14,455 research outputs found
Topological Interference Management with Alternating Connectivity
The topological interference management problem refers to the study of the
capacity of partially connected linear (wired and wireless) communication
networks with no channel state information at the transmitters (no CSIT) beyond
the network topology, i.e., a knowledge of which channel coefficients are zero
(weaker than the noise floor in the wireless case). While the problem is
originally studied with fixed topology, in this work we explore the
implications of varying connectivity, through a series of simple and
conceptually representative examples. Specifically, we highlight the
synergistic benefits of coding across alternating topologies
On the Optimality of Treating Interference as Noise: General Message Sets
In a K-user Gaussian interference channel, it has been shown that if for each
user the desired signal strength is no less than the sum of the strengths of
the strongest interference from this user and the strongest interference to
this user (all values in dB scale), then treating interference as noise (TIN)
is optimal from the perspective of generalized degrees-of-freedom (GDoF) and
achieves the entire channel capacity region to within a constant gap. In this
work, we show that for such TIN-optimal interference channels, even if the
message set is expanded to include an independent message from each transmitter
to each receiver, operating the new channel as the original interference
channel and treating interference as noise is still optimal for the sum
capacity up to a constant gap. Furthermore, we extend the result to the
sum-GDoF optimality of TIN in the general setting of X channels with arbitrary
numbers of transmitters and receivers
Multilevel Topological Interference Management
The robust principles of treating interference as noise (TIN) when it is
sufficiently weak, and avoiding it when it is not, form the background for this
work. Combining TIN with the topological interference management (TIM)
framework that identifies optimal interference avoidance schemes, a baseline
TIM-TIN approach is proposed which decomposes a network into TIN and TIM
components, allocates the signal power levels to each user in the TIN
component, allocates signal vector space dimensions to each user in the TIM
component, and guarantees that the product of the two is an achievable number
of signal dimensions available to each user in the original network.Comment: To be presented at 2013 IEEE Information Theory Worksho
Vector meson-vector meson interaction in a hidden gauge unitary approach
The formalism developed recently to study vector meson--vector meson
interaction, and applied to the case of , is extended to study the
interaction of the nonet of vector mesons among themselves. The interaction
leads to poles of the scattering matrix corresponding to bound states or
resonances. We show that 11 states (either bound or resonant) get dynamically
generated in nine strangeness-isospin-spin channels. Five of them can be
identified with those reported in the PDG, i.e., the , ,
, , and . The masses of the latter three
tensor states have been used to fine-tune the free parameters of the unitary
approach, i.e., the subtraction constants in evaluating the vector meson
-vector meson loop functions in the dimensional regularization scheme. The
branching ratios of these five dynamically generated states are found to be
consistent with data. The existence of the other six states should be taken as
predictions to be tested by future experiments.Comment: typos corrected; more discussions; one of the appendix rearrange
On Charge Quantization and Abelian Gauge Horizontal Symmetries
Under the assumption that there exists a local gauge horizontal symmetry
wich allows only for a top quark mass at tree level, we look for the
constraints that charge quatization and the family structure of the standard
model imposes on that symmetry.Comment: 13 pages, LaTeX, Acepted in Physics Letters
Low-lying even parity meson resonances and spin-flavor symmetry
A study is presented of the wave meson-meson interactions involving
members of the nonet and of the octet. The starting point is an
SU(6) spin-flavor extension of the SU(3) flavor Weinberg-Tomozawa Lagrangian.
SU(6) symmetry breaking terms are then included to account for the physical
meson masses and decay constants, while preserving partial conservation of the
axial current in the light pseudoscalar sector. Next, the matrix amplitudes
are obtained by solving the Bethe Salpeter equation in coupled-channel with the
kernel built from the above interactions. The poles found on the first and
second Riemann sheets of the amplitudes are identified with their possible
Particle Data Group (PDG) counterparts. It is shown that most of the low-lying
even parity PDG meson resonances, specially in the and sectors,
can be classified according to multiplets of the spin-flavor symmetry group
SU(6). The , and some resonances cannot be
accommodated within this SU(6) scheme and thus they would be clear candidates
to be glueballs or hybrids. Finally, we predict the existence of five exotic
resonances ( and/or ) with masses in the range 1.4--1.6 GeV,
which would complete the , , and multiplets of
SU(3)SU(2).Comment: 43 pages, 2 figures, 61 tables. Improved discussion of Section II. To
appear in Physical Review
Two-photon and one photon-one vector meson decay widths of the , , , , and
We calculate the radiative decay widths, two-photon () and one
photon-one vector meson (), of the dynamically generated resonances
from vector meson-vector meson interaction in a unitary approach based on the
hidden-gauge Lagrangians. In the present paper we consider the following
dynamically generated resonances: , , ,
, , two strangeness=0 and isospin=1 states, and two
strangeness=1 and isospin=1/2 states. For the and we
reproduce the previous results for the two-photon decay widths and further
calculate their one photon-one vector decay widths. For the and
the calculated two-photon decay widths are found to be consistent
with data. The , and decay widths of
the , , , are compared with the
results predicted by other approaches. The and
decay rates of the are also calculated and compared with the
results obtained in the framework of the covariant oscillator quark model. The
results for the two states with strangeness=0, isospin=1 and two states with
strangeness=1, isospin=1/2 are predictions that need to be tested by future
experiments.Comment: More discussions about the relation between qqbar states and
dynamically generated states; version published in PRD
Neutral current coherent pion production
We investigate the neutrino induced coherent pion production reaction at low
and intermediate energies. The model includes pion, nucleon and Delta(1232)
resonance as the relevant hadronic degrees of freedom. Nuclear medium effects
on the production mechanisms and pion distortion are taken into account. We
obtain that the dominance of the Delta excitation holds due to large
cancellations among the background contributions. We consider two sets of
vector and axial-vector N-Delta transition form-factors, evidencing the strong
sensitivity of the results to the axial coupling C5A(0). The differences
between neutrino and antineutrino cross sections, emerging from interference
terms, are also discussed.Comment: 4 pages, 3 figures, minor corrections, a few references adde
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