40 research outputs found
Non-Perturbative Asymptotic Improvement of Perturbation Theory and Mellin-Barnes Representation
Using a method mixing Mellin-Barnes representation and Borel resummation we
show how to obtain hyperasymptotic expansions from the (divergent) formal power
series which follow from the perturbative evaluation of arbitrary "-point"
functions for the simple case of zero-dimensional field theory. This
hyperasymptotic improvement appears from an iterative procedure, based on
inverse factorial expansions, and gives birth to interwoven non-perturbative
partial sums whose coefficients are related to the perturbative ones by an
interesting resurgence phenomenon. It is a non-perturbative improvement in the
sense that, for some optimal truncations of the partial sums, the remainder at
a given hyperasymptotic level is exponentially suppressed compared to the
remainder at the preceding hyperasymptotic level. The Mellin-Barnes
representation allows our results to be automatically valid for a wide range of
the phase of the complex coupling constant, including Stokes lines. A numerical
analysis is performed to emphasize the improved accuracy that this method
allows to reach compared to the usual perturbative approach, and the importance
of hyperasymptotic optimal truncation schemes.Comment: v2: one reference added, one paragraph added in the conclusions,
small changes in the text, corrected typos; v3: published versio
Asymptotic expansions of Feynman diagrams and the Mellin-Barnes representation
In this talk, we describe part of our recent work \cite{FGdeR05} (see also
\cite{F05,G05}) that gives new results in the context of asymptotic expansions
of Feynman diagrams using the Mellin-Barnes representation.Comment: Talk given at the High-Energy Physics International
Conference on Quantum Chromodynamics, 4-8 July (2005), Montpellier (France
On Ruby's solid angle formula and some of its generalizations
Using the Mellin-Barnes representation, we show that Ruby's solid angle
formula and some of its generalizations may be expressed in a compact way in
terms of the Appell F4 and Lauricella Fc functions.Comment: 10 pages, accepted in Nucl. Instr. and Meth. in Phys. Res.
The L-R Correlator and its Chiral Condensates in the MHA and MHA+V' Approximations to Large-Nc QCD
In this talk, we describe part of a recent work on the correlation function of a V-A current with a V+A current in the framework of QCD in the limit of a large number of colours Nc. The discussion takes place within two successive approximations of this theory, called MHA and MHA+V'. Results concerning the evaluation of chiral condensates of dimension six and eight, as well as matrix elements of the Q7 and Q8 electroweak penguin operators, are given
Geometrical methods for the analytic evaluation of multiple Mellin-Barnes integrals
Two recently developed techniques of analytic evaluation of multifold
Mellin-Barnes (MB) integrals are presented. Both approaches rest on the
definition of geometrical objets conveniently associated with the MB
integrands, which can then be used along with multivariate residues analysis to
derive series representations of the MB integrals. The first method is based on
introducing conic hulls and considering specific intersections of the latter,
while the second one rests on point configurations and their regular
triangulations. After a brief description of both methods, which have been
automatized in the MBConicHulls.wl Mathematica package, we review some of their
applications. In particular, we show how the conic hulls method was used to
obtain the first analytic calculation of complicated Feynman integrals, such as
the massless off-shell conformal hexagon and double-box. We then show that the
triangulation method is even more efficient, as it allows one to compute these
nontrivial objects and harder ones in a much faster way.Comment: 12 pages, 3 figures, presented by S. Friot at the XLV International
Conference of Theoretical Physics "Matter to the Deepest", Warsaw, Poland,
17-22 September 2023 (extended version of the contribution to the proceedings
published in Acta Physica Polonica B
Multiple Mellin-Barnes integrals and triangulations of point configurations
We present a novel technique for the analytic evaluation of multifold
Mellin-Barnes (MB) integrals, which commonly appear in physics, as for instance
in the calculations of multi-loop multi-scale Feynman integrals. Our approach
is based on triangulating a set of points which can be assigned to a given MB
integral, and yields the final analytic results in terms of linear combinations
of multiple series, each triangulation allowing the derivation of one of these
combinations. When this technique is applied to the computation of Feynman
integrals, the involved series are of the (multivariable) hypergeometric type.
We implement our method in the Mathematica package MBConicHulls.wl, an already
existing software dedicated to the analytic evaluation of multiple MB
integrals, based on a recently developed computational approach using
intersections of conic hulls. The triangulation method is remarkably faster
than the conic hulls approach and can thus be used for the calculation of
higher-fold MB integrals as we show here by computing triangulations for highly
complicated objects such as the off-shell massless scalar one-loop 15-point
Feynman integral whose MB representation has 104 folds. As other applications
we show how this technique can provide new results for the off-shell massless
conformal hexagon and double box Feynman integrals, as well as for the hard
diagram of the two loop hexagon Wilson loop.Comment: 16 pages, 4 figures, code repository
https://github.com/SumitBanikGit/MBConicHull
Constant terms in threshold resummation and the quark form factor
We verify to order alpha_s^4 two previously conjectured relations, valid in
four dimensions, between constant terms in threshold resummation (for Deep
Inelastic Scattering and the Drell-Yan process) and the second logarithmic
derivative of the massless quark form factor. The same relations are checked to
all orders in the large beta_0 limit; as a byproduct a dispersive
representation of the form factor is obtained. These relations allow to compute
in a symmetrical way the three-loop resummation coefficients B_3 and D_3 in
terms of the three-loop contributions to the virtual diagonal splitting
function and to the quark form factor, confirming results obtained in the
literature.Comment: 39 pages, no figure; version 2: same content, but improved
presentation, with a new section devoted to the variety of resummation
procedures; version 3: journal version, where a remark about the all orders
validity of the conjecture in the DIS case is reporte
Asymptotics of Feynman Diagrams and The Mellin-Barnes Representation
It is shown that the integral representation of Feynman diagrams in terms of
the traditional Feynman parameters, when combined with properties of the
Mellin--Barnes representation and the so called {\it converse mapping theorem},
provide a very simple and efficient way to obtain the analytic asymptotic
behaviours in both the large and small ratios of mass scales.Comment: References added. This is the version published in Physics Letters