4,855 research outputs found
Full NLO massive gauge boson pair production at the LHC
Electroweak gauge boson pair production is a very important process at the
LHC as it probes the non-abelian structure of electroweak interactions and is a
background process for many searches. We present full next-to-leading order
predictions for the production cross sections and distributions of on-shell
massive gauge boson pair production in the Standard Model, including both QCD
and electroweak corrections. The hierarchy between the ZZ, WW and WZ channels,
observed in the transverse momentum distributions, will be analyzed. We will
also present a comparison with experimental data for the total cross sections
including a study of the theoretical uncertainties.Comment: 4 pages, 4 figures. Proceeding of the inaugural conference "Windows
on the Universe" (August 11-17, Quy Nhon, Vietnam) including updated results
compared to arXiv:1307.433
Ionization processes in a local analogue of distant clumpy galaxies: VLT MUSE IFU spectroscopy and FORS deep images of the TDG NGC 5291N
We present IFU observations with MUSE@VLT and deep imaging with FORS@VLT of a
dwarf galaxy recently formed within the giant collisional HI ring surrounding
NGC 5291. This TDG-like object has the characteristics of typical z=1-2
gas-rich spiral galaxies: a high gas fraction, a rather turbulent clumpy ISM,
the absence of an old stellar population, a moderate metallicity and star
formation efficiency. The MUSE spectra allow us to determine the physical
conditions within the various complex substructures revealed by the deep
optical images, and to scrutinize at unprecedented spatial resolution the
ionization processes at play in this specific medium. Starburst age, extinction
and metallicity maps of the TDG and surrounding regions were determined using
the strong emission lines Hbeta, [OIII], [OI], [NII], Halpha and [SII] combined
with empirical diagnostics. Discrimination between different ionization
mechanisms was made using BPT--like diagrams and shock plus photoionization
models. Globally, the physical conditions within the star--forming regions are
homogeneous, with in particular an uniform half-solar oxygen abundance. At
small scales, the derived extinction map shows narrow dust lanes. Regions with
atypically strong [OI] emission line immediately surround the TDG. The [OI] /
Halpha ratio cannot be easily accounted for by photoionization by young stars
or shock models. At larger distances from the main star--forming clumps, a
faint diffuse blue continuum emission is observed, both with the deep FORS
images and MUSE data. It does not have a clear counterpart in the UV regime
probed by GALEX. A stacked spectrum towards this region does not exhibit any
emission line, excluding faint levels of star formation, nor stellar absorption
lines that might have revealed the presence of old stars. Several hypotheses
are discussed for the origin of these intriguing features.Comment: 13 pages, 15 figures, accepted for publication in A&
NLO corrections to WWZ and ZZZ production at the ILC
We calculate the full one-loop electroweak corrections to tri-boson
production (ZZZ and WWZ) at the ILC. This is important to understand the
Standard Model (SM) gauge quartic couplings which can be a window on the
mechanism of spontaneous symmetry breaking. We find that even after subtracting
the leading QED corrections, the electroweak corrections can still be large
especially as the energy increases.Comment: 7 pages, proceedings of the 3rd CPP Workshop, September 23-25, 2010,
KEK Tsukuba Japa
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
Star Forming Objects in the Tidal Tails of Compact Groups
A search for star forming objects belonging to tidal tails has been carried
out in a sample of deep Halpha images of 16 compact groups of galaxies. A total
of 36 objects with Halpha luminosity larger than 10^38 erg s-1 have been
detected in five groups. The fraction of the total Halpha luminosity of their
respective parent galaxies shown by the tidal objects is always below 5% except
for the tidal features of HCG95, whose Halpha luminosity amounts to 65% of the
total luminosity. Out of this 36 objects, 9 star forming tidal dwarf galaxy
candidates have been finally identified on the basis of their projected
distances to the nuclei of the parent galaxies and their total Halpha
luminosities. Overall, the observed properties of the candidates resemble those
previously reported for the so-called tidal dwarf galaxies.Comment: 5 gif figures. Accepted for publication in Astrophysical Journa
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