Is Flux Tube a Bosonic String? What Does Lattice Say?

I will present my work on the spectrum of the confining flux tube using lattice techniques both in 3D as well as 4D SU(N) gauge theories. Recent years have witnessed unprecedented progress in the investigation of the spectrum of the closed confining flux-tube in the Yang-Mills (YM) theory. Long flux-tubes can be thought of as infinitesimally thin strings; hence their spectrum is expected to be described by an Effective String Theory. Furthermore, the flux-tube's internal structure makes possible the existence of massive states in addition to string modes. Calculations on the spectrum of the flux tube in 3D SU(N) gauge theories have shown that this is very well described by the Nambu-Goto non-critical string up to small deviations for very short strings. Results in 4D SU(N) gauge theories demonstrate that most states exhibit spectrum which can be approximated adequately by Nambu-Goto but also provides strong evidence for the existence of a massive particle with particular (axionic) quantum numbers on the world-sheet of the QCD flux-tube.