The role of fundamental solution in Potential and Regularity Theory for subelliptic PDE Andrea Bonfiglioli, Giovanna Citti, Giovanni Cupini, Maria Manfredini, Annamaria Montanari, Daniele Morbidelli, Andrea Pascucci, Sergio Polidoro, Francesco Uguzzoni tu se’ lo mio maestro e ’l mio autore tu se’ solo colui da cu’ io tolsi lo bello stilo che m’ha fatto onore. Dante Alighieri Abstract In this survey we consider a general Hormander¨ type operator, represented as a sum of squares of vector fields plus a drift and we outline the central role of the fundamental solution in developing Potential and Regularity Theory for solu- tions of related PDEs. After recalling the Gaussian behavior at infinity of the kernel, we show some mean value formulas on the level sets of the fundamental solution, which are the starting point to obtain a comprehensive parallel of the classical Po- tential Theory. Then we show that a precise knowledge of the fundamental solution leads to global regularity results, namely estimates at the boundary or on the whole space. Finally in the regularity problem of non linear differential equations we use an ad hoc modification of the parametrix method, based on the properties of the fundamental solution of an approximating problem. Andrea Bonfiglioli, Giovanna Citti, Giovanni Cupini, Maria Manfredini, Annamaria Montanari, Daniele Morbidelli, Andrea Pascucci, Sergio Polidoro, Francesco Uguzzoni Dipartimento di Matematica, Universita` di Bologna, e-mail: andrea.bonfiglioli6@ unibo.it,
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