In this paper, we establish new sufficient conditions for the polynomial f to be SOS in terms of the Newton polyhedron of f (Theorems 2.6 and 2.12). These new sufficient conditions include results which were proved earlier by Lasserre [13, Theorem 3], Fidalgo and Kovacec [6, Theorem 4.3], Ghasemi and Marshall [7, Theorems 2.1 and 2.3], and Ghasemi and Marshall [8, Theorem 2.3].
"Sufficient conditions for a real polynomial to be a sum of squares of polynomials." Kodai Math. J. 39 (2) 253 - 275, June 2016. https://doi.org/10.2996/kmj/1467830136