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Ivancevic_Applied-Diff-Geom

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920 <strong>Applied</strong> <strong>Diff</strong>erential <strong>Geom</strong>etry: A Modern IntroductionTreating the equalities (5.357) – (5.359) as the equations for a gauge–invariant Lagrangian, let us solve these equations for a LagrangianL = L(t, q i , a r µ, a r λµ)ω : J 1 (Q, C) → ∧ n T ∗ Q (5.360)without matter fields. In this case, the equations (5.357) – (5.359) readc r pq(a p µ∂ µ r L + a p λµ ∂λµ r L) = 0, (5.361)∂ q µ L + c r pqa p α∂ r µλ L = 0, (5.362)∂ p µλ L + ∂p λµ L = 0. (5.363)Let rewrite them relative to the coordinates (a q µ, Sµλ r , F µλ r ) (5.341) and(5.345), associated to the canonical splitting (5.343) of the jet spaceJ 1 (Q, C). The equation (5.363) reads∂L∂S r µλ= 0. (5.364)Then a simple computation brings the equation (5.362) into the form∂ µ q L = 0. (5.365)The equations (5.364) and (5.365) shows that the gauge–invariant Lagrangian(5.360) factorizes through the strength F (5.341) of gauge potentials.As a consequence, the equation (5.361) takes the form∂Lc r pqF p λµ∂Fλµr= 0.It admits a unique solution in the class of quadratic Lagrangians which isthe conventional Yang–Mills Lagrangian L Y M of gauge potentials on theconfiguration space J 1 (Q, C). In the presence of a background world metricg on the base Q, it readsL Y M = 14ε 2 aG pqg λµ g βν F p λβ F √µνq |g|ω, (where g = det(gµν )), (5.366)where a G is a G−invariant bilinear form on the Lie algebra of g r and ε isa coupling constant.5.11.6 Hamiltonian Gauge TheoryLet us consider gauge theory of principal connections on a principal bundleP −→ X with a structure Lie group G. Principal connections on P −→ X

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