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Journal of Convex Analysis 33 (2026), No. 3&4, 691--736 Copyright Heldermann Verlag 2026 Calibrations for Minimal Surfaces with Free Boundary and Cheeger-Type Problems Guy Bouchitté Lab IMATH, Université de Toulon, La Garde, France bouchitte@univ-tln.fr Minh Phan The University of Danang, University of Science and Education, Danang, Vietnam ptdminh@ued.udn.vn We study a problem of minimal surfaces with free boundary written in the form of a non convex minimization problem. Our aim is to characterize optimal solutions by finding a suitable calibration field. A natural upper bound of the infimum is given by a variant of the Cheeger problem that we solve explicitly proving the optimality thanks to the construction of a cut-locus potential. The comparison with the original problem is then discussed in detail. Keywords: Free boundary problems, calibrations, minimal surfaces, shape derivative, Cheeger sets, cut-locus potential. MSC: 49J45, 49N15, 49Q10, 65K10, 90C26. [ Fulltext-pdf (2310 KB)] for subscribers only. |