The Primakoff mechanism is one of the primary channels for the production of solar axions. In canonical estimations of the Primakoff photon-axion conversion rate, the recoil effect is neglected and a static structure factor in adopted. By use of linear response theory, we provide a dynamic description of the solar Primakoff process. It is found that the collective electrons overtake ions as the dominant factor, in contrast to the static screening picture, where ions contribute more to the photon-axion conversion. Nonetheless, the resulting axion flux is only 1% to 2% lower than the standard estimate based on the static structure factor.

We calculate the effect of dark matter on the ringdown waveform and shadow of supermassive black holes at the core of galaxies. Our main focus is on the supermassive black hole at the core of M87, which is large enough to allow for viable observational data. We compare the effects of a dark matter spike to those expected from a galactic halo of the same mass. Our calculation for the halo starts from the Hernquist density function and assumes anisotropic pressure that is zero in the radial direction. The resulting Tolman-Oppenheimer-Volkoff equations allow the corresponding metric to be obtained analytically in closed form. The geometry of the anisotropic dark matter spike is the same as that obtained in [Astrophys. J. 940, 33 (2022)] under the assumption of isotropy. The effect of the spike is orders of magnitude more significant than the halo as long as the distribution scale of the latter is within a few orders of magnitude of the value expected from observations. Our results indicate that the impact of the spike surrounding M87* on the ringdown waveform may in principle be detectable. Finally, we point out the somewhat surprising fact that existing Event Horizon Telescope observations of black hole shadows are within an order of magnitude from being able to detect, or rule out, the presence of a spike.

We explore a mechanism for producing the baryon asymmetry and dark matter in models with multiple hidden sectors that are Standard-Model-like but with varying Higgs mass parameters. If the field responsible for reheating the Standard Model and the exotic sectors carries an asymmetry, it can be converted into a baryon asymmetry using the standard sphaleron process. A hidden sector with positive Higgs mass squared can accommodate dark matter with its baryon asymmetry, and the larger abundance of dark matter relative to baryons is due to dark sphalerons being active all the way down the hidden sector QCD scale. This scenario predicts that dark matter is clustered in large dark nuclei and gives a lower bound on the effective relativistic degrees of freedom, $\mathrm{\Delta }{N}_{\mathrm{eff}}\gtrsim 0.05$, which may be observable in the next-generation cosmic microwave background experiment CMB-S4.

A lattice QCD calculation for the four-gluon one-particle irreducible Green function in the Landau gauge is discussed. Results for some of the associated form factors are reported for kinematical configurations with a single momentum scale. Our results show that the computation of this Green function requires large statistical ensembles with 10 K or larger number of gauge configurations. The simulations considered herein have a clear Monte Carlo signal for momenta up to $\sim 1\mathrm{GeV}$. The form factors show an hierarchy, with the form factor associated with the tree level Feynman rule being dominant and essentially constant for the range of momenta accessed. The remaining form factors seem to increase as the momentum decreases, suggesting that a possible $\log$ divergence may occur. The computed form factors are, at least, in qualitative agreement with the results obtained with continuum approaches to this vertex, when available.

We investigate a nonperturbative approach to quantum gravity built in terms of analogies between quadratic gravity and quantum chromodynamics. This approach is based on a conjectured phase transition between quadratic gravity in the trans-Planckian regime and an effective field theory, with general relativity as the leading-order term, below the Planck scale. We point out that not all aspects of the analogy between quadratic gravity and quantum chromodynamics are desired. A possible mechanism of chiral symmetry breaking driven by quantum gravity fluctuations could make this setup incompatible with our observed Universe. Here, we put forward a first investigation of chiral symmetry breaking in the context of quadratic gravity. We find indication that gravity, despite being an attractive force, does not trigger chiral symmetry breaking in a nonperturbative regime. This result is based on a (functional) renormalization group analysis of four-fermion interactions coupled to quadratic gravity. We also comment on the particularities associated with the single-flavor case. In summary, the analogy between quadratic gravity and chromodynamics passes this first phenomenological viability test.

The quantization of a massive spin-$1/2$ field that satisfies the Klein-Gordon equation is studied. The framework is consistent, provided it is formulated as a pseudo-Hermitian quantum field theory by the redefinition of the dual field and the identification of an operator that modifies the inner product of states in Hilbert space to preserve a real energy spectrum and unitary evolution. Since the fermion field has mass dimension one, the theory admits renormalizable fermion self-interactions.

In this work, we use the dynamical system approach to explore the cosmological background evolution of the scalar-tensor representation of $f(R,T)$ gravity, where $R$ is the Ricci scalar and $T$ is the trace of the stress-energy tensor. The motivation for this work resides in finding dynamical cosmological behaviors comparable with the $\mathrm{\Lambda }\mathrm{CDM}$ model without the necessity of recurring to a dark energy component. We introduce a set of dynamical variables that allow for a direct comparison with the cosmological standard model and the current experimental measurements, and develop a dynamical system framework to analyze the cosmological evolution of Friedmann-Lemaître-Robertson-Walker universes within this theory. In this framework, we obtain the critical points in the cosmological phase space and perform fully numerical integrations of the dynamical system to extract the cosmological behavior, subjected to initial conditions compatible with the measurements by the Planck satellite. The phase space of the theory is proven to feature fixed points associated with cosmological behaviors analogous to those of GR, whereas variations in the scalar field associated to the dependency in $T$ affect the phase space structure only quantitatively. Our results indicate that cosmological solutions featuring a radiation dominated epoch, followed by a transition into a matter dominated epoch, and finally a transition into an exponentially accelerated epoch, are allowed by the theory, while maintaining a present state compatible with the current measurements from the Planck satellite and solar system dynamics, and preserving the regularity of the scalar fields and their interaction potential.

The CMS and ATLAS Collaborations recently published their results searching for light Higgs bosons, using the complete Run 2 data of the LHC. Both reported an excess in the diphoton invariant mass distribution at $m_{\gamma \gamma }\simeq 95.4\mathrm{GeV}$ with compatible signal strengths. The combined result corresponded to a local significance of $3.1\sigma$. Besides, the mass of the diphoton signal coincided with that of the $b\overline{b}$ excess observed at the Large Electron Positron. Given the remarkable theoretical advantages of the general next-to-minimal supersymmetric Standard Model, we interpret these excesses by the resonant productions of the singlet-dominated $CP$-even Higgs boson predicted by the theory. Using both analytic formulas and numerical results, we show that the idea can interpret the excesses by broad parameter space without contradicting current experimental restrictions, including those from the 125 GeV Higgs data, the dark matter relic abundance and direct detection experiments, and the collider searches for supersymmetry and extra Higgs bosons. Although the explanations are scarcely affected by present Higgs data and the LHC search for supersymmetry, the dark matter physics may leave footprints on them. We also survey the other signals of the light Higgs boson at the LHC.

Modifications of the QCD perturbative expansions by the subtraction of the dominant infrared renormalon have been proposed recently as attempts to solve the longstanding discrepancy between fixed-order and contour-improved perturbation theory for the hadronic $\tau$ decays. In this approach, the modified perturbative series is supplemented by a modified gluon condensate in the operator product expansion of the Adler function. Motivated by these works, we revisited recently a formulation of the QCD perturbation theory, proposed some time ago, which takes into account the renormalons by means of the conformal mapping of the Borel plane. One expects that the modified perturbative series obtained in this framework should be accompanied by modified power-suppressed nonperturbative corrections. However, in the previous studies the focus was on the perturbative series and the question of the possible power corrections has not been considered. In the present paper, we investigate for the first time this problem. Using techniques from the mathematical resurgence theory, we derive the expression of the dominant power correction to the perturbative series obtained by conformal mapping of the Borel plane, and discuss its implications for phenomenological applications.

The direction of individual ${}^8\mathrm{B}$ solar neutrinos has been reconstructed using the $\mathrm{SNO}+$ liquid scintillator detector. Prompt, directional Cherenkov light was separated from the slower, isotropic scintillation light using time information, and a maximum likelihood method was used to reconstruct the direction of individual scattered electrons. A clear directional signal was observed, correlated with the solar angle. The observation was aided by a period of low primary fluor concentration that resulted in a slower scintillator decay time. This is the first time that event-by-event direction reconstruction in high light-yield liquid scintillator has been demonstrated in a large-scale detector.

Based on a data sample of 10 billion $J/\psi$ events collected with the BESIII detector, improved measurements of the Dalitz decays $\eta /{\eta }^{\prime }\to \gamma e^{+}{e}^{-}$ are performed, where the $\eta$ and ${\eta }^{\prime }$ are produced through the radiative decays $J/\psi \to \gamma \eta /{\eta }^{\prime }$. The branching fractions of $\eta \to \gamma e^{+}{e}^{-}$ and ${\eta }^{\prime }\to \gamma e^{+}{e}^{-}$ are measured to be $(7.07\pm 0.05\pm 0.23)\times {10}^{-3}$ and $(4.83\pm 0.07\pm 0.14)\times {10}^{-4}$, respectively. Within the single-pole model, the parameter of electromagnetic transition form factor for $\eta \to \gamma e^{+}{e}^{-}$ is determined to be ${\mathrm{\Lambda }}_{\eta }=(0.749\pm 0.027\pm 0.007)\mathrm{GeV}/c^2$. Within the multipole model, we extract the electromagnetic transition form factors for ${\eta }^{\prime }\to \gamma e^{+}{e}^{-}$ to be ${\mathrm{\Lambda }}_{{\eta }^{\prime }}=(0.802\pm 0.007\pm 0.008)\mathrm{GeV}/c^2$ and ${\gamma }_{{\eta }^{\prime }}=(0.113\pm 0.010\pm 0.002)\mathrm{GeV}/c^2$. The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the $\eta$ and ${\eta }^{\prime }$ are calculated to be $(0.645\pm 0.023\pm 0.007)\mathrm{fm}$ and $(0.596\pm 0.005\pm 0.006)\mathrm{fm}$, respectively. In addition, we search for the dark photon in $\eta /{\eta }^{\prime }\to \gamma e^{+}{e}^{-}$, and the upper limits of the branching fractions as a function of the dark photon are given at 90% confidence level.

We investigate the complexity of states and operators evolved with the modular Hamiltonian by using the Krylov basis. In the first part, we formulate the problem for states and analyze different examples, including quantum mechanics, two-dimensional conformal field theories and random modular Hamiltonians, focusing on relations with the entanglement spectrum. We find that the modular Lanczos spectrum provides a different approach to quantum entanglement, opening new avenues in many-body systems and holography. In the second part, we focus on the modular evolution of operators and states excited by local operators in two-dimensional conformal field theories. We find that, at late modular time, the spread complexity is universally governed by the modular Lyapunov exponent ${\lambda }_L^{\text{mod}}=2\pi$ and is proportional to the local temperature of the modular Hamiltonian. Our analysis provides explicit examples where entanglement entropy is indeed not enough; however the entanglement spectrum is, and encodes the same information as complexity.

We perform a general analysis of thin-wall $Q$-balls in anti–de Sitter (AdS) space. We provide numeric solutions and highly accurate analytic approximations over much of the parameter space. These analytic solutions show that AdS $Q$-balls exhibit significant differences from the corresponding flat-space solitons. This includes having a maximum radius beyond which the $Q$-balls are unstable to a new type of state where the $Q$-ball coexists with a gas of massive particles. The phase transition to this novel state is found to be a zero-temperature third-order transition. This, through the AdS/CFT correspondence, has implications for a scalar condensate in the boundary theory.

The action growth proposal relates the holographic complexity to the value of the action on the Wheeler-de Witt patch. We introduce a new method of calculating the gravitational action using the “bulk” term, i.e., the part of the Einstein-Hilbert action quadratic in connection coefficients. We demonstrate how to address the issue of noncovariance of the bulk action and evaluate it using the tetrad formalism. Due to the boundary term-free nature of the bulk action, we can gain further insights into the spatial structure of the action on the Wheeler-de Witt patch. We then argue that our entire scheme can be naturally covariantized within the framework of teleparallel geometry.

We consider a new type of $\mathcal{N}=4$, $d=1$ semidynamical multiplet based on the nonlinear version of the mirror multiplet $(\mathbf{3},\mathbf{4},\mathbf{1})$, with the triplet of bosonic physical fields parametrizing a three-dimensional sphere $S^3$ of the radius $R$. The limit $R\to \infty$ amounts to the contraction $S^3\to {\mathbb{R}}^3$ and leads to the linear mirror multiplet $(\mathbf{3},\mathbf{4},\mathbf{1})$. Spin degrees of freedom described by a Wess-Zumino action specify a two-dimensional surface embedded in the sphere $S^3$. A pair of the examples considered correspond to the round and squashed “fuzzy” 2-spheres. We couple the squashed 2-sphere model to the dynamical mirror multiplet $(\mathbf{2},\mathbf{4},\mathbf{2})$. A notable feature of this coupling is the dependence of the squashing parameter on the bosonic fields $z$, $\overline{z}$ of the chiral multiplet.

The topology of photons in vacuum is interesting because there are no photons with $\mathit{k}=0$, creating a hole in momentum space. We show that while the set of all photons forms a trivial vector bundle $\gamma$ over this momentum space, the $R$ and $L$ photons form topologically nontrivial subbundles ${\gamma }_{\pm }$ with first Chern numbers $\mp 2$. In contrast, $\gamma$ has no linearly polarized subbundles, and there is no Chern number associated with linear polarizations. It is a known difficulty that the standard version of Wigner’s little group method produces singular representations of the Poincaré group for massless particles. By considering representations of the Poincaré group on vector bundles we obtain a version of Wigner’s little group method for massless particles which avoids these singularities. We show that any massless bundle representation of the Poincaré group can be canonically decomposed into irreducible bundle representations labeled by helicity, which in turn can be associated to smooth irreducible Hilbert space representations. This proves that the $R$ and $L$ photons are globally well defined as particles and that the photon wave function can be uniquely split into $R$ and $L$ components. This formalism offers a method of quantizing the electromagnetic field without invoking discontinuous polarization vectors as in the traditional scheme. We also demonstrate that the spin-Chern number of photons is not a purely topological quantity. Lastly, there has been an extended debate on whether photon angular momentum can be split into spin and orbital parts. Our work explains the precise issues that prevent this splitting. Photons do not admit a spin operator; instead, the angular momentum associated with photons’ internal degree of freedom is described by a helicity-induced subalgebra corresponding to the translational symmetry of $\gamma$.

The $\mathcal{S}\mathcal{W}(3/2,2)$ current algebras come in two discrete series indexed by central charge, with the chiral algebra of a supersymmetric sigma model on a Spin(7) manifold as a special case. The unitary representations of these algebras were classified by Gepner and Noyvert, and we use their results to perform an analysis of null descendants and compute the characters for every representation. We obtain threshold relations between the characters of discrete representations and those with continuous conformal weights. Modular transformations are discussed, and we show that the continuous characters can be written as bilinear combinations of characters for consecutive minimal models.

We examine the implications of the weak gravity conjecture for the mechanisms for discharging cosmological constant via membrane nucleations. Once screening fluxes and membranes which source them enter, and weak gravity bounds are enforced, a generic de Sitter space must be unstable. We show that when all the flux terms which screen and discharge the cosmological constant are dominated by quadratic and higher order terms, the bounds from weak gravity conjecture and naturalness lead toward anthropic outcomes. In contrast, when the flux sectors are dominated by linear flux terms, anthropics may be avoided, and the cosmological constant may naturally decay toward smallest possible values.