Gravitational waves from walking technicolor

We study gravitational waves from the first-order electroweak phase transition in the SU(Nc) gauge theory with Nf/Nc ≫ 1 (“large Nf QCD”) as a candidate for the walking technicolor, which is modeled by the U(Nf ) × U(Nf ) linear sigma model with classical scale symmetry (without mass term), particularly for Nf = 8 (“one-family model”). This model exhibits spontaneous breaking of the scale symmetry as well as the U(Nf ) × U(Nf ) radiatively through the Coleman-Weinberg mechanism a la Gildener-Weinberg, thus giving rise to a light pseudo dilaton (technidilaton) to be identified with the 125 GeV Higgs. This model possess a strong first-order electroweak phase transition due to the resultant Coleman-Weinberg type potential. We estimate the bubble nucleation that exhibits an ultra supercooling and then the signal for a stochastic gravitational wave produced via the strong first-order electroweak phase transition. We show that the amplitude can be reached to the expected sensitivities of the LISA.