3,659 research outputs found
New Coordinates for de Sitter Space and de Sitter Radiation
We introduce a simple coordinate system covering half of de Sitter space. The
new coordinates have several attractive properties: the time direction is a
Killing vector, the metric is smooth at the horizon, and constant-time slices
are just flat Euclidean space. We demonstrate the usefulness of the coordinates
by calculating the rate at which particles tunnel across the horizon. When
self-gravitation is taken into account, the resulting tunneling rate is only
approximately thermal. The effective temperature decreases through the emission
of radiation.Comment: LaTeX, 10 pages; v2. references added; v3. minor sign errors fixed,
reference added, journal versio
Bilingual early functional-lexical mixing and the activation of formal features
ProducciĂłn CientĂficaWe have argued that the grammatical features spell-out hypothesis (GFSH) (Liceras, Spradlin, Perales, FernĂĄndez, & Ălvarez, 2003; Spradlin, Liceras & FernĂĄndez, 2003a) accounts for the functional-lexical mixing patterns that prevail in the case of Determiner Phrases produced by bilingual (English-Spanish) children. This hypothesis (Liceras, 2002; Spradlin, Liceras & FernĂĄndez, 2003b) states that in the process of activating the features of the two grammars, the child, who will rely on the two lexicons, will make codemixing choices which will favor the functional categories containing the largest array of uninterpretable features (Chomsky, 1998, 1999). This implies that in the case of English/ Spanish child acquisition data, mixed utterances such as el book (Spanish Determiner + English Noun) will prevail over mixed utterances such as the libro (English Determiner + Spanish Noun). Thus, in the process of acquisition, children pay special attention to the visible morpho-phonological triggers which lead to the activation of abstract formal features.Faculty of Arts of the University of Ottawa (T-0207-076-77)Ministerio de Ciencia y TecnologĂa - FEDER (Project BFF2002-00442
Abelian Gauge Theory in de Sitter Space
Quantization of spinor and vector free fields in 4-dimensional de Sitter
space-time, in the ambient space notation, has been studied in the previous
works. Various two-points functions for the above fields are presented in this
paper. The interaction between the spinor field and the vector field is then
studied by the abelian gauge theory. The U(1) gauge invariant spinor field
equation is obtained in a coordinate independent way notation and their
corresponding conserved currents are computed. The solution of the field
equation is obtained by use of the perturbation method in terms of the Green's
function. The null curvature limit is discussed in the final stage.Comment: 10 pages, typos corrected, reference adde
A Study on the Nature of Anomalous Current Conduction in Gallium Nitride
Current leakage in GaN thin films limits reliable device fabrication. A variety of Ga and N rich MBE GaN thin films grown by Rf, NH3, and Rf+ NH3, are examined with electrical measurements on NiIAu Schottky diodes and CAFM. Current-voltage (IV) mechanisms will identify conduction mechanisms on diodes, and CAFM measurements will investigate the microstructure of conduction in GaN thin films. With CAFM, enhanced conduction has been shown to decorate some extended defects and surface features, while CAFM spectroscopy on a MODFET structure indicates a correlation between extended defects and field conduction behavior at room temperature. A remedy for poor conduction characteristics is presented in molten KOH etching, as evidenced by CAFM measurements, Schottky diodes, and MODFET\u27s. The aim of this study is to identify anomalous conduction mechanisms, the likely cause of anomalous conduction, and a method for improving the conduction characteristics. Keywords: 111-Nitride, 111-V, Gallium Nitride, GaN, Electrical Properties, Conduction, Conductivity, Mobility, Hall Measurements, Resistivity, Schottky Diode, Modulation Doped Field Effect Transistor (MODFET), Conductive Atomic Force Microscopy (AFM), Defects, Molten Potassium Hydroxide (KOH) etching, Silvaco, Atlas, and Illumination
Degravitation, Inflation and the Cosmological Constant as an Afterglow
In this report, we adopt the phenomenological approach of taking the
degravitation paradigm seriously as a consistent modification of gravity in the
IR, and investigate its consequences for various cosmological situations. We
motivate degravitation-- where Netwon's constant is promoted to a scale
dependent filter function-- as arising from either a small (resonant) mass for
the graviton, or as an effect in semi-classical gravity. After addressing how
the Bianchi identities are to be satisfied in such a set up, we turn our
attention towards the cosmological consequences of degravitation. By
considering the example filter function corresponding to a resonantly massive
graviton (with a filter scale larger than the present horizon scale), we show
that slow roll inflation, hybrid inflation and old inflation remain
quantitatively unchanged. We also find that the degravitation mechanism
inherits a memory of past energy densities in the present epoch in such a way
that is likely significant for present cosmological evolution. For example, if
the universe underwent inflation in the past due to it having tunneled out of
some false vacuum, we find that degravitation implies a remnant `afterglow'
cosmological constant, whose scale immediately afterwards is parametrically
suppressed by the filter scale () in Planck units . We discuss circumstances through which this scenario reasonably
yields the presently observed value for . We also
find that in a universe still currently trapped in some false vacuum state,
resonance graviton models of degravitation only degravitate initially Planck or
GUT scale energy densities down to the presently observed value over timescales
comparable to the filter scale.Comment: To appear in JCAP; sections discussing degravitation as a
semi-classical effect and the modified Bianchi identities adde
Graviton-Scalar Interaction in the PP-Wave Background
We compute the graviton two scalar off-shell interaction vertex at tree level
in Type IIB superstring theory on the pp-wave background using the light-cone
string field theory formalism. We then show that the tree level vertex vanishes
when all particles are on-shell and conservation of p_{+} and p_{-} are
imposed. We reinforce our claim by calculating the same vertex starting from
the corresponding SUGRA action expanded around the pp-wave background in the
light-cone gauge.Comment: 26 pages, harvmac One reference added. A few comments changed in the
introduction. The "cyclic perms." term removed from some equations as
unnecessary and equations (2.38) and (3.19) are corrected accordingl
Orientifolded Locally AdS3 Geometries
Continuing the analysis of [arXiv:1003.4089[hep-th]], we classify all locally
AdS3 stationary axi-symmetric unorientable solutions to AdS3 Einstein gravity
and show that they are obtained by applying certain orientifold projection on
AdS3, BTZ or AdS3 self-dual orbifold, respectively O-AdS3, O-BTZ and O-SDO
geometries. Depending on the orientifold fixed surface, the O-surface, which is
either a space-like 2D plane or cylinder, or a light-like 2D plane or cylinder
one can distinguish four distinct cases. For the space-like orientifold plane
or cylinder cases these geometries solve AdS3 Einstein equations and are hence
locally AdS3 everywhere except at the O-surface, where there is a
delta-function source. For the light-like cases the geometry is a solution to
Einstein equations even at the O-surface. We discuss the causal structure for
static, extremal and general rotating O-BTZ and O-SDO cases as well as the
geodesic motion on these geometries. We also discuss orientifolding Poincare
patch AdS3 and AdS2 geometries as a way to geodesic completion of these spaces
and comment on the 2D CFT dual to the O-geometries.Comment: 26 page, 4 .eps figure
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