390 research outputs found
CLASH: accurate photometric redshifts with 14 HST bands in massive galaxy cluster cores
We present accurate photometric redshifts for galaxies observed by the Cluster Lensing And Supernova survey with Hubble (CLASH). CLASH observed 25 massive galaxy cluster cores with the Hubble Space Telescope in 16 filters spanning 0.2–1.7 μm. Photometry in such crowded fields is challenging. Compared to our previously released catalogues, we make several improvements to the photometry, including smaller apertures, intracluster light subtraction, point spread function matching and empirically measured uncertainties. We further improve the Bayesian photometric redshift estimates by adding a redder elliptical template and by inflating the photometric uncertainties of the brightest galaxies. The resulting photometric redshift accuracies are dz/(1+z) ∼ 0.8, 1.0 and 2.0 per cent for galaxies with I-band F814W AB magnitudes < 18, 20 and 23, respectively. These results are consistent with our expectations. They improve on our previously reported accuracies by a factor of 4 at the bright end and a factor of 2 at the faint end. Our new catalogue includes 1257 spectroscopic redshifts, including 382 confirmed cluster members. We also provide stellar mass estimates. Finally, we include lensing magnification estimates of background galaxies based on our public lens models. Our new catalogue of all 25 CLASH clusters is available via Mikulski Archive for Space Telescopes. The analysis techniques developed here will be useful in other surveys of crowded fields, including the Frontier Fields and surveys carried out with Javalambre-Physics of the Accelerated Universe Astrophysical Survey and James Webb Space Telescope
RG-improved single-particle inclusive cross sections and forward-backward asymmetry in production at hadron colliders
We use techniques from soft-collinear effective theory (SCET) to derive
renormalization-group improved predictions for single-particle inclusive (1PI)
observables in top-quark pair production at hadron colliders. In particular, we
study the top-quark transverse-momentum and rapidity distributions, the
forward-backward asymmetry at the Tevatron, and the total cross section at
NLO+NNLL order in resummed perturbation theory and at approximate NNLO in fixed
order. We also perform a detailed analysis of power corrections to the leading
terms in the threshold expansion of the partonic hard-scattering kernels. We
conclude that, although the threshold expansion in 1PI kinematics is
susceptible to numerically significant power corrections, its predictions for
the total cross section are in good agreement with those obtained by
integrating the top-pair invariant-mass distribution in pair invariant-mass
kinematics, as long as a certain set of subleading terms appearing naturally
within the SCET formalism is included.Comment: 55 pages, 14 figures, 6 table
NNLO corrections to top-pair production at hadron colliders: the all-fermionic scattering channels
This is a second paper in our ongoing calculation of the
next-to-next-to-leading order (NNLO) QCD correction to the total inclusive
top-pair production cross-section at hadron colliders. In this paper we
calculate the reaction which was not considered
in our previous work on due to its phenomenologically
negligible size. We also calculate all remaining fermion-pair-initiated
partonic channels and that contribute to top-pair
production starting from NNLO. The contributions of these reactions to the
total cross-section for top-pair production at the Tevatron and LHC are small,
at the permil level. The most interesting feature of these reactions is their
characteristic logarithmic rise in the high energy limit. We compute the
constant term in the leading power behavior in this limit, and achieve
precision that is an order of magnitude better than the precision of a recent
theoretical prediction for this constant. All four partonic reactions computed
in this paper are included in our numerical program Top++. The calculation of
the NNLO corrections to the two remaining partonic reactions,
and , is ongoing.Comment: 1+16 pages; 3 figure
Complete off-shell effects in top quark pair hadroproduction with leptonic decay at next-to-leading order
Results for next-to-leading order QCD corrections to the pp(p\bar{p}) -> t
\bar{t} -> W^+W^- b\bar{b} -> e^{+} \nu_{e} \mu^{-} \bar{\nu}_{\mu} b \bar{b}
+X processes with complete off-shell effects are presented for the first time.
Double-, single- and non-resonant top contributions of the order
{\cal{O}}(\alpha_{s}^3 \alpha^4) are consistently taken into account, which
requires the introduction of a complex-mass scheme for unstable top quarks.
Moreover, the intermediate W bosons are treated off-shell. Comparison to the
narrow width approximation for top quarks, where non-factorizable corrections
are not accounted for is performed. Besides the total cross section and its
scale dependence, several differential distributions at the TeVatron run II and
the LHC are given. In case of the TeVatron the forward-backward asymmetry of
the top is recalculated afresh. With inclusive selection cuts, the
forward-backward asymmetry amounts to A^{t}_{FB} = 0.051 +/- 0.0013.
Furthermore, the corrections with respect to leading order are positive and of
the order 2.3% for the TeVatron and 47% for the LHC. A study of the scale
dependence of our NLO predictions indicates that the residual theoretical
uncertainty due to higher order corrections is 8% for the TeVatron and 9% for
the LHC.Comment: 35 pages, 39 figures, 3 tables. References and note added, version to
appear in JHE
The cusp anomalous dimension at three loops and beyond
We derive an analytic formula at three loops for the cusp anomalous dimension
Gamma_cusp(phi) in N=4 super Yang-Mills. This is done by exploiting the
relation of the latter to the Regge limit of massive amplitudes. We comment on
the corresponding three loops quark anti-quark potential. Our result also
determines a considerable part of the three-loop cusp anomalous dimension in
QCD. Finally, we consider a limit in which only ladder diagrams contribute to
physical observables. In that limit, a precise agreement with strong coupling
is observed.Comment: 34 pages, 6 figures. v2: references added, typos correcte
Left-right symmetry at LHC and precise 1-loop low energy data
Despite many tests, even the Minimal Manifest Left-Right Symmetric Model
(MLRSM) has never been ultimately confirmed or falsified. LHC gives a new
possibility to test directly the most conservative version of left-right
symmetric models at so far not reachable energy scales. If we take into account
precise limits on the model which come from low energy processes, like the muon
decay, possible LHC signals are strongly limited through the correlations of
parameters among heavy neutrinos, heavy gauge bosons and heavy Higgs particles.
To illustrate the situation in the context of LHC, we consider the "golden"
process . For instance, in a case of degenerate heavy neutrinos
and heavy Higgs masses at 15 TeV (in agreement with FCNC bounds) we get
fb at TeV which is consistent with muon
decay data for a very limited masses in the range (3008 GeV, 3040 GeV).
Without restrictions coming from the muon data, masses would be in the
range (1.0 TeV, 3.5 TeV). Influence of heavy Higgs particles themselves on the
considered LHC process is negligible (the same is true for the light, SM
neutral Higgs scalar analog). In the paper decay modes of the right-handed
heavy gauge bosons and heavy neutrinos are also discussed. Both scenarios with
typical see-saw light-heavy neutrino mixings and the mixings which are
independent of heavy neutrino masses are considered. In the second case heavy
neutrino decays to the heavy charged gauge bosons not necessarily dominate over
decay modes which include only light, SM-like particles.Comment: 16 pages, 10 figs, KL-KS and new ATLAS limits taken into accoun
Master integrals for massive two-loop Bhabha scattering in QED
We present a set of scalar master integrals (MIs) needed for a complete
treatment of massive two-loop corrections to Bhabha scattering in QED,
including integrals with arbitrary fermionic loops. The status of analytical
solutions for the MIs is reviewed and examples of some methods to solve MIs
analytically are worked out in more detail. Analytical results for the pole
terms in epsilon of so far unknown box MIs with five internal lines are given.Comment: 23 pages, 5 tables, 12 figures, references added, appendix B enlarge
Galaxy Cluster Scaling Relations between Bolocam Sunyaev-Zel'dovich Effect and Chandra X-ray Measurements
We present scaling relations between the integrated Sunyaev-Zel'dovich Effect
(SZE) signal, , its X-ray analogue, , and total mass, , for the 45 galaxy clusters in
the Bolocam X-ray-SZ (BOXSZ) sample. All parameters are integrated within
. values are measured using SZE data collected with
Bolocam, operating at 140 GHz at the Caltech Submillimeter Observatory (CSO).
The temperature, , and mass, , of the intracluster
medium are determined using X-ray data collected with Chandra, and is derived from assuming a constant gas mass fraction. Our
analysis accounts for several potential sources of bias, including: selection
effects, contamination from radio point sources, and the loss of SZE signal due
to noise filtering and beam-smoothing effects. We measure the
-- scaling to have a power-law index of , and
a fractional intrinsic scatter in of at fixed , both of which are consistent with previous analyses. We also measure the
scaling between and , finding a power-law index of
and a fractional intrinsic scatter in at fixed mass of
. While recent SZE scaling relations using X-ray mass proxies have
found power-law indices consistent with the self-similar prediction of 5/3, our
measurement stands apart by differing from the self-similar prediction by
approximately 5. Given the good agreement between the measured
-- scalings, much of this discrepancy appears to be caused
by differences in the calibration of the X-ray mass proxies adopted for each
particular analysis.Comment: 31 pages, 15 figures, accepted by ApJ 04/11/2015. This version is
appreciably different from the original submission: it includes an entirely
new appendix, extended discussion, and much of the material has been
reorganize
Yangian Symmetry at Two Loops for the su(2|1) Sector of N=4 SYM
We present the perturbative Yangian symmetry at next-to-leading order in the
su(2|1) sector of planar N=4 SYM. Just like the ordinary symmetry generators,
the bi-local Yangian charges receive corrections acting on several neighboring
sites. We confirm that the bi-local Yangian charges satisfy the necessary
conditions: they transform in the adjoint of su(2|1), they commute with the
dilatation generator, and they satisfy the Serre relations. This proves that
the sector is integrable at two loops.Comment: 13 pages, v2: minor correction
Dimensional recurrence relations: an easy way to evaluate higher orders of expansion in
Applications of a method recently suggested by one of the authors (R.L.) are
presented. This method is based on the use of dimensional recurrence relations
and analytic properties of Feynman integrals as functions of the parameter of
dimensional regularization, . The method was used to obtain analytical
expressions for two missing constants in the -expansion of the most
complicated master integrals contributing to the three-loop massless quark and
gluon form factors and thereby present the form factors in a completely
analytic form. To illustrate its power we present, at transcendentality weight
seven, the next order of the -expansion of one of the corresponding
most complicated master integrals. As a further application, we present three
previously unknown terms of the expansion in of the three-loop
non-planar massless propagator diagram. Only multiple values at integer
points are present in our result.Comment: Talk given at the International Workshop `Loops and Legs in Quantum
Field Theory' (April 25--30, 2010, W\"orlitz, Germany)
- …