637 research outputs found
D-brane potentials in the warped resolved conifold and natural inflation
In this paper we obtain a model of Natural Inflation from string theory with
a Planckian decay constant. We investigate D-brane dynamics in the background
of the warped resolved conifold (WRC) throat approximation of Type IIB string
compactifications on Calabi-Yau manifolds. When we glue the throat to a compact
bulk Calabi-Yau, we generate a D-brane potential which is a solution to the
Laplace equation on the resolved conifold. We can exactly solve this equation,
including dependence on the angular coordinates. The solutions are valid down
to the tip of the resolved conifold, which is not the case for the more
commonly used deformed conifold. This allows us to exploit the effect of the
warping, which is strongest at the tip. We inflate near the tip using an
angular coordinate of a D5-brane in the WRC which has a discrete shift
symmetry, and feels a cosine potential, giving us a model of Natural Inflation,
from which it is possible to get a Planckian decay constant whilst maintaining
control over the backreaction. This is because the decay constant for a wrapped
brane contains powers of the warp factor, and so can be made large, while the
wrapping parameter can be kept small enough so that backreaction is under
control.Comment: 41 pages, 3 appendices, 1 figure, PDFLaTex; various clarifications
added along with a new appendix on b-axions and wrapped D5 branes;version
matches the one published in JHE
Transplanckian axions !?
We discuss quantum gravitational effects in Einstein theory coupled to
periodic axion scalars to analyze the viability of several proposals to achieve
superplanckian axion periods (aka decay constants) and their possible
application to large field inflation models. The effects we study correspond to
the nucleation of euclidean gravitational instantons charged under the axion,
and our results are essentially compatible with (but independent of) the Weak
Gravity Conjecture, as follows: Single axion theories with superplanckian
periods contain gravitational instantons inducing sizable higher harmonics in
the axion potential, which spoil superplanckian inflaton field range. A similar
result holds for multi-axion models with lattice alignment (like the
Kim-Nilles-Peloso model). Finally, theories with axions can still achieve a
moderately superplanckian periodicity (by a factor) with no higher
harmonics in the axion potential. The Weak Gravity Conjecture fails to hold in
this case due to the absence of some instantons, which are forbidden by a
discrete gauge symmetry. Finally we discuss the realization of
these instantons as euclidean D-branes in string compactifications.Comment: 46 pages, 6 figures. Added references, clarifications, and missing
factor of 1/2 to instanton action. Conclusions unchange
Planck intermediate results. XLI. A map of lensing-induced B-modes
The secondary cosmic microwave background (CMB) -modes stem from the
post-decoupling distortion of the polarization -modes due to the
gravitational lensing effect of large-scale structures. These lensing-induced
-modes constitute both a valuable probe of the dark matter distribution and
an important contaminant for the extraction of the primary CMB -modes from
inflation. Planck provides accurate nearly all-sky measurements of both the
polarization -modes and the integrated mass distribution via the
reconstruction of the CMB lensing potential. By combining these two data
products, we have produced an all-sky template map of the lensing-induced
-modes using a real-space algorithm that minimizes the impact of sky masks.
The cross-correlation of this template with an observed (primordial and
secondary) -mode map can be used to measure the lensing -mode power
spectrum at multipoles up to . In particular, when cross-correlating with
the -mode contribution directly derived from the Planck polarization maps,
we obtain lensing-induced -mode power spectrum measurement at a significance
level of , which agrees with the theoretical expectation derived
from the Planck best-fit CDM model. This unique nearly all-sky
secondary -mode template, which includes the lensing-induced information
from intermediate to small () angular scales, is
delivered as part of the Planck 2015 public data release. It will be
particularly useful for experiments searching for primordial -modes, such as
BICEP2/Keck Array or LiteBIRD, since it will enable an estimate to be made of
the lensing-induced contribution to the measured total CMB -modes.Comment: 20 pages, 12 figures; Accepted for publication in A&A; The B-mode map
is part of the PR2-2015 Cosmology Products; available as Lensing Products in
the Planck Legacy Archive http://pla.esac.esa.int/pla/#cosmology; and
described in the 'Explanatory Supplement'
https://wiki.cosmos.esa.int/planckpla2015/index.php/Specially_processed_maps#2015_Lensing-induced_B-mode_ma
The ISO LWS grating spectrum of NGC 7027
We present a high signal-to-noise ISO Long Wavelength Spectrometer (LWS) grating spectrum of the planetary nebula NGC 7027 from 43-194μm. In total 40 emission lines have been detected, with 30 identified. From the ionized region, we observe fine-structure lines from [N II], [N III] and [O III]. The [O I] and [C II] fine-structure lines from the photodissociation region are the strongest features observed in this spectral region. Amongst the molecular lines, 11 pure rotation CO lines from J=14-13 up to J=24-23 have been detected. The most striking result, however, is the detection in this carbon-rich nebula of the o-H_2_O 179.53μm and the OH 119.3μm fundamental lines. Astrophysical implications are briefly discussed
Calibration and performance of the ISO Long-Wavelength Spectrometer
The wavelength and flux calibration, and the in-orbit performance of the Infrared Space Observatory Long-Wavelength Spectrometer (LWS) are described. The LWS calibration is mostly complete and the instrument's performance in orbit is largely as expected before launch. The effects of ionising radiation on the detectors, and the techniques used to minimise them are outlined. The overall sensitivity figures achieved in practice are summarised. The standard processing of LWS data is described
PIBF+ extracellular vesicles from mouse embryos affect IL-10 production by CD8+ cells
Earlier evidence suggests, that the embryo signals to the maternal immune system. Extracellular vesicles (EVs) are produced by all types of cells, and because they transport different kinds of molecules from one cell to the other, they can be considered as means of intercellular communication. The aim of this work was to test, whether the embryo is able to produce sufficient amounts of EVs to alter the function of peripheral lymphocytes. Embryo-derived EVs were identified by their Annexin V biding capacity, and sensitivity to Triton X dependent lysis, using flow cytometry. Transmission electron microscopy was used to detect EVs at the implantation site. Progesterone-induced blocking factor (PIBF) expression in embryo-derived EVs was demonstrated with immuno-electron microscopy. The % of IL-10 + murine lymphocytes was determined by flow cytometry. EVs were present in embryo culture media, but not in empty media. Mouse embryo-derived EVs adhere to the surface of both CD4+ and CD8+ murine peripheral T lymphocytes, partly, via phosphatidylserine binding. The number of IL-10+ murine peripheral CD8+ cells increases in the presence of embryo-derived EVS, and this effect is counteracted by pre-treatment of EVs with an anti-PIBF antibody, suggesting that the embryo communicates with the maternal immune system via EVs
The ISO long-wavelength spectrometer
The Long-Wavelength Spectrometer (LWS) is one of two complementary spectrometers aboard the European Space Agency's Infrared Space Observatory (ISO) (Kessler et al., 1996A&A...315L..49D). It operates over the wavelength range 43-196.9μm at either medium (about 150 to 200) or high (6800 to 9700) spectral resolving power. This Letter describes the instrument and its modes of operation; a companion paper (Swinyard et al, 1996) describes its performance and calibration
An overview of digital speech watermarking
Digital speech watermarking is a robust way to hide and thus secure data like audio and video from any intentional or unintentional manipulation through transmission. In terms of some signal characteristics including bandwidth, voice/non-voice and production model, digital speech signal is different from audio, music and other signals. Although, various review articles on image, audio and video watermarking are available, there are still few review papers on digital speech watermarking. Therefore this article presents an overview of digital speech watermarking including issues of robustness, capacity and imperceptibility. Other issues discussed are types of digital speech watermarking, application, models and masking methods. This article further highlights the related challenges in the real world, research opportunities and future works in this area, yet to be explored fully
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