Non-Euclidean elasticity for rods and almost isometric embeddings of geodesic tubes

We consider a geodesic $\gamma$ of length $2L$ in an oriented Riemannian manifold $(\mathcal M, g)$ and a thin tube $\Omega^*_h$ around $\gamma$ of radius $h$. We study an 'elastic' energy per unit volume $E_h(u)$ of maps $u$ from $\Omega^*_h$ into another oriented Riemannian manifold $(\tilde {\mathcal M},\tilde g)$. The energy $E_h$ is based on the squared distance of the differentials $du$ from the set of orientation preserving linear maps between the corresponding tangent spaces. We prove a compactness result for sequences of maps $u_h$ for which $h^{-4} E_h(u_h)$ remains bounded and we study the $\Gamma$-Limit of $h^{-4} E_h(u_h)$ as $h \to 0$ with respect to a suitable notion of convergence for $u_h$ that involves certain blow-ups in the radial direction. This $\Gamma$-convergence result ge\-ne\-ra\-lizes work by Mora and M\"uller on the limiting energy of thin rods in the Euclidean setting. We also obtain an expression for the minimum of the limiting energy as a specific quadratic functional in the difference of the pullbacks of the curvature tensors of $\mathcal M$ and $\tilde{\mathcal M}$ along the curves $\gamma$ and $u \circ \gamma$, respectively, thus answering a question by Maor and Shachar, J. Elasticity 134 (2019), pp. 149--173.