4,787 research outputs found
Massive 3-loop Feynman diagrams reducible to SC* primitives of algebras of the sixth root of unity
In each of the 10 cases with propagators of unit or zero mass, the finite
part of the scalar 3-loop tetrahedral vacuum diagram is reduced to 4-letter
words in the 7-letter alphabet of the 1-forms and , where is the sixth root of unity. Three diagrams
yield only . In two cases combines
with the Euler-Zagier sum ; in three cases it combines with the square of Clausen's
. The case
with 6 masses involves no further constant; with 5 masses a
Deligne-Euler-Zagier sum appears: . The previously unidentified term in the
3-loop rho-parameter of the standard model is merely . The remarkable simplicity of these results stems
from two shuffle algebras: one for nested sums; the other for iterated
integrals. Each diagram evaluates to 10 000 digits in seconds, because the
primitive words are transformable to exponentially convergent single sums, as
recently shown for and , familiar in QCD. Those are
SC constants, whose base of super-fast computation is 2. Mass involves
the novel base-3 set SC. All 10 diagrams reduce to SCSC constants and their products. Only the 6-mass case entails both bases.Comment: 41 pages, LaTe
Hopf algebras and Markov chains: Two examples and a theory
The operation of squaring (coproduct followed by product) in a combinatorial
Hopf algebra is shown to induce a Markov chain in natural bases. Chains
constructed in this way include widely studied methods of card shuffling, a
natural "rock-breaking" process, and Markov chains on simplicial complexes.
Many of these chains can be explictly diagonalized using the primitive elements
of the algebra and the combinatorics of the free Lie algebra. For card
shuffling, this gives an explicit description of the eigenvectors. For
rock-breaking, an explicit description of the quasi-stationary distribution and
sharp rates to absorption follow.Comment: 51 pages, 17 figures. (Typographical errors corrected. Further fixes
will only appear on the version on Amy Pang's website, the arXiv version will
not be updated.
Flows and stochastic Taylor series in Ito calculus
For stochastic systems driven by continuous semimartingales an explicit
formula for the logarithm of the Ito flow map is given. A similar formula is
also obtained for solutions of linear matrix-valued SDEs driven by arbitrary
semimartingales. The computation relies on the lift to quasi-shuffle algebras
of formulas involving products of Ito integrals of semimartingales. Whereas the
Chen-Strichartz formula computing the logarithm of the Stratonovich flow map is
classically expanded as a formal sum indexed by permutations, the analogous
formula in Ito calculus is naturally indexed by surjections. This reflects the
change of algebraic background involved in the transition between the two
integration theories
The algebra of cell-zeta values
In this paper, we introduce cell-forms on , which are
top-dimensional differential forms diverging along the boundary of exactly one
cell (connected component) of the real moduli space
. We show that the cell-forms generate the
top-dimensional cohomology group of , so that there is a
natural duality between cells and cell-forms. In the heart of the paper, we
determine an explicit basis for the subspace of differential forms which
converge along a given cell . The elements of this basis are called
insertion forms, their integrals over are real numbers, called cell-zeta
values, which generate a -algebra called the cell-zeta algebra. By
a result of F. Brown, the cell-zeta algebra is equal to the algebra of
multizeta values. The cell-zeta values satisfy a family of simple quadratic
relations coming from the geometry of moduli spaces, which leads to a natural
definition of a formal version of the cell-zeta algebra, conjecturally
isomorphic to the formal multizeta algebra defined by the much-studied double
shuffle relations
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