333 research outputs found
Constraints on Brane Inflation and Cosmic Strings
By considering simple, but representative, models of brane inflation from a
single brane-antibrane pair in the slow roll regime, we provide constraints on
the parameters of the theory imposed by measurements of the CMB anisotropies by
WMAP including a cosmic string component. We find that inclusion of the string
component is critical in constraining parameters. In the most general model
studied, which includes an inflaton mass term, as well as the brane-antibrane
attraction, values n_s < 1.02 are compatible with the data at 95 % confidence
level. We are also able to constrain the volume of internal manifold (modulo
factors dependent on the warp factor) and the value of the inflaton field to be
less than 0.66M_P at horizon exit. We also investigate models with a mass term.
These observational considerations suggest that such models have r < 2*10^-5,
which can only be circumvented in the fast roll regime, or by increasing the
number of antibranes. Such a value of r would not be detectable in CMB
polarization experiment likely in the near future, but the B-mode signal from
the cosmic strings could be detectable. We present forecasts of what a similar
analysis using PLANCK data would yield and find that it should be possible to
rule out G\mu > 6.5*10^-8 using just the TT, TE and EE power spectra.Comment: 11 pages, 3 figures, revtex4, typos corrected, references adde
Quantitative Chemically-Specific Coherent Diffractive Imaging of Buried Interfaces using a Tabletop EUV Nanoscope
Characterizing buried layers and interfaces is critical for a host of
applications in nanoscience and nano-manufacturing. Here we demonstrate
non-invasive, non-destructive imaging of buried interfaces using a tabletop,
extreme ultraviolet (EUV), coherent diffractive imaging (CDI) nanoscope. Copper
nanostructures inlaid in SiO2 are coated with 100 nm of aluminum, which is
opaque to visible light and thick enough that neither optical microscopy nor
atomic force microscopy can image the buried interfaces. Short wavelength (29
nm) high harmonic light can penetrate the aluminum layer, yielding
high-contrast images of the buried structures. Moreover, differences in the
absolute reflectivity of the interfaces before and after coating reveal the
formation of interstitial diffusion and oxidation layers at the Al-Cu and
Al-SiO2 boundaries. Finally, we show that EUV CDI provides a unique capability
for quantitative, chemically-specific imaging of buried structures, and the
material evolution that occurs at these buried interfaces, compared with all
other approaches.Comment: 12 pages, 8 figure
D-term inflation in non-minimal supergravity
D-term inflation is one of the most interesting and versatile models of
inflation. It is possible to implement naturally D-term inflation within high
energy physics, as for example SUSY GUTs, SUGRA, or string theories. D-term
inflation avoids the -problem, while in its standard form it always ends
with the formation of cosmic strings. Given the recent three-year WMAP data on
the cosmic microwave background temperature anisotropies, we examine whether
D-term inflation can be successfully implemented in non-minimal supergravity
theories. We show that for all our choices of K\"ahler potential, there exists
a parameter space for which the predictions of D-term inflation are in
agreement with the measurements. The cosmic string contribution on the measured
temperature anisotropies is always dominant, unless the superpotential coupling
constant is fine tuned; a result already obtained for D-term inflation within
minimal supergravity. In conclusion, cosmic strings and their r\^ole in the
angular power spectrum cannot be easily hidden by just considering a non-flat
K\"ahler geometry.Comment: 29 pages, 9 figures; minor changes to match publihed versio
String Necklaces and Primordial Black Holes from Type IIB Strings
We consider a model of static cosmic string loops in type IIB string theory,
where the strings wrap cycles within the internal space. The strings are not
topologically stabilised, however the presence of a lifting potential traps the
windings giving rise to kinky cycloops. We find that PBH formation occurs at
early times in a small window, whilst at late times we observe the formation of
dark matter relics in the scaling regime. This is in stark contrast to previous
predictions based on field theoretic models. We also consider the PBH
contribution to the mass density of the universe, and use the experimental data
to impose bounds on the string theory parameters.Comment: 45 pages, 9 figures, LaTeX; published versio
Textures and Semi-Local Strings in SUSY Hybrid Inflation
Global topological defects may account for the large cold spot observed in
the Cosmic Microwave Background. We explore possibilities of constructing
models of supersymmetric F-term hybrid inflation, where the waterfall fields
are globally SU(2)-symmetric. In contrast to the case where SU(2) is gauged,
there arise Goldstone bosons and additional moduli, which are lifted only by
masses of soft-supersymmetry breaking scale. The model predicts the existence
of global textures, which can become semi-local strings if the waterfall fields
are gauged under U(1)_X. Gravitino overproduction can be avoided if reheating
proceeds via the light SU(2)-modes or right-handed sneutrinos. For values of
the inflaton- waterfall coupling >=10^-4, the symmetry breaking scale imposed
by normalisation of the power spectrum generated from inflation coincides with
the energy scale required to explain the most prominent of the cold spots. In
this case, the spectrum of density fluctuations is close to scale-invariant
which can be reconciled with measurements of the power spectrum by the
inclusion of the sub-dominant component due to the topological defects.Comment: 29 page
Measuring NIR Atmospheric Extinction Using a Global Positioning System Receiver
Modeling molecular absorption by Earth's atmosphere is important for a wide
range of astronomical observations, including broadband NIR photometry and
high-resolution NIR spectroscopy. Using a line-by-line radiative transfer
approach, we calculate theoretical transmission spectra in the deep red optical
(700 to 1050 nm) for Apache Point Observatory. In this region the spectrum is
dominated by H2O, which is known to be highly variable in concentration on
short timescales. We fit our telluric models to high-resolution observations of
A stars and estimate the relative optical depth of H2O absorption under a wide
range of observing conditions. We compare these optical depth estimates to
simultaneous measurements of Precipitable Water Vapor (PWV) based on data from
a Global Positioning System (GPS) receiver located at Apache Point. We find
that measured PWV correlates strongly with the scaling of H2O absorption lines
in our spectra, indicating that GPS-based PWV measurements combined with
atmospheric models may be a powerful tool for the real-time estimation of total
molecular absorption in broad NIR bands. Using photometric measurements from
the Sloan Digital Sky Survey (SDSS) DR8 database we demonstrate that PWV biases
the calibrated r-z colors and z-band fluxes of mid-M stars but not mid-G stars.
While this effect is small compared to other sources of noise in the SDSS
z-band observations, future surveys like the Large Synoptic Survey Telescope
aim for higher precision and will need to take time-variable molecular
transmission into account for the global calibration of NIR measurements of
objects having strong spectral features at these wavelengths. Empirical
calibrations based on PWV may be immediately applicable to ongoing efforts to
make mmag differential measurements of M stars to detect transiting exoplanets.Comment: 19 pages, 9 figures. Accepted for publication in PAS
Magnetogenesis from Cosmic String Loops
Large-scale coherent magnetic fields are observed in galaxies and clusters,
but their ultimate origin remains a mystery. We reconsider the prospects for
primordial magnetogenesis by a cosmic string network. We show that the magnetic
flux produced by long strings has been overestimated in the past, and give
improved estimates. We also compute the fields created by the loop population,
and find that it gives the dominant contribution to the total magnetic field
strength on present-day galactic scales. We present numerical results obtained
by evolving semi-analytic models of string networks (including both one-scale
and velocity-dependent one-scale models) in a Lambda-CDM cosmology, including
the forces and torques on loops from Hubble redshifting, dynamical friction,
and gravitational wave emission. Our predictions include the magnetic field
strength as a function of correlation length, as well as the volume covered by
magnetic fields. We conclude that string networks could account for magnetic
fields on galactic scales, but only if coupled with an efficient dynamo
amplification mechanism.Comment: 10 figures; v3: small typos corrected to match published version.
MagnetiCS, the code described in paper, is available at
http://markcwyman.com/ and
http://www.damtp.cam.ac.uk/user/dhw22/code/index.htm
Has the 'Fast-Track' referral system affected the route of presentation and/or clinical outcomes in patients with colorectal cancer?
Background: The aim of this study is to determine whether the 'Fast-Track' referral system has changed the route by which patients present with colorectal cancer (CRC) and whether the route of presentation has any effect on clinical outcome. Methods: A retrospective cohort study of patients diagnosed with CRC under the care of two consultant colorectal surgeons between April 2006 and December 2012. The route by which patients presented was categorised as Fast-Track (FT), non-Fast-Track (non-FT) or acute. Outcome variables were operative intent, disease stage and 2- and 5-year survival. Results: A total of 558 patients were identified. One hundred ninety-seven patients (35.3%) were referred as FT, 108 (19.4%) presented acutely and 253 patients (45.3%) presented via other routes (non-FT). Over the study period, the route of presentation did not change significantly (P=0.135). There was no significant difference between FT and non-FT groups in terms of the proportion of patients undergoing potentially curative surgery (70.6 vs 74.3%, P=0.092) or with node-negative disease (48.2 vs 52.2%, P=0.796) nor was there any difference in 2-year or 5-year survival (74.1 vs 73.9%, P=0.837 and 52.3 vs 53.8%, P=0.889, respectively). Patients who presented acutely were less likely to undergo curative resection, had more advanced disease and had worse 2- and 5-year survival. Conclusions: The Fast-Track referral system has not affected the route by which patients present with CRC nor has it had any effect on clinical outcomes. Alternative strategies are required if the desired improvement in outcomes is to be achieved
Effects of quantum gravity on the inflationary parameters and thermodynamics of the early universe
The effects of generalized uncertainty principle (GUP) on the inflationary
dynamics and the thermodynamics of the early universe are studied. Using the
GUP approach, the tensorial and scalar density fluctuations in the inflation
era are evaluated and compared with the standard case. We find a good agreement
with the Wilkinson Microwave Anisotropy Probe data. Assuming that a quantum gas
of scalar particles is confined within a thin layer near the apparent horizon
of the Friedmann-Lemaitre-Robertson-Walker universe which satisfies the
boundary condition, the number and entropy densities and the free energy
arising form the quantum states are calculated using the GUP approach. A
qualitative estimation for effects of the quantum gravity on all these
thermodynamic quantities is introduced.Comment: 15 graghes, 7 figures with 17 eps graph
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