79 research outputs found
N-flation from multiple DBI type actions
In this letter we present a new N-flation model constructed by making use of
multiple scalar fields which are being described by their own DBI action. We
show that the dependence of the e-folding number and of the curvature
perturbation on the number of fields changes compared with the normal N-flation
model. Our model is also quite different from the usual DBI N-flation which is
still based on one DBI action but involves many moduli components. Some
specific examples of our model have been analyzed.Comment: 4 pages, 1 figur
Deformations of calibrated D-branes in flux generalized complex manifolds
We study massless deformations of generalized calibrated cycles, which
describe, in the language of generalized complex geometry, supersymmetric
D-branes in N=1 supersymmetric compactifications with fluxes. We find that the
deformations are classified by the first cohomology group of a Lie algebroid
canonically associated to the generalized calibrated cycle, seen as a
generalized complex submanifold with respect to the integrable generalized
complex structure of the bulk. We provide examples in the SU(3) structure case
and in a `genuine' generalized complex structure case. We discuss cases of
lifting of massless modes due to world-volume fluxes, background fluxes and a
generalized complex structure that changes type.Comment: 52 pages, added references, added comment on ellipticity in appendix
B, made minor changes according to instructions referee JHE
GUTs in Type IIB Orientifold Compactifications
We systematically analyse globally consistent SU(5) GUT models on
intersecting D7-branes in genuine Calabi-Yau orientifolds with O3- and
O7-planes. Beyond the well-known tadpole and K-theory cancellation conditions
there exist a number of additional subtle but quite restrictive constraints.
For the realisation of SU(5) GUTs with gauge symmetry breaking via U(1)_Y flux
we present two classes of suitable Calabi-Yau manifolds defined via del Pezzo
transitions of the elliptically fibred hypersurface P_{1,1,1,6,9}[18] and of
the Quintic P_{1,1,1,1,1}[5], respectively. To define an orientifold projection
we classify all involutions on del Pezzo surfaces. We work out the model
building prospects of these geometries and present five globally consistent
string GUT models in detail, including a 3-generation SU(5) model with no
exotics whatsoever. We also realise other phenomenological features such as the
10 10 5 Yukawa coupling and comment on the possibility of moduli stabilisation,
where we find an entire new set of so-called swiss-cheese type Calabi-Yau
manifolds. It is expected that both the general constrained structure and the
concrete models lift to F-theory vacua on compact Calabi-Yau fourfolds.Comment: 138 pages, 9 figures; v2, v3: typos corrected, one reference adde
Progress in D-brane model building
The state of the art in D-brane model building is briefly reviewed, focusing
on recent achievements in the construction of D=4 N = 1 type II string vacua
with semi-realistic gauge sectors. Such progress relies on a better
understanding of the spectrum of BPS D-branes, the effective field theory
obtained from them and the explicit construction of vacua. We first consider
D-branes in standard Calabi-Yau compactifications, and then the more involved
case of compactifications with fluxes. We discuss how the non-trivial interplay
between D-branes and fluxes modifies the previous model-building rules, as well
as provides new possibilities to connect string theory to particle physics.Comment: Using w-art.cls, 27 pages, 6 figures. Based on a talk given at the
RTN `Constituents, Fundamental Forces and Symmetries of the Universe'
Workshop and Midterm meeting in Napoli, October 2006. v2: typos corrected and
references adde
~l-Analogs of PLG (L-Prolyl-L-Leucyl-Glycinamide): Ex-Chiral Pool Syntheses and Dopamine D 2 Receptor Modulating Effects
Abstract: Starting from (S)-and (R)-aspartic acid enantiomerically pure 13-proline derivatives were synthesized. These chiral building blocks were transformed into 13-analogs of the dopamine receptor modulating peptide PLG. According to dopamine receptor binding studies, significant enhancement of [3H]pramipexole binding was observed for the isomeres la,b and 2a-c. The derivative lb revealed an activity comparable to PLG
Identification of the Beer Component Hordenine as Food-Derived Dopamine D2 Receptor Agonist by Virtual Screening a 3D Compound Database
The dopamine D2 receptor (D2R) is involved in food reward and compulsive food intake. The present study developed a virtual screening (VS) method to identify food components, which may modulate D2R signalling. In contrast to their common applications in drug discovery, VS methods are rarely applied for the discovery of bioactive food compounds. Here, databases were created that exclusively contain substances occurring in food and natural sources (about 13,000 different compounds in total) as the basis for combined pharmacophore searching, hit-list clustering and molecular docking into D2R homology models. From 17 compounds finally tested in radioligand assays to determine their binding affinities, seven were classified as hits (hit rateâ=â41%). Functional properties of the five most active compounds were further examined in ÎČ-arrestin recruitment and cAMP inhibition experiments. D2R-promoted G-protein activation was observed for hordenine, a constituent of barley and beer, with approximately identical ligand efficacy as dopamine (76%) and a Ki value of 13âÎŒM. Moreover, hordenine antagonised D2-mediated ÎČ-arrestin recruitment indicating functional selectivity. Application of our databases provides new perspectives for the discovery of bioactive food constituents using VS methods. Based on its presence in beer, we suggest that hordenine significantly contributes to mood-elevating effects of beer
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