The Physics Society of Iran Iranian Journal of Physics Research 1682-6957 26 1 2026 05 22 Composite Higgs Model Involving a Light Scalar Sigma and the study of Phenomenological Constraints Composite Higgs Model Involving a Light Scalar Sigma and the study of Phenomenological Constraints 159 176 3782 10.47176/ijpr.26.1.12225 FA Reza Asgharzadeh Jelodar Faculty of Physics, Shahrood University of Technology, Shahrood, Iran Kazem Bitaghsir Fadafan Faculty of Physics, Shahrood University of Technology, Shahrood, Iran 0000-0001-9835-7128 Moslem Ahmadvand Faculty of Physics, Shahrood University of Technology, Shahrood, Iran Journal Article 2025 11 12 In this research, we consider Composite Higgs Models with a relatively small global symmetry-breaking scale, f, in the strong coupling sector, where the Higgs boson emerges as a pseudo-Nambu-Goldstone boson. The model also includes a singlet scalar resonance, the sigma particle (σ), which mixes with the Higgs. Using an effective chiral Lagrangian, the structure of the vacuum minima of the theory is analyzed. It is shown that, in the absence of σ, achieving values of f above 1 TeV requires a small amount of fine-tuning to be consistent with experimental constraints. However, mixing with this light scalar particle resolves this tension and allows for a lower value of f. Subsequently, we impose up-to-date experimental constraints based on combined LHC Run-2 fits to the Higgs couplings to gauge bosons and the top quark. By also applying limits from searches for exotic Higgs decays, the parameter space of the model is quantitatively determined, and viable benchmark points are extracted. Furthermore, an alternative scenario based on the CDF results is investigated to illustrate the model's sensitivity to independent collider data. The analyses demonstrate that the presence of the light scalar σ can effectively alleviate constraints arising from the electroweak precision parameters S and T, as well as from deviations in the Higgs couplings. In this research, we consider Composite Higgs Models with a relatively small global symmetry-breaking scale, f, in the strong coupling sector, where the Higgs boson emerges as a pseudo-Nambu-Goldstone boson. The model also includes a singlet scalar resonance, the sigma particle (σ), which mixes with the Higgs. Using an effective chiral Lagrangian, the structure of the vacuum minima of the theory is analyzed. It is shown that, in the absence of σ, achieving values of f above 1 TeV requires a small amount of fine-tuning to be consistent with experimental constraints. However, mixing with this light scalar particle resolves this tension and allows for a lower value of f. Subsequently, we impose up-to-date experimental constraints based on combined LHC Run-2 fits to the Higgs couplings to gauge bosons and the top quark. By also applying limits from searches for exotic Higgs decays, the parameter space of the model is quantitatively determined, and viable benchmark points are extracted. Furthermore, an alternative scenario based on the CDF results is investigated to illustrate the model's sensitivity to independent collider data. The analyses demonstrate that the presence of the light scalar σ can effectively alleviate constraints arising from the electroweak precision parameters S and T, as well as from deviations in the Higgs couplings. https://ijpr.iut.ac.ir/article_3782_f87e955fd6b89f8963b6934beb077d6e.pdf