44 research outputs found
From Dynkin diagram symmetries to fixed point structures
Any automorphism of the Dynkin diagram of a symmetrizable Kac-Moody algebra
induces an automorphism of the algebra and a mapping between its highest weight
modules. For a large class of such Dynkin diagram automorphisms, we can
describe various aspects of these maps in terms of another Kac-Moody algebra,
the `orbit Lie algebra'. In particular, the generating function for the trace
of the map on modules, the `twining character', is equal to a character of the
orbit Lie algebra. Orbit Lie algebras and twining characters constitute a
crucial step towards solving the fixed point resolution problem in conformal
field theory.Comment: Latex, 60 pages (extended version 63 pages), 4 uuencoded figures
Formula (6.25) corrected. While this correction might be important in
applications of our work, the results of the paper are not affected by it. In
the present submission the "extended version" is default. In this version the
corrected formula is (6.32
Twining characters, orbit Lie algebras, and fixed point resolution
We describe the resolution of field identification fixed points in coset
conformal field theories in terms of representation spaces of the coset chiral
algebra. A necessary ingredient from the representation theory of Kac Moody
algebras is the recently developed theory of twining characters and orbit Lie
algebras, as applied to automorphisms representing identification currents.Comment: Latex, 24 pages. Slightly extended version of lectures by J. Fuchs at
a workshop in Razlog (Bulgaria) in August 199
Discriminating MSSM families in (free-field) Gepner Orientifolds
A complete analysis of orientifold compactifications involving Gepner models
that are free fields (k=1,2) is performed. A set of tadpole solutions is found
that are variants of a single chiral spectrum. The vacua found have the
property that different families have different U(1) charges so that one family
cannot obtain masses in perturbation theory. Its masses must come from
instantons, allowing for a hierarchy of masses. The phenomenological aspects of
such vacua are analyzed.Comment: 31 pages; misprints corrected, references adde
Bounds on the number and size of extra dimensions from molecular spectroscopy
Presentación de 30 diapositivas; 70th International Symposium on Molecular Spectroscopy (ISMS), University of Illinois at Urbana−Champaign, June 22 to 26, 2015Peer Reviewe
Instanton Induced Neutrino Majorana Masses in CFT Orientifolds with MSSM-like spectra
Recently it has been shown that string instanton effects may give rise to
neutrino Majorana masses in certain classes of semi-realistic string
compactifications. In this paper we make a systematic search for supersymmetric
MSSM-like Type II Gepner orientifold constructions admitting boundary states
associated with instantons giving rise to neutrino Majorana masses and other L-
and/or B-violating operators. We analyze the zero mode structure of D-brane
instantons on general type II orientifold compactifications, and show that only
instantons with O(1) symmetry can have just the two zero modes required to
contribute to the 4d superpotential. We however discuss how the addition of
fluxes and/or possible non-perturbative extensions of the orientifold
compactifications would allow also instantons with and U(1) symmetries
to generate such superpotentials. In the context of Gepner orientifolds with
MSSM-like spectra, we find no models with O(1) instantons with just the
required zero modes to generate a neutrino mass superpotential. On the other
hand we find a number of models in one particular orientifold of the Gepner
model with instantons with a few extra uncharged
non-chiral zero modes which could be easily lifted by the mentioned effects. A
few more orientifold examples are also found under less stringent constraints
on the zero modes. This class of instantons have the interesting
property that R-parity conservation is automatic and the flavour structure of
the neutrino Majorana mass matrices has a simple factorized form.Comment: 68 pages, 2 figures; v2. typos corrected, refs adde
Free Fermion Orientifolds
We investigate a class of orientifold models based on tensor products of 18
Ising models. Using the same search criteria as for the comparable case of
Gepner model orientifolds we find that there are no three-family standard model
configurations with tadpole cancellation. Even if we do not impose the latter
requirement, we only find one such configuration in the special case of complex
free fermions. In order to allow a comparison with other approaches we
enumerate the Hodge numbers of the type-IIB theories we obtain. We provide
indications that there are fermionic IIB vacua that are not
orbifolds.Comment: 18 pages + Appendix; references adde
Serotonin controlling feeding and satiety
Serotonin has been implicated in the control of satiety for almost four decades. Historically, the insight that the appetite suppressant effect of fenfluramine is linked to serotonin has stimulated interest in and research into the role of this neurotransmitter in satiety. Various rodent models, including transgenic models, have been developed to identify the involved 5-HT receptor subtypes. This approach also required the availability of receptor ligands of different selectivity, and behavioural techniques had to be developed simultaneously which allow differentiating between unspecific pharmacological effects of these ligands and ‘true’ satiation and satiety. Currently, 5-HT1B, 5-HT2C and 5-HT6 receptors have been identified to mediate serotonergic satiety in different ways. The recently approved anti-obesity drug lorcaserin is a 5-HT2C receptor agonist. In brain, both hypothalamic (arcuate nucleus, paraventricular nucleus) and extrahypothalamic sites (parabrachial nucleus, nucleus of the solitary tract) have been identified to mediate the serotonergic control of satiety. Serotonin interacts within the hypothalamus with endogenous orexigenic (Neuropeptide Y/Agouti related protein) and anorectic (α-melanocyte stimulating hormone) peptides. In the nucleus of the solitary tract serotonin integrates peripheral satiety signals. Here, the 5-HT3, but possibly also the 5-HT2C receptor play a role. It has been found that 5-HT acts in concert with such peripheral signals as cholecystokinin and leptin. Despite the recent advances of our knowledge, many of the complex interactions between 5-HT and other satiety factors are not fully understood yet. Further progress in research will also advance the development of new serotonergic anti-obesity drugs