All-Order Corrections To Higgs Boson Production In Association With Jets

We present a new framework for calculating multi-jet observables. The framework is based on the factorisation of scattering amplitudes in the kinematical limit of large invariant mass between all particles. We show that by constraining the analyticity of scattering amplitudes away from this limits, we get good agreement order by order with the full, fixed order perturbative calculation at the low orders where these are available, and therefore get firm predictions on the all-order behaviour. As an example, we study Higgs boson production through gluon fusion in association with at least two jets at the LHC.Comment: Invited talk at 44th Rencontres de Moriond on QCD and High Energy Interactions, La Thuile, Valle d'Aosta, Italy, 14-21 Mar 200

Quantum Size Effects in the Terahertz Nonlinear Response of Metallic Armchair Graphene Nanoribbons

We use time dependent perturbation theory to study quantum size effects on the terahertz nonlinear response of metallic graphene armchair nanoribbons of finite length under an applied electric field. Our work shows that quantization due to the finite length of the nanoribbon, the applied field profile, and the broadening of the graphene spectrum all play a significant role in the resulting nonlinear conductances. In certain cases, these effects can significantly enhance the nonlinearity over that for infinitely-long metallic armchair graphene nanoribbon.Comment: 8 pages, 4 figure

A New approach to inclusive decay spectra.

The main obstacle in describing inclusive decay spectra in QCD — which, in particular, limits the precision in extrapolating the measured ¯B −→ Xs rate to the full phase space as well as in extracting |Vub| from inclusive measurements of charmless semileptonic decays — is their sensitivity to the non-perturbative momentum distribution of the heavy quark in the meson. We show that, despite this sensitivity, resummed perturbation theory has high predictive power. Conventional Sudakov–resummed perturbation theory describing the decay of an onshell heavy quark yields a divergent expansion. Detailed understanding of this divergence in terms of infrared renormalons has paved the way for making quantitative predictions. In particular, the leading renormalon ambiguity cancels out between the Sudakov factor and the quark pole mass. This cancellation requires renormalon resummation but involves no non-perturbative information. Additional effects due to the Fermi motion of the quark in the meson can be systematically taken into account through power corrections, which are only important near the physical endpoint. This way the moments of the ¯B −→ Xs spectrum with experimentally–accessible cuts — which had been so far just parametrized — were recently computed by perturbative means. At Moriond these predictions were confronted with new data from BaBar

Plasmon dispersion in semimetallic armchair graphene nanoribbons

The dispersion relations for plasmons in intrinsic and extrinsic semimetallic armchair graphene nanoribbons (acGNR) are calculated in the random phase approximation using the orthogonal p_z-orbital tight binding method. Our model predicts new plasmons for acGNR of odd atomic widths N=5,11,17,... Our model further predicts plasmons in acGNR of even atomic width N=2,8,14,... related to those found using a Dirac continuum model, but with different quantitative dispersion characteristics. We find that the dispersion of all plasmons in semimetallic acGNR depends strongly on the localization of the p_z electronic wavefunctions. We also find that overlap integrals for acGNR behave in a more complex way than predicted by the Dirac continuum model, suggesting that these plasmons will experience a small damping for all q not equal to 0. Plasmons in extrinsic semimetallic acGNR with the chemical potential in the lowest (highest) conduction (valence) band are found to have dispersion characteristics nearly identical to their intrinsic counterparts, with negligible differencs in dispersion arising from the slight differences in overlap integrals for the interband and intraband transitions.Comment: 8 pages, 9 figure

All-Order Corrections and Multi-Jet Rates

We discuss results from a recently proposed all-order description of hard, radiative corrections to certain multi-jet processes at hadron colliders. The description is based on obtaining an all-order estimate of the t-channel singularities of scattering amplitudes. As a simple example, we illustrate the similarities between qQ and qg-scattering. In particular, we discuss how at tree-level, all non-suppressed helicity-amplitudes for these processes consist of a pure t-channel pole. This structure is used in the construction of all-order approximations.Comment: 6 pages. Talk given at RADCOR 2009 - 9th International Symposium on Radiative Corrections (Applications of Quantum Field Theory to Phenomenology), October 25 - 30 2009, Ascona, Switzerlan

The Intrinsic Ellipticity of Spiral Disks

We have measured the distribution of intrinsic ellipticities for a sample of 28 relatively face-on spiral disks. We combine H-alpha velocity fields and R and I-band images to determine differences between kinematic and photometric inclination and position angles, from which we estimate intrinsic ellipticities of galaxy disks. Our findings suggest disks have a log-normal distribution of ellipticities (mean epsilon =0.06) and span a range from epsilon= 0 (circular) to epsilon=0.2. We are also able to construct a tight Tully-Fisher relation for our face-on sample. We use this to assess the contribution of disk ellipticity on the observed Tully-Fisher scatter.Comment: 4 pages, 2 figures, to appear in "Disks of Galaxies: Kinematics, Dynamics and Perturbations" (ASP Conference Series), eds E.Athanassoula and A. Bosm

A Study of the gluon ladder in diffractive processes.

The solution to the non–forward BFKL equation in the Leading Logarithmic approximation is expressed in terms of a sum of iterations of its kernel directly in transverse momentum and rapidity space. Several studies of the non–forward solution are performed both at the level of the gluon Green’s function and for a toy cross–section, including an analysis of the diffusion properties as found in this approach. The method developed in this paper allows for a direct inspection of the momenta in the BFKL ladder, and can be applied to solving the non–forward BFKL equation to next–to–leading logarithmic accuracy, when the corresponding kernel is available

Statistical Analysis of Project Pyro Liquid Propellant Explosion Data

Statistical regression analysis of Project Pyro cryogenic propellant explosion test dat

Band structure and atomic sum rules for x-ray dichroism

Corrections to the atomic orbital sum rule for circular magnetic x-ray dichroism in solids are derived using orthonormal LMTOs as a single-particle basis for electron band states.Comment: 7 pages, no figure