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Perturbation theory, Intermediate states, Virtual particles

  1. Jan 23, 2016 #1
    The following is taken from page 13 of Peskin and Schroeder.

    Any relativistic process cannot be assumed to be explained in terms of a single particle, since ##E=mc^{2}## allows for the creation of particle-antiparticle pairs. Even when there is not enough energy for pair creation, multiparticle states appear, for example, as intermediate states in second-order perturbation theory. We can think of such states as existing only for a very short time, according to ##\Delta E \cdot{\Delta t}=\hbar##. As one goes to higher orders in perturbation theory, arbitrarily many such virtual particles can be created.

    I have the following questions regarding the above paragraph:
    1. What is meant by a multiparticle state?
    2. What is meant by an intermediate state in second-order perturbation theory?
    3. Why do multiparticle states appear as intermediate states in second-order perturbation theory
    4. In what other ways do multiparticle states appear?
    5. What is the range of energies over which multiparticle states appear?
    Last edited: Jan 23, 2016
  2. jcsd
  3. Jan 23, 2016 #2

    A. Neumaier

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