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Register a new userSearching for Weak Singlet Charged Scalar at the Large Hadron Collider
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Weak singlet charged scalar exists in many new physics models beyond the Standard Model. In this work we show that a light singlet charged scalar with mass above 65~GeV is still allowed by the LEP and LHC data. The interactions of the singlet charged scalar with the Standard Model particles are described by operators up to dimension-5. Dominant decay modes of the singlet charged scalar are obtained, and a subtlety involving field redefinition and gauge fixing due to a dimension-5 operator is also clarified. We demonstrate that it is promising to observe the singlet charged scalar at the LHC.
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A weak singlet charged scalar exists in many new physics models beyond the Standard Model. The discovery potential of the singlet charged scalar is explored at future lepton colliders, e.g. the CEPC, ILC-350 and ILC-500. We demonstrate that one can discover the singlet charged scalar up to 118 GeV at the CEPC with an integrated luminosity of $5~mathrm{ab}^{-1}$. At the ILC-350 and the ILC-500 with an integrated luminosity of $1~mathrm{ab}^{-1}$ such a discovery limit can be further improved to 136 GeV and 160 GeV, respectively.
We investigate the prospects for the discovery of massive color-octet vector bosons at the CERN Large Hadron Collider with $sqrt{s} = 14$ TeV. A phenomenological Lagrangian is adopted to evaluate the cross section of a pair of colored vector bosons (colorons, $tilde{rho}$) decaying into four colored scalar resonances (hyper-pions, $tilde{pi}$), which then decay into eight gluons. We include the dominant physics background from the production of $8g,7g1q, 6g2q$, and $5g3q$, and determine the masses of $tilde{pi}$ and $tilde{rho}$ where discovery is possible. For example, we find that a 5$sigma$ signal can be established for $M_{tilde{pi}} alt 495$ GeV ($M_{tilde{rho}} alt 1650$ GeV). More generally we give the reach of this process for a selection of possible cuts and integrated luminosities.
Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, t-bar t production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. We present a detailed study of the discovery potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu b-bar bq-bar q (ell=e, mu) final state. We utilize final states with one or two tagged b-quarks, and two, three or four jets (including b-jets). Our calculations take into account the finite resolution of detectors, the energy loss due to b-quark decays, the expected reduced b-tagging efficiency at large t-bar t invariant masses, and include the background originating from Wb-bar b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios, and compare them with those for KK gravitons, and a Z_H boson in the Littlest Higgs model. We also analyze the capabilities of the LHC experiments to differentiate between individual KK gluon models and measure the couplings of KK gluons to quarks. We find that, for the parameters and models chosen, KK gluons with masses up to about 4 TeV can be discovered at the LHC. The ability of the LHC to discriminate between different bulk RS models, and to measure the couplings of the KK gluons is found to be highly model dependent.
In recent years, evidence for lepton flavour universality violation beyond the Standard Model has been accumulated. In this context, a singly charged $SU(2)_L$ singlet scalar ($phi^pm$) is very interesting, as it can only have flavour off-diagonal couplings to neutrinos and charged leptons, therefore necessarily violating lepton flavour (universality). In fact, it gives a (necessarily constructive) tree-level effect in $elltoell^prime u u$ processes, while contributing to charged lepton flavour violating only at the loop-level. Therefore, it can provide a common explanation of the hints for new physics in $tautomu u u/tau(mu)to e u u$ and of the Cabibbo Angle Anomaly. Such an explanation predicts ${rm Br }[tauto egamma]$ to be of the order of a few times $10^{-11}$ while ${ rm Br}[tauto emumu]$ can be of the order of $10^{-9}$ for order one couplings and therefore in the reach of forthcoming experiments. Furthermore, we derive a {novel} coupling-independent lower limit on the scalar mass of $approx 200,$GeV by recasting LHC slepton searches. In the scenario preferred by low energy precision data, the lower limit is even strengthened to $approx300,$GeV, showing the complementary between LHC searches and flavour observables. Furthermore, we point out that this model can be tested by reinterpreting DM mono-photon searches at future $e^+e^-$ colliders.
Upon assuming the $B-L$ Supersymmetric Standard Model (BLSSM) as theoretical framework accommodating a multi-Higgs sector, we assess the scope of the High Luminosity Large Hadron Collider (HL-LHC) in accessing charged Higgs bosons ($H^pm$) produced in pairs from $Z$ decays. We show that, by pursuing both di-jet and tau-neutrino decays, several signals can be established for $H^pm$ masses ranging from about $M_{W}$ to above $m_t$ and $Z$ masses between 2.5 TeV and 3.5 TeV. The discovery can be attained, even in a background free environment in some cases, owing to the fact that the very massive resonating $Z$ ejects the charged Higgs bosons at very high transverse momentum, a kinematic region where any SM noise is hugely depleted.
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