$T{\overline T}$ deformations and the width of fundamental particles

Understand

We provide a simple geometric meaning for deformations of so-called $T{\overline T}$ type in relativistic and non-relativistic systems.

• Deformations by the cross products of energy and momentum currents in integrable quantum field theories are known to modify the thermodynamic Bethe ansatz equations by a "CDD factor".
• In turn, CDD factors may be interpreted as additional, fixed shifts incurred in scattering processes: a finite width added to the fundamental particles (or, if negative, to the free space between them).
• We suggest that this physical effect is a universal way of understanding $T{\overline T}$ deformations, both in classical and quantum systems.