1 8 N ov 2 00 9 Chessboard complexes indomitable ∗

Chessboard complexes indomitable

We give a simpler, degree-theoretic proof of the striking new Tverberg type theorem of Blagojević, Ziegler and Matschke, arXiv:0910.4987v2. Our method also yields some new examples of “constrained Tverberg theorems” including a simple colored Radon’s theorem for d + 3 points in Rd. This gives us an opportunity to review some of the highlights of this beautiful theory and reexamine the role of c...

ar X iv : h ep - e x / 02 11 06 9 v 1 2 8 N ov 2 00 2 Jet Production at CDF Mario Mart́ınez

Cycle-free chessboard complexes and symmetric homology of algebras

Chessboard complexes and their relatives have been an important recurring theme of topological combinatorics (see [1], [5], [10], [11], [13], [14], [20], [23], [24], [25]). Closely related “cycle-free chessboard complexes” have been recently introduced by Ault and Fiedorowicz in [2] and [9] as a tool for computing symmetric analogues of the cyclic homology of algebras. We study connectivity pro...

N ov 2 00 8 EQUIVARIANT CW - COMPLEXES AND THE ORBIT CATEGORY

We give a general framework for studying G-CW complexes via the orbit category. As an application we show that the symmetric group G = S 5 admits a finite G-CW complex X homotopy equivalent to a sphere, with cyclic isotropy subgroups.

ar X iv : 0 71 1 . 45 13 v 1 [ gr - q c ] 2 8 N ov 2 00 7 Conformal classes of asymptotically flat , static vacuum data

We show that time-reflection symmetric, asymptotically flat, static vacuum data which admit a non-trivial conformal rescaling which leads again to such data must be axi-symmetric and admit a conformal Killing field. Moreover, it is shown that there exists a 3-parameter family of such data. PACS: 04.20.Ex, 04.20.Ha, 04.20.Jb