ABSTRACT
Taking “square roots” of quadratic forms is one of the primary reasons for working in the Clifford algebra context. In particular, one can consider the square root of the Laplacian and still be within the class of differential operators. Originating in the pioneering work of Moisil [Mo], [MT], Teodorescu [Te] and Fueter [Fu] among others, the study of the resulting elliptic first-order differential operator, much in the spirit of the Cauchy-Riemann ∂ ¯ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315139548/2af6e4bd-72bf-419b-b1f3-52d645c48a21/content/eq877.tif"/> operator, has become by now a well-established, active area of research (see for instance the monographs [BDS], [HS], [GM2], [M3], and the references therein).
