Narrow Results

The CMS collaboration reported an intriguing $\sim 3\sigma$ (local) excess at 96 GeV in the light Higgs-boson search in the diphoton decay mode. This mass coincides with a $\sim 2\sigma$ (local) excess in the $b\bar{b}$ final state at LEP. We briefly review the proposed combined interpretations for the two excesses. In more detail, we review the interpretation of this possible signal as the lightest Higgs boson in the 2 Higgs Doublet Model with an additional real Higgs singlet (N2HDM). We show which channels have the best prospects for the discovery of additional Higgs bosons at the upcoming Run 3 of the LHC.

In this paper, we present the novel analytical expressions for the bounded-from-below or the vacuum stability conditions of scalar potential for a general two-Higgs-doublet model by using the concepts of co-positivity and the gauge orbit spaces. More precisely, several sufficient conditions and necessary conditions are established for the vacuum stability of the general 2HDM potential, respectively. We also give an equivalent condition of the vacuum stability of the general 2HDM potential in theory, and then, apply it to derive the analytical necessary conditions of the general 2HDM potential. Meanwhile, the semi-positive definiteness is proved for a class of 4th-order two-dimensional complex tensor.

The oblique parameters S, T and U and their higher-order extensions (V, W and X) are observables that combine electroweak precision data to quantify deviation from the Standard Model. These parameters were calculated at one loop in the basis-independent CP-violating Two-Higgs Doublet Model (2HDM). The scalar parameter space of the 2HDM was randomly sampled within limits imposed by unitarity and found to produce values of the oblique parameters within experimental bounds, with the exception of T. The experimental limits on T were used to predict information about the mass of the charged Higgs boson and the difference in mass between the charged Higgs boson and the heaviest neutral Higgs boson. In particular, it was found that the 2HDM predicts -600 GeV < m_H^± - m₃ < 100 GeV, with values of m_H^± > 250 GeV being preferred. The mass scale of the new physics (M_NP) produced by random sampling was consistently fairly high, with the average of the scalar masses falling between 400 and 800 GeV for , although the model can be tuned to produce a light neutral Higgs mass (~120 GeV). Hence, the values produced for V, W and X fell well within 0.01 of zero, confirming the robustness of the linear expansion approximation. Taking the CP-conserving limit of the model was found to not significantly affect the values generated for the oblique parameters.

In this paper, the analytic sufficient and necessary conditions are obtained for the CP conserving two-Higgs-doublet potential to be bounded from below by using the co-positivity of tensors. This is achieved by treating the potential as a fourth-order homogeneous polynomial about the moduli of the two Higgs doublet fields, where the “angles” is described as the misalignment of the two doublets, then solving three minimum problems with respect to the misalignment. Finally, the analytic conditions are established with the help of the corresponding theory and methods of higher-order tensors.

Studying the properties of the Higgs boson can be an important window to explore the physics beyond the Standard Model (SM). In this work, we present studies on the implications of the Higgs precision measurements at future Higgs Factories. We perform a global fit to various Higgs search channels to obtain the 95% C.L. constraints on the model parameter spaces of two-Higgs Doublet Model (2HDM) and Minimal Supersymmetric Standard Model (MSSM). In the 2HDM, we analyze tree-level effects as well as one-loop contributions from the heavy Higgs bosons. The strong constraints on $cos(\beta -\alpha )$, heavy Higgs masses and their mass splitting are complementary to direct search of the LHC as well as possible future $Z$ pole precision measurements. For the MSSM, we study both the Higgs couplings and mass precisions. The constraints on the CP-odd Higgs mass $m_A$ and stop mass scale $m_{\mathrm{\text{SUSY}}}$ can be complementary to the direct search of HL-LHC. We also compare the sensitivity of various future Higgs factories, namely, Circular Electron Positron Collider (CEPC), Future Circular Collider (FCC)-ee and International Linear Collider (ILC).

In this paper we present a phenomenological analysis of the Partially Aligned Two Higgs Doublet Model (PA-2HDM) by using leptonic decays of mesons and $B_{d,s}^0$–${\bar{B}}_{d,s}^0$ mixing. We focus our attention in a scenario where the leading contribution to FCNC is given by the tree-level interaction with the light pseudoscalar $A^0$ ($M_{A^0}\sim 250$ GeV). We show how an underlying flavor symmetry controls FCNC in the quark and lepton couplings with the pseudoscalar, without alignment between Yukawa matrices. Upper bounds on the free parameters are calculated in the context of the leptonic decays $B_{s,d}^0\to {\mu }^{+}{\mu }^{-}$ and $K_L^0\to {\mu }^{+}{\mu }^{-}$ and $B_{s,d}^0$ mixing. Also, our assumptions imply that bounds on New Physics contribution in the quark sector coming from $B_{s,d}^0$ mixing impose an upper bound on the parameters for the leptonic sector. Finally we give predictions of branching ratios for leptonic decay of mesons with FCNC and LFV.

In a version of the PA-2HDM where only mixing between third and second fermion generations is allowed, we propose a mechanism to generate the second Yukawa matrix through a Unitary V-spin flavor transformation on the mass matrix for quarks and leptons. This flavor structure is constrained to be universal, that is, we use the same parameters to generate Yukawa matrix elements in the quark and leptonic sectors, reducing drastically the number of free parameters of the PA-2HDM.

As a consequence of this restrictive condition, we obtain relations between the Yukawa matrix elements, that we call the Universal Texture Constraint (UTC). We obtained an interval of values for the second Yukawa matrix elements, expressed in terms of the Cheng and Sher ansatz, for $\tau \to \mu {\mu }^{+}{\mu }^{-}$ and $\tau \to \gamma \mu$ coming from the UTC and experimental bounds for light scalar masses. Finally, we find the allowed parameter region when the experimental bounds and values for $B_s\to \mu \mu$ decays, $B_s^0-{\bar{B}}_s^0$ mixing, $\tau \to \mu {\mu }^{+}{\mu }^{-}$ and $\tau \to \gamma \mu$ are considered.

The nonconservation of the lepton number has been explored at the LHC through the lepton-flavor violating (LFV) Higgs decays $h\to {\ell }_a{\ell }_b$, with ${\ell }_{a,b}=e,\mu ,\tau$$(a\ne b)$. Current limits on these decays are a source of valuable information on the structure of the Yukawa and Higgs sectors. The LFV Higgs couplings can arise within the general two-Higgs doublet model (2HDM). The predicted rates for these decay modes depend on the specific Yukawa structure being considered, ranging from a vanishing branching ratio at tree-level for some versions (2HDM-I, II, X, Y), up to large and detectable ratios within the general 2HDM-III. An attractive scenario is given by the texturized version of the model (2HDM-Tx), with the Yukawa matrices having some texture zeros such as the minimal version with the so-called Cheng–Sher ansatz. We study the constraints on the parameter space of the 2HDM provided by experimental and theoretical restrictions, and use them to study the detection of LFV Higgs modes at LHC. We find several encouraging scenarios to the search for the decay $h\to \tau \mu$ that could be achieved in the high-luminosity LHC. On the other hand, LFV Higgs couplings can also be induced at one-loop level in the 2HDM with neutrino masses, with the loops being mediated by neutrino interactions; we find that the resulting branching ratios are of order $10^{-7}$ at best, which is out of the reach of current and future phases of the LHC.