2,951 research outputs found
Arnold diffusion in the dynamics of a 4-machine power system undergoing a large fault
We focus on the seemingly complicated dynamics of a four-machine power system which is undergoing a sudden fault. Adopting a Hamiltonian (energy) formulation, we consider the system as an interconnection of (one degree of freedom) subsystems. Under certain configuration (a star network) and parameter values we establish the presence of Arnold diffusion which entails periodic, almost periodic, and complicated nonperiodic dyanmics all simultaneously present; and erratic transfer of energies between the subsystems. In section 1 we introduce the transient stability problem in a mathematical setting and explain what our results mean in the power systems context. Section 2 provides insights into Arnold diffusion and summarizes its mathematical formulation as in [8], [1]. Section 3 gives conditions for which Arnold diffusion arises on certain energy levels of the swing equations. These conditions are verified analytically in the case when all but one subsystem (machine) undergo relatively small oscillations
The spread of the gluon k_t-distribution and the determination of the saturation scale at hadron colliders in resummed NLL BFKL
The transverse momentum distribution of soft hadrons and jets that accompany
central hard-scattering production at hadron colliders is of great importance,
since it has a direct bearing on the ability to separate new physics signals
from Standard Model backgrounds. We compare the predictions for the gluonic
k_t-distribution using two different approaches: resummed NLL BFKL and DGLAP
evolution. We find that as long as the initial and final virtualities (k_t)
along the emission chain are not too close to each other, the NLL resummed BFKL
results do not differ significantly from those obtained using standard DGLAP
evolution. The saturation momentum Q_s(x), calculated within the resummed BFKL
approach, grows with 1/x even slower than in the leading-order DGLAP case.Comment: 24 pages, 8 figures, An improved, slightly more precise NLL
resummation is used and the figures are updated accordingly. The conclusions
are unchange
Extending QCD perturbation theory to higher energies
On the basis of the results of a new renormalisation group improved small-x
resummation scheme, we argue that the range of validity of perturbative
calculations is considerably extended in rapidity with respect to leading log
expectations. We thus provide predictions for the energy dependence of the
gluon Green function in its perturbative domain and for the resummed splitting
function. As in previous analyses, high-energy exponents are reduced to
phenomenologically acceptable values. Additionally, interesting preasymptotic
effects are observed. In particular, the splitting function shows a shallow dip
in the moderate small-x region, followed by the expected power increase.Comment: 12 pages, 4 figures. Expanded some discussions, clarified a figure,
added some references. Version to appear in Phys. Lett.
Inclusive jet spectrum for small-radius jets
Following on our earlier work on leading-logarithmic (LLR) resummations for
the properties of jets with a small radius, R, we here examine the
phenomenological considerations for the inclusive jet spectrum. We discuss how
to match the NLO predictions with small-R resummation. As part of the study we
propose a new, physically-inspired prescription for fixed-order predictions and
their uncertainties. We investigate the R-dependent part of the
next-to-next-to-leading order (NNLO) corrections, which is found to be
substantial, and comment on the implications for scale choices in inclusive jet
calculations. We also examine hadronisation corrections, identifying potential
limitations of earlier analytical work with regards to their -dependence.
Finally we assemble these different elements in order to compare matched
(N)NLO+LLR predictions to data from ALICE and ATLAS, finding improved
consistency for the R-dependence of the results relative to NLO predictions.Comment: 42 pages, 24 figures, additional material at
http://microjets.hepforge.org/, updated to match published versio
Quark mass hierarchy in 3-3-1 models
We study the mass spectrum of the quark sector in an special type I-like
model with gauge symmetry . By
considering couplings with scalar triplets at large () and small
() scales, we obtain specific zero-texture mass matrices for the
quarks which predict three massless quarks () and three massive quarks
() at the electroweak scale ( GeV). Taking into account mixing
couplings with three heavy quarks at large scales predicted by the model, the
three massless quarks obtain masses at small order that depends on the inverse
of the large scale. Thus, masses of the form
and can be obtained naturally from the gauge structure of
the model
Spectrum of D=6, N=4b Supergravity on AdS_3 x S^3
The complete spectrum of D=6, N=4b supergravity with n tensor multiplets
compactified on AdS_3 x S^3 is determined. The D=6 theory obtained from the K_3
compactification of Type IIB string requires that n=21, but we let n be
arbitrary. The superalgebra that underlies the symmetry of the resulting
supergravity theory in AdS_3 coupled to matter is SU(1,1|2)_L x SU(1,1|2)_R.
The theory also has an unbroken global SO(4)_R x SO(n) symmetry inherited from
D=6. The spectrum of states arranges itself into a tower of spin-2
supermultiplets, a tower of spin-1, SO(n) singlet supermultiplets, a tower of
spin-1 supermultiplets in the vector representation of SO(n) and a special
spin-1/2 supermultiplet also in the vector representation of SO(n). The SU(2)_L
x SU(2)_R Yang-Mills states reside in the second level of the spin-2 tower and
the lowest level of the spin-1, SO(n) singlet tower and the associated field
theory exhibits interesting properties.Comment: 37 pages, latex, 5 tables and 3 figures, typos corrected, a reference
adde
Resummation
We review the work discussed and developed under the topic ``Resummation'' at
Working Group 2 ``Multijet final states and energy flow'', of the HERA-LHC
Workshop. We emphasise the role played by HERA observables in the development
of resummation tools via, for instance, the discovery and resummation of
non-global logarithms. We describe the event-shapes subsequently developed for
hadron colliders and present resummed predictions for the same using the
automated resummation program CAESAR. We also point to ongoing studies at HERA
which can be of benefit for future measurements at hadron colliders such as the
LHC, specifically dijet and angular spectra and the transverse momentum
of the Breit current hemisphere.Comment: 15 pages, 6 figures. Submitted to the HERA-LHC workshop proceeding
Cascading and Local-Field Effects in Non-Linear Optics Revisited; A Quantum-Field Picture Based on Exchange of Photons
The semi-classical theory of radiation-matter coupling misses local-field
effects that may alter the pulse time-ordering and cascading that leads to the
generation of new signals. These are then introduced macroscopically by solving
Maxwell's equations. This procedure is convenient and intuitive but ad hoc. We
show that both effects emerge naturally by including coupling to quantum modes
of the radiation field in the vacuum state to second order. This approach is
systematic and suggests a more general class of corrections that only arise in
a QED framework. In the semi-classical theory, which only includes classical
field modes, the susceptibility of a collection of non-interacting
molecules is additive and scales as . Second-order coupling to a vacuum mode
generates an effective retarded interaction that leads to cascading and local
field effects both of which scale as
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