Summary
Hamilton’s principle is applied to an invariant integral in which the field variables, regarded as independent, are the coefficients Γμν α defining a symmetric affine connection, the metric tensorg μνand the electromagnetic four-vectorx μ. Variation of the Γμν α yields an expression for the Γμν α in terms ofg μνandx μVariations with respect to thex μand theg μνlead respectively to the field equations\(\begin{gathered} F^{\mu \nu } _{i\nu } \hfill \\ G_{\mu \nu } - \frac{1}{2}g_{\mu \nu } G + \lambda g_{\mu \nu } = B\left( {F_{\mu \alpha } F_\nu ^\alpha - \frac{1}{4}g_{\mu \nu } F_{\alpha \beta } F^{\alpha \beta } } \right) \hfill \\ \end{gathered} \)% MathType!End!2!1! whereB is a constant which experience requires to be positive,\(F_{\mu \nu } = \frac{{\partial _{\kappa _\mu } }}{{\partial _{x_\mu } }} - \frac{{\partial _{\kappa \nu } }}{{\partial _{x_\mu } }}\)% MathType!End!2!1! and a semi-colon denotes covariant differentiation.
Riassunto
Si applioa il principio di Hamilton ad un integrale invariante in cui le variabili di campo, considerate indipendenti, sono i coefflcienti Γμν α che definiscono una connessione simmetrica affine, il tensore metricog μνe il quadrivettore elettromagneticox μ. Una variazione dei Γμν α dà un’espressione dei Γμν α in funzione dig μνex μ. Le variazioni rispetto ax μe ag μνportano rispettivamente alle equazioni di eampo\(\begin{gathered} F^{\mu \nu } _{i\nu } \hfill \\ G_{\mu \nu } - \frac{1}{2}g_{\mu \nu } G + \lambda g_{\mu \nu } = B\left( {F_{\mu \alpha } F_\nu ^\alpha - \frac{1}{4}g_{\mu \nu } F_{\alpha \beta } F^{\alpha \beta } } \right) \hfill \\ \end{gathered} \)% MathType!End!2!1! in cuiB è una costante che l’esperienza richiede sia positiva,\(F_{\mu \nu } = \frac{{\partial _{\kappa _\mu } }}{{\partial _{x_\mu } }} - \frac{{\partial _{\kappa \nu } }}{{\partial _{x_\mu } }}\)% MathType!End!2!1! ed il punto e virgola indica la differenziazione covariante.
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References
A. S. Eddington:Mathematical Theory of Relativity, 2nd edition (Cambridge, 1924).
W. Pauli:Theory of Relativity (translated byG. Field) (London, 1958).
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Clark, G.L. An action principle in general relativity. Nuovo Cim 26, 637–651 (1962). https://doi.org/10.1007/BF02781793
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DOI: https://doi.org/10.1007/BF02781793