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Register a new userElectroweak phase transitions in the MSSM with an extra $U(1)$
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We investigate the possibility of electroweak phase transition in the minimal supersymmetric standard model (MSSM) with an extra $U(1)$. This model has two Higgs doublets and a singlet, in addition to a singlet exotic quark superfield. We find that at the one-loop level this model may accommodate the electroweak phase transitions that are strongly first-order in a reasonably large region of the parameter space. In the parameter region where the phase transitions take place, we observe that the lightest scalar Higgs boson has a smaller mass when the strength of the phase transition becomes weaker. Also, the other three heavier neutral Higgs bosons get more large masses when the strength of the phase transition becomes weaker.
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We study that a minimal supersymmetric standard model with an extra $U(1)$ gauge symmetry may accommodate the explicit CP violation at the one-loop level through radiative corrections. This model is CP conserving at the tree level and cannot realize the spontaneous CP violation for a wide parameter space at the one-loop level. In explicit CP violation scenario, we calculate the Higgs boson masses and the magnitude of the scalar-pseudoscalar mixings in this model at the one-loop level by taking into account the contributions of top quarks, bottom quarks, exotic quarks, and their superpartners. In particular, we investigate how the exotic quarks and squarks would affect the scalar-pseudoscalar mixings. It is observed that the size of the mixing between the heaviest scalar and pseudoscalar Higgs bosons is changed up to 20 % by a complex phase originated from the exotic quark sector of this model.
The possibility of a strongly first-order electroweak phase transition is established in the minimal supersymmetric standard model with an extra $U(1)$, where a nontrivial CP violating phase is introduced in its Higgs sector. We find that there is a wide region in the parameter space of the model that allows the strongly first-order electroweak phase transition. The mass of stop quark need not be smaller than the top quark mass to ensure the first-order electroweak phase transition be strong. The effect of the CP violating phase upon the strength of the phase transition is discovered. The strength of the phase transition is reduced when the size of the CP violation is increased. For a given CP violating phase, we find that the model has a larger mass for the lightest Higgs boson when it has a stronger phase transition.
We propose a simple extension of the Standard Model (SM) by adding an extra U(1) symmetry which is hidden from the SM sector. Such a hidden U(1) has not been considered before, and its existence at the TeV scale can be explored at the LHC. This hidden U(1) does not couple directly to the SM particles, and couples only to new SU(2)_L singlet exotic quarks and singlet Higgs bosons, and is broken at the TeV scale. The dominant signals at the high energy hadron colliders are multi lepton and multi b-jet final states with or without missing energy. We calculate the signal rates as well as the corresponding Standard Model background for these final states. A very distinctive signal is 6 high p_T b-jets in the final state with no missing energy. For a wide range of the exotic quarks masses the signals are observable above the background at the LHC.
In the $U(1)_X$ extension of the minimal supersymmetric standard model, we study a two step phase transition for the universe. The first step happens at high temperature from origin to z coordinate axis. The second step is the electroweak phase transition(EWPT) with barrier between two minima, which is the first order EWPT. We study the condition for this type phase transition to occur. The strong first order EWPT is our expection, and with the supposed parameters the evolution of the universe is plotted by the figures.
The electroweak phase transition in GUT inspired $SO(5) times U(1) times SU(3)$ gauge-Higgs unification is shown to be of weakly first-order and occurs at $T = T_c^{ rm EW} sim 163 ,$GeV, which is very similar to the behavior in the standard model in perturbation theory. There appears a new phase at higher temperature. $SU(2)_L times U(1)_Y$ ($ theta_H=0$) and $SU(2)_R times U(1)_{Y}$ ($ theta_H= pi$) phases become almost degenerate above $T sim m_{rm KK}$ where $m_{rm KK}$ is the Kaluza-Klein mass scale typically around 13TeV and $theta_H$ is the Aharonov-Bohm phase along the fifth dimension. The two phases become degenerate at $T = T_c^{rm LR} sim m_{rm KK}$. As the temperature drops in the evolution of the early universe the $SU(2)_R times U(1)_{Y}$ phase becomes unstable. The tunneling rate from the $SU(2)_R times U(1)_{Y}$ phase to the $SU(2)_L times U(1)_Y$ phase becomes sizable and a first-order phase transition takes place at $T=2.5 sim 2.6,$TeV. It is shown that the $W$ boson, $Z$ boson and photon, with $theta_H$ varying from 0 to $pi$, are transformed to gauge bosons in the $SU(2)_R times U(1)_{Y}$ phase. Gauge couplings and wave functions of quarks, leptons and dark fermions in the $SU(2)_R times U(1)_{Y}$ phase are determined.
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