39 research outputs found
F-term uplifting via consistent D-terms
The issue of fine-tuning necessary to achieve satisfactory degree of
hierarchy between moduli masses, the gravitino mass and the scale of the
cosmological constant has been revisited in the context of supergravities with
consistent D-terms. We have studied (extended) racetrack models where
supersymmetry breaking and moduli stabilisation cannot be separated from each
other. We show that even in such cases the realistic hierarchy can be achieved
on the expense of a single fine-tuning. The presence of two condensates changes
the role of the constant term in the superpotential, W_0, and solutions with
small vacuum energy and large gravitino mass can be found even for very small
values of W_0. Models where D-terms are allowed to vanish at finite vevs of
moduli fields - denoted `cancellable' D-terms - and the ones where D-terms may
vanish only at infinite vevs of some moduli - denoted `non-cancellable' -
differ markedly in their properties. It turns out that the tuning with respect
to the Planck scale required in the case of cancellable D-terms is much weaker
than in the case of non-cancellable ones. We have shown that, against
intuition, a vanishing D-term can trigger F-term uplifting of the vacuum energy
due to the stringent constraint it imposes on vacuum expectation values of
charged fields. Finally we note that our models only rely on two dimensionful
parameters: M_P and W_0.Comment: 10 pages, 2 figures, plain Latex, references adde
Sterile neutrinos: the dark side of the light fermions
The discovery of neutrino masses suggests the likely existence of gauge
singlet fermions that participate in the neutrino mass generation via the
seesaw mechanism. The masses of the corresponding degrees of freedom can range
from well below the electroweak scale to the Planck scale. If some of the
singlet fermions are light, the sterile neutrinos appear in the low-energy
effective theory. They can play an important role in astrophysics and
cosmology. In particular, sterile neutrinos with masses of several keV can
account for cosmological dark matter, which can be relatively warm or cold,
depending on the production mechanism. The same particles can explain the
observed velocities of pulsars because of the anisotropy in their emission from
a cooling neutron star born in a supernova explosion. Decays of the relic
sterile neutrinos can produce a flux of X-rays that can affect the formation of
the first stars. Existing and future X-ray telescopes can be used to search for
the relic sterile neutrinos.Comment: 54 page
The Next-to-Minimal Supersymmetric Standard Model
We review the theoretical and phenomenological aspects of the Next-to-Minimal
Supersymmetric Standard Model: the Higgs sector including radiative corrections
and the 2-loop beta-functions for all parameters of the general NMSSM; the
tadpole and domain wall problems, baryogenesis; NMSSM phenomenology at
colliders, B physics and dark matter; specific scenarios as the constrained
NMSSM, Gauge Mediated Supersymmetry Breaking, U(1)'-extensions, CP and R-parity
violation.Comment: 144 pages, 11 figures, corrections in Eqs.(2.2), (2.21), (B.9
Enantiomeric Natural Products: Occurrence and Biogenesis
In nature, chiral natural products are usually produced in optically pure form—however, occasionally both enantiomers are formed. These enantiomeric natural products can arise from a single species or from different genera and/or species. Extensive research has been carried out over the years in an attempt to understand the biogenesis of naturally occurring enantiomers; however, many fascinating puzzles and stereochemical anomalies still remain. Two sides to the story : The formation of enantiomerically opposite natural products by nature is known, although rare (see examples). To date, many puzzles and stereochemical anomalies remain regarding the biogenesis of these unique natural products, despite the substantial body of research that has been carried out over the years in an attempt to understand the biogenesis of enantiomeric metabolites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92098/1/4802_ftp.pd
Enantiomere Naturstoffe: Vorkommen und Biogenese
In der Natur werden chirale Substanzen meist in enantiomerenreiner Form synthetisiert – manchmal entstehen aber auch beide Enantiomere. Solche enantiomeren Naturstoffe können von einer Art oder von verschiedenen Gattungen und/oder Arten gebildet werden. Intensive Forschungen wurden über viele Jahre durchgeführt, um die Biogenese natürlich vorkommender Enantiomere zu verstehen, doch viele faszinierende Rätsel und stereochemische Anomalien sind nach wie vor ungelöst. Bild und Spiegelbild in der Natur: Die Bildung von natürlich vorkommenden Enantiomerenpaaren ist bekannt, wenn auch selten (siehe Beispiel). Bis heute sind noch viele Rätsel und stereochemische Anomalien bei der Biogenese dieser einmaligen Naturstoffe ungelöst, auch wenn im Laufe der Jahre viel Arbeit investiert worden ist, um die Entstehung enantiomerer Metaboliten zu verstehen.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91315/1/4886_ftp.pd
Small Yukawa couplings in particle physics and cosmology from Type 1 string theory
Within the framework of Type I string theory we construct phenomenologically interesting models. The string theory is formulated in a 10 dimensional space of which 6 are compact and the anisotropies in the compact dimensions lead to a hierarchy of gauge and Yukawa couplings. We make use of this hierarchy to construct a model of inflationary particle physics and a consistent model for Dirac neutrino masses. The inflation model solves the strong CP and μ problems of the MSSM and predicts a range of allowed ratios for μ and the soft masses for the Higgs doublets. We demonstrate that it is possible to obtain Dirac masses in agreement with current experimental data.</p
Small Yukawa couplings in particle physics and cosmology from Type 1 string theory
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Inflationary solution to the strong CP and mu problems
We show that the vacuum expectation value of the inflaton at the Peccei-Quinn
axion scale can generate the supersymmetric Higgs mass term. This
provides an inflationary simultaneous solution to the strong CP problem and the
problem of the Minimal Supersymmetric Standard Model, and gives a
testable prediction for the parameter: ,
where is the soft Higgs scalar mass. Our model involves a very small
Yukawa coupling of order , which could originate from an
extra-dimensional scenario or type I string theory.Comment: Version to appear in Physics Letters B. 14 page