101,109 research outputs found
Light-quark two-loop corrections to heavy-quark pair production in the gluon fusion channel
Full text linkBonciani R, Ferroglia A, Gehrmann T, von Manteuffel A, Studerus C. Light-quark two-loop corrections to heavy-quark pair production in the gluon fusion channel. Journal of High Energy Physics. 2013;2013(12): 38.We calculate the two-loop corrections to heavy-quark pair production in the gluon fusion channel which arise from diagrams involving a closed light-quark loop. The calculation is carried out by keeping the exact dependence on the heavy-quark mass. The analytic results are written in terms of logarithms, classical polylogarithms Li_n (n=2,3,4), and genuine multiple polylogarithms Li_{2,2}. The functional arguments are rational expressions of two independent external invariants and they are chosen in such a way that the functions are real in all the physical phase-space points. Through systematic changes in the functional basis, we obtain expansions of the results in both the production threshold and small mass limits
Two-Loop Corrections to Top-Antitop Production at Hadron Colliders
Full text linkBonciani R, Ferroglia A, Gehrmann T, von Manteuffel A, Studerus C. Two-Loop Corrections to Top-Antitop Production at Hadron Colliders. In: PoS. Vol ICHEP2010. 2010: 098
Probing top quark electromagnetic dipole moments in single-top-plus-photon production
Full text linkThe production of a single top quark in association with an isolated photon probes the electromagnetic coupling structure of the top quark. We investigate the sensitivity of kine- matical distributions at the LHC in single-top-plus-photon production in view of a detection of anomalous electric and magnetic dipole moments of the top quark
Two-loop QCD corrections to the V → qq ̄ g helicity amplitudes with axial-vector couplings
Full text linkWe compute the two-loop corrections to the helicity amplitudes for the coupling of a massive vector boson to a massless quark-antiquark pair and a gluon, accounting for vector and axial-vector couplings of the vector boson and distinguishing isospin non-singlet and singlet contributions. A new four-dimensional basis for the decomposition of the amplitudes into 12 invariant tensor structures is introduced. The associated form factors are then computed up to two loops in QCD using dimensional regularization. After performing renormalization and infrared subtraction, the finite parts of the renormalized non-singlet vector and axial-vector form factors are shown agree with each other, and to reproduce the previously known two-loop amplitudes. The singlet axial-vector amplitude receives a contribution from the axial anomaly from two loops onwards. This amplitude is computed for massless and massive internal quarks. Our results provide the last missing two-loop amplitudes entering the NNLO QCD corrections of vector-boson-plus-jet production at hadron colliders
Pseudo-scalar form factors at three loops in QCD
Full text linkThe coupling of a pseudo-scalar Higgs boson to gluons is mediated through a heavy quark loop. In the limit of large quark mass, it is described by an effective Lagrangian that only admits light degrees of freedom. In this effective theory, we compute the three-loop massless QCD corrections to the form factor that describes the coupling of a pseudo-scalar Higgs boson to gluons. Due to the axial anomaly, the pseudo-scalar operator for the gluonic field strength mixes with the divergence of the axial vector current. Working in dimensional regularization and using the ’t Hooft-Veltman prescription for the axial vector current, we compute the three-loop pseudo-scalar form factors for massless quarks and gluons. Using the universal infrared factorization properties, we independently derive the three-loop operator mixing and finite operator renormalisation from the renormalisation group equation for the form factors, thereby confirming recent results in the operator product expansion. The finite part of the three-loop form factor is an important ingredient to the precise prediction of the pseudo-scalar Higgs boson production cross section at hadron colliders. We discuss potential applications and derive the hard matching coefficient in soft-collinear effective theory
Infrared subtraction at next-to-next-to-leading order for gluonic initial states
Full text linkIn this thesis we describe a procedure for isolating the infrared singularities present in gluonic scattering amplitudes at
next-to-leading and next-to-next-to-leading order. We adopted the
antenna subtraction framework which has been successfully applied to the
calculation of NNLO corrections to the 3-jet cross section and related
event shape distributions in electron-positron annihilation. We consider
processes with coloured particles in the initial state, and in
particular two-jet production in hadron-hadron collisions at
accelerators such as the Large Hadron Collider (LHC). We derive explicit
formulae for subtracting the single and double unresolved contributions
from the double radiation gluonic processes using
antenna functions with initial state partons. We show numerically that
the subtraction term effectively approximates the matrix element in the
various single and double unresolved configurations
Master integrals for massless three-loop form-factors: One-loop and two-loop insertions
No full textGehrmann T, Heinrich G, Huber T, Studerus C. Master integrals for massless three-loop form-factors: One-loop and two-loop insertions. Phys.Lett.B. 2006;640(5-6):252-259.The three-loop form factors in massless QCD can be expressed as a linear combination of master integrals. Besides a number of master integrals which factorise into products of one-loop and two-loop integrals, one finds 16 genuine three-loop integrals. Of these, six have the form of a bubble insertion inside a one-loop or two-loop vertex integral. We compute all master integrals with these insertion topologies
The monetary value of sport participation and volunteering: The wellbeing valuation approach
No full textThormann T, Gehrmann S, Wicker P. The monetary value of sport participation and volunteering: The wellbeing valuation approach. In: Deutscher C, Wicker P, eds. 12th ESEA Conference on Sport Economics – Book of Abstracts. 68-70. 2021
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