2,581 research outputs found
Joint source-channel coding with feedback
This paper quantifies the fundamental limits of variable-length transmission
of a general (possibly analog) source over a memoryless channel with noiseless
feedback, under a distortion constraint. We consider excess distortion, average
distortion and guaranteed distortion (-semifaithful codes). In contrast to
the asymptotic fundamental limit, a general conclusion is that allowing
variable-length codes and feedback leads to a sizable improvement in the
fundamental delay-distortion tradeoff. In addition, we investigate the minimum
energy required to reproduce source samples with a given fidelity after
transmission over a memoryless Gaussian channel, and we show that the required
minimum energy is reduced with feedback and an average (rather than maximal)
power constraint.Comment: To appear in IEEE Transactions on Information Theor
The inflation bias under Calvo and Rotemberg pricing
New Keynesian analysis relies heavily on two workhorse models of nominal inertia – due to Calvo (1983) and Rotemberg (1982), respectively – to generate a meaningful role for monetary policy. These are often used interchangeably since they imply an isomorphic linearized Phillips curve and, if the steady-state is efficient, the same policy conclusions. In this paper we compute time-consistent optimal monetary policy in the benchmark New Keynesian model containing each form of price stickiness using global solution techniques. We find that, due to an offsetting endogenous impact on average markups, the inflation bias problem under Calvo contracts is often significantly greater than under Rotemberg pricing, despite the fact that the former typically exhibits far greater welfare costs of inflation. The nonlinearities inherent in the New Keynesian model are significant and the form of nominal inertia adopted is not innocuous
Erasure Multiple Descriptions
We consider a binary erasure version of the n-channel multiple descriptions
problem with symmetric descriptions, i.e., the rates of the n descriptions are
the same and the distortion constraint depends only on the number of messages
received. We consider the case where there is no excess rate for every k out of
n descriptions. Our goal is to characterize the achievable distortions D_1,
D_2,...,D_n. We measure the fidelity of reconstruction using two distortion
criteria: an average-case distortion criterion, under which distortion is
measured by taking the average of the per-letter distortion over all source
sequences, and a worst-case distortion criterion, under which distortion is
measured by taking the maximum of the per-letter distortion over all source
sequences. We present achievability schemes, based on random binning for
average-case distortion and systematic MDS (maximum distance separable) codes
for worst-case distortion, and prove optimality results for the corresponding
achievable distortion regions. We then use the binary erasure multiple
descriptions setup to propose a layered coding framework for multiple
descriptions, which we then apply to vector Gaussian multiple descriptions and
prove its optimality for symmetric scalar Gaussian multiple descriptions with
two levels of receivers and no excess rate for the central receiver. We also
prove a new outer bound for the general multi-terminal source coding problem
and use it to prove an optimality result for the robust binary erasure CEO
problem. For the latter, we provide a tight lower bound on the distortion for
\ell messages for any coding scheme that achieves the minimum achievable
distortion for k messages where k is less than or equal to \ell.Comment: 48 pages, 2 figures, submitted to IEEE Trans. Inf. Theor
Recent results and perspectives on cosmology and fundamental physics from microwave surveys
Recent cosmic microwave background data in temperature and polarization have
reached high precision in estimating all the parameters that describe the
current so-called standard cosmological model. Recent results about the
integrated Sachs-Wolfe effect from cosmic microwave background anisotropies,
galaxy surveys, and their cross-correlations are presented. Looking at fine
signatures in the cosmic microwave background, such as the lack of power at low
multipoles, the primordial power spectrum and the bounds on non-Gaussianities,
complemented by galaxy surveys, we discuss inflationary physics and the
generation of primordial perturbations in the early Universe. Three important
topics in particle physics, the bounds on neutrinos masses and parameters, on
thermal axion mass and on the neutron lifetime derived from cosmological data
are reviewed, with attention to the comparison with laboratory experiment
results. Recent results from cosmic polarization rotation analyses aimed at
testing the Einstein equivalence principle are presented. Finally, we discuss
the perspectives of next radio facilities for the improvement of the analysis
of future cosmic microwave background spectral distortion experiments.Comment: 27 pages, 9 figures. Review Article. International Journal of Modern
Physics D, in press. [Will appear also on the proceedings of the Fourteenth
Marcel Grossmann Meeting University of Rome "La Sapienza" - Rome, July 12-18,
2015 (http://www.icra.it/mg/mg14/), eds. Robert T. Jantzen, Kjell Rosquist,
Remo Ruffini. World Scientific, Singapore
CMB Spectral Distortions from an Axion-Dark Photon-Photon Interaction
The presence of a plethora of light spin 0 and spin 1 fields is motivated in
a number of BSM scenarios, such as the axiverse. The study of the interactions
of such light bosonic fields with the Standard Model has focused mostly on
interactions involving only one such field, such as the axion () coupling
to photons, , or the kinetic mixing between photon and the
dark photon, . In this work, we continue the exploration of
interactions involving two light BSM fields and the standard model, focusing on
the mixed axion-photon-dark-photon interaction . If either
the axion or dark photon are dark matter, we show that this interaction leads
to conversion of the CMB photons into a dark sector particle, leading to a
distortion in the CMB spectrum. We present the details of these unique
distortion signatures and the resulting constraints on the
coupling. In particular, we find that for a wide range of masses, the
constraints from these effect are stronger than on the more widely studied
axion-photon coupling.Comment: body 18 pages, appendix 13 pages, 8 figure
The EDGES signal: An imprint from the mirror world?
Recent results from the Experiment to Detect the Global Epoch of Reionization
Signature (EDGES) show an anomalous spectral feature at redshifts
in its 21-cm absorption signal. This deviation from cosmological predictions
can be understood as a consequence of physics that either lower the hydrogen
spin temperature or increases the radiation temperature through the injection
of soft photons in the bath. In the latter case, standard model neutrino decays
induced by effective magnetic and electric transition
moments () are precluded by the tight astrophysical constraints
on . We show that if mirror neutrinos are present in the bath
at early times, an analogous mechanism in the mirror sector can lead to a
population of mirror photons that are then "processed" into visible photons
through resonant conversion, thus accounting for the EDGES signal. We point out
that the mechanism can work for mirror neutrinos which are either heavier than
or degenerate with the standard model (SM) neutrinos, a scenario naturally
realized in mirror twin Higgs models.Comment: 8 pages, 2 figure
Optical and plasmonic properties of twisted bilayer graphene: Impact of interlayer tunneling asymmetry and ground-state charge inhomogeneity
We present a theoretical study of the local optical conductivity, plasmon
spectra, and thermoelectric properties of twisted bilayer graphene (TBG) at
different filling factors and twist angles . Our calculations are based
on the electronic band structures obtained from a continuum model that has two
tunable parameters, and , which parametrize the intra-sublattice
inter-layer and inter-sublattice inter-layer tunneling rate, respectively. In
this Article we focus on two key aspects: i) we study the dependence of our
results on the value of , exploring the whole range ;
ii) we take into account effects arising from the intrinsic charge density
inhomogeneity present in TBG, by calculating the band structures within the
self-consistent Hartree approximation. At zero filling factor, i.e. at the
charge neutrality point, the optical conductivity is quite sensitive to the
value of and twist angle, whereas the charge inhomogeneity brings about
only modest corrections. On the other hand, away from zero filling, static
screening dominates and the optical conductivity is appreciably affected by the
charge inhomogeneity, the largest effects being seen on the intra-band
contribution to it. These findings are also reflected by the plasmonic spectra.
We compare our results with existing ones in the literature, where effects i)
and ii) above have not been studied systematically. As natural byproducts of
our calculations, we obtain the Drude weight and Seebeck coefficient. The
former displays an enhanced particle-hole asymmetry stemming from the
inhomogeneous ground-state charge distribution. The latter is shown to display
a broad sign-changing feature even at low temperatures ()
due to the reduced slope of the bands, as compared to those of single-layer
graphene.Comment: 28 pages, 16 figures, 6 appendice
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