Primordial non-Gaussianities of scalar and tensor perturbations in general bounce cosmology: Evading the no-go theorem

关于膨胀前的非高斯性

More on Pre-Inflationary Non Gaussianities

该研究将爬升场景中曲率扰动的三阶幅值推广到更广泛的指数势能函数，并计算了引力子模式的三阶幅值，揭示了转折点处无特殊贡献。

Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem

We extend the matter bounce scenario to a more general theory in which the background dynamics and cosmological perturbations are generated by a $k$-essence scalar field with an arbitrary sound speed. When the sound speed is small, the curvature perturbation is enhanced, and the tensor-to-scalar ratio, which is excessively large in the original model, can be sufficiently suppressed to be consistent with observational bounds. Then, we study the primordial three-point correlation function generated during the matter-dominated contraction stage and find that it only depends on the sound speed par…

Non-Gaussianity in a Matter Bounce

A nonsingular bouncing cosmology in which the scales of interest today exit the Hubble radius in a matter-dominated contracting phase yields an alternative to inflation for producing a scale-invariant spectrum of adiabatic cosmological fluctuations. In this paper we identify signatures in the non-Gaussianities of the fluctuations which are specific to this scenario and allow it to be distinguished from the results of inflationary models.

线性区域之外的Cuscuton反弹：双谱与强耦合约束

Cuscuton Bounce Beyond the Linear Regime: Bispectrum and Strong Coupling Constraints

针对Cuscuton反弹非奇异宇宙学模型，研究通过线性分析、三阶扰动作用量推导及三点函数计算，验证其全演化红外微扰性、紫外标度层级，无强耦合问题且可观测尺度非高斯性可忽略，是符合观测的稳健弱耦合模型。

Non-Gaussianity excess problem in classical bouncing cosmologies

The simplest possible classical model leading to a cosmological bounce is examined in the light of the non-Gaussianities it can generate. Concentrating solely on the transition between contraction and expansion, and assuming initially purely Gaussian perturbations at the end of the contracting phase, we find that the bounce acts as a source such that the resulting value for the post-bounce $f_{\mathrm{NL}}$ may largely exceed all current limits, to the point of potentially casting doubts on the validity of the perturbative expansion. We conjecture that if one can assume that the non-Gaussianit…

带有额外标量场的完全可行DHOST反弹宇宙模型

Fully viable DHOST bounce with extra scalar

本文首次构造了带有额外标量场的双场DHOST反弹宇宙模型，该模型无BKL不稳定性、鬼场和梯度不稳定性及超光速问题，能产生近尺度不变扰动和极小张标比，并与观测相容。

论暴胀前非高斯性

On Pre-Inflationary non Gaussianities

本文研究弦理论高尺度超对称破缺场景中暴胀前曲率扰动三点振幅，发现与攀爬阶段转折点相关的第二类贡献在e-fold数62-66内可能可观测。

The pre-inflationary dynamics of loop quantum cosmology: Confronting quantum gravity with observations

Using techniques from loop quantum gravity, the standard theory of cosmological perturbations was recently generalized to encompass the Planck era. We now apply this framework to explore pre-inflationary dynamics. The framework enables us to isolate and resolve the true trans-Planckian difficulties, with interesting lessons both for theory and observations. Specifically, for a large class of initial conditions at the bounce, we are led to a self consistent extension of the inflationary paradigm over the 11 orders of magnitude in density and curvature, from the big bounce to the onset of slow r…

非奇异反弹中的RRR涨落

RRR fluctuations from non-singular bounce

本文在含收缩、非奇异反弹及慢滚到超慢滚转变的暴胀框架中，一致处理正则化、重正化和重求和，计算功率谱量子修正，产生太阳质量原初黑洞并规避不可行定理，且满足因果性和幺正性约束。

正则化-重整化-重求和圈修正的非奇异反弹原初黑洞形成功率谱

Regularized-Renormalized-Resummed loop corrected power spectrum of non-singular bounce with Primordial Black Hole formation

针对收缩-非奇异反弹-暴胀（含SR到USR转变）生成PBHs的模型，通过EFT方法研究各阶段量子圈修正，消除紫外发散、软化红外发散，生成太阳质量PBHs并规避禁则，分析质量范围与约束，为PBH研究提供支持。

圈量子宇宙学：理论与观测的关系

Loop quantum cosmology: relation between theory and observations

本文综述圈量子宇宙学的宇宙微扰理论框架、早期宇宙模型应用及观测效应，讨论其扩展方向与局限性，并总结圈量子宇宙学与完整圈量子引力关联的研究进展。