7,439 research outputs found
The young, wide and very low mass visual binary LOri167
We look for wide, faint companions around members of the 5 Myr Lambda Orionis
open cluster. We used optical, near-infrared, and Spitzer/IRAC photometry. We
report the discovery of a very wide very low mass visual binary, LOri167,
formed by a brown dwarf and a planetary-mass candidate located at 5 arcsec,
which seems to belong to the cluster. We derive Teff of 2125 and 1750 K. If
they are members, comparisons with theoretical models indicate masses of 17
(20-15) Mjup and 8 (13-7) Mjup, with a projected separation of 2000 AU. Such a
binary system would be difficult to explain in most models, particularly those
where substellar objects form in the disks surrounding higher mass stars.Comment: Astronomy & Astrophysics Letters, in pres
Dual Interpretations of Seiberg-Witten and Dijkgraaf-Vafa curves
We give dual interpretations of Seiberg-Witten and Dijkgraaf-Vafa (or matrix
model) curves in n=1 supersymmetric U(N) gauge theory. This duality
interchanges the rank of the gauge group with the degree of the superpotential;
moreover, the constraint of having at most log-normalizable deformations of the
geometry is mapped to a constraint in the number of flavors N_f < N in the dual
theory.Comment: Latex2e, 22 pages, 2 figure
Conserved current for the Cotton tensor, black hole entropy and equivariant Pontryagin forms
The Chern-Simons lagrangian density in the space of metrics of a
3-dimensional manifold M is not invariant under the action of diffeomorphisms
on M. However, its Euler-Lagrange operator can be identified with the Cotton
tensor, which is invariant under diffeomorphims. As the lagrangian is not
invariant, Noether Theorem cannot be applied to obtain conserved currents. We
show that it is possible to obtain an equivariant conserved current for the
Cotton tensor by using the first equivariant Pontryagin form on the bundle of
metrics. Finally we define a hamiltonian current which gives the contribution
of the Chern-Simons term to the black hole entropy, energy and angular
momentum.Comment: 13 page
The Effects of Gravity on the Climate and Circulation of a Terrestrial Planet
The climate and circulation of a terrestrial planet are governed by, among
other things, the distance to its host star, its size, rotation rate,
obliquity, atmospheric composition and gravity. Here we explore the effects of
the last of these, the Newtonian gravitational acceleration, on its atmosphere
and climate. We first demonstrate that if the atmosphere obeys the hydrostatic
primitive equations, which are a very good approximation for most terrestrial
atmospheres, and if the radiative forcing is unaltered, changes in gravity have
no effect at all on the circulation except for a vertical rescaling. That is to
say, the effects of gravity may be completely scaled away and the circulation
is unaltered. However, if the atmosphere contains a dilute condensible that is
radiatively active, such as water or methane, then an increase in gravity will
generally lead to a cooling of the planet because the total path length of the
condensible will be reduced as gravity increases, leading to a reduction in the
greenhouse effect. Furthermore, the specific humidity will decrease, leading to
changes in the moist adiabatic lapse rate, in the equator-to-pole heat
transport, and in the surface energy balance because of changes in the sensible
and latent fluxes. These effects are all demonstrated both by theoretical
arguments and by numerical simulations with moist and dry general circulation
models.Comment: 17 pages, 9 figures. Submitted to QJRMS on 23/01/1
Large Charge Four-Dimensional Extremal N=2 Black Holes with R^2-Terms
We consider N=2 supergravity in four dimensions with small R^2 curvature
corrections. We construct large charge extremal supersymmetric and
non-supersymmetric black hole solutions in all space, and analyze their
thermodynamic properties.Comment: 18 pages. v2,3: minor fixe
Softly broken supersymmetric Yang-Mills theories: Renormalization and non-renormalization theorems
We present a minimal version for the renormalization of softly broken
Super-Yang-Mills theories using the extended model with a local gauge coupling.
It is shown that the non-renormalization theorems of the case with unbroken
supersymmetry are valid without modifications and that the renormalization of
soft-breaking parameters is completely governed by the renormalization of the
supersymmetric parameters. The symmetry identities in the present context are
peculiar, since the extended model contains two anomalies: the Adler-Bardeen
anomaly of the axial current and an anomaly of supersymmetry in the presence of
the local gauge coupling. From the anomalous symmetries we derive the exact
all-order expressions for the beta functions of the gauge coupling and of the
soft-breaking parameters. They generalize earlier results to arbitrary
normalization conditions and imply the NSVZ expressions for a specific
normalization condition on the coupling.Comment: 24 pages, LaTeX, v2: one reference adde
Characterization of tomographically faithful states in terms of their Wigner function
A bipartite quantum state is tomographically faithful when it can be used as
an input of a quantum operation acting on one of the two quantum systems, such
that the joint output state carries a complete information about the operation
itself. Tomographically faithful states are a necessary ingredient for
tomography of quantum operations and for complete quantum calibration of
measuring apparatuses. In this paper we provide a complete classification of
such states for continuous variables in terms of the Wigner function of the
state. For two-mode Gaussian states faithfulness simply resorts to correlation
between the modes.Comment: 9 pages. IOPAMS style. Some improvement
Physical renormalization condition for the quark-mixing matrix
We investigate the renormalization of the quark-mixing matrix in the
Electroweak Standard Model. We show that the corresponding counterterms must be
gauge independent as a consequence of extended BRS invariance. Using rigid
SU(2)_L symmetry, we proof that the ultraviolet-divergent parts of the
invariant counterterms are related to the field renormalization constants of
the quark fields. We point out that for a general class of renormalization
schemes rigid SU(2)_L symmetry cannot be preserved in its classical form, but
is renormalized by finite counterterms. Finally, we discuss a genuine physical
renormalization condition for the quark-mixing matrix that is gauge independent
and does not destroy the symmetry between quark generations.Comment: 20 pages, LaTeX, minor changes, references adde
Generalized Massive Gravity and Galilean Conformal Algebra in two dimensions
Galilean conformal algebra (GCA) in two dimensions arises as contraction of
two copies of the centrally extended Virasoro algebra ( with ). The central charges of
GCA can be expressed in term of Virasoro central charges. For finite and
non-zero GCA central charges, the Virasoro central charges must behave as
asymmetric form . We propose that, the bulk
description for 2d GCA with asymmetric central charges is given by general
massive gravity (GMG) in three dimensions. It can be seen that, if the
gravitational Chern-Simons coupling behaves as of order
O() or (), the central charges
of GMG have the above dependence. So, in non-relativistic scaling
limit , we calculated GCA parameters and finite
entropy in term of gravity parameters mass and angular momentum of GMG.Comment: 9 page
A Parallel General Purpose Multi-Objective Optimization Framework, with Application to Beam Dynamics
Particle accelerators are invaluable tools for research in the basic and
applied sciences, in fields such as materials science, chemistry, the
biosciences, particle physics, nuclear physics and medicine. The design,
commissioning, and operation of accelerator facilities is a non-trivial task,
due to the large number of control parameters and the complex interplay of
several conflicting design goals. We propose to tackle this problem by means of
multi-objective optimization algorithms which also facilitate a parallel
deployment. In order to compute solutions in a meaningful time frame a fast and
scalable software framework is required. In this paper, we present the
implementation of such a general-purpose framework for simulation-based
multi-objective optimization methods that allows the automatic investigation of
optimal sets of machine parameters. The implementation is based on a
master/slave paradigm, employing several masters that govern a set of slaves
executing simulations and performing optimization tasks. Using evolutionary
algorithms as the optimizer and OPAL as the forward solver, validation
experiments and results of multi-objective optimization problems in the domain
of beam dynamics are presented. The high charge beam line at the Argonne
Wakefield Accelerator Facility was used as the beam dynamics model. The 3D beam
size, transverse momentum, and energy spread were optimized
- …