6,392 research outputs found
Complexified sigma model and duality
We show that the equations of motion associated with a complexified
sigma-model action do not admit manifest dual SO(n,n) symmetry. In the process
we discover new type of numbers which we called `complexoids' in order to
emphasize their close relation with both complex numbers and matroids. It turns
out that the complexoids allow to consider the analogue of the complexified
sigma-model action but with (1+1)-worldsheet metric, instead of
Euclidean-worldsheet metric. Our observations can be useful for further
developments of complexified quantum mechanics.Comment: 15 pages, Latex, improved versio
Metaanalysis of the Relationship Between Violent Video Game Play and Physical Aggression Over Time
To clarify and quantify the influence of video game violence (VGV) on aggressive behavior, we conducted a metaanalysis of all prospective studies to date that assessed the relation between exposure to VGV and subsequent overt physical aggression. The search strategy identified 24 studies with over 17,000 participants and time lags ranging from 3 months to 4 years. The samples comprised various nationalities and ethnicities with mean ages from 9 to 19 years. For each study we obtained the standardized regression coefficient for the prospective effect of VGV on subsequent aggression, controlling for baseline aggression. VGV was related to aggression using both fixed [ÎČ = 0.113, 95% CI = (0.098, 0.128)] and random effects models [ÎČ = 0.106 (0.078, 0.134)]. When all available covariates were included, the size of the effect remained significant for both models [ÎČ = 0.080 (0.065, 0.094) and ÎČ = 0.078 (0.053, 0.102), respectively]. No evidence of publication bias was found. Ethnicity was a statistically significant moderator for the fixed-effects models (P †0.011) but not for the random-effects models. Stratified analyses indicated the effect was largest among Whites, intermediate among Asians, and nonsignificant among Hispanics. Discussion focuses on the implications of such findings for current debates regarding the effects of violent video games on physical aggression
Generalized Geometry and M theory
We reformulate the Hamiltonian form of bosonic eleven dimensional
supergravity in terms of an object that unifies the three-form and the metric.
For the case of four spatial dimensions, the duality group is manifest and the
metric and C-field are on an equal footing even though no dimensional reduction
is required for our results to hold. One may also describe our results using
the generalized geometry that emerges from membrane duality. The relationship
between the twisted Courant algebra and the gauge symmetries of eleven
dimensional supergravity are described in detail.Comment: 29 pages of Latex, v2 References added, typos fixed, v3 corrected
kinetic term and references adde
Cation composition effects on oxide conductivity in the Zr_2Y_2O_7-Y_3NbO_7 system
Realistic, first-principles-based interatomic potentials have been used in
molecular dynamics simulations to study the effect of cation composition on the
ionic conductivity in the Zr2Y2O7-Y3NbO7 system and to link the dynamical
properties to the degree of lattice disorder. Across the composition range,
this system retains a disordered fluorite crystal structure and the vacancy
concentration is constant. The observed trends of decreasing conductivity and
increasing disorder with increasing Nb5+ content were reproduced in simulations
with the cations randomly assigned to positions on the cation sublattice. The
trends were traced to the influences of the cation charges and relative sizes
and their effect on vacancy ordering by carrying out additional calculations in
which, for example, the charges of the cations were equalised. The simulations
did not, however, reproduce all the observed properties, particularly for
Y3NbO7. Its conductivity was significantly overestimated and prominent diffuse
scattering features observed in small area electron diffraction studies were
not always reproduced. Consideration of these deficiencies led to a preliminary
attempt to characterise the consequence of partially ordering the cations on
their lattice, which significantly affects the propensity for vacancy ordering.
The extent and consequences of cation ordering seem to be much less pronounced
on the Zr2Y2O7 side of the composition range.Comment: 22 pages, 8 figures, submitted to Journal of Physics: Condensed
Matte
Harmonic superpositions of non-extremal p-branes
The plot of allowed p and D values for p-brane solitons in D-dimensional
supergravity is the same whether the solitons are extremal or non-extremal. One
of the useful tools for relating different points on the plot is vertical
dimensional reduction, which is possible if periodic arrays of p-brane solitons
can be constructed. This is straightforward for extremal p-branes, since the
no-force condition allows arbitrary multi-centre solutions to be constructed in
terms of a general harmonic function on the transverse space. This has also
been shown to be possible in the special case of non-extremal black holes in
D=4 arrayed along an axis. In this paper, we extend previous results to include
multi-scalar black holes, and dyonic black holes. We also consider their
oxidation to higher dimensions, and we discuss general procedures for
constructing the solutions, and studying their symmetries.Comment: Latex, 23 page
Primary Beam Shape Calibration from Mosaicked, Interferometric Observations
Image quality in mosaicked observations from interferometric radio telescopes
is strongly dependent on the accuracy with which the antenna primary beam is
calibrated. The next generation of radio telescope arrays such as the Allen
Telescope Array (ATA) and the Square Kilometer Array (SKA) have key science
goals that involve making large mosaicked observations filled with bright point
sources. We present a new method for calibrating the shape of the telescope's
mean primary beam that uses the multiple redundant observations of these bright
sources in the mosaic. The method has an analytical solution for simple
Gaussian beam shapes but can also be applied to more complex beam shapes
through minimization. One major benefit of this simple, conceptually
clean method is that it makes use of the science data for calibration purposes,
thus saving telescope time and improving accuracy through simultaneous
calibration and observation. We apply the method both to 1.43 GHz data taken
during the ATA Twenty Centimeter Survey (ATATS) and to 3.14 GHz data taken
during the ATA's Pi Gigahertz Sky Survey (PiGSS). We find that the beam's
calculated full width at half maximum (FWHM) values are consistent with the
theoretical values, the values measured by several independent methods, and the
values from the simulation we use to demonstrate the effectiveness of our
method on data from future telescopes such as the expanded ATA and the SKA.
These results are preliminary, and can be expanded upon by fitting more complex
beam shapes. We also investigate, by way of a simulation, the dependence of the
accuracy of the telescope's FWHM on antenna number. We find that the
uncertainty returned by our fitting method is inversely proportional to the
number of antennas in the array.Comment: Accepted by PASP. 8 pages, 8 figure
Toroidal Orientifolds in IIA with General NS-NS Fluxes
Type IIA toroidal orientifolds offer a promising toolkit for model builders,
especially when one includes not only the usual fluxes from NS-NS and R-R field
strengths, but also fluxes that are T-dual to the NS-NS three-form flux. These
new ingredients are known as metric fluxes and non-geometric fluxes, and can
help stabilize moduli or can lead to other new features. In this paper we study
two approaches to these constructions, by effective field theory or by toroidal
fibers twisted over a toroidal base. Each approach leads us to important
observations, in particular the presence of D-terms in the four-dimensional
effective potential in some cases, and a more subtle treatment of the
quantization of the general NS-NS fluxes. Though our methods are general, we
illustrate each approach on the example of an orientifold of T^6/Z_4.Comment: 59 pages, references adde
Properties of HxTaS2
The preparation of Hx TaS2 (0 \u3c x \u3c 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly Hp in air). Magnetic susceptibility data show that a low temperature transformation in 2H ... TaS2 (at soâąK) is suppressed with the addition of hydrogen, and· at the same time the superconducting transition temperature T c rises from 0.8 to ~4.2âąK at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and T c measurements in other intercalation compounds, we suggest that the rise of T c (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity
Canonical Formulation of A Bosonic Matter Field in 1+1 Dimensional Curved Space
We study a Bosonic scalar in 1+1 dimensional curved space that is coupled to
a dynamical metric field. This metric, along with the affine connection, also
appears in the Einstein-Hilbert action when written in first order form. After
illustrating the Dirac constraint analysis in Yang-Mills theory, we apply this
formulation to the Einstein-Hilbert action and the action of the Bosonic scalar
field, first separately and then together. Only in the latter case does a
dynamical degree of freedom emerge.Comment: 21 page
Super Weyl invariance: BPS equations from heterotic worldsheets
It is well-known that the beta functions on a string worldsheet correspond to
the target space equations of motion, e.g. the Einstein equations. We show that
the BPS equations, i.e. the conditions of vanishing supersymmetry variations of
the space-time fermions, can be directly derived from the worldsheet. To this
end we consider the RNS-formulation of the heterotic string with (2,0)
supersymmetry, which describes a complex torsion target space that supports a
holomorphic vector bundle. After a detailed account of its quantization and
renormalization, we establish that the cancellation of the Weyl anomaly
combined with (2,0) finiteness implies the heterotic BPS conditions: At the one
loop level the geometry is required to be conformally balanced and the gauge
background has to satisfy the Hermitean Yang-Mills equations.Comment: 1+31 pages LaTeX, 5 figures; final version, discussion relation Weyl
invariance and (2,0) finiteness extended, typos correcte
- âŠ