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Register a new userSingle production of excited neutrinos at future e^{+}e^{-}, ep and pp colliders
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O. Cakir
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We study the potential of the linear collider (LC) with sqrt{s}=0.5 TeV, linac-ring type ep collider (LCxLHC) with sqrt{s}=3.74 TeV and the large hadron collider (LHC) with sqrt{s}=14 TeV to search for excited neutrinos through transition magnetic type couplings with gauge bosons. The excited neutrino signal and corresponding backgrounds are studied in detail to obtain accessible mass limits and couplings for these three types of colliders.
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For the search for additional Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM) as well as for future precision analyses in the Higgs sector a precise knowledge of their production properties is mandatory. We review the evaluation of the cross sections for the neutral Higgs boson production in association with a photon at future $e^+e^-$ colliders in the MSSM with complex parameters (cMSSM). The evaluation is based on a full one-loop calculation of the production mechanism $e^+e^- to h_i gamma$ ($i = 1,2,3$). The dependence of the lightest Higgs-boson production cross sections on the relevant cMSSM parameters is analyzed numerically. We find relatively small numerical depedences of the production cross sections on the underlying parameters.
Motivated by the ATLAS and CMS announcements of the excesses of di-photon events, we discuss the production and decay processes of di-photon resonance at future $e^+e^-$ colliders. We assume that the excess of the di-photon events at the LHC is explained by a scalar resonance decaying into a pair of photons. In such a case, the scalar interacts with standard model gauge bosons and, consequently, the production of such a scalar is possible at the $e^+e^-$ colliders. We study the production of the scalar resonance via the associated production with photon or $Z$, as well as via the vector-boson fusion, and calculate the cross sections of these processes. We also study the backgrounds, and discuss the detectability of the signals of scalar production with various decay processes of the scalar resonance. We also consider the case where the scalar resonance has an invisible decay mode, and study how the invisible decay can be observed at the $e^+e^-$ colliders.
The Inert Doublet Model (IDM) is one of the simplest extensions of the Standard Model (SM), providing a dark matter candidate. It is a two Higgs doublet model with a discrete $Z_2$ symmetry, that prevents the scalars of the second doublet (inert scalars) from coupling to the SM fermions and makes the lightest of them stable. We study a large number of IDM scenarios, which are consistent with current constraints on direct detection and relic density of dark matter, as well as with all collider and low-energy limits. We propose a set of benchmark points with different kinematic features, that promise detectable signals at future $e^+e^-$ colliders. Two inert scalar pair-production processes are considered, $e^+e^- to A~H $ and $e^+e^- to H^+H^-$, followed by decays of $A$ and $H^pm$ into final states which always include the lightest and stable neutral scalar dark matter candidate $H$. Significance of the expected observations is studied for different benchmark models and different running scenarios, for centre-of-mass energies from 250 GeV up to 3 TeV. For low mass scenarios, high significance can be obtained for the signal signatures with two muons or an electron and a muon in the final state. For high mass scenarios, which are only accessible at high energy stages of CLIC, the significance is too low for the leptonic signature and the semi-leptonic final state has to be used as the discovery channel. Results presented for this channel are based on the fast simulation of the CLIC detector response with the DELPHES package.
Large Hadron Collider (LHC) has provided direct evidence of Yukawa couplings between the third generation charged fermions and the 125 GeV Higgs boson. Whether the first two generation charged fermions arise from exactly the same mechanism becomes the next interesting question. Therefore, direct measurements of charm or muon Yukawa couplings will be crucial to answering this puzzle. The charm Yukawa measurement at the LHC suffers from severe QCD background and it is extremely difficult to reach the sensitivity. In this paper, we compare the potential of probing charm Yukawa coupling at the two proposed future Higgs Factory experiments, the Large Hadron electron Collider (LHeC) and Circular electron positron collider (CEPC). At the LHeC, Higgs bosons will be produced via weak boson fusion and the energetic forward jet may suppress the background significantly. However, due to huge $gamma-g$ scattering background, the potential of LHeC search is still limited. With $-80%$ polarized electron beam of 60 GeV, the signal significance can only reach $2sigma$ for $ kappa_{c}simeq 1$ with a 3 ab$^{-1}$ integrated luminosity. In comparison, measurement at the CEPC can then reach $8.0sigma$ for $kappa_{c}simeq 1$ with a 2 ab$^{-1}$ of data.
The Inert Doublet Model (IDM) is one of the simplest extensions of the Standard Model (SM), providing a dark matter candidate. It is a two Higgs doublet model with a discrete $Z_2$ symmetry, that prevents the scalars of the second doublet (inert scalars) from coupling to the SM fermions and makes the lightest of them stable. We study a large group of IDM scenarios, which are consistent with current constraints on direct detection, including the most recent bounds from the XENON1T experiment and relic density of dark matter, as well as with all collider and low-energy limits. We propose a set of benchmark points with different kinematic features, that promise detectable signals at future $e^+e^-$ colliders. Two inert scalar pair-production processes are considered, $e^+e^- to H^+H^-$ and $e^+e^- to AH$, followed by decays of $H^pm$ and $A$ into final states which include the lightest and stable neutral scalar dark matter candidate $H$. Significance of the expected observations is studied for different benchmark models and different running scenarios, for centre-of-mass energies up to 3 TeV. Numerical results are presented for the signal signatures with two muons or an electron and a muon in the final state. For high mass scenarios, when the significance is too low for the leptonic signatures, the semi-leptonic signature can be used as the discovery channel.
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