479 research outputs found
Antenna subtraction for gluon scattering at NNLO
We use the antenna subtraction method to isolate the double real radiation
infrared singularities present in gluonic scattering amplitudes at
next-to-next-to-leading order. The antenna subtraction framework has been
successfully applied to the calculation of NNLO corrections to the 3-jet cross
section and related event shape distributions in electron-positron
annihilation. Here we consider processes with two coloured particles in the
initial state, and in particular two-jet production at hadron colliders such as
the Large Hadron Collider (LHC). We construct a subtraction term that describes
the single and double unresolved contributions from the six-gluon tree-level
process using antenna functions with initial state partons and show numerically
that the subtraction term correctly approximates the matrix elements in the
various single and double unresolved configurations.Comment: 71 pages, JHEP3 class; corrected typos, equivalent but more compact
version of eq. (5.12), results unchange
W boson production at hadron colliders: the lepton charge asymmetry in NNLO QCD
We consider the production of W bosons in hadron collisions, and the
subsequent leptonic decay W->lnu_l. We study the asymmetry between the rapidity
distributions of the charged leptons, and we present its computation up to the
next-to-next-to-leading order (NNLO) in QCD perturbation theory. Our
calculation includes the dependence on the lepton kinematical cuts that are
necessarily applied to select W-> lnu_l events in actual experimental analyses
at hadron colliders. We illustrate the main differences between the W and
lepton charge asymmetry, and we discuss their physical origin and the effect of
the QCD radiative corrections. We show detailed numerical results on the charge
asymmetry in ppbar collisions at the Tevatron, and we discuss the comparison
with some of the available data. Some illustrative results on the lepton charge
asymmetry in pp collisions at LHC energies are presented.Comment: 37 pages, 21 figure
The fully differential hadronic production of a Higgs boson via bottom quark fusion at NNLO
The fully differential computation of the hadronic production cross section
of a Higgs boson via bottom quarks is presented at NNLO in QCD. Several
differential distributions with their corresponding scale uncertainties are
presented for the 8 TeV LHC. This is the first application of the method of
non-linear mappings for NNLO differential calculations at hadron colliders.Comment: 27 pages, 13 figures, 1 lego plo
The Mass of the Planet-hosting Giant Star Beta Geminorum Determined from its p-mode Oscillation Spectrum
We use precise radial velocity measurements and photometric data to derive
the frequency spacing of the p-mode oscillation spectrum of the planet-hosting
star Beta Gem. This spacing along with the interferometric radius for this star
is used to derive an accurate stellar mass. A long time series of over 60 hours
of precise stellar radial velocity measurements of Beta Gem were taken with an
iodine absorption cell and the echelle spectrograph mounted on the 2m Alfred
Jensch Telescope. Complementary photometric data for this star were also taken
with the MOST microsatellite spanning 3.6 d. A Fourier analysis of the radial
velocity data reveals the presence of up to 17 significant pulsation modes in
the frequency interval 10-250 micro-Hz. Most of these fall on a grid of
equally-spaced frequencies having a separation of 7.14 +/- 0.12 micro-Hz. An
analysis of 3.6 days of high precision photometry taken with the MOST space
telescope shows the presence of up to 16 modes, six of which are consistent
with modes found in the spectral (radial velocity) data. This frequency spacing
is consistent with high overtone radial pulsations; however, until the
pulsation modes are identified we cannot be sure if some of these are nonradial
modes or even mixed modes. The radial velocity frequency spacing along with
angular diameter measurements of Beta Gem via interferometry results in a
stellar mass of M = 1.91 +/- 0.09 solar masses. This value confirms the
intermediate mass of the star determined using stellar evolutionary tracks.
Beta Gem is confirmed to be an intermediate mass star. Stellar pulsations in
giant stars along with interferometric radius measurements can provide accurate
determinations of the stellar mass of planet hosting giant stars. These can
also be used to calibrate stellar evolutionary tracks.Comment: Accepted by Astronomy and Astrophysic
Antenna subtraction at NNLO with hadronic initial states: real-virtual initial-initial configurations
The antenna subtraction method handles real radiation contributions in higher
order corrections to jet observables. The method is based on antenna functions,
which encapsulate all unresolved radiation between a pair of hard radiator
partons. To apply this method to compute hadron collider observables,
initial-initial antenna functions with both radiators in the initial state are
required. In view of extending the antenna subtraction method to
next-to-next-to-leading order (NNLO) calculations at hadron colliders, we
derive the one-loop initial-initial antenna functions in unintegrated and
integrated form.Comment: 24 page
Antenna subtraction at NNLO with hadronic initial states: double real initial-initial configurations
The antenna subtraction method handles real radiation contributions in higher
order corrections to jet observables. The method is based on antenna functions,
which encapsulate all unresolved radiation between a pair of hard radiator
partons. To apply this method to compute hadron collider observables,
initial-initial antenna functions with both radiators in the initial state are
required in unintegrated and integrated forms. In view of extending the antenna
subtraction method to next-to-next-to-leading order (NNLO) calculations at
hadron colliders, we derive the full set of initial-initial double real
radiation antenna functions in integrated form.Comment: 38 pages; a FORM file with the integrated antennae is included with
this submission. arXiv admin note: text overlap with arXiv:1011.6631,
arXiv:1107.403
Planets around evolved intermediate-mass stars. I. Two substellar companions in the open clusters NGC 2423 and NGC 4349
Context. Many efforts are being made to characterize extrasolar planetary
systems and unveil the fundamental mechanisms of planet formation. An important
aspect of the problem, which remains largely unknown, is to understand how the
planet formation process depends on the mass of the parent star. In particular,
as most planets discovered to date orbit a solar-mass primary, little is known
about planet formation around more massive stars. Aims. To investigate this
point, we present first results from a radial velocity planet search around red
giants in the clump of intermediate-age open clusters. We choose clusters
harbouring red giants with masses between 1.5 and 4 M_sun, using the well-known
cluster parameters to accurately determine the stellar masses. We are therefore
exploring a poorly-known domain of primary masses, which will bring new
insights into the properties of extrasolar planetary systems. Methods. We are
following a sample of about 115 red giants with the Coralie and HARPS
spectrographs to obtain high-precision radial velocity (RV) measurements and
detect giant planets around these stars. We use bisector and activity index
diagnostics to distinguish between planetary-induced RV variations and stellar
photospheric jitter. Results. We present the discoveries of a giant planet and
a brown dwarf in the open clusters NGC 2423 and NGC 4349, orbiting the 2.4
M_sun-star NGC2423 No3 (TYC 5409-2156-1) and the 3.9 M_sun-star NGC4349 No127
(TYC 8975-2606-1). These low-mass companions have orbital periods of 714 and
678 days and minimum masses of 10.6 and 19.8 M_jup, respectively. Combined with
the other known planetary systems, these detections indicate that the frequency
of massive planets is higher around intermediate-mass stars, and therefore
probably scales with the mass of the protoplanetary disk.Comment: 9 pages, 11 figures, accepted for publication in A&
The real radiation antenna function for at NNLO QCD
As a first step towards the application of the antenna subtraction formalism
to NNLO QCD reactions with massive quarks, we determine the real radiation
antenna function and its integrated counterpart for reactions of the type , where denotes an uncolored initial state and
, a massive and massless quark, respectively. We compute the
corresponding integrated antenna function in terms of harmonic polylogarithms.
As an application and check of our results we calculate the contribution
proportional to to the inclusive heavy-quark pair
production cross ection in annihilation.Comment: Latex, 32 page
Current research into brain barriers and the delivery of therapeutics for neurological diseases: a report on CNS barrier congress London, UK, 2017.
This is a report on the CNS barrier congress held in London, UK, March 22-23rd 2017 and sponsored by Kisaco Research Ltd. The two 1-day sessions were chaired by John Greenwood and Margareta Hammarlund-Udenaes, respectively, and each session ended with a discussion led by the chair. Speakers consisted of invited academic researchers studying the brain barriers in relation to neurological diseases and industry researchers studying new methods to deliver therapeutics to treat neurological diseases. We include here brief reports from the speakers
Space-like (vs. time-like) collinear limits in QCD: is factorization violated?
We consider the singular behaviour of QCD scattering amplitudes in
kinematical configurations where two or more momenta of the external partons
become collinear. At the tree level, this behaviour is known to be controlled
by factorization formulae in which the singular collinear factor is universal
(process independent). We show that this strict (process-independent)
factorization is not valid at one-loop and higher-loop orders in the case of
the collinear limit in space-like regions (e.g., collinear radiation from
initial-state partons). We introduce a generalized version of all-order
collinear factorization, in which the space-like singular factors retain some
dependence on the momentum and colour charge of the non-collinear partons. We
present explicit results on one-loop and two-loop amplitudes for both the
two-parton and multiparton collinear limits. At the level of square amplitudes
and, more generally, cross sections in hadron--hadron collisions, the violation
of strict collinear factorization has implications on the non-abelian structure
of logarithmically-enhanced terms in perturbative calculations (starting from
the next-to-next-to-leading order) and on various factorization issues of mass
singularities (starting from the next-to-next-to-next-to-leading order).Comment: 81 pages, 5 figures, typos corrected in the text, few comments added
and inclusion of NOTE ADDED on recent development
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