It has been recently claimed that there is no correlation between the distribution of galaxies and their peculiar velocities within the Local Volume (LV), namely a sphere of R=7/h Mpc around the Local Group (LG). It has been then stated that this implies that either locally dark matter is not distributed in the same way as luminous matter, or peculiar velocities are not due to fluctuations in mass. To test that statement a set of constrained N-body cosmological simulations, designed to reproduce the main observed large scale structure, have been analyzed. The simulations were performed within the flat-Lambda, open and flat matter only CDM cosmogonies. Two unconstrained simulations of the flat-Lambda and open CDM models were performed for comparison. LG-like objects have been selected so as to mimic the real LG environment. The local gravitational field due to all halos found within each LV is compared with the exact gravitational field induced by all matter in the simulation. We conclude that there is no correlation between the exact and the local gravitational field obtained by pairwise newtonian forces between halos. Moreover, the local gravitational field is uncorrelated with the peculiar velocities of halos. The exact gravitational field has a linear correlation with peculiar velocities but the proportionality constant relating the velocity with gravitational field falls below the prediction of the linear theory. Upon considering all matter inside the LVs, the exact and local gravitational accelerations show a much better correlation, but with a considerable scatter independent on the cosmological models. The main conclusion is that the lack of correlation between the local gravitation and the peculiar velocity fields around LG-like objects is naturally expected in the CDM cosmologies.
Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe
几年前，Cornish，Spergel和Starkman（CSS）提出，一个多重连接的“小”宇宙可以允许经典的混沌混合作为暴胀前的均匀化过程。体积越小，过程越重要。此外，一个较小的宇宙有更大的概率自发创建。DeWitt，Hart and Isham（DHI）计算了静态多连通平坦时空的Casimir能量。由于对小体积双曲宇宙（如CSS）的兴趣，我们通过对静态宇宙中共形耦合的大质量标量场的Casimir能量进行数值研究来推广DHI计算，静态宇宙的空间截面是Weeks流形，这是已知的最小的负曲率宇宙。尽管是数值计算，我们的结果实际上是精确的。结果表明，存在低多极分量的真空自发激发。
