Resummation of QCD Corrections to the eta_c Decay Rate

We examine the ratio of the decay rate of the eta_c into light hadrons to the decay rate into photons and find that most of the large next-to-leading-order (NLO) correction is associated with running of the strong coupling alpha_s. We resum such contributions by analyzing final-state chains of vacuum-polarization bubbles. We show that the nonperturbative parts of the bubble chains can be absorbed into a color-octet matrix element, once one has used contour deformations of the phase-space integrals to cancel certain contributions. We argue that these contributions are incompatible with the uncertainty principle. We also argue that perturbation theory is reliable only if one carries out the phase-space integrations before the perturbation summation. Our results are in good agreement with experiment and differ considerably from those that one obtains by applying the scale-setting method of Brodsky, Lepage, and Mackenzie to the NLO result.Comment: 41 pages, REVTEX, corrected minor typos in tex

InGaAs/AlGaAsSb avalanche photodiode with high gain - bandwidth product

Increasing reliance on the Internet places greater and greater demands for high -speed optical communication systems. Increasing their data transfer rate allows more data to be transferred over existing links. With optical receivers being essential to all optical links, bandwidth performance of key components in receivers, such as avalanche photodiodes (APDs), must be improved. The APDs rely on In0.53Ga0.47As (grown lattice-matched to InP substrates) to efficiently absorb and detect the optical signals with 1310 or 1550 nm wavelength, the optimal wavelengths of operation for these optical links. Thus developing InP -compatible APDs with high gain-bandwidth product (GBP) is important to the overall effort of increasing optical links’ data transfer rate. Here we demonstrate a novel InGaAs/AlGaAsSb APD, grown on an InP substrate, with a GBP of 424 GHz, the highest value reported for InP -compatible APDs, which is clearly applicable to future optical communication systems at or above 10 Gb/s

GRK6 regulates the hemostatic response to injury through its rate-limiting effects on GPCR signaling in platelets.

G protein-coupled receptors (GPCRs) mediate the majority of platelet activation in response to agonists. However, questions remain regarding the mechanisms that provide negative feedback toward activated GPCRs to limit platelet activation and thrombus formation. Here we provide the first evidence that GPCR kinase 6 (GRK6) serves this role in platelets, using GRK6-/- mice generated by CRISPR-Cas9 genome editing to examine the consequences of GRK6 knockout on GPCR-dependent signaling. Hemostatic thrombi formed in GRK6-/- mice are larger than in wild-type (WT) controls during the early stages of thrombus formation, with a rapid increase in platelet accumulation at the site of injury. GRK6-/- platelets have increased platelet activation, but in an agonist-selective manner. Responses to PAR4 agonist or adenosine 5\u27-diphosphate stimulation in GRK6-/- platelets are increased compared with WT littermates, whereas the response to thromboxane A2 (TxA2) is normal. Underlying these changes in GRK6-/- platelets is an increase in Ca2+ mobilization, Akt activation, and granule secretion. Furthermore, deletion of GRK6 in human MEG-01 cells causes an increase in Ca2+ response and PAR1 surface expression in response to thrombin. Finally, we show that human platelet activation in response to thrombin causes an increase in binding of GRK6 to PAR1, as well as an increase in the phosphorylation of PAR1. Deletion of GRK6 in MEG-01 cells causes a decrease in PAR1 phosphorylation. Taken together, these data show that GRK6 regulates the hemostatic response to injury through PAR- and P2Y12-mediated effects, helping to limit the rate of platelet activation during thrombus growth and prevent inappropriate platelet activation

Production of the PP-Wave Excited BcB_c-States through the Z0Z^0 Boson Decays

In Ref.[7],we have dealt with the production of the two color-singlet $S$-wave $(c\bar{b})$-quarkonium states $B_c(|(c\bar{b})_{\bf 1}[^1S_0]>)$ and $B^*_c(|(c\bar{b})_{\bf 1}[^3S_1]>)$ through the $Z^0$ boson decays. As an important sequential work, we make a further discussion on the production of the more complicated $P$-wave excited $(c\bar{b})$-quarkonium states, i.e. $|(c\bar{b})_{\bf 1}[^1P_1]>$ and $|(c\bar{b})_{\bf 1}[^3P_J]>$ (with $J=(1,2,3)$). More over, we also calculate the channel with the two color-octet quarkonium states $|(c\bar{b})_{\bf 8}[^1S_0]g>$ and $|(c\bar{b})_{\bf 8}[^3S_1]g>$, whose contributions to the decay width maybe at the same order of magnitude as that of the color-singlet $P$-wave states according to the naive nonrelativistic quantum chromodynamics scaling rules. The $P$-wave states shall provide sizable contributions to the $B_c$ production, whose decay width is about 20% of the total decay width $\Gamma_{Z^0\to B_c}$. After summing up all the mentioned $(c\bar{b})$-quarkonium states' contributions, we obtain $\Gamma_{Z^0\to B_c} =235.9^{+352.8}_{-122.0}$ KeV, where the errors are caused by the main uncertainty sources.Comment: 8 pages, 5 figures and 2 tables. basic formulae in the appendix are cut off to match the published version, which can be found in v1. to be published in Eur.Phys.J.

Supergravity Null Scissors and Super-Crosses

In this paper we construct the supergravity solutions for the orthogonally intersecting null scissors and the fluxed D-strings. We name the latter as the super-crosses according to their shape. It turns out that the smeared solutions are U-dual related to the intersecting $(p,q)$-strings. Their open string properties are also studied. As a by-product, we clarify the supersymmetry conditions of D2-D2 pairs with most generic fluxes.Comment: 16 pages, 1 figure;v2. minor comment revised;v3. references added, final to JHE

The staggered domain wall fermion method

A different lattice fermion method is introduced. Staggered domain wall fermions are defined in 2n+1 dimensions and describe 2^n flavors of light lattice fermions with exact U(1) x U(1) chiral symmetry in 2n dimensions. As the size of the extra dimension becomes large, 2^n chiral flavors with the same chiral charge are expected to be localized on each boundary and the full SU(2^n) x SU(2^n) flavor chiral symmetry is expected to be recovered. SDWF give a different perspective into the inherent flavor mixing of lattice fermions and by design present an advantage for numerical simulations of lattice QCD thermodynamics. The chiral and topological index properties of the SDWF Dirac operator are investigated. And, there is a surprise ending...Comment: revtex4, 7 figures, minor revisions, 2 references adde

Renormalization group analysis of the QCD quark potential to order v^2

A one-loop renormalization group analysis of the order v^2 relativistic corrections to the static QCD potential is presented. The velocity renormalization group is used to simultaneously sum ln(m/mv) and ln(m/mv^2) terms. The results are compared to previous calculations in the literature.Comment: 13 pages. important change: running of soft Lagrangian include

Creation of photons in an oscillating cavity with two moving mirrors

We study the creation of photons in a one dimensional oscillating cavity with two perfectly conducting moving walls. By means of a conformal transformation we derive a set of generalized Moore's equations whose solution contains the whole information of the radiation field within the cavity. For the case of resonant oscillations we solve these equations using a renormalization group procedure that appropriately deals with the secular behaviour present in a naive perturbative approach. We study the time evolution of the energy density profile and of the number of created photons inside the cavity.Comment: LaTex file, 17 pages, 3 figures, uses epsf.st

Exploration of (p,pi˚) as a Way of Studying Pionic Atoms

This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440

The Hyperfine Spin Splittings In Heavy Quarkonia

The hyperfine spin splittings in heavy quarkonia are studied using the recently developed renormalization group improved spin-spin potential which is independent of the scale parameter $\mu$. The calculated energy difference between the $J/\psi$ and the $\eta_c$ fits the experimental data well, while the predicted energy difference $\Delta M_p$ between the center of the gravity of $1^3P_{0,1,2}$ states and the $1^1P_1$ state of charmonium has the correct sign but is somewhat larger than the experimental data. This is not surprising since there are several other contributions to $\Delta M_p$, which we discuss, that are of comparable size ($\sim 1$ MeV) that should be included, before precise agreement with the data can be expected. The mass differences of the $\psi'-\eta_c'$, $\Upsilon(1S)-\eta_b$, $\Upsilon(2S)-\eta_b'$, and $B_c^*-B_c$ are also predicted.Comment: 17 page