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Register a new userNew Mechanism for Neutrino Mass Generation and Triply Charged Higgs Boson at the LHC
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S. Nandi
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In this talk, I present a new mechanism for the generation of neutrino masses via dimension 7 operators: llHH(H*H)/M^3. This leads to new formula for the light neutrino masses, m_ u~v^4/M^3. This is distinct from the usual see-saw formulae: m_ u~v^2/M. The scale of new physics can naturally be at the TeV scale. Microscopic theory that generated d=7 operator has an isospin 3/2 Higgs multiplet Phi, which contains a triply charged Higgs boson with mass around ~TeV or less. These particles can be produced at the LHC (and possibly at the Tevatron) with distinctive multi-W and multi-lepton final states. For some choice of the parameter space, these particles can also be long-lived with the possibility of displaced vertices, or even escaping the detector. Their leptonic decay modes carry information about the nature of the neutrino mass hierarchy.
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We propose a new mechanism for generating small neutrino masses which predicts the relation m_ u ~ v^4/M^3, where v is the electroweak scale, rather than the conventional seesaw formula m_ u ~ v^2/M. Such a mass relation is obtained via effective dimension seven operators LLHH(H*H)/M^3, which arise when an isospin 3/2 Higgs multiplet Phi is introduced along with iso-triplet leptons. The masses of these particles are naturally in the TeV scale. The neutral member of Phi acquires an induced vacuum expectation value and generates neutrino masses, while its triply charged partner provides the smoking gun signal of this scenario. These triply charged bosons can be pair produced at the LHC and the Tevatron, with Phi^{+++} decaying into W^+l^+l^+ or W^+W^+W^+, possibly with displaced vertices. The leptonic decays of Phi^{+++} will help discriminate between normal and inverted hierarchies of neutrino masses. This scenario also allows for raising the standard Higgs boson mass to values in excess of 500 GeV.
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 Higgs 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.
Unification at M_{GUT}sim 3times 10^{16} GeV of the three Standard Model (SM) gauge couplings can be achieved by postulating the existence of a pair of vectorlike fermions carrying SM charges and masses of order 300 GeV -- 1 TeV. The presence of these fermions significantly modifies the vacuum stability and perturbativity bounds on the mass of the SM Higgs boson. The new vacuum stability bound in this extended SM is estimated to be 117 GeV, to be compared with the SM prediction of about 128 GeV. An upper bound of 190 GeV is obtained based on perturbativity arguments. The impact on these predictions of type I seesaw physics is also discussed. The discovery of a relatively `light Higgs boson with mass sim 117 GeV could signal the presence of new vectorlike fermions within reach of the LHC.
We generalize the scalar triplet neutrino mass model, the type II seesaw. Requiring fine-tuning and arbitrarily small parameters to be absent leads to dynamical lepton number breaking at the electroweak scale and a rich LHC phenomenology. A smoking gun signature at the LHC that allows to distinguish our model from the usual type II seesaw scenario is identified. Besides, we discuss other interesting phenomenological aspects of the model such as the presence of a massless Goldstone boson and deviations of standard model Higgs couplings
We analyse the phenomenological implications of a light Higgs boson, $h$, within the CP-conserving 2-Higgs Doublet Model (2HDM) Type-I, for the detection prospects of the charged $H^pm$ state at Run II of the Large Hadron Collider (LHC), assuming $sqrt{s}=13$ TeV as energy and ${cal O}(100~{rm fb}^{-1})$ as luminosity. When sufficiently light, this $h$ state can open up the bosonic decay channel $H^pm to W^{pm(*)}h$, which may have a branching ratio significantly exceeding those of the $H^pm to tau u$ and $H^pm to cs$ channels. We perform a broad scan of the 2HDM Type-I parameter space, assuming the heavier of the two CP-even Higgs bosons, $H$, to be the observed SM-like state with a mass near 125 GeV. Through these scans we highlight regions in which $m_{H^pm} < m_t +m_b$ that are still consistent with the most recent limits from experimental searches. We find in these regions that, when the $H^pm to W^{pm(*)}h$ decay mode is the dominant one, the $h$ can be highly fermiophobic, with a considerably large decay rate in the $gammagamma$ channel. This can result in the total cross section of the $sigma(ppto H^pm h to W^{pm(*)} + 4gamma)$ process reaching up to ${cal O}(100~{rm fb})$. We therefore investigate the possibility of observing this spectacular signal at the LHC Run II.
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