分类： 农、林、牧、渔 >> 农、林、牧、渔业科学其他学科 提交时间： 2024-07-17 合作期刊: 《智慧农业（中英文）》
摘要： ［目的/意义］丘陵山区的机械化、智能化是未来农机行业研究和发展的热点。中国丘陵山区耕地面积占 比超过50%，且面临坡陡路窄、地块碎小、地形地貌复杂等多种环境因素制约，各生产环节存在“无机可用，无 好机用”的现实问题，并且缺乏适合丘陵山区大坡度农机装备研发的理论支撑。［进展］ 综述了国内外丘陵山地 拖拉机调平及防翻系统的研究现状。其中拖拉机车身调平技术平行四杆与液压差高式结构简单，折腰扭腰式更适 合连续起伏的崎岖路面，重心可调与全向调平式坡地牵引性与适应性均较好；驾驶室及座椅调平技术基于角度传 感器自适应控制，关键在于缓解驾驶疲劳提高舒适度；车身与农具姿态协同控制技术大都采用PID控制技术实现 协同控制，但缺乏作业效果反馈机制；拖拉机防翻保护装置与预警技术在防翻保护架的基础上，通过环境模拟感 知提前预判翻车危险信号并及时反馈。［结论/展望］未来丘陵山地拖拉机调平、防翻预警及无人化、自动化技术 的发展方向：1） 结构优化、灵敏度高、稳定性好的山地拖拉机调平系统研究；2） 坡地适应性好的农机具仿形系 统研究；3） 环境感知、自动干涉的防翻预警技术研究；4） 农机精准导航技术、智能化监测技术和农机作业远程 调度与管理技术研究；5） 坡地纵向稳定性理论研究。以期为研发符合中国丘陵山地复杂作业环境的高可靠性、高 安全性山地拖拉机提供借鉴参考。
分类： 医学、药学 >> 临床医学 提交时间： 2024-07-16 合作期刊: 《中国全科医学》
摘要： 背景 急性缺血性卒中（AIS）高发，及时恢复脑血流是治疗的关键，超时间窗就诊患者无更多促进脑血流恢复的治疗手段。研究远隔缺血后适应（RIPostC）治疗对 AIS 超时间窗就诊患者的临床疗效、并发症和预后，具有重要的临床意义。目的 探究远隔缺血后适应（RIPostC）治疗对 AIS 超时间窗患者干预的影响，为超时间窗就诊的 AIS 患者寻求安全、有效的脑血流恢复治疗方式。方法 本研究采用随机、分组、安慰剂对照法进行试验。选取2021-09-02—2022-08-31 于北京航天总医院神经内科病房住院治疗的超溶栓时间窗（发病时间 >6 h）的 AIS 患者为研究对象。依据随机数字表法将患者分为对照组和试验组。试验期 + 随访期共 90 d，均使用同等的一般治疗、脑血管病常规治疗，试验组再次基础上给予 RIPostC 治疗 14 d（28 次），对照组给予模拟的 RIPostC 治疗 14 d（28 次）。在干预前和干预后 30 d、干预后 90 d，采用改良 Rankin 量表（mRS）、美国国立卫生研究院卒中量表（NIHSS）评估两组患者神经功能，简易智力状况检查法（MMSE）、蒙特利尔认知评估量表（MoCA）评估患者认知功能，工具性日常生活能力量表（IADL）评估日常生活能力，焦虑自评量表（SAS）、抑郁自评量表（SDS）评估精神状态，经颅多普勒超声（TCD）评估脑血流速度，以白介素（IL）-6 反映炎症情况。结果 122 例患者中，最终完试验及随访 99 例，其中试验组 49 例，对照组 50 例。两组患者性别、年龄、基础疾病（高血压、糖尿病、冠心病）及基线 NHISS 评分比较，差异无统计学意义（P>0.05）。重复测量方差分析结果示，时间与组别对 MMSE、MoCA、mRS、NIHSS、脑血流速度、IL-6 存在交互作用（P0.05）；对照组患者皮肤瘀斑发生率［4.00%（2/50）与 12.24%（6/49）］、总不良反应发生率［12.00%（6/50）与 34.69%（17/49）］低于试验组（P<0.05）。结论 RIPostC 治疗可降低 AIS 患者的炎症反应，对神经功能、认知功能抑郁情绪及颅内血流速度可起到积极的改善效果。
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Solar System's orbital structure is thought to have been sculpted by an episode of dynamical instability among the giant planets. However, the instability trigger and timing have not been clearly established. Hydrodynamical modeling has shown that while the Sun's gaseous protoplanetary disk was present the giant planets migrated into a compact orbital configuration in a chain of resonances. Here we use dynamical simulations to show that the giant planets' instability was likely triggered by the dispersal of the gaseous disk. As the disk evaporated from the inside-out, its inner edge swept successively across and dynamically perturbed each planet's orbit in turn. The associated orbital shift caused a dynamical compression of the exterior part of the system, ultimately triggering instability. The final orbits of our simulated systems match those of the Solar System for a viable range of astrophysical parameters. The giant planet instability therefore took place as the gaseous disk dissipated, constrained by astronomical observations to be a few to ten million years after the birth of the Solar System. Terrestrial planet formation would not complete until after such an early giant planet instability; the growing terrestrial planets may even have been sculpted by its perturbations, explaining the small mass of Mars relative to Earth.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： A general covariant local field theory of the holographic dark energy model is presented. It turns out the low energy effective theory of the holographic dark energy is the massive gravity theory whose graviton has 3 polarisations, including one scalar mode and two tensor modes. The Compton wavelength is the size of the future event horizon of the universe. The UV-IR correspondence in the holographic dark energy model stems from the scalar graviton's strong coupling at the energy scale that marks the breaking down of the effective field theory.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Thermoelastic loss is one of the main energy dissipation mechanisms in resonant systems. A careful analysis of the thermoelastic loss is critical to design low-noise resonators for high-precision applications, such as gravitational-wave detectors. This paper presents an analytical solution to the thermoelastic loss in multimaterial coated finite substrates with realistic assumptions on the model structure and the elastic fields. The mechanism responsible for thermoelastic loss is taken as a function of material properties, operating temperature and frequency, and other design parameters. We calculate the thermoelastic loss for specific applications over a wide range of frequencies (1 Hz to 10 GHz) and temperatures (1 K to 300 K), and for a variety of substrate and coating materials. The result is relevant for gravitational-wave detectors and for experiments sensitive to mechanical dissipation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Building accurate and predictive models of the underlying mechanisms of celestial motion has inspired fundamental developments in theoretical physics. Candidate theories seek to explain observations and predict future positions of planets, stars, and other astronomical bodies as faithfully as possible. We use a data-driven learning approach, extending that developed in Lu et al. ($2019$) and extended in Zhong et al. ($2020$), to a derive stable and accurate model for the motion of celestial bodies in our Solar System. Our model is based on a collective dynamics framework, and is learned from the NASA Jet Propulsion Lab's development ephemerides. By modeling the major astronomical bodies in the Solar System as pairwise interacting agents, our learned model generate extremely accurate dynamics that preserve not only intrinsic geometric properties of the orbits, but also highly sensitive features of the dynamics, such as perihelion precession rates. Our learned model can provide a unified explanation to the observation data, especially in terms of reproducing the perihelion precession of Mars, Mercury, and the Moon. Moreover, Our model outperforms Newton's Law of Universal Gravitation in all cases and performs similarly to, and exceeds on the Moon, the Einstein-Infeld-Hoffman equations derived from Einstein's theory of general relativity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Presolar grains are microscopic dust grains that formed in the stellar winds or explosions of ancient stars that died before the formation of the solar system. The majority (~90% in number) of presolar silicon carbide (SiC) grains, including types mainstream (MS), Y, and Z, came from low-mass C-rich asymptotic giant branch (AGB) stars, which is supported by the ubiquitous presence of SiC dust observed in the circumstellar envelope of AGB stars and the signatures of slow neutron-capture process preserved in these grains. Here, we review the status of isotope studies of presolar AGB SiC grains with an emphasis on heavy-element isotopes and highlight the importance of presolar grain studies for nuclear astrophysics. We discuss the sensitives of different types of nuclei to varying AGB stellar parameters and how their abundances in presolar AGB SiC grains can be used to provide independent, detailed constraints on stellar parameters, including 13C formation, stellar temperature, and nuclear reaction rates.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The exchange of a pair of neutrinos between two objects, seperated by a distance $r$, leads to a long-range effective potential proportional to $1/r_{}^5$, assuming massless neutrinos and four-fermion contact interactions. In this paper, we investigate how this known form of neutrino-mediated potentials might be altered if the distance $r$ is sufficiently short, corresponding to a sufficiently large momentum transfer which could invalidate the contact interactions. We consider two possible scenarios to open up the contact interactions by introducing a $t$-channel or an $s$-channel mediator. We derive a general formula that is valid to describe the potential in all regimes as long as the external particles remain non-relativistic. In both scenarios, the potential decreases as $1/r_{}^5$ in the long-range limit as expected. In the short-range limit, the $t$-channel potential exhibits the Coulomb-like behavior (i.e. proportional to $1/r$), while the $s$-channel potential exhibits $1/r_{}^4$ and $1/r_{}^2$ behaviors.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Inverse mass cascade is a key feature of statistically steady state for self-gravitating collisionless dark matter flow (SG-CFD). Continuous mass transfer from small to large mass scales (inverse) is formulated. Direct effect of mass cascade on halo mass function is presented. Mass cascade is local, two-way, and asymmetric in mass space. Halos inherit/pass their mass from/to halos of similar size. Two regimes are identified: a propagation range with scale-independent rate of mass transfer and a deposition range with cascaded mass consumed to grow halos. Dimensional analysis leads to a power-law mass function in propagation range with a geometry exponent ${\lambda}$. A fundamental merging frequency $f_0{\sim}m_p^{\lambda-1}a^{-1}$ is identified, where $a$ is scale factor. Particle mass $m_p$ can be determined if that frequency is known. Rate of mass transfer ${\epsilon}_m{\sim}a^{-1}$ is independent of halo mass, a key feature of propagation range. Typical halos grow as $m_h{\sim}a^{3/2}$ and halo lifespan scales as ${\sim}m_h^{-\lambda}$. Chain reaction of mass cascade provides non-equilibrium dark matter flow a mechanism to continuously release energy and maximize entropy. Continuous injection of mass ("free radicals") at the smallest scale is required to sustain the everlasting inverse mass cascade such that total halo mass $M_h$ increases as $a^{1/2}$. These "radicals" might be directly generated at the smallest Planck scale or by a direct cascade from large to small scales. Entire mass cascade can be formulated by random walk in mass space, where halos migrate with an exponential distribution of waiting time. This results in a heterogeneous diffusion model, where Press-Schechter mass function can be fully derived without relying on any specific collapse models. A double-$\lambda$ mass function is proposed with different $\lambda$ for two ranges and agrees with N-body simulations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Measuring the Cosmic X-ray Background (CXB) is a key to understand the Active Galactic Nuclei population, their absorption distribution and their average spectra. However, hard X-ray instruments suffer from time-dependent backgrounds and cross-calibration issues. The uncertainty of the CXB normalization remain of the order of 20%. To obtain a more accurate measurement, the Monitor Vsego Neba (MVN) instrument was built in Russia but not yet launched to the ISS (arXiv:1410.3284). We follow the same ideas to develop a CXB detector made of four collimated spectrometers with a rotating obturator on top. The collimators block off-axis photons below 100 keV and the obturator modulates on-axis photons allowing to separate the CXB from the instrumental background. Our spectrometers are made of 20 mm thick CeBr$_{3}$ crystals on top of a SiPM array. One tube features a $\sim$20 cm$^2$ effective area and more energy coverage than MVN, leading to a CXB count rate improved by a factor of $\sim$10 and a statistical uncertainty $\sim$0.5% on the CXB flux. A prototype is being built and we are seeking for a launch opportunity.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Correlated red noise recently reported from pulsar timing observations may be an indication of stochastic gravitational waves emitted by cosmic strings that formed during a primordial phase transition near the Grand Unification energy scale. Unfortunately, known probes of cosmic strings, namely the Cosmic Microwave Background anisotropies and string lensing of extragalactic galaxies, are not sensitive enough for low string tensions of $G\mu = 10^{-10}-10^{-7}$ that are needed to explain this putative signal. We show that strong gravitational lensing of Fast Radio Bursts (FRBs) by cosmic strings is a potentially unambiguous avenue to probe that range of string tension values. The image pair of string lensing are expected to have identical magnification factor and parity, and have a typical time delay of $\sim 10^2\,\,(G\,\mu/10^{-8})^2$ seconds. The unique spectral fingerprint of each FRB, as well as the possibility to detect correlations in the time series of the electric field of the radio waves, will enable verification of the string lensing interpretation. Very-Long-Baseline Interferometry (VLBI) observations can spatially resolve the image pair and provide a lower bound on the string tension based on the image separation. We calculate the FRB lensing rate as a function of FRB detection number for several different models of the FRB redshift distribution. We find that a survey detecting $\sim 10^5$ FRBs, in line with estimates for the detection rate of the forthcoming survey CHORD, can uncover a strong lensing event for a string tension of $G\mu \simeq 10^{-7}$. Larger FRB surveys, such as Phase 2 of the Square Kilometre Array (SKA), have the potential to significantly improve the sensitivity on the string tension to $G\mu \simeq 10^{-9}$.
分类： 农、林、牧、渔 >> 农、林、牧、渔业科学其他学科 提交时间： 2024-07-17 合作期刊: 《智慧农业（中英文）》
摘要： ［目的/意义］土壤是农业基本的生产资料，其质量与农业高效生产和可持续发展密切相关。由于以往对 农田的高强度利用以及土壤侵蚀等原因，导致部分农田出现土壤有机质明显下降、地力减弱和生态功能退化等现 象。土壤理化参数作为揭示土壤空间特征、评估土壤肥力的关键指标，对农田可持续利用起着至关重要的作用。 因此，土壤理化参数信息的快速获取极为必要。［进展］探讨了农田土壤理化参数获取技术的研究意义，总结了当 前用于农田土壤理化参数信息获取的主要技术，包括以电化学分析和光谱分析为主的实验室快速检验技术，以电 磁感应、探地雷达、多光谱、高光谱和热红外为主的近地快速感知技术，以直接反演法、间接反演法和结合分析 法为主的卫星遥感技术，以及近年的新型快速获取技术，如生物传感、环境磁学、太赫兹光谱和伽马能谱等，梳 理了各方法的优缺点及适用情况。［结论/展望］结合农田环境的作业需求，依据未来研究的侧重方向提出发展建 议，包括开发便携化、智能化和经济型的近地土壤信息获取系统及设备，实现土壤信息的原位快速检测。优化低 空土壤信息获取平台的性能，完善数据的解译方法；联合多因素构建卫星遥感反演模型，利用多种共享开放的云 计算平台实现数据的深度挖掘。深入探索多源数据融合在土壤理化参数信息获取中的研究与应用，构建泛化能力 强、可靠性高的土壤信息感知算法和模型等，从而实现土壤理化参数信息快速、精准和智能化获取。
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Salvatore Ferrone
Paola Di Matteo
Alessandra Mastrobuono-Battisti
Misha Haywood
Owain N. Snaith
Marco Montouri
Sergey Khoperskov
David Valls-Gabaud
摘要： We present the e-TidalGCs Project which aims at modeling and predicting the extra-tidal features surrounding all Galactic globular clusters for which 6D phase space information, masses and sizes are available (currently 159 globular clusters). We focus the analysis and presentation of the results on the distribution of extra-tidal material on the sky, and on the different structures found at different heliocentric distances. We emphasize the wide variety of morphologies found: beyond the canonical tidal tails, our models reveal that the extra-tidal features generated by globular clusters take a wide variety of shapes, from thin and elongated shapes, to thick, and complex halo-like structures. We also compare some of the most well studied stellar streams found around Galactic globular clusters to our model predictions, namely those associated to the clusters NGC 3201, NGC 4590, NGC 5466 and Pal 5. Additionally, we investigate how the distribution and extension in the sky of the simulated streams vary with the Galactic potential by making use of three different models, containing or not a central spheroid, or a stellar bar. Overall, our models predict that the mass lost by the current globular cluster population in the field from the last 5 Gyrs is between $0.3-2.1\times10^{7}M_{\odot}$, an amount comparable between 7-55 % of current mass. Most of this lost mass is found in the inner Galaxy, with the half-mass radius of this population being between 4-6 kpc. The outputs of the simulations will be publicly available, at a time when the ESA Gaia mission and complementary spectroscopic surveys are delivering exquisite data to which these models can be compared.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Dark radiation (DR) is generally predicted in new physics scenarios that address fundamental puzzles of the Standard Model or tensions in the cosmological data. Cosmological data has the sensitivity to constrain not only the energy density of DR, but also whether it is interacting. In this paper, we present a systematic study of five types of interacting DR (free-streaming, fluid, decoupling, instantaneous decoupling, and recoupling DR) and their impact on cosmological observables. We modify the Boltzmann hierarchy to describe all these types of interacting DR under the relaxation time approximation. We, for the first time, robustly calculate the collision terms for recoupling scalar DR and provide a better estimation of the recoupling transition redshift. We demonstrate the distinct features of each type of DR on the CMB and matter power spectra. We perform MCMC scans using the Planck 2018 data and BAO data. Assuming no new physics in the SM neutrino sector, we find no statistically significant constraints on the couplings of DR, although there is a slight preference for a late transition redshift for instantaneous decoupling DR around recombination, and for the fluid-like limit of all the cases. The $\Delta N_{\rm eff}$ constraint varies marginally depending on the type of DR.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Compact Obscured Nuclei (CONs) account for a significant fraction of the population of luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs). These galaxy nuclei are compact, with radii of 10-100~pc, with large optical depths at submm and far-infrared wavelengths, and characterized by vibrationally excited HCN emission. It is not known what powers the large luminosities of the CON host galaxies because of the extreme optical depths towards their nuclei. CONs represent an extreme phase of nuclear growth, hiding either a rapidly accreting supermassive black hole or an abnormal mode of star formation. Here we apply principal component analysis (PCA) tomography to high-resolution (0.06$^{\prime\prime}$) ALMA observations at frequencies 245 to 265~GHz of the nearby CON (59~Mpc) IC~860. PCA is a technique to unveil correlation in the data parameter space, and we apply it to explore the morphological and chemical properties of species in our dataset. The leading principal components reveal morphological features in molecular emission that suggest a rotating, infalling disk or envelope, and an outflow analogous to those seen in Galactic protostars. One particular molecule of astrochemical interest is methanimine (CH$_2$NH), a precursor to glycine, three transitions of which have been detected towards IC 860. We estimate the average CH$_2$NH column density towards the nucleus of IC~860 to be $\sim10^{17}$cm$^{-2}$, with an abundance exceeding $10^{-8}$ relative to molecular hydrogen, using the rotation diagram method and non-LTE radiative transfer models. This CH$_2$NH abundance is consistent with those found in hot cores of molecular clouds in the Milky Way. Our analysis suggests that CONs are an important stage of chemical evolution in galaxies, that are chemically and morphologically similar to Milky Way hot cores.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Christopher J. White
Patrick D. Mullen
Yan-Fei Jiang
Shane W. Davis
James M. Stone
Viktoriya Morozova
Lizhong Zhang
摘要： We extend the general-relativistic magnetohydrodynamics (GRMHD) capabilities of Athena++ to incorporate radiation. The intensity field in each finite-volume cell is discretized in angle, with explicit transport in both space and angle properly accounting for the effects of gravity on null geodesics, and with matter and radiation coupled in a locally implicit fashion. Here we describe the numerical procedure in detail, verifying its correctness with a suite of tests. Motivated in particular by black hole accretion in the high-accretion-rate, thin-disk regime, we demonstrate the application of the method to this problem. With excellent scaling on flagship computing clusters, the port of the algorithm to the GPU-enabled AthenaK code now allows the simulation of many previously intractable radiation-GRMHD systems.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Supernova (SN) cosmology is based on the assumption that the width-luminosity relation (WLR) and the color-luminosity relation (CLR) in the type Ia SN luminosity standardization would not show {absolute magnitude differences} with progenitor age. Unlike this expectation, recent age datings of stellar populations in host galaxies have shown significant correlations between progenitor age and Hubble residual (HR). Here we show that this correlation originates from a strong progenitor age dependence of the zero-points of the WLR and the CLR, in the sense that SNe from younger progenitors are fainter each at given light-curve parameters $x_1$ and $c$. This $4.6\sigma$ result is reminiscent of Baade's discovery of the zero-point variation of the Cepheid period-luminosity relation with age, and, as such, causes a serious systematic bias with redshift in SN cosmology. Other host properties show substantially smaller and insignificant offsets in the WLR and CLR for the same dataset. We illustrate that the differences between the high-$z$ and low-$z$ SNe in the WLR and CLR, and in HR after the standardization, are fully comparable to those between the correspondingly young and old SNe at intermediate redshift, indicating that the observed dimming of SNe with redshift may well be an artifact of over-correction in the luminosity standardization. When this systematic bias with redshift is properly taken into account, there is little evidence left for an accelerating universe, in discordance with other probes, urging the follow-up investigations with larger samples at different redshift bins.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We develop a framework for using clustering-based redshift inference (cluster-$z$) to measure the evolving galaxy luminosity function (GLF) and galaxy stellar mass function (GSMF) using WISE W1 ($3.4\mu m$) mid-infrared photometry and positions. We use multiple reference sets from the Galaxy And Mass Assembly (GAMA) survey, Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS). Combining the resulting cluster-$z$s allows us to enlarge the study area, and by accounting for the specific properties of each reference set, making best use of each reference set to produce the best overall result. Thus we are able to measure the GLF and GSMF over $\sim 7500\, \mathrm{deg}^2 $ of the Northern Galactic Cap (NGC) up to $z<0.6$. Our method can easily be adapted for new studies with fainter magnitudes, which pose difficulties for the derivation of photo-$z$s. The measurement of the GSMF is currently limited by the models for k-corrections and mass-to-light ratios, rather than more complicated effects tied to the evolution of the differential galaxy bias. With better statistics in future surveys this technique is a strong candidate for studies with new emerging data from, e.g. the Vera C. Rubin Observatory, the Euclid mission or the Nancy Grace Roman Space Telescope.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The dynamics of magnetic reconnection in the solar current sheet (CS) is studied by high-resolution 2.5-dimensional MHD simulation. With the commence of magnetic reconnection, a number of magnetic islands are formed intermittently and move quickly upward and downward along the CS. When colliding with the semi-closed flux of flare loops, the downflow islands cause a second reconnection with a rate even comparable with that in the main CS. Though the time-integrated magnetic energy release is still dominated by the reconnection in main CS, the second reconnection can release substantial magnetic energy, annihilating the main islands and generating secondary islands with various scales at the flare loop top. The distribution function of the flux of the second islands is found to follow a power-law varying from $f\left(\psi\right)\sim\psi^{-1}$ (small scale) to $\psi^{-2}$ (large scale), which seems to be independent with background plasma $\beta$ and if including thermal conduction. However, the spatial scale and the strength of the termination shocks driven by main reconnection outflows or islands decrease if $\beta$ increases or thermal conduction is included. We suggest that the annihilation of magnetic islands at the flare loop top, which is not included in the standard flare model, plays a non-negligible role in releasing magnetic energy to heat flare plasma and accelerate particles.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The recent NANOGrav finding of a common-spectrum process has invited interpretations as possible evidence of a primordial stochastic gravitational-wave background (SGWB) stronger than predicted by standard inflation+LCDM. Such an SGWB would contribute an extra radiation component to the background Universe which may affect its expansion history. As such, it may help alleviate the current Hubble tension, a novel connection between gravitational waves and cosmology. We demonstrate this by considering a cosmological model, the "standard inflation + stiff amplification" scenario, with two components added to the LCDM model: a stiff component (w=1) and the primordial SGWB. Previously, we showed that even for standard inflation, the SGWB may be detectable at the high frequencies probed by laser interferometers, if it is amplified by a possible early stiff era after reheating. Models that boost the SGWB enough to cause significant backreaction, however, must still preserve the well-measured radiation-matter equality, as precision cosmology demands. For that, we calculate the fully-coupled evolution of the SGWB and expansion history, sampling parameter space (tensor-to-scalar ratio, reheating temperature and temperature at stiff-to-radiation equality). We then perform a joint analysis of the NANOGrav results and latest upper bounds from Planck, big bang nucleosynthesis and Advanced LIGO-Virgo, to constrain the model. The resulting blue-tilted, stiff-amplified SGWB is still too small to explain the NANOGrav results. However, if someday, Advanced LIGO-Virgo detects the SGWB, our model can explain it within standard inflation (without requiring an initial blue tilt). Meanwhile, this model may bring current high-z measurements of the Hubble constant within 3.4 sigma of the low-z measurements by SH0ES (from 4.4 sigma) and within 2.6 sigma of those by H0LiCOW (from 3.1 sigma), reducing the tension.
点击量
时间
通过
点击量
下载量
评论
待评议
