In the Friedmann cosmology the deceleration of the expansion q plays a fundamental role. We derive the deceleration as a function of redshift $q(z)$ in two scenarios: $Λ$ CDM model and modified Chaplygin gas (MCG) model, without assuming spatial flatness. The expression relating the transition redshift from decelerated to accelerated expansion $z_t$ to the cosmological parameters is obtained; it is seen that the curvature parameter does not appear in this expression. Of course the numerical value of $z_t$ depends on $Ω_k$, since $Ω_L + Ω_M + Ω_k = 1$. The exact function $q(z)$ allows the calculation of an infection point at $z \approx 0.1$ for the flat $Λ$ CDM model. This inflection point is visible in Fig.5 of the work of Daly and Djorgovski, Ap.J. 612,652 (2004), where the deceleration was plotted directly from observational data. We also consider the possibility of a small contribution of the curvature, namely, $Ω_k = - 0.1 Ω_L $, and calculate the transition redshift to be $z_t = 0.56$, which falls inside the interval $0.46 \pm 0.13$ obtained by Riess et al., Ap.J. 607, 665 (2004). The calculated transition redshift for the MCG model is considerably lower $z_t \approx 0.2$, but the observational data do not exclude a pure Chaplygin gas.
There are different constructions of the flux of triad in loop quantum gravity, namely the fundamental and alternative flux operators. In parallel to the consistency check on the two versions of operator by the algebraic calculus in the literature, we check their consistency by the graphical calculus. Our calculation based on the original Brink graphical method is obviously simpler than the algebraic calculation. It turns out that our consistency check fixes the regulating factor $κ_{\rm reg}$ of the Ashtekar-Lewandowski volume operator as $\frac12$, which corrects its previous value in the li…
In this short paper we determine the effects of structure on the cosmological consistency relation which is valid in a perfect Friedmann Universe. We show that within $Λ$CDM the consistency relation is violated by about 1.5% for redshifts $z\simeq 2$ and this violation raises up to 2% at $z\simeq 5$ and 3% at $z\simeq 10$ after which it settles at about 2.7% for $z>10$. This effect of cosmic structure on the distance redshift relation is also very sensitive to the determination of the dark energy equation of state via cosmic distances. It actually leads to an apparent unphysical behavior of $w…
We investigate the validity of a \emph{minimal} cosmological model derived from the renormalizable Ho$\check{\textrm{r}}$ava action at low redshift scales by using different cosmological and statistical tests. Assuming pure attractive gravity, i.e., $λ>1/3$ in the Ho$\check{\textrm{r}}$ava action, we compare the Union 2.1 supernova type Ia data with the kinematics following from a model-independent approach. The two approaches, although compatible, lead to explicit cosmographic constraints on the free parameters of the Ho$\check{\textrm{r}}$ava action, which turn out to be in strong disagreeme…
Consistency of LCDM with Geometric and Dynamical Probes
LCDM宇宙学模型假设存在一个小的宇宙学常数，以解释观测到的宇宙加速膨胀。尽管在过去的十年里宇宙学数据的质量有了很大的提高，但它仍然是最简单的模型，非常适合（几乎）所有的宇宙学观测。在这次演讲中，我回顾了LCDM提供的越来越成功的拟合最近的宇宙膨胀的几何探测数据。我还简要讨论了一些新出现的缺点，试图适应特定类别的数据（如宇宙速度偶极子流和集群晕配置文件）的模型。最后，我总结了最近的结果，理论上预测的物质过密度（$δ_m=\frac{δρ_m}{ρ_m}$）的演变（宇宙膨胀的动力学探测），强调其规模和规范的依赖大宇宙尺度的背景下，广义相对论。一个新的标度相关参数化可以精确地描述甚至在大于100 h ^{-1}Mpc的标度上的微扰增长率，它是在较小的宇宙学标度上有效的著名的标度无关参数化f（a）= \omms（a）^γ的直接推广.
We consider single-field inflation in light of string-motivated "swampland" conjectures suggesting that effective scalar field theories with a consistent UV completion must have field excursion $Δϕ\lesssim M_{\rm Pl}$, in combination with a sufficiently steep potential, $M_{\rm Pl} V_ϕ/V \gtrsim {\cal O}(1)$. Here, we show that the swampland conjectures are inconsistent with existing observational constraints on single-field inflation. Focusing on the observationally favoured class of concave potentials, we map the allowed swampland region onto the $n_S$-$r$ "zoo plot" of inflationary models, …
We study the bulk flow of the local universe using Type Ia supernova data by considering a class of cosmological model which is spatially flat,(FRW) space-times and contains cold dark matter and $Q$ component (QCDM models) of the fluid as a scalar field, with self interactions determined by a potential $V(Q)=V_{0}Exp(-λQ)$ evolving in Universe. We use different cumulative redshift slices of the Union 2 catalogue. A maximum-likelihood analysis of peculiar velocities confirms that at low redshift $0.015 <z<0.1$, bulk flow is moving towards the $(l; b) = (302^{o}\pm20^{o}; 3^{o}\pm10^{o})$ direct…
The Copernican principle (CP), i.e. the assumption that we are not privileged observers of the Universe, is a fundamental tenet of the standard cosmological model. A violation of this postulate implies the possibility that the apparent cosmic acceleration could be explained without the need of a cosmological constant, dark energy or paper we present a new test of the CP relating the distance and the expansion rate, derived via Noether's theorem, which is complementary to other tests found in the literature. We also simulate fiducial data based on upcoming stage IV galaxy surveys and use them t…
