The White Horse Patrol

Men will always love beauty and a beautiful horse will always arouse the fancy and admiration of horsemen and laymen alike. To them nothing is more awe-inspiring than matched and intelligent horses. Horses skilled in acting are usually found only in the circus, but occasionally an individual will delight in owning and training a trick horse. When a number of such men are brought together by this mutual interest, the arrangement that results may well lead to something unique in that it deals with living creatures by nature of different conformation, temperament, and capability

SUSY Scalar Production in the Electroweak Sudakov Regime of Lepton Colliders

We consider the production of SUSY scalar pairs at lepton colliders, for c.m. energies much larger than the mass of the heaviest SUSY (real or virtual) particle involved in the process. In that energy regime, we derive the leading and subleading terms of the electroweak Sudakov logarithms in the MSSM, first working at one loop with physical states and then resumming to all orders with asymptotic expansions. We show that the first order of the resummed expression reproduces the physical one loop approximation, and compute systematically the possible effects on various observables both at one loop and to all orders. We discuss the regimes and the processes where the one loop approximation can or cannot be trusted, working in an energy range between 1 TeV and 4 TeV under a "light" SUSY mass assumption. As a byproduct of our analysis, we propose a determination of the MSSM parameter tan(beta) showing how a relative accuracy of about 25 percent can be easily achieved in the region tan(beta)>14, under reasonable experimental assumptions.Comment: 35 pages and 15 figures e-mail: [email protected]

Precise measurement of Γ(H⟶γγ)\Gamma (H \longrightarrow \gamma \gamma) at a PLC and theoretical consequences

With the LEP II Higgs search approaching exclusion limits on low values of $\tan \beta \sim 2$ it becomes increasingly important to investigate physical quantities sensitive to large masses of a pseudoscalar Higgs mass. This regime is difficult and over a large range of $\tan \beta$ impossible to cover at the LHC proton proton collider. In this paper we focus on the achievable statistical precision of the Higgs decay into two photons at a future $\gamma \gamma$ collider (PLC) in the MSSM mass range below 130 GeV. The MSSM and SM predictions for $\Gamma (H \longrightarrow \gamma \gamma)$ can differ by up to 10 % even in the decoupling limit of large $m_A$. We summarize recent progress in both the theoretical understanding of the background process $\gamma \gamma \longrightarrow q \bar{q}$, $q=\{b,c\}$, and in the expected detector performance allow for a high accuracy of the lightest MSSM or SM Higgs boson decay into a $b \bar{b}$ pair. We find that for optimized but still realistic detector and accelerator assumptions, statistically a 1.4% accuracy is feasible after about four years of collecting data for a Higgs boson mass which excludes $\tan \beta <2$.Comment: 14 pages, 7 figures, contributed to LP99 at Stanford, C

Resummation of Yukawa enhanced and subleading Sudakov logarithms in longitudinal gauge boson and Higgs production

Future colliders will probe the electroweak theory at energies much larger than the gauge boson masses. Large double (DL) and single (SL) logarithmic virtual electroweak Sudakov corrections lead to significant effects for observable cross sections. Recently, leading and subleading universal corrections for external fermions and transverse gauge boson lines were resummed by employing the infrared evolution equation method. The results were confirmed at the DL level by explicit two loop calculations with the physical Standard Model (SM) fields. Also for longitudinal degrees of freedom the approach was utilized for DL-corrections via the Goldstone boson equivalence theorem. In all cases, the electroweak Sudakov logarithms exponentiate. In this paper we extend the same approach to both Yukawa enhanced as well as subleading Sudakov corrections to longitudinal gauge boson and Higgs production. We use virtual contributions to splitting functions of the appropriate Goldstone bosons in the high energy regime and find that all universal subleading terms exponentiate. The approach is verified by employing a non-Abelian version of Gribov's factorization theorem and by explicit comparison with existing one loop calculations. As a side result, we obtain also all top-Yukawa enhanced subleading logarithms for chiral fermion production at high energies to all orders. In all cases, the size of the subleading contributions at the two loop level is non-negligible in the context of precision measurements at future linear colliders.Comment: 32 pages, 7 figures, uses LaTeX2

The role of universal and non universal Sudakov logarithms in four fermion processes at TeV energies: the one-loop approximation revisited

We consider the separate effects on four fermion processes, in the TeV energy range, produced at one loop by Sudakov logarithms of universal and not universal kind, working in the 't Hooft xi=1 gauge. Summing the various vertex and box contributions allows to isolate two quite different terms.The first one is a combination of vertex and box quadratic and linear logarithms that are partially universal and partially not universal and independent of the scattering angle theta. The second one is theta-dependent, not universal, linearly logarithmic and only produced by weak boxes. We show that for several observables, measurable at future linear e+e- colliders (LC, CLIC), the role of the latter term is dominant and we discuss the implications of this fact for what concerns the reliability of a one-loop approximation.Comment: 22 pages and 13 figures; version to appear in Phys.Rev.D. e-mail: [email protected]

The Two-Loop Scale Dependence of the Static QCD Potential including Quark Masses

The interaction potential V(Q^2) between static test charges can be used to define an effective charge $\alpha_V(Q^2)$ and a physically-based renormalization scheme for quantum chromodynamics and other gauge theories. In this paper we use recent results for the finite-mass fermionic corrections to the heavy-quark potential at two-loops to derive the next-to-leading order term for the Gell Mann-Low function of the V-scheme. The resulting effective number of flavors $N_F(Q^2/m^2)$ in the $\alpha_V$ scheme is determined as a gauge-independent and analytic function of the ratio of the momentum transfer to the quark pole mass. The results give automatic decoupling of heavy quarks and are independent of the renormalization procedure. Commensurate scale relations then provide the next-to-leading order connection between all perturbatively calculable observables to the analytic and gauge-invariant $\alpha_V$ scheme without any scale ambiguity and a well defined number of active flavors. The inclusion of the finite quark mass effects in the running of the coupling is compared with the standard treatment of finite quark mass effects in the $\bar{MS}$ scheme.Comment: 27 pages, 13 figure

Methicillin-susceptible Staphylococcus aureus from clinical and community sources are genetically diverse.

Despite the association of methicillin-susceptible S. aureus (MSSA) with several life-threatening diseases, relatively little is known about their clinical epidemiology in Malaysia. We characterized MSSA isolates (n=252) obtained from clinical and community (carriage) sources based on spa sequencing and multilocus sequence typing (MLST). The prevalence of several important virulence genes was determined to further define the molecular characteristics of MSSA clones circulating in Malaysia. Among the 142 clinical and 110 community-acquired MSSA isolates, 98 different spa types were identified, corresponding to 8 different spa clonal clusters (spa-CCs). In addition, MLST analysis revealed 22 sequence types (STs) with 5 singletons corresponding to 12 MLST-CCs. Interestingly, spa-CC084/085 (MLST-CC15) (p=0.038), spa-non-founder 2 (MLST-ST188) (p=0.002), and spa-CC127 (MLST-CC1) (p=0.049) were identified significantly more often among clinical isolates. spa-CC3204 (MLST-CC121) (p=0.02) and spa-CC015 (MLST-CC45) (p=0.0002) were more common among community isolates. Five dominant MLST-CCs (CC8, CC121, CC1, CC45, and CC5) having clear counterparts among the major MRSA clones were also identified in this study. While the MSSA strains are usually genetically heterogeneous, a relatively high frequency (19/7.5%) of ST188 (t189) strains was found, with 57.8% of these strains carrying the Panton-Valentine leukocidin (PVL). Analysis of additional virulence genes showed a frequency of 36.5% and 36.9% for seg and sei and 0.8% and 6.3% for etb and tst genes, respectively. Arginine catabolic mobile element (ACME) was detected in 4 community isolates only. These represent the first isolates harbouring this gene in an Asian region. In conclusion, MSSA from the Malaysian community and their clinical counterparts are genetically diverse, but certain clones occur more often among clinical isolates than among carriage isolates and vice versa

Electroweak Radiative Corrections to Neutral-Current Drell-Yan Processes at Hadron Colliders

We calculate the complete electroweak O(alpha) corrections to pp, pbar p -> l+l- X (l=e, mu) in the Standard Model of electroweak interactions. They comprise weak and photonic virtual one-loop corrections as well as real photon radiation to the parton-level processes q bar q -> gamma,Z -> l+l-. We study in detail the effect of the radiative corrections on the l+l- invariant mass distribution, the cross section in the Z boson resonance region, and on the forward-backward asymmetry, A_FB, at the Fermilab Tevatron and the CERN Large Hadron Collider. The weak corrections are found to increase the Z boson cross section by about 1%, but have little effect on the forward-backward asymmetry in the Z peak region. Threshold effects of the W box diagrams lead to pronounced effects in A_FB at m(l+l-) approx 160 GeV which, however, will be difficult to observe experimentally. At high di-lepton invariant masses, the non-factorizable weak corrections are found to become large.Comment: Revtex3 file, 39 pages, 2 tables, 12 figure

Resummation of double logarithms in electroweak high energy processes

At future linear $e^+e^-$ collider experiments in the TeV range, Sudakov double logarithms originating from massive boson exchange can lead to significant corrections to the cross sections of the observable processes. These effects are important for the high precision objectives of the Next Linear Collider. We use the infrared evolution equation, based on a gauge invariant dispersive method, to obtain double logarithmic asymptotics of scattering amplitudes and discuss how it can be applied, in the case of broken gauge symmetry, to the Standard Model of electroweak processes. We discuss the double logarithmic effects to both non-radiative processes and to processes accompanied by soft gauge boson emission. In all cases the Sudakov double logarithms are found to exponentiate. We also discuss double logarithmic effects of a non-Sudakov type which appear in Regge-like processes.Comment: 26 pages, 3 figures, Latex2

Binary IS Typing for Staphylococcus aureus

Background: We present an easily applicable test for rapid binary typing of Staphylococcus aureus: binary interspace (IS) typing. This test is a further development of a previously described molecular typing technique that is based on length polymorphisms of the 16S-23S rDNA interspace region of S. aureus. Methodology/Principal Findings: A novel approach of IS-typing was performed in which binary profiles are created. 424 human and animal derived MRSA and MSSA isolates were tested and a subset of these isolates was compared with multi locus sequence typing (MLST) and Amplified Fragment Length Polymorphism (AFLP). Binary IS typing had a high discriminatory potential and a good correlation with MLST and AFLP. Conclusions/Significance: Binary IS typing is easy to perform and binary profiles can be generated in a standardized fashion. These two features, combined with the high correlation with MLST clonal complexes, make the techniqu