Recent observations of near supernova show that the acceleration expansion of Universe decreases. This phenomenon is called the transient acceleration. In the second part of work we consider the 3-component Universe composed of a scalar field, interacting with the dark matter on the agegraphic dark energy background. We show that the transient acceleration appears in frame of such a model. The obtained results agree with the latest cosmological observations, namely, the 557 SNIa sample (Union2) was released by the Supernova Cosmology Project (SCP) Collaboration.
Recent discussions about supernova magnitude evolution have raised doubts about the robustness of the late-universe acceleration. In a previous letter, Huang did a null test of the cosmic acceleration by using a Parameterization based on the cosmic Age (PAge), which covers a broad class of cosmological models including the standard $Λ$ cold dark matter model and its many extensions. In this work, we continue to explore the cosmic expansion history with the PAge approximation. Using baryon acoustic oscillations ({\it without} a CMB prior on the acoustic scale), gravitational strong lens time de…
We argue that dark energy with multiple fields is theoretically well-motivated and predicts distinct observational signatures, in particular when cosmic acceleration takes place along a trajectory that is highly non-geodesic in field space. Such models provide novel physics compared to $Λ$CDM and quintessence by allowing cosmic acceleration on steep potentials. From the theoretical point of view, these theories can easily satisfy the conjectured swampland constraints and may in certain cases be technically natural, potential problems which are endemic to standard single-field dark energy. Obse…
Directly comparing the 6 expansion rate measured by type Ia supernovae data and the lower bound on the expansion rate set by the strong energy conditions or the null hypothesis that there never exists cosmic acceleration, we see $3σ$ direct evidence of cosmic acceleration and the $Rh=ct$ model is strongly excluded by the type Ia supernovae data. We also use Gaussian process method to reconstruct the expansion rate and the deceleration parameter from the 31 cosmic chronometers data and the 6 data points on the expansion rate measured from type Ia supernoave data, the direct evidence of cosmic a…
Cosmic acceleration sourced by modification of gravity without extra degrees of freedom
在本文中，我们研究的情况下，晚时间宇宙加速可能会出现由于暗物质和重子物质之间的耦合，而不诉诸暗能量或大规模修改的重力与额外的自由度。这种情形在Jordan系中产生了晚时加速度，而在Einstein系中没有加速度--由非形式耦合引起的\textit{generic modification of gravity}.利用耦合函数的一个简单参数化，在最大非正式的情况下，我们通过使用年龄约束，由于球状星团数据来约束模型参数。我们还获得了观测约束的参数使用$H(z)+SNIa+BAO$数据集。在这种情况下，我们区分幻影和非幻影加速度，并表明该模型可以引起幻影的行为在一个狭窄的区域参数空间。
A novel, interesting class of scalar-tensor gravity theories is those with a limit on the field motion, where the scalar field either goes to a constant acceleration or stops accelerating and goes to a constant velocity. We combine these with the ability to dynamically cancel a high energy cosmological constant, e.g. through the well tempered or self tuning approaches. One can successfully have a cosmic expansion history with a matter dominated epoch and late time acceleration despite a large cosmological constant, although the late time de Sitter limit may be unstable. Pole models, such as in…
We study the effect of an explicit interaction between two scalar fields components describing dark matter in the context of a recent proposal framework for interaction. We find that, even assuming a very small coupling, it is sufficient to explain the observational effects of a cosmological constant, and also overcome the problems of the $Λ$CDM model without assuming an exotic dark energy.
This report summarizes the envisioned research activities as gathered from the Snowmass 2021 CF5 working group concerning Dark Energy and Cosmic Acceleration: Cosmic Dawn and Before. The scientific goals are to study inflation and to search for new physics through precision measurements of relic radiation from the early universe. The envisioned research activities for this decade (2025-35) are constructing and operating major facilities and developing critical enabling capabilities. The major facilities for this decade are the CMB-S4 project, a new Stage-V spectroscopic survey facility, and ex…
Physical condition for the slowing down of cosmic acceleration
宇宙加速的可能减慢被广泛研究。然而，强加的暗能量参数化带来了一些紧张局势。在我们最近的论文中，我们使用模型独立的方法，高斯过程来测试这种可能性。然而，产生这些紧张局势的原因仍然是封闭的。本文通过分析减速参数的导数来解决这一问题。导数的重建再次表明，在95% C. L.内没有出现加速度减慢。根据目前的观测数据。然后我们推导出它对暗能量的约束。相应的约束清楚地揭示了以前工作中不同模型之间紧张的原因。我们还研究了为什么现有的数据不能令人信服地衡量加速度的减缓的根本原因。这些约束表明当前大部分数据不在允许的区域中。
Galaxy clusters host the largest particle accelerators in the Universe: Shock waves in the intracluster medium (ICM), a hot and ionised plasma, that accelerate particles to high energies. Radio observations pick up synchrotron emission in the ICM, proving the existence of accelerated cosmic-ray electrons. However, a sign of cosmic-ray protons, in form of $γ$-rays. remains undetected. This is know as the missing $γ$-ray problem and it directly challenges the shock acceleration mechanism at work in the ICM. Over the last decade, theoretical and numerical studies focused on improving our knowledg…
