3,512 research outputs found
Impact of Cosmic Variance on the Galaxy-Halo Connection for Lyman- Emitters
In this paper we study the impact of cosmic variance and observational
uncertainties in constraining the mass and occupation fraction, ,
of dark matter halos hosting Ly- Emitting Galaxies (LAEs) at high
redshift. To this end, we construct mock catalogs from an N-body simulation to
match the typical size of observed fields at (). In
our model a dark matter halo with mass in the range can only host one detectable LAE at most. We proceed to explore
the parameter space determined by , and
with a Markov Chain Monte-Carlo algorithm using the angular correlation
function (ACF) and the LAEs number density as observational constraints. We
find that the preferred minimum and maximum masses in our model span a wide
range , ; followed by a wide range in the
occupation fraction . As a consequence the
median mass, , of all the consistent models has a large uncertainty
. However,
we find that the same individual models have a relatively tight
scatter around the median mass dex.
We are also able to show that \focc\ is uniquely determined by ,
regardless of . We argue that upcoming large surveys covering at
least deg should be able to put tighter constraints on
and through the LAE number density distribution width constructed
over several fields of deg.Comment: 7 Pages, 5 figures. Accepted for publication in Ap
Identifying Fiscal Policy Shocks in Chile and Colombia
Structural VAR and Structural VEC models were estimated for Chile and Colombia, aiming at identifying fiscal policy shocks in both countries between 1990 and 2005. The impulse responses obtained allow the calculation of a peso-for-peso () effect on output of a shock to public spending and to the government's net tax revenues, providing a good notion of the incidence of fiscal policy shocks in both countries. When public finances are under control, as they are in Chile, fiscal policy seems to be more effective than when they lack stability and credibility, as seems to be the case of Colombia since the mid nineties.
From old wars to new wars and global terrorism
Even before 9/11 there were claims that the nature of war had changed
fundamentally. The 9/11 attacks created an urgent need to understand
contemporary wars and their relationship to older conventional and terrorist
wars, both of which exhibit remarkable regularities. The frequency-intensity
distribution of fatalities in "old wars", 1816-1980, is a power-law with
exponent 1.80. Global terrorist attacks, 1968-present, also follow a power-law
with exponent 1.71 for G7 countries and 2.5 for non-G7 countries. Here we
analyze two ongoing, high-profile wars on opposite sides of the globe -
Colombia and Iraq. Our analysis uses our own unique dataset for killings and
injuries in Colombia, plus publicly available data for civilians killed in
Iraq. We show strong evidence for power-law behavior within each war. Despite
substantial differences in contexts and data coverage, the power-law
coefficients for both wars are tending toward 2.5, which is a value
characteristic of non-G7 terrorism as opposed to old wars. We propose a
plausible yet analytically-solvable model of modern insurgent warfare, which
can explain these observations.Comment: For more information, please contact [email protected] or
[email protected]
IDENTIFYING FISCAL POLICY SHOCKS IN CHILE AND COLOMBIA
Structural VAR and Structural VEC models were estimated for Chile and Colombia, aiming at identifying fiscal policy shocks in both countries between 1990 and 2005. The impulse responses obtained allow the calculation of a pesofor- peso () effect on output of a shock to public spending and to the government's net tax revenues, providing a good notion of the incidence of fiscal policy shocks in both countries. When public finances are under control, as they are in Chile, fiscal policy seems to be more effective than when they lack stability and credibility, as seems to be the case of Colombia since the mid nineties.Identification, Fiscal Policy, SVAR, SVEC
Maximum approximate entropy and r threshold: A new approach for regularity changes detection
Approximate entropy (ApEn) has been widely used as an estimator of regularity
in many scientific fields. It has proved to be a useful tool because of its
ability to distinguish different system's dynamics when there is only available
short-length noisy data. Incorrect parameter selection (embedding dimension
, threshold and data length ) and the presence of noise in the signal
can undermine the ApEn discrimination capacity. In this work we show that
() can also be used as a feature to
discern between dynamics. Moreover, the combined use of and
allows a better discrimination capacity to be accomplished, even in
the presence of noise. We conducted our studies using real physiological time
series and simulated signals corresponding to both low- and high-dimensional
systems. When is incapable of discerning between different
dynamics because of the noise presence, our results suggest that
provides additional information that can be useful for classification purposes.
Based on cross-validation tests, we conclude that, for short length noisy
signals, the joint use of and can significantly decrease
the misclassification rate of a linear classifier in comparison with their
isolated use
Indirect detection of gravitino dark matter including its three-body decays
It was recently pointed out that in supersymmetric scenarios with gravitino
dark matter and bilinear R-parity violation, gravitinos with masses below Mw
typically decay with a sizable branching ratio into the 3-body final states
W^*+lepton and Z^*+neutrino. In this paper we study the indirect detection
signatures of gravitino dark matter including such final states. First, we
obtain the gamma ray spectrum from gravitino decays, which features a
monochromatic contribution from the decay into photon+neutrino and a continuum
contribution from the three-body decays. After studying its dependence on
supersymmetric parameters, we compute the expected gamma ray fluxes and derive
new constraints, from recent FERMI data, on the R-parity breaking parameter and
on the gravitino lifetime. Indirect detection via antimatter searches, a new
possibility brought about by the three-body final states, is also analyzed. For
models compatible with the gamma ray observations, the positron signal is found
to be negligible whereas the antiproton one can be significant.Comment: 21 pages,16 figures v2: one numerical error corrected, one figure
added, main results unchange
Critical behavior of ferromagnetic pure and random diluted nanoparticles with competing interactions: variational and Monte Carlo approaches
The magnetic properties and critical behavior of both ferromagnetic pure and
metallic nanoparticles having concurrently atomic disorder, dilution and
competing interactions, are studied in the framework of an Ising model. We have
used both the free energy variational principle based on the Bogoliubov
inequality and Monte Carlo simulation. As a case of study for random diluted
nanoparticles we have considered the FeMnAl alloy
characterized for exhibiting, under bulk conditions, low temperature reentrant
spin glass (RSG) behavior and for which experimental and simulation results are
available. Our results allow concluding that the variational model is
successful in reproducing features of the particle size dependence of the Curie
temperature for both pure and random diluted particles. In this last case, low
temperature magnetization reduction was consistent with the same type of RSG
behavior observed in bulk in accordance with the Almeida-Thouless line at low
fields and a linear dependence of the freezing temperature with the reciprocal
of the particle diameter was also obtained. Computation of the correlation
length critical exponent yielded the values via Bogoliubov
and via Monte Carlo. This fact indicates that even though
thermodynamical models can be indeed used in the study of nanostructures and
they can reproduce experimental features, special attention must be paid
regarding critical behavior. From both approaches, differences in the
exponent with respect to the pure Ising model agree with Harris and Fisher
arguments.Comment: 11 pages, 11 figures. Submitted to Phys. Rev.
Novel Higgs decay signals in R-parity violating models
In supersymmetric models the lightest Higgs boson may decay with a sizable
branching ratio into a pair of light neutralinos. We analyze such decays within
the context of the minimal supersymmetric standard model with R-parity
violation, where the neutralino itself is unstable and decays into Standard
Model fermions. We show that the R-parity violating couplings induce novel
Higgs decay signals that might facilitate the discovery of the Higgs boson at
colliders. At the LHC, the Higgs may be observed, for instance, through its
decay -via two neutralinos- into final states containing missing energy and
isolated charged leptons such as , and .
Another promising possibility is the search for the displaced vertices
associated with the neutralino decay. We also point out that Higgs searches at
the LHC might additionally provide the first evidence of R-parity violation.Comment: 15 pages, 7 figures. Corrected affiliation
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