Hasil untuk "Geophysics. Cosmic physics"

T. Gaisser

Yong Ren, Minghui Zhu, Lei Dai et al.

Abstract Substorms are often described by a loading‐unloading cycle, where onset follows gradual accumulation of solar wind magnetic flux in the magnetosphere. Yet observations indicate that intense substorms can also be directly driven, though the underlying mechanism remains unresolved. For the first time, global observations strongly indicate that substorm triggering is linked to enhanced dayside‐driven convection and Region 1 FAC, supported by simulations. At 17:17UT during the May 2024 superstorm, a shock‐compressed southward interplanetary magnetic field enhanced sunward convection and auroral currents. These rapidly extended to the nightside, initiating substorm expansion within 6 min. Simulations reproduce this response, revealing that dayside‐driven convection of closed field lines depleted nightside flux and thinned the current sheet. This lowered onset threshold and triggered substorm expansion with negligible flux loading. Following onset, nightside flux loading became significant as a reconnection X‐line formed near 10 Earth radii, extended azimuthally, and supported a global substorm current wedge.

Yann Gouttenoire, S. Trifinopoulos, M. Vanvlasselaer

The detection of compact binary mergers with sub-solar masses at gravitational-wave observatories could mark the groundbreaking discovery of primordial black holes (PBHs). Concurrently, evidence for a nHz stochastic gravitational wave background observed by pulsar timing arrays (PTAs) could suggest a non-astrophysical origin, potentially arising from scalar-induced gravitational waves (SIGW). In this work, we analyze the connection between the two phenomena in the case where they share a common origin: the collapse of large primordial curvature perturbations in the early universe. We focus on sub-solar PBH populations within reach of upcoming experiments, including the current and future runs of LIGO-Virgo-KAGRA as well as the third generation observatories such as the Einstein Telescope and Cosmic Explorer. Using a Bayesian framework with physically motivated priors, we perform a consistent model comparison that incorporates existing astrophysical bounds together with the discovery potential of future detectors. Our analysis shows that if PBHs are discovered then the SIGW interpretation — especially in the presence of primordial non-Gaussianities — could become favored over the astrophysical one, as the narrowed priors place greater weight on the region of highest likelihood. Ultimately, we illustrate that combining PTA data with interferometer searches can deliver correlated evidence for new physics across multiple gravitational-wave bands.

Jie Zheng, Da-chun Qiang, Zhi-Qiang You et al.

The cosmic distance duality relation (CDDR) is a fundamental and practical condition in observational cosmology that connects the luminosity distance and angular diameter distance. Testing its validity offers a powerful tool to probe new physics beyond the standard cosmological model. In this work, for the first time, we present a novel consistency test of CDDR by combining HII galaxy data with a comprehensive set of Baryon Acoustic Oscillations (BAO) measurements. The BAO measurements include two-dimensional (2D) BAO and three-dimensional (3D) BAO from the Sloan Digital Sky Survey (SDSS), as well as the latest 3D BAO data from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2). We adopt four different parameterizations of the distance duality relation parameter, η(z), to investigate possible deviations and their evolution with cosmic time. To ensure accurate redshift matching across datasets, we reconstruct the distance measures through a model-independent Artificial Neural Network (ANN) approach. We find no significant deviation from the CDDR (less than 68% confidence level) among four parameterizations. Furthermore, our results show that the constraints on η(z) obtained separately from 2D and 3D BAO measurements are consistent at the 68% confidence level. This indicates that there is no significant tension between the two datasets under the four parameterizations considered. Our ANN reconstruction of HII galaxies could provide constraints on the CDDR at redshifts beyond the reach of Type Ia supernovae. Finally, the consistency of our results supports the standard CDDR and demonstrates the robustness of our analytical approach.

A. Greljo, Xavier Ponce D'iaz, A. E. Thomsen

We investigate the phenomenology of a model [1] in which the proton is rendered absolutely stable by an IR mechanism that remains robust against unknown quantum gravity effects. A linear combination of baryon number and lepton flavors is gauged and spontaneously broken to a residual ℤ9 discrete gauge symmetry enforcing a strict selection rule: ΔB = 0 (mod 3). Despite its minimal field content, the model successfully accounts for established empirical evidence of physics beyond the SM. High-scale symmetry breaking simultaneously provides a seesaw mechanism explaining the smallness of neutrino masses, minimal thermal leptogenesis, and a viable phenomenology of the majoron as dark matter. Any cosmic string-wall network remaining after inflation is unstable for numerous charge assignments. Lepton flavor non-universality, central to the construction, leads to predictive neutrino textures testable via oscillation experiments, neutrinoless double beta decay, and cosmology. The model motivates searches in X- and γ-ray lines, neutrino telescopes, and predicts CMB imprints.

Anson Chen

The tensions between cosmological parameter measurements from the early-universe and the late-universe datasets offer an exciting opportunity to explore new physics, if not accounted for unknown systematics. Apart from the well-known Hubble tension, a tension up to ∼4.9σ in the cosmic dipole has also been reported. While the cosmic dipole is mainly induced by the observer's kinetic motion, an intrinsic dipole arising from the anisotropy of the universe could also play an import role. Such an intrinsic anisotropy can be a dark energy mimicker that causes the observed accelerating expansion of the universe. As a new and powerful tool, gravitational waves can serve as an independent probe to the cosmic dipole. A useful type of events to achieve this is the “golden dark sirens”, which are near-by well-localized compact binary coalescences whose host galaxies can be identified directly due to precise localization. By forecasting golden dark sirens obtained from 10-year observations using different possible detector networks in the future, we find that the standard LIGO-Virgo-KAGRA detectors are not able to detect a meaningful amount of golden dark sirens, and hence next-generation ground-based detectors are essential to obtain a strong constraint on the cosmic dipole. In particular, we find that a three-detector network consisting of more than one next-generation detectors can yield a constraint on the cosmic dipole at an order of 10-3 when jointly measured with H 0. Moreover, a constraint on the cosmic dipole at an order of 10-4 can be achieved when fixing H 0.

Md. Sabur Uddin, Alrazi Abdeljabbar, Harun-Or-Roshid et al.

Clément Stahl, V. Poulin, Benoit Famaey et al.

The Hubble (H 0) tension between direct measurements of the expansion rate and the prediction of the ΛCDM cosmological model calibrated on the Cosmic Microwave Background (CMB), is a strong motivation to explore alternative cosmological models. A popular class of such models includes an additional component of dark energy relevant in the early Universe, which solves the Hubble tension. These Early Dark Energy (EDE) models however typically overpredict the value of the S 8 parameter. Here, we show how combining EDE with scale-dependent primordial non-Gaussianities (sPNG) can in principle both increase H 0 and decrease S 8 at once, even conceivably allowing to solve the potential S 8 tension between measurements of weak gravitational lensing and the ΛCDM expectation. Such sPNG are related to non-trivial inflationary physics, and observationally affect the non-linear regime of structure formation while leaving the linear regime mostly untouched. Depending on the amplitude of the sPNG, such models can either yield back the ΛCDM expectation for the power spectrum in the non-linear regime, and hence an S 8 parameter compatible with ΛCDM, or can even reconcile the value of S 8 from old weak-lensing measurements with the CMB, while solving the Hubble tension in all cases. In such models, both tensions would then be entirely related to pre-CMB physics of the early Universe.

Federico Cima, F. D’Eramo

Observations of the hydrogen hyperfine transition through the 21 cm line near the end of the cosmic dark ages provide unique opportunities to probe new physics. In this work, we investigate the potential of the sky-averaged 21 cm signal to constrain metastable particles produced in the early universe that decay at later times, thereby modifying the thermal and ionization history of the intergalactic medium. The study begins by extending previous analyses of decaying dark matter (DM), incorporating back-reaction effects and tightening photon decay constraints down to DM masses as low as 20.4 eV. The focus then shifts to non-minimal dark sectors with multiple interacting components. The analysis covers two key scenarios: a hybrid setup comprising a stable cold DM component alongside a metastable sub-component, and a two-component dark sector of nearly degenerate states with a metastable heavier partner. A general parameterization based on effective mass spectra and fractional densities allows for a model-independent study. The final part presents two explicit realizations: an axion-like particle coupled to photons, and pseudo-Dirac DM interacting via vector portals or electromagnetic dipoles. These scenarios illustrate how 21 cm cosmology can set leading bounds and probe otherwise inaccessible regions of parameter space.

Elena Vanetti, E. Vanzan, N. Bellomo et al.

Hydrogen 21-cm Line Intensity Mapping offers the unique opportunity to access the Dark Ages and trace the formation and evolution of the large scale structure of the Universe prior to star and galaxy formation. In this work we investigate the potential of future Earth- and Moon-based 21-cm surveys to constrain the growth of structures during the currently unexplored redshift range 30 < z < 200. On the one hand we show how foreground contamination could limit the capabilities of future instruments in achieving precision below the 10% level. On the other hand, observations from the far side of the Moon have the potential to reach percent or even sub-percent precision in terms of reconstructing the growth of cosmic structures, if foregrounds are robustly accounted for. Such exquisite precision will provide tight constraints on models that induce deviations from ΛCDM, not only during the Dark Ages, but also during recombination or that manifest mostly in the low-redshift Universe, like Early Dark Energy and nDGP models, respectively. Thus, because of their insensitivity to non-linearities or astrophysical processes, line intensity mapping surveys will provide a formidable consistency check to potential claims of discoveries of new physics that affect the growth of structures.

P. K. Batrakov, V. Yurovsky, I. Kudryashov

Yang Li, Ligong Bian, Rong-Gen Cai et al.

Recently, pulsar timing array experiments observed a signature of the stochastic gravitational wave (GW) background around the nanohertz frequency range, but the first direct evidence of particle dark matter in the laboratory is still missing. Topological defects in the early universe, such as cosmic strings and domain walls, can emit GW radiation and particles that may act as dark matter, thus providing an opportunity to bridge observable gravitational wave signatures with the phenomenology of particle physics. Based on high-resolution real-time simulations of the early Universe, we demonstrate for the first time that axion-like particles of topological defects origin can simultaneously account for dark matter and the stochastic GW background observed in recent pulsar timing array experiments. Our simulations incorporate the evolution of cosmic strings and string-wall networks following both a high-scale Peccei-Quinn phase transition and a subsequent low-scale QCD phase transition. Our findings reveal that these string-wall networks generate observable GW signatures in the nanohertz to millihertz frequency band, which corresponds to axion-like particle dark matter masses ranging from keV to GeV.

Jue Ning, Xu Chen, Tao Wang et al.

Abstract The modulation of anticyclonic subsurface‐intensified mode‐water eddies (MWEs) on the oceanic physical and biological responses to tropical cyclones (TCs) is investigated using satellite measurements, in situ observations and numerical model outputs. Extreme cooling of the surface (4.2°C) and mixed‐layer (2.3°C) is observed in a MWE, which can be remarkably stronger than those in adjacent cyclonic eddy and non‐eddy environments. The special thermodynamic structure above the lens of MWEs, which would favor the TC‐induced entrainment more efficiently, facilitates the elevation of substantial subsurface cold water. It also leads to increased mixed‐layer salinity and deepening of the mixed‐layer. Additionally, variations in nitrate and chlorophyll‐a concentrations appear to be depressed and exhibit intricate multi‐layer patterns due to TC‐induced and MWE‐influenced vertical processes. This study provides novel insights into the interactions between TCs and subsurface‐intensified eddies.

Shujie Gu, Xu Liu, Lunjin Chen et al.

Abstract Electromagnetic ion cyclotron (EMIC) waves are discrete electromagnetic emissions separated by multiple ion gyrofrequencies. Harmonic EMIC waves are defined as waves with a strong electric or magnetic field (or both) at the harmonics of the fundamental EMIC mode. In this paper, for the first time, we present a statistical study on harmonic EMIC waves by the Van Allen Probes. The EMIC waves are categorized into three types based on their harmonics: (a) Fundamental mode only (without higher harmonics), (b) electrostatic (ES) harmonics, and (c) electromagnetic (EM) harmonics. We find that most harmonic EMIC wave events are observed on the dayside, outside the plasmasphere and are associated with a low fpe/fce, a high proton βH, and a strong fundamental EMIC mode. ES harmonic EMIC waves tend to exhibit a larger Ew/cBw ratio compared to EM harmonic EMIC waves. The results advance our understanding of harmonic EMIC waves and their generation mechanisms.

Samarth Urs M, Nagendra P, B.V. Suresh Kumar

We present mapping and comparision of the geology of the southern block of the Chitradurga schist belt (CSB). We have used ASTER images and geophysical data to compare the geology. Consequently, present study confirms how remote sensing integrated with geophysical surveys can enhance the efficiency and accuracy of regional geological mapping. False colour composites, band ratios, rock indices (QI, MI, and CI), mineral indices, and broadband albedo were used for lithological mapping. Remote sensing results were correlated with digitized thematic geophysical data viz. gravity anomalies, magnetic and radiometric data. The results were validated with lithological data obtained from the Geological Survey of India. Results showed that southern portion of CSB is fringed within a gneiss and dominated by amphibolites interbedded with narrow quartzite bands. To its west, occurs a narrow belt of ultramafites and acidic intrusions. In some localities, the amphibolites are overlain by mica schists.

Yuanning Li, Chao Xu, Fei Geng et al.

为揭示诱发地震和天然地震对建筑结构影响及其破坏概率分布的影响，本文以我国典型砌体结构为研究对象，开展了考虑诱发地震影响的易损性研究。首先建立了典型三层和六层砌体结构分析模型，然后以40条震级和震中距都接近的天然地震地震动和诱发地震地震动为输入开展Pushover分析，分别建立基于峰值加速度PGA和结构基本周期加速度反应谱值Sa的易损性曲线，最后采用循环往复加载方法对两次诱发地震作用下的结构倒塌易损性进行了分析讨论。结果表明：当以PGA作为易损性输入地震动参数时，天然地震地震动作用下的易损性显著高于诱发地震地震动；当以Sa作为易损性输入地震动参数时，三层砌体结构由于以基本振型为主导，在两类地震动作用下其易损性曲线比较接近，而六层砌体结构高阶振型由于对结构地震响应具有一定影响，且诱发地震地震动的高频成分较天然地震地震动丰富，因此六层砌体结构在诱发地震地震动作用下的易损性高于天然地震。此外，对两次诱发地震作用下的砌体结构易损性分析结果表明两次地震作用下结构的损伤概率明显增加。

Jian Zhang, Yanxia Fan, Wei Chu et al.

长白山天池火山是晚新生代中心喷发式复合型层状火山，全新世以来发生过多次大规模喷发，与深部岩浆热扰动活动相关的构造地震、地表形变、温泉气体组份等均显示该火山仍可能再次喷发，是我国东部潜在的高温地热资源区。长白山天池火山周边地下水十分丰富，具有形成高温水热活动的岩浆囊热源。为探索地壳浅层隐伏的高温地热资源，本文在野外考察基础上，利用地热学方法，计算了该区地层结构与热状态，分析了地表下的火山地热系统。结果表明：长白山天池火山区地下2 km深处的温度在66—110℃之间，12 km深处的温度在313—417℃之间；该区居里面深度较浅，平均深度为12.7 km，居里点温度为375℃，其中长白山天池火山喷发中心和望天鹅火山喷发中心为居里面上隆区；在人工地震基底速度约束下，通过沉积地层重力反演发现，在约3.5—5.5 km深度处存在密度梯级高压带，该高压带与12 km深度处的岩浆囊之间的区域是形成隐伏高温地热资源的有利区域。

Peilin Wang, Bingxin Liu, Ying Li et al.

As shipping routes and resource exploration move toward high-latitude oceans, sea ice becomes a major threat to the safety of ship navigation, posing significant challenges to the shipping industry and offshore resource development. Continuous development of satellite remote sensing and deep learning has made large-scale and wide-ranging ship detection (SD) possible, which is of great significance for ship safety. However, existing ship datasets used for deep learning only include ship images in open waters (OW), such as ports and inland rivers. Currently, remote sensing datasets suitable for SD in ice-infested waters (IIW) are lacking. SD in IIW is more difficult than SD in OW because of complex background interference from sea ice. Thus, it is infeasible to directly use the features of ships in OW for SD in IIW. Herein, we propose a remote sensing SD dataset called IceRegionShip, which includes subdatasets IceRegionShip&#x2013;red, green and blue (RGB) and IceRegionShip&#x2013;ice region ship index (IRSI). IceRegionShip&#x2013;IRSI consists of low-resolution images processed with IRSI. IceRegionShip&#x2013;RGB and IceRegionShip&#x2013;IRSI contain 11&#x2009;436 and 9073 ship instances, respectively. IRSI was proposed to address false alarms caused by ice interference. To the best of our knowledge, this is the first dataset designed specifically for SD in IIW. In addition, the dataset was evaluated using several advanced detection algorithms, providing a benchmark for SD in IIW and demonstrating the effectiveness of IRSI for SD in low-resolution optical remote sensing images.

Xiaomin Ruan, Mingchun Chen, Zhendong Liu et al.

Seismic exploration is a key method for the study of underground structures. Active seismic surveys can acquire high signal-to-noise ratio reflection data; however, the operation of active seismic surveys is complicated, and the exploration cost is high. Passive seismic exploration is another type of seismic exploration, which requires no active human build source but utilizes the natural noise recorded by seismograph stations or geophones. As a low-cost and environmentally friendly method, passive seismic reflection exploration can be used to create higher resolution seismic profiles than the surface wave method and plays an increasingly important role in underground mineral exploration, dynamic monitoring of carbon storage, and urban underground structure detection. However, passive source reflection imaging technology faces several challenges. For example, because ambient noise is mainly controlled by surface wave energy, the reflected body wave signal can be weak and difficult to extract. Actual underground sources are limited in number and are unevenly distributed, which leads to artifacts in the virtual shot gathers reconstructed by seismic interference. There are also constraints of massive data computation and storage for long-term observation by a large number of geophones. With the rapid development of portable node geophones and high-performance computing, passive seismic reflection exploration has achieved considerable progress in both method research and practical applications in recent years. This paper briefly reviews the history of seismic interferometry and the construction of virtual shot gathers using various seismic interferometry methods and then introduces in detail how the reflection signals from ambient noise records dominated by surface waves are identified and extracted. We discuss the identification and extraction of weak body wave reflection signals based on various characteristics of surface and body waves, such as differences in signal-to-noise ratio, velocity, and azimuth angle. We then focus on the processing of passive source reflection data, including the beginning of raw data preprocessing, virtual shot gather static correction, coherent noise suppression, multiple suppression, velocity analysis, and direct migration imaging. We also introduce examples of passive seismic reflection applications, including CO2 storage site monitoring, metal mining, and coal mine underground structure research. Finally, we give an outlook for research prospects in passive seismic reflection exploration.