A framework for constructing new kinds of gauge theories is suggested. Essentially it consists in replacing Lie algebras by Lie or Courant algebroids. Besides presenting novel topological theories defined in arbitrary spacetime dimensions, we show that equipping Lie algebroids E with a fiber metric having sufficiently many E-Killing vectors leads to an astonishingly mild deformation of ordinary Yang-Mills theories: Additional fields turn out to carry no propagating modes. Instead they serve as moduli parameters gluing together in part different Yang-Mills theories. This leads to a symmetry enhancement at critical points of these fields, as is also typical for String effective field theories.Yang-Mills (YM) theories and Lie group symmetries are part and parcel of present day fundamental physics. Both of these concepts are "nondeformable" under very mild assumptions [1]. The advent of supersymmetry, possible after changing the perspective on symmetries, is an example of the fruitfulness of enlarging that framework. In the present Letter we suggest a possibly similar broadening, which in its essence replaces Lie groups by Lie groupoids in the context of Yang-Mills theories; for trivial bundles this reduces to replacing the structural Lie algebra of a YM-theory by a Lie algebroid. In part this generalization is related to rather old attempts [2] for constructing so-called "non-linear gauge theories"; the recent mathematical understanding of Lie algebroids and groupoids [3,4], however, provides new tools and a new focus for approaching such a generalization.In the theories under discussion generically one encounters structure functions in the symmetry algebra, typical for gravitational theories; but there will exist a finite dimensional object underlying the infinite dimensional space of symmetries: infinitesimally the symmetries are generated by sections in a Lie algebroid. Two spacetime dimensions already provides an example where these concepts have been realized successfully in terms of Poisson Sigma Models (PSMs) [5,6], which, on the physical side, permit to unify gravitational and YM gauge theories [7]. Using the PSM, as well as Chern-Simons (CS) theory defined in d = 3, as a guideline, we will leave behind low dimensions in this Letter and, besides suggesting possibly also interesting topological models, permit theories with propagating degrees of freedom.We briefly recall some mathematical background For later use we remark that the image of ρ is integrable so that M is foliated into orbits. Moreover, due to the Leibniz rule, the bracket reduces to a fiberwise Lie algebra structure for elements in the kernel of ρ, which is isomorphic for any two points in the same orbit.In local coordinates (and frame (b I ) rankE
I=1the Lie algebroid data are encoded in structural functionsGuided by the other obvious example of a Lie algebroid, E = T M with ρ = id, one may introduce differential geometrical notions on Lie algebroids. With b I denoting the dual basis in E * , the Leibniz extension ofentails all the differenti...