User:PhDblackhole/sandbox

Strings and gravitons

The simplest case to imagine is a single string traveling in a flat spacetime in d dimensions. As the string moves around in spacetime, it sweeps out a surface in spacetime called the string worldsheet, a two-dimensional surface with one dimension of space (s) and one dimension of time (t). There are many ways to examine this string theory. One way is to expand the string coordinates Xa(s,t) into oscillator modes and demand spacetime Lorentz invariance and the absence of negative norm states. A different way to examine the string theory is through the field theory defined on the worldsheet, which is described by the action