Narrow Results

In this review we consider the distinctive phenomenology of supersymmetric models in which the scale of SUSY breaking is very low, , focusing on the Higgs sector and the process of electroweak breaking. Using an effective Lagrangian description of the interactions between the observable fields and the SUSY breaking sector, it is shown how the conventional MSSM picture can be substantially modified. For instance, the Higgs potential has non-negligible SUSY breaking quartic couplings that can modify completely the pattern of electroweak breaking and the Higgs spectrum with respect to that of the conventional MSSM-like models.

We suggest the model with the gauge group ⋯ ⊗ SU(6)⊗ SU(5) ⊗ SU(4)⊗ SU(3)⊗ SU(2)⊗ U(1). This group is the infinite continuation of the gauge group SU(4)⊗ SU(3)⊗ SU(2) ⊗ U(1) of Farhi–Susskind model. The constructed model contains fermions from the fundamental representations of any SU(N) subgroups of the gauge group. In the construction of the model we use essentially the requirement that it possesses an additional discrete symmetry that is the continuation of the Z₆ symmetry of the Standard Model. It has been found that there exists such a choice of the hypercharges of the fermions that the chiral anomaly is absent while the symmetry is preserved.

We consider the model, which contains a nonminimal coupling of Dirac spinors to torsion. Due to the action for torsion that breaks parity, the left–right asymmetry of the spinors appears. This construction is used in order to provide dynamical electroweak symmetry breaking. Namely, we arrange all Standard Model fermions in the left-handed spinors. The additional technifermions are arranged in right-handed spinors. Due to the interaction with torsion, the technifermions are condensed and, therefore, cause appearance of the gauge boson masses. In order to provide all fermions with masses, we consider two possibilities. The first one is related to an additional coupling of a real massive scalar field to the considered spinors. The second possibility is to introduce the explicit mass term for the mentioned Dirac spinors composed of the Standard Model fermions and the technifermions.

The trilinear terms of the form $\sqrt{2}f{𝜖}^{ijk}{\rho }_i{\chi }_j{\varphi }_k$ in the scalar potential of a 3-3-1 gauge model are considered. When looking for the eigenbasis of the massive physical Higgs bosons that survive the spontaneous symmetry breakdown of the model — in light of the observed SM-like Higgs boson with mass $m_h\simeq 125$ GeV reported in 2012 at the LHC — one gets a strong constraint to the cubic term. It has to be $f\ll w$, in flagrant contradiction with the large one $f\simeq w$ which is propagated in the literature to date.

We analyze the Next-to-minimal supersymmetric Standard Model with Grand unification boundary conditions under current theoretical and experimental constraints. We compute the mass spectrum of the model and focus on the three lightest particles in the Higgs sector (two CP-even scalars, $h_1$, $h_2$ and one CP-odd, $a_1$). The reduced couplings of such particles, singlet-doublet components, their branching ratios to bosons and reduced cross-section to photons and massive gauge bosons via gluon fusion are thoroughly and systematically scrutinized. Our analysis is focused on the parameter space where the singlet-doublet coupling $\lambda$ is as large as possible (keeping the perturbativity bound intact) and the ratio between the vacuum expectation values of the up-type and down-type Higgses $(\mathrm{\text{tan}}\beta )$ is as small as possible, which is the region representing the most natural case of the NMSSM. We show the impact of recent constraints from the LHC on the SM-Higgs couplings to bosons and fermions on the parameter space of the model and the consequent implications on the Higgs sector. The results show that while the model is still able to account for current data, and provide an opportunity for discovery of extended Higgs sectors, recent LHC Higgs couplings constraints rule-out parts of the parameter space where $h_2$ (non-SM-like) and $a_1$ are non-singlet with masses below 400 GeV.

We explore some aspects of the phenomenology of the Higgs sector in a model that includes right-handed neutrinos, with a mass of the order of the electroweak scale. In this model all scales arise from spontaneous symmetry breaking, thus the Higgs sector includes an extra Higgs singlet, in addition to the Standard Model Higgs doublet. The scalar spectrum includes two neutral CP-even states (h and H, with m_h < m_H) and a neutral CP-odd state (σ) that can be identified as a pseudo-Majoron. The parameter of the Higgs potential are constrained using a perturbativity criteria, which amounts to solve the corresponding RGE. The relevant Higgs branching ratios and some cross-sections are discussed, with special emphasis on the detection of the invisible Higgs signal at the LHC.

We point out that gravitational wave detectors such as LISA have the potential of probing a cosmological time evolution of the Higgs boson self-coupling constant $\lambda$ and thus the Higgs boson’s mass $m_H=\sqrt{2\lambda }v$. The phase transition of the Standard Model could have been a first order one if the Higgs mass was below 72 GeV at a temperature $T_{\star }\ge 100$ GeV. Gravitational waves could thus have been produced during the electroweak phase transition. A discovery by LISA of a stochastic background of gravitational waves with a characteristic frequency $k_{\star }\ge 10^{-5}$ Hz could be interpreted as a sign that the Higgs boson self-coupling constant was smaller in the past. This interpretation would be particularly tempting if the Large Hadron Collider did not discover any physics beyond the Standard Model by the time such waves are seen. The same mechanism could also account for baryogenesis.