Effects of R-Parity Violating Supersymmetry in Top Pair Production at Linear Colliders with Polarized Beams

In the minimal supersymmetric standard model with R-parity violation, the lepton number violating top quark interactions can contribute to the top pair production at a linear collider via tree-level u-channel squark exchange diagrams. We calculate such contributions and find that in the allowed range of these R-violating couplings, the top pair production rate as well as the top quark polarization and the forward-backward asymmetry can be significantly altered. By comparing the unpolarized beams with the polarized beams, we find that the polarized beams are more powerful in probing such new physics.

Associated Productions of HZZ and HHZ at Linear Colliders in Large Extra Dimension Model

In this paper we investigate the effects of the large extra dimensions on the two processes e＋ e-→＋ H^0 Z^0 Z^0 and e^＋e^-→ H^0H^0 Z^0 at linear colliders in both unpolarized and polarized collision modes. We find that the virtual Kaluza-Klein graviton exchange can significantly enhance the cross section from their standard model expectations for these two processes. The results show that the LED effect on the process e＋ e-→＋ H^0 Z^0 Z^0 allows the observation limits on the effective scale Ms to be probed up to 9. 75 TeV and 10.1 TeV in the unpolarized and ＋-（λe＋ =1/2, λe-= -1/2） polarized beam collision modes （with Pe＋ = 0.6, Pe-=0.8）, respectively. For the process e＋ e-→＋ H^0 H^0 Z^0, these limits on Ms can be probed up to 6.06 TeV and 6.38 TeV in the unpolarized and polarized collision modes separately. We find that the λe＋ = 1/2, λe-= -1/2 polarization collision mode in both processe＋ e-→＋ H^0 Z^0 Z^0 and e＋ e-→＋ H^0 H^0 Z^0 may provide a possibility to improve the sensitivity in probing the LED effects.

Charged Higgs Pair Production in a General Two Higgs Doublet Model at e^+e^- and μ^+μ^- Linear Colliders

In this paper, charged Higgs pair production through l^＋l^- → H^＋ H^-, where l = e or μ, is studied within the framework of a general Two Higgs Doublet Model （2HDM）. The analysis is relevant to a future e^＋e^- or μ^＋ μ^- collider operating at center of mass energy of √s = 500 GeV. Two different scenarios of small and large a values are studied. Here a is the parameter, which diagonMizes the neutral CP-even Higgs boson mass matrix. Within the Minimal Supersymmetric Standard Model （MSSM）, cross section of this process is almost the same at e＋ e- and #＋#- colliders. It is shown that at e^＋e^- eolliders within a general 2HDM, cross section is not sensitive to the mass of neutral Higgs bosons, however, it can acquire large values up to several picobarn at μ^＋μ^- colliders with the presence of heavy neutral Higgs bosons. A scan over Higgs boson mass parameter space is performed to analyze the effect of large masses of neutral Higgs bosons involved in the s-channel propagator and thus in the total cross section of this process.

Single Charged Top-Pion Production at the Next Generation e^＋e^- Colliders

The single charged top-pion production processes e~+ e~- → tbΠ_t~- and e~+e~- → W~+Π_t~- are studied in the framework of top-color-assisted technicolor (TC2) model. Ourstudies show that the cross section σ(e~+ e~- → tbΠ_t~-) Teaches the level of tens of fb andσ(e~+ e~- → W~+Π_t~-) reaches the level of a few fb. With the yearly integrated luminosity of ￡～ 500 fb~(-1) expected at the planned colliders, one could collect thousands of charged top-pion ofevents via the process e~+ e~- → tbΠ_t~- and hundreds of events via the process e~+ e~- →W~+Π_t~-. The flavor changing decay mode Π_t~- → bc is the best channel to detect chargedtop-pion due to the clean SM background. With a large number of events and the clean background, thecharged top-pion should be observable at the planned colliders. Therefore, our studies in thispaper can help us to search for charged top-pion, and furthermore, to test the TC2 model.

Production of Top-Pions Associated with W Boson at Next Generation γγ Colliders

In the context of topcolor-assisted technicolor （TC2） model, we study the charged and neutral top-pions production process γγ →W＋ ∏t-∏t^0. We find that the production cross section is larger than that of the process γγ→ W＋ H-H in the minimal supersymmetric standard model. With reasonable values of the parameters in the TC2 model, the cross section can reach the level of a few fb. Furthermore, the flavor-changing （FC） decay mode ∏t^0 → te^- is the best channel to detect 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 at future linear colliders operating in γγ mode at the TeV energy scale.

Unparticle Effects on Top Quark Pair Production at Photon Collider

The unparticle effects on tt^- production at the future photon collider are investigated. Distributions of tt^- invariant mass and that for transverse momentum of top quark with respect to Standard Model and unparticle production are predicted. An odd valley with scalar unparticle contribution appears for some values of du, which is due to the big cancellation between the contribution from SM and that from unparticle. This character may be used to study the properties of scalar unparticle. Our investigations also show that scalar unparticle may play a significant role in tt^- production at the photon collider if it exists.

Searching for Flavor-Changing Neutral-Current Signals via e^+e^-(γγ)→th_t^0 in Topcolor-Assisted Technicolor Model

In the context of the top-color-assisted technicolor （TC2） model, the flavor-changing neutral-current （FCNC） interaction induced by the top-higgs （hOt） are predicted at tree level. We study the relevant processes of e＋e-（γγ）→tcht0 at the International Linear Collider （ILC）. It is found that these rare processes production rates can be enhanced significantly in the TC2 model. Especially for the process γγ→tcht0, the total cross section will reach a few fb in the reasonable parameter space. We also calculate the distributions of transverse momenta, pseudo-rapid and invariant mass of the top-higgs. In view of the main decay modes of top-higgs for mho 〈 2mr, we find that there will be several hundreds FCNC events produced at the ILC with annually integral luminosity of 500 fb-1. Due to the clean background, such FCNC signals can possibly be detected at the ILC.

Process e^-у→ e^-H in Littlest Higgs Model

In the context of the littlest Higgs （LH） model, we estimate the production cross section of the process e^-у→ e^-H in the future high-energy linear e^＋e^- collider （ILC） with the center-of-mass （CM） energy √S = 500 GeV. Our numerical results show that the contributions of the LH model Co this process are very small in most of the parameter space allowed by the electroweak precision measurement data, and are very diffcult to be detected in the future ILC experiments.

Associated production of a neutral top-Higgs with a heavy-quark pair in the γγ collisions at ILC

We have studied the associated production processes of a neutral top-Higgs in the topcolor assisted technicolor model with a pair of heavy quarks in γγ collisions at the International Linear Collider （ILC）. We find that the cross section for ttht in γγ collisions is at the level of a few fb with the c.m. energy √s=1000 GeV, which is consistent with the results of the cross section of ttH in the standard model and the cross section of tth in the minimal supersymmetric standard model. It should be clear that hundreds of to thousands of ht per year can be produced at the ILC. This process of γγ→ttht is really interesting in testing the standard model and searching the signs of technicolor.

Some aspects in accelerator structure studies at SLAC

Recent progress in the accelerator structure studies at SLAC is reported. This paper covers the room temperature accelerator structures for the ILC e+/e- sources; RF structures for some photon science projects including RF deffectors and the LCLS RF gun; the high gradient accelerator R&D in a global CLIC collaboration for the future multi-TeV linear colliders.

Bunch transverse emittance increase in electron storage rings

In this paper a theoretical framework to estimate the bunch transverse emittance growing in electron storage rings due to short range transverse wakefield of the machine is established. New equilibrium emittance equations are derived and applied to explain the experimentally obtained results in ATF damping ring. This equation will be useful for linear collider damping ring design.

Detection of Charged Higgs Bosons in e^+e^-(γγ)→tφ^- Production at the ILC

Abstract In the context of the left-right twin Higgs （LRTH） model, we have studied the charged Higgs bosons production processes e＋e-（γγ） →tbФ- at the International Linear Collider （ILC）. It is found that the cross sections of these two processes could reach a few Fo with reasonable parameter values. With the yearly integrated luminosity of L 500 fb-1 expected at the ILC, one could collect hundreds up to thousands of charged ttiggs events via these two processes. Therefore, our researches in this paper can help us search for charged Higgs bosons, and furthermore, to test the LRTH model.