Ultralight bosons are compelling dark-matter candidates. Both scalar and vector bosons can be produced through black hole superradiance, forming a boson cloud surrounding a rotating black hole. In binary systems, the gravitational perturbation from a companion can trigger various dynamical processes. In this work, we investigate the dynamics of both scalar and vector boson clouds in binary black hole systems. We develop a variational molecular-orbital framework, in which the cloud wave function is expanded using a single bound state of the primary black hole and an extended set of bound states centered on the companion black hole, to study boson-cloud mass transfer in unequal-mass binaries with arbitrary companion-spin orientations. Our results show that mass transfer and subsequent absorption by the companion provide a dominant depletion channel for vector clouds, whereas scalar clouds are primarily depleted by hyperfine mixing into the primary. We identify critical mass ratios below which molecular orbitals fail to form efficiently, and special resonant mass ratios where enhanced binding leads to depletion at larger orbital separations. Furthermore, when the companion’s spin is not aligned with that of the primary, the efficiency of vector cloud depletion is significantly suppressed—a feature absent in the scalar case due to the spherical symmetry of the dominant decaying mode.

We present a comprehensive analysis of the sensitivity of atomic transitions to light dark matter pair absorption. Unlike scattering, where only a fraction of the dark matter energy is deposited, pair absorption processes absorb the full mass and are therefore capable of constraining far lighter dark matter. Spin-flip and fine-structure transitions are able to constrain electroweak scale axial-vector couplings for bosonic dark matter with $\mathrm{\mu }\mathrm{eV}$ to eV masses, while principal quantum number transitions are able to set similar constraints on bosonic dark matter with scalar couplings. Unfortunately, pair absorption is largely insensitive to light fermionic dark matter due to its necessarily tiny density at low masses. We also demonstrate the sensitivity of pair absorption to the cosmic neutrino background and find that spin-flip transitions can set constraints on the overdensity parameter of ${\eta }_{\nu }\lesssim {10}^9$ for neutrino masses $m_{\nu }\lesssim 1\mathrm{meV}$, around 100 times stronger than existing constraints.

We present measurements of the depth of shower maximum, $X_{\max }$, for cosmic-ray-induced extensive air showers recorded by the fluorescence detector of the Pierre Auger Observatory over 17 years. The dataset covers primary energies from ${10}^{17.7}\mathrm{eV}$ to beyond ${10}^{19.6}\mathrm{eV}$. With improved event reconstruction and an exposure 2.4 times larger than in our previous analysis, this work confirms and refines our conclusions on the mass composition at ultrahigh energies. The energy evolution of the mean $X_{\max }$ exhibits a pronounced break at a cosmic-ray energy of about ${10}^{18.4}\mathrm{eV}$, providing direct, model-independent evidence for a change in the evolution of the mass composition. Independently, the observed decrease of the $X_{\max }$ fluctuations with energy indicates a transition toward a heavier and less diverse primary mass composition. No statistically significant declination dependence of the $X_{\max }$ distributions is observed within the exposure of the Observatory, consistent with an isotropic mass composition at the sensitivity of this analysis. The mean and standard deviation of the $X_{\max }$ distributions, interpreted with air-shower simulations, yield the energy dependence of the average and variance of the logarithmic mass of cosmic rays arriving at Earth. Furthermore, energy-dependent fractional abundances of four representative primary-mass groups (p, He, CNO, Fe) are obtained by fitting the observed $X_{\max }$ distributions in each energy bin with a weighted sum of elemental templates. These results provide strong evidence against a long-standing assumption that ultrahigh-energy cosmic rays are predominantly protons: above $\sim {10}^{18.4}\mathrm{eV}$, the average cosmic-ray mass increases, accompanied by a steadily decreasing diversity in the elemental composition.

The analytic structure of the partition function in finite-volume systems is investigated at complex chemical potentials in a minimal mean-field effective model of QCD with finite-size effects incorporated. We discuss the temperature dependence of the Lee-Yang zeros and their relation to the edge singularity for various system sizes. Different methods for locating the critical point based on finite-size scaling of Lee-Yang zeros and susceptibility ratios are compared. We demonstrate that these methods can successfully identify the critical point, whereas a careful treatment of corrections from irrelevant operators is crucial for its accurate determination.

We investigate the $T_{cc}$ tetraquark, treating it as a bound state of a heavy diquark and a light antidiquark. Using the Silvestre-Brac potential and solving the Schrödinger equation via the Gaussian expansion method, we find that the excitation energy between the heavy diquark and light antidiquark is unexpectedly larger than that between the two light antiquarks within the antidiquark—contrary to the naive expectation where the former is smaller than the latter. We trace this inversion of the mass hierarchy to the centrifugal force acting on the light degree of freedom. Applying the same framework to other systems ($T_{bb},{\mathrm{\Lambda }}_b,{\mathrm{\Lambda }}_c$) yields qualitatively identical behavior, demonstrating the robustness of the mechanism. These results provide new insights into diquark dynamics and the mass structure of exotic hadrons.

$Q$-balls are large bound-state systems of scalar particles, described classically through localized solutions of the equations of motion. Promoting the required stabilizing $U(1)$ symmetry to a gauge symmetry leads to gauged $Q$-balls, which cannot grow beyond some maximal size and charge on account of the repulsive gauge interactions. These gauged $Q$-balls have been studied extensively for scalar potentials that satisfy Coleman’s thin-wall criterion; here, we explore gauged $Q$-balls in flat potentials, which often occur in supersymmetric models. Even though global $Q$-balls in flat potentials are qualitatively different from Coleman’s $Q$-balls, we find that the gauged versions are remarkably similar. We provide analytic approximations for these solitons and compare to numerical solutions. In addition, we study Proca $Q$-balls, i.e., make the gauge bosons massive, which interpolates between the global and gauged cases.

We study energy correlators as probes of strongly coupled nearly conformal field theories within their holographically dual descriptions, focusing on the important features that appear in realistic theories going beyond the standard model. In particular, we study warped geometries which asymptote to ${\mathrm{AdS}}_5$, as well as IR-truncations dual to a 4D gap. Our correlators are computed by in-in type Witten perturbative diagrams, corresponding to a large-$N$ expansion of the strong dynamics. We describe how this sets the stage for phenomenological applications for collider searches beyond the standard model as well as for new theoretical explorations in Lorentzian holography.

This paper presents a systematic study of the substructure of dijets produced in direct and resolved photoproduction events and subsequent quark and gluon jet identification in dijets, considering the kinematic reach of the upcoming Electron-Ion Collider (EIC) experiment. We investigate the substructure of jets produced in dijet photoproduction events with center-of-mass energies $\sqrt{s}=64–140\mathrm{GeV}$ at the EIC. Events are simulated using event generator pythia and contributions from direct and resolved photoproduction subprocesses are analyzed at different energies. Jets are reconstructed using longitudinally invariant $k_T$ algorithm within the fastjet framework. Substructure of quark and gluon initiated jets in the selected dijet photoproduction sample is studied in detail by using jet-shape variables. Predictions for subjet multiplicities and integrated jet shapes are presented in the gluon-initiated and quark-initiated jets in the dijet photoproduction events at the EIC energies. These results demonstrate the feasibility of distinguishing quark and gluon jets in the photoproduction events at the EIC and provide a baseline for further QCD studies.

We present a precise and systematic analysis of $D\to VV$ decays within the factorization-assisted topological-amplitude approach, where $D$ denotes the set $\{D^0,D^{+},D_s^{+}\}$ and $V$ represents the vector mesons $\rho$, $K^{*}$, $\omega$, and $\varphi$. Given the limited current experimental data, the factorization-assisted topological-amplitude approach serves as a available phenomenological framework for predicting charmed meson decays to both vector mesons. In this framework, incorporating flavor SU(3) symmetry-breaking effects, we can express nonfactorizable contributions of different modes as a minimal set of universal parameters globally fitted to experimental data. Utilizing 36 experimental data points for $D\to VV$ decays, we precisely extract ten nonfactorizable parameters associated with the $C$ and $E$ topological diagrams with ${\chi }^2/\mathrm{d}.\mathrm{o}.\mathrm{f}.=8.43$. We find that a large strong phase in the longitude $E$ amplitude causes strong destructive interference with the $C$ longitudinal component, yielding $f_{\parallel }>f_L$, contrary to the naive factorization predictions. Additionally, for modes processing exclusively by the $E$ diagram, the amplitude hierarchy $|S|<|D|$ leads to a $D$-wave branching fraction larger than that of the $S$ wave. This explains recent observations that contradict $S$-wave dominance predictions. The predicted branching fractions and polarizations for 28 decay modes are consistent with existing experimental data. Unobserved modes, especially those with branching fractions of the order of ${10}^{-3}–{10}^{-2}$, the $D$-wave-dominated modes, and modes exhibiting $f_{\parallel }>f_L$, await measurement by BESIII, STCF, Belle II, and LHCb.

In strongly interacting massive particle (SIMP) scenarios, dark matter is comprised of stable dark pions whose $3\to 2$ or $4\to 2$ reactions set the dark matter relic abundance. Recent work has shown that shallow two-pion bound states significantly affect the freeze-out, but did not establish whether such states actually form. In this work we demonstrate that a scalar isosinglet bound state does exist in a well-defined region of parameter space by solving an on shell Lippmann-Schwinger equation in a chiral-unitary framework and analyzing the $S$-wave $\pi \pi$ amplitude in the complex energy plane. We determine the range of $m_{\pi }/f_{\pi }$ and the momentum cutoff for which a pole appears below the two-pion threshold, extract the corresponding residue, and, in the nonrelativistic limit, obtain the bound-state wave function at the origin, $|\mathrm{\Psi }(0)|$, which controls bound-state-assisted annihilation and decay rates relevant for catalyzed freeze-out. Comparing this T-matrix based result with variational estimates using simple finite-range potentials, we find agreement within order-one factors for shallow binding. For binding energies of order the freeze-out temperature, $E_B\sim m_{\pi }/20$, we obtain $|\mathrm{\Psi }(0)|\sim \mathcal{O}(0.1)m_{\pi }^{3/2}$, thereby supporting the parametric assumptions used in previous phenomenological analyses.

Minimal electroweak dark matter models are compelling due to their simplicity, though calculations of their freeze-out abundance are complicated by nonperturbative effects due to Sommerfeld enhancement and bound-state formation. It has been shown that all individual multiplet scenarios beyond the doublet lead to direct-detection signals above the neutrino floor and thus within the reach of next-generation experiments. If no signals are found, would minimal dark matter be excluded? Yes for the simplest models, but it has been unknown for the important extension of two multiplets coupled by Higgs interactions (Higgs-coupled minimal dark matter). We present a generalized framework for calculating nonperturbative effects for such models that also covers the case of individual multiplets. In this framework, we calculate nonperturbative effects on freeze-out as well as the prospects for direct detection, correcting shortcomings and omissions in the literature. Importantly, for the mixed Majorana (odd) and Dirac (even) multiplet combination $3M2D$ (and marginally the $5M4D$), we find that the predicted direct-detection signals can extend below the neutrino floor. Fully testing minimal dark matter will thus require more than direct-detection experiments.

Multimessenger astroparticle physics provides a new approach to probe new physics beyond the Standard Model. We propose to probe the light dark matter which can interact via the electromagnetic force. To be concrete, we derive the new constraint on the millicharged dark matter from the multimessenger observations of GW170817. In the neutron star merger event GW170817, the first detection of a $\gamma$-ray burst delayed by approximately 1.7 seconds relative to the gravitational wave emission was observed. Utilizing this delay, we constrain the parameter space of the millicharged dark matter within the large-scale structure of the Universe. For dark matter mass below ${10}^{-17}\mathrm{eV}$, the parameter $\epsilon$ is constrained to be less than ${10}^{-14}$, representing the most stringent limits achieved to date.

We investigate the possibility of realizing strong first-order electroweak phase transition (SFOEWPT) in an effective field theory framework where the Standard Model is extended with a complex scalar singlet ($\varphi$) charged under a local $U(1{)}_D$ gauge group. The tree-level scalar potential contains a dimension-six term of the form $|H{|}^2|\varphi {|}^4$. We show that this higher-dimensional operator plays a crucial role in the phase transition dynamics by weakening the correlation between the Higgs-singlet portal coupling and the scalar mixing angle that typically constrains singlet-extended models. Consequently, SFOEWPT can be achieved over a significantly extended region of parameter space. The strength of the phase transition is primarily driven by the vacuum expectation value of the singlet scalar, which plays a central role in this analysis. We analyze the phase transition in this model and identify regions of parameter space consistent with SFOEWPT. The resulting phase transition can generate stochastic gravitational-wave signals potentially observable at future interferometers. The extended scalar sector in presence of the dimension-six operator also leads to distinctive multiscalar production signatures at the LHC, intimately correlated with the singlet scalar VEV.

A starting point in the study of the minimal supersymmetric Standard Model (MSSM) is the vacuum moduli space, which is a highly complicated algebraic variety; it is the image of an affine variety $X\subset {\mathbb{C}}^{49}$ under a symplectic quotient map $\varphi$ to ${\mathbb{C}}^{973}$. Previous work [Y.-H. He et al., The geometry of generations, Commun. Math. Phys. 339, 149 (2015)] computed the vacuum moduli space of the electroweak sector; geometrically this corresponds to studying a restriction of $\varphi$: ${\mathbb{C}}^{13}\stackrel{{\varphi }^{\mathsf{res}}}{\to }{\mathbb{C}}^{22}$. We analyze the geometry of the full vacuum moduli space for superpotentials $W_{\text{minimal}}$ (without neutrinos) and $W_{\mathrm{MSSM}}$ (with neutrinos) in ${\mathbb{C}}^{973}$. In both cases, we prove that $X$ consists of three irreducible components $X_1$, $X_2$, and $X_3$, and determine the images $M_i$ of the $X_i$ under $\varphi$. For $W_{\text{minimal}}$ we show they have, respectively, dimensions 1, 15, and 29, and prove that each of the $M_i$ is a rational variety, while for $W_{\mathrm{MSSM}}$ we show that $M_3$ is the only component. Restricting the $M_i$ to the electroweak sector, we recover the results in He et al. [The geometry of generations, Commun. Math. Phys. 339, 149 (2015)]. We describe the components of the vacuum moduli space geometrically in terms of incidence varieties to a product of Segrè varieties.

The pattern of chiral symmetry breaking is exploited to compute vector and axial-vector pion matrix elements in a uniform magnetic field. Our results are model independent, and thereby constitute low-energy theorems that must be obeyed by QCD in external magnetic fields. Chiral perturbation theory, lattice QCD, and Nambu–Jona-Lasinio results are compared. While there is some tension between chiral perturbation theory and lattice QCD, the tension between low-energy QCD and the Nambu–Jona-Lasinio model is more acute. As an application, the matrix elements are utilized to compute pion decay rates in a magnetic field.

We consider the problem of identifying the onset of the conformal window for QCD with $N_f$ massless flavors in the fundamental representation and propose a new effective method to determine it from lattice simulations. This method is based on the investigation of the so-called Roberge-Weiss transition temperature $T_{\mathrm{RW}}$, which is encountered at specific values of the imaginary baryon chemical potential, and can also be interpreted as the inverse of the critical spatial size at which charge conjugation is spontaneously broken in a finite box. Since $T_{\mathrm{RW}}$ corresponds to a genuine phase transition for any value of the quark masses, it is a well-defined quantity; we argue that the critical $N_f$ at which $T_{\mathrm{RW}}$ vanishes in the chiral limit coincides with the onset of the conformal window. We implement our proposal by investigating QCD with $N_f=8$ flavors, discretized via stout improved staggered fermions and the tree-level improved Symanzik pure gauge action, at Euclidean temporal extents $N_t=8$, 10, 12, 16, 24. In this case, our numerical results are consistent with a $T_{\mathrm{RW}}$ that vanishes in the chiral limit, which would indicate that $N_f=8$ is already in the conformal window.

The analytical expressions of the shear viscosity of both one and two particle species with Boltzmann statistics and $2\to 2$ elastic scatterings are known from the Chapman-Enskog method and have been shown to be quite accurate. The expression for a multispecies hadronic gas under $2\to 2$ elastic scatterings is also known. Here we use the Chapman-Enskog method to derive the explicit expression of shear viscosity of a massless quark-gluon gas of $N_f$ quark flavors in chemical equilibrium subjected to all $2\to 2$ parton scatterings including for the first time inelastic scatterings. We then verify the expression in a general single-species limit, where the shear viscosity of the quark-gluon gas should reduce to the result for a single particle species. In addition, we show the explicit analytical result in terms of the seven independent cross sections for the special case of isotropic and energy-independent cross sections. The analytical expressions derived here can be useful for determining the shear viscosity of parton transport models with any $2\to 2$ scattering cross sections. They can also be coupled with finite temperature QCD cross sections to help study the shear viscosity of the quark gluon plasma.

We propose a holographic model for quarkonia using the WKB approximation with the Langer correction to properly reproduce nonlinear Regge trajectories of the form $m_n^2=\beta (n+c_0{)}^{2/3}+c_1$. This form is expected from previous studies involving the solution of Cornell potential for heavy quark-antiquark interactions using a model based on the quadratic form of the spinless Salpeter-type equation. The model fits experimental masses with very good accuracy. As a by-product, the corresponding decay constants also show a reasonable agreement with the results obtained from experimental data.

Hadrons with explicit gluonic degrees of freedom, such as charmonium hybrids, are key to understanding nonperturbative behavior of strong interaction, yet they remain experimentally elusive. Within a constituent gluon model treating the hybrid as a $c\overline{c}g$ three-body system with a transverse electric gluon, we predict the masses of the lightest hybrid multiplet ($J^{PC}=1^{--},0^{-+},1^{-+},2^{-+}$) to lie in the range 4.19–4.32 GeV. By analyzing their decay patterns, we provide specific, experimentally testable signatures to guide the search for these exotic states at current and future facilities.