386,990 research outputs found
Polarized Curvature Radiation in Pulsar Magnetosphere
The propagation of polarized emission in pulsar magnetosphere is investigated
in this paper. The polarized waves are generated through curvature radiation
from the relativistic particles streaming along curved magnetic field lines and
co-rotating with the pulsar magnetosphere. Within the 1/{\deg} emission cone,
the waves can be divided into two natural wave mode components, the ordinary
(O) mode and the extraord nary (X) mode, with comparable intensities. Both
components propagate separately in magnetosphere, and are aligned within the
cone by adiabatic walking. The refraction of O-mode makes the two components
separated and incoherent. The detectable emission at a given height and a given
rotation phase consists of incoherent X-mode and O-mode components coming from
discrete emission regions. For four particle-density models in the form of
uniformity, cone, core and patches, we calculate the intensities for each mode
numerically within the entire pulsar beam. If the co-rotation of relativistic
particles with magnetosphere is not considered, the intensity distributions for
the X-mode and O-mode components are quite similar within the pulsar beam,
which causes serious depolarization. However, if the co-rotation of
relativistic particles is considered, the intensity distributions of the two
modes are very different, and the net polarization of out-coming emission
should be significant. Our numerical results are compared with observations,
and can naturally explain the orthogonal polarization modes of some pulsars.
Strong linear polarizations of some parts of pulsar profile can be reproduced
by curvature radiation and subsequent propagation effect.Comment: 12 pages, 9 figures, Accepted for publication in MNRA
QCD Factorization for Quarkonium Production in Hadron Collions at Low Transverse Momentum
Inclusive production of a quarkonium in hadron collisions at low
transverse momentum can be used to extract various
Transverse-Momentum-Dependent(TMD) gluon distributions of hadrons, provided the
TMD factorization for the process holds. The factorization involving
unpolarized TMD gluon distributions of unpolarized hadrons has been examined
with on-shell gluons at one-loop level. In this work we study the factorization
at one-loop level with diagram approach in the most general case, where all TMD
gluon distributions at leading twist are involved. We find that the
factorization holds and the perturbative effects are represented by one
perturbative coefficient. Since the initial gluons from hadrons are off-shell
in general, there exists the so-called super-leading region found recently. We
find that the contributions from this region can come from individual diagrams
at one-loop level, but they are cancelled in the sum. Our factorized result for
the differential cross-section is explicitly gauge-invariant.Comment: discussions and references are added. Published version on Phys. Rev.
QCD Evolutions of Twist-3 Chirality-Odd Operators
We study the scale dependence of twist-3 distributions defined with
chirality-odd quark-gluon operators. To derive the scale dependence we
explicitly calculate these distributions of multi-parton states instead of a
hadron. Taking one-loop corrections into account we obtain the leading
evolution kernel in the most general case. In some special cases the evolutions
are simplified. We observe that the obtained kernel in general does not get
simplified in the large- limit in contrast to the case of those twist-3
distributions defined only with chirality-odd quark operators. In the later,
the simplification is significant.Comment: 9 pages, 2 figure
Positivity-preserving H∞ model reduction for positive systems
This is the post-print version of the Article - Copyright @ 2011 ElevierThis paper is concerned with the model reduction of positive systems. For a given stable positive system, our attention is focused on the construction of a reduced-order model in such a way that the positivity of the original system is preserved and the error system is stable with a prescribed H∞ performance. Based upon a system augmentation approach, a novel characterization on the stability with H∞ performance of the error system is first obtained in terms of linear matrix inequality (LMI). Then, a necessary and sufficient condition for the existence of a desired reduced-order model is derived accordingly. Furthermore, iterative LMI approaches with primal and dual forms are developed to solve the positivity-preserving H∞ model reduction problem. Finally, a compartmental network is provided to show the effectiveness of the proposed techniques.The work was partially supported by GRF HKU 7137/09E
Quantum phase transitions of polar molecules in bilayer systems
We investigate the quantum phase transitions of bosonic polar molecules in a
two-dimensional double layer system. We show that an interlayer bound state of
dipoles (dimers) can be formed when the dipole strength is above a critical
value, leading to a zero-energy resonance in the interlayer s-wave scattering
channel. In the positive detuning side of the resonance, the strong repulsive
interlayer pseudopotential can drive the system into a maximally entangled
state, where the wave function is a superposition of two states that have all
molecules in one layer and none in the other. We discuss how the zero-energy
resonance, dimer states, and the maximally entangled state can be measured in
time-of-flight experiments.Comment: Minor correction
Breakdown of QCD Factorization for P-Wave Quarkonium Production at Low Transverse Momentum
Quarkonium production at low transverse momentum in hadron collisions can be
used to extract Transverse-Momentum-Dependent(TMD) gluon distribution
functions, if TMD factorization holds there. We show that TMD factorization for
the case of P-wave quarkonium with holds at one-loop
level, but is violated beyond one-loop level. TMD factorization for other
P-wave quarkonium is also violated already at one-loop.Comment: Published version in Physics Letters B (2014), pp. 103-10
- …