We study discovery prospects for a real triplet extension of the Standard Model scalar sector at the Large Hadron Collider (LHC) and a possible future 100 TeV $pp$ collider. We focus on the scenario in which the neutral triplet scalar is stable and contributes to the dark matter relic density. When produced in $pp$ collisions, the charged triplet scalar decays to the neutral component plus a soft pion or soft lepton pair, yielding a disappearing charged track in the detector. We recast current 13TeV LHC searches for disappearing tracks, and find that the LHC presently excludes a real triplet scalar lighter than 248 (275) GeV, for a mass splitting of 172 (160) MeV with $\mathcal{L}=\rm36\,$fb$^{-1}$. The reach can extend to 497 (520) GeV with the collection of $3000\,$fb$^{-1}$. We extrapolate the 13 TeV analysis to a prospective 100 TeV $pp$ collider, and find that a $\sim3$ TeV triplet scalar could be discoverable with $\mathcal{L}=30$ ab$^{-1}$, depending on the degree to which pile up effects are under control. We also investigate the dark matter candidate in our model and corresponding present and prospective constraints from dark matter direct detection. We find that currently XENON1T can exclude a real triplet dark matter lighter than $\sim3$ TeV for a Higgs portal coupling of order one or larger, and the future XENON20T will cover almost the entire dark matter viable parameter space except for vanishingly small portal coupling.
We investigate the potential of future TeV linear e^+e^- colliders to observe singly-charged Higgs bosons ($H^\pm$) via the coupling $H^\pm W^\mp Z$, which would signal the existence of exotic Higgs representations. In the context of a Higgs-triplet model compatible with the electroweak oblique parameters, we estimate the cross section for pro- ducing charged Higgs-triplet bosons that couple predominantly to $W$ and $Z$ bosons in 0.5--2 TeV-$e^+e^-$ colliders. The principal backgrounds are evaluated and the viability of the signal is discussed and illustrated.
We examine the collider and dark matter phenomenology of the Standard Model extended by a hypercharge-zero SU(2) triplet scalar and gauge singlet scalar. In particular, we study the scenario where the singlet and triplet are both charged under a single $\mathbb{Z}_2$ symmetry. We find that such an extension is capable of generating the observed dark matter density, while also modifying the collider phenomenology such that the lower bound on the mass of the triplet is smaller than in minimal triplet scalar extensions to the Standard Model. A high triplet mass is in tension with the parameter sp…
We study the signatures of the triplet-quadruplet dark matter model at the LHC and future colliders, including the 100 TeV Super Proton-Proton Collider and the 240 GeV Circular Electron Positron Collider. The dark sector in this model contains one fermionic electroweak triplet and two fermionic quadruplets, which have two kinds of Yukawa couplings to the Higgs doublet. Electroweak production signals of the dark sector fermions in the $\text{monojet}+/\!\!\!\!E_\mathrm{T}$, disappearing track, and $\text{multilepton}+/\!\!\!\!E_\mathrm{T}$ channels at the LHC and the Super Proton-Proton Collide…
The signature of heavy fermionic triplets belonging to Type III seesaw at the International Linear Collider (ILC) is probed. Presence of charged fermionic triplets upto a mass of about $ 750$ GeV could be established through single production at a 1 TeV ILC with moderate luminosity of 300 fb$^{-1}$, assuming a fermion triplet-electron mixing of about 0.05. Unlike the case of LHC, the production process is highly sensitive to the mixing, making the process interesting. The single production of neutral triplet is found to be somewhat harder, considering the large SM background present. Pair prod…
The novel feature of a Higgs-triplet representation is a nonzero tree-level coupling of $H^+ W^- Z$, which is absent in all Higgs-doublet models. We study the associated production of a singly-charged Higgs boson of the Higgs-triplet representation with a $W$ or $Z$ boson at hadron colliders, followed by the $H^+ \to W^+ Z$ decay. We find that the $2\ell+4j$ final state gives an interesting level of signal with a negligible background, plus it allows a full mass reconstruction of the charged-Higgs boson. The cover range of the charged-Higgs mass is between 110 and 200 GeV.
We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a pair of Higgs triplet superfields. The neutral components of the Higgs triplets develop small vacuum expectation values (VEVs) quadratic in the bilinear R-parity breaking parameters. In this scheme the atmospheric neutrino mass scale arises from bilinear R-parity breaking while for reasonable values of parameters the solar neutrino mass scale is generated from the small Higgs triplet VEVs. We calculate neutrino masses and mixing angles in this model and show how the model can be tested at future c…
We investigate simplified models involving an inert scalar triplet and vector-like leptons that can account for the muon $g-2$ anomaly. These simplified scenarios are embedded in a model that features W' and Z' bosons, which are subject to stringent collider bounds. The constraints coming from the muon $g-2$ anomaly are put into perspective with collider bounds, as well as bounds coming from lepton flavor violation searches. The region of parameter space that explains the $g-2$ anomaly is shown to be within reach of lepton flavor violation probes and future colliders such as HL-LHC and HE-LHC.
We consider the possibility that the dark matter particle is a scalar WIMP messenger associated to neutrino mass generation, made stable by the same symmetry responsible for the radiative origin of neutrino mass. We focus on some of the implications of this proposal as realized within the singlet-triplet scotogenic dark matter model.We identify consistent parameter sets consistent both with neutrino mass and the observed dark matter abundance. Finally we characterize the expected phenomenological profile of heavy Higgs boson physics at the LHC as well as at future linear Colliders.
The signatures of heavy fermionic triplets ($Σ$) arising in scenarios like Type III seesaw model are probed through their direct production and subsequent decay at high energy electron-positron collider. Unlike the case of LHC, the production process has strong dependence on the mixing parameter ($V_{e,μ}$), making the leptonic collider unique to probe such mixing. We have established that with suitably chosen kinematic cuts, a 1 TeV $e^+e^-$ collider could probe the presence of $Σ$ of mass in the range of 500 GeV having $V_e=0.05$ with a few inverse femto barn luminosity through single produc…
We investigate the collider phenomenology of the scalar triplet particles in the Type-II seesaw model at a 100 TeV $pp$ collider. Depending on triplet vacuum expectation value $v_Δ$, the dominant discovery channels could be $H^{++} H^{--}$ and $H^{\pm\pm}H^\mp$. We find the $H^{\pm\pm}H^\mp\to W^\pm W^\pm h W^\mp/\ell^\pm \ell^\pm h W^\mp$ channels are promising for both model discovery at relatively large $v_Δ$ and determination of the Higgs portal couplings $λ_4$ and $λ_5$. We also find that these two channels are complementary to indirect determination of $λ_4$ from future precise measureme…
In this work, we investigate the prospects of future $e^{+}e^{-}$ colliders in testing a Higgs triplet model with a scalar triplet and a scalar singlet under $SU(2)$. The parameters of the model are fixed so that the lightest $CP-$even state corresponds to the Higgs particle observed at the LHC at around $125$ GeV. This study investigates if the second heaviest $CP-$even, the heaviest $CP-$odd and the singly charged states can be observed at existing and future colliders by computing their accessible production and decay channels. In general, the LHC is not well equipped to produce a Higgs bos…
We study the search potential of heavy triplet leptons in Type III Seesaw mechanism at future high-energy and high-luminosity muon colliders. The impact of up-to-date neutrino oscillation results is taken into account on neutrino parameters and the consequent decay patterns of heavy leptons in Type III Seesaw. The three heavy leptons in the Casas-Ibarra parametrization with diagonal unity matrix are distinguishable in their decay modes. We consider the pair production of charged triplet leptons $E^+ E^-$ through both $μ^+μ^-$ annihilation and vector boson fusion (VBF) processes. The leading-or…
We investigate the possibility of probing the triplet Higgs boson sector via single charged Higgs production in the process $e^+ e^- \to H^+ l ν_l$, at high energy electron-positron colliders, using the tree level $H^+W^-Z$ coupling which is a unique feature of such models. We find that even LEP-200 can give nontrivial information upto $M_{H^{\pm}} \simeq 120 $ GeV if the doublet -triplet mixing is not restricted by the current value of the $ρ$ parameter which is the case in models with a custodial symmetry. Further we point out that in such models, the 4-body, tree level decay $H^+ \to W^*Z^*…
Fermion dark matter (DM) as an admixture of additional singlet and doublet vector like fermions provides an attractive and allowed framework by relic density and direct search constraints within TeV scale, although limited by its discovery potential at the Large Hadron Collider (LHC). An extension of the model with scalar triplet can yield neutrino masses and provide some cushion to the direct search constraint of the DM through pseudo-Dirac mass splitting. This in turn, allow the model to live in a larger region of the parameter space and open the door for detection at LHC, even if slightly. …
In this study we consider an extension of the Standard Model with a complex hypercharge zero triplet scalar. In this scenario one of the charged Higgs bosons remains purely triplet and does not couple to the fermions, making it elusive at colliders. Also the physical pseudoscalar is a pure triplet and this purity makes it a suitable dark matter candidate without the need of discrete symmetries, unlike other extensions. The bounds from relic density and direct dark matter search experiments select its mass to be $\sim 1.35-1.60$ TeV. The pure triplet charged Higgs gives rise to displaced signat…
The extension of the Standard Model (SM) with two complex $SU(2)_{L}$ scalar triplets enables one to have the Type II seesaw mechanism operative consistently with texture-zero neutrino mass matrices. This framework predicts additional doubly charged, singly charged and neutral spinless states. We show that, for certain values of the model parameters, there is sufficient mass splitting between the two doubly charged states ( $H_1^{\pm\pm}, H_2^{\pm\pm}$) that allows the decay $H_1^{\pm\pm} \to H_2^{\pm\pm} h $, and thus leads to a unique signature of this scenario. We show that the final state …
Much theoretical effort and automatization are required to confront new physics models with experimental data for many types of particle reactions at future colliders. In this context, we extend GRACE, an automatic calculation system for invariant amplitudes, to incorporate particles and interactions in the Georgi-Machacek model. With the extended GRACE system, we study fermiophobic Higgs boson production processes at $e^+ e^-$ and $e^- e^-$ colliders in the model. The results show some advantages of $e^- e^-$ colliders over $e^+ e^-$ colliders for new physics search and thus its complementary…
The Higgs sector of the standard model can be extended by introducing an $SU(2)_L$ Higgs triplet $Δ$ to generate the tiny neutrino masses in the framework of type-II seesaw mechanism. In this paper, we study the pair production of the introduced Higgs triplet at future $e^{-}p$ colliders. The corresponding production cross sections via vector boson fusion process at FCC-ep and ILC$\otimes$FCC are predicted, where the production of a pair of doubly charged Higgs is found to be dominant and then used to investigate the collider phenomenology of the Higgs triplet. Depending on the size of the Hig…
We study the scalar triplet extension of the standard model with a low cutoff, preventing large corrections to the quadratic masses that would otherwise worsen the hierarchy problem. We explore the reach of LISA to test the parameter space region of the scalar potential (not yet excluded by Higgs to diphoton measurements) in which the electroweak phase transition is strongly first-order and produces sizeable gravitational waves. We also demonstrate that the collider phenomenology of the model is drastically different from its renormalizable counterpart. We study the reach of the LHC in ongoing…
ATLAS and CMS have discovered a Standard Model Higgs-like particle. One of the main discovery channels is the Higgs decay to two photons, which, at the moment, seems to be considerably enhanced over the Standard Model expectation. Models with additional charged matter coupling to the Higgs sector can enhance or decrease the Higgs to two photons branching ratio. We take this as motivation to confront the so-called Georgi-Machacek model of Higgs triplets with the results of recent searches for a SM Higgs boson performed at the LHC. We also investigate the model in regions of the allowed paramete…
We consider the production of singly charged Higgs bosons in the Higgs triplet and two Higgs doublet models. We evaluate the cross sections for the pair production and the single production of charged higgses at linear collider. The decay modes of $H^+$ and the Standard Model backgrounds are considered. We analyze the possibilities to differentiate between triplet and two Higgs doublet models.
We study the phenomenology of the type-II seesaw model at a linear e^-e^- collider. We show that the process e^-e^- \rightarrow alpha^-beta^- (alpha, beta = e, mu, tau being charged leptons) mediated by a doubly charged scalar is very sensitive to the neutrino parameters, in particular the absolute neutrino mass scale and the Majorana CP-violating phases. We identify the regions in parameter space in which appreciable collider signatures in the channel with two like-sign muons in the final state are possible. This includes Higgs triplet masses beyond the reach of the LHC.
The Higgs triplet model (HTM) predicts the existence of a pair of doubly charged Higgs bosons $H^{\pm \pm}$. Single production of $H^{\pm \pm}$ via e collision at the next generation e+e- International Linear Collider (ILC) and the Large Hadron electron Collider (LHeC) is considered. The numerical results show that the production cross sections are very sensitive to the neutrino oscillation parameters. Their values for the inverted hierarchy mass spectrum are larger than those for the normal hierarchy mass spectrum at these two kinds of collider experiments. With reasonable values of the relev…
Long-lived, colour-triplet scalars are a generic prediction of unnatural, or split, composite Higgs models where the spontaneous global-symmetry breaking scale $f \gtrsim 10$ TeV and an unbroken $SU(5)$ symmetry is preserved. Since the triplet scalars are pseudo Nambu-Goldstone bosons they are split from the much heavier composite-sector resonances and are the lightest exotic, coloured states. This makes them ideal to search for at colliders. Due to discrete symmetries the triplet scalar decays via a dimension-six term and given the large suppression scale $f$ is often metastable. We show that…
The minimal SU(5) theory augmented by the fermionic adjoint representation restores the coupling constant unification and gives realistic neutrino masses and mixing through the hybrid Type I and Type III seesaw. The crucial prediction of the theory is an SU(2) lepton triplet with the mass below TeV. We study the signature of these heavy leptons and propose the strategy to test this mechanism at the hadron and lepton colliders. The smoking gun evidence of the theory is Delta L=2 lepton number violation through events of a pair of like-sign leptons plus four jets without significant missing ener…
We revisit the process of inverse neutrino-less double beta decay (e e -> W W) at future linear colliders. The cases of Majorana neutrino and Higgs triplet exchange are considered. We also discuss the processes e mu -> W W and mu mu -> W W, which are motivated by the possibility of muon colliders. For heavy neutrino exchange and center-of-mass energies larger than 1 TeV, we show that masses up to 10^6 (10^5) GeV could be probed for e-e and e-mu machines, respectively. The stringent limits for mixing of heavy neutrinos with muons render mu mu -> W W less promising, even though this process is n…
While the triplet-like Higgses up to a few hundred GeV masses are already excluded for a vast region of the model parameter space from the LHC searches, strikingly, there is a region of this parameter space that is beyond the reach of the existing LHC searches, and doubly/singly-charged and neutral Higgses as light as 200 GeV or even lighter are still allowed by the LHC data. We study several search strategies targeting different parts of this LHC elusive parameter space at two configurations of $e^-e^+$ colliders -- 500 GeV and 1 TeV centre of mass energies. We find that a vast region of this…
The addition of $SU(2)_L$ triplet fermions of zero hypercharge with the Standard Model (SM) helps to explain the origin of the neutrino mass by the so-called seesaw mechanism. Such a scenario is commonly know as the type-III seesaw model. After the electroweak symmetry breaking the mixings between the light and heavy mass eigenstates of the neutral leptons are developed which play important roles in the study of the charged and neutral multiplets of the triplet fermions at the colliders. In this article we study such interactions to produce these multiplets of the triplet fermion at the electr…
We analyze a novel signature of the type II seesaw model - same-sign tetra-lepton signal arising from the mixing of neutral Higgs bosons and their subsequent decays to singly and doubly charged Higgs bosons. For this, we consider wide ranges of the triplet vacuum expectation value (vev) and Yukawa couplings, that are consistent with the observed neutrino masses and mixing as well as the LHC search limits. We find that a doubly charged Higgs boson with mass around 250 GeV and triplet vev around $10^{-4}-10^{-2}$ GeV can give significantly large number of events through it decay to same-sign $W$…
We reconsider the single production of the doubly charged Higgs bosons Delta_R^{++} and Delta_L^{++} at the LHC and TEVATRON in the framework of the left-right symmetric model and the Higgs triplet model. We show that in the left-right symmetric model the production of Delta_R^{++} by Drell-Yan process via W_R exchange may give the dominant contribution. The same channel for the production of Delta_L^{++} in the Higgs triplet model is insignificant.
Type-III seesaw is a simple extension of the Standard Model~(SM) with the SU$(2)_\text{L}$ triplet fermion with zero hypercharge. It can explain the origin of the tiny neutrino mass and flavor mixing. After the electroweak symmetry breaking the light neutrino mass is generated by the seesaw mechanism which further ensures the mixings between the light neutrino and heavy neutral lepton mass eigenstates. If the triplet fermions are around the electroweak scale having sizable mixings with the SM sector allowed by the correct gauge symmetry, they can be produced at the high energy colliders leavin…
We present a new solution to the doublet-triplet splitting problem which also works in a supersymmetric SU(5) grand unified theory and is testable at TeV-scale collider experiments. In our model, the SU(5) symmetry is broken through the Hosotani mechanism. Thanks to the phase nature of the Hosotani-breaking, the "missing VEV" can be realized even in an SU(5) model. A general and distinctive prediction of this solution is the existence of light adjoint chiral supermultiplets with masses of the supersymmetry breaking scale. Though these disturb the gauge coupling unification, it can be recovered…
In a previous publication, we showed that a high energy muon collider can make decisive statements about the electroweak (WIMP) Dark Matter (DM), reaching a DM mass which could give the observed thermal relic abundance. In this document, we report new studies of the spin-$0$ minimal WIMP DM at high energy muon colliders, and update our results on the fermionic spin-$1/2$ case. We find that, by combining multiple inclusive missing mass search channels, it is possible to fully cover the thermal targets of fermionic and scalar doublets, and Dirac triplet, with a 10 TeV muon collider. Higher energ…
To connect the scalar field (acceleron) responsible for dark energy to neutrinos, the usual strategy is to add unnaturally light neutral singlet fermions (right-handed neutrinos) to the Standard Model. A better choice is actually a Higgs triplet, through the coupling of the acceleron to the trilinear Higgs triplet-double-doublet interaction. This hypothesis predicts an easily observable doubly-charged Higgs boson at the forthcoming Large Hadron Collider (LHC).
We explain the current excess seen at the Large Hadron Collider via the $gg\to H\toγγ$ channel in the search for a neutral Higgs boson in terms of both singly (marginally) and doubly (predominantly) charged Higgs bosons predicted by the Higgs Triplet Model.
In this report our main attention is focused on the problems which can be solved at Photon Colliders naturally but are hardly solved at LHC and e^+e^- Linear Collider: The New Physics - new particles, new interactions, supersymmetry, Dirac monopole, extra dimensions... SM and the case of a SM--like scenario - EWSB, Higgs bosons, anomalies in interactions of gauge bosons, QCD, Pomeron and odderon... By-product: Production of light Goldstone particles from region of e\toγconversion.
Current searches for doubly charged Higgs bosons (H^{\pm\pm}) at the Fermilab Tevatron are sensitive to single production of H^{\pm\pm}, although the pair production mechanism q\bar q\to H^{++}H^{--} is assumed to be dominant. In the context of a Higgs Triplet Model we study the mechanism q'\bar q\to H^{\pm\pm}H^{\mp} at the Tevatron and CERN Large Hadron Collider, and show that its inclusion can significantly improve the search potential for H^{\pm\pm}. Moreover, assuming that the neutrino mass is generated solely by the triplet field Yukawa coupling to leptons, we compare the branching ratio…
We review a class of models in which the Standard Model (SM) is augmented by vector-like leptons: one doublet and a singlet, which are odd under an unbroken discrete $Z_2$ symmetry. As a result, the neutral component of these additional vector-like leptons are stable and behave as dark matter. We study the phenomenological constraints on the model parameters and elucidate the parameter space for relic density, direct detection and collider signatures of dark matter. In such models, we further add a scalar triplet of hypercharge two and study the consequences. In particular, after electro weak …
We study how to unravel the dark matter blind spots by phase transition gravitational waves in synergy with collider signatures at electroweak one-loop level taking the inert doublet model as an example. We perform a detailed Monte Carlo study at the future lepton colliders in the favored parameter space, which is consistent with current dark matter experiments and collider constraints. Our studies demonstrate that the Circular Electron Positron Collider and other future lepton colliders have the potential to explore the dark matter blind spots.
Little Higgs models contain heavy scalars in their content of particles as a result of extended symmetry group of SM. In the littlest Higgs model of little Higgs models there exists a new heavy scalar triplet.The physical states of this triplet contains a double charged scalar, a single charged scalar, as well as a neutral scalar and a neutral pseudo scalar. In little Higgs models a Majorana type mass term can also be implemented in Yukawa Lagrangian, resulting lepton flavor violation. In this talk the pair productions of double charged scalars in the context of littlest Higgs model in $e^+e^-…
Collider searches for first-, second-, and third-generation scalar (S) or vector (V) leptoquarks (LQs) focus on the quark-lepton decay modes S,V -> q l. For SU(2)-doublet and -triplet leptoquarks with a sufficiently large splitting between the components, decays involving real W-boson emission (such as S_2^{(+5/3)} -> S_2^{(+2/3)} W^{+} and others) become possible and can change the patterns of leptoquark decays. For third-generation leptoquarks, where these mass splittings might be large, such modes could dominate certain leptoquark decays as they are (if kinematically allowed) guaranteed to …
The type-II seesaw model can explain neutrino masses and address the baryon asymmetry problem of the Universe simultaneously. In this letter, we explore its phase transition and the resulting gravitational wave signals. We find a strong first-order electroweak phase transition generically prefers a relatively light triplet in the $300\sim500$GeV range, which is ideal for collider searches and can generate gravitational waves within the sensitivity reach of BBO and Ultimate-DECIGO. While above $\sim$1TeV where a future 100TeV $pp$ collider will play a key role in model discovery, we integrate o…
We study $J/Ψ$ production at photon-photon colliders, which can be realised with Compton scaterring of laser photons at $e^+e^-$ colliders. We find that the production rate through the color-octet channel is comparable to that through the color-singlet channel. Experimentally the two mechanisms can be studied separately because the processes have different signals.
We propose a minimal extension of the standard model (SM) by including a scalar triplet with hypercharge 2 and two vector-like leptons: one doublet and a singlet, to explain simulatenously the non-zero neutrino mass and dark matter (DM) content of the Universe. The DM emerges out as a mixture of the neutral component of vector-like lepton doublet and singlet, being odd under a discrete $Z_2$ symmetry. After electroweak symmetry breaking the triplet scalar gets an induced vev, which give Majorana masses not only to the light neutrinos but also to the DM. Due to the Majorana mass of DM, the $Z$ …
We study the fermionic couplings of the neutral Higgs bosons in the THDM, assuming a four-texture structure for the Yukawa matrices. We then derive the low-energy constraints on the model, focusing in b-quark and lepton physics, and apply them to study Higgs boson detection at future colliders.
We propose a radiative seesaw model with an inert triplet scalar field in which Majorana neutrino masses are generated at the two loop level. There are fermionic or bosonic dark matter candidates in the model. We find that each candidate can satisfy the WMAP data when its mass is taken to be around the half of the mass of the standard model like Higgs boson. We also discuss phenomenology of the inert triplet scalar bosons, especially focusing on the doubly-charged scalar bosons at Large Hadron Collider in parameter regions constrained by the electroweak precision data and WMAP data. We study h…
The Georgi-Machacek model, introducing a complex and a real scalar triplet as additional components of the electroweak symmetry breaking sector, enables substantial triplet contributions to the weak gauge boson masses, subject to the equality of the complex and the real triplet vacuum expectation values (vev) via a custodial SU(2) symmetry. We present an updated set of constraints on this scenario, from collider data (including those from 137/139~fb$^{-1}$ of luminosity at the Large Hadron Collider), available data on the 125-GeV scalar, indirect limits and also theoretical restrictions from v…
We describe how to probe new physics through examination of the form factors describing the Ztt couplings via the scattering process e^-e^+->t+tbar. We focus on experimental methods on how the top quark momentum can be determined and show how this can be applied to select polarized samples of $t\bar{t}$ pairs through the angular correlations in the final state leptons. We also study the dependence on the energy and luminosity of an \ee\ collider to probe a CP violating asymmetry at the $10^{-2}$ level.}
For contact-interaction searches at the Linear Collider, we discuss the advantages of polarizing both the electron and the positron beams as compared with polarizing only the electron beam. In particular, for the processes e^+e^-\to μ^+μ^-, τ^+τ^-, b\bar{b} and c\bar{c} at a future e^+e^- collider with \sqrt{s}=0.5 TeV we derive model-independent bounds on the four-fermion contact interaction parameters from studies of the helicity cross sections.
