31 research outputs found
Inflation Assisted by Heterotic Axions
We explore the possibility of obtaining inflation in weakly coupled heterotic
string theory, where the model dependent axions are responsible for driving
inflation. This model can be considered as a certain extrapolation of
-inflation, and is an attempt to explicitly realize the so
called N-flation proposal in string theory. The instanton generated potential
for the axions essentially has two parameters; a natural mass scale and the
string coupling . For isotropic compactifications leading to of order
axions in the four dimensional spectrum we find that with
the observed temperature fluctuations in the
CMB are correctly reproduced. We assume an initially random distribution for
the vevs of the axions. The spectral index, , is generically more red
than for -inflation. The greater the vevs, the more red the
spectral index becomes. Allowing for a wide range of vevs 55 -foldings from
the end of inflation, we find . The
tensor-to-scalar ratio, , is more sensitive to the vevs, but typically
smaller than in -inflation. Furthermore, in the regime where the
leading order theory is valid, is bounded by . The spectral index
and the tensor-to-scalar ratio are correlated. For example,
corresponds to .Comment: 1+21 pages, 2 figures, v2: Typos corrected, v3: Typos, very minor
corrections, reference added, to appear in JCA
Significant Carrier Extraction Enhancement at the Interface of an InN/p-GaN Heterojunction under Reverse Bias Voltage
In this paper, a superior-quality InN/p-GaN interface grown using pulsed metalorganic vapor-phase epitaxy (MOVPE) is demonstrated. The InN/p-GaN heterojunction interface based on high-quality InN (electron concentration 5.19 × 1018 cm−3 and mobility 980 cm2/(V s)) showed good rectifying behavior. The heterojunction depletion region width was estimated to be 22.8 nm and showed the ability for charge carrier extraction without external electrical field (unbiased). Under reverse bias, the external quantum efficiency (EQE) in the blue spectral region (300⁻550 nm) can be enhanced significantly and exceeds unity. Avalanche and carrier multiplication phenomena were used to interpret the exclusive photoelectric features of the InN/p-GaN heterojunction behavior
Enhanced Non-Gaussianity from Excited Initial States
We use the techniques of effective field theory in an expanding universe to
examine the effect of choosing an excited inflationary initial state built over
the Bunch-Davies state on the CMB bi-spectrum. We find that even for Hadamard
states, there are unexpected enhancements in the bi-spectrum for certain
configurations in momentum space due to interactions of modes in the early
stages of inflation. These enhancements can be parametrically larger than the
standard ones and are potentially observable in current and future data. These
initial state effects have a characteristic signature in -space which
distinguishes them from the usual contributions, with the enhancement being
most pronounced for configurations corresponding to flattened triangles for
which two momenta are collinear.Comment: 33 pages, 1 figure. Refs added and minor addition
Chern-Simons Modified General Relativity
Chern-Simons modified gravity is an effective extension of general relativity
that captures leading-order, gravitational parity violation. Such an effective
theory is motivated by anomaly cancelation in particle physics and string
theory. In this review, we begin by providing a pedagogical derivation of the
three distinct ways such an extension arises: (1) in particle physics, (2) from
string theory and (3) geometrically. We then review many exact and approximate,
vacuum solutions of the modified theory, and discuss possible matter couplings.
Following this, we review the myriad astrophysical, solar system, gravitational
wave and cosmological probes that bound Chern-Simons modified gravity,
including discussions of cosmic baryon asymmetry and inflation. The review
closes with a discussion of possible future directions in which to test and
study gravitational parity violation.Comment: 104 pages, 2 figures, 186 references, Invited Review accepted for
publication in Phys. Repts. This version corrects a minor typo in Eq. (174)
of the published versio
Implications of Canonical Gauge Coupling Unification in High-Scale Supersymmetry Breaking
We systematically construct two kinds of models with canonical gauge coupling
unification and universal high-scale supersymmetry breaking. In the first we
introduce standard vector-like particles while in the second we also include
non-standard vector-like particles. We require that the gauge coupling
unification scale is from 5 x 10^{15} GeV to the Planck scale, that the
universal supersymmetry breaking scale is from 10 TeV to the unification scale,
and that the masses of the vector-like particles (M_V) are universal and in the
range from 200 GeV to 1 TeV. Using two-loop renormalization group equation
(RGE) running for the gauge couplings and one-loop RGE running for Yukawa
couplings and the Higgs quartic coupling, we calculate the supersymmetry
breaking scales, the gauge coupling unification scales, and the corresponding
Higgs mass ranges. When the vector-like particle masses are less than 1 TeV,
these models can be tested at the LHC.Comment: 25 pages, 4 figure
Cyanobacterial lipopolysaccharides and human health – a review
Cyanobacterial lipopolysaccharide/s (LPS) are frequently cited in the cyanobacteria literature as toxins responsible for a variety of heath effects in humans, from skin rashes to gastrointestinal, respiratory and allergic reactions. The attribution of toxic properties to cyanobacterial LPS dates from the 1970s, when it was thought that lipid A, the toxic moiety of LPS, was structurally and functionally conserved across all Gram-negative bacteria. However, more recent research has shown that this is not the case, and lipid A structures are now known to be very different, expressing properties ranging from LPS agonists, through weak endotoxicity to LPS antagonists. Although cyanobacterial LPS is widely cited as a putative toxin, most of the small number of formal research reports describe cyanobacterial LPS as weakly toxic compared to LPS from the Enterobacteriaceae. We systematically reviewed the literature on cyanobacterial LPS, and also examined the much lager body of literature relating to heterotrophic bacterial LPS and the atypical lipid A structures of some photosynthetic bacteria. While the literature on the biological activity of heterotrophic bacterial LPS is overwhelmingly large and therefore difficult to review for the purposes of exclusion, we were unable to find a convincing body of evidence to suggest that heterotrophic bacterial LPS, in the absence of other virulence factors, is responsible for acute gastrointestinal, dermatological or allergic reactions via natural exposure routes in humans. There is a danger that initial speculation about cyanobacterial LPS may evolve into orthodoxy without basis in research findings. No cyanobacterial lipid A structures have been described and published to date, so a recommendation is made that cyanobacteriologists should not continue to attribute such a diverse range of clinical symptoms to cyanobacterial LPS without research confirmation
Type 3 porous liquids based on non-ionic liquid phases – a broad and tailorable platform of selective, fluid gas sorbents
Pancreatic Ductal Adenocarcinoma Arising in Young and Old Patients Displays Similar Molecular Features
International audiencePancreatic ducal adenocarcinoma is classically diagnosed in the 7th decade, but approximately 10% of patients are diagnosed under 55 years (y.o.). While the genomic and transcriptomic landscapes of late-onset tumors (LOT) have been described, little is known about early-onset tumors (EOT). Ageing is known to impact DNA methylation and proteome integrity through carbonylation-related oxidative damages. We therefore aimed to assess the global molecular features of EOT. We compared 176 EOT (≤55 y.o.) and 316 LOT (≥70 y.o.) from three distinct surgical cohorts at the clinical/genomic/epigenomic/transcriptomic level. Furthermore, we assessed oxidative stress responses and oxidative proteome damages using 2D gel electrophoresis followed by mass spectrometry protein identification. There was no consistent clinical difference between EOT and LOT across the three cohorts. The mutational landscape of key driver genes and the global methylation profile were similar in the two groups. LOT did display age-related features such as enriched DNA repair gene signatures and upregulation of oxidative stress defenses together with increased proteome carbonylation. However, these age-related differences were more preeminent in non-tumor tissues while tumor proteome and proteome damages were fairly comparable. In conclusion, this multi-omics comparison showed that EOT harbor a comparable molecular profile to that of LOT