43,116 research outputs found
Multiple Hard Partonic Collisions with Correlations in Proton-Proton Scattering
We propose a simple method for incorporating correlations into the impact
parameter space description of multiple (semi-)hard partonic collisions in high
energy hadron-hadron scattering. The perturbative QCD input is the standard
factorization theorem for inclusive dijet production with a lower cutoff on
transverse momentum. The width of the transverse distribution of hard partons
is fixed by parameterizations of the two-gluon form factor. We then reconstruct
the hard contribution to the total inelastic profile function and obtain
corrections due to correlations to the more commonly used eikonal description.
Estimates of the size of double correlation corrections are based on the rate
of double collisions measured at the Tevatron. We find that, if typical values
for the lower transverse momentum cutoff are used in the calculation of the
inclusive hard dijet cross section, then the correlation corrections are
necessary for maintaining consistency with expectations for the total inelastic
proton-proton cross section at LHC energies.Comment: Typos fixed, Figures 2,9 and 10 added, matches version published in
Phys. Rev.
Observational signatures of convectively driven waves in massive stars
We demonstrate observational evidence for the occurrence of convectively
driven internal gravity waves (IGW) in young massive O-type stars observed with
high-precision CoRoT space photometry. This evidence results from a comparison
between velocity spectra based on 2D hydrodynamical simulations of IGW in a
differentially-rotating massive star and the observed spectra.We also show that
the velocity spectra caused by IGW may lead to detectable line-profile
variability and explain the occurrence of macroturbulence in the observed line
profiles of OB stars. Our findings provide predictions that can readily be
tested by including a sample of bright slowly and rapidly rotating OB-type
stars in the scientific programme of the K2 mission accompanied by
high-precision spectroscopy and their confrontation with multi-dimensional
hydrodynamic simulations of IGW for various masses and ages.Comment: 4 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
A spectroscopic search for absorption due to ammonia dimers in the far infra red region of the spectrum
Imperial Users onl
On the Tidal Dissipation of Obliquity
We investigate tidal dissipation of obliquity in hot Jupiters. Assuming an
initial random orientation of obliquity and parameters relevant to the observed
population, the obliquity of hot Jupiters does not evolve to purely aligned
systems. In fact, the obliquity evolves to either prograde, retrograde or
90^{o} orbits where the torque due to tidal perturbations vanishes. This
distribution is incompatible with observations which show that hot jupiters
around cool stars are generally aligned. This calls into question the viability
of tidal dissipation as the mechanism for obliquity alignment of hot Jupiters
around cool stars.Comment: 6 pages, 4 figures, accepted at ApJ
Muon capture in the front end of the IDS neutrino factory
We discuss the design of the muon capture front end of the neutrino factory
International Design Study. In the front end, a proton bunch on a target
creates secondary pions that drift into a capture transport channel, decaying
into muons. A sequence of rf cavities forms the resulting muon beams into
strings of bunches of differing energies, aligns the bunches to (nearly) equal
central energies, and initiates ionization cooling. The muons are then
accelerated to high energy where their decays provide neutrino beams. For the
International Design Study (IDS), a baseline design must be developed and
optimized for an engineering and cost study. We present a baseline design that
can be used to establish the scope of a future neutrino Factory facility.Comment: 3 pp. 1st International Particle Accelerator Conference: IPAC'10,
23-28 May 2010: Kyoto, Japa
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