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Amid China-US geopolitical competition in the Asia-Pacific, it is imperative for both China and Singapore to adapt and respond to evolving circumstances for mutual benefit. The enduring trust and solid foundation between China and Singapore in economic and trade cooperation are validated through their active involvement in each other's initiatives. This proved true even when the recent COVID-19 pandemic strained political interactions. The political-security dimensions of the relationship between China and Singapore are complex and constantly evolving, influenced as they are by factors such as Singapore's military training in Taiwan, the contentious South China Sea disputes, and US foreign policy in the region. However, Singapore's longstanding hedging strategy between the two superpowers may face increasingly severe tests as China-US rivalry escalates. If carefully managed, Singapore's successful track record of facilitating dialogue between conflicting parties can continue to make it a valuable player in easing tensions between China and the US.

We examine a method to detect the light speed variation from gamma ray burst data observed by the Fermi Gamma-ray Space Telescope (FGST). We suggest new criteria to determine the characteristic time for low energy photons by the energy curve and the average energy curve respectively, and obtain similar results compared with those from the light curve. We offer a new criterion with both the light curve and the average energy curve to determine the characteristic time for low energy photons. We then apply the new criteria to the GBM NaI data, the GBM BGO data, and the LAT LLE data, and obtain consistent results for three different sets of low energy photons from different FERMI detectors.

As a basic symmetry of space-time, Lorentz symmetry has played important roles in various fields of physics, and it is a glamorous question whether Lorentz symmetry breaks. Since Einstein proposed special relativity, Lorentz symmetry has withstood very strict tests, but there are still motivations for Lorentz symmetry violation (LV) research from both theoretical consideration and experimental feasibility, that attract physicists to work on LV theories, phenomena and experimental tests with enthusiasm. There are many theoretical models including LV effects, and different theoretical models predict different LV phenomena, from which we can verify or constrain LV effects. Here, we introduce three types of LV theories: quantum gravity theory, space-time structure theory and effective field theory with extra-terms. Limited by the energy of particles, the experimental tests of LV are very difficult; however, due to the high energy and long propagation distance, high-energy particles from astronomical sources can be used for LV phenomenological researches. Especially with cosmic photons, various astronomical observations provide rich data from which one can obtain various constraints for LV researches. Here, we review four common astronomical phenomena which are ideal for LV studies, together with current constraints on LV effects of photons.

Wheat head detection can estimate various wheat traits, such as density, health, and the presence of wheat head. However, traditional detection methods have a huge array of problems, including low efficiency, strong subjectivity, and poor accuracy. In this paper, a method of wheat-head detection based on a deep neural network is proposed to enhance the speed and accuracy of detection. The YOLOv4 is taken as the basic network. The backbone part in the basic network is enhanced by adding dual spatial pyramid pooling (SPP) networks to improve the ability of feature learning and increase the receptive field of the convolutional network. Multilevel features are obtained by a multipath neck part using a top-down to bottom-up strategy. Finally, YOLOv3′s head structures are used to predict the boxes of wheat heads. For training images, some data augmentation technologies are used. The experimental results demonstrate that the proposed method has a significant advantage in accuracy and speed. The mean average precision of our method is 94.5%, and the detection speed is 71 FPS that can achieve the effect of real-time detection.

Lorentz invariance violation (LIV) can change the threshold behavior predicted by special relativity and cause threshold anomalies which affect the propagation of cosmic photons. In this work, we focus on the threshold anomaly effect on cosmic photon attenuations by extragalactic background light (EBL) and discuss how to identify LIV from observations of very high energy (VHE) photons propagated from long distance in the universe. We point out that the Large High Altitude Air Shower Observatory (LHAASO), one of the most sensitive gamma-ray detector arrays currently operating at TeV and PeV energies, is an ideal facility for performing such LIV searching. We apply the proposed strategy to discuss the newly observed gamma-ray burst GRB 221009A to demonstrate the predictive ability of our suggestions.

A bstract Previous studies on high-energy gamma-ray burst neutrinos from IceCube suggest a neutrino speed variation at the Lorentz violation (LV) scale of ~6 . 4 × 10 17 GeV, with opposite velocity variances between neutrinos and antineutrinos. Within a spacetime foam model, inspired by string theory, we develop an approach to describe the suggested neutrino/antineutrino propagation properties with both Lorentz invariance and CPT symmetry breaking. A threshold analysis on the bremsstrahlung of electron-positron pair ( ν → νee + ) for the superluminal (anti)neutrino is performed. We find that, due to the energy violation caused by the quantum foam, such reaction may be restricted to occur at sufficient high energies and could even be kinematically forbidden. Constraints on neutrino LV from vacuum ee + pair emission are naturally avoided. Future experiments are appealed to test further the CPT violation of cosmic neutrinos and/or neutrino superluminality.

Leggett–Garg inequality (LGI) is a time analogue of Bell’s inequality that concerns measurements performed on a system at different times. Violation to LGI indicates quantum coherence. We present a Leggett–Garg-type inequality compatible with more general neutrino oscillation frameworks, allowing the effects of decoherence to be taken into consideration. The inequality is applied to test coherence for data from Daya Bay, MINOS, and KamLAND experiments, and their results are compared to theoretical predictions to investigate decoherence. Both Daya Bay and MINOS data exhibit clear violations of over 10σ, and of over 90% of theoretical predictions, while the KamLAND data exhibit violation of 1.9σ, being of 58% of the theoretical prediction. The present work is the first to have considered the energy uncertainties in neutrino coherence tests.

A bstract We entertain the constraints that the absence of vacuum Cherenkov radiation of ultrahigh-energy electrons inferred from LHAASO observations of the Crab Nebula can impose on generic models in which Lorentz symmetry of the particle vacuum is violated, as established by some recent studies in Phys. Lett. B 829 (2022) 137034; Phys. Lett. B 835 (2022) 137536; Phys. Rev. D 108 (2023) 063006. We demonstrate in the present paper, that implementing a phenomenological approach to the Lorentz violation, the rates of this vacuum process are substantial such that one is justified in deriving bounds on the violation scales from simple threshold analysis just as these works did. Albeit such results are likely effective then, they do not apply in the same form among scenarios. Specifically, we show that these Cherenkov constraints are naturally evaded in models of space-time foam inspired from (supercritical) string theory, involving D-branes as space-time defects in a brane-world scenario, in which subluminous energy-dependent refractive indices of light have been suggested. We examine here two specific foam situations and find for both cases (though, for different reasons) the potentiality that charged quanta such as electrons do not radiate as they pass through the gravitational vacuum ‘medium’ despite moving faster than photons.

A bstract Neutrinos from the cosmos have proven to be ideal for probing the nature of space-time. Previous studies on high-energy events of IceCube suggested that some of these events might be gamma-ray burst neutrinos, with their speeds varying linearly with their energy, implying also the coexistence of subluminal and superluminal propagation. However, a recent reanalysis of the data, incorporating revised directional information, reveals stronger signals that neutrinos are actually being slowed down compared to previous suggestion of neutrino speed variation. Thus, it is worth discussing its implications for the brane/string inspired framework of space-time foam, which has been used to explain previous observations. We revisit effects on neutrino propagation from specific foam models within the framework, indicating that the implied violation of Lorentz invariance could necessarily cause the neutrino to decelerate. We therefore argue that this sort of model is in agreement with the updated phenomenological indication just mentioned. An extended analysis of the revised IceCube data will further test these observations and stringy quantum gravity.

The cosmic-ray spectrum structures help to study the acceleration and propagation mechanism of ultra-high energy cosmic rays, and these structures were predicted to culminate in a cut-off, named the Greisen–Zatsepin–Kuzmin (GZK) cut-off, near 5 × 10 19 eV as a result of the inelastic interaction of protons with the 2.73 K black body radiation. The confirmation of the existence of GZK cut-off was tortuous, leading to activities to explore new physics, such as the cosmic-ray new components, unidentified cosmic-ray origins, unknown propagation mechanism and the modification of fundamental physics concepts like the tiny Lorentz invariance violation (LV). The confirmation of the GZK cut-off provides an opportunity to constrain the LV effect. We use a phenomenological framework to restudy the GZK mechanism under the Planck scale deformation of the proton and pion dispersion relations. Restudying the photon induced pion production of the proton p + γ → p + π 0 , we predict abnormal threshold behaviors of this reaction under different LV modifications. Therefore we can study the LV effects not only from the conventional GZK cut-off, but also from potentially threshold anomalies of the pion production process. We divide the LV parameter space into three regions, and analyze the constraints from current observations in each region. The current observations have set strict restrictions on a certain LV region. However, for others LV regions, further experimental observations and theoretical researches are still needed, and we also find survival space for some theoretical explorations that permit specific LV effects.