Probing Top-Quark Couplings at Lepton and Photon Colliders

The ability of high energy lepton and photon colliders to probe the gauge couplings of the top-quark is summarized.Comment: 10 pages, LaTex, to appear in the Proceedings of the 2nd International Workshop on e-e- Interactions at TeV Energies, Santa Cruz, CA, 22-24 September 199

Subleading Shape Functions in Inclusive B Decays

The contributions of subleading shape functions to inclusive decay distributions of B mesons are derived from a systematic two-step matching of QCD current correlators onto soft-collinear and heavy-quark effective theory. At tree-level, the results can be expressed in terms of forward matrix elements of bi-local light-cone operators. Four-quark operators, which arise at O(g^2), are included. Their effects can be absorbed entirely into a redefinition of other shape functions. Our results are in disagreement with some previous studies of subleading shape-function effects in the literature. A numerical analysis of B->X_u+l+nu decay distributions suggests that power corrections are small, with the possible exception of the endpoint region of the charged-lepton energy spectrum.Comment: 22 pages, 2 figures; several typos corrected; version published in JHE

New interpretation of arterial stiffening due to cigarette smoking using a structurally motivated constitutive model

Cigarette smoking is the leading self-inflicted risk factor for cardiovascular diseases; it causes arterial stiffening with serious sequelea including atherosclerosis and abdominal aortic aneurysms. This work presents a new interpretation of arterial stiffening caused by smoking based on data published for rat pulmonary arteries. A structurally motivated “four fiber family” constitutive relation was used to fit the available biaxial data and associated best-fit values of material parameters were estimated using multivariate nonlinear regression. Results suggested that arterial stiffening caused by smoking was reflected by consistent increase in an elastin-associated parameter and moreover by marked increase in the collagen-associated parameters. That is, we suggest that arterial stiffening due to cigarette smoking appears to be isotropic, which may allow simpler phenomenological models to capture these effects using a single stiffening parameter similar to the approach in isotropic continuum damage mechanics. There is a pressing need, however, for more detailed histological information coupled with more complete biaxial mechanical data for a broader range of systemic arteries

Top-quark spin correlation at Linear Colliders with anomalous couplings

We investigate the feasibility of probing anomalous top-quark couplings of $Wtb$, $Z t \bar{t}$, and $\gamma t \bar{t}$ in terms of an effective Lagrangian with dimension-six operators at future $e^+e^-$ linear colliders with a c. m. energy $\sqrt s \sim 500-800$ GeV. We first examine the constraints on these anomalous couplings from the $Z\to b \bar{b}$ data at LEP I and from unitarity considerations. We then consider in detail the effects of anomalous couplings on $t \bar{t}$ spin correlations in the top-pair production and decay with three spin bases: the helicity, beamline and off-diagonal bases. Our results show that the polarized beams are more suitable for exploring the effects of different new operators. For polarized beams, the helicity basis yields the best sensitivity.Comment: 23 pages, 10 figures, references adde

Quark-Squark Alignment Revisited

We re-examine the possibility that the solution to the supersymmetric flavor problem is related to small mixing angles in gaugino couplings induced by approximate horizontal Abelian symmetries. We prove that, for a large class of models, there is a single viable structure for the down quark mass matrix with four holomorphic zeros. Consequently, we are able to obtain both lower and upper bounds on the supersymmetric mixing angles and predict the contributions to various flavor changing neutral current processes. We find that the most likely signals for alignment are $\Delta m_D$ close to the present bound, significant CP violation in $D^0-\bar{D^0}$ mixing, and shifts of order a few percent in various CP asymmetries in $B^0$ and $B_s$ decays. In contrast, the modifications to radiative B decays, to $\epsilon^\prime/\epsilon$ and to $K\to\pi\nu\bar\nu$ decays are small. We further investigate a new class of alignment models, where supersymmetric contributions to flavor changing processes are suppressed by both alignment and RGE-induced degeneracy.Comment: 20 pages, 3 figure

Phenomenology of V_ub from Ratios of Inclusive B Decay Rates

We explore the theoretical feasibility of extracting V_ub from two ratios built from B meson inclusive partial decays, R_1 = Gamma(b-> u cbar s)/3Gamma(b -> c l nu), and R_2 = [Gamma(b -> c X) - Gamma(b -> cbar X)]/Gamma(b -> c ubar d). We discuss contributions to these quantities from perturbative and nonperturbative physics, and show that they can be computed with overall uncertainties at the level of 10%.Comment: 19 pages, 8 embedded EPS figures, uses REVTe

Dark matter and Colliders searches in the MSSM

We study the complementarity between dark matter experiments (direct detection and indirect detections) and accelerator facilities (the CERN LHC and a $\sqrt{s}= 1$ TeV $e^+e^-$ Linear Collider) in the framework of the constrained Minimal Supersymmetric Standard Model (MSSM). We show how non--universality in the scalar and gaugino sectors can affect the experimental prospects to discover the supersymmetric particles. The future experiments will cover a large part of the parameter space of the MSSM favored by WMAP constraint on the relic density, but there still exist some regions beyond reach for some extreme (fine tuned) values of the supersymmetric parameters. Whereas the Focus Point region characterized by heavy scalars will be easily probed by experiments searching for dark matter, the regions with heavy gauginos and light sfermions will be accessible more easily by collider experiments. More informations on both supersymmetry and astrophysics parameters can be thus obtained by correlating the different signals.Comment: 25 pages, 10 figures, corrected typos and reference adde

The lifetime of B_c-meson and some relevant problems

The lifetime of the B_c-meson is estimated with consistent considerations on all of the heavy mesons ($B^0, B^\pm, B_s, D^0, D^\pm D_s$) and the double heavy meson B_c. In the estimate, the framework, where the non-spectator effects for nonleptonic decays are taken into account properly, is adopted, and the parameters needed to be fixed are treated carefully and determined by fitting the available data. The bound-state effects in it are also considered. We find that in decays of the meson B_c, the QCD correction terms of the penguin diagrams and the main component terms c_1O_1, c_2O_2 of the effective interaction Lagrangian have direct interference that causes an enhancement about 3 ~ 4% in the total width of the B_c meson.Comment: 27 pages, 0 figur

Spin configuration of top quark pair production with large extra dimensions at photon-photon colliders

Top quark pair production at photon-photon colliders is studied in low scale quantum gravity scenario. From the dependence of the cross sections on the spin configuration of the top quark and anti-quark, we introduce a new observable, top spin asymmetry. It is shown that there exists a special top spin basis where with the polarized parent electron beams the top spin asymmetry vanishes in the standard model but retains substantial values with the large extra dimension effects. We also present lower bounds of the quantum gravity scale $M_S$ from total cross sections with various combinations of the laser, electron beam, and top quark pair polarizations. The measurements of the top spin state $(t_\uparrow\bar{t}_\downarrow)$ with unpolarized initial beams are shown to be most effective, enhancing by about 5% the $M_S$ bounds with respect to totally unpolarized case.Comment: 18 pages, 4 figures, ReVTe

Four-fermion heavy quark operators and light current amplitudes in heavy flavor hadrons

We introduce and study the properties of the "color-straight" four-quark operators containing heavy and light quark fields. They are of the form (\bar b\Gamma_b b)(\bar q\Gamma_q q) where both brackets are color singlets. Their expectation values include the bulk of the nonfactorizable contributions to the nonleptonic decay widths of heavy hadrons. The expectation values of the color-straight operators in the heavy hadrons are related to the momentum integrals of the elastic light-quark formfactors of the respective heavy hadron. We calculate the asymptotic behavior of the light-current formfactors of heavy hadrons and show that the actual decrease is 1/(q^2)^3/2 rather than 1/q^4. The two-loop hybrid anomalous dimensions of the four-quark operators and their mixing (absent in the first loop) are obtained. Using plausible models for the elastic formfactors, we estimate the expectation values of the color-straight operators in the heavy mesons and baryons. Improved estimates will be possible in the future with new data on the radiative decays of heavy hadrons. We give the Wilson coefficients of the four-fermion operators in the 1/m_b expansion of the inclusive widths and discuss the numerical predictions. Estimates of the nonfactorizable expectation values are given.Comment: 51 pages. The case of flavor-singlet operators is added for the two-loop anomalous dimension