6,977 research outputs found
Realised and Optimal Monetary Policy Rules in an Estimated Markov-Switching DSGE Model of the United Kingdom
This paper conducts a systematic investigation of parameter instability in a small open economy DSGE model of the UK economy over the past thirty-five years. Using Bayesian analysis, we find a number of Markov-switching versions of the model provide a better fit for the UK data than a model with time-invariant parameters. The Markov-switching DSGE model that has two independent Markov-chains - one governing the shifts in UK monetary policy and nominal price rigidity and one governing the standard deviations of shocks - is selected as the best fitting model. The preferred model is then used to evaluate and design monetary policy. For the latter, we use the Markov-Jump-Linear-Quadratic (MJLQ) model, as it incorporates abrupt changes in structural parameters into derivations of the optimal and arbitrary policy rules. It also reveals the entire forecasting distribution of the targeted variables. To our knowledge, this is the first paper that attempts to evaluate and design UK monetary policy based on an estimated open economy Markov-switching DSGE model.DSGE models; Markov-switching; Bayesian analysis
Revisiting the Dollar-Euro Permanent Equilibrium Exchange Rate: Evidence from Multivariate Unobserved Components Models
We propose an alterative approach to obtaining a permanent equilibrium exchange rate (PEER), based on an unobserved components (UC) model. This approach offers a number of advantages over the conventional cointegration-based PEER. Firstly, we do not rely on the prerequisite that cointegration has to be found between the real exchange rate and macroeconomic fundamentals to obtain non-spurious long-run relationships and the PEER. Secondly, the impact that the permanent and transitory components of the macroeconomic fundamentals have on the real exchange rate can be modelled separately in the UC model. This is important for variables, where the long and short-run effects may drive the real exchange rate in opposite directions, such as the relative government expenditure ratio.Permanent Equilibrium Exchange Rate; Unobserved Components Model; Exchange rate forecasting.
Embedded Lensing Time Delays, the Fermat Potential, and the Integrated Sachs-Wolfe Effect
We derive the Fermat potential for a spherically symmetric lens embedded in
an FLRW cosmology and use it to investigate the late-time integrated
Sachs-Wolfe (ISW) effect, i.e., secondary temperature fluctuations in the
cosmic microwave background (CMB) caused by individual large scale clusters and
voids. We present a simple analytical expression for the temperature
fluctuation in the CMB across such a lens as a derivative of the lens' Fermat
potential. This formalism is applicable to both linear and nonlinear density
evolution scenarios, to arbitrarily large density contrasts, and to all open
and closed background cosmologies. It is much simpler to use and makes the same
predictions as conventional approaches. In this approach the total temperature
fluctuation can be split into a time-delay part and an evolutionary part. Both
parts must be included for cosmic structures that evolve and both can be
equally important. We present very simple ISW models for cosmic voids and
galaxy clusters to illustrate the ease of use of our formalism. We use the
Fermat potentials of simple cosmic void models to compare predicted ISW effects
with those recently extracted from WMAP and \emph{Planck} data by stacking
large cosmic voids using the aperture photometry method. If voids in the local
universe with large density contrasts are no longer evolving we find that the
time delay contribution alone predicts values consistent with the measurements.
However, we find that for voids still evolving linearly, the evolutionary
contribution cancels a significant part of the time delay contribution and
results in predicted signals that are much smaller than recently observed.Comment: 25 pages, 4 figures, ApJ in pres
Red Clump Stars in the Sagittarius Tidal Streams
We have probed a section (l ~ 150, b ~ -60) of the trailing tidal arm of the
Sagittarius dwarf spheroidal galaxy by identifying a sample of Red Clump stream
stars. Red Clump stars are not generally found in the halo field, but are found
in significant numbers in both the Sagittarius galaxy and its tidal streams,
making them excellent probes of stream characteristics. Our target sample was
selected using photometric data from the Sloan Digital Sky Survey, Data Release
6, which was constrained in color to match the Sagittarius Red Clump stars.
Spectroscopic observations of the target stars were conducted at Kitt Peak
National Observatory using the WIYN telescope. The resulting spectroscopic
sample is magnitude limited and contains both main sequence disk stars and
evolved Red Clump stars. We have developed a method to systematically separate
these two stellar classes using kinematic information and a Bayesian approach
for surface gravity determination. The resulting Red Clump sample allows us to
determine an absolute stellar density of {\rho} = 2.7 +/- 0.5 RC stars kpc-3 at
this location in the stream. Future measurements of stellar densities for a
variety of populations and at various locations along the streams will lead to
a much improved understanding of the original nature of the Sagittarius galaxy
and the physical processes controlling its disruption and subsequent stream
generation.Comment: 16 figures, 5 tables, accepted to A
A Simple Gravitational Lens Model For Cosmic Voids
We present a simple gravitational lens model to illustrate the ease of using
the embedded lensing theory when studying cosmic voids. It confirms the
previously used repulsive lensing models for deep voids. We start by estimating
magnitude fluctuations and weak lensing shears of background sources lensed by
large voids. We find that sources behind large () and deep
voids (density contrast about ) can be magnified or demagnified with
magnitude fluctuations of up to and that the weak-lensing
shear can be up to the level in the outer regions of large
voids. Smaller or shallower voids produce proportionally smaller effects. We
investigate the "wiggling" of the primary cosmic microwave background (CMB)
temperature anisotropies caused by intervening cosmic voids. The void-wiggling
of primary CMB temperature gradients is of the opposite sign to that caused by
galaxy clusters. Only extremely large and deep voids can produce wiggling
amplitudes similar to galaxy clusters, by a large void of
radius and central density contrast at redshift 0.5
assuming a CMB background gradient of . The
dipole signal is spread over the entire void area, and not concentrated at the
lens' center as it is for clusters. Finally we use our model to simulate CMB
sky maps lensed by large cosmic voids. Our embedded theory can easily be
applied to more complicated void models and used to study gravitational lensing
of the CMB, to probe dark-matter profiles, to reduce the lensing-induced
systematics in supernova Hubble diagrams, as well as study the integrated
Sachs-Wolfe effect.Comment: 25 pages, 4 figures, ApJ accepte
Efficient Multi-Point Local Decoding of Reed-Muller Codes via Interleaved Codex
Reed-Muller codes are among the most important classes of locally correctable
codes. Currently local decoding of Reed-Muller codes is based on decoding on
lines or quadratic curves to recover one single coordinate. To recover multiple
coordinates simultaneously, the naive way is to repeat the local decoding for
recovery of a single coordinate. This decoding algorithm might be more
expensive, i.e., require higher query complexity. In this paper, we focus on
Reed-Muller codes with usual parameter regime, namely, the total degree of
evaluation polynomials is , where is the code alphabet size
(in fact, can be as big as in our setting). By introducing a novel
variation of codex, i.e., interleaved codex (the concept of codex has been used
for arithmetic secret sharing \cite{C11,CCX12}), we are able to locally recover
arbitrarily large number of coordinates of a Reed-Muller code
simultaneously at the cost of querying coordinates. It turns out that
our local decoding of Reed-Muller codes shows ({\it perhaps surprisingly}) that
accessing locations is in fact cheaper than repeating the procedure for
accessing a single location for times. Our estimation of success error
probability is based on error probability bound for -wise linearly
independent variables given in \cite{BR94}
Efficient and Error-Correcting Data Structures for Membership and Polynomial Evaluation
We construct efficient data structures that are resilient against a constant
fraction of adversarial noise. Our model requires that the decoder answers most
queries correctly with high probability and for the remaining queries, the
decoder with high probability either answers correctly or declares "don't
know." Furthermore, if there is no noise on the data structure, it answers all
queries correctly with high probability. Our model is the common generalization
of a model proposed recently by de Wolf and the notion of "relaxed locally
decodable codes" developed in the PCP literature.
We measure the efficiency of a data structure in terms of its length,
measured by the number of bits in its representation, and query-answering time,
measured by the number of bit-probes to the (possibly corrupted)
representation. In this work, we study two data structure problems: membership
and polynomial evaluation. We show that these two problems have constructions
that are simultaneously efficient and error-correcting.Comment: An abridged version of this paper appears in STACS 201
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