Improved interpolation inequalities, relative entropy and fast diffusion equations

Dolbeault, Jean; Toscani, Giuseppe

Annales de l'I.H.P. Analyse non linéaire, Tome 30 (2013) no. 5, pp. 917-934.

We consider a family of Gagliardo–Nirenberg–Sobolev interpolation inequalities which interpolate between Sobolevʼs inequality and the logarithmic Sobolev inequality, with optimal constants. The difference of the two terms in the interpolation inequalities (written with optimal constant) measures a distance to the manifold of the optimal functions. We give an explicit estimate of the remainder term and establish an improved inequality, with explicit norms and fully detailed constants. Our approach is based on nonlinear evolution equations and improved entropy–entropy production estimates along the associated flow. Optimizing a relative entropy functional with respect to a scaling parameter, or handling properly second moment estimates, turns out to be the central technical issue. This is a new method in the theory of nonlinear evolution equations, which can be interpreted as the best fit of the solution in the asymptotic regime among all asymptotic profiles.

Classification : 26D10, 46E35, 35K55
Mots clés : Gagliardo–Nirenberg–Sobolev inequalities, Improved inequalities, Manifold of optimal functions, Entropy–entropy production method, Fast diffusion equation, Barenblatt solutions, Second moment, Intermediate asymptotics, Sharp rates, Optimal constants

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