1,464 research outputs found
Invariant Killing spinors in 11D and type II supergravities
We present all isotropy groups and associated groups, up to discrete
identifications of the component connected to the identity, of spinors of
eleven-dimensional and type II supergravities. The groups are products
of a Spin group and an R-symmetry group of a suitable lower dimensional
supergravity theory. Using the case of SU(4)-invariant spinors as a paradigm,
we demonstrate that the groups, and so the R-symmetry groups of
lower-dimensional supergravity theories arising from compactifications, have
disconnected components. These lead to discrete symmetry groups reminiscent of
R-parity. We examine the role of disconnected components of the groups
in the choice of Killing spinor representatives and in the context of
compactifications.Comment: 22 pages, typos correcte
Bulge RR Lyrae stars in the VVV tile
The VISTA Variables in the V\'ia L\'actea (VVV) Survey is one of the six ESO
public surveys currently ongoing at the VISTA telescope on Cerro Paranal,
Chile. VVV uses near-IR () filters that at present provide
photometry to a depth of mag in up to 36 epochs spanning
over four years, and aim at discovering more than 10 variable sources as
well as trace the structure of the Galactic bulge and part of the southern
disk. A variability search was performed to find RR Lyrae variable stars. The
low stellar density of the VVV tile , which is centered at
() (), makes it suitable to search for
variable stars. Previous studies have identified some RR Lyrae stars using
optical bands that served to test our search procedure. The main goal is to
measure the reddening, interstellar extinction, and distances of the RR Lyrae
stars and to study their distribution on the Milky Way bulge. A total of 1.5 sq
deg were analyzed, and we found 39 RR Lyrae stars, 27 of which belong to the
ab-type and 12 to the c-type. Our analysis recovers all the previously
identified RR Lyrae variables in the field and discovers 29 new RR Lyrae stars.
The reddening and extinction toward all the RRab stars in this tile were
derived, and distance estimations were obtained through the period--luminosity
relation. Despite the limited amount of RR Lyrae stars studied, our results are
consistent with a spheroidal or central distribution around and
kpc. for either the Cardelli or Nishiyama extinction law.Comment: 10 pages, 8 figures, accepted for publication in Astronomy and
Astrophysic
Reduction of parasitic currents in level-set calculations with a consistent discretization of the surface-tension force for the CSF model
Parasitic currents may develop in grid-based interface simulations because of inaccurate representation of the surface forces in the discretized equations. This is due to two causes : firstly, inconsistent discretization of the surface tension force and the pressure gradient, such that the force balance is not fulfilled for a drop or a bubble at rest. Secondly, the problem is inaccurate approximation of the curvature. The least you should demand from a discretization is that it preserves a stationary solution. In this article, it is shown that this can be accomplished by rewriting the interfacial force term in the momentum equation. Using exact curvature, the exact solution for a drop is preserved to machine accuracy. In general, with this discretization, the calculation of the curvature is the only remaining source of spurious currents. Contrary to common practice for the level-set method, we stress that the curvature should be evaluated at the point on the interface whose normal cross the discretization point, and not at the gridpoint in the smeared-out region outside the interface. In 2D, a simple geometrical argument may be used to find the curvature at the interface, whereas in 3D we use extrapolation normal to the interface to create the correct curvature field in a small region around the interface
On the equivalence of bound state solutions
In this paper we show the equivalence of various (non-threshold) bound state
solutions of branes, or equivalently branes in background potentials, in ten-
and eleven-dimensional supergravity. We compare solutions obtained in two very
different ways. One method uses a zero mode analysis to make an Ansatz which
makes it possible to solve the full non-linear supergravity equations. The
other method utilises T-duality techniques to turn on the fields on the brane.
To be specific, in eleven dimensions we show the equivalence for the (M2,M5)
bound state, or equivalently an M5-brane in a C_3 field, where we also consider
the (MW,M2,M2',M5) solution, which can be obtained from the (M2,M5) bound state
by a boost. In ten dimensions we show the equivalence for the ((F,D1),D3) bound
state as well as the bound states of (p,q) 5-branes with lower dimensional
branes in type IIB, corresponding to D3-branes in B_2 and C_2 fields and (p,q)
5-branes in B_2, C_2 and C_4 fields. We also comment on the recently proposed
V-duality related to infinitesimally boosted solutions.Comment: 19 pages, LaTe
All the supersymmetric solutions of N=1,d=5 ungauged supergravity
We classify the supersymmetric solutions of ungauged N=1 d=5 SUGRA coupled to
vector multiplets and hypermultiplets. All the solutions can be seen as
deformations of solutions with frozen hyperscalars. We show explicitly how the
5-dimensional Reissner-Nordstrom black hole is deformed when hyperscalars are
living on SO(4,1)/SO(4) are turned on, reducing its supersymmetry from 1/2 to
1/8. We also describe in the timelike and null cases the solutions that have
one extra isometry and can be reduced to N=2,d=4 solutions. Our formulae allows
the uplifting of certain N=2,d=4 black holes to N=1,d=5 black holes on KK
monopoles or to pp-waves propagating along black strings.Comment: Some typos fixed and some paragraphs improved. 44 pages, Latex 2e
file, no figures. Version to be published in JHE
A hybrid landmark Aalen-Johansen estimator for transition probabilities in partially non-Markov multi-state models
Multi-state models are increasingly being used to model complex
epidemiological and clinical outcomes over time. It is common to assume that
the models are Markov, but the assumption can often be unrealistic. The Markov
assumption is seldomly checked and violations can lead to biased estimation for
many parameters of interest. As argued by Datta and Satten (2001), the
Aalen-Johansen estimator of occupation probabilities is consistent also in the
non-Markov case. Putter and Spitoni (2018) exploit this fact to construct a
consistent estimator of state transition probabilities, the landmark
Aalen-Johansen estimator, which does not rely on the Markov assumption. A
disadvantage of landmarking is data reduction, leading to a loss of power. This
is problematic for less traveled transitions, and undesirable when such
transitions indeed exhibit Markov behaviour. Using a framework of partially
non-Markov multi-state models we suggest a hybrid landmark Aalen-Johansen
estimator for transition probabilities. The proposed estimator is a compromise
between regular Aalen-Johansen and landmark estimation, using transition
specific landmarking, and can drastically improve statistical power. The
methods are compared in a simulation study and in a real data application
modelling individual transitions between states of sick leave, disability,
education, work and unemployment. In the application, a birth cohort of 184951
Norwegian men are followed for 14 years from the year they turn 21, using data
from national registries
Pulsating stars in ω Centauri. Near-IR properties and period-luminosity relations
Indexación: Scopus.ω Centauri (NGC 5139) contains many variable stars of different types, including the pulsating type II Cepheids, RR Lyrae and SX Phoenicis stars. We carried out a deep, wide-field, near-infrared (IR) variability survey of ω Cen, using the VISTA telescope. We assembled an unprecedented homogeneous and complete J and KS near-IR catalog of variable stars in the field of ω Cen. In this paper we compare optical and near-IR light curves of RR Lyrae stars, emphasizing the main differences. Moreover, we discuss the ability of near-IR observations to detect SX Phoenicis stars given the fact that the amplitudes are much smaller in these bands compared to the optical. Finally, we consider the case in which all the pulsating stars in the three different variability types follow a single period-luminosity relation in the near-IR bands.https://www.epj-conferences.org/articles/epjconf/pdf/2017/21/epjconf_puls2017_07005.pd
Maximally Minimal Preons in Four Dimensions
Killing spinors of N=2, D=4 supergravity are examined using the spinorial
geometry method, in which spinors are written as differential forms. By making
use of methods developed in hep-th/0606049 to analyze preons in type IIB
supergravity, we show that there are no simply connected solutions preserving
exactly 3/4 of the supersymmetry.Comment: 18 pages. References added, comments added discussing the possibility
of discrete quotients of AdS(4) preserving 3/4 supersymmetry
Aspects of spinorial geometry
We review some aspects of the spinorial geometry approach to the
classification of supersymmetric solutions of supergravity theories. In
particular, we explain how spinorial geometry can be used to express the
Killing spinor equations in terms of a linear system for the fluxes and the
geometry of spacetime. The solutions of this linear system express some of the
fluxes in terms of the spacetime geometry and determine the conditions on the
spacetime geometry imposed by supersymmetry. We also present some of the recent
applications like the classification of maximally supersymmetric G-backgrounds
in IIB, this includes the most general pp-wave solution preserving 1/2
supersymmetry, and the classification of N=31 backgrounds in ten and eleven
dimensions.Comment: 17 pages. Invited review for Modern Physics Letters
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