Associated production of neutral toppion with a pair of heavy quarks in γγ\gamma\gamma collisions

We have studied a neutral toppion production process $\gamma\gamma\to f\bar{f}\Pi_{t}^{0}(f=t,b)$ in the topcolor-assisted technicolor(TC2) model. We find that the cross section of $\gamma\gamma\to t\bar{t}\Pi_{t}^{0}$ is much larger than that of $\gamma\gamma\to b\bar{b}\Pi_{t}^{0}$. On the other hand, the cross section can be obviously enhanced with the increasing of c.m.energy. With $\sqrt{s}=1600$ GeV, the cross section of $t\bar{t}\Pi_t^0$ production can reach the level of a few fb. The results show that $\gamma\gamma\to t\bar{t}\Pi^0_t \to t\bar{t}(t\bar{c})$ is the most ideal channel to detect neutral toppion due to the clean SM background. With such sufficient signals and clean background, neutral toppion could be detected at TESLA with high c.m.energy.Comment: 11 pages, 5 figure

Using Scalars to Probe Theories of Low Scale Quantum Gravity

Arkani-Hamed, Dimopoulos and Dvali have recently suggested that gravity may become strong at energies near 1 TeV which would remove the hierarchy problem. Such a scenario can be tested at present and future colliders since the exchange of towers of Kaluza-Klein gravitons leads to a set of new dimension-8 operators that can play important phenomenological roles. In this paper we examine how the production of pairs of scalars at $e^+e^-$, $\gamma \gamma$ and hadron colliders can be used to further probe the effects of graviton tower exchange. In particular we examine the tree-level production of pairs of identical Higgs fields which occurs only at the loop level in both the Standard Model and its extension to the Minimal Supersymmetric Standard Model. Cross sections for such processes are found to be potentially large at the LHC and the next generation of linear colliders. For the $\gamma\gamma$ case the role of polarization in improving sensitivity to graviton exchange is emphasized.Comment: 32 pages, 12 figures, latex, remarks added to tex

Measurements of the SUSY Higgs self-couplings and the reconstruction of the Higgs potential

We address the issue of the reconstruction of the scalar potential of a two-Higgs doublet model having in mind that of the MSSM. We first consider the general CP conserving dim-4 effective potential. To fully reconstruct this potential, we show that even if all the Higgs masses and their couplings to the standard model particles are measured one needs not only to measure certain trilinear Higgs self-couplings but some of the quartic couplings as well. We also advocate expressing the Higgs self couplings in the mass basis. We show explicitly, that in the so-called decoupling limit, the most easily accessible Higgs self-couplings are given in terms of the Higgs mass while all other dependencies on the parameters of the general effective potential are screened. This helps also easily explain how, in the MSSM, the largest radiative corrections which affect these self couplings are reabsorbed by using the corrected Higgs mass. We also extend our analysis to higher order operators in the effective Higgs potential. While the above screening properties do not hold, we argue that these effects must be small and may not be measured considering the foreseen poor experimental precision in the extraction of the SUSY Higgs self-couplings.Comment: 25 pages, 3 figure

Neutral Higgs boson pair production via γγ\gamma\gamma collision in the minimal supersymmetric standard model at linear colliders

We investigate in detail the $\gamma\gamma$ fusion production mechanisms of two neutral Higgs bosons ($h^0A^0$, $H^0A^0$, $h^0H^0$ and $H^0H^0$) within the framework of the mSUGRA-inspired minimal supersymmetric standard model(MSSM) at an $e^+e^-$ linear colliders, which provide a probe of the trilinear Higgs self-couplings. We calculate the dependence of the production rates on Higgs boson masses, the ratio of the vacuum expectation values $\tan \beta$ and the CMS energy $\sqrt{s}$. We find that the cross section for the $H^0H^0$ production at LC can reach $0.2 fb$, while the cross section of $A^0H^0$ production is only $10^{-4}\sim 10^{-3} fb$ under our parameters.Comment: Accepted by Phys. Rev.

Single Top Quark at Future Hadron Colliders. Complete Signal and Background Study

We perform a detail theoretical study including decays and jet fragmentation of all the important modes of the single top quark production and all basic background processes at the upgraded Tevatron and LHC colliders. Special attention was paid to the complete tree level calculation of the QCD fake background which was not considered in the previous studies. Analysis of the various kinematical distributions for the signal and backgrounds allowed to work out a set of cuts for an efficient background suppression and extraction of the signal. It was shown that the signal to background ratio after optimized cuts could reach about 0.4 at the Tevatron and 1 at the LHC. The remaining after cuts rate of the signal at the LHC for the $lepton+jets$ signature is expected to be about 6.1 pb and will be enough to study the single top physics even during the LHC operation at a low luminosity.Comment: 15 pages, LaTex, 7 figure

Polarized Single Top Quark Production in e\gamma Collision and Anomalous Wtb Couplings

We investigate the potential of $e\gamma$ collisions to probe anomalous $Wtb$ couplings via the polarized single top quark production process $e^{+} \gamma \to t \bar{b} \bar{\nu_{e}}$. We find 95% confidence level limits on the anomalous coupling parameters $F_{2L}$ and $F_{2R}$ with an integrated luminosity of $500 fb^{-1}$ and $\sqrt{s}=0.5, 1$ and 1.5 TeV energies. The effects of top quark spin polarization on the anomalous $Wtb$ couplings are discussed. It is shown that polarization leads to a considerable improvement in the sensitivity limits.Comment: published versio