287 research outputs found
Parallel integer relation detection: techniques and applications
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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.Comment: 5 pages, 1 figure, presented at "Loops and Legs in Quantum Field
Theory 2010", Woerlitz, Germany, April 201
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
Central Binomial Sums, Multiple Clausen Values and Zeta Values
We find and prove relationships between Riemann zeta values and central
binomial sums. We also investigate alternating binomial sums (also called
Ap\'ery sums). The study of non-alternating sums leads to an investigation of
different types of sums which we call multiple Clausen values. The study of
alternating sums leads to a tower of experimental results involving
polylogarithms in the golden ratio. In the non-alternating case, there is a
strong connection to polylogarithms of the sixth root of unity, encountered in
the 3-loop Feynman diagrams of {\tt hep-th/9803091} and subsequently in
hep-ph/9910223, hep-ph/9910224, cond-mat/9911452 and hep-th/0004010.Comment: 17 pages, LaTeX, with use of amsmath and amssymb packages, to appear
in Journal of Experimental Mathematic
Hopf Algebra Primitives in Perturbation Quantum Field Theory
The analysis of the combinatorics resulting from the perturbative expansion
of the transition amplitude in quantum field theories, and the relation of this
expansion to the Hausdorff series leads naturally to consider an infinite
dimensional Lie subalgebra and the corresponding enveloping Hopf algebra, to
which the elements of this series are associated. We show that in the context
of these structures the power sum symmetric functionals of the perturbative
expansion are Hopf primitives and that they are given by linear combinations of
Hall polynomials, or diagrammatically by Hall trees. We show that each Hall
tree corresponds to sums of Feynman diagrams each with the same number of
vertices, external legs and loops. In addition, since the Lie subalgebra admits
a derivation endomorphism, we also show that with respect to it these
primitives are cyclic vectors generated by the free propagator, and thus
provide a recursion relation by means of which the (n+1)-vertex connected Green
functions can be derived systematically from the n-vertex ones.Comment: 21 pages, accepted for publication in J.Geom.and Phy
Metabolomics reveals mouse plasma metabolite responses to acute exercise and effects of disrupting AMPK-glycogen interactions
Introduction: The AMP-activated protein kinase (AMPK) is a master regulator of energy homeostasis that becomes activated by exercise and binds glycogen, an important energy store required to meet exercise-induced energy demands. Disruption of AMPK-glycogen interactions in mice reduces exercise capacity and impairs whole-body metabolism. However, the mechanisms underlying these phenotypic effects at rest and following exercise are unknown. Furthermore, the plasma metabolite responses to an acute exercise challenge in mice remain largely uncharacterized. Methods : Plasma samples were collected from wild type (WT) and AMPK double knock-in (DKI) mice with disrupted AMPK-glycogen binding at rest and following 30-min submaximal treadmill running. An untargeted metabolomics approach was utilized to determine the breadth of plasma metabolite changes occurring in response to acute exercise and the effects of disrupting AMPK-glycogen binding. Results: Relative to WT mice, DKI mice had reduced maximal running speed (p \u3c 0.0001) concomitant with increased body mass (p \u3c 0.01) and adiposity (p \u3c 0.001). A total of 83 plasma metabolites were identified/annotated, with 17 metabolites significantly different (p \u3c 0.05; FDR \u3c 0.1) in exercised (↑ 6; ↓ 11) versus rested mice, including amino acids, acylcarnitines and steroid hormones. Pantothenic acid was reduced in DKI mice versus WT. Distinct plasma metabolite profiles were observed between the rest and exercise conditions and between WT and DKI mice at rest, while metabolite profiles of both genotypes converged following exercise. These differences in metabolite profiles were primarily explained by exercise-associated increases in acylcarnitines and steroid hormones as well as decreases in amino acids and derivatives following exercise. DKI plasma showed greater decreases in amino acids following exercise versus WT. Conclusion : This is the first study to map mouse plasma metabolomic changes following a bout of acute exercise in WT mice and the effects of disrupting AMPK-glycogen interactions in DKI mice. Untargeted metabolomics revealed alterations in metabolite profiles between rested and exercised mice in both genotypes, and between genotypes at rest. This study has uncovered known and previously unreported plasma metabolite responses to acute exercise in WT mice, as well as greater decreases in amino acids following exercise in DKI plasma. Reduced pantothenic acid levels may contribute to differences in fuel utilization in DKI mice
The Sextet Arcs: a Strongly Lensed Lyman Break Galaxy in the ACS Spectroscopic Galaxy Survey towards Abell 1689
We present results of the HST Advanced Camera for Surveys spectroscopic
ground-based redshift survey in the field of A1689. We measure 98 redshifts,
increasing the number of spectroscopically confirmed objects by sixfold. We
present two spectra from this catalog of the Sextet Arcs, images which arise
from a strongly-lensed Lyman Break Galaxy (LBG) at a redshift of z=3.038.
Gravitational lensing by the cluster magnifies its flux by a factor of ~16 and
produces six separate images with a total r-band magnitude of r_625=21.7. The
two spectra, each of which represents emission from different regions of the
LBG, show H I and interstellar metal absorption lines at the systemic redshift.
Significant variations are seen in Ly-alpha profile across a single galaxy,
ranging from strong absorption to a combination of emission plus absorption. A
spectrum of a third image close to the brightest arc shows Ly-alpha emission at
the same redshift as the LBG, arising from either another spatially distinct
region of the galaxy, or from a companion galaxy close to the LBG. Taken as a
group, the Ly-alpha equivalent width in these three spectra decreases with
increasing equivalent width of the strongest interstellar absorption lines. We
discuss how these variations can be used to understand the physical conditions
in the LBG. Intrinsically, this LBG is faint, ~0.1L*, and forming stars at a
modest rate, ~4 solar masses per year. We also detect absorption line systems
toward the Sextet Arcs at z=2.873 and z=2.534. The latter system is seen across
two of our spectra.Comment: Accepted for publication in Ap
New Constraints on the Complex Mass Substructure in Abell 1689 from Gravitational Flexion
In a recent publication, the flexion aperture mass statistic was found to
provide a robust and effective method by which substructure in galaxy clusters
might be mapped. Moreover, we suggested that the masses and mass profile of
structures might be constrained using this method. In this paper, we apply the
flexion aperture mass technique to HST ACS images of Abell 1689. We demonstrate
that the flexion aperture mass statistic is sensitive to small-scale structures
in the central region of the cluster. While the central potential is not
constrained by our method, due largely to missing data in the central
0.5 of the cluster, we are able to place constraints on the masses and
mass profiles of prominent substructures. We identify 4 separate mass peaks,
and use the peak aperture mass signal and zero signal radius in each case to
constrain the masses and mass profiles of these substructures. The three most
massive peaks exhibit complex small-scale structure, and the masses indicated
by the flexion aperture mass statistic suggest that these three peaks represent
the dominant substructure component of the cluster (). Their complex structure indicates that the cluster --
far from being relaxed -- may have recently undergone a merger. The smaller,
subsidiary peak is located coincident with a group of galaxies within the
cluster, with mass . These results are in
excellent agreement with previous substructure studies of this cluster.Comment: 18 pages, 10 figures, MNRAS accepted (7 Dec 2010
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