{ "id": "1904.06533", "version": "v1", "published": "2019-04-13T12:34:33.000Z", "updated": "2019-04-13T12:34:33.000Z", "title": "Lichnerowicz-Obata Estimate, Almost Parallel $p$-form and Almost Product Manifolds", "authors": [ "Masayuki Aino" ], "comment": "76 pages", "categories": [ "math.DG" ], "abstract": "We show a Lichnerowicz-Obata type estimate for the first eigenvalue of the Laplacian of $n$-dimensional closed Riemannian manifolds with an almost parallel $p$-form ($2\\leq p \\leq n/2$) in $L^2$-sense, and give a pinching result about the almost equality case when $2\\leq p