分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We consider a specific dark energy model, which only includes the Lagrangian up to the cubic order in terms of the vector field self-interactions in the generalized Proca theory. We examine the cosmological parameters in the model by using the data sets of CMB and CMB+HST, respectively. In particular, the Hubble constant is found to be $H_0=71.80^{+1.07}_{-0.72}$ ($72.48^{+0.72}_{-0.60}$) $\rm kms^{-1}Mpc^{-1}$ at $68\%$~C.L. with CMB (CMB+HST), which would alleviate the Hubble constant tension. We also obtain that the reduced $\chi^2$ values in our model are close to unity when fitting with CMB and CMB+HST, illustrating that our model is a good candidate to describe the cosmological evolutions of the universe.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We use the Weakly Interacting Massive Particle (WIMP) thermal decoupling scenario to probe Cosmologies in dilatonic Einstein Gauss-Bonnet (dEGB) gravity, where the Gauss-Bonnet term is non-minimally coupled to a scalar field with vanishing potential. We put constraints on the model parameters when the ensuing modified cosmological scenario drives the WIMP annihilation cross section beyond the present bounds from DM indirect detection searches. In our analysis we assumed WIMPs that annihilate to Standard Model particles through an s-wave process. For the class of solutions that comply with WIMP indirect detection bounds, we find that dEGB typically plays a mitigating role on the scalar field dynamics at high temperature, slowing down the speed of its evolution and reducing the enhancement of the Hubble constant compared to its standard value. For such solutions, we observe that the corresponding boundary conditions at high temperature correspond asymptotically to a vanishing deceleration parameter q, so that the effect of dEGB is to add an accelerating term that exactly cancels the deceleration predicted by General Relativity. The bounds from WIMP indirect detection are nicely complementary to late-time constraints from compact binary mergers. This suggest that it could be interesting to use other Early Cosmology processes to probe the dEGB scenario.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The Hubble tension arises from different observations between the late-time and early Universe. We explore a new model with dark fluid, called the exponential Acoustic Dark Energy (eADE) model, to relieve the Hubble tension. The eADE model gives an exponential form of the equation of state (EoS) in the acoustic dark energy, which is the first time to explore an exponential form for the EoS. In this model, the gravitational effects from the acoustic oscillations of the model can impact the CMB phenomena at the matter radiation equally epoch. We give the constraints of the eADE model by the current cosmological dataset. The comparison of the phenomena with the standard model can be shown through CMB and matter power spectra. The fitting results of our model have $H_0 = 70.06^{+1.13}_{-1.09}$ in 95$\%$ C.L. and a smaller best-fit value than $\Lambda$CDM.
分类: 生物学 >> 生物化学 提交时间: 2020-02-08
摘要: 新型冠状病毒(2019-nCoV)自2019年12月在湖北省武汉市爆发,并迅速传播到中国多地及其他国家。在本研究中,我们报告了来自中国深圳早期的2019-nCoV感染患者的流行病学、临床指标、生化指标和影像学特征,以及可用于预测疾病严重程度的潜在生物标记物。所有12例2019-nCoV感染的肺炎患者均发展为肺炎,其中一半患者进一步发展为急性呼吸窘迫综合征(acute respiratory distress syndrome,ARDS)。最常见的实验室检测生化指标异常是低白蛋白(albumine,ALB)血症、淋巴细胞(lymphocytes,LYM)计数减少,淋巴细胞百分比和中性粒细胞(neutrophils,NEU)百分比降低,C反应蛋白(C-reactive protein,CRP)和乳酸脱氢酶(lactate dehydrogenase,LDH)水平升高,以及CD8细胞计数降低。从患者呼吸道特别是下呼吸道检测到的2019-nCoV病毒滴度与肺部疾病的严重程度正相关。 ALB、LYM、LYM(%)、LDH、NEU(%)和CRP的水平与急性肺损伤程度高度相关。年龄、病毒滴度、肺损伤评分和血液生化指标:ALB、CRP、LDH、LYM(%)、LYM和NEU(%)可能是疾病严重程度的预测指标。此外, 2019-nCoV感染患者的血浆血管紧张素II水平显着升高,并且与病毒滴度和肺损伤程度线性相关。我们的研究结果提供了多种潜在的可用于诊断的生物标志物, 并提出了血管紧张素 II受体阻滞剂(angiotensin II receptor blocker,ARB)药物或可作为治疗2019-nCoV感染的潜在药物进行深入研究。