2,307 research outputs found
Online learning for design students
This paper describes the development of a Web‐based learning resource for Design students at De Montfort University, and presents the results of a study to investigate the effectiveness of this system. Some issues regarding further improvements to the online resource are also discussed
Can TeVeS avoid Dark Matter on galactic scales?
A fully relativistic analysis of gravitational lensing in TeVeS is presented.
By estimating the lensing masses for a set of six lenses from the CASTLES
database, and then comparing them to the stellar mass, the deficit between the
two is obtained and analysed. Considering a parametrised range for the TeVeS
function , which controls the strength of the modification to gravity,
it is found that on galactic scales TeVeS requires additional dark matter with
the commonly used . A soft dependence of the results on the cosmological
framework and the TeVeS free parameters is discussed. For one particular form
of , TeVeS is found to require very little dark matter. This choice is
however ruled out by rotation curve data. The inability to simultaneously fit
lensing and rotation curves for a single form of is a challenge to a
"no dark matter" TeVeS proposal.Comment: Four pages LaTeX, three eps figures incorporate
Black Hole Entropy from Quantum Mechanics
We provide evidence for a holographic duality between superconformal quantum
mechanics on the moduli space of Yang-Mills instantons and M-theory in certain
asymptotically backgrounds with a plane-wave boundary
metric. We show that the gravitational background admits a supersymmetric black
hole solution whose entropy is precisely reproduced by the superconformal index
of the dual quantum mechanics
Incompatibility of Rotation Curves with Gravitational Lensing for TeVeS
We constrain the one-parameter class of TeVeS models by testing the theory
against both rotation curve and strong gravitational lensing data on galactic
scales, remaining fully relativistic in our formalism. The upshot of our
analysis is that -- at least in its simplest original form, which is the only
one studied in the literature so far -- TeVeS is ruled out, in the sense that
the models cannot consistently fit simultaneously the two sets of data without
including a significant dark matter component. It is also shown that the
details of the underlying cosmological model are not relevant for our analysis,
which pertains to galactic scales. The choice of the stellar Initial Mass
Function -- which affects the estimates of baryonic mass -- is found not to
change our conclusions.Comment: 12 pages, 4 figure
Redshift-weighted constraints on primordial non-Gaussianity from the clustering of the eBOSS DR14 quasars in Fourier space
We present constraints on local primordial non-Gaussianity (PNG),
parametrized through , using the Sloan Digital Sky Survey
IV extended Baryon Oscillation Spectroscopic Survey Data Release 14 quasar
sample. We measure and analyze the anisotropic clustering of the quasars in
Fourier space, testing for the scale-dependent bias introduced by primordial
non-Gaussianity on large scales. We derive and employ a power spectrum
estimator using optimal weights that account for the redshift evolution of the
PNG signal. We find constraints of at 95%
confidence level. These are amont the tightest constraints from Large Scale
Structure (LSS) data. Our redshift weighting improves the error bar by 15% in
comparison to the unweighted case. If quasars have lower response to PNG, the
constraint degrades to , with a 40% improvement
over the standard approach. We forecast that the full eBOSS dataset could reach
using optimal methods and full
range of scales.Comment: 28 pages, 12 figures. Comments welcome
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