Alpha_s from the Lattice Potential

We present an extensive study on the direct determination of the running coupling alpha_s from the static quark antiquark force at short distances, in quenched QCD. We find from our high statistics potential analysis that alpha_qq exhibits two-loop asymptotic behaviour for momenta as low as .5 GeV. As a result, we determine the zero flavour Lambda-parameter to be Lambda^0_MSBAR = 0.630(38)\sqrt{\sigma} = 293(18)^{+25}_{-63} MeV. A rough estimate of full QCD effects leads to the five flavour value alpha_MSBAR(m_Z) = .102^{+6}_{-11}. A comparison with other lattice results is made.Comment: 6 pages (LaTeX) with 7 postscript figures (epsf required), Invited talk by K. Schilling held at Lattice '93 conference, Dallas, T

Synchronized pulse control of decoherence

We present a new strategy for multipulse control over decoherence. When a two-level system interacts with a reservoir characterized by a specific frequency, we find that the decoherence is effectively suppressed by synchronizing the pulse-train application with the dynamical motion of the reservoir.Comment: 14 pages, 8 figure

Comparative Study of full QCD Hadron Spectrum and Static Quark Potential with Improved Actions

We investigate effects of action improvement on the light hadron spectrum and the static quark potential in two-flavor QCD for $a^{-1} \approx 1$ GeV and $m_{PS}/m_V = 0.7-0.9$. We compare a renormalization group improved action with the plaquette action for gluons, and the SW-clover action with the Wilson action for quarks. We find a significant improvement in the hadron spectrum by improving the quark action, while the gluon improvement is crucial for a rotationally invariant static potential. We also explore the region of light quark masses corresponding to $m_{PS}/m_V \geq 0.4$ on a 2.7 fm lattice using the improved gauge and quark action. A flattening of the potential is not observed up to 2 fm.Comment: LaTeX, 35 pages, 22 eps figures, uses revtex and eps

Scaling Laws and Effective Dimension in Lattice SU(2) Yang-Mills Theory with a Compactified Extra Dimension

Monte Carlo simulations are performed in a five-dimensional lattice SU(2) Yang-Mills theory with a compactified extra dimension, and scaling laws are studied. Our simulations indicate that as the compactification radius $R$ decreases, the confining phase spreads more and more to the weak coupling regime, and the effective dimension of the theory changes gradually from five to four. Our simulations also indicate that the limit $a_4 to 0$ with $R/a_4$ kept fixed exists both in the confining and deconfining phases if $R/a_4$ is small enough, where $a_4$ is the lattice spacing in the four-dimensional direction. We argue that the color degrees of freedom in QCD are confined only for $R < R_{\rm max}$, where a rough estimate shows that $1/R_{\rm max}$ lies in the TeV range. Comments on deconstructing extra dimensions are given.Comment: 15 pages, TeX, 5 figure

Electroweak Corrections to the Charged Higgs Boson Decay into Chargino and Neutralino

The electroweak corrections to the partial widths of the $H^+ \to \tilde{\chi}^+_i \tilde{\chi}_j^0 (i=1,j=1,2)$ decays including one-loop diagrams of the third generation quarks and squarks, are investigated within the Supersymmetric Standard Model. The relative corrections can reach the values about 10%, therefore they should be taken into account for the precise experimental measurement at future colliders.Comment: 21 pages, 6 eps figures, 1 Latex fil

Mutation of Ser172 in Yeast β Tubulin Induces Defects in Microtubule Dynamics and Cell Division

Ser172 of β tubulin is an important residue that is mutated in a human brain disease and phosphorylated by the cyclin-dependent kinase Cdk1 in mammalian cells. To examine the role of this residue, we used the yeast S. cerevisiae as a model and produced two different mutations (S172A and S172E) of the conserved Ser172 in the yeast β tubulin Tub2p. The two mutants showed impaired cell growth on benomyl-containing medium and at cold temperatures, altered microtubule (MT) dynamics, and altered nucleus positioning and segregation. When cytoplasmic MT effectors Dyn1p or Kar9p were deleted in S172A and S172E mutants, cells were viable but presented increased ploidy. Furthermore, the two β tubulin mutations exhibited synthetic lethal interactions with Bik1p, Bim1p or Kar3p, which are effectors of cytoplasmic and spindle MTs. In the absence of Mad2p-dependent spindle checkpoint, both mutations are deleterious. These findings show the importance of Ser172 for the correct function of both cytoplasmic and spindle MTs and for normal cell division

Running Coupling and the Lambda-Parameter from SU(3) Lattice Simulations

We present new results on the static qq-potential from high statistics simulations on 32^4 and smaller lattices, using the standard Wilson beta = 6.0, 6.4, and 6.8. Within our statistical errors we do not observe any finite size effects affecting the potential values, on varying the spatial lattice extent from 0.9fm up to 3.3fm. We are able to see and quantify the running of the coupling from the Coulomb behaviour of the interquark force. From this we extract the ratio \sqrt{sigma}/Lambda_L. We demonstrate that scaling violations on the string tension can be considerably reduced by introducing effective coupling schemes, which allow for a safe extrapolation of \Lambda_L to its continuum value. Both methods yield consistent values for Lambda: Lambda_MSbar = 0.558_{-0.007}^{+0.017}\sqrt{sigma} = 246_{-3}^{+7}MeV. At the highest energy scale attainable to us we find alpha(5 GeV) = 0.150(3)Comment: 19 pages (LaTex), +6 pages with figures (Postscript, 432K), WUB 92--2

Quantum regression theorem for non-Markovian Lindblad equations

We find the conditions under which a quantum regression theorem can be assumed valid for non-Markovian master equations consisting in Lindblad superoperators with memory kernels. Our considerations are based on a generalized Born-Markov approximation, which allows us to obtain our results from an underlying Hamiltonian description. We demonstrate that a non-Markovian quantum regression theorem can only be granted in a stationary regime if the dynamics satisfies a quantum detailed balance condition. As an example we study the correlations of a two level system embedded in a complex structured reservoir and driven by an external coherent field.Comment: 14 pages, 5 figures. Extended version. The GBMA is deduced from projector technique. A new appendix is adde