分类： 地球科学 >> 地理学 提交时间： 2024-05-15 合作期刊: 《干旱区科学》
摘要： Ecological stability is a core issue in ecological research and holds significant implications for humanity. The increased frequency and intensity of drought and wet climate events resulting from climate change pose a major threat to global ecological stability. Variations in stability among different ecosystems have been confirmed, but it remains unclear whether there are differences in stability within the same terrestrial vegetation ecosystem under the influence of climate events in different directions and intensities. China's grassland ecosystem includes most grassland types and is a good choice for studying this issue. This study used the Standardized Precipitation Evapotranspiration Index-12 (SPEI-12) to identify the directions and intensities of different types of climate events, and based on Normalized Difference Vegetation Index (NDVI), calculated the resistance and resilience of different grassland types for 30 consecutive years from 1990 to 2019 (resistance and resilience are important indicators to measure stability). Based on a traditional regression model, standardized methods were integrated to analyze the impacts of the intensity and duration of drought and wet events on vegetation stability. The results showed that meadow steppe exhibited the highest stability, while alpine steppe and desert steppe had the lowest overall stability. The stability of typical steppe, alpine meadow, temperate meadow was at an intermediate level. Regarding the impact of the duration and intensity of climate events on vegetation ecosystem stability for the same grassland type, the resilience of desert steppe during drought was mainly affected by the duration. In contrast, the impact of intensity was not significant. However, alpine steppe was mainly affected by intensity in wet environments, and duration had no significant impact. Our conclusions can provide decision support for the future grassland ecosystem governance.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： If the sparticles are relatively heavy (a few TeV) while the Higgs sector is not so heavy (m(A) is not so large), the Higgs boson Yukawa couplings can harbor sizable quantum effects of sparticles and these large residual effects may play a special role in probing supersymmetry at foreseeable colliders. In this work, focusing on the supersymmetric QCD effects in the hb (b) over bar coupling (h is the lightest CP-even Higgs boson), we give a comparative study for the two popular supersymmetric models: the MSSM and NMSSM. While for both models the supersymmetric QCD can leave over large residual quantum effects in hb (b) over bar coupling, the NMSSM can allow for a much broader region of such effects. Since these residual effects can be over 20% for the hb (b) over bar coupling (and thus over 40% for the ratio Br(h -> b (b) over bar)/Br(h -> tau(+)tau(-))), future measurements may unravel the effects of heavy sparticles or even distinguish the two models. (C) 2009 Elsevier B.V. All rights reserved.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-14
摘要： We examine the present and future XENON limits on the neutralino dark matter in split supersymmetry (split-SUSY). Through a scan over the parameter space under the current constraints from collider experiments and the WMAP measurement of the dark matter relic density, we find that in the allowed parameter space a large part has been excluded by the present XENON100 limits and a further largish part can be covered by the future exposure (6000 kg day). In case of unobservation of dark matter with such an exposure in the future, the lightest neutralino will remain bino-like and its annihilation is mainly through exchanging the SM-like Higgs boson in order to get the required relic density. (C) 2011 Elsevier B.V. All rights reserved.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： We recalculate the two-loop beta functions for three gauge couplings taking into account all low energy threshold corrections in split supersymmetry(split-SUSY) which assumes a very high scalar mass scale M-S. We find that in split-SUSY with a gaugino mass unification assumption and with a large M-S the gauge coupling unification requires a lower bound on the gaugino mass. Combined with the constraints from the dark matter relic density and direct detection limits, we find that split-SUSY is very restricted and for dark matter mass below 1 TeV the allowed parameter space can be fully covered by XENON-1T(2017).
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： We propose to split the sparticle spectrum from the hierarchy between the GUT scale and the Planck scale. A split supersymmetric model, which gives non-universal gaugino masses, is built with proper high dimensional operators in the framework of SO(10) GUT. Based on a calculation of two-loop beta functions for gauge couplings (taking into account all weak scale threshold corrections), we check the gauge coupling unification and dark matter constraints (relic density and direct detections). We find that our scenario can achieve the gauge coupling unification and satisfy the dark matter constraints in some part of parameter space. We also examine the sensitivity of the future XENON1T experiment and find that the currently allowed parameter space in our scenario can be covered for a neutralino dark matter below about 1.0 TeV.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： From generalized gravity mediation we build a SUGRA scenario in which the gluino is much heavier than the electroweak gauginos at the GUT scale. We find that such a non-universal gaugino scenario with very heavy gluino at the GUT scale can be naturally obtained with proper high dimensional operators in the framework of SU( 5) GUT. Then, due to the effects of heavy gluino, at the weak scale all colored sparticles are heavy while the uncolored sparticles are light, which can explain the Brookhaven muon g - 2 measurement while satisfying the collider constraints (both the 125 GeV Higgs mass and the direct search limits of sparticles) and dark matter requirements. We also find that, in order to explain the muon g - 2 measurement, the neutralino dark matter is lighter than 200GeV in our scenario, which can be mostly covered by the future Xenon1T experiment.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-14
摘要： In order to have massive neutrinos, the right-handed neutrino/sneutrino superfield (N) need to be introduced in supersymmetry. In the framework of NMSSM (the MSSM with a singlet S) such an extension will dynamically lead to a TeNT-scale Majorana mass for the right-handed neutrino through the S N N coupling when S develops a vev (the free Majorana mass term is forbidden by the assumed Z(3) symmetry). Also, through the couplings S N N and SHuHd the SM-like Higgs boson (a mixture of H-u, H-d and S) can naturally couple with the right-handed neutrino/sneutrino. As a result, the TeV-scale right-handed neutrino/sneutrino may significantly contribute to the Higgs boson mass. Through an explicit calculation, we find that the Higgs boson mass can indeed be sizably altered by the right-handed neutrino/sneutrino. Such new contribution can help to push up the SM-like Higgs boson mass and thus make the NMSSM more natural.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： In this work we show that the general singlet extension of the minimal supersymmetric standard model (MSSM) can naturally provide a self-interacting singlino dark matter to solve the small cosmological scale anomalies (a large Sommerfeld enhancement factor can also be obtained). However, we find that the NMSSM (the singlet extension of the MSSM with Z(3) symmetry) cannot achieve this due to the restricted parameter space. In our analysis we introduce the concept of symmetric and antisymmetric viscosity cross sections to deal with the nonrelativistic Majorana-fermion dark matter scattering.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-09
摘要： We propose a deflected anomaly mediation scenario from SUSY QCD which can lead to both positive and negative deflection parameters (there is a smooth transition between these two deflection parameter regions by adjusting certain couplings). Such a scenario can naturally give a SUSY spectrum in which all the colored sparticles are heavy while the sleptons are light. As a result, the discrepancy between the Brookheaven g(mu) - 2 experiment and LHC data can be reconciled in this scenario. We also find that the parameter space for explaining the g(mu) - 2 anomaly at 1 sigma level can be fully covered by the future LUX-ZEPLIN 7.2 Ton experiment.
分类： 物理学 >> 核物理学 提交时间： 2024-05-20
摘要： Tritium, a radioactive nuclide discharged by nuclear power plants, poses challenges for removal. Continuous online monitoring of tritium in water is crucial for real-time radiation data, given its predominant existence in the environment as water. This paper presents the design, simulation, and development of a tritium monitoring device utilizing a plastic scintillation fiber (PSF) array. Experimental validation confirmed the device’s detection efficiency and minimum detectable activity. The recorded detection efficiency of the device is 1.6 × 10−3 , which exceeds the theoretically simulated value of 4 × 10−4 by four times. Without shielding, the device can achieve a minimum detectable activity of 3165 Bq L−1 over a 1600-second measurement duration. According to simulation and experimental results, enhancing detection efficiency is possible by increasing the number and length of PSFs and implementing rigorous shielding measures. Additionally, reducing the diameter of PSFs can also improve detection efficiency. The minimum detectable activity of the device can be further reduced using the aforementioned methods.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Motivated by the current strong constraints on the spin-independent dark matter (DM)-nucleus scattering, we investigate the spin-dependent (SD) interactions of the light Majorana DM with the nucleus mediated by an axial-vector boson. Due to the small nucleus recoil energy, the ionization signals have now been used to probe the light dark matter particles in direct detection experiments. With the existing ionization data, we derive the exclusion limits on the SD DM-nucleus scattering through Migdal effect in the MeV-GeV DM mass range. It is found that the lower limit of the DM mass can reach about several MeVs. Due to the momentum transfer correction induced by the light mediator, the bounds on the SD DM-nucleus scattering cross sections can be weakened in comparison with the heavy mediator.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： White laser covering the visible color spectrum is critical in various applications including vivid display, holographic imaging and light-based version of Wi-Fi, but it is still challenging to realize the white microlaser due to the rigorous requirement in the balance between the optical gain and the feedback at different wavelengths. Here, we employ Tm, Er and Yb ions corporately for the upconversion white lasing in a single ultrahigh quality (Q) (up to 108) doped microcavity, where the thresholds of the red, green and blue lasers are about 90, 500 and 300 {\mu}W, respectively. To the best of our knowledge, it is the first rare-earth elements based room-temperature, continuous-wave white microlaser, which exhibits relatively stable chromaticity over 180 minutes, making it possible for practical applications.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： As discussed recently by Hooper and Tait, the singlino-like dark matter in the Minimal Supersymmetric Standard Model (MSSM) extended by a singlet Higgs superfield can give a perfect explanation for both the relic density and the Pamela result through the Sommerfeld-enhanced annihilation into singlet Higgs bosons (a or h followed by h -> aa) with a being light enough to decay dominantly to muons or electrons. In this work we analyze the parameter space required by such a dark matter explanation and also consider the constraints from the LEP experiments. We find that although the light singlet Higgs bosons have small mixings with the Higgs doublets in the allowed parameter space, their couplings with the SM-like Higgs boson h(SM) (the lightest doublet-dominant Higgs boson) can be enhanced by the soft parameter A(kappa) and, in order to meet the stringent LEP constraints, the h(SM) tends to decay into the singlet Higgs pairs a a or hh instead of b (b) over bar. So the h(SM) produced at the LHC will give a multi-muon signal, h(SM) -> aa -> 4 mu or h(SM) -> hh -> 4a -> 8 mu.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-14
摘要： For the experimental search of neutralino dark matter, it is important to know its allowed mass and scattering cross section with the nucleon. In order to figure out how light a neutralino dark matter can be predicted in low energy supersymmetry, we scan over the parameter space of the NMSSM (next-to-minimal supersymmetric model), assuming all the relevant soft mass parameters to be below TeV scale. We find that in the parameter space allowed by current experiments the neutralino dark matter can be as light as a few GeV and its scattering rate off the nucleon can reach the sensitivity of XENON100 and CoGeNT. As a result, a sizable parameter space is excluded by the current XENON100 and CoGeNT data (the plausible CoGeNT dark matter signal can also be explained). The future 6000 kg-days exposure of XENON100 will further explore (but cannot completely cover) the remained parameter space. Moreover, we find that in such a light dark matter scenario a light CP-even or CP-odd Higgs boson must be present to satisfy the measured dark matter relic density. Consequently, the SM-like Higgs boson h(SM) may decay predominantly into a pair of light Higgs bosons or a pair of neutralinos so that the conventional decays like h(SM) -> gamma gamma is much suppressed. (C) 2011 Elsevier B.V. All rights reserved.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： In split supersymmetry, gauginos and higgsinos are the only supersymmetric particles possibly accessible at foreseeable colliders like the CERN Large Hadron Collider (LHC) and the International Linear Collider (ILC). In order to account for the cosmic dark matter measured by WMAP, these gauginos and higgsinos are stringently constrained and could be explored at the colliders through their direct productions and/or virtual effects in some processes. The clean environment and high luminosity of the ILC render the virtual effects at percent level meaningful in unraveling the new physics effects. In this work we assume split supersymmetry and calculate the virtual effects of the WMAP-allowed gauginos and higgsinos in the Higgs productions e(+) e(-) -> Zh and e(+) e(-) ->nu(e)(nu) over bar (e)h through WW fusion at the ILC. We find that the production cross section of e+ e-. Zh can be altered by a few percent in some part of the WMAP-allowed parameter space, while the correction to the WW fusion process e(+) e(-) ->nu(e) (nu) over bar (e)h is below 1%. Such virtual effects are correlated with the cross sections of chargino pair productions and can offer complementary information in probing split supersymmetry at the colliders.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： In the next-to-minimal supersymmetric model (NMSSM) a light CP-odd Higgs boson is so far allowed by current experiments, which, together with a large tan beta, may greatly enhance the rare dileptonic decays B -> X(s)l(+)l(-) and B(s)-> l(+)l(-)gamma. We examine these decays paying special attention to the new operator allowed by the light CP-odd Higgs boson. We find that in the parameter space allowed by current experiments like CERN LEP II and b -> s gamma, the branching ratios of these rare decays can be greatly enhanced, and thus the existing experimental data on B -> X(s)mu(+)mu(-) can further stringently constrain the parameter space (especially the region with a superlight CP-odd Higgs boson and large tan beta). In the surviving parameter space we give the predictions for other dileptonic decay branching ratios and also show the results for the forward-backward asymmetry.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the minimal supersymmetric standard model (MSSM) extended by a singlet superfield, when the coupling between the singlet sector and the MSSM sector is tiny, the singlet sector can be a quasi dark sector with supersymmetry (SUSY). We investigate the cosmological phenomena in this scenario and obtain the following observations: (i) In the parameter space solving the small cosmological scale anomalies via self-interacting singlino dark matter (SIDM), a first-order phase transition (FOPT) can readily happen but requires rather light dark matter below MeV; (ii) The corresponding parameter space indicated by FOPT and SIDM can be partially covered by detecting the phase-transition gravitational waves (GWs) at the near-future projects, such as LISA, TianQin and Taiji. Therefore, the recently developed GW astronomy could be a novel probe to such a SUSY scenario.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2016-05-15
摘要： We perform a comparative study of the neutralino dark matter scattering on nucleon in three popular supersymmetric models: the minimal (MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). First, we give the predictions of the elastic cross section by scanning over the parameter space allowed by various direct and indirect constraints, which are from the measurement of the cosmic dark matter relic density, the collider search for Higgs boson and sparticles, the precision electroweak measurements and the muon anomalous magnetic moment. Then we demonstrate the property of the allowed parameter space with/without the new limits from CDMS II. We obtain the following observations: (i) For each model the new CDMS limits can exclude a large part of the parameter space allowed by current collider constraints; (ii) The property of the allowed parameter space is similar for MSSM and NMSSM, but quite different for nMSSM; (iii) For each model the future SuperCDMS can cover most of the allowed parameter space given that all soft breaking parameters are below 1 TeV.
分类： 核科学技术 >> 核科学与技术 提交时间： 2023-08-27
摘要： Intensity-modulated particle therapy (IMPT) with carbon ions is comparatively susceptible to various uncertainties caused by breathing motion, including range, setup, and target positioning uncertainties. To determine relative biological effectiveness-weighted dose (RWD) distributions that are resilient to these uncertainties, the reference phase-based four-dimensional (4D) robust optimization (RP-4DRO) and each phase-based 4D robust optimization (EP-4DRO) method in carbon-ion IMPT treatment planning were evaluated and compared. Based on RWD distributions, 4DRO methods were compared with 4D conventional optimization using planning target volume (PTV) margins (PTV-based optimization) to assess the effectiveness of the robust optimization methods. Carbon-ion IMPT treatment planning was conducted in a cohort of five lung cancer patients. The results indicated that the EP-4DRO method provided better robustness (P=0.080) and improved plan quality (P=0.225) for the clinical target volume (CTV) in the individual respiratory phase when compared with the PTV-based optimization. Compared with the PTV-based optimization, the RP-4DRO method ensured the robustness (P = 0.022) of the dose distributions in the reference breathing phase, albeit with a slight sacrifice of the target coverage (P=0.450). Both 4DRO methods successfully maintained the doses delivered to the organs at risk (OARs) below tolerable levels, which were lower than the doses in the PTV-based optimization (P<0.05). Furthermore, the RP-4DRO method exhibited significantly superior performance when compared with the EP-4DRO method in enhancing overall OAR sparing in either the individual respiratory phase or reference respiratory phase (P<0.05). In general, both 4DRO methods outperformed the PTV-based optimization in terms of OAR sparing and robustness.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： A novel detection of sub-GeV dark matter is proposed in the paper. The electron cloud is boosted by the dark matter and emits an electron when it is dragged back by the heavy nucleus, namely the coherent scattering of the electron cloud of the atom. The survey in the X-ray diffraction shows that the atomic form factors are much more complicate than the naive consideration. The results of the relativistic Hartree-Fock(RHF) method give non-trivial shapes of the atoms. The detailed calculation of the recoil of the electron cloud, the kinetics, the fiducial cross section and the corresponding calculation of detection rate are given analytically. The numerical results show that the limits of the RHF form factors are much stringent than the recoil of a single electron, almost 4 orders stronger, and also gives tight limitations comparing to the Migdal effect below about several hundred MeV. The physical picture and the corresponding results are promising and need further explorations.
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