Decays of mesons with charm quarks on the lattice

We investigate mesons containing charm quarks on fine lattices with a^{-1} \sim 5 GeV. The quenched approximation is employed using the Wilson gauge action at \beta = 6.6 and nonperturbatively O(a) improved Wilson quarks. We present results for decay constants using various interpolating fields and give preliminary results for form factors of semileptonic decays of D_s mesons to light pseudoscalar mesons.Comment: 7 pages, 3 figures, talk presented at the XXV International Symposium on Lattice Field Theory, 30 July - 4 August 2007, Regensburg, German

Mechanisms of airfoil noise near stall conditions

The focus of this paper is on investigating the noise produced by an airfoil at high angles of attack over a range of Reynolds number Re≈2×10⁵–4×10⁵. The objective is not modeling this source of noise but rather understanding the mechanisms of generation for surface pressure fluctuations, due to a separated boundary layer, that are then scattered by the trailing edge. To this aim, we use simultaneous noise and surface pressure measurement in addition to velocimetric measurements by means of hot wire anemometry and time-resolved particle image velocimetry. Three possible mechanisms for the so-called “separation-stall noise” have been identified in addition to a clear link between far-field noise, surface pressure, and velocity fields in the noise generation

Semileptonic form factors D → \rightarrow π \pi , K and B → \rightarrow π \pi , K from a fine lattice

We extract the form factors relevant for semileptonic decays of D and B mesons from a relativistic computation on a fine lattice in the quenched approximation. The lattice spacing is a = 0.04 fm (corresponding to a -1 = 4.97 GeV), which allows us to run very close to the physical B meson mass, and to reduce the systematic errors associated with the extrapolation in terms of a heavy-quark expansion. For decays of D and Ds mesons, our results for the physical form factors at \ensuremath q^2 = 0 are as follows: \ensuremath f_+^{D\rightarrow\pi}(0) = 0.74(6)(4) , \ensuremath f_+^{D \rightarrow K}(0) = 0.78(5)(4) and \ensuremath f_+^{D_s \rightarrow K} (0) = 0.68(4)(3) . Similarly, for B and Bs we find \ensuremath f_+^{B\rightarrow\pi}(0) = 0.27(7)(5) , \ensuremath f_+^{B\rightarrow K} (0) = 0.32(6)(6) and \ensuremath f_+^{B_s\rightarrow K}(0) = 0.23(5)(4) . We compare our results with other quenched and unquenched lattice calculations, as well as with light-cone sum rule predictions, finding good agreemen

Spectral Curves and Localization in Random Non-Hermitian Tridiagonal Matrices

Eigenvalues and eigenvectors of non-Hermitian tridiagonal periodic random matrices are studied by means of the Hatano-Nelson deformation. The deformed spectrum is annular-shaped, with inner radius measured by the complex Thouless formula. The inner bounding circle and the annular halo are stuctures that correspond to the two-arc and wings observed by Hatano and Nelson in deformed Hermitian models, and are explained in terms of localization of eigenstates via a spectral duality and the Argument principle.Comment: 5 pages, 9 figures, typographical error corrected in reference

On the manipulation of flow and acoustic fields of a blunt trailing edge aerofoil by serrated leading edges

This paper employs serrated leading edges to inject streamwise vorticity to the downstream boundary layer and wake to manipulate the flow field and noise sources near the blunt trailing edge of an asymmetric aerofoil. The use of a large serration amplitude is found to be effective to suppress the first noise source—bluntness-induced vortex shedding tonal noise—through the destruction of the coherent eigenmodes in the wake. The second noise source is the instability noise, which is produced by the interaction between the boundary layer instability and separation bubble near the blunt edge. The main criterion needed to suppress this noise source is related to a small serration wavelength because, through the generation of more streamwise vortices, it would facilitate a greater level of destructive interaction with the separation bubble. If the leading edge has both a large serration amplitude and wavelength, the interaction between the counter-rotating vortices themselves would trigger a turbulent shear layer through an inviscid mechanism. The turbulent shear layer will produce strong hydrodynamic pressure fluctuations to the trailing edge, which then scatter into broadband noise and transform into a trailing edge noise mechanism. This would become the third noise source that can be identified in several serrated leading edge configurations. Overall, a leading edge with a large serration amplitude and small serration wavelength appears to be the optimum choice to suppress the first and second noise sources and, at the same time, avoid the generation of the third noise source

A lattice calculation of vector meson couplings to the vector and tensor currents using chirally improved fermions

We present a quenched lattice calculation of $f_V^\perp/f_V$, the coupling of vector mesons to the tensor current normalized by the vector meson decay constant. The chirally improved lattice Dirac operator, which allows us to reach small quark masses, is used. We put emphasis on analyzing the quark mass dependence of $f_V^\perp/f_V$ and find only a rather weak dependence. Our results at the $\rho$ and $\phi$ masses agree well with QCD sum rule calculations and those from previous lattice studies.Comment: 6 pages, 3 figures, one sentence remove

Decay constants of charm and beauty pseudoscalar heavy-light mesons on fine lattices

We compute decay constants of heavy-light mesons in quenched lattice QCD with a lattice spacing of a ~ 0.04 fm using non-perturbatively O(a) improved Wilson fermions and O(a) improved currents. We obtain f_{D_s} = 220(6)(5)(11) MeV, f_D = 206(6)(3)(22) MeV, f_{B_s} = 205(7)(26)(17) MeV and f_B = 190(8)(23)(25) MeV, using the Sommer parameter r_0 = 0.5 fm to set the scale. The first error is statistical, the second systematic and the third from assuming a +-10% uncertainty in the experimental value of r_0. A detailed discussion is given in the text. We also present results for the meson decay constants f_K and f_\pi and the \rho meson mass.Comment: 13 pages, 7 figures. Replaced version contains analysis in terms of improved quark masses instead of bare quark masses, result for f_B changed by 1 MeV. Several typos corrected, in particular error bars in table 4. Version accepted in PL

Chiral extrapolation of lattice data for the hyperfine splittings of heavy mesons

Hyperfine splittings between the heavy vector (D*, B*) and pseudoscalar (D, B) mesons have been calculated numerically in lattice QCD, where the pion mass (which is related to the light quark mass) is much larger than its physical value. Naive linear chiral extrapolations of the lattice data to the physical mass of the pion lead to hyperfine splittings which are smaller than experimental data. In order to extrapolate these lattice data to the physical mass of the pion more reasonably, we apply the effective chiral perturbation theory for heavy mesons, which is invariant under chiral symmetry when the light quark masses go to zero and heavy quark symmetry when the heavy quark masses go to infinity. This leads to a phenomenological functional form with three parameters to extrapolate the lattice data. It is found that the extrapolated hyperfine splittings are even smaller than those obtained using linear extrapolation. We conclude that the source of the discrepancy between lattice data for hyperfine splittings and experiment must lie in non-chiral physics.Comment: 27 pages, 6 figure

An underwater towed vehicle to monitor the Sicily-Malta channel

The problem of monitoring pollution coming from oil spills assumes wide importance for the highly congested Sicily-Malta channel. Hydrocarbons, as well as other polluting substances, have a huge influence on the health status of the sea. In this paper we present the preliminary design of an underwater towed vehicle (UTV) to monitor the Sicily-Malta channel. The design of this towfish incorporates ideas for a camera, lens system and stroboscope illumination system that can be used to take images of phytoplankton and zooplankton having a size range of 100 microns up to 1 centimeter. The underwater platform includes a high definition (HD) camera for monitoring jellyfish population at different sea depths. Unlike the autonomous underwater vehicles (AUVs), an UTV is not independent and must be towed by a surface boat. This disadvantage is balanced by having a simpler design and control system and an increased payload for instruments, sensors and cameras due to the absence of heavy battery systems. In order to increase maneuverability, stability and depth control, actuated hydroplanes are used to vary the angle of attack and to change the total downward force exerted on the moving towfish. The depth of dive of the towfish is automatically controlled to a set value. Automatic control is preferred so as to reduce the work and human concentration necessary during a monitoring mission. The hydroplanes are used to control rolling and pitching of the towfish. This kind of corrective action and a means of knowing the inclination of the towfish are deemed to be necessary because of the effect that underwater currents may have on the dynamics of the towfish. In addition to active control against the rolling action, the main hydroplanes (wings) of the towfish are at a small anhedral angle in order to create a passive anti roll action by creating a corrective moment acting about the main longitudinal axis of the towfish. The stern of the towfish also carries a rudder. The rudder would mainly be used when turning and to steer the towfish away from the surface boat wake when taking surface or close to surface measurements. The towfish is towed via an umbilical cord which carries all the power supply and signal lines necessary for towfish control and data acquisition. The umbilical cord is mechanically strong enough in order to tow the underwater towfish which is subjected to hydrodynamic drag. For proper logging and mapping of pollutants and camera images it is required to know the exact position and positional depth of the towfish during a mission. The positional depth of the towfish is recorded by means of a depth sensor. The position of the towfish is found by having a Global Positioning System (GPS) on the surface boat coupled with a commercially available sonar based instrument that can be used to calculate the relative position between the surface boat and the towfish.peer-reviewe