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.

Prospects for SUSY discoveries and measurements at future colliders LHC and ILC are discussed. The problem of reconstructing the underlying theory and SUSY breaking mechanism is also addressed.

The top pions are the typical particles predicted by the top-color-assisted technicolor (TC2) model, and the observation of these particles can be regarded as the direct evidence of the TC2 model. In this paper, we study the charged and neutral top pion production process . The results show that the production rates can reach the level of tens of fb with reasonable parameter values. So one can expect that enough signals could be produced in the International Linear Collider (ILC) experiments. Furthermore, the flavor-changing (FC) decay mode is the best channel for detecting the neutral top pion, due to the clean SM background. With a large number of events and the clean background, the neutral top pion should be observable in future ILC experiments.

Phenomenology of unparticle physics at linear as well as hadron colliders was briefly reviewed in this talk, including real emissions and virtual exchanges of unparticle. Existing constraints from collider as well as astrophysics experiments were briefly discussed.

The Technicolor (TC) model is a dynamical theory without fundamental scalars. Due to the pseudo-Goldstone bosons, there exist some new flavor-changing (FC) couplings in the TC model which can contribute to the production rates of some FC processes. In this paper, we study the production process in the one-generation technicolor model (OGTM) at the ILC, i.e. . We find that the cross section with the OGTM's contributions can be largely enhanced and the signal should be observable at the ILC. Our predictions can be viewed as valid estimates of other TC models. Therefore, the process may provide a unique window for studying the TC theory.

In the framework of the topcolor-assisted technicolor (TC2) model, we study the neutral top-Higgs production processes , and . The results show that the production rates can reach the level of a few fb with reasonable parameter values. With the clean background of the flavor-changing channel, the top-Higgs events can possibly be detected at the International Linear Collider (ILC) experiments. Therefore, such neutral top-Higgs production processes offer a useful way to probe for neutral top-Higgs and test the TC2 model directly.

In the left–right twin Higgs (LRTH) model, we first examine the effects in production in γγ collision and find that, in the favorable parameter spaces, the absolute values of the relative correction can be significantly large. We also estimate the new production process , our results show that its cross-section can reach the level of a few fb for M = 150 GeV. A simply phenomenological analysis is also given for the decay modes T→ϕ⁺b and T→W⁺b. As long as the new T-quark is not too heavy, we conclude that this new channel might be used to test the LRTH model in the future ILC experiment.

The single top quark production has an electroweak nature and provides an additional support to the top pair production source of the top quarks. The processes involving single top have unique properties and are very interesting from both theoretical and experimental viewpoints. Short review of the single top quark production processes is given in the paper.

Besides the SM-like Higgs boson h, the left–right twin Higgs (LRTH) model predicts the existence of three additional Higgs bosons: one neutral Higgs ϕ⁰ and a pair of charged Higgs bosons ϕ^±. In this paper, we focus on the study of the triple Higgs production at the ILC, i.e. e⁺e^-→ϕ⁰ ϕ⁺ϕ^- and e⁺e^-→hhϕ⁰. We present the production cross-sections and the distributions of the various observables, such as, the distributions of the energy and the transverse momenta of neutral and charged Higgs bosons, the differential cross-section of the invariant mass of final Higgs bosons pair, and the production angle distributions of neutral Higgs boson and charged Higgs boson. Our numerical results show that, for the processes e⁺e^-→ϕ⁰ϕ⁺ϕ^- and e⁺e^-→hhϕ⁰, the production rates are at the level of 10^-1 fb with reasonable parameter values while the resonance production cross-section can be significantly enhanced and reach several tens fb. The signatures for signals and corresponding standard model backgrounds are also investigated for the decay mode .

We search for leptophilic gauge boson Z_l via the process e⁺e^- → μ⁺μ^- at ILC with . In the leptonic extension of SM we have predicted that ILC with will enable searching Z_l with masses up to the center-of-mass energy if the related coupling constant g_l exceeds 10^-3 for 3σ observations and 5σ discovery. Furthermore similar results have been obtained by using artificial neural network (ANN) method.

I summarize our recent works on using differential observables to explore the physics potential of future $e^{+}{e}^{-}$ colliders in the framework of Higgs effective field theory. This proceeding is based upon Refs. 1 and 2. We study angular observables in the $e^{+}{e}^{-}\to ZH{\ell }^{+}{\ell }^{-}b\bar{b}$ channel at future circular $e^{+}{e}^{-}$ colliders such as CEPC and FCC-ee. Taking into account the impact of realistic cut acceptance and detector effects, we forecast the precision of six angular asymmetries at CEPC (FCC-ee) with center-of-mass energy $\sqrt{s}=240$ GeV and 5 (30) ab${}^{-1}$ integrated luminosity. We then determine the projected sensitivity to a range of operators relevant for the Higgsstrahlung process in the dimension-6 Higgs EFT. Our results show that angular observables provide complementary sensitivity to rate measurements when constraining various tensor structures arising from new physics. We further find that angular asymmetries provide a novel means of constraining the “blind spot” in indirect limits on supersymmetric scalar top partners. We also discuss the possibility of using $ZZ$-fusion at $e^{+}{e}^{-}$ machines at different energies to probe new operators.

In the framework of the minimal $U{(1)}_{B-L}$ extension of the Standard Model, we investigate the Higgs boson production processes $e^{+}{e}^{-}\to ZH$, $e^{+}{e}^{-}\to {\nu }_e{\bar{\nu }}_{e}H$, $e^{+}{e}^{-}\to t\bar{t}H$, $e^{+}{e}^{-}\to ZHH$ and $e^{+}{e}^{-}\to {\nu }_e{\bar{\nu }}_{e}HH$ at the International Linear Collider (ILC). We present the production cross-sections, the relative corrections and compare our results with the expected experimental accuracies for Higgs decay channel $H\to b\bar{b}$. In the allowed parameter space, we find that the effects of the three single Higgs boson production processes might approach the observable threshold of the ILC. But the Higgs signal strengths ${\mu }_{b\bar{b}}$ of the two double Higgs boson production processes are all out of the observable threshold so that these effects will be difficult to be observed at the ILC.

The Georgi–Machacek (GM) model predicts the existence of the doubly-charged scalars $H_5^{\pm \pm }$, which can be seen the typical particles in this model and their diboson decay channels are one of the most promising ways to discover such new doubly-charged scalars. Based on the constraints of the latest combined ATLAS and CMS Higgs boson diphoton signal strength data at $2\sigma$ confidence level, we focus on the study of the triple scalar production in $\gamma \gamma$ collisions at the future International Linear collider (ILC): $\gamma \gamma \to h{H}_5^{++}{H}_5^{--}$, where the production cross-sections are very sensitive to the triple scalar coupling parameter $g_{\mathrm{\text{hHH}}}$. Considering the typical same-sign diboson decay modes for the doubly-charged scalars, the possible final signals might be detected via this process at the future ILC experiments.