1,444 research outputs found
Dimensional renormalization: ladders to rainbows
Renormalization factors are most easily extracted by going to the massless
limit of the quantum field theory and retaining only a single momentum scale.
We derive factors and renormalized Green functions to all orders in
perturbation theory for rainbow graphs and vertex (or scattering diagrams) at
zero momentum transfer, in the context of dimensional renormalization, and we
prove that the correct anomalous dimensions for those processes emerge in the
limit D -> 4.Comment: RevTeX, no figure
Lectures on multiloop calculations
I discuss methods of calculation of propagator diagrams (massless, those of
Heavy Quark Effective Theory, and massive on-shell diagrams) up to 3 loops.
Integration-by-parts recurrence relations are used to reduce them to linear
combinations of basis integrals. Non-trivial basis integrals have to be
calculated by some other method, e.g., using Gegenbauer polynomial technique.
Many of them are expressed via hypergeometric functions; in the massless and
HQET cases, their indices tend to integers at . I discuss the
algorithm of their expansion in , in terms of multiple
values. These lectures were given at Calc-03 school, Dubna, 14--20 June 2003.Comment: 52 pages, 49 figures. Lectures at Calc-03 school, Dubna, 14--20 June
2003. v2: 2 references added, minor typos corrected. v3: methodical
improvements, typo in eq. (3.19) corrected, 2 references adde
A Free-Form Lensing Grid Solution for A1689 with New Mutiple Images
Hubble Space Telescope imaging of the galaxy cluster Abell 1689 has revealed
an exceptional number of strongly lensed multiply-imaged galaxies, including
high-redshift candidates. Previous studies have used this data to obtain the
most detailed dark matter reconstructions of any galaxy cluster to date,
resolving substructures ~25 kpc across. We examine Abell 1689 (hereafter,
A1689) non-parametrically, combining strongly lensed images and weak
distortions from wider field Subaru imaging, and we incorporate member galaxies
to improve the lens solution. Strongly lensed galaxies are often locally
affected by member galaxies, however, these perturbations cannot be recovered
in grid based reconstructions because the lensing information is too sparse to
resolve member galaxies. By adding luminosity-scaled member galaxy deflections
to our smooth grid we can derive meaningful solutions with sufficient accuracy
to permit the identification of our own strongly lensed images, so our model
becomes self consistent. We identify 11 new multiply lensed system candidates
and clarify previously ambiguous cases, in the deepest optical and NIR data to
date from Hubble and Subaru. Our improved spatial resolution brings up new
features not seen when the weak and strong lensing effects are used separately,
including clumps and filamentary dark matter around the main halo. Our
treatment means we can obtain an objective mass ratio between the cluster and
galaxy components, for examining the extent of tidal stripping of the luminous
member galaxies. We find a typical mass-to-light ratios of M/L_B = 21 inside
the r<1 arcminute region that drops to M/L_B = 17 inside the r<40 arcsecond
region. Our model independence means we can objectively evaluate the
competitiveness of stacking cluster lenses for defining the geometric
lensing-distance-redshift relation in a model independent way.Comment: 23 pages with 25 figures Replced with MNRAS submitted version. Some
figures have been corrected and minor text edit
Young Red Spheroidal Galaxies in the Hubble Deep Fields: Evidence for a Truncated IMF at ~2M_solar and a Constant Space Density to z~2
The optical-IR images of the Northern and Southern Hubble Deep Fields are
used to measure the spectral and density evolution of early-type galaxies. The
mean optical SED is found to evolve passively towards a mid F-star dominated
spectrum by z ~ 2. We demonstrate with realistic simulations that hotter
ellipticals would be readily visible if evolution progressed blueward and
brightward at z > 2, following a standard IMF. The colour distributions are
best fitted by a `red' IMF, deficient above ~2 M_solar and with a spread of
formation in the range 1.5 < z_f < 2.5. Traditional age dating is spurious in
this context, a distant elliptical can be young but appear red, with an
apparent age >3 Gyrs independent of its formation redshift. Regarding density
evolution, we demonstrate that the sharp decline in numbers claimed at z > 1
results from a selection bias against distant red galaxies in the optical,
where the flux is too weak for morphological classification, but is remedied
with relatively modest IR exposures revealing a roughly constant space density
to z ~ 2. We point out that the lack of high mass star-formation inferred here
and the requirement of metals implicates cooling-flows of pre-enriched gas in
the creation of the stellar content of spheroidal galaxies. Deep-field X-ray
images will be very helpful to examine this possibility.Comment: 6 pages, 3 figures, submitted to Astrophysical Journal Letters,
typographical errors corrected, simulated images with different IMFs
illustrated at http://astro.berkeley.edu/~bouwens/ellip.htm
Higgs Decay to Top Quarks at O(\alpha_s^2)
Three-loop corrections to the scalar and pseudo-scalar current correlator are
calculated. By applying the large momentum expansion mass terms up to order
(m^2/q^2)^4 are evaluated analytically. As an application O(\alpha_s^2)
corrections to the decay of a scalar and pseudo-scalar Higgs boson into top
quarks are considered. It is shown that for a Higgs mass not far above the
threshold these higher order mass corrections are necessary to get
reliable results.Comment: Latex, 20 pages, 14 ps-figures. The complete paper, including
figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Three-loop QCD corrections and b-quark decays
We present three-loop (NNNLO) corrections to the heavy-to-heavy quark
transitions in the limit of equal initial and final quark masses. In analogy
with the previously found NNLO corrections, the bulk of the result is due to
the beta_0^2 alpha_s^3 corrections. The remaining genuine three-loop effects
for the semileptonic b --> c decays are estimated to increase the decay
amplitude by 0.2(2)%. The perturbative series for the heavy-heavy axial current
converges very well.Comment: 5 page
Using Weak Lensing Dilution to Improve Measurements of the Luminous and Dark Matter in A1689
The E/SO sequence of a cluster defines a boundary redward of which a reliable
weak lensing signal can be obtained from background galaxies, uncontaminated by
cluster members. For bluer colors, both background and cluster members are
present, reducing the distortion signal by the proportion of unlensed cluster
members. In deep Subaru and HST/ACS images of A1689 the tangential distortion
of galaxies with bluer colors falls rapidly toward the cluster center relative
to the lensing signal of the red background. We use this dilution effect to
derive the cluster light profile and luminosity function to large radius, with
the advantage that no subtraction of far-field background counts is required.
The light profile declines smoothly to the limit of the data, r<2Mpc/h, with a
constant slope, dlog(L)/dlog(r)=-1.12+-0.06, unlike the lensing mass profile
which steepens continuously with radius, so that M/L peaks at an intermediate
radius, ~100kpc/h. A flatter behavior is found for the more physically
meaningful ratio of dark-matter to stellar-matter, when accounting for the
color-mass relation of cluster members. The cluster luminosity function has a
flat slope, alpha=-1.05+-0.07, independent of radius and with no faint upturn
to M_i'<-12. We establish that the very bluest objects are negligibly
contaminated by the cluster V-i'<0.2, because their distortion profile rises
towards the center following the red background, but offset higher by ~20%.
This larger amplitude is consistent with the greater estimated depth of the
faint blue galaxies, z~=2.0 compared to z~=0.85 for the red background, a
purely geometric effect related to cosmological parameters. Finally, we improve
upon our earlier mass profile by combining both the red and blue background
populations, clearly excluding low concentration CDM profiles.Comment: 17 pages, 21 figures, revised version in response to referee
comments,(added some discussion, references), conclusions unchanged. Accepted
for publication in Ap
Lattice Green functions in all dimensions
We give a systematic treatment of lattice Green functions (LGF) on the
-dimensional diamond, simple cubic, body-centred cubic and face-centred
cubic lattices for arbitrary dimensionality for the first three
lattices, and for for the hyper-fcc lattice. We show that there
is a close connection between the LGF of the -dimensional hypercubic lattice
and that of the -dimensional diamond lattice. We give constant-term
formulations of LGFs for all lattices and dimensions. Through a still
under-developed connection with Mahler measures, we point out an unexpected
connection between the coefficients of the s.c., b.c.c. and diamond LGFs and
some Ramanujan-type formulae for Comment: 30 page
Heavy-Light Meson Decay Constant from QCD Sum Rules in Three-Loop Approximation
In this paper we compute the decay constant of the pseudo-scalar heavy-light
mesons in the heavy quark effective theory framework of QCD sum rules. In our
analysis we include the recently evaluated three-loop result of order
for the heavy-light current correlator. The value of the bottom
quark mass, which essentially limits the accuracy of the sum rules for
meson, is extracted from the nonrelativistic sum rules for
resonances in the next-to-next-to-leading approximation. We find stability of
our result with respect to all types of corrections and the specific form of
the sum rule which reduces the uncertainty. Our results MeV and
MeV for the and meson decay constants are in impressive
agreement with recent lattice calculations.Comment: minor editorial changes, references added, to appear in PR
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