1,164 research outputs found
Heterotic orbifold models on Lie lattice with discrete torsion
We provide a new class of Z_N x Z_M heterotic orbifolds on non-factorisable
tori, whose boundary conditions are defined by Lie lattices. Generally, point
groups of these orbifolds are generated by Weyl reflections and outer
automorphisms of the lattices. We classify abelian orbifolds with and without
discrete torsion. Then we find that some of these models have smaller Euler
numbers than those of models on factorisable tori T^2 x T^2 x T^2. There is a
possibility that these orbifolds provide smaller generation numbers of N=1
chiral matter fields than factorisable models.Comment: 24 pages, 5 figures; v2: a few errors on tables are corrected, typos
corrected, version to appear in JHE
Can Africa replicate Asia's green revolution in rice ?
Asia's green revolution in rice was transformational and improved the lives of millions of poor households. Rice has become an increasingly important part of African diets and imports of rice have grown. Agronomists point out that large areas in Africa are well suited for rice and are encouraged by the field tests of new rice varieties. So is Africa poised for its own green revolution in rice? This study reviews the recent literature on rice technologies and their impact on productivity, incomes, and poverty, and compares current conditions in Africa with the conditions that prevailed in Asia as its rice revolution got under way. An important conclusion is that, to a degree, a rice revolution has already begun in Africa. Moreover, many of the same practices that have proved successful in Asia and in Africa can be applied where yields are currently low. At the same time, for many reasons, Africa's rice revolution has been, and will continue to be, characterized by a mosaic of successes, situated where the conditions are right for new technologies to take hold. This can have profound effects in some places. But because diets, markets, and geography are heterogeneous in Africa, the successful transformation of the Africa's rice sector must be matched by productivity gains in other crops to fully launch Africa's Green Revolution.Agricultural Research,Crops&Crop Management Systems,Climate Change and Agriculture,Food&Beverage Industry,Agricultural Knowledge&Information Systems
Supersymmetric Rotating Black Hole in a Compactified Spacetime
We construct a supersymmetric rotating black hole with asymptotically flat
four-dimensional spacetime times a circle, by superposing an infinite number of
BMPV black hole solutions at the same distance in one direction. The near
horizon structure is the same as that of the five-dimensional BMPV black hole.
The rotation of this black hole can exceed the Kerr bound in general relativity
(), if the size is small.Comment: 7 pages, 3 figures; v2: comparison with black ring removed, detailed
discussion of rotation added, refs. added, v3: minor corrections, version to
appear in PR
Testing Higgs models via the vertex by a recoil method at the International Linear Collider
In general, charged Higgs bosons appear in non-minimal Higgs models.
The vertex is known to be related to the violation of the
global symmetry (custodial symmetry) in the Higgs sector. Its magnitude
strongly depends on the structure of the exotic Higgs models which contain
higher isospin representations such as triplet Higgs bosons. We study
the possibility of measuring the vertex via single charged
Higgs boson production associated with the boson at the International
Linear Collider (ILC) by using the recoil method. The feasibility of the signal
is analyzed assuming the polarized
electron and positron beams and the expected detector performance for the
resolution of the two-jet system at the ILC. The background events can be
reduced to a considerable extent by imposing the kinematic cuts even if we take
into account the initial state radiation. For a relatively light charged Higgs
boson whose mass is in the region of 120-130 GeV , the vertex would be precisely testable especially
when the decay of is lepton specific. The exoticness of the extended
Higgs sector can be explored by using combined information for this vertex and
the rho parameter.Comment: 22 pages, 23 figure
Anisotropic Pressures at Ultra-stiff Singularities and the Stability of Cyclic Universes
We show that the inclusion of simple anisotropic pressures stops the
isotropic Friedmann universe being a stable attractor as an initial or final
singularity is approached when pressures can exceed the energy density. This
shows that the situation with isotropic pressures, studied earlier in the
context of cyclic and ekpyrotic cosmologies, is not generic, and Kasner-like
behaviour occurs when simple pressure anisotropies are present. We find all the
asymptotic behaviours and determine the dynamics when the anisotropic principal
pressures are proportional to the density. We expect distortions and
anisotropies to be significantly amplified through a simple cosmological bounce
in cyclic or ekpyrotic cosmologies when ultra-stiff pressures are present.Comment: 18 pages, 2 figure
Optimal error bounds in the absence of constraint qualifications with applications to the -cones and beyond
We prove tight H\"olderian error bounds for all -cones. Surprisingly, the
exponents differ in several ways from those that have been previously
conjectured; moreover, they illuminate -cones as a curious example of a
class of objects that possess properties in 3 dimensions that they do not in 4
or more. Using our error bounds, we analyse least squares problems with
-norm regularization, where our results enable us to compute the
corresponding KL exponents for previously inaccessible values of . Another
application is a (relatively) simple proof that most -cones are neither
self-dual nor homogeneous. Our error bounds are obtained under the framework of
facial residual functions, and we expand it by establishing for general cones
an optimality criterion under which the resulting error bound must be tight.Comment: 36 pages, comments welcome. Some small fixes and three new figures
were added in order to better explain the result
Numerical Simulations of Equatorially-Asymmetric Magnetized Supernovae: Formation of Magnetars and Their Kicks
A series of numerical simulations on magnetorotational core-collapse
supernovae are carried out. Dipole-like configurations which are offset
northward are assumed for the initially strong magnetic fields together with
rapid differential rotations. Aims of our study are to investigate effects of
the offset magnetic field on magnetar kicks and on supernova dynamics. Note
that we study a regime where the proto-neutron star formed after collapse has a
large magnetic field strength approaching that of a ``magnetar'', a highly
magnetized slowly rotating neutron star. As a result, equatorially-asymmetric
explosions occur with a formation of the bipolar jets. Resultant magnetar's
kick velocities are km s. We find that the acceleration
is mainly due to the magnetic pressure while the somewhat weaker magnetic
tension works toward the opposite direction, which is due to stronger magnetic
field in the northern hemisphere. Noted that observations of magnetar's proper
motions are very scarce, our results supply a prediction for future
observations. Namely, magnetars possibly have large kick velocities, several
hundred km s, as ordinary neutron stars do, and in an extreme case they
could have those up to 1000 km s.Comment: 36 pages, 9 figures, accepted by the Astrophysical Journa
Creation of the universe with a stealth scalar field
The stealth scalar field is a non-trivial configuration without any
back-reaction to geometry, which is characteristic for non-minimally coupled
scalar fields. Studying the creation probability of the de Sitter universe with
a stealth scalar field by the Hartle and Hawking's semi-classical method, we
show that the effect of the stealth field can be significant. For the class of
scalar fields we consider, creation with a stealth field is possible for a
discrete value of the coupling constant and its creation probability is always
less than that with a trivial scalar field. However, those creation rates can
be almost the same depending on the parameters of the theory.Comment: 7 pages; v2, references added; v3, creation of the open universe
adde
Generalized power cones: optimal error bounds and automorphisms
Error bounds are a requisite for trusting or distrusting solutions in an
informed way. Until recently, provable error bounds in the absence of
constraint qualifications were unattainable for many classes of cones that do
not admit projections with known succinct expressions. We build such error
bounds for the generalized power cones, using the recently developed framework
of one-step facial residual functions. We also show that our error bounds are
tight in the sense of that framework. Besides their utility for understanding
solution reliability, the error bounds we discover have additional applications
to the algebraic structure of the underlying cone, which we describe. In
particular we use the error bounds to compute the dimension of the automorphism
group for the generalized power cones, and to identify a set of generalized
power cones that are self-dual, irreducible, nonhomogeneous, and perfectComment: 24 pages, title change, some minor fixes throughout the paper and
removed the appendix. Comments welcom
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