arXiv subjects

Hong-Guang Zhang

Publications and source records attributed to Hong-Guang Zhang.

4 recordsLinked to original sources

arXiv2010

Observe the open universe in the sky?

We first review the related works on the observable consequence of landscape and the regulation of e-foldings during inflation. We focus on a branch of observable consequence of landscape which predicts an open universe with negative curvature if e-foldings $N>62$. After discussing the observable regulation from the aspect by Kaloper, Kleban and Sorbo, we make an argument that in the non-flat background the observable $N$ is suppressed by a factor $k/ρ_{0}$. We point out that this seems to detect the information where e-foldings $N>62$ possibly. Finally, we discuss our outcomes with the recent work by Arkani-Hamed et al.

hep-th↗

arXiv2009

Modification from Noncommutative Inflation

We explore the noncommutative effect on single field inflation and compare with WMAP five-year data. First, we calculate the noncommutative effect from the potential and dynamical terms, and construct the general form of modified power spectrum. Second, we consider the leading order modification of slow-roll, DBI and K-inflation and unite the modification, which means the modification is nearly model independent at this level. Finally, comparing with the WMAP5 data, we find that the modified can be well realized as the origin of the relative large spectral index and the quite small running.

astro-ph↗

arXiv2009

Exploring trans-Planckian physics and the curvature effect by primordial power spectrum with WMAP five-year data

The vacuum inflation with a boundary condition specified at a short-distance scale in a generally primeval non-flat Universe, and implications of the correspondingly modified primordial power spectrum via the WMAP data are investigated. We obtain a general form of the modified primordial power spectrum including the effects of both possibly new physics scale and the spatial curvature. The modulation of the primordial power spectrum due to new physics is of the order $H/Λ$, where $H$ is the Hubble parameter during inflation and $Λ$ is the new physics scale that is key to inflation, while the modulation from the curvature effect is of the order $K/k^2$, where $K$ is the spatial curvature before inflation and $k$ is the comoving wave number. We also find that a closed Universe before inflation is favored by WMAP five-year data.

astro-ph↗

arXiv2008

Exact solutions of embedding the 4D Universe in a 5D Einstein manifold

One of the simplest way to extend 4D cosmological models is to add another spatial dimension to make them 5D. In particular, it has been shown that the simplest of such 5D models, i.e., one in which the right hand side of the Einstein equation is empty, induces a 4D nonempty Universe. Accordingly, the origin of matter in the 4D real Universe might be mathematically attributed to the existence of one (fictitious) extra spatial dimension. Here we consider the case of an empty 5D Universe possessing a cosmological constant $Λ$ and obtain exact solutions for both positive and negative values of $Λ$. It is seen that such a model can naturally reduce to a power law $Λ$CDM model for the real Universe. Further, it can be seen that, the arbitrary constants and functions appearing in this model are endowed with definite physical meanings.

astro-ph↗