TH String Theory Seminar
From Effective Strings to Critical Strings and Back
4-3-006 - TH Conference Room (CERN)
4-3-006 - TH Conference Room
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String-like objects arise in many quantum field theories. Well known examples include flux tubes in QCD and cosmic strings. To a first approximation, their dynamics is governed by the Nambu-Goto action. For QCD flux tubes numerical calculations of their energy levels have become so accurate that a systematic understanding of the corrections to this action is desirable. In the first part of my talk, I discuss an effective field theory describing these long relativistic strings in static gauge. At first sight in this way of quantizing the string nothing seems special about D=26. To recover the critical number of dimensions, and to understand its physical meaning, I will present the results of the calculation of the S-matrix describing the scattering of excitations on the string worldsheet. In the second part of my talk, I will discuss critical strings from the same point of view and show that their worldsheet S-matrix is non-trivial but can be calculated exactly. I will show that it encodes the familiar square-root formula for the energy levels of the string. This S-matrix also implies that the theory on the string worldsheet in several ways does not behave like a conventional 1+1 dimensional quantum field theory but instead displays features that are usually associated with gravitational theories. In the last part of the talk, I will return to the task of computing the energy levels of flux-tubes. Rather surprisingly, using lessons learned from the second part of my talk will allow us to significantly improve on previous results. The improved analytic control makes it manifest that existing lattice data provides strong evidence for the existence of a massive pseudoscalar on the worldsheet of QCD fluxtubes.