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Question about time limits of time-dependent perturbation theory

  1. Aug 10, 2010 #1
    I have been using time-dependent perturbation theory for quite a while. Yet, one thing is still not clear to me. I have seen in many books and papers that when they calculate the transition amplitudes, they integrate from 0 to t. While in many other papers and books, the limit is taken to be - infinity to t. Those two limits give completely different results for transition amplitudes and transition probabilities. So which one to use?
  2. jcsd
  3. Aug 10, 2010 #2
    I would expect only 0 to t for the time that the perturbed field is switched on.

    How can you use a transition amplitude based on an infinite amount of time being exposed to the field?
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