Hasil untuk "Geophysics. Cosmic physics"

E. J. Copeland, M. Sami, S. Tsujikawa

We review in detail a number of approaches that have been adopted to try and explain the remarkable observation of our accelerating universe. In particular we discuss the arguments for and recent progress made towards understanding the nature of dark energy. We review the observational evidence for the current accelerated expansion of the universe and present a number of dark energy models in addition to the conventional cosmological constant, paying particular attention to scalar field models such as quintessence, K-essence, tachyon, phantom and dilatonic models. The importance of cosmological scaling solutions is emphasized when studying the dynamical system of scalar fields including coupled dark energy. We study the evolution of cosmological perturbations allowing us to confront them with the observation of the Cosmic Microwave Background and Large Scale Structure and demonstrate how it is possible in principle to reconstruct the equation of state of dark energy by also using Supernovae Ia observational data. We also discuss in detail the nature of tracking solutions in cosmology, particle physics and braneworld models of dark energy, the nature of possible future singularities, the effect of higher order curvature terms to avoid a Big Rip singularity, and approaches to modifying gravity which leads to a late-time accelerated expansion without recourse to a new form of dark energy.

Xu Wang, Chang Wang

Aiming at the problems that the clock bias prediction model of the Wavelet Neural Network (WNN) is greatly affected by the selection of network parameters, and the Particle Swarm Optimization Wavelet Neural Network is prone to fall into local optima and has insufficient convergence efficiency in clock bias prediction, a short-term clock bias prediction model for BDS-3 based on the Rime Optimization Algorithm (RIME)-optimized Wavelet Neural Network is proposed. Firstly, the specific steps of the WNN model based on the RIME optimization algorithm in clock bias prediction are elaborated in detail. Then, the stability characteristics and training efficiency of the RIME optimization algorithm during the optimization stage are analyzed to determine the population size that suits the characteristics of clock bias data. Finally, using the BDS-3 clock bias data provided by the Wuhan University Data Center, short-term clock bias prediction experiments with durations of 1 h, 3 h, and 6 h are carried out. The experimental results show that in the 6h prediction, the average prediction accuracy of the RIME-WNN model is better than 0.1 ns, which is 93.92%, 88.35%, and 48.11% higher than that of the Quadratic Polynomial model, the Grey Model (GM(1,1)), and the PSO-WNN model, respectively. In addition, when the RIME-WNN model predicts different types of Beidou satellites, the maximum difference in the Root Mean Square Error (RMSE) is relatively smaller, which fully demonstrates that the model has a wide and good accuracy adaptability when predicting various types of Beidou satellites.

Lianhui Liang, Shuai Yuan, Yixuan Zeng et al.

Hyperspectral image classification (HSIC) is a crucial task in remote sensing. In existing HSIC architectures, convolutional neural networks excel at capturing local information through regional feature representations, while transformers are adept at establishing long-range dependencies with the self-attention mechanism. However, these methods still encounter challenges of imbalanced global–local feature explorations and boundary feature extractions. To address these issues, this study proposes the cross-stage attention edge enhancement and Fourier-wavelet transformer integrated network (CAEEFT-Net), which effectively balances global context modeling with local detail preservation and boundary feature extraction for HSIC tasks. Specifically, for spatial feature refinement, three key modules are designed: the cross-stage attention module to enable the interaction of features across different stages, thereby strengthening the model’s feature representation ability, the global–local attention module to jointly enhance global and local features, and the pyramid-stripe attention module to capture discriminative edge features. For spectral feature extraction, this article proposes a spectral Fourier-wavelet transformer to integrate the strengths of both global frequency-domain patterns and local token-level features. Experimental results on three benchmark datasets demonstrate that CAEEFT-Net achieved superior performance compared to state-of-the-art methods, validating the effectiveness of the proposed CAEEFT-Net model for HSIC.

Ryan N. Ing, Peter W. Nienow, Andrew J. Sole et al.

Abstract Extreme melt and rainfall events can induce temporary acceleration of Greenland Ice Sheet motion, leading to increased advection of ice to lower elevations where melt rates are higher. In a warmer climate, these events are likely to become more frequent. In September 2022, seasonally unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to ∼240% relative to pre‐event velocities. However, ice motion returned rapidly to pre‐event levels, and the speed‐ups caused a regional increase in annual ice discharge of only ∼2% compared to when the effects of the speed‐ups were excluded. Therefore, although late melt‐season events are forecast to become more frequent and drive significant runoff, their impact on net mass loss via ice discharge is minimal.

Xiaofei Yin, Wenjun Li, Yingcai Xu et al.

本文开展了基于地震活动图像预测华北地区地震的机器学习方法研究。根据华北地区M≥5.0中强震、强震及大震的地震平均时间间隔，采用1970年以来华北地区M≥5.0中强震、强震及大震震前大量不同时窗长的ML≥3.0地震活动图像作为输入数据集，提出了基于地震活动图像预测地震的机器学习方法，并进行了震例回溯。利用本文提出的方法选取“未拓展图像数据集”和“含拓展图像数据集”对华北地区发生中强地震进行预测对比，结果显示，数据集样本量的增加有利于提高地震预测模型的精度，其中“含拓展图像数据集”预测地震的准确率可达77%；对于华北地区无震区、少震区的M≥5.0地震，可采用非1年窗长的较大时间间隔（3年、7年以上）的ML≥3.0地震活动图像验证。

Anan Yaghmour, Saurabh Prasad, Melba M. Crawford

In geospatial image analysis, domain shifts caused by differences between datasets often undermine the performance of deep learning models due to their limited generalization ability. This issue is particularly pronounced in hyperspectral imagery, given the high dimensionality of the per-pixel reflectance vectors and the complexity of the resulting deep learning models. We introduce a semisupervised domain adaptation technique that improves on the adversarial discriminative framework, incorporating a novel multiclass discriminator to address low discriminability and negative transfer issues from which current approaches suffer. Significantly, our method addresses mode collapse by incorporating limited labeled data from the target domain for targeted guidance during adaptation. In addition, we integrate an attention mechanism that focuses on challenging spatial regions for the target mode. We tested our approach on three unique hyperspectral remote sensing datasets to demonstrate its efficacy in diverse conditions (e.g., cloud shadows, atmospheric variability, and terrain). This strategy improves discrimination and reduces negative transfer in domain adaptation for geospatial image analysis.

Emmanouil Vourliotis

Many new physics models, e.g., leptoquarks, extra dimensions, extended Higgs sectors, supersymmetric theories, and dark sector extensions, are expected to manifest themselves in the final states with hadronic jets. Novel experimental techniques, including a dedicated scouting trigger stream and advanced machine learning techniques can be employed to identify such signals. This talk presents searches in CMS for new phenomena in the final states that include jets, focusing on the most recent results obtained using the full Run-II data-set collected at the LHC.

P. Volchugov, I. Astapov, P. Bezyazeekov et al.

A. Alexandrov, A. Anokhina, S. Vasina et al.

M. Shalaby, T. Thomas, C. Pfrommer et al.

We study the underlying physics of cosmic ray (CR)-driven instabilities that play a crucial role for CR transport across a wide range of scales, from interstellar to galaxy cluster environments. By examining the linear dispersion relation of CR-driven instabilities in a magnetised electron–ion background plasma, we establish that both the intermediate and gyroscale instabilities have a resonant origin, and show that these resonances can be understood via a simple graphical interpretation. These instabilities destabilise wave modes parallel to the large-scale background magnetic field at significantly distinct scales and with very different phase speeds. Furthermore, we show that approximating the electron–ion background plasma with either magnetohydrodynamics (MHD) or Hall-MHD fails to capture the fastest-growing instability in the linear regime, namely the intermediate-scale instability. This finding highlights the importance of accurately characterising the background plasma for resolving the most unstable wave modes. Finally, we discuss the implications of the different phase speeds of unstable modes on particle–wave scattering. Further work is needed to investigate the relative importance of these two instabilities in the nonlinear, saturated regime and to develop a physical understanding of the effective CR transport coefficients in large-scale CR hydrodynamics theories.

Arun Rana, A. Pendse, Sebastian Wuester et al.

Early during the era of cosmic inflation, rotational invariance may have been broken, only later emerging as a feature of low-energy physics. This motivates ongoing searches for residual signatures of anisotropic space-time, for example in the power spectrum of the cosmic microwave background. We propose that dipolar Bose–Einstein condensates (BECs) furnish a laboratory quantum simulation platform for the anisotropy evolution of fluctuation spectra during inflation, exploiting the fact that the speed of dipolar condensate sound waves depends on direction. We construct the anisotropic analogue space-time metric governing sound, by linking the time-varying strength of dipolar and contact interactions in the BEC to the scale factors in different coordinate directions. Based on these, we calculate the dynamics of phonon power spectra during an inflation that renders the initially anisotropic Universe isotropic. We find that the expansion speed provides an experimental handle to control and study the degree of final residual anisotropy. Gravity analogues using dipolar condensates can thus provide tuneable experiments for a field of cosmology that was until now confined to a single experiment, our Universe.

A. Alexandrov, A. Anokhina, S. Vasina et al.

I. I. Mokhov

A. Ringwald

SM*A*S*H is an extension of the Standard Model of particle physics which has just the minimal number of fields in order to solve six puzzles of particle physics and cosmology in one smash: vacuum stability, inflation, baryon asymmetry, neutrino masses, strong CP, and dark matter. The parameters of SM*A*S*H are constrained by symmetries and requirements to solve these puzzles. This provides various firm predictions for observables which can be confronted with experiments. We discuss the prospects and timeline to scrutinise or smash SM*A*S*H by cosmic microwave background polarisation experiments, axion haloscopes, and future space-borne gravitational wave detectors.

L. Sveshnikova, I. Astapov, P. Bezyazykov et al.

Guo-Yuan Huang

The in-ice or in-water Cherenkov neutrino telescope, such as IceCube, has already proved its power in measuring the Glashow resonance by searching for the bump around arising from the W-boson production. There are many proposals for the next few decades for observations of cosmic tau neutrinos with extensive air showers, also known as tau neutrino telescopes. The air shower telescope is, in principle, sensitive to the Glashow resonance via the channel followed by the tau decay in the air (e.g., TAMBO, which has a geometric area of approximately ). Using a thorough numerical analysis, we find that the discovery significance can be up to 90% with a TAMBO-like setup if PeV neutrinos primarily originate from neutron decays, considering the flux parameters measured by IceCube as the input. The presence of new physics affecting the neutrino flavor composition can also increase the significance. However, if ultrahigh-energy neutrinos are dominantly produced from meson decays, it will be statistically difficult for an advanced proposal such as TAMBO to discriminate the Glashow resonance induced by from the intrinsic background. We have identified several limitations for such advanced telescopes, in comparison with the in-ice or in-water telescope, when measuring resonances: (i) a suppressed branching ratio of 11% for the decay ; (ii) the smearing effect and reduced acceptance because the daughter neutrino takes away 75% of the energy from the W decay; and (iii) a large attenuation effect for Earth-skimming neutrinos with the resonance.

D. Volpe

Since July 2021, LHAASO is fully operational and collecting data. The Nature paper in 2021, revealing 12 VHE new sources, was just the start of LHAASO science, revealing the huge scientific potential of this experiment. LHAASO opened the multi-TeV era in γ-ray astronomy and cosmic ray physics. Many analysis efforts in different areas are ongoing in different areas and several results are already published. In this contribution, we will show some highlights from LHAASO science together with the status of calibrations and performances achieved.

V. Gubenko, V. Andreev, I. Kirillovich et al.

V. Okorokov

The processes with single top quark production provide a prototype search for the types of final state that are expected in many new physics scenarios. Some distinctive features are considered for particle production in the top sector in ultra-high energy domain which can be covered partly in the collisions of cosmic ray particles with atmosphere. The single top quark production through electroweak interaction is studied within the Standard Model and the Effective Field Theory approach used for calculations of total partonic cross sections in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$s$$\end{document}–channel. These quantitative results can be important for both the future collider experiments at center-of-mass energy frontier and the improvement of the phenomenological models for development of the cosmic ray cascades in ultra-high energy domain. Thus the study allows the better understanding of heavy particle production and emphasizes the exciting interrelation between the high-energy physics on accelerators and ultra-high energy cosmic ray measurements.

V. Latypova, V. Nemchenko, C. Azra et al.