2,199 research outputs found
On the emergence of scale-free production networks
We propose a simple dynamical model of the formation of production networks
among monopolistically competitive firms. The model subsumes the standard
general equilibrium approach \`a la Arrow-Debreu but displays a wide set of
potential dynamic behaviors. It robustly reproduces key stylized facts of
firms' demographics. Our main result is that competition between intermediate
good producers generically leads to the emergence of scale-free production
networks.Comment: 31 pages, 15 figure
Wisdom of the institutional crowd
The average portfolio structure of institutional investors is shown to have
properties which account for transaction costs in an optimal way. This implies
that financial institutions unknowingly display collective rationality, or
Wisdom of the Crowd. Individual deviations from the rational benchmark are
ample, which illustrates that system-wide rationality does not need nearly
rational individuals. Finally we discuss the importance of accounting for
constraints when assessing the presence of Wisdom of the Crowd.Comment: 11 pages, 12 figure
Modular Entanglement
We introduce and discuss the concept of modular entanglement. This is the
entanglement that is established between the end points of modular systems
composed by sets of interacting moduli of arbitrarily fixed size. We show that
end-to-end modular entanglement scales in the thermodynamic limit and rapidly
saturates with the number of constituent moduli. We clarify the mechanisms
underlying the onset of entanglement between distant and non-interacting
quantum systems and its optimization for applications to quantum repeaters and
entanglement distribution and sharing.Comment: 4 pages, 6 figure
Optimal Inflation Target: Insights from an Agent-Based Model
Which level of inflation should Central Banks be targeting? We investigate
this issue in the context of a simplified Agent Based Model of the economy.
Depending on the value of the parameters that describe the behaviour of agents
(in particular inflation anticipations), we find a rich variety of behaviour at
the macro-level. Without any active monetary policy, our ABM economy can be in
a high inflation/high output state, or in a low inflation/low output state.
Hyper-inflation, deflation and "business cycles" between coexisting states are
also found. We then introduce a Central Bank with a Taylor rule-based inflation
target, and study the resulting aggregate variables. Our main result is that
too-low inflation targets are in general detrimental to a CB-monitored economy.
One symptom is a persistent under-realisation of inflation, perhaps similar to
the current macroeconomic situation. Higher inflation targets are found to
improve both unemployment and negative interest rate episodes. Our results are
compared with the predictions of the standard DSGE model.Comment: 19 pages, 6 figures. The paper is under review for the online journal
"Economics". The reviews are public at this link:
http://www.economics-ejournal.org/economics/discussionpapers/2017-64 . This
version has been modified and improved following the advice of the reviewers
and commentator
Maximal compression of the redshift space galaxy power spectrum and bispectrum
We explore two methods of compressing the redshift space galaxy power
spectrum and bispectrum with respect to a chosen set of cosmological
parameters. Both methods involve reducing the dimension of the original
data-vector ( e.g. 1000 elements ) to the number of cosmological parameters
considered ( e.g. seven ) using the Karhunen-Lo\`eve algorithm. In the first
case, we run MCMC sampling on the compressed data-vector in order to recover
the one-dimensional (1D) and two-dimensional (2D) posterior distributions. The
second option, approximately 2000 times faster, works by orthogonalising the
parameter space through diagonalisation of the Fisher information matrix before
the compression, obtaining the posterior distributions without the need of MCMC
sampling. Using these methods for future spectroscopic redshift surveys like
DESI, EUCLID and PFS would drastically reduce the number of simulations needed
to compute accurate covariance matrices with minimal loss of constraining
power. We consider a redshift bin of a DESI-like experiment. Using the power
spectrum combined with the bispectrum as a data-vector, both compression
methods on average recover the 68% credible regions to within 0.7% and 2% of
those resulting from standard MCMC sampling respectively. These confidence
intervals are also smaller than the ones obtained using only the power spectrum
by (81%, 80%, 82%) respectively for the bias parameter b_1, the growth rate f
and the scalar amplitude parameter A_s.Comment: 27 pages, 8 figures, 1 table, Accepted 2018 January 28. Received 2018
January 25; in original form 2017 September 11. Added clarifications in the
text on the bias modelling and compression limits following referee's
comments. Removed tetraspectrum term from the pk-bk cross covariance +
correction in the appendi
Reconstruction of Markovian Master Equation parameters through symplectic tomography
In open quantum systems, phenomenological master equations with unknown
parameters are often introduced. Here we propose a time-independent procedure
based on quantum tomography to reconstruct the potentially unknown parameters
of a wide class of Markovian master equations. According to our scheme, the
system under investigation is initially prepared in a Gaussian state. At an
arbitrary time t, in order to retrieve the unknown coefficients one needs to
measure only a finite number (ten at maximum) of points along three
time-independent tomograms. Due to the limited amount of measurements required,
we expect our proposal to be especially suitable for experimental
implementations.Comment: 7 pages, 3 figure
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