The gravitational wave (GW) background produced at the cosmological chiral phase transition in a conformal extension of the standard model is studied. To obtain the bounce solution of coupled field equations we implement an iterative method. We find
that the corresponding $O(3)$ symmetric Euclidean action $S_3$ divided by the temperature $T$ has a simple behavior near the critical temperature $T_C$: $S_3/T propto (1-T/T_C)^{-gamma}$, which is subsequently used to determine the transitions inverse duration $beta$ normalized to the Hubble parameter $H$. It turns out that $beta/H gtrsim 10^3$, implying that the sound wave period $tau_text{sw}$ as an active GW source, too, can be much shorter than the Hubble time. We therefore compute $tau_text{sw} H$ and use it as the reduction factor for the sound wave contribution. The signal-to-noise ratio (SNR) for Deci-Hertz Interferometer Gravitational Wave Observatory (DECIGO) and Big Bang Observer (BBO) is evaluated, with the result: SNR$^text{DECIGO} lesssim 1.2$ and SNR$^text{BBO} lesssim 12.0$ for five years observation, from which we conclude that the GW signal predicted by the model in the optimistic case could be detected at BBO.
We study bounds on Higgs boson masses from perturbative unitarity in the Georgi-Machacek model, whose Higgs sector is composed of a scalar isospin doublet, a real and a complex isospin triplet fields. This model can be compatible with the electroweak
precision data without fine tuning because of the imposed global SU(2)_R symmetry in the Higgs potential, by which the electroweak rho parameter is unity at the tree level. All possible two-body elastic-scattering channels are taken into account to evaluate the S-wave amplitude matrix, and then the condition of perturbative unitarity is imposed on the eigenvalues to obtain constraint on the Higgs parameters. Masses of all scalar bosons turn out to be bounded from above, some of which receive more strict upper bounds as compared to that in the standard model (712 GeV). In particular, the upper bound of the lightest scalar boson, whatever it would be, is about 270 GeV.
Doubly charged Higgs bosons (H^++) are a distinctive signature of the Higgs Triplet Model of neutrino mass generation. If H^++ is relatively light (m_{H^++} < 400GeV) it will be produced copiously at the LHC, which could enable precise measurements o
f the branching ratios of the decay channels H^++ to l_i l_j. Such branching ratios are determined solely by the neutrino mass matrix which allows the model to be tested at the LHC. We quantify the dependence of the leptonic branching ratios on the absolute neutrino mass and Majorana phases, and present the permitted values for the channels ee, emu and mumu. It is shown that precise measurements of these three branching ratios are sufficient to extract information on the neutrino mass spectrum and probe the presence of CP violation from Majorana phases.
