$$ \mathcal{N} $$ = 2 heterotic strings revisited

A bstract We show that 1 + 1 dimensional vacua of the (0 , 2) heterotic string have many properties in common with more recently studied physical systems. The free theory exhibits a symmetric product CFT structure. The single-string Hilbert space splits into sectors labeled by the string winding, w , that contain purely left-moving (for w &gt; 0) and right-moving (for w &lt; 0) excitations. These sectors exhibit infinite-dimensional left and right-moving symmetry algebras, respectively, with central extensions that depend on w . String interactions between left and right-movers appear to lead to a $$ T\overline{T} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>T</mml:mi> <mml:mover> <mml:mi>T</mml:mi> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> deformation of the free theory.