119 research outputs found

    Electroweak Sudakov corrections

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    At energies much larger than the mass of the weak gauge bosons, electroweak radiative corrections can lead to significant corrections. At 1 TeV the one loop corrections can be of O(20{\cal O} (20 %) due to large contributions of the Sudakov type. We summarize recent progress in the evaluation and resummation of the double and single logarithmic corrections to general scattering amplitudes for fermions, transversely as well as longitudinally polarized external lines.Comment: contribution to LCWS2000 at Fermila

    Resummation of angular dependent corrections in spontaneously broken gauge theories

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    Recent investigations of electroweak radiative corrections have revealed the importance of higher order contributions in high energy processes, where the size of typical corrections can exceed those associated with QCD considerably. Beyond one loop, only universal (angular independent) corrections are known to all orders except for massless e+effe^+ e^- \longrightarrow f {\overline f} processes where also angular dependent corrections exist in the literature. In this paper we present general arguments for the consistent resummation of angular dependent subleading (SL) logarithmic corrections to all orders in the regime where all invariants are still large compared to the gauge boson masses. We discuss soft isospin correlations, fermion mass and gauge boson mass gap effects, the longitudinal and Higgs boson sector as well as mixing contributions including CKM effects for massive quarks. Two loop arguments are interpreted in the context of the effective high energy effective theory based on the Standard Model Lagrangian in the symmetric basis with the appropriate matching conditions to include the soft QED regime. The result is expressed in exponentiated operator form in a CKM-extended isospin space in the symmetric basis. Thus, a full electroweak SL treatment based on the infrared evolution equation method is formulated for arbitrary high energy processes at future colliders. Comparisons with known results are presented.Comment: 22 pages, 3 eps-figures, uses LaTeX2

    Mass gap effects and higher order electroweak Sudakov logarithms

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    The infrared structure of spontaneously broken gauge theories is phenomenologically very important and theoretically a challenging problem. Various attempts have been made to calculate the higher order behavior of large double-logarithmic (DL) corrections originating from the exchange of electroweak gauge bosons resulting in contradictory claims. We present results from two loop electroweak corrections for the process gfRfˉLg \longrightarrow f_{\rm R} {\bar f}_{\rm L} to DL accuracy. This process is ideally suited as a theoretical model reaction to study the effect of the mass gap of the neutral electroweak gauge bosons at the two loop level. Contrary to recent claims in the literature, we find that the calculation performed with the physical Standard Model fields is in perfect agreement with the results from the infrared evolution equation method. In particular, we can confirm the exponentiation of the electroweak Sudakov logarithms through two loops.Comment: 10 pages, 3 figures, LaTeX2e, uses epsfi

    Two loop mass effects in the static position space QCD-potential

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    The perturbatively calculable short distance QCD potential is known to two loops including the effect of massive quarks. Recently, a simple approximate solution in momentum space was utilized to obtain the potential in coordinate space. The latter is important in several respects. A comparison with non-perturbative lattice results is feasible in the overlap regime using light MSˉ\bar{MS} masses. This might be even more promising employing the concept of the force between the heavy color singlet sources, which can be easily derived from the potential. In addition, the better than two percent accuracy bottom mass determination from Υ\Upsilon-mesons is sensitive to massive charm loops at the two loop order. We summarize recent results using exact one loop functions and explicit decoupling parametrizations.Comment: Version to appear in Proceedings of QCD0

    Renormalization Group Improved Heavy Quark Production in Polarized \gamma \gamma Collisions

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    The experimental determination of the partial width Γ(Hγγ)\Gamma (H \longrightarrow \gamma \gamma) of an intermediate mass Higgs is among the most important measurements at a future photon photon collider. Recently it was shown that large non-Sudakov as well as Sudakov double logarithmic (DL) corrections can be summed to all orders in the background process γγ(Jz=0)qqˉ\gamma \gamma (J_z=0) \longrightarrow q \bar{q}. It was found that positivity and stability of the cross section was only restored at the four-loop level. One remaining large source of uncertainty stems from the fact that the scale of the strong coupling is unspecified within the double logarithmic approximation. In this paper we include the leading and next-to-leading order running coupling to all orders. We thus remove the inherent scale uncertainty of both the exact one-loop and all-orders DL result without encountering any Landau-pole singularities. The effect is significant and, for the non-Sudakov form factor, is found to correspond to an effective scale of roughly αs(9mq2)\alpha_s(9m_q^2).Comment: 23 pages, 10 eps-figure

    The Standard Model Higgs in γγ\gamma \gamma Collisions

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    For a Higgs boson below the W±W^\pm threshold, the γγ\gamma \gamma collider option of a future linear e+ee^+ e^- machine is compelling. In this case one can measure the ``gold-plated'' loop induced Γ(Hγγ)\Gamma (H \longrightarrow \gamma \gamma) partial width to high precision, testing various extensions of the Standard Model. With recent progress in the expected γγ\gamma \gamma luminosity at TESLA, we find that for a Higgs of 115 GeV a statistical accuracy of the two photon partial width of 1.4 % is possible. The total width depends thus solely on the accuracy of BR(Hγγ)BR(H \longrightarrow \gamma \gamma) and is of O(10{\cal O} (10 %).Comment: contribution to LCWS2000 at Fermila