目前我们宇宙的加速膨胀可能是由一种未知的能量成分(暗能量)或广义相对论的修正(修正引力)驱动的。本文重新讨论了一个唯象模型的约束条件,该模型介于纯\LambdaCDM模型和带附加参数α的Dvali-Gabadadze-Porrati(DGP)膜世界模型之间.结合宇宙微波背景辐射(CMB)、重子声学振荡(BAO)和Ia型超新星(SNIa),以及伽马射线暴(GRB)和线性增长因子(LGF)等高红移观测,我们得到了参数α=0.254 \pm 0.153(68% C. L.)的严格约束,这意味着平坦的DGP模型与当前的观测结果不相容,而纯\LambdaCDM模型仍然非常好地拟合数据。最后,我们以更高的精度模拟了未来的测量,发现与现有的约束相比,对α的约束可以提高两倍。
英文摘要:
The accelerating expansion of our universe at present could be driven by an unknown energy component (Dark Energy) or a modification of general relativity (Modified Gravity). In this note we revisit the constraints on a phenomenological model which interpolates between the pure \LambdaCDM model and the Dvali-Gabadadze-Porrati (DGP) braneworld model with an additional parameter α. Combining the cosmic microwave background (CMB), baryon acoustic oscillations (BAO) and type Ia supernovae (SNIa), as well as some high-redshift observations, such as the gamma-ray bursts (GRB) and the measurements of linear growth factors (LGF), we obtain the tight constraint on the parameter α=0.254\pm0.153 (68% C.L.), which implies that the flat DGP model is incompatible with the current observations, while the pure \LambdaCDM model still fits the data very well. Finally, we simulate the future measurements with higher precisions and find that the constraint on αcan be improved by a factor two, when compared to the present constraints.
In this work we explore and test new formulations of cosmological scenarios in $f(Q)$ theories. In these settings, the non-metricity scalar ($Q$) is the main source of gravity and Friedmann equations are modified to account for the associated degrees of freedom. This work focuses first on the derivation, and then theoretical and observational analysis of two such (new) exact cosmological models; they both display a non-standard behaviour in which an additional parameter encoding non-metricity effects acts in the fashion of a screened cosmological constant. One of the new settings has the same …
Testing consistency of general relativity with kinematic and dynamical probes
在这项工作中,我们测试的一致性关系的运动学探针,观测哈勃数据,和动力学探针,宇宙大尺度结构的增长率,这应该成立,如果广义相对论是正确的引力理论在宇宙尺度上。此外,我们还总结了参数化方法在测试中的发展历史,并对参数化方法进行了改进,利用参数化和非参数化方法给出的Hubble参数,提出了三个方程,并对其中两个方程进行了二维参数化测试,其中一个方程采用了三角函数。结果表明,在$1σ$ CL下,一致性关系满足良好的条件,三角函数是参数化的有效工具。此外,为了验证检验的有效性,我们还引入了一种改进的重力模型--DGP模型,并将其在$Λ$ CDM、“DGP in GR”和DGP模型下的检验结果与模拟数据进行了比较。可以看出,正是一致性关系的建立主导了测试的结果。总的来说,目前的观测哈勃数据和增长率数据令人信服地支持广义相对论是宇宙尺度上正确的引力理论。
Observational constraints on non-minimally coupled Galileon model
作为Dvali-Gabadadze-Porrati(DGP)模型的推广,Galileon理论被用来解释“自加速问题”和“鬼不稳定性问题”。本文推广了Galileon理论,考虑了与引力非极小耦合的Galileon标量。对状态发现器分析、$Om(z)$诊断和模型参数约束进行了研究,发现了$Ω_\text{m0}=0.263_{-0.031}^{+0.031}$、$n=1.53_{-0.37}^{+0.21}$(在$95\%$置信水平下)与$χ^2_{\text{min}}=473.376$的关系。此外,我们表明,由于SNe Ia + BAO数据,我们的模型表现得像一个幻影般的暗能量。
Constraining dark matter-dark energy interaction with gas mass fraction in galaxy clusters
最近的观测证据表明,目前的宇宙加速激发了人们对替代宇宙学的新兴趣,例如在暗区(暗物质和暗能量)相互作用的场景。一般来说,这样的模型包含一个未知的负压暗分量,与无压的暗物质和/或重子耦合,导致宇宙的演化与标准$Λ$ CDM模型预测的宇宙演化截然不同。在这项工作中,我们使用最新的星系团气体质量分数与红移数据(42个X射线发光,动态弛豫的星系团,跨越红移范围0.063 < z < 1.063)(Allen et al. 2008)对表征暗物质/暗能量耦合的参数$ε$设置界限,以测试这种情况下的观测可行性。结果与其他宇宙学数据一致,并且通常具有约束力。虽然与时间无关的宇宙学常数($Λ$ CDM模型)与这些星系团数据很好地吻合,但仍不能排除相互作用的暗能量成分。
We consider several well-known f(R) cosmological models and constrain their parameters, namely the deviation parameter b and the cosmological parameters Ω_m and h. We first obtain analytical approximations for the Hubble rate H(z) and the luminosity distance d_L(z) in terms of these parameters, and then test these against the observational expansion rate derived from cosmic chronometers and the distance modulus in the HII galaxy Hubble diagram, obtained in a model-independent way using Gaussian Processes (GP). We first optimize the models based solely on the cosmic chronometers and then repeat…
Strongly gravitational lensing systems (SGL) encodes cosmology information in source/lens distance ratios $\mathcal{D}_{\rm obs}=\mathcal{D}_{\rm ls}/\mathcal{D}_{\rm s}$, which can be used to precisely constrain cosmological parameters. In this paper, based on future measurements of 390 strong lensing systems from the forthcoming LSST survey, we have successfully reconstructed the distance ratio $\mathcal{D}_{\rm obs}$ (with the source redshift $z_s\sim 4.0$), directly from the data without assuming any parametric form. A recently developed method based on model-independent reconstruction app…
We demonstrate the potential of an emulator-based approach to analyzing galaxy formation models in the domain where constraining data is limited. We have applied the open-source Python package PRISM to the galaxy formation model Meraxes. Meraxes is a semi-analytic model, purposefully built to study the growth of galaxies during the Epoch of Reionization (EoR). Constraining such models is however complicated by the scarcity of observational data in the EoR. PRISM's ability to rapidly construct accurate approximations of complex scientific models using minimal data is therefore key to performing…
Recently, the observed equation of state for dark energy appears to favor values below $-1$. The tendency implies that the nature of dark energy may be quite different from that of the cosmological constant. In view of the adjustment on the equation of state keeps decreasing, the introduction of the phantom energy seems inevitable. By employing observational constraints from supernovae and from the acoustic scale in which the accuracy of the data has become extraordinary, we apply a phenomenological scenario to be acquainted with the evolution of our universe. The demonstration on the constrai…
The $β$-exponential inflation is driven by a class of primordial potentials, derived in the framework of braneworld scenarios, that generalizes the well-known power law inflation. In this paper we update previous constraints on the minimal coupled $β$-exponential model [1] and extend the results also deriving the equations for the non-minimal coupled scenario. The predictions of both models are tested in light of the latest temperature and polarization maps of the Cosmic Microwave Background and clustering data. We also compare the predictions of these models with the standard $Λ$CDM cosmology…
Given that the reionization history of cosmic hydrogen is yet to be stringently constrained, it is worth checking the prospects of doing so using physically motivated models and available observational data. For this purpose, we use an extended version of the explicitly photon-conserving semi-numerical model of reionization, $\texttt{SCRIPT}$, which also includes thermal evolution of the intergalactic medium (IGM). The model incorporates the effects of inhomogeneous recombination and radiative feedback self-consistently and is characterized by five free parameters (two for the redshift-depende…
We investigate the potential of cosmological observations, such as galaxy surveys, for constraining degenerate higher-order scalar-tensor (DHOST) theories, focusing in particular on the linear growth of the matter density fluctuations. We develop a formalism to describe the evolution of the matter density fluctuations during the matter dominated era and in the early stage of the dark energy dominated era in DHOST theories, and give an approximate expression for the gravitational growth index in terms of several parameters characterizing the theory and the background solution under consideratio…
Constraints on a dark energy dominated Universe are obtained from an interplay between Bayesian Machine Learning and string Swampland criteria. The approach here differs from previous studies, since in the generative process Swampland criteria are used and, only later, the results of the fit are validated, by using observational data-sets. A generative process based Bayesian Learning approach is applied to two models and the results are validated by means of available $H(z)$ data. For the first model, a parametrization of the Hubble constant is considered and, for the second, a parametrization…