1,154 research outputs found
Scattering amplitudes for e^+e^- --> 3 jets at next-to-next-to-leading order QCD
We present the calculation of the fermionic contribution to the QCD two-loop
amplitude for e^+e^- --> q qbar g.Comment: 5 pages, 4 figures, espcrc2.sty (included), Talk given at QCD '02,
Montpellier, France, 2-9th July 200
NNLO phase space master integrals for two-to-one inclusive cross sections in dimensional regularization
We evaluate all phase space master integrals which are required for the total
cross section of generic 2 -> 1 processes at NNLO as a series expansion in the
dimensional regulator epsilon. Away from the limit of threshold production, our
expansion includes one order higher than what has been available in the
literature. At threshold, we provide expressions which are valid to all orders
in terms of Gamma functions and hypergeometric functions. These results are a
necessary ingredient for the renormalization and mass factorization of
singularities in 2 -> 1 inclusive cross sections at NNNLO in QCD.Comment: 37 pages, plus 3 ancillary files containing analytic expressions in
Maple forma
The NNLO gluon fusion Higgs production cross-section with many heavy quarks
We consider extensions of the Standard Model with a number of additional
heavy quarks which couple to the Higgs boson via top-like Yukawa interactions.
We construct an effective theory valid for a Higgs boson mass which is lighter
than twice the lightest heavy quark mass and compute the corresponding Wilson
coefficient through NNLO. We present numerical results for the gluon fusion
cross-section at the Tevatron for an extension of the Standard Model with a
fourth generation of heavy quarks. The gluon fusion cross-section is enhanced
by a factor of roughly 9 with respect to the Standard Model value. Tevatron
experimental data can place stringent exclusion limits for the Higgs mass in
this model.Comment: 14 pages, 1 tabl
The fully differential hadronic production of a Higgs boson via bottom quark fusion at NNLO
The fully differential computation of the hadronic production cross section
of a Higgs boson via bottom quarks is presented at NNLO in QCD. Several
differential distributions with their corresponding scale uncertainties are
presented for the 8 TeV LHC. This is the first application of the method of
non-linear mappings for NNLO differential calculations at hadron colliders.Comment: 27 pages, 13 figures, 1 lego plo
Magnetic dipole operator contributions to the photon energy spectrum in anti-B -> X(s) gamma at O(alpha(s)^2)
We compute the O(\alpha_s^2) contributions to the photon energy spectrum of
the inclusive decay \bar{B} -> X_s \gamma associated with the magnetic penguin
operator O_7. They are an essential part of the ongoing NNLO calculation of
this important decay. We use two different methods to evaluate the master
integrals, one based on the differential equation approach and the other on
sector decomposition, leading to identical results which in turn agree with
those of a recent independent calculation by Melnikov and Mitov. We study the
numerical relevance of this set of NNLO contributions in the photon energy
spectrum and discuss the change of bottom quark mass scheme.Comment: 18 pages, uses axodraw.st
Hepta-Cuts of Two-Loop Scattering Amplitudes
We present a method for the computation of hepta-cuts of two loop scattering
amplitudes. Four dimensional unitarity cuts are used to factorise the integrand
onto the product of six tree-level amplitudes evaluated at complex momentum
values. Using Gram matrix constraints we derive a general parameterisation of
the integrand which can be computed using polynomial fitting techniques. The
resulting expression is further reduced to master integrals using conventional
integration by parts methods. We consider both planar and non-planar topologies
for 2 to 2 scattering processes and apply the method to compute hepta-cut
contributions to gluon-gluon scattering in Yang-Mills theory with adjoint
fermions and scalars.Comment: 37 pages, 6 figures. version 2 : minor updates, published versio
Re imagining the family
This exegesis will address the following questions: How can the disruptions caused specifically by one familyâs experience of the margin that is migration and the margin that is death be represented in art and how might these art works allow for the possibility of resonance for the viewer? How are margins defined and how might they help to provide a theoretical underpinning for this research? How does the medium used, influence the understanding? This work is informed and underpinned by the writings of important contemporary cultural theory of the margins as described by Homi K. Bhabha, (Rutherford,1990) but also by Foucault whose discussion in Of Other Spaces (1967) involved a new concept of spatial analytics. Foucault identified the space of the margins, which he called âheterotopiasâ and claimed that once identified within a particular society, those margins would reveal who we are as a society. I propose an experiential investigation of those times or situations where we find ourselves in the margins. The resulting videos are about the margins that I have experienced, of migration, death and the way in which, through video, this particular family is re imagined. I also propose that, while the works come from a personal archive, they will have resonance in the public realm, precisely through that particularity
- XSummer - Transcendental Functions and Symbolic Summation in Form
Harmonic sums and their generalizations are extremely useful in the
evaluation of higher-order perturbative corrections in quantum field theory. Of
particular interest have been the so-called nested sums,where the harmonic sums
and their generalizations appear as building blocks, originating for example
from the expansion of generalized hypergeometric functions around integer
values of the parameters. In this Letter we discuss the implementation of
several algorithms to solve these sums by algebraic means, using the computer
algebra system Form.Comment: 21 pages, 1 figure, Late
On the Numerical Evaluation of Loop Integrals With Mellin-Barnes Representations
An improved method is presented for the numerical evaluation of multi-loop
integrals in dimensional regularization. The technique is based on
Mellin-Barnes representations, which have been used earlier to develop
algorithms for the extraction of ultraviolet and infrared divergencies. The
coefficients of these singularities and the non-singular part can be integrated
numerically. However, the numerical integration often does not converge for
diagrams with massive propagators and physical branch cuts. In this work,
several steps are proposed which substantially improve the behavior of the
numerical integrals. The efficacy of the method is demonstrated by calculating
several two-loop examples, some of which have not been known before.Comment: 13 pp. LaTe
High-precision QCD at hadron colliders: electroweak gauge boson rapidity distributions at NNLO
We compute the rapidity distributions of W and Z bosons produced at the
Tevatron and the LHC through next-to-next-to leading order in QCD. Our results
demonstrate remarkable stability with respect to variations of the
factorization and renormalization scales for all values of rapidity accessible
in current and future experiments. These processes are therefore
``gold-plated'': current theoretical knowledge yields QCD predictions accurate
to better than one percent. These results strengthen the proposal to use W and
Z production to determine parton-parton luminosities and constrain parton
distribution functions at the LHC. For example, LHC data should easily be able
to distinguish the central parton distribution fit obtained by MRST from that
obtained by Alekhin.Comment: 47 pages, 17 figures. Minor typos, 1 reference correcte
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