arXiv subjects

Ai-Chen Li

Publications and source records attributed to Ai-Chen Li.

3 recordsLinked to original sources

arXiv2022

Complexity of non-trivial sound speed in inflation

In this paper, we study the impact of non-trivial sound on the evolution of cosmological complexity in inflationary period. The vacuum state of curvature perturbation could be treated as squeezed states with two modes, characterized by the two most essential parameters: angle parameter $ϕ_k$ and squeezing parameter $r_k$. Through $Schr\ddot{o}dinger$ equation, one can obtain the corresponding evolution equation of $ϕ_k$ and $r_k$. Subsequently, the quantum circuit complexity between a squeezed vacuum state and squeezed states are evaluated in scalar curvature perturbation with a type of non-trivial sound speed. Our results reveal that the evolution of complexity at early times shows the rapid solution comparing with $c_S=1$, in which we implement the resonant sound speed with various values of $ξ$. In these cases, it shows that the scrambling time will be lagged with non-vanishing $ξ$. Further, our methodology sheds a new way of distinguishing various cosmological models.

gr-qc↗

arXiv2021

Revised $f_{\rm NL}$ parameter in Curvaton Scenario

We revise the Non-Gaussianity of canonical curvaton scenario with a generalized $δN$ formalism, in which it could handle the generic potentials. In various curvaton models, the energy density is dominant in different period including the secondary inflation of curvaton, matter domination and radiation domination. Our method could unify to deal with these periods since the non-linearity parameter $f_{\rm NL}$ associated with Non-Gaussianity is a function of equation of state $w$. We firstly investigate the most simple curvaton scenario, namely the chaotic curvaton with quadratic potential. Our study shows that most parameter space satisfies with observational constraints. And our formula will nicely recover the well-known value of $f_{\rm NL}$ in the absence of non-linear evolution. From the micro origin of curvaton, we also investigate the Pseudo-Nambu-Goldstone curvaton. Our result clearly indicates that the second short inflationary process for Pseudo-Nambu-Goldstone curvaton is ruled out in light of observations. Finally, our method sheds a new way for investigating the Non-Gaussianity of curvaton mechanism, espeically for exploring the Non-Gaussianity in MSSM curvaton model.

astro-ph.CO↗

arXiv2019

Dynamic domain wall in charged dilaton black hole spacetimes

In this paper we study the dynamics of $ n-1$ dimensional domain wall universe embedded in a $n$ dimensional charged dilaton black hole bulk with the non-asymptotically flat and non-asymptotically (A)dS characters. We find that domain wall can always cross horizon, for which the dilaton coupling constant $a$ and the ratio of pressure to density $w$ play the role of controlling parameters. Then the consequent domain wall motion outside the black hole generally falls into four situations: all time accelerating expansion, slow expansion with a constant speed, expansion followed by collapsing into horizon, and accelerating collapsing into horizon. However, there exists a small patch of parametric sphere, in which the domain wall expansion first slows down and then accelerates. Our analysis also reveals that the big bang theory applies to the domain wall world scenario, while big bounce will not appear in our paper. Furthermore, we find that when we choose the expansion stage as radiation or matter stage, the resultant coupling strength between dilaton field and Maxwell field depends on the different black hole models.

gr-qc↗