78 research outputs found
NLO inclusive jet production in --factorization
The inclusive production of jets in the central region of rapidity is studied
in -factorization at next-to-leading order (NLO) in QCD perturbation
theory. Calculations are performed in the Regge limit making use of the NLO
BFKL results. A jet cone definition is introduced and a proper phase--space
separation into multi-Regge and quasi-multi-Regge kinematic regions is carried
out. Two situations are discussed: scattering of highly virtual photons, which
requires a symmetric energy scale to separate the impact factors from the gluon
Green's function, and hadron-hadron collisions, where a non--symmetric scale
choice is needed.Comment: 36 pages, 5 figures. Version to be published in JHEP. Some typos
correcte
Energy Conservation and Saturation in Small-x Evolution
Important corrections to BFKL evolution are obtained from non-leading
contributions and from non-linear effects due to unitarisation or saturation.
It has been difficult to estimate the relative importance of these effects, as
NLO effects are most easily accounted for in momentum space while unitarisation
and saturation are easier in transverse coordinate space. An essential
component of the NLO contributions is due to energy conservation effects, and
in this paper we present a model for implementing such effects together with
saturation in Mueller's dipole evolution formalism. We find that energy
conservation severely dampens the small-x rise of the gluon density and, as a
consequence, the onset of saturation is delayed. Using a simple model for the
proton we obtain a reasonable qualitative description of the x-dependence of F2
at low Q^2 as measured at HERA even without saturation effects. We also give
qualitative descriptions of the energy dependence of the cross section for
gamma*-gamma* and gamma*-nucleus scattering
Jet angular correlation in vector-boson fusion processes at hadron colliders
Higgs boson and massive-graviton productions in association with two jets via
vector-boson fusion (VBF) processes and their decays into a vector-boson pair
at hadron colliders are studied. They include scalar and tensor boson
production processes via weak-boson fusion in quark-quark collisions, gluon
fusion in quark-quark, quark-gluon and gluon-gluon collisions, as well as their
decays into a pair of weak bosons or virtual gluons which subsequently decay
into , or . We give the helicity amplitudes
explicitly for all the VBF subprocesses, and show that the VBF amplitudes
dominate the exact matrix elements not only for the weak-boson fusion processes
but also for all the gluon fusion processes when appropriate selection cuts are
applied, such as a large rapidity separation between two jets and a slicing cut
for the transverse momenta of the jets. We also show that our off-shell
vector-boson current amplitudes reduce to the standard quark and gluon
splitting amplitudes with appropriate gluon-polarization phases in the
collinear limit. Nontrivial azimuthal angle correlations of the jets in the
production and in the decay of massive spin-0 and -2 bosons are manifestly
expressed as the quantum interference among different helicity states of the
intermediate vector-bosons. Those correlations reflect the spin and the CP
nature of the Higgs bosons and the massive gravitons.Comment: 47 pages, 7 figures, 10 tables; references added, version to appear
in JHE
W+jets Matrix Elements and the Dipole Cascade
We extend the algorithm for matching fixed-order tree-level matrix element
generators with the Dipole Cascade Model in Ariadne to apply to processes with
incoming hadrons. We test the algoritm on for the process W+n jets at the
Tevatron, and find that the results are fairly insensitive to the cutoff used
to regularize the soft and collinear divergencies in the tree-level matrix
elements. We also investigate a few observables to check the sensitivity to the
matrix element correction
Quasiparticle excitation in and around the vortex core of underdoped YBa_2Cu_4O_8 studied by site-selective NMR
We report a site-selective ^{17}O spin-lattice relaxation rate T_1^{-1} in
the vortex state of underdoped YBa_2Cu_4O_8. We found that T_1^{-1} at the
planar sites exhibits an unusual nonmonotonic NMR frequency dependence. In the
region well outside the vortex core, T_1^{-1} cannot be simply explained by the
density of states of the Doppler-shifted quasiparticles in the d-wave
superconductor. Based on T_1^{-1} in the vortex core region, we establish
strong evidence that the local density of states within the vortex core is
strongly reduced.Comment: 5 pages, 3 figure
Electroproduction of two light vector mesons in next-to-leading BFKL: study of systematic effects
The forward electroproduction of two light vector mesons is the first example
of a collision process between strongly interacting colorless particles for
which the amplitude can be written completely within perturbative QCD in the
Regge limit with next-to-leading accuracy. In a previous paper we have given a
numerical determination of the amplitude in the case of equal photon
virtualities by using a definite representation for the amplitude and a
definite optimization method for the perturbative series. Here we estimate the
systematic uncertainty of our previous determination, by considering a
different representation of the amplitude and different optimization methods of
the perturbative series. Moreover, we compare our result for the differential
cross section at the minimum momentum transfer with a different approach, based
on collinear kernel improvement.Comment: 17 pages, 11 figures; journal version, new figures and discussion
adde
Spectral and transport properties of doped Mott-Hubbard systems with incommensurate magnetic order
We present spectral and optical properties of the Hubbard model on a
two-dimensional square lattice using a generalization of dynamical mean-field
theory to magnetic states in finite dimension. The self-energy includes the
effect of spin fluctuations and screening of the Coulomb interaction due to
particle-particle scattering. At half-filling the quasiparticles reduce the
width of the Mott-Hubbard `gap' and have dispersions and spectral weights that
agree remarkably well with quantum Monte Carlo and exact diagonalization
calculations. Away from half-filling we consider incommensurate magnetic order
with a varying local spin direction, and derive the photoemission and optical
spectra. The incommensurate magnetic order leads to a pseudogap which opens at
the Fermi energy and coexists with a large Mott-Hubbard gap. The quasiparticle
states survive in the doped systems, but their dispersion is modified with the
doping and a rigid band picture does not apply. Spectral weight in the optical
conductivity is transferred to lower energies and the Drude weight increases
linearly with increasing doping. We show that incommensurate magnetic order
leads also to mid-gap states in the optical spectra and to decreased scattering
rates in the transport processes, in qualitative agreement with the
experimental observations in doped systems. The gradual disappearence of the
spiral magnetic order and the vanishing pseudogap with increasing temperature
is found to be responsible for the linear resistivity. We discuss the possible
reasons why these results may only partially explain the features observed in
the optical spectra of high temperature superconductors.Comment: 22 pages, 18 figure
First cosmology results using SNe Ia from the dark energy survey: analysis, systematic uncertainties, and validation
International audienceWe present the analysis underpinning the measurement of cosmological parameters from 207 spectroscopically classified type Ia supernovae (SNe Ia) from the first three years of the Dark Energy Survey Supernova Program (DES-SN), spanning a redshift range of 0.01
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