7,986 research outputs found
Dynkin operators and renormalization group actions in pQFT
Renormalization techniques in perturbative quantum field theory were known,
from their inception, to have a strong combinatorial content emphasized, among
others, by Zimmermann's celebrated forest formula. The present article reports
on recent advances on the subject, featuring the role played by the Dynkin
operators (actually their extension to the Hopf algebraic setting) at two
crucial levels of renormalization, namely the Bogolioubov recursion and the
renormalization group (RG) equations. For that purpose, an iterated integrals
toy model is introduced to emphasize how the operators appear naturally in the
setting of renormalization group analysis. The toy model, in spite of its
simplicity, captures many key features of recent approaches to RG equations in
pQFT, including the construction of a universal Galois group for quantum field
theories
Confluent Orthogonal Drawings of Syntax Diagrams
We provide a pipeline for generating syntax diagrams (also called railroad
diagrams) from context free grammars. Syntax diagrams are a graphical
representation of a context free language, which we formalize abstractly as a
set of mutually recursive nondeterministic finite automata and draw by
combining elements from the confluent drawing, layered drawing, and smooth
orthogonal drawing styles. Within our pipeline we introduce several heuristics
that modify the grammar but preserve the language, improving the aesthetics of
the final drawing.Comment: GD 201
The diamond rule for multi-loop Feynman diagrams
An important aspect of improving perturbative predictions in high energy
physics is efficiently reducing dimensionally regularised Feynman integrals
through integration by parts (IBP) relations. The well-known triangle rule has
been used to achieve simple reduction schemes. In this work we introduce an
extensible, multi-loop version of the triangle rule, which we refer to as the
diamond rule. Such a structure appears frequently in higher-loop calculations.
We derive an explicit solution for the recursion, which prevents spurious poles
in intermediate steps of the computations. Applications for massless propagator
type diagrams at three, four, and five loops are discussed
Exact results for an asymmetric annihilation process with open boundaries
We consider a nonequilibrium reaction-diffusion model on a finite one
dimensional lattice with bulk and boundary dynamics inspired by Glauber
dynamics of the Ising model. We show that the model has a rich algebraic
structure that we use to calculate its properties. In particular, we show that
the Markov dynamics for a system of a given size can be embedded in the
dynamics of systems of higher sizes. This remark leads us to devise a technique
we call the transfer matrix Ansatz that allows us to determine the steady state
distribution and correlation functions. Furthermore, we show that the disorder
variables satisfy very simple properties and we give a conjecture for the
characteristic polynomial of Markov matrices. Lastly, we compare the transfer
matrix Ansatz used here with the matrix product representation of the steady
state of one-dimensional stochastic models.Comment: 18 page
On the Relative Strength of Pebbling and Resolution
The last decade has seen a revival of interest in pebble games in the context
of proof complexity. Pebbling has proven a useful tool for studying
resolution-based proof systems when comparing the strength of different
subsystems, showing bounds on proof space, and establishing size-space
trade-offs. The typical approach has been to encode the pebble game played on a
graph as a CNF formula and then argue that proofs of this formula must inherit
(various aspects of) the pebbling properties of the underlying graph.
Unfortunately, the reductions used here are not tight. To simulate resolution
proofs by pebblings, the full strength of nondeterministic black-white pebbling
is needed, whereas resolution is only known to be able to simulate
deterministic black pebbling. To obtain strong results, one therefore needs to
find specific graph families which either have essentially the same properties
for black and black-white pebbling (not at all true in general) or which admit
simulations of black-white pebblings in resolution. This paper contributes to
both these approaches. First, we design a restricted form of black-white
pebbling that can be simulated in resolution and show that there are graph
families for which such restricted pebblings can be asymptotically better than
black pebblings. This proves that, perhaps somewhat unexpectedly, resolution
can strictly beat black-only pebbling, and in particular that the space lower
bounds on pebbling formulas in [Ben-Sasson and Nordstrom 2008] are tight.
Second, we present a versatile parametrized graph family with essentially the
same properties for black and black-white pebbling, which gives sharp
simultaneous trade-offs for black and black-white pebbling for various
parameter settings. Both of our contributions have been instrumental in
obtaining the time-space trade-off results for resolution-based proof systems
in [Ben-Sasson and Nordstrom 2009].Comment: Full-length version of paper to appear in Proceedings of the 25th
Annual IEEE Conference on Computational Complexity (CCC '10), June 201
Data-Oblivious Stream Productivity
We are concerned with demonstrating productivity of specifications of
infinite streams of data, based on orthogonal rewrite rules. In general, this
property is undecidable, but for restricted formats computable sufficient
conditions can be obtained. The usual analysis disregards the identity of data,
thus leading to approaches that we call data-oblivious. We present a method
that is provably optimal among all such data-oblivious approaches. This means
that in order to improve on the algorithm in this paper one has to proceed in a
data-aware fashion
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