Single slepton production associated with a top quark at LHC in NLO QCD

Single slepton production in association with a top quark at the CERN Large Hadron Collider (LHC) is one of the important processes in probing the R-parity violation couplings. We calculate the QCD next-to-leading order (NLO) corrections to the $pp \to t\tilde{\ell}^{-}(\bar{t}\tilde{\ell}^{+})+X$ process at the LHC and discuss the impacts of the QCD corrections on kinematic distributions. We investigate the dependence of the leading order (LO) and the NLO QCD corrected integrated cross section on the factorization/renormalization energy scale, slepton, stop-quark and gluino masses. We find that the uncertainty of the LO cross section due to the energy scale is obviously improved by the NLO QCD corrections, and the exclusive jet event selection scheme keeps the convergence of the perturbative series better than the inclusive scheme. The results show that the polarization asymmetry of the top-quark will be reduced by the NLO QCD corrections, and the QCD corrections generally increase with the increment of the $\tilde{t}_{1}$ or $\tilde {g}$ mass value.     

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.     

SU（3） Simple Group Model and New Z＇ Properties in Future Linear Colliders

In the SU（3） simple group model, the new neutral gauge boson Z＇ couples to pairs of SM fermions with couplings fixed in terms of the SM gauge couplings and depending only on the choice of the fermion embedding. In this paper, we calculate the contributions of this new particle to the processes e^＋e^-→l^＋l^-, bb^-, and cc^- and study the possibility of detecting this new particle via these processes in the future high-energy linear e^＋e^- collider（LC） experiments with √s= 500 GeV and ￡int= 340 fb^-1. We find that the new gauge boson Z＇ is most sensitive to the process e^＋e^-→b^＋b^-. As long as Mz,≤2 TeV , the absolute values of the relative correction parameter are larger than 5%. We calculate the forward-backward asymmetries and left-right asymmetries for the process e^＋e^-→c^＋c^-, with both the universal and anomaly-free fermion embeddings. Bounds on Z＇ masses are also estimated within 95% confidence level.     

Radiative Decays of (0+,1+) Strange-Bottom Mesons

In this article, we assume that the (0⁺,1⁺) strange-bottom mesons are the conventional b\bar{s} mesons, and calculate the electromagnetic coupling constants d, g₁, g₂, and g₃ using the light-cone QCD sum rules. Then we study the radiative decays B_{s0 →} B_s* γ, B_{s1→ ^{Bs* γ,}} B_{s1 →} B_s* γ, and B_s1→ B_{s0 ^γ}, and observe that the widths are rather narrow. We can search for the (0⁺,1⁺) strange-bottom mesons in the invariant B_s π⁰ and B_s*π⁰ mass distributions in the strongdecays or in the invariant B_s*γ and B_s^γ mass distributions in the radiative decays.     

\bar{K} Condensation in Neutron Star Matter with Δ Quartet

In the framework of relativistic mean field theory, the condensations of K^- and \bar{K}⁰ in neutron star matter including baryon octet and Δ quartet are studied. We find that in this case K^- and \bar{K}⁰ condensations canoccur at relative shallow optical potential depth of \bar{K} from -80 MeV to -160 MeV. Both K^- and \bar{K}⁰ condensations favor the appearances of Δ resonances. With \bar{K} condensations all the Δ quartet can appear well inside the maximum mass stars. The appearances of Δ resonances change the composition and distribution of particles at high densities. The populations ofΔ resonances can enhance K^- condensation. It is found that in the core of massive neutron stars, neutron star matter includes rich particle species, such as antikaons, baryon octet, and Δ quartet. In the presence of Δ resonances and \bar{K} condensation, the EOS becomes softer and results in smaller maximum mass stars. Furthermore the impact of antikaon condensations,hyperons, and Δ resonances on direct Urca process with nucleons is also discussed briefly.     

Studies on chargino production and decay at a photon collider

A Monte-Carlo analysis on production and decay of supersymmetric charginos at a future photon-collider is presented. A photon collider offers the possibility of a direct branching-ratio measurement. In this study, the process has been considered for a specific mSUGRA scenario. Various backgrounds and a parameterised detector simulation have been included. Depending on the centre-of-mass energy, a statistical error for the directly measurable branching ratio BR( ) of up to 3.5% can be reached.Received: 14 March 2005, Revised: 31 May 2005, Published online: 28 June 2005G. Klämke: Now at: Institut für Theoretische Physik, Universität Karlsruhe, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe, Germany     

On the relation between x-dependences of the higher-twist contribution to F 3 and g 1 p -g 1 n

We compare the higher-twist (HT) contribution to the unpolarized structure function F ₃ with its contribution to the nonsinglet combination g ₁ ^p -g ₁ ⁿ of the polarized proton and neutron structure functions using the assumption that the HT contributions to the Gross-Llewellyn Smith and the Bjorken sum rules are similar. We have found that the relation is valid for x≥0.1 and for x≥0.2 in the case of LO and NLO QCD approximations, respectively. The text was submitted by the author in English.     

Photon structure function in supersymmetric QCD revisited

We investigate the virtual photon structure function in the supersymmetric QCD (SQCD), where we have squarks and gluinos in addition to the quarks and gluons. Taking into account the heavy particle mass effects to the leading order in QCD and SQCD we evaluate the photon structure function and numerically study its behavior for the QCD and SQCD cases.     

Precise predictions for Higgs production in association with a W-boson pair at ILC

Higgs-boson production in association with a W-boson pair at e ⁺ e ⁻ linear colliders is one of the important processes in probing the coupling between the Higgs boson and vector gauge bosons and discovering the signature of new physics. We describe the impact of the complete electroweak (EW) radiative corrections of to this process in the standard model (SM) at the International Linear Collider (ILC), and investigate the dependence of the lowest-order (LO) and EW next-to-leading order (NLO) corrected cross sections on the colliding energy and the Higgs-boson mass. The LO and NLO EW corrected distributions of the invariant mass of the W-boson pair and the transverse momenta of the final W-boson and Higgs boson are presented. Our numerical results show that the relative EW radiative correction (δ _ew) varies from −19.4% to 0.2% when m _H=120 GeV and grows from 300 GeV to 1.2 TeV.     

Radiative corrections to the structure functions and sum rules in polarized dis

The one-loop NLO radiative corrections (RC) to the observables in polarized DIS using assumption that a quark is an essential massive particle are considered. If compared with classical QCD formulae the obtained results are identical for the unpolarized and different for polarized sum rules, that can be explained as the influence of the finite quark mass effects on NLO QCD corrections. The explicit expression for one-loop NLO QCD contribution to the structure function g ₂ is presented.     

Study of semileptonic decay of ${\bar{B}}_{s}^{0} \rightarrow \phi {l}^{+}{l}^{-}$ in QCD sum rule

In this work we study the semileptonic decay of ${\bar{B}}_{s}^{0}\to \phi {l}^{+}{l}^{-}$ (l=e, μ, τ) with the QCD sum rule method. We calculate the ${\bar{B}}_{s}^{0}\to \phi $ translation form factors relevant to this semileptonic decay, then the branching ratios of ${\bar{B}}_{s}^{0}\to \phi {l}^{+}{l}^{-}$ (l=e, μ, τ) decays are calculated with the form factors obtained here. Our result for the branching ratio of ${\bar{B}}_{s}^{0}\to \phi {\mu }^{+}{\mu }^{-}$ agree very well with the recent experimental data. For the unmeasured decay modes such as ${\bar{B}}_{s}^{0}\to \phi {e}^{+}{e}^{-}$ and ${\bar{B}}_{s}^{0}\to \phi {\tau }^{+}{\tau }^{-}$, we give theoretical predictions.     

Quark-Antiquark and Diquark Condensates in Vacuum in Two-Flavor Four-Fermion Interaction Models with Any Color Number Nc

The color number Nc-dependence of the interplay between quark-antiquark condensates （q^-q） and diquark condensates （qq） in vacuum in two-flavor four-fermion interaction models is researched. The results show that the Gs-Hs （the coupling constant of scalar （q^-q）2-scalar （qq）2 channel） phase diagrams will be qualitatively consistent with the case of Nc = 3 as Nc varies in 4D Nambu-Jona-Lasinio model and 219 Gross Neveu （GN） model, However, in 3D GN model, the behavior of the Gs-Hp （the coupling constant of pseudoscalar （qq）^2 channel） phase diagram will obviously depend on No. The known characteristic that a 3D GN model does not have the coexistence phase of the condensates （q^-q） and （qq） is proven to appear only in the case of Nc ≤ 4. In all the models, the regions occupied by the phases containing the diquark condensates （qq） in corresponding phase diagrams will gradually decrease as Nc grows up and finally go to zero if Nc → ∞, i.e. in this limit only the pure （q^-q） phase could exist.     

{Q\bar{s}}{\bar{Q}(') s} Molecular States in QCD Sum Rules

We systematically investigate the mass spectra of {Q\bar{s}}{bar{Q}^(')s}molecular states in the framework of QCD sum rules. The interpolating currents representing the molecular states are proposed. Technically, contributions of the operators up to dimension six are included in operator product expansion (OPE). The masses for molecular states with various{Q\bar{s}} {\bar{Q}^(')s} configurations are presented. The result 4.36±0.08 GeV for the D^*_s\bar{D}^*_s0 molecular state is consistent withthe mass 4350^+4.6_-5.1 ± 0.7 MeV of the newly observed X(4350), which could support X(4350) interpreted as a D^*_s\bar{D^}*_s0 molecular state.     

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⁺ Π_t^-Π_t⁰. 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 Π_t⁰ → t\bar{c} is the best channel to detect theneutral 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.     

A detailed next-to-leading order QCD analysis of deeply virtual Compton scattering observables

We present a detailed next-to-leading order (NLO) leading twist QCD analysis of deeply virtual Compton scattering (DVCS) observables, for several different input scenarios, in the scheme. We discuss the size of the NLO effects and the behavior of the observables in skewedness , momentum transfer,t, and photon virtuality, . We present results on the amplitude level for unpolarized and longitudinally polarized lepton probes, and unpolarized and longitudinally polarized proton targets. We make predictions for various asymmetries and for the DVCS cross section and compare with the available data. Received: 30 November 2001 / Revised version: 12 February 2002 / Published online: 15 March 2002     

Searching for Flavor-Changing Neutral-Current Signalsvia e+e-(γγ) → t\bar{c}h0t 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 (h⁰_t) are predicted at tree level. We study the relevant processes of e⁺e^-(γγ)→ t\bar{c}h⁰_t 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 → t\bar{c}h⁰_t, 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 m_h⁰t<2m_t, we find that there will be several hundreds FCNC events produced at the ILC with annuallyintegral luminosity of 500 fb^-1. Due to the clean background, such FCNC signals can possibly be detected at the ILC.     

Two photon exchange contributions to elastic $\vec{e}+p\rightarrow e+\vec{p}$ process in the non-local field formalism

We compute the two photon exchange contributions to elastic scattering of polarized electrons from target protons. We use a non-local field theory formalism for this calculation. The formalism maintains gauge invariance and provides a systematic procedure for making this calculation. The results depend on one unknown parameter, . We compute the two photon exchange correction to the ratio of electric to magnetic form factors extracted using polarization transfer experiments. The correction is found to be small if . However, for larger values of , the correction can be quite significant. The correction to the polarization transfer results goes in the right direction to explain their difference with the ratio measured by the Rosenbluth separation method. We find that the difference between the two experimental results can be explained for a wide range of values of the parameter . We also find that the corrections due to two photon exchange depend on the photon longitudinal polarization ε. Hence, we predict an ε dependence of the form factor ratio extracted using the polarization transfer technique. Finally, we obtain a limit on by requiring that the non-linearity in ε dependence of the unpolarized reduced cross section is within experimental errors.     

Precision Calculations for the T-Odd Quark Pair Production at the CLIC e+e- Linear Collider

We perform the precision calculations for the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes up to the QCD next-to-leading order (NLO) including full weak decays for the final T-odd mirror quarks in the littlest Higgs model with T-parity (LHT) at the Compact Linear Collider (CLIC). We show the dependence of the leading order (LO) and NLO QCD corrected cross sections on the colliding energy √s, and provide the LO and QCD NLO kinematic distributions of final particles. The results show that the LO cross section can be enhanced by the NLO QCD correction and the K-factor increases obviously when the threshold of the on-shell q_q_-pair production approaches the colliding energy √s. The K-factor value varies in the range of 1.04 ～ 1.41 in our chosen parameter space. We find that a simple approximation of multiplying the LO kinematic distribution with the integrated K-factor is not appropriate for precision study of the e⁺e^-→q_q_(q_q_=u_u_, c_c_, d_d_,s_s_) processes, since the NLO QCD corrections are phase space dependent. It is necessary to calculate the differential cross sections including full NLO QCD corrections to get reliable results.     

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

The single charged top-pion production processes e⁺e^-→t\bar{b}Π_t^- and e⁺e^-→ W⁺Π_t^- are studied in the framework of top-color-assisted technicolor (TC2) model. Our studies show that the cross section σ(e⁺e^-→t\bar{b}Π_t^-) reaches the level of tens of fb and σ(e⁺e^-→W⁺Π_t^-) reaches the level of a few fb. With the yearly integrated luminosity of L～500 fb^-1 expected at the planned colliders, one could collect thousands of charged top-pion of events via the process e⁺e^-→t\bar{b}Π_t^- and hundreds of events via the process e⁺e^-→W⁺Π_t^-. The flavor changing decay mode Π_t^-→b\bar{c} is the best channel to detect charged top-pion due to the clean SM background. With a large number of events and the clean background, the charged top-pion should be observable at the planned colliders. Therefore, our studies in this paper can help us to search for charged top-pion, and furthermore, to test the TC2 model.     

NLO contributions to <Emphasis Type="Italic">B</Emphasis>→<Emphasis Type="Italic">KK</Emphasis><Superscript>*</Superscript> decays in the pQCD approach

We calculate the important next-to-leading-order (NLO) contributions to the B→KK ^* decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD (pQCD) factorization approach. The pQCD predictions for the CP-averaged branching ratios are , , and Br(B ⁰→K ⁺ K ^*−+K ⁻ K ^*+)≈1.3×10⁻⁷, which agree well with both the experimental upper limits and the predictions based on the QCD factorization approach. Furthermore, the CP violating asymmetries of the considered decay modes are also evaluated. The NLO pQCD predictions for and decays are and .