Similar unitarity bounds imply that the amplitudes and cross section cannot increase too much with energy or they must decrease as quickly as a certain formula dictates. For example, Froissart bound says that the total cross section of two particles scattering is bounded by c ln 2 ⁡ ⁡ s , where c is a constant, and s is the square of the center-of-mass energy. (See Mandelstam variables)