Elsevier, Journal of Differential Equations, 1(205), p. 253-269, 2004
DOI: 10.1016/j.jde.2004.03.024
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By variational methods, we prove the inequality: $ ∫_{ℝ} u''{}^2 dx-∫_{ℝ} u'' u^2 dx≥ I ∫_{ℝ} u^4 dx\quad ∀ u𝟄 L^4({ℝ}) {such that} u''𝟄 L^2({ℝ}) $ for some constant $I𝟄 (-9/64,-1/4)$. This inequality is connected to Lieb-Thirring type problems and has interesting scaling properties. The best constant is achieved by sign changing minimizers of a problem on periodic functions, but does not depend on the period. Moreover, we completely characterize the minimizers of the periodic problem. ; Comment: 19 pages, 2 figures