Physics (Internal)

From Effective Strings to the Simplest theory of Quantum Gravity and Back

This event is part of the HET Seminar Series.

Abstract: 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,
but for QCD flux tubes numerical calculations of the energy levels of
these objects have become so accurate that a systematic understanding
of corrections to this simple description is desirable.
In the first part of my talk, I discuss an effective field theory
describing long relativistic strings. The construction parallels that
of the chiral Lagrangian in that it is based on the pattern of
symmetry breaking. To compare with previous works, 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 the worldsheet S-matrix in this
case 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, the Hagedorn behavior of strings, and argue that the theory on
the string worldsheet behaves like a 1+1 dimensional theory of quantum
gravity rather than a field theory.
In the last part of the talk, I will return to the task of computing
of the energy
levels of flux-tubes using lessons learned from the second part and
compare the results to lattice data.