233 research outputs found
The singular behavior of massive QCD amplitudes
We discuss the structure of infrared singularities in on-shell QCD amplitudes
with massive partons and present a general factorization formula in the limit
of small parton masses. The factorization formula gives rise to an all-order
exponentiation of both, the soft poles in dimensional regularization and the
large collinear logarithms of the parton masses. Moreover, it provides a
universal relation between any on-shell amplitude with massive external partons
and its corresponding massless amplitude. For the form factor of a heavy quark
we present explicit results including the fixed-order expansion up to three
loops in the small mass limit. For general scattering processes we show how our
constructive method applies to the computation of all singularities as well as
the constant (mass-independent) terms of a generic massive n-parton QCD
amplitude up to the next-to-next-to-leading order corrections.Comment: version to appear in JHEP (sec. 3 with expanded discussion and
appendix with added results
Solving the Sports League Scheduling Problem with Tabu Search
In this paper we present a tabu approach for a version of the Sports League Scheduling Problem. The approach adopted is based on a formulation of the problem as a Constraint Satisfaction Problem (CSP). Tests were carried out on problem instances of up to 40 teams representing 780 integer variables with 780 values per variable. Experimental results show that this approach outperforms some existing methods and is one of the most promising methods for solving problems of this type
Two-Loop g -> gg Splitting Amplitudes in QCD
Splitting amplitudes are universal functions governing the collinear behavior
of scattering amplitudes for massless particles. We compute the two-loop g ->
gg splitting amplitudes in QCD, N=1, and N=4 super-Yang-Mills theories, which
describe the limits of two-loop n-point amplitudes where two gluon momenta
become parallel. They also represent an ingredient in a direct x-space
computation of DGLAP evolution kernels at next-to-next-to-leading order. To
obtain the splitting amplitudes, we use the unitarity sewing method. In
contrast to the usual light-cone gauge treatment, our calculation does not rely
on the principal-value or Mandelstam-Leibbrandt prescriptions, even though the
loop integrals contain some of the denominators typically encountered in
light-cone gauge. We reduce the integrals to a set of 13 master integrals using
integration-by-parts and Lorentz invariance identities. The master integrals
are computed with the aid of differential equations in the splitting momentum
fraction z. The epsilon-poles of the splitting amplitudes are consistent with a
formula due to Catani for the infrared singularities of two-loop scattering
amplitudes. This consistency essentially provides an inductive proof of
Catani's formula, as well as an ansatz for previously-unknown 1/epsilon pole
terms having non-trivial color structure. Finite terms in the splitting
amplitudes determine the collinear behavior of finite remainders in this
formula.Comment: 100 pages, 33 figures. Added remarks about leading-transcendentality
argument of hep-th/0404092, and additional explanation of cut-reconstruction
uniquenes
On the B and J/Psi Cross Section Measurements at Ua1 and CDF
We analise the implications of the measurement of and inclusive
\pt\ distributions performed in collisions by the UA1 and CDF
experiments.Comment: 16 pages + 8 topdrawer figs included at the end, Latex, IFUP-TH 2/9
Loss of Tiparp results in aberrant layering of the cerebral cortex
Yes2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible poly-ADP-ribose polymerase (TIPARP) is an enzyme that adds a single ADP-ribose moiety to itself or other proteins. Tiparp is highly expressed in the brain; however, its function in this organ is unknown. Here, we used Tiparp–/– mice to determine Tiparp’s role in the development of the prefrontal cortex. Loss of Tiparp resulted in an aberrant organization of the mouse cortex, where the upper layers presented increased cell density in the knock-out mice compared with wild type. Tiparp loss predominantly affected the correct distribution and number of GABAergic neurons. Furthermore, neural progenitor cell proliferation was significantly reduced. Neural stem cells (NSCs) derived from Tiparp–/– mice showed a slower rate of migration. Cytoskeletal components, such as α-tubulin are key regulators of neuronal differentiation and cortical development. α-tubulin mono-ADP ribosylation (MAR) levels were reduced in Tiparp–/– cells, suggesting that Tiparp plays a role in the MAR of α-tubulin. Despite the mild phenotype presented by Tiparp–/– mice, our findings reveal an important function for Tiparp and MAR in the correct development of the cortex. Unravelling Tiparp’s role in the cortex, could pave the way to a better understanding of a wide spectrum of neurological diseases which are known to have increased expression of TIPARP.European Union Seventh Framework Program (FP7-PEOPLE-2013-COFUND) Grant n609020-Scientia Fellows (to G.G.) and by the Johan Throne Holst Foundation and the University of Oslo (J.M.)
Two-Loop Helicity Amplitudes for Quark-Quark Scattering in QCD and Gluino-Gluino Scattering in Supersymmetric Yang-Mills Theory
We present the two-loop QCD helicity amplitudes for quark-quark and
quark-antiquark scattering. These amplitudes are relevant for
next-to-next-to-leading order corrections to (polarized) jet production at
hadron colliders. We give the results in the `t Hooft-Veltman and
four-dimensional helicity (FDH) variants of dimensional regularization and
present the scheme dependence of the results. We verify that the finite
remainder, after subtracting the divergences using Catani's formula, are in
agreement with previous results. We also provide the amplitudes for
gluino-gluino scattering in pure N=1 supersymmetric Yang-Mills theory. We
describe ambiguities in continuing the Dirac algebra to D dimensions, including
ones which violate fermion helicity conservation. The finite remainders after
subtracting the divergences using Catani's formula, which enter into physical
quantities, are free of these ambiguities. We show that in the FDH scheme, for
gluino-gluino scattering, the finite remainders satisfy the expected
supersymmetry Ward identities.Comment: arXiv admin note: substantial text overlap with arXiv:hep-ph/030416
Testing J/psi Production and Decay Properties in Hadronic Collisions
The polar and azimuthal angular distributions for the lepton pair arising
from the decay of a J/psi meson produced at transverse momentum p_T balanced by
a photon [or gluon] in hadronic collisions are calculated in the color singlet
model (CSM). It is shown that the general structure of the decay lepton
distribution is controlled by four invariant structure functions, which are
functions of the transverse momentum and the rapidity of the J/psi. We found
that two of these structure functions [the longitudinal and transverse
interference structure functions] are identical in the CSM. Analytical and
numerical results are given in the Collins-Soper and in the Gottfried-Jackson
frame. We present a Monte Carlo study of the effect of acceptance cuts applied
to the leptons and the photon for J/psi+ gamma production at the Tevatron.Comment: 22 pages (LaTeX) plus 11 postscript figures, MAD/PH/822, YUMS94-11.
Figures are available from the authors or as a compressed tar file via
anonymous ftp at phenom.physics.wisc.edu in directory
{}~pub/preprints/madph-94-822-figs.tar.
Z boson pair production at LHC in a stabilized Randall-Sundrum scenario
We study the Z boson pair production at LHC in the Randall-Sundrum scenario
with the Goldberger-Wise stabilization mechanism. It is shown that
comprehensive account of the Kaluza-Klein graviton and radion effects is
crucial to probe the model: The KK graviton effects enhance the cross section
of on the whole so that the resonance peak of the radion becomes
easy to detect, whereas the RS effects on the process are
rather insignificant. The and invariant-mass distributions are presented
to study the dependence of the RS model parameters. The production of
longitudinally polarized Z bosons, to which the SM contributions are
suppressed, is mainly due to KK gravitons and the radion, providing one of the
most robust methods to signal the RS effects. The sensitivity bounds
on with are also obtained such that
the effective weak scale of order 5 TeV can be experimentally
probed.Comment: 28 pages, LaTex file, 18 eps figure
Two-Loop Helicity Amplitudes for Quark-Gluon Scattering in QCD and Gluino-Gluon Scattering in Supersymmetric Yang-Mills Theory
We present the two-loop QCD helicity amplitudes for quark-gluon scattering,
and for quark-antiquark annihilation into two gluons. These amplitudes are
relevant for next-to-next-to-leading order corrections to (polarized) jet
production at hadron colliders. We give the results in the `t Hooft-Veltman and
four-dimensional helicity (FDH) variants of dimensional regularization. The
transition rules for converting the amplitudes between the different variants
are much more intricate than for the previously discussed case of gluon-gluon
scattering. Summing our two-loop expressions over helicities and colors, and
converting to conventional dimensional regularization, gives results in
complete agreement with those of Anastasiou, Glover, Oleari and Tejeda-Yeomans.
We describe the amplitudes for 2 to 2 scattering in pure N=1 supersymmetric
Yang-Mills theory, obtained from the QCD amplitudes by modifying the color
representation and multiplicities, and verify supersymmetry Ward identities in
the FDH scheme.Comment: 77 pages. v2: corrected errors in eqs. (3.7) and (3.8) for one-loop
assembly; remaining results unaffecte
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.
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