39,459 research outputs found
Global Poles of the Two-Loop Six-Point N=4 SYM integrand
Recently, a recursion relation has been developed, generating the
four-dimensional integrand of the amplitudes of N=4 supersymmetric Yang-Mills
theory for any number of loops and legs. In this paper, I provide a comparison
of the prediction for the two-loop six-point maximally helicity-violating (MHV)
integrand against the result obtained by use of the leading singularity method.
The comparison is performed numerically for a large number of randomly selected
momenta and in all cases finds agreement between the two results to high
numerical accuracy.Comment: 32+34 pages, 16 figures, 1 notebook; minor typos corrected, ref.
added; version accepted by Phys. Rev.
An Annotated Checklist of Scarab Beetles (Coleoptera: Scarabaeidae) from Northeastern Iowa
A survey of scarab beetles (Coleoptera: Scarabaeidae) was conducted during 2009 in the geographically distinct area of Winneshiek and Allamakee counties in extreme Northeast Iowa. Four plant communities distributed among 10 locations, including tallgrass prairie, mixed grassland and forest, oak-hickory forest, and pasture were sampled during 2009 using black light traps, banana- beer traps, rodent burrow pitfalls, manure-baited pitfalls, and gleaning. Additionally, previous specimen records were examined. Forty-nine scarab species were documented for Winneshiek and Allamakee counties, including five species not previously reported in Iowa. Mixed grassland and forest habitat contained the greatest scarab species richness (n=31); black light trapping yielded the greatest number of individual beetles and collected the most species
A dynamical and kinematical model of the Galactic stellar halo and possible implications for galaxy formation scenarios
We re-analyse the kinematics of the system of blue horizontal branch field
(BHBF) stars in the Galactic halo (in particular the outer halo), fitting the
kinematics with the model of radial and tangential velocity dispersions in the
halo as a function of galactocentric distance r proposed by Sommer-Larsen,
Flynn & Christensen (1994), using a much larger sample (almost 700) of BHBF
stars. The basic result is that the character of the stellar halo velocity
ellipsoid changes markedly from radial anisotropy at the sun to tangential
anisotropy in the outer parts of the Galactic halo (r greater than approx 20
kpc). Specifically, the radial component of the stellar halo's velocity
ellipsoid decreases fairly rapidly beyond the solar circle, from approx 140 +/-
10 km/s at the sun, to an asymptotic value of 89 +/- 19 km/s at large r. The
rapid decrease in the radial velocity dispersion is matched by an increase in
the tangential velocity dispersion, with increasing r.
Our results may indicate that the Galaxy formed hierarchically (partly or
fully) through merging of smaller subsystems - the 'bottom-up' galaxy formation
scenario, which for quite a while has been favoured by most theorists and
recently also has been given some observational credibility by HST observations
of a potential group of small galaxies, at high redshift, possibly in the
process of merging to a larger galaxy (Pascarelle et al 1996).Comment: Latex, 16 pages. 2 postscript figures. Submitted to the Astrophysical
Journal. also available at http://astro.utu.fi/~cflynn/outerhalo.htm
The galaxy counterpart of the high-metallicity and 16 kpc impact parameter DLA towards Q0918+1636 - a challenge to galaxy formation models?
The quasar Q0918+1636 (z=3.07) has an intervening high-metallicity Damped
Lyman-alpha Absorber (DLA) along the line of sight, at a redshift of z=2.58.
The DLA is located at a large impact parameter of 16.2 kpc, and has an almost
solar metallicity. It is shown, that a novel type of cosmological galaxy
formation models, invoking a new SNII feedback prescription, the Haardt & Madau
(2012) UVB field and explicit treatment of UVB self-shielding, can reproduce
the observed characteristics of the DLA. UV radiation from young stellar
populations in the galaxy, in particular in the photon energy range 10.36-13.61
eV (relating to Sulfur II abundance), are also considered in the analysis. It
is found that a) for L~L* galaxies (at z=2.58), about 10% of the sight-lines
through the galaxies at impact parameter 16.2 kpc will display a Sulfur II
column density N(SII) 10 cm (the observed value for the
DLA), and b) considering only cases where a near-solar metallicity will be
detected at 16.2 kpc impact parameter, the probability distribution of galaxy
SFR peaks near the value observed for the DLA galaxy counterpart of ~27
Msun/yr. It is argued, that the bulk of the alpha-elements, like Sulfur, traced
by the high metal column density, b=16.2 kpc absorption lines, were produced by
evolving young stars in the inner galaxy, and later transported outward by
galactic winds.Comment: 22 pages, 24 figures, MNRAS in pres
Integration-by-parts reductions from unitarity cuts and algebraic geometry
We show that the integration-by-parts reductions of various two-loop integral
topologies can be efficiently obtained by applying unitarity cuts to a specific
set of subgraphs and solving associated polynomial (syzygy) equations.Comment: 5 pages, 1 figure; a Mathematica package implementing the algorithm
is attached as an ancillary file; v3: minor change
Globular Clusters in NGC 4365: New K-band Imaging and a Reassessment of the Case for Intermediate-age Clusters
We study the globular cluster (GC) system of the Virgo giant elliptical
galaxy NGC 4365, using new wide-field VIK imaging. The GC colour distribution
has (at least) two peaks, but the colours of the red GCs appear more strongly
weighted towards intermediate colours compared to most other large ellipticals
and the integrated galaxy light. The intermediate-color/red peak may itself be
composed of two sub-populations, with clusters of intermediate colours more
concentrated towards the centre of the galaxy than both the blue and red GCs.
Nearly all intermediate-colour and red GCs in our sample show an offset towards
red V-K and/or blue V-I colours compared to SSP models for old ages in a
(V-K,V-I) diagram. This has in the past been interpreted as evidence for
intermediate ages. We also combine our VIK data with previously published
spectroscopy. The differences between observed and model colour-metallicity
relations are consistent with the offsets observed in the two-colour diagram,
with the metal-rich GCs being too red (by about 0.2 mag) in V-K and too blue
(by about 0.05 mag) in V-I compared to the models at a given metallicity. These
offsets cannot easily be explained as an effect of younger ages. We conclude
that, while intermediate GC ages cannot be definitively ruled out, an
alternative scenario is more likely whereby all the GCs are old but the
relative number of intermediate-metallicity GCs is greater than typical for
giant ellipticals. The main obstacle to reaching a definitive conclusion is the
lack of robust calibrations of integrated spectral and photometric properties
for stellar populations with near-solar metallicity. In any case, it is
puzzling that the intermediate-colour GCs in NGC 4365 are not accompanied by a
corresponding shift of the integrated galaxy light towards bluer colours.Comment: 23 pages, including 20 figures and 5 tables. Accepted for publication
in A&
MultivariateResidues - a Mathematica package for computing multivariate residues
We present the Mathematica package MultivariateResidues, which allows for the
efficient evaluation of multivariate residues based on methods from
computational algebraic geometry. Multivariate residues appear in several
contexts of scattering amplitude computations. Examples include applications to
the extraction of master integral coefficients from maximal unitarity cuts, the
construction of canonical bases of loop integrals and the construction of tree
amplitudes from scattering equations.Comment: 7 pages, 2 figures, contribution to the proceedings of the 13th
International Symposium on Radiative Corrections (RADCOR 2017
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