308 research outputs found
Iterated amplitudes in the high-energy limit
We consider the high-energy limits of the colour ordered four-, five- and
six-gluon MHV amplitudes of the maximally supersymmetric QCD in the multi-Regge
kinematics where all the gluons are strongly ordered in rapidity. We show that
various building blocks occurring in the Regge factorisation (the Regge
trajectory, the coefficient functions and the Lipatov vertex) satisfy an
iterative structure very similar to the Bern-Dixon-Smirnov (BDS) ansatz. This
iterative structure, combined with the universality of the building blocks,
enables us to show that in the Euclidean region any two- and three-loop
amplitude in multi-Regge kinematics is guaranteed to satisfy the BDS ansatz. We
also consider slightly more general kinematics where the strong rapidity
ordering applies to all the gluons except the two with either the largest or
smallest rapidities, and we derive the iterative formula for the associated
coefficient function. We show that in this kinematic limit the BDS ansatz is
also satisfied. Finally, we argue that only for more general kinematics - e.g.
with three gluons having similar rapidities, or where the two central gluons
have similar rapidities - can a disagreement with the BDS ansatz arise.Comment: Version corresponding to the Erratum sent to JHEP on October 16th
200
Vector boson Pair Production at Supercolliders; useful approximate helicity amplitudes
We study vector boson pair production at and , taking into account
the effects generated by the anomalous vector boson and Higgs couplings induced
by the operators and , which are the only dim=6
operators preserving . These operators lead to enhanced production of
transverse vector bosons, as opposed to the enhanced production of longitudinal
gauge bosons, induced in case M_H\gsim 1\ TeV, by dim=4 terms already
existing in the Standard Model lagrangian. For vector boson pair masses larger
than , we establish very simple approximate expressions for the
standard as well as the non-standard helicity amplitudes for
annihilation and vector boson fusion, which accurately describe the physics.
These expressions should simplify the experimental search for such
interactions. We finally discuss the observability and the disentangling of
these interactions.Comment: 22 pages, 6 figures avaible by air mail upon request , (e-mail
[email protected] PM/93-26 THES-TP 93/
Subtraction terms for one-loop amplitudes with one unresolved parton
Fully differential next-to-next-to-leading order calculations require a
method to cancel infrared singularities. In a previous publication, I discussed
the general setup for the subtraction method at NNLO. In this paper I give all
subtraction terms for electron-positron annihilation associated with one-loop
amplitudes with one unresolved parton. These subtraction terms are integrated
within dimensional regularization over the unresolved one-particle phase space.
The results can be used with all variants of dimensional regularization
(conventional dimensional regularization, the 't Hooft-Veltman scheme and the
four-dimensional scheme).Comment: 27 page
A comparative study of Higgs boson production from vector-boson fusion
The data taken in Run II at the Large Hadron Collider have started to probe Higgs boson production at high transverse momentum. Future data will provide a large sample of events with boosted Higgs boson topologies, allowing for a detailed understanding of electroweak Higgs boson plus two-jet production, and in particular the vector-boson fusion mode (VBF). We perform a detailed comparison of precision calculations for Higgs boson production in this channel, with particular emphasis on large Higgs boson transverse momenta, and on the jet radius dependence of the cross section. We study fixed-order predictions at next-to-leading order and next-to-next-to-leading order QCD, and compare the results to NLO plus parton shower (NLOPS) matched calculations. The impact of the NNLO corrections on the central predictions is mild, with inclusive scale uncertainties of the order of a few percent, which can increase with the imposition of kinematic cuts. We find good agreement between the fixed-order and matched calculations in non-Sudakov regions, and the various NLOPS predictions also agree well in the Sudakov regime. We analyze backgrounds to VBF Higgs boson production stemming from associated production, and from gluon-gluon fusion. At high Higgs boson transverse momenta, the ∆yjj and/or mjj cuts typically used to enhance the VBF signal over background lead to a reduced efficiency. We examine this effect as a function of the jet radius and using different definitions of the tagging jets. QCD radiative corrections increase for all Higgs production modes with increasing Higgs boson pT, but the proportionately larger increase in the gluon fusion channel results in a decrease of the gluon-gluon fusion background to electroweak Higgs plus two jet production upon requiring exclusive two-jet topologies. We study this effect in detail and contrast in particular a central jet veto with a global jet multiplicity requirement
On the Resolution of Singularities of Multiple Mellin-Barnes Integrals
One of the two existing strategies of resolving singularities of multifold
Mellin-Barnes integrals in the dimensional regularization parameter, or a
parameter of the analytic regularization, is formulated in a modified form. The
corresponding algorithm is implemented as a Mathematica code MBresolve.mComment: LaTeX, 10 page
Subtraction terms at NNLO
Perturbative calculations at next-to-next-to-leading order for multi-particle
final states require a method to cancel infrared singularities. I discuss the
subtraction method at NNLO. As a concrete example I consider the leading-colour
contributions to e+ e- --> 2 jets. This is the simplest example which exhibits
all essential features. For this example, explicit subtraction terms are given,
which approximate the four-parton and three-parton final states in all double
and single unresolved limits, such that the subtracted matrix elements can be
integrated numerically.Comment: 41 page
Associated Production of a Z Boson and a Single Heavy-Quark Jet
The leading-order process for the production of a Z boson and a heavy-quark
jet at hadron colliders is gQ -> ZQ (Q=c,b). We calculate this cross section at
next-to-leading order at the Tevatron and the LHC, and compare it with other
sources of ZQ events. This process is a background to new physics, and can be
used to measure the heavy-quark distribution function.Comment: 15 pages, 9 figures. Version to appear in Phys. Rev.
Conformal properties of four-gluon planar amplitudes and Wilson loops
We present further evidence for a dual conformal symmetry in the four-gluon
planar scattering amplitude in N=4 SYM. We show that all the momentum integrals
appearing in the perturbative on-shell calculations up to five loops are dual
to true conformal integrals, well defined off shell. Assuming that the complete
off-shell amplitude has this dual conformal symmetry and using the basic
properties of factorization of infrared divergences, we derive the special form
of the finite remainder previously found at weak coupling and recently
reproduced at strong coupling by AdS/CFT. We show that the same finite term
appears in a weak coupling calculation of a Wilson loop whose contour consists
of four light-like segments associated with the gluon momenta. We also
demonstrate that, due to the special form of the finite remainder, the
asymptotic Regge limit of the four-gluon amplitude coincides with the exact
expression evaluated for arbitrary values of the Mandelstam variables.Comment: 25 pages, 6 figures; v3: minor corrections, references adde
Complete Order alpha_s^3 Results for e^+ e^- to (gamma,Z) to Four Jets
We present the next-to-leading order (O(alpha_s^3)) perturbative QCD
predictions for e^+e^- annihilation into four jets. A previous calculation
omitted the O(alpha_s^3) terms suppressed by one or more powers of 1/N_c^2,
where N_c is the number of colors, and the `light-by-glue scattering'
contributions. We find that all such terms are uniformly small, constituting
less than 10% of the correction. For the Durham clustering algorithm, the
leading and next-to-leading logarithms in the limit of small jet resolution
parameter y_{cut} can be resummed. We match the resummed results to our
fixed-order calculation in order to improve the small y_{cut} prediction.Comment: Latex2e, 17 pages with 5 encapsulated figures. Note added regarding
subsequent related work. To appear in Phys. Rev.
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