effective currents in electromagnetic background fields. However, the calculation of these signals often requires transforming the GW metric to all orders into the laboratory frame of the detector. Here, we derive a closed-form expression for the metric transformation of general chirplike waveforms expressed in terms of the transverse-traceless GW metric components, their integral, and their derivative. For more complex signals, where analytical integration is impractical, we provide an efficient approximation based on Taylor expansions of the retarded time to coalescence. We find that quasi-Newtonian chirp signals can be accurately transformed using a monochromatic approximation, while also demonstrating that more complex waveforms require the general transformation, which we derive. Thus, the calculated transformations provide essential tools for designing high-frequency GW experiments and analyzing signals from compact object mergers at mega- to gigahertz frequencies.

Inflation is known to produce large infrared scalar fluctuations. Further, if a scalar field ($\chi$) is nonminimally coupled with gravity through $\xi {\chi }^{2}R$, those infrared modes experience tachyonic instability during and after inflation. Those large nonperturbative infrared modes can collectively produce hot big bang universe upon their horizon entry during the postinflationary period. We indeed find that for reheating equation of state (EOS), $w_{\varphi }>1/3$, and coupling strength, $\xi >1/6$, large infrared fluctuations lead to successful reheating. We further analyze perturbative reheating by solving the standard Boltzmann equation in both Jordan and Einstein frames, and compare the results with the nonperturbative ones. Finally, embedding this infrared reheating scenario into the well-known $\alpha$-attractor inflationary model, we examine possible constraints on the model parameters in light of the latest Atacama Cosmology Telescope (ACT), Dark Energy Spectroscopic Instrument (DESI) results. To arrive at the constraints, we take into account the latest bounds on tensor-to-scalar ratio, $r_{0.05}\le 0.038$, isocurvature power spectrum, ${\mathcal{P}}_{\mathcal{S}}\lesssim 8.3\times {10}^{-11}$, and effective number of relativistic degrees of freedom, $\mathrm{\Delta }{N}_{\mathrm{eff}}\lesssim 0.17$. Subject to these constraints, we find successful reheating to occur only for EOS $w_{\varphi }\gtrsim 0.6$, which translates to a subclass of $\alpha$-attractor models being favored and placing them within the $2\sigma$ region in the $n_s-r$ plane of the latest ACT, DESI data. In this range of EOS, we find that the coupling strength should lie within $2.11\lesssim \xi \lesssim 2.95$ for $w_{\varphi }=0.6$, and for $w_{\varphi }>0.6$, the allowed range becomes even tighter. Finally, we compute secondary gravitational wave signals induced by the scalar infrared modes, which are found to be strong enough to be detected by future GW observatories, namely BBO, DECIGO, LISA, and ET.

Wave dark matter is composed of particles sufficiently light that their de Broglie wavelength exceeds the average interparticle separation. A typical wave dark matter halo exhibits granular substructures due to wave interference. In this paper, we explore the wave interference effects around caustics. These are locations of formally divergent density in cold collisionless systems. Examples include splashback in galaxy clusters, and tidal shells in merging galaxies, where the pileup of dark matter close to apogee gives rise to caustics. We show that wave interference modifies the density profile in the vicinity of the caustics, giving rise to a fringe pattern well described by the Airy function. This follows from approximating the gravitational potential as linear close to apogee. This prediction is verified in a series of numerical simulations in which the gravitational potential is computed exactly. We provide a formula expressing the fringe separation in terms of the wave dark matter mass and halo parameters, which is useful for interpreting and stacking data. The fringe separation near caustics can be significantly larger than the naive de-Broglie scale (the latter set by the system’s velocity dispersion). This opens up the possibility of detecting caustic fringes for a wide range of wave dark matter masses.

The eponymous BL Lac object BL Lacertae is one of the most well-monitored active galactic nuclei, frequently observed from radio to gamma rays. Its relatively soft $\gamma$-ray spectrum peaks near 500 MeV, and since 2020 it has undergone an exceptional series of flaring episodes. The observed emission is well described by synchrotron self-Compton (SSC) models, with negligible contribution from external seed photons. We investigate the physical origin of BL Lacertae’s $\gamma$-ray temporal and spectral variability using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and show that this variability can be explained by a single varying parameter, namely, the electrons’ peak energy ${\gamma }_p$, under a single-zone SSC scenario with a log-parabolic electron distribution. We use a Markov chain Monte Carlo to estimate the spectral parameters of BL Lacertae over time, selected from an adaptive-binned gamma-ray light curve. We then study the correlation between the inverse Compton peak luminosity $L_{\mathrm{IC}}$ and the position of this peak on the spectral energy distribution energy axis, $E_p$, and compare it with what is expected for a single-zone SSC scenario when only one parameter is free to vary. We find a correlation $L_{\mathrm{IC}}={10}^{42.33\pm 0.15\pm 0.18_{\mathrm{sys}}}{E}_p^{0.98\pm 0.05\pm 0.06_{\mathrm{sys}}}$, consistent, within the errors, with the linear relation $L_{\mathrm{IC}}\propto E_p$, expected when ${\gamma }_p$ is the only free parameter in the assumed SSC model. This result supports a minimalist SSC scenario in which changes in ${\gamma }_p$ dominate the observed temporal and spectral variability of BL Lacertae.

Attempts to understand the formation of binary black hole (BBH) systems detected via gravitational wave (GW) emission are affected by many unknowns and uncertainties, from both the observational and theoretical (astrophysical modeling) sides. Binary component spins have been proposed as a means to investigate formation channels, however obtaining clear inferences is challenging, given the apparently low magnitude of almost all merging BH spins and their high measurement uncertainties. Even for the effective aligned spin ${\chi }_{\mathrm{eff}}$ which is more precisely measured than component spins, specific model assumptions have been required to identify any clear trends. Here, we reconstruct the joint component mass and ${\chi }_{\mathrm{eff}}$ distribution of BBH mergers with minimal assumptions using the GWTC-3 catalog, using an iterative kernel density estimation-based method. We reproduce some features seen in previous analyses, for instance a small but preferentially positive ${\chi }_{\mathrm{eff}}$ for low-mass mergers; we also identify a possible subpopulation of higher-spin BBH with $|{\chi }_{\mathrm{eff}}|$ up to $\sim 0.75$ for primary masses $m_1\gtrsim 40M_{\odot }$, in addition to the bulk of the distribution with $|{\chi }_{\mathrm{eff}}|\lesssim 0.2$. This finding is consistent with previous studies indicating a broader spin distribution at high mass, suggesting a distinct origin for the high-spin systems. We also identify a new potential trend of low-mass BBHs; the derivative of ${\chi }_{\mathrm{eff}}$ with respect to $m_1$ ($m_2$) is positive (negative) over the $10–15M_{\odot }$ range. This apparent structure may be related to a previously reported anticorrelation between mass ratio and ${\chi }_{\mathrm{eff}}$.

The gauge problem arises in second order gravitational waves due to mode mixing. Here, we introduce the transverse-traceless (TT) gauge to cosmological backgrounds and find that if we choose the TT gauge at first order, the second order tensor mode would be gauge invariant. Analogous to the Ricci flat spacetime, the vacuum condition is the key to guarantee the existence of the TT gauge on cosmological backgrounds. When we have the vacuum condition, the Poisson gauge, the uniform curvature gauge, the synchronous gauge, and the total matter gauge are all equivalent to the TT gauge. Once the vacuum condition is approximately satisfied, the Poisson gauge would reduce to the TT gauge at the same order of approximation. With the subhorizon limit, the vacuum condition could be obtained approximately, and the Poisson gauge, the uniform curvature gauge, and the synchronous gauge are all the approximated TT gauge. Our findings explain several existing results in the literature and indicate that the proposed TT gauge is useful to discuss higher order gravitational waves.

Hadronization, a nonperturbative process, cannot be calculated from first principles. It can be investigated either by using phenomenological models or by examining the behavior of produced hadrons or through fragmentation functions. These fragmentation functions are nonperturbative quantities whose determination relies entirely on experimental data. However, higher-twist fragmentation functions present significant challenges for their determination due to power suppression. In this paper, we propose an asymmetry to study twist-3 fragmentation functions. This asymmetry is defined as the transverse momentum asymmetry of the fragmenting quark and/or the produced jet with respect to the observed hadron direction within the semi-inclusive electron positron annihilation process. As a twist-3 effect, this asymmetry is sensitive to the distribution of the jet relative to the produced hadron direction during hadronization. Furthermore, it is closely related to twist-3 transverse momentum dependent fragmentation functions and provides a set of measurable quantities for their determination.

The cross sections for the single exclusive production of (pseudo)scalar and (pseudo)tensor hadrons, as well as of even-spin QED bound states formed by pairs of opposite-charge leptons or hadrons, are estimated for photon-fusion processes in ultraperipheral collisions (UPCs) of proton-proton, proton-nucleus, and nucleus-nucleus at the Relativistic Heavy-Ion Collider, Large Hadron Collider (LHC) and Future Circular Collider, as well as in proton-air interactions at the highest energies reached by cosmic rays impinging on Earth. The UPC cross sections are computed in the equivalent photon approximation with realistic photon fluxes from the charged form factors of proton, lead, gold, and nitrogen ions. The production of four types of even-spin systems are considered: quarkonium (spin-0, 2, 4 meson bound states, from the lightest ${\pi }^0$ meson up to toponium), exotic hadrons (including candidate multiquark states), leptonium (positronium, dimuonium, and ditauonium), as well as mesonium (pionium, kaonium, D-onium, and B-onium) and baryonium (notably, protonium) QED atoms. The expected yields at the different colliders are presented for about 50 such even-spin composite resonances, for which the ALICE and LHCb experiments have potential reconstruction capabilities at the LHC. The impact of the diphoton decays of such even-spin states is also discussed as resonant backgrounds in the measurement of light-by-light scattering ($\gamma \gamma \to \gamma \gamma$) over $m_{\gamma \gamma }\approx 0.1–15$-GeV masses in Pb-Pb UPCs at the LHC.

Dark matter (DM), in spite of being stable or long-lived on cosmological scales, can decay in the early Universe due to finite-temperature effects. In particular, a first order phase transition (FOPT) in the early Universe can provide a finite window for such decay, guaranteeing DM stability at lower temperatures, consistent with observations. The FOPT can lead to the generation of stochastic gravitational waves (GW) with peak frequencies correlated with DM mass. On the other hand, early DM decay into neutrinos can create a large neutrino asymmetry which can have interesting cosmological consequences in terms of enhanced effective relativistic degrees of freedom $N_{\mathrm{eff}}$, providing a solution to the recently observed helium anomaly among others. Allowing DM decay to occur below sphaleron decoupling temperature, thereby avoiding overproduction of baryon asymmetry, forces the FOPT to occur at subelectroweak scale. This leaves the stochastic GW within range of experiments like LISA, $\mu \mathrm{ARES}$, NANOGrav etc.

By fitting the two-point correlation functions of topological charge density operators calculated on two $2+1$-flavor gauge ensembles with physical pion mass, we determine both the $\eta$ and ${\eta }^{\prime }$ masses and also the mixing angle to be $m_{\eta }=0.505(72)(75)\mathrm{GeV}$, $m_{{\eta }^{\prime }}=0.952(47)(40)\mathrm{GeV}$, and ${\theta }_1=-8.9(2.1)(1.8)°$, respectively, where the first error is the statistical uncertainty and the second one is the systematic uncertainty. This is the first extraction of both $\eta /{\eta }^{\prime }$ masses and the mixing angle ${\theta }_1$ using topological charge operators. Compared with previous studies using quark bilinear operators, the error of the $\eta$ mass is relatively large, but the mixing angle has comparable precision. This demonstrates that the topological charge operators are well suited to study the $\eta$ and ${\eta }^{\prime }$ mesons.

We present a comprehensive analysis of electroweak sphaleron decay dynamics, employing both analytical techniques and high-resolution numerical simulations. Using a spherically symmetric ansatz, we reformulate the system as a ($1+1$)-dimensional problem and analyze its stability properties with current Standard Model parameters ($m_H=125.1\mathrm{GeV}$, $m_W=80.4\mathrm{GeV}$). We identify precisely one unstable mode with eigenvalue ${\omega }_{-}^2\simeq -2.7m_W^2$ and numerically evolve the full nonlinear field equations under various initial conditions. Through spectral decomposition, we quantify the particle production resulting from the sphaleron decay. Our results demonstrate that the decay process is dominated by transverse gauge bosons, which constitute approximately 80% of the total energy and multiplicity, while Higgs bosons account for only 7%–8%. On average, the sphaleron decays into $49W$ bosons and 4 Higgs bosons. The particle spectra consistently peak at momenta $k\sim 1–1.5m_W$, reflecting the characteristic size of the sphaleron. Remarkably, these properties remain robust across different decay scenarios, suggesting that the fundamental structure of the sphaleron, rather than specific triggering mechanisms, determines the decay outcomes. These findings provide distinctive experimental signatures of nonperturbative topological transitions in the electroweak theory, with significant implications for baryon number violation in the early universe and potentially for high-energy collider physics.

The electroweak sphaleron is a static, unstable solution of the Standard Model classical field equations, representing the energy barrier between topologically distinct vacua. In this work, we present a comprehensive updated analysis of the sphaleron using current Standard Model parameters with the physical Higgs boson mass of $m_H=125.1\mathrm{GeV}$ and $m_W=80.4\mathrm{GeV}$, rather than the $m_H=m_W$ approximation common in earlier studies. The study includes: (i) a complete derivation of the $SU(2)\times U(1)$ electroweak Lagrangian and field equations without gauge fixing constraints, (ii) high-precision numerical solutions for the static sphaleron configuration yielding a sphaleron energy $E_{\mathrm{sph}}\simeq 9.1\mathrm{TeV}$, (iii) an analysis of the minimum energy path in field space connecting the sphaleron to the vacuum (a 1D “potential barrier” as a function of Chern-Simons number), and (iv) calculation of the sphaleron single unstable mode with negative eigenvalue ${\omega }_{-}^2=-2.7m_W^2$, providing analytical fits for its eigenfunction. We find that using the measured Higgs mass modifies the unstable mode frequency, with important implications for baryon number violation rates in both early universe cosmology and potential high-energy collider signatures. These results provide essential input for accurate lattice simulations of sphaleron transitions and precision calculations of baryon number violation processes.

We consider how the Born rule, a fundamental principle of quantum mechanics, can be tested for particles created on the shortest timescales ($\sim {10}^{-25}\mathrm{s}$) currently accessible at high-energy colliders. We focus on targeted tests of the Born rule for spin or polarization probabilities, which offer a particularly clean experimental signal, and which can be described by a simple hidden-variables model of two-state systems proposed by Bell. These probabilities test a remarkable feature of the quantum formalism, whereby expectation values for incompatible experiments are linearly related. Born-rule violations can be parametrized by nonlinear expectation values for quantum measurements of spin or polarization, together with anomalies in ensemble averages, which may then be constrained by experiments. Notable experiments considered here include the recent detection of single photons from top-quark decay, and the indirect measurement of tau-lepton polarization. Repurposing these experiments as tests of the Born rule, however, presents several challenges, which are discussed in this paper.