2,191 research outputs found
Dirac Gauginos in Low Scale Supersymmetry Breaking
It has been claimed that Dirac gaugino masses are necessary for realistic
models of low-scale supersymmetry breaking, and yet very little attention has
been paid to the phenomenology of a light gravitino when gauginos have Dirac
masses. We begin to address this deficit by investigating the couplings and
phenomenology of the gravitino in the effective Lagrangian approach. We pay
particular attention to the phenomenology of the scalar octets, where new decay
channels open up. This leads us to propose a new simplified effective scenario
including only light gluinos, sgluons and gravitinos, allowing the squarks to
be heavy -- with the possible exception of the third generation. Finally, we
comment on the application of our results to Fake Split Supersymmetry.Comment: 40 pages, 3 figures. Minor typos fixed; matches version in Nuclear
Physics
The stochastic background of gravitational waves due to the f-mode instability in neutron stars
This paper presents an estimate for the spectral properties of the stochastic
background of gravitational waves emitted by a population of hot, young,
rapidly rotating neutron stars throughout the Universe undergoing -mode
instabilities, formed through either core-collapse supernova explosions or the
merger of binary neutron star systems. Their formation rate, from which the
gravitational wave event rate is obtained, is deduced from observation-based
determinations of the cosmic star formation rate. The gravitational wave
emission occurs during the spin-down phase of the -mode instability. For low
magnetized neutron stars and assuming 10\% of supernova events lead to -mode
unstable neutron stars, the background from supernova-derived neutron stars
peaks at for the -mode, which
should be detectable by cross-correlating a pair of second generation
interferometers (e.g. Advanced LIGO/Virgo) with an upper estimate for the
signal-to-noise ratio of 9.8. The background from supramassive
neutron stars formed from binary mergers peaks at and should not be detectable, even with third generation
interferometers (e.g. Einstein Telescope)
Fiscal Decentralization and Public Sector Efficiency: Evidence from OECD Countries
This paper attempts to identify the effect of fiscal decentralization on public sector efficiency (PSE). We employ data envelopment analysis on a panel of 21 OECD countries over the period 1970-2000 to construct two alternative PSE indicators that reflect the governmental goals of economic performance and stability. In turn, using a novel technique that merges the methodologies of Simar and Wilson (2007) and Khan and Lewbel (2007), we regress the PSE scores obtained on an extensive set of alternative fiscal decentralization measures. Backed by strong empirical results, obtained from a number of different specifications, we contend that PSE is increasing with fiscal decentralization.public sector efficiency, fiscal decentralization, semi-parametric models
Are democratic governments more efficient?
This paper explores the relationship between public sector efficiency (PSE) and the level of democracy, both theoretically and empirically. At the theoretical level a simple model of elections with two time periods is presented, which takes into account whether the political regime is democratic or not. Specifically, we assume that elected officials in democracies are âmoreâ accountable to voters than the respective ones in autocracies. This mechanism induces the democratic politicians to produce the public good in a more efficient way, in order to remain in power. In the empirical section we examine the effect of democracy on PSE for a panel dataset of 50 developing and developed countries over the period 1980-2000. Our results suggest that the relationship between PSE and democracy is positive and statistically significant, thus confirming our theoretical priors.H11; D7
Public sector efficiency: Leveling the playing field between OECD countries
In this paper we seek a robust methodology to measure the relative public spending efficiency of 19 OECD countries over the period 1980-2000. Based on the functional classification of government expenditure, we decompose total public spending into its separate accounts and we employ a semi-parametric method to obtain relative efficiency scores (for the separate accounts as well as for aggregate public spending). The econometric method isolates the impact of government inefficiency from the inefficiency arising from the socioeconomic environment or luck, thus leveling the playing field between the examined countries. The results suggest that the quality of governance is more important than the socioeconomic environment or luck. Finally, we propose a technique to measure the allocative efficiency of public spending, in an effort to proxy the optimal allocation of public funds when the governments set specific targets.Public spending; Technical and allocative efficiency; Stochastic DEA
Uniqueness of Petrov type D spatially inhomogeneous irrotational silent models
The consistency of the constraint with the evolution equations for spatially
inhomogeneous and irrotational silent (SIIS) models of Petrov type I, demands
that the former are preserved along the timelike congruence represented by the
velocity of the dust fluid, leading to \emph{new} non-trivial constraints. This
fact has been used to conjecture that the resulting models correspond to the
spatially homogeneous (SH) models of Bianchi type I, at least for the case
where the cosmological constant vanish. By exploiting the full set of the
constraint equations as expressed in the 1+3 covariant formalism and using
elements from the theory of the spacelike congruences, we provide a direct and
simple proof of this conjecture for vacuum and dust fluid models, which shows
that the Szekeres family of solutions represents the most general class of SIIS
models. The suggested procedure also shows that, the uniqueness of the SIIS of
the Petrov type D is not, in general, affected by the presence of a non-zero
pressure fluid. Therefore, in order to allow a broader class of Petrov type I
solutions apart from the SH models of Bianchi type I, one should consider more
general ``silent'' configurations by relaxing the vanishing of the vorticity
and the magnetic part of the Weyl tensor but maintaining their ``silence''
properties i.e. the vanishing of the curls of and the pressure
.Comment: Latex, 19 pages, no figures;(v2) some clarification remarks and an
appendix are added; (v3) minor changes to match published versio
Dark stars: gravitational and electromagnetic observables
Theoretical models of self-interacting dark matter represent a promising
answer to a series of open problems within the so-called collisionless cold
dark matter (CCDM) paradigm. In case of asymmetric dark matter,
self-interactions might facilitate gravitational collapse and potentially lead
to formation of compact objects predominantly made of dark matter. Considering
both fermionic and bosonic equations of state, we construct the equilibrium
structure of rotating dark stars, focusing on their bulk properties, and
comparing them with baryonic neutron stars. We also show that these dark
objects admit the -Love- universal relations, which link their moments of
inertia, tidal deformabilities, and quadrupole moments. Finally, we prove that
stars built with a dark matter equation of state are not compact enough to
mimic black holes in general relativity, thus making them distinguishable in
potential events of gravitational interferometers.Comment: 14 pages, 7 figure
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