Hi everyone, I'm a new member but it's not the first time I look at the forum.(adsbygoogle = window.adsbygoogle || []).push({});

Well, I don't know if this is the right section to post my question. I think it is related to quantum mechanics interpretation too. Anyway, let's have a look at my problem.

I've computed cross section for photon scattering on a nucleus. What I get is a kinematic factor (not really interesting) and a dynamic part which is substantially what I call response function. This response function is proportional to matrix elements of nucleus currents between initial and final states. Then I performed a multipolar expansion and untill now it's all ok.

Consider in particular the dipolar term, i.e.

[itex]R(\omega)\propto<\psi_f|\hat{D}|\psi_i>[/itex]

where we have the expectation value of the dipole operator between an initial and final state.

Now, what is the physical interpretation of the dipole operator acting between these two states?

This response function describes just how the system responds to a perturbation induced by the photon field. So computing it I would say that we are going to see how the system changes when I perturb it with a photon of given energy [itex]\omega[\itex]. But where the dipole operator enters in this?!?!? I would say the same if instead of the dipole operator i would have the quadrupole operator.

What does the dipole operator do? I start with an initial wavefunction, I act on it with the dipole operator and then i want to see the overlap of this state with a final one. How is the wavefunction modified? Is it really modified? Can I still use a wavefunction interpretation?

P.S. I've seen already a similar discussion on this forum but the answers did not convinced me.

Thanx for the attention!

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# Dipole excitation response function - physical interpretation

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