Carrot John domains in variational problems

Abstract: In this paper, we explore carrot John domains within variational problems, dividing our examination into two distinct sections. The initial part is dedicated to establishing the lower semicontinuity of the (optimal) John constant concerning Hausdorff convergence for bounded John domains. This result holds promising implications for both shape optimization problems and Techm\"uller theory. In the subsequent section, we demonstrate that an unbounded open set satisfying the carrot John condition with a center at $\infty$, appearing in the Mumford-Shah problem, can be covered by a uniformly finite number of unbounded John domains (defined conventionally through cigars). These domains, in particular, support Sobolev-Poincar\'e inequalities.