Narrow Results

In the off-diagonal basis, we explore the effects of extra neutral gauge boson Z' predicted in two versions of SU(3)_C × SU(3)_L × U(1)_X model on the spin configuration of the top quark pair production in the high energy linear e⁺e^- collider (ILC). Our numerical results show that, the cross sections for the suppressed spin configurations can be enhanced with the effects of the Z' boson through the modification of the spin configuration by producing enough top quark pairs to be measured in the future ILC experiments, which provides the way to observe the effects of Z' predicted in the 3-3-1 model and discriminate the various versions of 3-3-1 model.

Recently the ATLAS and CMS experiments at the LHC have found a Higgs-like boson h with a mass around 125 GeV from several decay modes. The decay mode h →γγ is one of the most important modes in studying whether h is actually the Standard Model (SM) Higgs boson. Current data indicate that h→γγ has a branching ratio larger than the SM prediction for h being identified as the SM Higgs boson. To decide whether the h discovered at the LHC is the SM Higgs boson, more data are needed. We study how γγ collider can help to provide some of the most important information about the Higgs boson properties. We show that a γγ collider can easily verify whether the enhanced h →γγ observed at the LHC hold. Different models can be tested by studying Higgs boson decay to γZ. Studying angular distribution of the γγ through on-shell production of h and its subsequent decays into a γγ pair can decide whether the Higgs-like boson h at the LHC is a spin-0 or a spin-2 boson.

The characteristic feature of the Higgs Triplet Model (HTM) is the existence of the doubly charged Higgs bosons H^±±. In this paper, we study the pair production of doubly charged Higgs bosons in γγ collisions at the International Linear Collider (ILC). We present the production cross-sections and the distributions of the various observables, i.e. the distributions of the transverse momenta, the rapidity distributions for doubly charged Higgs bosons and the production angle distributions of the charged Higgs boson pair. Our numerical results show that, the values of the unpolarized cross-sections can reach a few hundreds of fb. We also study the possible final state for the decay mode H^±±→W^±W^± and relevant Standard Model (SM) background. Due to high produced rate and small SM background, the possible signals of H^±± might be detected via this process in the future ILC experiments.

Besides the Standard Model (SM)-like Higgs boson h, the Higgs Triplet Model (HTM) predicts the existence of charged and doubly charged Higgs bosons (H^± and H^±±). In this paper, we focus on the study of the triple Higgs production at the International Linear Collider (ILC): e^-e⁺→hH⁺H^- and e^-e⁺→hH⁺⁺H^–. We present the production cross-sections and discuss the relevant SM backgrounds. Our numerical results show that, with reasonable parameter values, the values of the cross-sections for two processes can reach the level several fb and tens of fb, respectively. Due to large production cross-section and small SM background, the possible signals of H^± and H^±± might be detected via these processes in the future ILC experiments.

A warped extra dimension model predicts an extra scalar particle beyond the Standard Model (SM) which is called a radion. Although interactions of the radion are similar to those of the Higgs boson in the SM, a relatively light radion (≲100 GeV) is not severely constrained from the Higgs search experiments at the LHC. In this paper we study discovery potential of the radion at a photon collider as an option of ILC. Owing to the trace anomaly of the energy–momentum tensor, both a production of radion in γγ collision and its decay to gluon pair are enhanced sizably. We find that the photon collider has a sensitivity for discovering the radion in low-mass region up to Λ_ϕ~3 TeV, where Λ_ϕ is a scale parameter which suppresses the interactions of radion to the SM particles.

In this paper, we will give a brief review of some important beam physics in circular and linear electron–positron collider designs, covering beam–beam tune limits, longitudinal and transverse single bunch collective effects, electron cloud and space charge effects, dynamic aperture estimations, etc. The main feature of this review is that the corresponding beam physics treatments are coming from author's previous research works which are scattered in different scientific publications both for circular and linear colliders. With the progresses of future linear colliders, such as ILC, and future circular electron–positron colliders, such as CEPC, it is high time to review the key beam physics issues in the optimization designs of these two kinds of machines.

The doubly-charged Higgs bosons $(H_5^{\pm \pm })$ are the typical particles predicted in the Georgi–Machacek (GM) model and their decay modes depend on the magnitude of the triplet vacuum expectation value (VEV) $v_{\mathrm{\Delta }}$. In this paper, we focus on the study of their pair production process at the International Linear Collider (ILC): $e^{+}{e}^{-}\to H_5^{++}{H}_5^{--}\to W^{+}{W}^{+}{W}^{-}{W}^{-}\to {\ell }^{-}{\ell }^{-}jjjjE{/}_T^{\mathrm{\text{miss}}}$, with the subsequent decay of two like-sign $W$ bosons through a pair of like-sign dileptons and the remaining two in their hadronic decays. The 5$\sigma$ confidence level discovery reach at the ILC is also studied with two collision energies of 1.0 TeV and 1.5 TeV.

An attempt is made to present the contribution of the scalar unparticle on some scattering processes in the Randall–Sundrum (RS) model. We have evaluated the contribution of the scalar unparticle on the W-pair production cross-sections at International Linear Colliders (ILC). The results indicate that at the low values of the scaling dimension and the bounds on scale ${\mathrm{\Lambda }}_U$ are around few TeV, the cross-sections are much enhanced, which is quite comparable with the W-production in the Standard Model and hence it is worthwhile to explore in future colliders.