arXiv subjects

David J. Broadhurst

Publications and source records attributed to David J. Broadhurst.

5 recordsLinked to original sources

arXiv2016

Massless scalar Feynman diagrams: five loops and beyond

Several powerful techniques for evaluating massless scalar Feynman diagrams are developed, viz: the solution of recurrence relations to evaluate diagrams with arbitrary numbers of loops in $n=4-2ω$ dimensions; the discovery and use of symmetry properties to restrict and compute Taylor series in $ω$; the reduction of triple sums over Chebyshev polynomials to products of Riemann zeta functions; the exploitation of conformal invariance to avoid four-dimensional Racah coefficients. As an example of the power of these techniques we evaluate all of the 216 diagrams, with 5 loops or less, which give finite contributions of order $1/k^2$ or $1/k^4$ to a propagator of momentum $k$ in massless four-dimensional scalar field theories. Remarkably, only 5 basic numbers are encountered: $ζ(3)$, $ζ(5)$, $ζ(7)$, $ζ(9)$ and the value of the most symmetrical diagram, which is calculated to 14 significant figures. It is conceivable that these are the only irrationals appearing in 6-loop beta functions. En route to these results we uncover and only partially explain many remarkable relations between diagrams.

hep-th↗

arXiv2010

Exponential suppression with four legs and an infinity of loops

The L-loop 4-point ladder diagram of massless phi^3 theory is finite when all 4 legs are off-shell and is given in terms of polylogarithms with orders ranging from L to 2L. We obtain the exact solution of the linear Dyson-Schwinger equation that sums these ladder diagrams and show that this sum vanishes exponentially fast at strong coupling.

hep-th↗

arXiv1999

Special Values of Multiple Polylogarithms

Historically, the polylogarithm has attracted specialists and non-specialists alike with its lovely evaluations. Much the same can be said for Euler sums (or multiple harmonic sums), which, within the past decade, have arisen in combinatorics, knot theory and high-energy physics. More recently, we have been forced to consider multidimensional extensions encompassing the classical polylogarithm, Euler sums, and the Riemann zeta function. Here, we provide a general framework within which previously isolated results can now be properly understood. Applying the theory developed herein, we prove several previously conjectured evaluations, including an intriguing conjecture of Don Zagier.

math.CA↗

arXiv1999

A seventeenth-order polylogarithm ladder

Cohen, Lewin and Zagier found four ladders that entail the polylogarithms ${\rm Li}_n(α_1^{-k}):=\sum_{r>0}α_1^{-k r}/r^n$ at order $n=16$, with indices $k\le360$, and $α_1$ being the smallest known Salem number, i.e. the larger real root of Lehmer's celebrated polynomial $α^{10}+α^9-α^7-α^6-α^5-α^4-α^3+α+1$, with the smallest known non-trivial Mahler measure. By adjoining the index $k=630$, we generate a fifth ladder at order 16 and a ladder at order 17 that we presume to be unique. This empirical integer relation, between elements of $\{{\rm Li}_{17}(α_1^{-k})\mid0\le k\le630\}$ and $\{π^{2j}(\logα_1)^{17-2j}\mid 0\le j\le8\}$, entails 125 constants, multiplied by integers with nearly 300 digits. It has been checked to more than 59,000 decimal digits. Among the ladders that we found in other number fields, the longest has order 13 and index 294. It is based on $α^{10}-α^6-α^5-α^4+1$, which gives the sole Salem number $α<1.3$ with degree $d<12$ for which $α^{1/2}+α^{-1/2}$ fails to be the largest eigenvalue of the adjacency matrix of a graph.

math.CA↗

arXiv1999

Parallel Integer Relation Detection: Techniques and Applications

Let $\{x_1, x_2, ..., x_n\}$ be a vector of real numbers. An integer relation algorithm is a computational scheme to find the $n$ integers $a_k$, if they exist, such that $a_1 x_1 + a_2 x_2 + ... + a_n x_n= 0$. In the past few years, integer relation algorithms have been utilized to discover new results in mathematics and physics. Existing programs for this purpose require very large amounts of computer time, due in part to the requirement for multiprecision arithmetic, yet are poorly suited for parallel processing. This paper presents a new integer relation algorithm designed for parallel computer systems, but as a bonus it also gives superior results on single processor systems. Single- and multi-level implementations of this algorithm are described, together with performance results on a parallel computer system. Several applications of these programs are discussed, including some new results in number theory, quantum field theory and chaos theory.

math.NA↗