A symmetry-preserving approach to the two valence-body continuum bound-state problem is used to calculate the elastic electromagnetic form factors of the ρ-meson and subsequently to study the evolution of vector-meson form factors with current-quark mass. To facilitate a range of additional comparisons, K * form factors are also computed. The analysis reveals that: vector mesons are larger than pseudoscalar mesons; composite vector mesons are non-spherical, with magnetic and quadrupole moments that deviate ∼ 30% from point-particle values; in many ways, vector-meson properties are as much influenced by emergent mass as those of pseudoscalars; and vector meson electric form factors possess a zero at spacelike momentum transfer. Qualitative similarities between the electric form factors of the ρ and the proton, G p E , are used to argue that the character of emergent mass in the Standard Model can force a zero in G p E . Morover, the existence of a zero in vector meson electric form factors entails that a single-pole vector meson dominance model can only be of limited use in estimating properties of off-shell vector mesons, providing poor guidance for systems in which the Higgs-mechanism of mass generation is dominant. *

We investigate the capability of the future electron collider CEPC in probing the parameter space of several dark matter models, including millicharged dark matter models, Z portal dark matter models, and effective field theory dark matter models. In our analysis, the monophoton final state is used as the primary channel to detect dark matter models at CEPC. To maximize the signal to background significance, we study the energy and angular distributions of the monophoton channel arising from dark matter models and from the standard model to design a set of detector cuts. For the Z portal dark matter, we also analyze the Z boson visible decay channel which is found to be complementary to the monophoton channel in certain parameter space. The CEPC reach in the parameter space of dark matter models is also put in comparison with Xenon1T. We find that CEPC has the unprecedented sensitivity to certain parameter space for the dark matter models considered; for example, CEPC can improve the limits on millicharge by one order of magnitude than previous collider experiments for O(1) − 100 GeV dark matter.

We consider the fidelity of the vector meson dominance (VMD) assumption as an instrument for relating the electromagnetic vector-meson production reaction $$e + p \rightarrow e^\prime + V + p$$ e + p → e ′ + V + p to the purely hadronic process $$V + p \rightarrow V+p$$ V + p → V + p . Analyses of the photon vacuum polarisation and the photon-quark vertex reveal that such a VMD Ansatz might be reasonable for light vector-mesons. However, when the vector-mesons are described by momentum-dependent bound-state amplitudes, VMD fails for heavy vector-mesons: it cannot be used reliably to estimate either a photon-to-vector-meson transition strength or the momentum dependence of those integrands that would arise in calculations of the different reaction amplitudes. Consequently, for processes involving heavy mesons, the veracity of both cross-section estimates and conclusions based on the VMD assumption should be reviewed, e.g., those relating to hidden-charm pentaquark production and the origin of the proton mass.

Exposing active sites and optimizing their binding strength to reaction intermediates are two essential strategies to significantly improve the catalytic performance of 2D materials. However, pursuing an efficient way to achieve these goals simultaneously remains a considerable challenge. Here, using 2D PtTe2 van der Waals material with a well‐defined crystal structure and atomically thin thickness as a model catalyst, it is observed that a moderate calcination strategy can promote the structural transformation of 2D crystal PtTe2 nanosheets (c‐PtTe2 NSs) into oxygen‐doped 2D amorphous PtTe2 NSs (a‐PtTe2 NSs). The experimental and theoretical investigations cooperatively reveal that oxygen dopants can break the inherent Pt‐Te covalent bond in c‐PtTe2 NSs, thereby triggering the reconfiguration of interlayer Pt atoms and exposing them thoroughly. Meanwhile, the structural transformation can effectively tailor the electronic properties (e.g., the density of state near the Fermi level, d‐band center, and conductivity) of Pt active sites via the hybridization of Pt 5d orbitals and O 2p orbitals. As a result, a‐PtTe2 NSs with large amounts of exposed Pt active sites and optimized binding strength to hydrogen intermediates exhibit excellent activity and stability in hydrogen evolution reaction.

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