Hasil untuk "Geophysics. Cosmic physics"

S. Furlanetto, S. Oh, F. Briggs

Abstract Observations of the high-redshift Universe with the 21 cm hyperfine line of neutral hydrogen promise to open an entirely new window onto the early phases of cosmic structure formation. Here we review the physics of the 21 cm transition, focusing on processes relevant at high redshifts, and describe the insights to be gained from such observations. These include measuring the matter power spectrum at z ∼ 50 , observing the formation of the cosmic web and the first luminous sources, and mapping the reionization of the intergalactic medium. The epoch of reionization is of particular interest, because large HII regions will seed substantial fluctuations in the 21 cm background. We also discuss the experimental challenges involved in detecting this signal, with an emphasis on the Galactic and extragalactic foregrounds. These increase rapidly toward low frequencies and are especially severe for the highest redshift applications. Assuming that these difficulties can be overcome, the redshifted 21 cm line will offer unique insight into the high-redshift Universe, complementing other probes but providing the only direct, three-dimensional view of structure formation from z ∼ 200 to 6.

M. Aguilar, L. A. Cavasonza, G. Ambrosi et al.

Abstract The Alpha Magnetic Spectrometer (AMS) is a precision particle physics detector on the International Space Station (ISS) conducting a unique, long-duration mission of fundamental physics research in space. The physics objectives include the precise studies of the origin of dark matter, antimatter, and cosmic rays as well as the exploration of new phenomena. Following a 16-year period of construction and testing, and a precursor flight on the Space Shuttle, AMS was installed on the ISS on May 19, 2011. In this report we present results based on 120 billion charged cosmic ray events up to multi-TeV energies. This includes the fluxes of positrons, electrons, antiprotons, protons, and nuclei. These results provide unexpected information, which cannot be explained by the current theoretical models. The accuracy and characteristics of the data, simultaneously from many different types of cosmic rays, provide unique input to the understanding of origins, acceleration, and propagation of cosmic rays.

Xianqi Meng, Yuefeng Zhao, Kaifa Cao et al.

Remote sensing image change captioning (RSICC) aims to generate textual descriptions of changes between bitemporal images. However, accurately describing fine-grained changes while capturing interscale relationships as well as distinguishing real changes from spurious changes (e.g., illumination, seasonal variations) are still major challenges for current methods. To address these issues, we propose DualFocus-CapNet, a novel model tailored for RSICC. DualFocus-CapNet employs a dual-stream architecture, where each stream is dedicated to processing a distinct pair of bitemporal features. Crucially, we introduce a scale-wise progressive convolution (ScalePro Conv) that employs a progressive scale-specific approach to decompose remote sensing features into pixel-level variations, regional continuities, and linear structures. Unlike conventional parallel multiscale processing methods, ScalePro Conv adopts a serial progressive structure to establish interscale relationships, thereby avoiding the fragmentation of feature information. Then, the bi-directional difference guided transformer (BDiGTrans) is proposed to eliminate interference from spurious changes by dynamically masking invariant regions and extracting bidirectional differential features. Furthermore, the cross-temporal adaptive fusion module (CTAF) is introduced to dynamically balance bitemporal features using learnable gating to enhance change discrimination and robust caption generation. Comprehensive experiments on the benchmark datasets LEVIR-CC and WHU-CDC show that our DualFocus-CapNet surpasses state-of-the-art change captioning methods in various evaluation metrics.

Elsy Ibrahim, Anne Gobin

The detection and exclusion of clouds and their shadows have been the primary focus of pixel contamination in spaceborne agricultural soil monitoring. However, contaminants affecting specific parts of agricultural fields, such as stationary features (large pylons and artificial soil cover) and dynamic sources (pylon shadows and passing aircraft with contrails), have been overlooked despite their importance in precision agriculture. This study investigates these underexplored sources of pixel contamination and their implications for agricultural soil monitoring. Using bare soil data from 2017 to 2023 and focusing on the field preparation period from mid-April to late May, we analyzed the effects of artificial soil cover, transmission tower shadows, and aircraft overflights on bare soil reflectance. These pixel contaminants significantly altered surface reflectance compared to clear bare soil pixels, with P <inline-formula><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula> 0.0001 for artificially covered, P <inline-formula><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula> 0.01 for aircraft-impacted and P <inline-formula><tex-math notation="LaTeX">$\leq$</tex-math></inline-formula> 0.05 for tower shadowed pixels. Artificial cover increased the surface reflectance of bare soil by 10&#x0025; to 50&#x0025; in the visible and near-infrared bands, with a smaller increase of 5&#x0025; in the shortwave infrared bands; pylon shadows reduced the surface reflectance by up to 5&#x0025; within a 10 m buffer around the shadow. Aircraft footprints caused a sixfold increase in reflectance, with contrails affecting large areas and increasing reflectance by up to 30&#x0025;. Important spectral indices for bare soil analyses were significantly affected by artificial cover, but not always by shadows or aircraft impact. The analysis provides insights into the spectral anomalies caused by pixel contaminants and highlights the need to account for such influences to improve the accuracy of spaceborne agricultural soil monitoring, particularly in small parcels or field zones.

Jing Wang, Shouwen Zhang, Yuanlong Li et al.

Abstract Interactions among the El Niño‐Southern Oscillation, Indian Ocean Basin mode (IOB), and Indian Ocean Dipole (IOD) significantly impact global climate variability and seasonal predictions. Traditionally, positive IOD (pIOD) and IOB warming events are associated with El Niño, driven by its influence on the tropical Indian Ocean through Walker Circulation anomalies. Our findings enrich this framework, revealing that a pIOD without El Niño can independently trigger IOB warming, and both types of pIODs can induce La Niña events. While El Niño primarily forces IOB warming and subsequent La Niña development via the atmospheric bridge across the Maritime Continent, pIODs independent of El Niño influence IOB warming through oceanic dynamics, which further favors La Niña development in the following year. The NMEFC‐CESM model sensitivity experiments underscore the critical role of thermocline processes in this mechanism, dependent on the pIOD's temperature amplitude, offering vital insights for forecasting post‐IOD, IOB, and La Niña events.

Yuanyuan Guo, Weizhong Li, Qi Peng et al.

Lossy compression exhibits remarkable capabilities in handling large volumes of data. However, information loss can affect spectral characteristics and spatial information to various degrees during hyperspectral compression. Therefore, it is essential to restrict the range of spectral changes, as each spectral curve corresponds to a distinct semantic context. In this article, we propose a spectral-constrained generative adversarial network (SCGAN) for hyperspectral compression. Specifically, SCGAN integrates compression and classification tasks within a unified framework. During generative adversarial learning, SCGAN uses a classification map to guide the generation of global spectral information. To deal with different hyperspectral images (HSIs) in one model, a three-stage training strategy is leveraged. Experiments conducted on three public HSI datasets illustrate that the proposed SCGAN effectively narrows the semantic gap. For instance, the average overall classification accuracy of SCGAN on Pavia University is above 0.9, which is the closest to the classification accuracy achieved with the original HSIs, even at a low bitrate of 0.05 bits per pixel per band.

Karthika Jayasankar Menon, Akhil CK, Balaji K et al.

Abstract The objective of this paper is to improve the performance of reusable launch vehicles (RLV) through the minimization of base drag. The X -33 scale down model selected for this study is numerically investigated using the Reynolds Average Navier Stokes equation with k- epsilon realizable turbulence model used to predict various drag like base drag and forebody drag. The results show that the increase in surface roughness leads to the minimized base drag of the launch vehicle up to 2%. The minimization of basedrag is used to decrease the fuel consumption, thermal issues and landing stability of reusable launching vehicle. The amount of drag increment achieved between 17% and 75% depends on the thickness. The novelty of the proposed work is to minimize the base drag of reusable launch vehicle using the sand grain roughness at different operating speeds. The proposed method can be applied for all types of launch vehicle and space related vehicles.

Vahe Atoyan, Vahe Atoyan, Thomas Bawin et al.

Hyperspectral imaging (HSI) captures rich spectral data across hundreds of contiguous bands for diverse applications. Dimension reduction (DR) techniques are commonly used to map the first three reduced dimensions to the red, green, and blue channels for RGB visualization of HSI data. In this study, we propose a novel approach, HSBDR-H, which defines pixel colors by first mapping the two reduced dimensions to hue and saturation gradients and then calculating per-pixel brightness based on band entropy so that pixels with high intensities in informative bands appear brighter. HSBDR-H can be applied on top of any DR technique, improving image visualization while preserving low computational cost and ease of implementation. Across all tested methods, HSBDR-H consistently outperformed standard RGB mappings in image contrast, structural detail, and informativeness, especially on highly detailed urban datasets. These results suggest that HSBDR-H can complement existing DR-based visualization techniques and enhance the interpretation of complex hyperspectral data in practical applications. Tested in remote sensing applications involving urban and agricultural datasets, the method shows potential for broader use in other disciplines requiring high-dimensional data visualization.

T. Ghosh, A. Ghoshal, Huai-Ke Guo et al.

In this paper, we analyse sound waves arising from a cosmic phase transition where the full velocity profile is taken into account as an explanation for the gravitational wave spectrum observed by multiple pulsar timing array groups. Unlike the broken power law used in the literature, in this scenario the power law after the peak depends on the macroscopic properties of the phase transition, allowing for a better fit with pulsar timing array (PTA) data. We compare the best fit with that obtained using the usual broken power law and, unsurprisingly, find a better fit with the gravitational wave (GW) spectrum that utilizes the full velocity profile. Even more importantly, the thermal parameters that produce the best fit are quite different. We then discuss models that can produce the best-fit point and complementary probes using CMB experiments and searches for light particles in DUNE, IceCUBE-Gen2, neutrinoless double β-decay, and forward physics facilities (FPF) at the LHC like FASERν, etc.

Zu-Cheng Chen, Lang Liu

The null energy condition (NEC) is a cornerstone of general relativity, and its violation could leave observable imprints in the cosmic gravitational wave spectrum. Theoretical models suggest that NEC violations during inflation can amplify the primordial tensor power spectrum, leading to distinct features in the stochastic gravitational wave background (SGWB). In this work, we search for these NEC-violating signatures in the SGWB using data from Advanced LIGO and Advanced Virgo's first three observing runs. Our analysis reveals no statistically significant evidence of such signals, allowing us to place stringent upper limits on the tensor power spectrum amplitude, P T,2, during the second inflationary stage. Specifically, we find that P T,2 ≲ 0.15 at a 95% confidence level. Notably, this upper limit is consistent with constraints derived from pulsar timing array observations, reinforcing the hypothesis that NEC violations during inflation could explain the signal detected by pulsar timing arrays. Our findings contribute to a deeper understanding of the early Universe and highlight the potential of current and future gravitational wave experiments in probing the physics of inflation and NEC violations.

H. Khodabakhshi, M. Farhang, H. Lü

This paper analyzes the possibility of bouncing and non-bouncing universes in the framework of four-dimensional Einstein-Gauss-Bonnet (4D-EGB) gravity, corresponding respectively to negative and positive coupling constants λ of the Gauss-Bonnet term. We also use the Horndeski-type scalar-tensor theory to assess the role of a scalar charge C as a geometrical contribution to the radiation in the Universe. We modify the expansion history of the universe to allow for modifications induced by the 4D-EGB gravity. Using Planck measurements of the cosmic microwave background anisotropies as well as various datasets of baryonic acoustic oscillations, we set the upper bounds λ ≤ 10-16(km/s/Mpc)-2 and λ ≤ 10-30(km/s/Mpc)-2 for the non-bouncing and bouncing scenarios. The upper limit in the latter case is mainly driven by the requirement to conservatively respect the thermal history at energy scales of the standard model of particle physics. We also find that the contribution of the geometrical radiation-like term of the model cannot exceed 10% of the current radiation in the Universe. The possibility of an early inflationary phase produced by a single scalar field is also studied and found to be feasible in both bouncing and non-bouncing scenarios. This study shows the feasibility of a bouncing universe, even with a normal matter sector, in the 4D-EGB gravity. More theoretical investigation is required to further explore possible observational predictions of the model that can distinguish between general relativity and 4D-EGB gravity.

A. Ambrosone, M. Chianese, A. Marinelli

Star-forming and starburst galaxies (SFGs and SBGs) are considered to be powerful emitters of non-thermal γ-rays and neutrinos, due to their intense phases of star-formation activity, which should confine high-energy Cosmic-Rays (CRs) inside their environments. On this regard, the Fermi-LAT collaboration has found a correlation between the γ-ray and infrared luminosities for a sample of local sources. Yet, the physics behind these non-thermal emission is still under debate. We provide novel constraints on the tight relation between γ-rays and star formation rate (SFR) exploiting 15 years of public Fermi-LAT data. Thus, we probe the calorimetric fraction Fcal of high-energy protons in SFGs and SBGs, namely, the fraction of high-energy protons actually producing high-energy γ-rays and neutrinos. Further, we extrapolate this information to their diffuse γ-ray and neutrino emissions constraining their contribution to the extra-galactic gamma-ray background (EGB) and the diffuse neutrino flux. Using the publicly-available fermitools, we analyse 15.3 years of γ-ray between 1-1000 GeV data for 70 sources, 56 of which were not previously detected. We relate this emission to a theoretical model for SBGs in order to constrain Fcal for each source and then study its correlation with the star formation rate of the sources. Firstly, we find at 4σ level an indication of γ-ray emission for other two SBGs, namely M 83 and NGC 1365. By contrast, we find that, even with the new description of background, the significance for the γ-ray emission of M 33 (initially reported as discovered) still stands at ~ 4σ (as already reported by previous works). Along with previous findings, the flux of each detected source is consistent with a ~ E -2.3/2.4 spectrum, compatible with the injected CR flux inferred in the Milky-Way. We also notice that the correlation between Fcal and the SFR is in accordance with the expected scaling relation for CR escape dominated by advection. We remark that undiscovered sources strongly constrain Fcal at 95% CL, providing fundamental information when we interpret the results as common properties of SFGs and SBGs. Finally, we find that these sources might contribute (12 ± 3)% to the EGB, while the corresponding diffuse neutrino flux strongly depends on the spectral index distribution along the source class.

C. Froggatt, H. B. Nielsen

We present the idea that replacing the cosmological constant $\Lambda$ in the $\Lambda$CDM model by a distribution of walls, with very low tension compared to what one would expect from new physics, could help explaining the tension in the Hubble constant fits in the Standard Cosmological Model. Using parameters from our model for dark matter as macroscopic pearls, we can get a promising order of magnitude for the correction to the Hubble constant estimated from observations of the cosmic microwave background. Our model is on the borderline of failing by predicting too large extra fluctuations as a function of direction in the cosmological microwave background radiation. However, imagining the bubbles in the voids to have come from more somewhat smaller big bubbles also occurring outside the big voids may help. We estimate that, in order to have big volumes of the new vacuum in intergalactic space, a very high temperature is needed and that such regions would be likely to get cooled, freeze and shrink down to the degenerate form of dark matter if hitting some ordinary matter, as is likely in the denser parts of the Universe. We also review our model for dark matter, and develop the understanding of the stopping of the dark matter particles in the shielding of say the DAMA-LIBRA underground experiment and the counting rate this experiment observes. We manage to obtain a consistent fit with a mass $M = 2 \cdot 10^{-18}$kg = $10^9$GeV and radius $R = 10^{-10}$m for the dark matter pearls, corresponding to a tension in the domain wall of $S= (8 {\rm MeV})^3$.

Alina Sabyr, C. Sierra, J. C. Hill et al.

Deviations of the cosmic microwave background (CMB) energy spectrum from a perfect blackbody uniquely probe a wide range of physics, ranging from fundamental physics in the primordial Universe (μ-distortion) to late-time baryonic feedback processes (y-distortion). While the y-distortion can be detected with a moderate increase in sensitivity over that of COBE/FIRAS, the ΛCDM-predicted μ-distortion is roughly two orders of magnitude smaller and requires substantial improvements, with foregrounds presenting a serious obstacle. Within the standard model, the dominant contribution to μ arises from energy injected via Silk damping, yielding sensitivity to the primordial power spectrum at wavenumbers k ≈ 1-104 Mpc-1. Here, we present a new instrument concept, SPECTER, with the goal of robustly detecting μ. The instrument technology is similar to that of LiteBIRD, but with an absolute temperature calibration system. Using a Fisher approach, we optimize the instrument's configuration to target μ while marginalizing over foreground contaminants. Unlike Fourier-transform-spectrometer-based designs, the specific bands and their individual sensitivities can be independently set in this instrument, allowing significant flexibility. We forecast SPECTER to observe the ΛCDM-predicted μ-distortion at ≈ 5σ (10σ) assuming an observation time of 1 (4) year(s) (corresponding to mission duration of 2 (8) years), after foreground marginalization. Our optimized configuration includes 16 bands spanning 1–2000 GHz with ∼degree-scale angular resolution at ∼ 150 GHz and 1100 total detectors. SPECTER will additionally measure the y-distortion at sub-percent precision and its relativistic correction at percent-level precision, yielding tight constraints on the total thermal energy and mean temperature of ionized gas.

Francesca Pistolato, Michele Stecconi

Spherical spin random fields are used to model the Cosmic Microwave Background polarization, the study of which is at the heart of modern Cosmology and will be the subject of the LITEBIRD mission, in the 2030s. Its scope is to collect datas to test the theoretical predictions of the Cosmic Inflation model. In particular, the Minkowski functionals, or the Lipschitz-Killing curvatures, of excursion sets can be used to detect deviations from Gaussianity and anisotropies of random fields, being fine descriptors of their geometry and topology. In this paper we give an explicit, non-asymptotic, formula for the expectation of the Lipshitz-Killing curvatures of the excursion set of the real part of an arbitrary left-invariant Gaussian spin spherical random field, seen as a field on $SO(3)$. Our findings are coherent with the asymptotic ones presented in Carr\'on Duque, J. et al."Minkowski Functionals in $SO(3)$ for the spin-2 CMB polarisation field", Journal of Cosmology and Astroparticle Physics (2024). We also give explicit expressions for the Adler-Taylor metric, and its curvature. We obtain such result as an application of a general formula that applies to any nondegenerate Gaussian random field defined on an arbitrary three dimensional compact Riemannian manifold. The novelty is that the Lipschitz-Killing curvatures are computed with respect to an arbitrary metric, possibly different than the Adler-Taylor metric of the field.

Daniel Thürmer, H. Luu, Nina Merkert

Pressure-induced phase transformation in iron and its alloys is a classic research topic in solid-state physics, material science, and geophysics. The crystal structure of iron undergoes a phase transformation at a hydrostatic pressure of 13 GPa, changing from a body-centered cubic system to a hexagonal close-packed system. Although extensive research has been carried out on the transformation in iron by using molecular dynamics simulations, there is very limited literature that focuses on the contribution of parent phase orientations, system size, and impurities to the phase evolution. In this work, classic molecular dynamics simulations have been employed to investigate the effects of system size, lattice orientation, and impurity concentration on the pressure-induced phase transformation of iron and iron alloys for the first time. Our results show that the lattice orientation has a strong influence on the phase transition behavior, while the influence of carbon is small. The phase transition is slightly delayed with increasing carbon content, whereas the transition pressure increases from [001] to [011] to [111] orientation. The amount of twinning and stacking faults highly depends on the orientation. It is easiest for solitary waves to travel through [111] lattice orientation. The addition of carbon has a slow-down effect on shock velocities, and this effect increases with carbon content and lattice orientation of the samples from [001] to [011] to [111].

Jiazheng Dou, Shamik Ghosh, Larissa Santos et al.

The correlations between T, E modes and B modes in cosmic microwave background (CMB) radiation, which are expected to vanish under parity symmetry, have become a sensitive probe of the new physics beyond the standard model. In this paper, we forecast the estimation of TB and EB cross power spectra using NILC and cILC on AliCPT-1 simulations together with Planck HFI and WMAP K maps as ancillary data. We find that, NILC performs better than cILC on measuring TB and EB correlations in light of its lower uncertainties. In terms of the birefringence angle estimation without assuming systematic errors, the combination of CMB TB and EB spectra from NILC cleaned simulations could reach a sensitivity of |β| < 0.058∘ with 2σ significance for the first observing season of AliCPT. Tripling the survey duration will improve this sensitivity to |β| < 0.041∘.

Zhenwei Li, Xuefei Chen

Gravitational Waves (GWs) provide a unique way to explore our Universe. The ongoing ground-based detectors, e.g., LIGO, Virgo, and KAGRA, and the upcoming next-generation detectors, e.g., Cosmic Explorer and Einstein Telescope, as well as the future space-borne GW antennas, e.g., LISA, TianQin, and TaiJi, cover a wide range of GW frequencies {from $\sim 10^{-4}\;\rm Hz$ to $\sim 10^3\;\rm Hz$} and almost all types of compact objects in close orbits serve as the potential target sources for these GW detectors. The synergistic multi-band GW and EM observations would allow us to study fundamental physics from stars to cosmology. {The formation of stellar GW sources has been extensively explored in recent years, and progress on physical processes in binary interaction has been made as well. Furthermore, some studies have shown that the progress in binary evolution may significantly affect the properties of the stellar GW sources.}

A. Tishevsky, F. Dubinin, A. Isupov et al.

L. Caloni, Patrick Stengel, M. Lattanzi et al.

Cosmological observations allow to measure the abundance of light relics produced in the early Universe. Most studies focus on the thermal freeze-out scenario, yet light relics produced by freeze-in are generic for models in which new light degrees of freedom do not couple strongly enough to the Standard Model (SM) plasma to allow for full thermalization in the early Universe. In ultraviolet (UV) freeze-in scenarios, rates for light relic production associated with non-renormalizable interactions typical of beyond the SM (BSM) models grow with temperature more quickly than the Hubble rate. Thus, relatively small couplings to the SM can be probed by current and next-generation cosmic microwave background (CMB) experiments. We investigate several representative benchmark BSM models, such as axion-like particles from Primakoff production, massless dark photons and light right-handed neutrinos. We calculate contributions to the effective number of neutrino species, ΔN eff, in corners of parameter space not previously considered and discuss the sensitivity of CMB experiments compared to other probes. In contrast to freeze-out scenarios, ΔN eff from UV freeze-in is more dependent on both the specific BSM physics model and the reheating temperature. Depending on the details of the BSM scenario, we find that the sensitivity of next-generation CMB experiments can complement or surpass the current astrophysical, laboratory or collider constraints on the couplings of the SM to the light relic.