Bilinear forms on potential spaces in the unit circle

Abstract

In this paper we characterize the boundedness on the product of Sobolev spaces $H^s(\mathbb{T}) \times H^s(\mathbb{T})$ on the unit circle $\mathbb{T}$, of the bilinear form $\Lambda_b$ with symbol $b \in H^s(\mathbb{T})$ given by $$ \Lambda_b(\varphi, \psi):=\int_{\mathbb{T}}\left((-\Delta)^s+I\right)(\varphi \psi)(\eta) b(\eta) d \sigma(\eta)$$