Rachid Benbrik

Inspired by a significance of $2.4\sigma$ in $h\to \mu \tau$ decay observed by CMS at $\sqrt{s} = 8$ TeV, we investigate the Higgs lepton flavor violating effects in the generic two-Higgs-doublet model (GTHDM), where the lepton flavor changing neutral currents are induced at tree level and arisen from Yukawa sector. We revisit the constraints for GTHDM by considering theoretical requirements, precision measurements of $\delta \rho$ and oblique parameters $S$, $T$, $U$ and Higgs measurements. The bounds from Higgs data now play the major role. With the values of parameters that simultaneously satisfy the Higgs bounds and the excess of Higgs coupling to $\mu$-$\tau$ at CMS, we find that the tree-level $\tau\to 3\mu$ and loop-induced $\tau\to \mu \gamma$ could be consistent with current experimental upper limits; the discrepancy in muon $g-2$ between experiment and standard model prediction could be solved; and an interesting relation between muon $g-2$ and branching ratio (BR) for $\mu\to e \gamma$ is found. The GTHM results that the ratio $BR(h\to e\tau)/BR(h\to \mu \tau)$ should be smaller than $10^{-4}$ in order of magnitude. Additionally, we also study the rare decay $Z\to \mu \tau$ and get $BR(Z\to \mu\tau)< 10^{-6}$.

Inspired by a significance of $2.4\sigma$ for the $h\to \mu \tau$ decay observed by the CMS experiment at $\sqrt{s}=8\mathrm{TeV}$, we investigate the Higgs lepton-flavor-violating effects in a generic two-Higgs-doublet model (THDM), where the lepton-flavor-changing neutral currents are induced at the tree level and arise from the Yukawa sector. We revisit the constraints for generic THDM by considering theoretical requirements, precision measurements of $\delta \rho$ and oblique parameters $S$, $T$, and $U$, and Higgs measurements. The bounds from Higgs data play the major limits. With parameter values that simultaneously satisfy the Higgs bounds and the CMS excess of the Higgs coupling to $\mu -\tau$, we find that the tree-level $\tau \to 3\mu$ and the loop-induced $\tau \to \mu \gamma$ decays are consistent with current experimental upper limits; the discrepancy in muon $g-2$ between experimental results and standard model predictions can be resolved, and an interesting relation between muon $g-2$ and the branching ratio (BR) for $\mu \to e\gamma$ is found. The generic THDM results show that the order of magnitude of the ratio $\mathrm{BR}(h\to e\tau )/\mathrm{BR}(h\to \mu \tau )$ is smaller than $10^{-4}$. Additionally, we also study the rare decay $Z\to \mu \tau$ and get $\mathrm{BR}(Z\to \mu \tau )<10^{-6}$.

ATLAS and CMS recently showed the first results from run 2 of the Large Hadron Collider (LHC) at $\sqrt{s}=13\mathrm{TeV}$. A resonant bump at a mass of around 750 GeV in the diphoton invariant mass spectrum was indicated and the corresponding diphoton production cross section is around 3–10 fb. Motivated by the LHC diphoton excess, we propose that the possible resonance candidate is a Higgs singlet. To produce the Higgs singlet via the gluon-gluon fusion process, we embed the Higgs singlet in the framework of the vector-like triplet quark (VLTQ) model. As a result, the Higgs singlet decaying to the diphoton final state is via VLTQ loops. Using the enhanced number of new quarks and new Yukawa couplings of the VLTQs and Higgs singlet, we successfully explain the diphoton production cross section. We find that the width of the Higgs singlet is below 1 GeV, its production cross section can be of the order of 1 pb at $\sqrt{s}=13\mathrm{TeV}$, and the branching ratio for it decaying to a diphoton is around 0.017 and is insensitive to the masses of VLTQs and new Yukawa couplings. We find a strong correlation between the Higgs Yukawa couplings to $s-b$ and $c-t$; the resulted branching ratio for $t\to ch$ can be $1.1\times {10}^{-4}$ when the constraint from $B_s$ oscillation is applied. With the constrained parameter values, the signal strength for the standard model Higgs decaying to a diphoton is ${\mu }_{\gamma \gamma }<1.18$, which is consistent with the current measurements at ATLAS and CMS.

We study the constraints of the generic two-Higgs-doublet model (2HDM) type-III and the impacts of the new Yukawa couplings. For comparisons, we revisit the analysis in the 2HDM type-II. To understand the influence of all involving free parameters and to realize their correlations, we employ $\chi$-square fitting approach by including theoretical and experimental constraints, such as S, T, and U oblique parameters, the production of standard model Higgs and its decay to $\gamma\gamma$, $WW^*/ZZ^*$, $\tau^+\tau^-$, etc. The errors of analysis are taken at $68\%$, $95.5\%$, and $99.7\%$ confidence levels. Due to the new Yukawa couplings being associated with $\cos(\beta-\alpha)$ and $\sin(\beta -\alpha)$, we find that the allowed regions for $\sin\alpha$ and $\tan\beta$ in the type-III model can be broader when the dictated parameter $\chi_F$ is positive; however, for negative $\chi_F$, the limits are stricter than those in the type-II model. By using the constrained parameters, we find that the deviation from the SM in the $h\to Z\gamma$ can be of ${\cal O}(10\%)$. Additionally, we also study the top-quark flavor-changing processes induced at the tree level in the type-III model and find that when all current experimental data are considered, we get $Br(t\to c(h, H) )< 10^{-3}$ for $m_h=125.36$ and $m_H=150$ GeV and $Br(t\to cA)$ slightly exceeds $10^{-3}$ for $m_A =130$ GeV.

We investigate the implication of the recent discovery of a Higgs-like particle in the first phase of the LHC Run 1 on the Inert Higgs Doublet Model (IHDM). The determination of the Higgs couplings to SM particles and its intrinsic properties will get improved during the new LHC Run 2 starting this year. The new LHC Run 2 would also shade some light on the triple Higgs coupling. Such measurement is very important in order to establish the details of the electroweak symmetry breaking mechanism. Given the importance of the Higgs couplings both at the LHC and $e^+e^-$ Linear Collider machines, accurate theoretical predictions are required. We study the radiative corrections to the triple Higgs coupling $hhh$ and to $hZZ$, $hWW$ couplings in the context of the IHDM. By combining several theoretical and experimental constraints on parameter space, we show that extra particles might modify the triple Higgs coupling near threshold regions. Finally, we discuss the effect of these corrections on the double Higgs production signal at the $e^+e^-$ LC and show that they can be rather important.

We study the correlation between the Standard Model Higgs decay $h\to \gamma \gamma$ and $h\to Z \gamma$ in the Inert Higgs Doublet Model. It is found that these two one-loop-induced decays are positively correlated, with the later channel having slightly smaller branching ratio than the former one. At the Linear Collider, we study the interplay of the off-shell extension of these two amplitudes that contributed significantly to the associated production of the Higgs boson with a photon in the process $e^+ e^- \to \gamma h$ and with an electron in the process $e^-\gamma \to e^- h$ in the $s$ and $t$ channels respectively via both $\gamma$ and $Z$ exchange for each process.