1,421 research outputs found

    QCD factorization with heavy quarks

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    We further analyze the definition and the calculation of the heavy quark impact factor at next-to-leading (NL) log⁥s\log s level, and we provide its analytical expression in a previously proposed k-factorization scheme. Our results indicate that k-factorization holds at NL level with a properly chosen energy scale, and with the same gluonic Green's function previously found in the massless probe case.Comment: LaTeX2e, 4pp, 2 figures, uses espcrc2.sty. Talk given at International Workshop on Diffraction in High-Energy Physics (Diffraction 2000), Cetraro, Italy, Sept. 2-7, 2000. The complete paper is also available at http://www-ttp.physik.uni-karlsruhe.de/Preprints

    Electroweak double logarithms in inclusive observables for a generic initial state

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    High energy observables are characterized by large electroweak radiative corrections of infrared origin; double logarithms are present even for inclusive cross sections, thus violating the Bloch Nordsieck theorem. This effect, related to the initial states carrying nonabelian isospin charges, is here investigated for {\sl any} inclusive cross section in the SU(2)⊗\otimesU(1) symmetric limit, that is appropriate for energies much higher than the weak scale. We develop a general formalism allowing to calculate the all order double log resummed cross sections once the hard (tree level) ones are known. The relevant cases of fermion-fermion, fermion-boson and boson-boson scattering are discussed.Comment: 6 pages, 2 figure

    Enhanced Electroweak Corrections to Inclusive Boson Fusion Processes at the TeV Scale

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    Electroweak radiative corrections with double-log enhancements occur in inclusive observables at the TeV scale because of a lack of compensation of virtual corrections with real emission due to the nonabelian (weak isospin) charges of the accelerator beams. Here we evaluate such Bloch-Nordsieck violating corrections in the case of initial longitudinal bosons, which is experimentally provided by boson fusion processes, and is related to the Goldstone-Higgs sector. All four states of this sector are involved in the group structure of the corrections, and cause in particular a novel double log effect due to hypercharge mixing in the longitudinal states. We study both the light- and the heavy-Higgs cases, and we analyze the symmetry breaking pattern of the corrections. The latter turn out to be pretty large, in the 5-10 % range, and show an interesting Higgs mass dependence, even for processes without Higgs boson in the final state.Comment: 15 pages, 6 figure

    Diffusion corrections to the hard pomeron

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    The high-energy behaviour of two-scale hard processes is investigated in the framework of small-x models with running coupling, having the Airy diffusion model as prototype. We show that, in some intermediate high-energy regime, the perturbative hard Pomeron exponent determines the energy dependence, and we prove that diffusion corrections have the form hinted at before in particular cases. We also discuss the breakdown of such regime at very large energies, and the onset of the non-perturbative Pomeron behaviour.Comment: 18 pages, 3 Postscript figure

    All Order Running Coupling BFKL Evolution from GLAP (and vice-versa)

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    We present a systematic formalism for the derivation of the kernel of the BFKL equation from that of the GLAP equation and conversely to any given order, with full inclusion of the running of the coupling. The running coupling is treated as an operator, reducing the inclusion of running coupling effects and their factorization to a purely algebraic problem. We show how the GLAP anomalous dimensions which resum large logs of x can be derived from the running-coupling BFKL kernel order by order, thereby obtaining a constructive all-order proof of small x factorization. We check this result by explicitly calculating the running coupling contributions to GLAP anomalous dimensions up to next-to-next-to leading order. We finally derive an explicit expression for BFKL kernels which resum large logs of Q^2 up to next-to-leading order from the corresponding GLAP kernels, thus making possible a consistent collinear improvement of the BFKL equation up to the same order

    Electroweak lights from Dark Matter annihilations

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    The energy spectra of Standard Model particles originated from Dark Matter annihilations can be significantly altered by the inclusion of electroweak gauge boson radiation from the final state. A situation where this effect is particularly important is when a Majorana Dark Matter particle annihilates into two light fermions. This process is in p-wave and hence suppressed by the small value of the relative velocity of the annihilating particles. The inclusion of electroweak radiation eludes this suppression and opens up a potentially sizeable s-wave contribution to the annihilation cross section. I will discuss the impact of this effect on the fluxes of stable particles resulting from the Dark Matter annihilations, which are relevant for Dark Matter indirect searches.Comment: 4 pages, 2 figures. Contribution to the conference proceedings of TAUP 2011, Munich - Germany (5-9 September 2011

    Can we trust small x resummation?

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    We review the current status of small x resummation of evolution of parton distributions and of deep-inelastic coefficient functions. We show that the resummed perturbative expansion is stable, robust upon different treatments of subleading terms, and that it matches smoothly to the unresummed perturbative expansions, with corrections which are of the same order as the typical NNLO ones in the HERA kinematic region. We discuss different approaches to small x resummation: we show that the ambiguities in the resummation procedure are small, provided all parametrically enhanced terms are included in the resummation and properly matched.Comment: 12 pages, 12 figures; LaTeX with espcrc2.sty. Talk given at the 2008 Ringberg workshop "New Trends in HERA Physics

    Electroweak Bloch-Nordsieck violation at the TeV scale: "strong" weak interactions ?

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    Hard processes at the TeV scale exhibit enhanced (double log) EW corrections even for inclusive observables, leading to violation of the Bloch-Nordsieck theorem. This effect, previously related to the non abelian nature of free EW charges in the initial state (e- e+, e- p, p p ...), is here investigated for fermion initiated hard processes and to all orders in EW couplings. We find that the effect is important, especially for lepton initiated processes, producing weak effects that in some cases compete in magnitude with the strong ones. We show that this (double log) BN violating effect has a universal energy dependence, related to the Sudakov form factor in the adjoint representation. The role of this form factor is to suppress cross section differences within a weak isospin doublet, so that at very large energy the cross sections for left-handed electron-positron and neutrino-positron scattering become equal. Finally, we briefly discuss the phenomenological relevance of our results for future colliders.Comment: 18 pages, 6 figures, uses epsfig.sty and subequation.st