We show that linearized E theory possesses a local symmetry at low levels provided the parameters of the local symmetry obey differential conditions that restrict their dependence on the extended space–time. In the decomposition of E theory that leads to Siegel theory, also known as double field theory, we also find the analogous restrictions on the parameters. They are different to the section conditions which are universally used in this context. We also show that the dilaton equation of Siegel theory is invariant under the local symmetry if the parameters satisfy an analogous nonlinear constraint on the parameters. We argue that there is no need to impose conditions on the fields of E theory or Siegel theory.
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,200 new measurements from 903 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Most of the 118 reviews are updated, including many that are heavily revised. The Review is divided into two volumes. Volume 1 includes the Summary Tables and 96 review articles. Volume 2 consists of the Particle Listings and contains also 22 reviews that address specific aspects of the data presented in the Listings. The complete Review (both volumes) is published online on the website of the Particle Data Group ( pdg.lbl.gov ) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is available in print, as a web version optimized for use on phones, and as an Android app. The PDG API (Application Programming Interface) provides access to the data published in the Review in machine-readable format.
The Circular Electron Positron Collider (CEPC), with its unprecedented scale encompassing a circumference of 100 kilometers and stringent alignment accuracy requirements, presents exceptional challenges for accelerator alignment and installation. The primary objective of this study is to develop the key technologies to address these challenges. For 100-kilometer range high-accuracy measurements, this paper proposes to conduct research on the geoid refinement, establishing a high-precision quasi-geoid model and a vertical deflection model covering the entire facility to serve as a global datum for observations reduction. Proposing to develop a visual instrument and a high-accuracy measurement field to facilitate efficient alignment measurements and automated component adjustments. Innovative alignment strategies will be investigated to address the challenges posed by the complex design of the MDI (Interaction Region) and tight alignment accuracy requirement of the accelerator superconducting magnets. The outcomes of this research will provide essential technical support for the high-accuracy alignment and efficient installation of CEPC, offering reusable methodologies and engineering paradigms for future large-scale scientific projects, thereby holding significant scientific value and engineering demonstration significance.
Primordial black holes (PBHs) formed through different mechanisms follow extended, rather than monochromatic, mass and spin distributions. Building on the public FRISBHEE code, implementing four PBH mass functions (log-normal, power-law, critical collapse, metric preheating), we introduce a multimodal framework modeling the global population as a superposition of these components, and compare alternative weighting schemes. Spin follows a Gaussian profile or the universal post-merger distribution of Fishbach et al. For [Formula: see text], we compute the gravitationally produced dark matter relic abundance across all distributions and spin configurations. Extended distributions suppress the relic abundance relative to the monochromatic benchmark according to the mass-function breadth, with the hierarchy reorganizing at non-zero spin. The weighting scheme is the dominant source of theoretical uncertainty, shifting predictions by up to [Formula: see text]38%; extended distributions relax the [Formula: see text] bound by up to [Formula: see text]2.4 and shift the Planck-compatible mass windows by 15–25%, showing that the PBH formation channel is itself an observable.
Rational Quantum Mechanics (RaQM) is a theory consistent with Gerard ’t Hooft’s proposals about the locally causal nature of quantum physics. Based on a specific discretization of the Riemann Sphere, the quantum state only is only defined in bases where squared amplitudes and complex phases (divided by [Formula: see text]) are rational numbers. These “rational bases” correspond to ’t Hooft’s ontological bases in which the quantum state has a beable representation. Bell’s inequality is violated without breaking realism, locality or free choice. Instead, for each run in a Bell experiment, a number-theoretic property of the cosine function ensures that the squared amplitude of the singlet state is an irrational number in at least one of the two counterfactual pairs of bases needed to derive Bell’s inequality. Hence, the Measurement Independence (MI) assumption is violated — not for the nominal settings under the experimenters’ free control, but for the exact settings which were never under their control anyway. None of the grotesque conspiracies that plague conventional superdeterministic explanations of Bell’s Theorem applies. Bell’s Theorem implies RaQM is a holistic theory. As such, implications for models of cosmology are discussed. An experimental test of RaQM, achievable in about 5 years, is described.
Flavor physics and jet research at the Circular Electron and Positron Collider (CEPC) impose increasingly stringent requirements on particle identification (PID). As an alternative central tracker for the CEPC reference detector, one of the key optimization objectives of the drift chamber is its PID capability. The dN/dx method offers superior PID performance for the drift chamber by counting primary ionization. A prototype system including a 120-channel drift chamber, high-bandwidth readout electronics and DAQ software was developed and tested with cosmic rays. Preliminary results show a high signal-to-noise ratio (SNR) of 108.87 and an average rise time of 2.08[Formula: see text]ns, thereby demonstrating the low-noise and high-bandwidth performance of the electronics. Calibration and preliminary reconstruction have been completed, which lays a foundation for subsequent studies on dN/dx resolution.
The motion and Lyapunov instability of charged particles around a rotating Einstein–Euler–Heisenberg black hole (EEHBH) is explored systematically, and the chaos-bound, [Formula: see text], is discussed in the light of that. The equilibrium positions and their stability are examined for various values of the angular momenta and the charge-to-mass ratios of the particles. We find that there exist certain values of the electric charge, rotation, and Euler–Heisenberg coupling for which the chaos bound is broken, even at relatively low angular momentum. For [Formula: see text], the Euler–Heisenberg coupling has little effect on the horizon radius; but, for larger charge values, its impact becomes noticeable. On the other hand, it greatly alters the surface gravity, especially when rotation and charge are present. The extremal case shows a larger chaos bound violation, while the non-extremal case shows a more complex angular momentum dependence. This work presents a comprehensive analysis of the effects of both the rotational and frame-dragging and/or nonlinear electrodynamics on the equilibrium structure, Lyapunov instability, and stability/chaos transitions associated with charged-particle motion, unlike previous studies which examined these combined effects separately.
We continue to investigate various instabilities of the fixed backgrounds related to the de Sitter space. It is shown that in many cases the in/in perturbation theory contains IR/UV mixing and thus is non-renormalizible. The application of this result to the global de Sitter space leads to the conclusion that even massive particles generate IR divergence and the huge back reaction. The expanding universe is also unstable but in a weaker sense. We further discuss, the strange features of the Gibbons-Hawking radiation and its relation to the above instabilities.
This paper is dedicated to the 80th birthday of Gerard ’t Hooft. After some personal recollections about being 25 years colleagues with Gerard at the ITP in Utrecht, I describe some aspects of asymptotically flat 3d gravity and holography, two topics to which Gerard made foundational and influential contributions. This work contains some new results about boundary descriptions of asymptotically flat 3d gravity in terms of new 2d BMS/Carroll invariant field theories living at null infinity. The results described here are part of a more extensive paper in collaboration with Diego Hidalgo and Huaxuan Zeng.
We draw on 't Hooft's seminal formulation of the holographic principle to analyse the methodological and conceptual role of information in quantum gravity. We argue that, in 't Hooft's work and in later developments, information functions as a substantive guiding principle. We distinguish three aspects of this role: First, holographic bounds on the amount of information that can be stored in a region function as theory selection criteria that constrain viable quantum gravity theories. Second, holography functions as a principle of theoretical equivalence: the bulk and boundary theories must describe the same physical content, even though 't Hooft privileges a more fundamental, lower-dimensional, and potentially deterministic boundary description. Third, the distribution and encoding of information connect 't Hooft's proposals to contemporary work on bulk reconstruction, holographic quantum error correction, and ER=EPR, where emergent spacetime structure is tied to patterns of entanglement and redundancy. On the basis of these three roles, we argue that purely epistemic or Shannon-style conceptions of information are inadequate in this context: we instead outline a distinction between what we call maximal and intermediate conceptions that aim to capture the methodological and interpretative roles of information in holographic quantum gravity. We therefore suggest that, in the context of holography and quantum gravity, a more systematic philosophical treatment of the role of information as an interpretation-guiding principle would be desirable.
The Beijing Spectrometer III (BESIII) experiment at the Beijing Electron-Positron Collider II (BEPCII) carries out precision measurements in tau-charm physics, hadron spectroscopy, nucleon form factors, and corrections to the muon anomalous magnetic moment. Initial State Radiation (ISR) return method provides a unique path to access lower center-of-mass energies without interrupting high-energy data taking, which will greatly support the BESIII energy-scan programs. However, the standard BESIII electromagnetic calorimeter (EMC) has low efficiency for forward ISR photons (∣ cos θ∣ > 0.99), and untagged ISR analyses suffer from large backgrounds and poor precision. A dedicated Zero Degree Calorimeter (ZDC) in the very forward region will strongly enhance ISR photons detection. This paper reports the full R&D status including detector design, simulation, readout electronics, prototyping, laboratory tests, beam-test trials, and future timeline of the BESIII ZDC project. The ZDC uses a radiation-hard LYSO+SiPM array with modular design to profile electromagnetic showers and achieve good energy and position resolution. Extensive tests have validated the design. Joint test, mass production and final commissioning are expected to be done by the end of 2026. The ZDC also serves as an R&D platform for future collider projects in China, including the Circular Electron-Positron Collider (CEPC) and the Super Tau-Charm Facility (STCF).
We report on recent results concerning neutrino oscillation in the presence of background torsion. In the context of Einstein-Cartan theory, we find new oscillation formulas for constant torsion and linearly time-dependent torsion. The oscillation formulas obtained depend on the orientation of the spin.
The paper presents the upgrade of the KL and muon detector for the Belle II experiment at the SuperKEKB collider. To maintain the performance under the elevated background levels associated with high luminosity, the original resistive plate chambers in the endcaps and the innermost barrel layers have been replaced with a scintillator-based system. The new technology utilizes extruded plastic scintillation strips equipped with wavelength-shifting fibers and silicon photomultipliers. The design and assembly of the detector modules, the front-end electronics based on the TARGETX ASIC, and the calibration methodology developed for the 17,000-channel system using single-photoelectron spectra are discussed. Performance tests indicate that the light yield significantly exceeds the design specifications, ensuring high reconstruction efficiency. The upgraded KLM system is currently operational and provides robust particle identification for the Belle II physics program.
Polarized lepton beams can substantially extend the physics capability of the Circular Electron Positron Collider (CEPC). Transversely polarized pilot bunches enable resonant-depolarization beam-energy calibration at the Z and W energies, while longitudinally polarized colliding beams would provide an additional spin observable for precision electroweak measurements and searches for physics beyond the Standard Model. This paper reviews the polarization requirements for CEPC and presents an updated source-to-collider strategy for generating, preserving, manipulating and measuring beam polarization. The proposed scheme combines a polarized electron source, a dual-purpose positron damping and polarizing ring, spin-preserving transport through the injector chain, booster-lattice optimization to avoid strong spin resonances, solenoid-based spin rotators in the collider ring and Compton polarimetry. Recent studies indicate that polarization transmission above 70% through the injector chain is achievable for applications at the Z and W energies, whereas polarization at the Higgs and t (t) over bar energies remains challenging because of stronger spin-resonance effects. The associated R&D program is summarized, and the main open issues for the CEPC Engineering Design Phase are identified.
We propose an effective refractive index definition neff and show its definition may turn into a coordinate dependent definition. As a naive example, we compute it within the Friedmann-Robertson-Walker (FRW) metric. Afterwards, we extend neff to a covariant definition and, remarkably, we show that coupling general relativity with nonlinear electrodynamics (NLED), in analogy to what may happen for regular black holes, permits to realize negative refraction. We clarify that a negative value obtained from a metric coefficient alone is not enough, by itself, since it is coordinate dependent. We conclude that one expects an effective metric, describing general relativity coupled with NLED, to account for negative refraction, with precise coordinate-independent criteria. Hence, in the field of general relativity only, i.e. with no couplings with further fields, dealing with negative refraction may be speculative. Last but not least, we also discuss the distinction between negative refraction and negative mass in general relativity and, finally, we outline how our refractive index construction can be generalized beyond spherical symmetry toward stationary axisymmetric configurations.
We investigate entanglement generation during cosmological inflation, focusing on the role of space-time perturbations generated by a scalar inflaton field. We first show that gravitational particle production associated with the inflaton quantum fluctuations generates momentum-space entanglement. In particular, we highlight how the Hubble horizon emerges as the natural separation scale for fluctuation modes in bipartite approaches, computing the von Neumann entropy between sub- and super-Hubble modes. We then generalize our treatment to multipartite scenarios. The corresponding entanglement amount is quantified via the recently proposed Entanglement Distance, providing a geometric interpretation of particle entanglement in terms of the Fubini-Study metric. We observe that, in the limit of negligible squeezing, the total amount of entanglement is dominated by the infrared cutoff scale, in agreement with standard bipartite scenarios. We then show that nonnegligible multipartite entanglement signatures may emerge across inflation, even during the latest stages of slow-roll, highlighting their dependence on inflationary momentum scales.
