The $f(R)$ gravity models proposed by Hu-Sawicki and Starobinsky are generic for local gravity constraints to be evaded. The large deviations from these models either result into violation of local gravity constraints or the modifications are not distinguishable from cosmological constant. The curvature singularity in these models is generic but can be avoided provided that proper fine tuning is imposed on the evolution of scalaron in the high curvature regime. In principle, the problem can be circumvented by incorporating quadratic curvature correction in the Lagrangian though it might be quite challenging to probe the relevant region numerically.
We use six different cosmological models to study the recently-released compilation of X-ray and UV flux measurements of 2038 quasars (QSOs) which span the redshift range $0.009 \leq z \leq 7.5413$. We find, for the full QSO data set, that the parameters of the X-ray and UV luminosities $L_X-L_{UV}$ relation used to standardized these QSOs depend on the cosmological model used to determine these parameters, i.e, it appears that the full QSO data set include QSOs that are not standardized and so cannot be used for the purpose of constraining cosmological parameters. Subsets of the QSO data, res…
We use 78 reverberation-measured Mg II time-lag quasars (QSOs) in the redshift range $0.0033 \leq z \leq 1.89$ to constrain cosmological parameters in six different cosmological models. The basis of our method is the use of the radius-luminosity or $R-L$ relation to standardize these 78 Mg II QSOs. In each cosmological model we simultaneously determine $R-L$ relation and cosmological model parameters, thus avoiding the circularity problem. We find that the $R-L$ relation parameter values are independent of the cosmological model used in the analysis thus establishing that current Mg II QSOs ar…
Our current measurements of the Standard Model parameters imply that the Higgs field resides in a metastable electroweak vacuum, where the vacuum can decay to a lower ground state, with cataclysmic repercussions for our Universe. According to our observations, no such event has happened in the observable universe, in spite of the various energetic processes that could have triggered it. This work serves as an overview of a method that uses the metastability of the false vacuum during cosmological inflation to provide constraints on the Higgs curvature coupling $ξ$. Considering also the effects…
In a recent work, it has been proposed that the recent cosmic passage to a cosmic acceleration era is the result of the existence of small anti-gravity sources in each galaxy and clusters of galaxies. In particular, a swiss-cheese cosmology model which relativistically integrates the contribution of all these anti-gravity sources on galactic scale has been constructed assuming the presence of an infrared fixed point for a scale dependent cosmological constant. The derived cosmological expansion provides explanation for both the fine tuning and the coincidence problem. The present work relaxes …
The observational evidence regarding the present cosmological aspects tells us about the presence of very little anisotropy in the universe on a large scale. Here, in this paper, we attempt to study locally rotationally symmetric (LRS) homogeneous Bianchi-I spacetime with the isotropic matter distribution. This is done within the framework of $f(\mathcal{R},\mathscr{L}_m)$ gravity. Particularly, we consider a non-linear $f(\mathcal{R},\mathscr{L}_m)$ model, $f(\mathcal{R},\mathscr{L}_m)=\dfrac{1}{2}\mathcal{R}+\mathscr{L}_m^{\,α}$. Furthermore, $ω$, the equation of state parameter, which is vi…
Constraining neutrino mass and extra relativistic degrees of freedom in dynamical dark energy models using Planck 2015 data in combination with low-redshift cosmological probes: basic extensions to $Λ$CDM cosmology
Constraining Early Dark Energy cosmological models with Big Bang Nucleosynthesis
Astronomical Institute of Romanian Academy, Cluj-Napoca Branch（罗马尼亚科学院天体物理研究所）；Babeş-Bolyai University（博拜-鲍约什大学）；Technical University of Cluj-Napoca（克卢日-纳波卡理工大学）
Constraining Inflationary Scenarios with Braneworld Models and Second Order Cosmological Perturbations
暴胀宇宙学是早期宇宙的主要解释。许多不同的暴胀模型已经建立起来，符合当前的观测数据。在这项工作中，理论和数值方法约束的参数空间的广泛的一类这样的模型进行了说明。首先，弦理论模型与大的非高斯签名进行了研究。对紫外Dirac Born Infeld暴胀产生的原初引力波振幅给出了一个上限。在所有的情况下，但最微调的情况下，这个界限是不兼容的下限来自暴胀模型，表现出红色光谱和可检测的非高斯性。通过对一般非正则作用的分析，找到了一类在扰动相速较小时可以避开上界的模型。具有有限数量膜的多重合膜场景就是这样一个模型。对于具有潜在可观测的引力波谱的模型，重合膜的数目只取很小的值。约束暴胀模型的第二种方法是数值计算一般单场模型的二阶微扰。本文数值求解了仅用标量场变量表示的二阶Klein-Gordon方程。慢滚版本的二阶源项被使用，该方法被证明是可扩展到完整的方程。这个程序允许一般的二阶扰动的演变和计算的非高斯参数的情况下，没有可用的解析解。
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…
