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Ivancevic_Applied-Diff-Geom

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Technical Preliminaries: Tensors, Actions and Functors 125where ∗ is the dual Hodge star operator and J is current 1−form.To understand the deeper meaning of the connection–potential 1−formγA, we can integrate it along a path γ in space–time, x ✲ y. Classically,the integral ∫ A represents an action for a charged point particleγto move along the path γ. Quantum–mechanically, exp(i ∫ )γ A representsa phase (within the unitary group U(1)) by which the particle’s wave–function changes as it moves along the path γ, so A is a U(1)−connection.The only thing that matters here is the difference α between two pathsγ 1 and γ 2 in the action ∫ A [Baez (2002)], which is a two–morphismγγ 1xα ❘ y∨ ✒γ 2To generalize this construction, consider any compact Lie group G. Aconnection A on a trivial G−bundle is a γ−valued 1−form. A assignsa holonomy P exp(i ∫ )γ A γ∈ G along any path x ✲ y and has acurvature F given byF = dA + A ∧ A.The curvature F implies the extended Bianchi relationdF + A ∧ F = 0,

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