We prove that in a ring of S-integers containing 1/2, any totally positive element is a sum of five squares. We also exhibit examples of such rings where some totally positive elements cannot be written as the sum of four squares.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-aa8363-2-2016, author = {Ga\"el Collinet}, title = {Sums of squares in rings of integers with 2 inverted}, journal = {Acta Arithmetica}, volume = {172}, year = {2016}, pages = {383-390}, zbl = {06602746}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa8363-2-2016} }
Gaël Collinet. Sums of squares in rings of integers with 2 inverted. Acta Arithmetica, Tome 172 (2016) pp. 383-390. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa8363-2-2016/