Speaker
Description
With the LHC Run-2 results at 13 TeV, we perform the calculation on the lower bound on the Z' boson mass in the context of the general U(1) gauged extension of the standard model with classically scale invariance and the electroweak vacuum stability at 2-loop level. The model is called the classically conformal U(1)' extended standard model which is a phenomenologically viable one that realizes Coleman-Weinberg-type breaking of the electroweak symmetry. The model can naturally provide a solution to one of the most important problem in the standard model, gauge hierarchy problem, and also solving the SM Higgs vacuum instability with having nonzero U(1)' charge of the SM Higgs, which is contrast to the U(1)$_{B-L}$ case. In this study, we perform the calculation at 2-loop level where we find the parameter regions for solving the SM Higgs instability. We plot the allowed parameter regions with three free parameters, the U(1)' gauge coupling, the U(1)' charge of the SM higgs, and the vacuum expectation value of the new additional singlet Higgs. We find that U(1)$_{B-L}$ and orthogonal model are excluded from having the electroweak vacuum stability with the currenct world average of the experimental data, $m_t =173.34$ GeV and $m_h=125.09$ GeV. Finally, we find that the current collider bounds are around $m_{Z'} > 3.5$ TeV, and naturalness bounds are around $m_{Z'} < 7$ TeV in order to avoid a fine-tuning severer than 10% level, where the Z' boson can be detected at the current LHC Run-2 experiment in the near future.
