Single Top Quark Production via FCNC Couplings at Hadron Colliders

We calculate single top-quark production at hadron colliders via the chromo-magnetic flavor-changing neutral current couplings $\bar tcg$ and $\bar tug$. We find that the strength for the anomalous $\bar tcg$ ($\bar tug$) coupling may be probed to $\kappa_c / \Lambda = 0.092 {TeV}^{-1}$ ($\kappa_u / \Lambda = 0.026 {TeV}^{-1}$) at the Tevatron with $2 {fb}^{-1}$ of data and $\kappa_c / \Lambda = 0.013 {TeV}^{-1}$ ($\kappa_u / \Lambda = 0.0061 {TeV}^{-1}$) at the LHC with $10 {fb}^{-1}$ of data. The two couplings may be distinguished by a comparision of the single top signal with the direct top and top decay signals for these couplings.Comment: 18 pages, 6 figures, 3 table

Probing Topcolor-Assisted Technicolor from Top-Charm Associated Production at LHC

We propose to probe the topcolor-assisted technicolor (TC2) model from the top-charm associated productions at the LHC, which are highly suppressed in the Standard Model. Due to the flavor-changing couplings of the top quark with the scalars (top-pions and top-Higgs) in TC2 model, the top-charm associated productions can occur via both the s-channel and t-channel parton processes by exchanging a scalar field at the LHC. We examined these processes through Monte Carlo simulation and found that they can reach the observable level at the LHC in quite a large part of the parameter space of the TC2 model.Comment: Version to appear in PRD (Rapid Communication

Dimension-six CP-conserving operators of the third-family quarks and their effects on collider observables

We list all possible dimension-six CP-conserving $SU_c(3)\times SU_L(2) \times U_Y(1)$ invariant operators involving the third-family quarks which could be generated by new physics at a higher scale. Expressions for these operators after electroweak gauge symmetry breaking and the induced effective couplings $Wt\bar b$, $Xb\bar b$ and $Xt\bar t$ $( X=Z,\gamma,g,H)$ are presented. Analytic expressions for the tree level contributions of all these operators to the observables $R_b$ and $A^b_{FB}$ at LEP I, $\sigma(e^+e^-\rightarrow b\bar b)$ and $A^b_{FB}$ at LEP II, $\sigma(e^+e^-\rightarrow t\bar t)$ and $A_{FB}^t$ at the NLC, as well as $\sigma(p\bar p\rightarrow t\bar b+X)$ at the Tevatron upgrade, are provided. The effects of these operators on different electroweak observables are discussed and numerical examples presented. Numerical analyses show that in the coupling region allowed by $R_b$ and $A^b_{FB}$ at LEP I, some of the new physics operators can still have significant contributions at LEP II, the Tevatron and the NLC.Comment: 25 page

Homologous and heterologous desensitization of guanylyl cyclase-B signaling in GH3 somatolactotropes

The guanylyl cyclases, GC-A and GC-B, are selective receptors for atrial and C-type natriuretic peptides (ANP and CNP, respectively). In the anterior pituitary, CNP and GC-B are major regulators of cGMP production in gonadotropes and yet mouse models of disrupted CNP and GC-B indicate a potential role in growth hormone secretion. In the current study, we investigate the molecular and pharmacological properties of the CNP/GC-B system in somatotrope lineage cells. Primary rat pituitary and GH3 somatolactotropes expressed functional GC-A and GC-B receptors that had similar EC50 properties in terms of cGMP production. Interestingly, GC-B signaling underwent rapid homologous desensitization in a protein phosphatase 2A (PP2A)-dependent manner. Chronic exposure to either CNP or ANP caused a significant down-regulation of both GC-A- and GC-B-dependent cGMP accumulation in a ligand-specific manner. However, this down-regulation was not accompanied by alterations in the sub-cellular localization of these receptors. Heterologous desensitization of GC-B signaling occurred in GH3 cells following exposure to either sphingosine-1-phosphate or thyrotrophin-releasing hormone (TRH). This heterologous desensitization was protein kinase C (PKC)-dependent, as pre-treatment with GF109203X prevented the effect of TRH on CNP/GC-B signaling. Collectively, these data indicate common and distinct properties of particulate guanylyl cyclase receptors in somatotropes and reveal that independent mechanisms of homologous and heterologous desensitization occur involving either PP2A or PKC. Guanylyl cyclase receptors thus represent potential novel therapeutic targets for treating growth-hormone-associated disorders

Ep-CAM expression in squamous cell carcinoma of the esophagus: a potential therapeutic target and prognostic marker

BACKGROUND: To evaluate the expression and test the clinical significance of the epithelial cellular adhesion molecule (Ep-CAM) in esophageal squamous cell carcinoma (SCC) to check the suitability of esophageal SCC patients for Ep-CAM directed targeted therapies. METHODS: The Ep-CAM expression was immunohistochemically investigated in 70 primary esophageal SCCs using the monoclonal antibody Ber-EP4. For the interpretation of the staining results, we used a standardized scoring system ranging from 0 to 3+. The survival analysis was calculated from 53 patients without distant metastasis, with R0 resection and at least 2 months of clinical follow-up. RESULTS: Ep-CAM neo-expression was observed in 79% of the tumors with three expression levels, 1+ (26%), 2+ (11%) and 3+ (41%). Heterogeneous expression was observed at all expression levels. Interestingly, tumors with 3+ Ep-CAM expression conferred a significantly decreased median relapse-free survival period (log rank, p = 0.0001) and median overall survival (log rank, p = 0.0003). Multivariate survival analysis disclosed Ep-CAM 3+ expression as independent prognostic factor. CONCLUSION: Our results suggest Ep-CAM as an attractive molecule for targeted therapy in esophageal SCC. Considering the discontenting results of the current adjuvant concepts for esophageal SCC patients, Ep-CAM might provide a promising target for an adjuvant immunotherapeutic intervention

Single top production at the LHC as a probe of R parity violation

We investigate the potential of the LHC to probe the R parity violating couplings involving the third generation by considering single top production. This study is based on particle level event generation for both signal and background, interfaced to a simplified simulation of the ATLAS detector.Comment: 11 pages, 5 figures, 5 tables (LaTeX, style revtex), few references adde

Anomalous production of top quarks at CLIC+LHC based gamma p colliders

The single production of top quark due to flavor changing neutral current (FCNC) interaction and its decay to bW are studied at CLIC+LHC based gamma-p colliders. We consider both t-c-gamma and t-u-gamma anomalous couplings. The anomalous charm (up) quark anomalous coupling parameter kappa_gamma^c (kappa_gamma^u) can be probed down to 9.5x10^-3 (8.0x10^-3) at a gamma-p collider with sqrt{s_ep}=6.48 TeV and L_int=100 fb^-1.Comment: 9 pages, 7 figures, 4 table

Supersymmetric effects in top quark decay into polarized W-boson

We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak (SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal or transverse W-boson. The corrections are presented in terms of the longitudinal ratio \Gamma(t-->W_L b)/\Gamma(t--> W b) and the transverse ratio \Gamma(t-->W_- b)/\Gamma(t--> W b). In most of the parameter space, both SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1% in magnitude and they tend to have opposite signs. The corrections to the total width \Gamma(t-->W b) are also presented for comparison with the existing results in the literature. We find that our SUSY-EW corrections to the total width differ significantly from previous studies: the previous studies give a large correction of more than 10% in magnitude for a large part of the parameter space while our results reach only few percent at most.Comment: Version in PRD (explanation and refs added