We analyse a light charged Higgs boson in the 2-Higgs Doublet Model (2HDM) Type-I, when its mass satisfies the condition $M_{H^{pm}} < M_{t}+M_{b}$ and the parameter space is consistent with theoretical requirements of self-consistency as well as the
latest experimental constraints from Large Hadron Collider (LHC) and other data. Over such a parameter space, wherein the Standard Model (SM)-like state discovered at the LHC in 2012 is the heaviest CP-even state of the 2HDM, it is found that the decay modes of the charged Higgs boson are dominated by $H^{pm} rightarrow W^{pm *} h$. Furthermore, the light neutral Higgs boson $h$ dominantly decays into two photons. Under these conditions, we find that the production and decay process $ p p to H^pm h to {W^pm}^{(*)} h h to l u_{l} + 4 gamma$ ($l=e,mu$) is essentially background free. However, since the $W^{pm(*)}$ could be largely off-shell and the $h$ state is very light, so that both the lepton coming from the former and the photons coming from the latter could be rather soft, we perform here a full Monte Carlo (MC) analysis at the detector level demonstrating that such a $W^{pm} + 4gamma$ signal is very promising, as it would be yielding significant excesses at the LHC with an integrated luminosity of $L=$ 300 $fb^{-1}$ at both $sqrt{s}= 13$ and $14 ~text{TeV}$.
At the Large Hadron Collider (LHC), both the ATLAS and CMS Collaborations have been searching for light charged Higgs bosons via top (anti)quark production and decays channels, like $ppto t bar{t}$ with one top (anti)quark decaying into a charged Hig
gs boson and a $b$ (anti)quark, when the decay is kinematically open (i.e., when $m_{H^pm}lesssim m_t$). In this paper, we propose new searches at the LHC involving light charged Higgs bosons via their pair production channels like $ppto H^pm h/A$ and $ppto H^+ H^-$ in the 2-Higgs Doublet Model (2HDM) Type-I and -X scenarios. By focusing on the case where the heavy $H$ state plays the role of the Standard Model (SM)-like Higgs boson with a mass near 125 GeV, we study the aforementioned Higgs boson pair production channels and investigate their bosonic decays, such as $H^pm to W^{pm } h$ and/or $H^pm to W^{pm } A$. We demonstrate that for a light charged Higgs boson state, with $m_{H^pm}lesssim m_t$, at the LHC, such di-Higgs production and decay channels can give rise to signatures with event rates much larger than those emerging from $ppto tbar{t}to tbar{b} H^-$ + c.c. We specifically study $h/Ato bbar b$ and $tau^+tau^-$ decays. We, therefore, claim that the discussed combination of new production and decay modes can result in an alternative discovery channel for charged Higgs bosons lighter than the top (anti)quark at the LHC within the above two 2HDM Types. Finally, in order to motivate experimentalists in ATLAS and CMS to search for such signatures, we propose 16 Benchmark Points (BPs) which are compatible with both theoretical and experimental constraints.
We study the one loop electroweak radiative corrections to $h^0to bbar{b}$ and $h^0to tau^+tau^-$ in the framework of two Higgs doublet Model (2HDM). We evaluate the deviation of these couplings from their Standard Model (SM) values. $h^0to bbar{b}
$ and $h^0to tau^+tau^-$ may receives large contribution from triple couplings $h^0H^0H^0$, $H^0h^0h^0$, $h^0A^0A^0$ and $h^0H^+H^-$ which are absent in the Standard Model. It is found that in 2HDM, these corrections could be significant and may reach more than 20% for not tow heavy $H^0$ or $A^0$ or $H^pm$. We also study the ratio of branching ratios $R=BR(h^0to bbar{b})/BR(h^0to tau^+tau^-)$ of Higgs boson decays which could be used to disentangle SM from other models such as 2HDM.
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 an
d 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 $gammagamma$, $WW^*/ZZ^*$, $tau^+tau^-$, 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 $sinalpha$ and $tanbeta$ 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 $hto Zgamma$ 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 $Br(tto c(h, H) )< 10^{-3}$ for $m_h=125.36$ and $m_H=150$ GeV and $Br(tto cA)$ slightly exceeds $10^{-3}$ for $m_A =130$ GeV.
We study the two photon decay channel of the Standard Model-like component of the CP-even Higgs bosons present in the type II Seesaw Model. The corresponding cross-section is found to be significantly enhanced in parts of the parameter space, due to
the (doubly-)charged Higgs bosons $(H^{pm pm})H^pm$ virtual contributions, while all the other Higgs decay channels remain Standard Model(SM)-like. In other parts of the parameter space $H^{pm pm}$ (and $H^{pm}$) interfere destructively, reducing the two photon branching ratio tremendously below the SM prediction. Such properties allow to account for any excess such as the one reported by ATLAS/CMS at $approx 125$ GeV if confirmed by future data; if not, for the fact that a SM-like Higgs exclusion in the diphoton channel around 114-115 GeV as reported by ATLAS, does not contradict a SM-like Higgs at LEP(!), and at any rate, for the fact that ATLAS/CMS exclusion limits put stringent lower bounds on the $H^{pm pm}$ mass, particularly in the parameter space regions where the direct limits from same-sign leptonic decays of $H^{pm pm}$ do not apply.
We perform in the type II seesaw setting, a detailed study of the dynamical features of the corresponding general renormalizable doublet/triplet Higgs potential that depends on five dimensionless couplings and two mass parameters after spontaneous sy
mmetry breaking, and highlight the implications for the Higgs phenomenology. In particular, we determine i) the complete set of tree-level unitarity constraints on the couplings of the potential and ii) the exact tree-level {sl all directions} boundedness from below constraints on these couplings. When combined, these constraints delineate precisely the theoretically allowed parameter space domain within our perturbative approximation. Among the seven physical Higgs states of this model, the mass of the lighter (heavier) CP-even state h0 (H0) will always satisfy a theoretical upper (lower) bound that is reached for a critical value mu_c of mu (the mass parameter controlling triple couplings among the doublet/triplet Higgses). Saturating the unitarity bounds we find m_h0 < {cal O}(0.7 - 1 TeV), while the upper bound for the remaining Higgses lies in the several tens of TeV. However, the actual masses can be much lighter. We identify two regimes corresponding to mu > mu_c and mu < mu_c. In the first regime the Higgs sector is typically very heavy and only h0 that becomes SM-like could be accessible to the LHC. In contrast, in the second regime, somewhat overlooked in the literature, most of the Higgs sector is light. In particular the heaviest state H0 becomes SM-like, the lighter states being the CP-odd Higgs, the (doubly) charged Higgses and a decoupled h0, possibly leading to a distinctive phenomenology at the colliders.
