13,481 research outputs found
Consistent Pauli reduction on group manifolds
We prove an old conjecture by Duff, Nilsson, Pope and Warner asserting that
the NS-NS sector of supergravity (and more general the bosonic string) allows
for a consistent Pauli reduction on any d-dimensional group manifold G, keeping
the full set of gauge bosons of the G x G isometry group of the bi-invariant
metric on G. The main tool of the construction is a particular generalised
Scherk-Schwarz reduction ansatz in double field theory which we explicitly
construct in terms of the group's Killing vectors. Examples include the
consistent reduction from ten dimensions on and on similar
product spaces. The construction is another example of globally geometric
non-toroidal compactifications inducing non-geometric fluxes.Comment: 16 page
Insensitive control technology development
THe investigation of two insensitive controller synthesis techniques was reported. The finite dimensional inverse approach produces a time varying insensitive controller and/or parameter identifier by constructing inverse functions derived from a finite number of input output pair relationships. The MD/IM concept relies on the information matrix theory that was developed in the estimation and identification field. The MD/IM synthesis technique is based on the hypothesis that minimizing the information matrix will reduce system identifiability and consequently system sensitivity to uncertain parameters. The controllers designed with both techniques were evaluated on a realistic C-5A aircraft flight control problem. Results indicate that the FDI controller is more suited to trajectory type problems because of its time varying nature. The MD/IM controller performed as well as the top-rated controllers of the initial effort and has direct application to aircraft flight control problems
Earnings Management to Avoid Losses: a cost of debt explanation
In this paper we analyze firmsâ earnings management behavior to avoid losses conditional on the (asymmetric) incentive underlying market (positive/negative) returns. Our intuition is that firms with negative returns in the period (bad news, BN) face a higher incentive to undertake earnings management, and that their ultimate intention is to hide from credit markets a signal (loss) that could be translated into a negative impact on their cost of debt. The empirical evidence supports this intuition. BN firms show higher earnings management pervasiveness than their counterparts with good news (GN), and the set with simultaneous BN and prior period positive earnings undertake more pervasive earnings manipulation than BN firms in general. Within this restricted set of firms, and consistent with a cost of debt explanation, we find that firms with larger needs of debt show a higher incidence of earnings management to avoid losses. The overall empirical evidence challenges the implicit assumption in Burgstahler and Dichev (1997) that the incentive to manage earnings is homogeneous to all firms, and suggests that the discontinuities around zero in the earnings distributions are driven, at least partly, by firmsâ earnings management behavior.earnings management, earnings thresholds, earnings discontinuities, cost of debt
Piecewise Linear Accrual Models: do they really control for the asymmetric recognition of gains and losses?
The asymmetric recognition of gains and losses underlying conservative accounting is not taken into account by Jones (1991)-type accrual models. Recently, Moreira (2002) and Ball and Shivakumar (2005a) have proposed piecewise linear accrual models designed to control for this asymmetric impact. Our paper first discusses the sign of the expected measurement error in discretionary accruals (DAC) estimates when models do not control for the asymmetry underlying conservatism. We find that DAC in firms with bad news (BN) are expected to be understated, while those in good news (GN) firms will be overstated. Based on this original result we empirically test, using graphical and statistical tools, whether piecewise linear accrual models correct such a measurement error. The empirical evidence shows mixed results. For GN firms the estimates are corrected downwards, as expected; for BN firms, unexpectedly, part of the estimates is also corrected downwards. The reason for this unexpected result seems to lie in a non-linear relationship between accruals and the proxy for BN that the models are unable to control for. Thus, DAC estimates under piecewise linear models are not deemed to be of better quality than those of traditional accrual models.accrual models; piecewise linear accrual models; conservatism; earnings management
Gamma-ray emission associated with Cluster-scale AGN Outbursts
Recent observations have revealed the existence of enormously energetic
~10^61 erg AGN outbursts in three relatively distant galaxy clusters. These
outbursts have produced bubbles in the intra-cluster medium, apparently
supported by pressure from relativistic particles and/or magnetic fields. Here
we argue that if > GeV particles are responsible then these particles are very
likely protons and nuclei, rather than electrons, and that the gamma-ray
emission from these objects, arising from the interactions of these hadrons in
the intra-cluster medium, may be marginally detectable with instruments such as
GLAST and HESS.Comment: 8 pages, 4 figures, accepted by MNRA
Correlation Functions in -Deformed N=6 Supergravity
Gauged N=8 supergravity in four dimensions is now known to admit a
deformation characterized by a real parameter lying in the interval
. We analyse the fluctuations about its anti-de Sitter
vacuum, and show that the full N=8 supersymmetry can be maintained by the
boundary conditions only for . For non-vanishing , and
requiring that there be no propagating spin s>1 fields on the boundary, we show
that N=3 is the maximum degree of supersymmetry that can be preserved by the
boundary conditions. We then construct in detail the consistent truncation of
the N=8 theory to give -deformed SO(6) gauged N=6 supergravity, again
with in the range . We show that this theory
admits fully N=6 supersymmetry-preserving boundary conditions not only for
, but also for . These two theories are related by a
U(1) electric-magnetic duality. We observe that the only three-point functions
that depend on involve the coupling of an SO(6) gauge field with the
U(1) gauge field and a scalar or pseudo-scalar field. We compute these
correlation functions and compare them with those of the undeformed N=6 theory.
We find that the correlation functions in the theory
holographically correspond to amplitudes in the U(N)_k x U(N)_{-k} ABJM model
in which the U(1) Noether current is replaced by a dynamical U(1) gauge field.
We also show that the -deformed N=6 gauged supergravities can be
obtained via consistent reductions from the eleven-dimensional or
ten-dimensional type IIA supergravities.Comment: 38 pages, one figur
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