175 research outputs found
Chiral fermions and anomaly cancellation on orbifolds with Wilson lines and flux
We consider six-dimensional supergravity compactified on orbifolds with
Wilson lines and bulk flux. Torus Wilson lines are decomposed into Wilson lines
around the orbifold fixed points, and twisted boundary conditions of matter
fields are related to fractional localized flux. Both, orbifold singularities
and flux lead to chiral fermions in four dimensions. We show that in addition
to the standard bulk and fixed point anomalies the Green-Schwarz term also
cancels the four-dimensional anomaly induced by the flux background. The two
axions contained in the antisymmetric tensor field both contribute to the
cancellation of the four-dimensional anomaly and the generation of a vector
boson mass via the Stueckelberg mechanism. An orthogonal linear combination of
the axions remains massless and couples to the gauge field in the standard way.
Furthermore, we construct convenient expressions for the wave functions of the
zero modes and relate their multiplicity and behavior at the fixed points to
the bulk flux quanta and the Wilson lines.Comment: 30 pages, 4 figures, 1 table, clarifying remarks adde
Moduli backreaction and supersymmetry breaking in string-inspired inflation models
We emphasize the importance of effects from heavy fields on supergravity
models of inflation. We study, in particular, the backreaction of stabilizer
fields and geometric moduli in the presence of supersymmetry breaking. Many
effects do not decouple even if those fields are much heavier than the inflaton
field. We apply our results to successful models of Starobinsky-like inflation
and natural inflation. In most scenarios producing a plateau potential it
proves difficult to retain the flatness of the potential after backreactions
are taken into account. Some of them are incompatible with non-perturbative
moduli stabilization. In natural inflation there exist a number of models which
are not constrained by backreactions at all. In those cases the correction
terms from heavy fields have the same inflaton-dependence as the uncorrected
potential, so that inflation may be possible even for very large gravitino
masses.Comment: 29 pages, 1 figure, comments added, subsection 2.3 added, published
versio
Rational F-Theory GUTs without exotics
We construct F-theory GUT models without exotic matter, leading to the MSSM
matter spectrum with potential singlet extensions. The interplay of engineering
explicit geometric setups, absence of four-dimensional anomalies, and realistic
phenomenology of the couplings places severe constraints on the allowed local
models in a given geometry. In constructions based on the spectral cover we
find no model satisfying all these requirements. We then provide a survey of
models with additional U(1) symmetries arising from rational sections of the
elliptic fibration in toric constructions and obtain phenomenologically
appealing models based on SU(5) tops. Furthermore we perform a bottom-up
exploration beyond the toric section constructions discussed in the literature
so far and identify benchmark models passing all our criteria, which can serve
as a guideline for future geometric engineering.Comment: 27 Pages, 1 Figur
Dokumentation SSYST-1: Ein Programmsystem zur Beschreibung des LWR-Brennstabverhaltens bei Kuehlmittelverluststoerfaellen
A perfect match of MSSM-like orbifold and resolution models via anomalies
Compactification of the heterotic string on toroidal orbifolds is a promising
set-up for the construction of realistic unified models of particle physics.
The target space dynamics of such models, however, drives them slightly away
from the orbifold point in moduli space. This resolves curvature singularities,
but makes the string computations very difficult. On these smooth manifolds we
have to rely on an effective supergravity approximation in the large volume
limit. By comparing an orbifold example with its blow-up version, we try to
transfer the computational power of the orbifold to the smooth manifold. Using
local properties, we establish a perfect map of the the chiral spectra as well
as the (local) anomalies of these models. A key element in this discussion is
the Green-Schwarz anomaly polynomial. It allows us to identify those
redefinitions of chiral fields and localized axions in the blow-up process
which are relevant for the interactions (such as Yukawa-couplings) in the model
on the smooth space.Comment: 2+35 pages, 1 figur
The endocannabinoid system controls food intake via olfactory processes
Comment in Sensory systems: the hungry sense. [Nat Rev Neurosci. 2014] Inhaling: endocannabinoids and food intake. [Nat Neurosci. 2014]; International audience; Hunger arouses sensory perception, eventually leading to an increase in food intake, but the underlying mechanisms remain poorly understood. We found that cannabinoid type-1 (CB1) receptors promote food intake in fasted mice by increasing odor detection. CB1 receptors were abundantly expressed on axon terminals of centrifugal cortical glutamatergic neurons that project to inhibitory granule cells of the main olfactory bulb (MOB). Local pharmacological and genetic manipulations revealed that endocannabinoids and exogenous cannabinoids increased odor detection and food intake in fasted mice by decreasing excitatory drive from olfactory cortex areas to the MOB. Consistently, cannabinoid agonists dampened in vivo optogenetically stimulated excitatory transmission in the same circuit. Our data indicate that cortical feedback projections to the MOB crucially regulate food intake via CB1 receptor signaling, linking the feeling of hunger to stronger odor processing. Thus, CB1 receptor-dependent control of cortical feedback projections in olfactory circuits couples internal states to perception and behavior
Modulation of Glucose Transporter 1 (GLUT1) Expression Levels Alters Mouse Mammary Tumor Cell Growth In Vitro and In Vivo
Tumor cells exhibit an altered metabolism characterized by elevated aerobic glycolysis and lactate secretion which is supported by an increase in glucose transport and consumption. We hypothesized that reducing or eliminating the expression of the most prominently expressed glucose transporter(s) would decrease the amount of glucose available to breast cancer cells thereby decreasing their metabolic capacity and proliferative potential
Gauged Linear Sigma Models for toroidal orbifold resolutions
Toroidal orbifolds and their resolutions are described within the framework
of (2,2) Gauged Linear Sigma Models (GLSMs). Our procedure describes two-tori
as hypersurfaces in (weighted) projective spaces. The description is chosen
such that the orbifold singularities correspond to the zeros of their
homogeneous coordinates. The individual orbifold singularities are resolved
using a GLSM guise of non-compact toric resolutions, i.e. replacing discrete
orbifold actions by Abelian worldsheet gaugings. Given that we employ the same
global coordinates for both the toroidal orbifold and its resolutions, our GLSM
formalism confirms the gluing procedure on the level of divisors discussed by
Lust et al. Using our global GLSM description we can study the moduli space of
such toroidal orbifolds as a whole. In particular, changes in topology can be
described as phase transitions of the underlying GLSM. Finally, we argue that
certain partially resolvable GLSMs, in which a certain number of fixed points
can never be resolved, might be useful for the study of mini-landscape orbifold
MSSMs.Comment: 71 pages, 2 figure
Searching for the Standard Model in the String Landscape : SUSY GUTs
The goal of the present review article is to describe the ingredients
necessary to find the Standard Model in the string landscape.Comment: 70 pages, 20 figures, this review article will be published in
Reports on Progress in Physic
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