How Does Equation (92) Follow from Equation (91) in the Breit-Wigner Derivation?

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SUMMARY

The discussion centers on the transition from Equation (91) to Equation (92) in the Breit-Wigner derivation. The key insight is that the wavefunction represented in Equation (91) is not an eigenstate of the Hamiltonian, which is crucial for understanding the derivation. The argument relies on the orthogonality of the set of functions \{e^{ikt}\}, allowing any integrable function to be expressed similarly to a Fourier transform. This foundational concept is essential for grasping the mathematical framework of the derivation.

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Homework Statement



The start of the derivation is shown in the attached image. I don't follow the argument that takes us from (91) to (92).

The Attempt at a Solution



I accept that the wavefunction of (91) is not an eigenstate of the Hamiltonian. I'm not clear where equation (92) came from though. Any comments that may offer an insight would be appreciated.
 

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They're just using the fact that the set of functions \left\{e^{ikt}\right\}, where k may be any real number, forms an orthogonal basis, in terms of which any integrable function may be expressed. Same idea as a Fourier transform.
 

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