Finite size effect

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introduction

  • Casimir effect in QED is one example of finite size effect
  • the stress on the bounding surfaces when quantum field is confined to finite volume of space
  • type of boundaries
    • real material media
    • interface between two different phases of the vacuum of a field theory such as QCD, in which case colored field may only exist in the interior region
    • topology of space
  • the boundaries restrict the modes of the quantum fields
  • give rise to measurable and important forces


how to compute the Casimir effect

  • zero-point energy in the presence of the boundaries
    • sum over all modes
    • any kind of constraint or boudary conditions on the the zero-point modes of the quantum fields in question, including backgrounds such as gravity
    • In a model without boundary conditions, the Hamiltonian value associated wih the vacuum or ground state, called zero-point energy, is usually discarded because, despite being infinite, may be reabsorbed in a suitable redefinition of the energy origin
    • there are several ways to put such an adjustment into practice, normal ordering being oneof the most popular
  • Green's functions method
    • represents the vacuum expectation value of the product of fields


QFT interpretation of the Casimir effect

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