Gravitational waves generated during a first-order electroweak phase transition have a typical frequency which today falls just within the band of the planned space interferometer LISA .
Contrary to what happens in the Standard Model , in its supersymmetric extensions the electroweak phase transition may be strongly first order , providing a mechanism for generating the observed baryon asymmetry in the Universe .
We show that during the same transition the production of gravitational waves can be rather sizable .
While the energy density in gravitational waves can reach at most h _ { 0 } ^ { 2 } \Omega _ { gw } \simeq 10 ^ { -16 } in the Minimal Supersymmetric Standard Model , in the Next-to-Minimal Supersymmetric Model , in some parameter range , h _ { 0 } ^ { 2 } \Omega _ { gw } can be as high as 4 \times 10 ^ { -11 } .
A stochastic background of gravitational waves of this intensity is within the reach of the planned sensitivity of LISA .
Since in the Standard Model the background of gravitational waves is totally neglegible , its detection would also provide a rather unexpected experimental signal of supersymmetry and a tool to descriminate among supersymmetric models with different Higgs content .