1,220 research outputs found
Integrating writing into a Chapter One reading program in grades seven and eight
The Chapter One reading program has traditionally consisted of teaching and re-teaching of isolated skills and has included much segmented reading. The small amount of writing that has taken place has been in the form of short answer or fill-in-the blanks activities
Reorganization of English in the junior high schools
This item was digitized by the Internet Archive. Thesis (Ed.M.)--Boston Universit
Spacetime structure of the global vortex
We analyse the spacetime structure of the global vortex and its maximal
analytic extension in an arbitrary number of spacetime dimensions. We find that
the vortex compactifies space on the scale of the Hubble expansion of its
worldvolume, in a manner reminiscent of that of the domain wall. We calculate
the effective volume of this compactification and remark on its relevance to
hierarchy resolution with extra dimensions. We also consider strongly
gravitating vortices and derive bounds on the existence of a global vortex
solution.Comment: 19 pages revtex, 2 figures, minor changes, references adde
A Global Fit of Non-Relativistic Effective Dark Matter Operators Including Solar Neutrinos
We perform a global fit of dark matter interactions with nucleons using a
non-relativistic effective operator description, considering both direct
detection and neutrino data. We examine the impact of combining the direct
detection experiments CDMSlite, CRESST-II, CRESST-III, DarkSide-50, LUX, LZ,
PandaX-II, PandaX-4T, PICO-60, SIMPLE, SuperCDMS, XENON100, and XENON1T along
with neutrino data from IceCube and ANTARES. While current neutrino telescope
data lead to increased sensitivity compared to underground nuclear scattering
experiments for dark matter masses above 100 GeV, our future projections show
that the next generation of underground experiments will significantly outpace
solar searches for most dark matter-nucleon elastic scattering interactions.Comment: 12+9 pages, 26 figures, Likelihoods available at
https://zenodo.org/records/1003221
Dark Matter from Monogem
As a supernova shock expands into space, it may collide with dark matter
particles, scattering them up to velocities more than an order of magnitude
larger than typical dark matter velocities in the Milky Way. If a supernova
remnant is close enough to Earth, and the appropriate age, this flux of
high-velocity dark matter could be detectable in direct detection experiments,
particularly if the dark matter interacts via a velocity-dependent operator.
This could make it easier to detect light dark matter that would otherwise have
too little energy to be detected. We show that the Monogem Ring supernova
remnant is both close enough and the correct age to produce such a flux, and
thus we produce novel direct detection constraints and sensitivities for future
experiments.Comment: 8 Pages of Text, 3 Figure
Random perfect lattices and the sphere packing problem
Motivated by the search for best lattice sphere packings in Euclidean spaces
of large dimensions we study randomly generated perfect lattices in moderately
large dimensions (up to d=19 included). Perfect lattices are relevant in the
solution of the problem of lattice sphere packing, because the best lattice
packing is a perfect lattice and because they can be generated easily by an
algorithm. Their number however grows super-exponentially with the dimension so
to get an idea of their properties we propose to study a randomized version of
the algorithm and to define a random ensemble with an effective temperature in
a way reminiscent of a Monte-Carlo simulation. We therefore study the
distribution of packing fractions and kissing numbers of these ensembles and
show how as the temperature is decreased the best know packers are easily
recovered. We find that, even at infinite temperature, the typical perfect
lattices are considerably denser than known families (like A_d and D_d) and we
propose two hypotheses between which we cannot distinguish in this paper: one
in which they improve Minkowsky's bound phi\sim 2^{-(0.84+-0.06) d}, and a
competitor, in which their packing fraction decreases super-exponentially,
namely phi\sim d^{-a d} but with a very small coefficient a=0.06+-0.04. We also
find properties of the random walk which are suggestive of a glassy system
already for moderately small dimensions. We also analyze local structure of
network of perfect lattices conjecturing that this is a scale-free network in
all dimensions with constant scaling exponent 2.6+-0.1.Comment: 19 pages, 22 figure
Bounds on the Complexity of Halfspace Intersections when the Bounded Faces have Small Dimension
We study the combinatorial complexity of D-dimensional polyhedra defined as
the intersection of n halfspaces, with the property that the highest dimension
of any bounded face is much smaller than D. We show that, if d is the maximum
dimension of a bounded face, then the number of vertices of the polyhedron is
O(n^d) and the total number of bounded faces of the polyhedron is O(n^d^2). For
inputs in general position the number of bounded faces is O(n^d). For any fixed
d, we show how to compute the set of all vertices, how to determine the maximum
dimension of a bounded face of the polyhedron, and how to compute the set of
bounded faces in polynomial time, by solving a polynomial number of linear
programs
Stable quantum systems in anti-de Sitter space: Causality, independence and spectral properties
If a state is passive for uniformly accelerated observers in n-dimensional
anti-de Sitter space-time (i.e. cannot be used by them to operate a perpetuum
mobile), they will (a) register a universal value of the Unruh temperature, (b)
discover a PCT symmetry, and (c) find that observables in complementary
wedge-shaped regions necessarily commute with each other in this state. The
stability properties of such a passive state induce a "geodesic causal
structure" on AdS and concommitant locality relations. It is shown that
observables in these complementary wedge-shaped regions fulfill strong
additional independence conditions. In two-dimensional AdS these even suffice
to enable the derivation of a nontrivial, local, covariant net indexed by
bounded spacetime regions. All these results are model-independent and hold in
any theory which is compatible with a weak notion of space-time localization.
Examples are provided of models satisfying the hypotheses of these theorems.Comment: 27 pages, 1 figure: dedicated to Jacques Bros on the occasion of his
70th birthday. Revised version: typos corrected; as to appear in J. Math.
Phy
Back-reaction of a conformal field on a three-dimensional black hole
The first order corrections to the geometry of the (2+1)-dimensional black
hole due to back-reaction of a massless conformal scalar field are computed.
The renormalized stress energy tensor used as the source of Einstein equations
is computed with the Green function for the black-hole background with
transparent boundary conditions. This tensor has the same functional form as
the one found in the nonperturbative case which can be exactly solved. Thus, a
static, circularly symmetric and asymptotically anti-de Sitter black hole
solution of the semiclassical equations is found. The corrections to the
thermodynamic quantities are also computed.Comment: 12 pages, RevTeX, no figure
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