# American Institute of Mathematical Sciences

July  2013, 33(7): 3153-3170. doi: 10.3934/dcds.2013.33.3153

## Harnack's inequality for fractional nonlocal equations

 1 Department of Mathematics, The University of Texas at Austin, 1 University Station, C1200, Austin, TX 78712-1202, United States 2 Department of Mathematics, Sun Yat-sen (Zhongshan) University, 510275 Guangzhou, China

Received  March 2012 Revised  June 2012 Published  January 2013

We prove interior Harnack's inequalities for solutions of fractional nonlocal equations. Our examples include fractional powers of divergence form elliptic operators with potentials, operators arising in classical orthogonal expansions and the radial Laplacian. To get the results we use an analytic method based on a generalization of the Caffarelli--Silvestre extension problem, the Harnack's inequality for degenerate Schrödinger operators proved by C. E. Gutiérrez, and a transference method. In this manner we apply local PDE techniques to nonlocal operators. On the way a maximum principle and a Liouville theorem for some fractional nonlocal equations are obtained.
Citation: Pablo Raúl Stinga, Chao Zhang. Harnack's inequality for fractional nonlocal equations. Discrete & Continuous Dynamical Systems - A, 2013, 33 (7) : 3153-3170. doi: 10.3934/dcds.2013.33.3153
##### References:
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##### References:
 [1] I. Abu-Falahah, R. A. Macías, C. Segovia and J. L. Torrea, Transferring strong boundedness among Laguerre orthogonal systems,, Proc. Indian Acad. Sci. Math. Sci., 119 (2009), 203.  doi: 10.1007/s12044-009-0021-4.  Google Scholar [2] I. Abu-Falahah and J. L. Torrea, Hermite function expansions versus Hermite polynomial expansions,, Glasgow Math. J., 48 (2006), 203.  doi: 10.1017/S0017089506003004.  Google Scholar [3] J. J. Betancor, J. Dziubański and J. L. Torrea, On Hardy spaces associated with Bessel operators,, J. Anal. Math., 107 (2009), 195.  doi: 10.1007/s11854-009-0008-1.  Google Scholar [4] S. Bochner, Sturm-Liouville and heat equations whose eigenfunctions are ultraspherical polynomials or associated Bessel functions,, in, (1956), 23.   Google Scholar [5] L. Caffarelli, Some nonlinear problems involving non-local diffusions,, in, (2009), 07.  doi: 10.4171/056-1/3.  Google Scholar [6] L. Caffarelli, S. Salsa and L. Silvestre, Regularity estimates for the solution and the free boundary of the obstacle problem for the fractional Laplacian,, Invent. Math., 171 (2008), 425.  doi: 10.1007/s00222-007-0086-6.  Google Scholar [7] L. Caffarelli and L. Silvestre, An extension problem related to the fractional Laplacian,, Comm. Partial Differential Equations, 32 (2007), 1245.  doi: 10.1080/03605300600987306.  Google Scholar [8] L. Caffarelli and A. Vasseur, Drift diffusion equations with fractional diffusion and the quasi-geostrophic equation,, Ann. of Math. (2), 171 (2010), 1903.  doi: 10.4007/annals.2010.171.1903.  Google Scholar [9] E. B. Davies, "Heat Kernels and Spectral Theory,", Cambridge Tracts in Mathematics 92, 92 (1989).  doi: 10.1017/CBO9780511566158.  Google Scholar [10] E. B. Fabes, C. E. Kenig and R. P. Serapioni, The local regularity of solutions to degenerate elliptic equations,, Comm. Partial Differential Equations, 7 (1982), 77.  doi: 10.1080/03605308208820218.  Google Scholar [11] D. Gilbarg and N. S. Trudinger, "Elliptic Partial Differential Equations of Second Order,", Classics in Mathematics, (2001).   Google Scholar [12] C. E. Gutiérrez, Harnack's inequality for degenerate Schrödinger operators,, Trans. Amer. Math. Soc., 312 (1989), 403.  doi: 10.2307/2001222.  Google Scholar [13] C. E. Gutiérrez, On the Riesz transforms for Gaussian measures,, J. Funct. Anal., 120 (1994), 107.  doi: 10.1006/jfan.1994.1026.  Google Scholar [14] C. E. Gutiérrez, A. Incognito and J. L. Torrea, Riesz transforms, $g$-functions, and multipliers for the Laguerre semigroup,, Houston J. Math., 27 (2001), 579.   Google Scholar [15] T. Lin, Y. Y. Li and J. Xiong, On a fractional Nirenberg problem, part I: Blow up analysis and compactness of solutions,, preprint (2011), (2011).   Google Scholar [16] N. S. Landkof, "Foundations of Modern Potential Theory,", Die Grundlehren der mathematischen Wissenschaften, (1972).   Google Scholar [17] N. N. Lebedev, "Special Functions and Their Applications,", Prentice-Hall, (1965).   Google Scholar [18] B. Muckenhoupt and E. M. Stein, Classical expansions and their relation to conjugate harmonic functions,, Trans. Amer. Math. Soc., 118 (1965), 17.   Google Scholar [19] L. Roncal and P. R. Stinga, Fractional Laplacian on the torus,, preprint (2012), (2012).   Google Scholar [20] W. Rudin, "Functional Analysis,", McGraw-Hill Series in Higher Mathematics, (1973).   Google Scholar [21] M. F. Shlesinger, G. M. Zaslavsky and J. Klafter, Strange kinetics,, Nature, 363 (1993), 31.   Google Scholar [22] L. Silvestre, Regularity of the obstacle problem for a fractional power of the Laplace operator,, Comm. Pure Appl. Math., 60 (2007), 67.  doi: 10.1002/cpa.20153.  Google Scholar [23] P. R. Stinga and J. L. Torrea, Extension problem and Harnack's inequality for some fractional operators,, Comm. Partial Differential Equations, 35 (2010), 2092.  doi: 10.1080/03605301003735680.  Google Scholar [24] G. Szegö, "Orthogonal Polynomials,", Fourth edition, XXIII (1975).   Google Scholar [25] J. Tan and J. Xiong, A Harnack inequality for fractional Laplace equations with lower order terms,, Discrete Contin. Dyn. Syst., 31 (2011), 975.  doi: 10.3934/dcds.2011.31.975.  Google Scholar [26] S. Thangavelu, "Lectures on Hermite and Laguerre Expansions,", Mathematical Notes 42, 42 (1993).   Google Scholar [27] E. C. Titchmarsh, "Intoduction to the Theory of Fourier Integrals,", Third edition, (1986).   Google Scholar [28] N. S. Trudinger, Linear elliptic operators with measurable coefficients,, Ann. Scuola Norm. Sup. Pisa (3), 27 (1973), 265.   Google Scholar [29] K. Yosida, "Functional Analysis,", Classics in Mathematics, (1995).   Google Scholar
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