11,126 research outputs found
Universal Non-perturbative Functions for SIDIS and Drell-Yan Processes
We update the well-known BLNY fit to the low transverse momentum Drell-Yan
lepton pair productions in hadronic collisions, by considering the constraints
from the semi-inclusive hadron production in deep inelastic scattering (SIDIS)
from HERMES and COMPASS experiments. We follow the Collins-Soper-Sterman (CSS)
formalism with the b_*-prescription. A universal non-perturbative form factor
associated with the transverse momentum dependent quark distributions is found
in the analysis with a new functional form different from that of BLNY. This
releases the tension between the BLNY fit to the Drell-Yan data with the SIDIS
data from HERMES/COMPASS in the CSS resummation formalism.Comment: 19 pages, 11 figures; updated the fit with running effects of
\alpha_{s}, \alpha_{em}, N_f; conclusion remains; more discussions on the
result
Resummation of High Order Corrections in Higgs Boson Plus Jet Production at the LHC
We study the effect of multiple parton radiation to Higgs boson plus jet
production at the LHC, by applying the transverse momentum dependent (TMD)
factorization formalism to resum large logarithmic contributions to all orders
in the expansion of the strong interaction coupling. We show that the
appropriate resummation scale should be the jet transverse momentum, rather
than the partonic center of mass energy which has been normally used in the TMD
resummation formalism. Furthermore, the transverse momentum distribution of the
Higgs boson, particularly near the lower cut-off applied on the jet transverse
momentum, can only be reliably predicted by the resummation calculation which
is free of the so-called Sudakov-shoulder singularity problem, present in
fixed-order calculations.Comment: 7 pages, 4 figure
Failure of Perturbation Theory Near Horizons: the Rindler Example
Persistent puzzles to do with information loss for black holes have
stimulated critical reassessment of the domain of validity of semiclassical EFT
reasoning in curved spacetimes, particularly in the presence of horizons. We
argue here that perturbative predictions about evolution for very long times
near a horizon are subject to problems of secular growth - i.e. powers of small
couplings come systematically together with growing functions of time. Such
growth signals a breakdown of naive perturbative calculations of late-time
behaviour, regardless of how small ambient curvatures might be. Similar issues
of secular growth also arise in cosmology, and we build evidence for the case
that such effects should be generic for gravitational fields. In particular,
inferences using free fields coupled only to background metrics can be
misleading at very late times due to the implicit assumption they make of
perturbation theory when neglecting other interactions. Using the Rindler
horizon as an example we show how this secular growth parallels similar
phenomena for thermal systems, and how it can be resummed to allow late-time
inferences to be drawn more robustly. Some comments are made about the
appearance of an IR/UV interplay in this calculation, as well as on the
possible relevance of our calculations to predictions near black-hole horizons.Comment: LaTeX, 17 pages plus appendix; added references and subsection on
back-reactio
Chandra and XMM-Newton Observations of the Double Cluster Abell 1758
Abell 1758 was classified as a single rich cluster of galaxies by Abell, but
a ROSAT observation showed that this system consists of two distinct clusters
(A1758N and A1758S) separated by approximately 8\arcmin (a projected
separation of 2 Mpc in the rest frame of the clusters). Only a few galaxy
redshifts have been published for these two clusters, but the redshift of the
Fe lines in the Chandra and XMM-Newton spectra shows that the recessional
velocities of A1758N and A1758S are within 2,100 km s. Thus, these two
clusters most likely form a gravitationally bound system, but our imaging and
spectroscopic analyses of the X-ray data do not reveal any sign of interaction
between the two clusters. The Chandra and XMM-Newton observations show that
A1758N and A1758S are both undergoing major mergers.
A1758N is in the late stages of a large impact parameter merger between two 7
keV clusters. The two remnant cores have a projected separation of 800 kpc.
Based on the measured pressure jumps preceding the two cores, they are receding
from one another at less than 1,600 km s. The two cores are surrounded
by hotter gas (--12 keV) that was probably shock heated during
the early stages of the merger. The gas entropy in the two remnant cores is
comparable with the central entropy observed in dynamically relaxed clusters,
indicating that the merger-induced shocks stalled as they tried to penetrate
the high pressure cores of the two merging systems.Each core also has a wake of
low entropy gas indicating that this gas was ram pressure stripped without
being strongly shocked (abridged). (A copy of the paper with higher resolution
images is available at http://asc.harvard.edu/~lpd/a1758.ps).Comment: paper plus 13 figure
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