| 1. | These results hypothesize assumptions on the Fourier coefficients of the perturbation term.
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| 2. | Ignoring higher-order perturbation terms, the following value is conserved:
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| 3. | Neglecting second-order terms in the perturbation term \ varepsilon \ gamma _ { \ mu \ nu }, we get:
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| 4. | Where \ varepsilon ( t, z ) is the perturbation term ( which, for mathematical convenience, has been multiplied by the same phase factor as A ).
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