Diphoton production at hadron colliders: a fully differential QCD calculation at next-to-next-to-leading order

We consider direct diphoton production in hadron collisions, and we compute the next-to-next-to-leading order QCD radiative corrections at the fully differential level. Our calculation uses the q(T) subtraction formalism, and it is implemented in a parton-level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on the final-state photons and the associated jet activity and to compute the corresponding distributions in the form of bin histograms. We present selected numerical results related to Higgs boson searches at the LHC and corresponding results at the Tevatron.     

Ultrafast photovoltaic response in ferroelectric nanolayers

We show that light drives large-amplitude structural changes in thin films of the prototypical ferroelectric PbTiO3 via direct coupling to its intrinsic photovoltaic response. Using time-resolved x-ray scattering to visualize atomic displacements on femtosecond time scales, photoinduced changes in the unit-cell tetragonality are observed. These are driven by the motion of photogenerated free charges within the ferroelectric and can be simply explained by a model including both shift and screening currents, associated with the displacement of electrons first antiparallel to and then parallel to the ferroelectric polarization direction.     

Island of stability for consistent deformations of Einstein's gravity

We construct deformations of general relativity that are consistent and phenomenologically viable, since they respect, in particular, cosmological backgrounds. These deformations have unique symmetries in accordance with their Minkowski cousins (Fierz-Pauli theory for massive gravitons) and incorporate a background curvature induced self-stabilizing mechanism. Self-stabilization is essential in order to guarantee hyperbolic evolution in and unitarity of the covariantized theory, as well as the deformation's uniqueness. We show that the deformation's parameter space contains islands of absolute stability that are persistent through the entire cosmic evolution.     

On the inter-instrument and the inter-laboratory transferability of a tandem mass spectral reference library. 3. Focus on ion trap and upfront CID

Mass spectral libraries represent versatile tools for the identification of small bioorganic molecules. Libraries based on electron impact spectra are rated robust and transferable. Tandem mass spectral libraries are often considered to work properly only on the instrument that has been used to build the library. An exception from that rule is the 'Wiley Registry of Tandem Mass Spectral Data, MSforID'. In various studies with data sets from different kinds of tandem mass spectrometric instruments, the outstanding sensitivity and robustness of this tandem mass spectral library search approach was demonstrated. The instrumental platforms tested, however, mainly included various tandem-in-space instruments. Herein, the results of a multicenter study with a focus on upfront and tandem-in-time fragmentation are presented. Five laboratories participated and provided fragment ion mass spectra from the following types of mass spectrometers: time-of-flight (TOF), quadrupole-hexapole-TOF, linear ion trap (LIT), 3-D ion trap and LIT-Orbitrap. A total number of 1231 fragment ion mass spectra were collected from 20 test compounds (amiloride, buphenin, cinchocaine, cyclizine, desipramine, dihydroergotamine, dyxirazine, dosulepin, ergotamine, ethambutol, etofylline, mefruside, metoclopramide, phenazone, phentermine, phenytoin, sulfamethoxazole, sulfamoxole, sulthiame and tetracycline) on seven electrospray ionization instruments using 18 different instrumental configurations for fragmentation. For 1222 spectra (99.3%), the correct compound was retrieved as the best matching compound. Classified matches (matches with 'relative average match probability' >40.0) were obtained for 1207 spectra (98.1%). This high percentage of correct identifications clearly supports the hypothesis that the tandem mass spectral library approach tested is a robust and universal identification tool.     

Implementation of the type III seesaw model in FeynRules/MadGraph and prospects for discovery with early LHC data

We discuss the implementation of the “minimal” type III seesaw model, i.e. with one fermionic triplet, in FeynRules/MadGraph. This is the first step in order to realize a real study of LHC data recorded in the LHC detectors. With this goal in mind, we comment on the possibility of discovering this kind of new physics at the LHC running at 7 TeV with a luminosity of few fb⁻¹.     

LES Study of Flow Between Shrouded Co-rotating Disks

Large eddy simulations of turbulent flow between shrouded co-rotating disks, representing a simplified model of a hard disk drive, are performed. The computation domain surrounds a complete disk and is bounded at top and bottom by half a disk. Therefore, it is possible to compute the fluctuating pressure field surrounding the middle disk. Also, the influence of the shroud geometry is taken into account by comparing a flat shroud wall and a wall with rib chambers. In the flat shroud case, the fluctuating pressure on the upper- and lower-surface of a disk indicates a strong correlation with fluid motion travelling across the disk-tip clearance region. However, in the ribbed shroud case the organized flow structure that is observed in the flat shroud case disappears and the fluctuating pressure acting on the surface of the disk is remarkably diminished.     

On Approximation and Computation of Navier-Stokes Flow

We present an approximation method for the non-stationary nonlinear incompressible Navier-Stokes equations in a cylindrical domain (0,T)×G,where G⊂R^3 is a smoothly bounded domain. Ourmethod is applicable to general three-dimensional flow without any symmetry restrictions and relies on existence, uniqueness and representation results from mathematical fluid dynamics. After a suitable time delay in the nonlinear convective term v·∇v we obtain globally (in time) uniquely solvable equations, which - by using semi-implicit time differences - can be transformed into a finite number of Stokes-type boundary value problems. For the latter a boundary element method based on a corresponding hydrodynamical potential theory is carried out. The method is reported in short outlines ranging from approximation theory up to numerical test calculations.     

A Gentle Stochastic Thermostat for Molecular Dynamics

We discuss a dynamical technique for sampling the canonical measure in molecular dynamics. We present a method that generalizes a recently proposed scheme (Samoletov et al., J. Stat. Phys. 128:1321–1336, 2007), and which controls temperature by use of a device similar to that of Nosé dynamics, but adds random noise to improve ergodicity. In contrast to Langevin dynamics, where noise is added directly to each physical degree of freedom, the new scheme relies on an indirect coupling to a single Brownian particle. For a model with harmonic potentials, we show under a mild non-resonance assumption that we can recover the canonical distribution. In spite of its stochastic nature, experiments suggest that it introduces a relatively weak perturbative effect on the physical dynamics, as measured by perturbation of temporal autocorrelation functions. The kinetic energy is well controlled even in the early stages of a simulation.