Let F be a power series centered at the origin in a real Banach space with radius of uniform convergence ϱ. We show that F is analytic in the open ball B of radius ϱ/√e, and furthermore, the Taylor series of F about any point a ∈ B converges uniformly within every closed ball centered at a contained in B.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-sm191-2-5, author = {Timothy Nguyen}, title = {A lower bound on the radius of analyticity of a power series in a real Banach space}, journal = {Studia Mathematica}, volume = {192}, year = {2009}, pages = {171-179}, zbl = {1193.32001}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm191-2-5} }
Timothy Nguyen. A lower bound on the radius of analyticity of a power series in a real Banach space. Studia Mathematica, Tome 192 (2009) pp. 171-179. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-sm191-2-5/