The fractional Laplacian , with
, is the nonlocal operator defined for suitably regular
functions on
by
where
is the Euclidean norm,
denotes the Cauchy principal
value, and
is the normalization constant. With the Fourier
transform convention using
, its multiplier is
. Thus it is a fractional power of the negative Laplacian.
When ,
the Riesz potential of order
gives its inverse on suitable functions. The fractional
Lane-Emden conjecture concerns a nonlinear system formed from this operator (Mei
and Wei 2026).