922 research outputs found
The F-Landscape: Dynamically Determining the Multiverse
We evolve our Multiverse Blueprints to characterize our local neighborhood of
the String Landscape and the Multiverse of plausible string, M- and F-theory
vacua. Building upon the tripodal foundations of i) the Flipped SU(5) Grand
Unified Theory (GUT), ii) extra TeV-Scale vector-like multiplets derived out of
F-theory, and iii) the dynamics of No-Scale Supergravity, together dubbed
No-Scale F-SU(5), we demonstrate the existence of a continuous family of
solutions which might adeptly describe the dynamics of distinctive universes.
This Multiverse landscape of F-SU(5) solutions, which we shall refer to as the
F-Landscape, accommodates a subset of universes compatible with the presently
known experimental uncertainties of our own universe. We show that by
secondarily minimizing the minimum of the scalar Higgs potential of each
solution within the F-Landscape, a continuous hypervolume of distinct minimum
minimorum can be engineered which comprise a regional dominion of universes,
with our own universe cast as the bellwether. We conjecture that an
experimental signal at the LHC of the No-Scale F-SU(5) framework's
applicability to our own universe might sensibly be extrapolated as
corroborating evidence for the role of string, M- and F-theory as a master
theory of the Multiverse, with No-Scale supergravity as a crucial and pervasive
reinforcing structure.Comment: 15 Pages, 7 Figures, 1 Tabl
Freund-Rubin Revisited
We utilise the duality between M theory and Type IIA string theory to show
the existence of Freund-Rubin compactifications of M theory on 7-manifolds with
singularities supporting chiral fermions. This leads to a concrete way to study
phenomenologically interesting quantum gravity vacua using a holographically
dual three dimensional field theory.Comment: reference adde
Paracrinicity: The Story of 30 Years of Cellular Pituitary Crosstalk
Living organisms represent, in essence, dynamic interactions of high complexity between membrane-separated compartments that cannot exist on their own, but reach behaviour in co-ordination. In multicellular organisms, there must be communication and co-ordination between individual cells and cell groups to achieve appropriate behaviour of the system. Depending on the mode of signal transportation and the target, intercellular communication is neuronal, hormonal, paracrine or juxtacrine. Cell signalling can also be self-targeting or autocrine. Although the notion of paracrine and autocrine signalling was already suggested more than 100 years ago, it is only during the last 30 years that these mechanisms have been characterised. In the anterior pituitary, paracrine communication and autocrine loops that operate during fetal and postnatal development in mammals and lower vertebrates have been shown in all hormonal cell types and in folliculo-stellate cells. More than 100 compounds have been identified that have, or may have, paracrine or autocrine actions. They include the neurotransmitters acetylcholine and γ-aminobutyric acid, peptides such as vasoactive intestinal peptide, galanin, endothelins, calcitonin, neuromedin B and melanocortins, growth factors of the epidermal growth factor, fibroblast growth factor, nerve growth factor and transforming growth factor-β families, cytokines, tissue factors such as annexin-1 and follistatin, hormones, nitric oxide, purines, retinoids and fatty acid derivatives. In addition, connective tissue cells, endothelial cells and vascular pericytes may influence paracrinicity by delivering growth factors, cytokines, heparan sulphate proteoglycans and proteases. Basement membranes may influence paracrine signalling through the binding of signalling molecules to heparan sulphate proteoglycans. Paracrine/autocrine actions are highly context-dependent. They are turned on/off when hormonal outputs need to be adapted to changing demands of the organism, such as during reproduction, stress, inflammation, starvation and circadian rhythms. Specificity and selectivity in autocrine/paracrine interactions may rely on microanatomical specialisations, functional compartmentalisation in receptor–ligand distribution and the non-equilibrium dynamics of the receptor–ligand interactions in the loops
Runaway dilatonic domain walls
We explore the stability of domain wall and bubble solutions in theories with
compact extra dimensions. The energy density stored inside of the wall can
destabilize the volume modulus of a compactification, leading to solutions
containing either a timelike singularity or a region where space
decompactifies, depending on the metric ansatz. We determine the structure of
such solutions both analytically and using numerical simulations, and analyze
how they arise in compactifications of Einstein--Maxwell theory and Type IIB
string theory. The existence of instabilities has important implications for
the formation of networks of topological defects and the population of vacua
during eternal inflation.Comment: 29 pages with 19 figures. Replaced to match published versio
Applications of an exact counting formula in the Bousso-Polchinski Landscape
The Bousso-Polchinski (BP) Landscape is a proposal for solving the
Cosmological Constant Problem. The solution requires counting the states in a
very thin shell in flux space. We find an exact formula for this counting
problem which has two simple asymptotic regime one of them being the method of
counting low states given originally by Bousso and Polchinski. We
finally give some applications of the extended formula: a robust property of
the Landscape which can be identified with an effective occupation number, an
estimator for the minimum cosmological constant and a possible influence on the
KKLT stabilization mechanism.Comment: 43 pages, 11 figures, 2 appendices. We have added a new section (3.4)
on the influence of the fraction of non-vanishing fluxes in the KKLT
mechanism. Other minor changes also mad
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Microbiomes Reduce Their Host's Sensitivity to Interspecific Interactions.
Bacteria associated with eukaryotic hosts can affect host fitness and trophic interactions between eukaryotes, but the extent to which bacteria influence the eukaryotic species interactions within trophic levels that modulate biodiversity and species coexistence is mostly unknown. Here, we used phytoplankton, which are a classic model for evaluating interactions between species, grown with and without associated bacteria to test whether the bacteria alter the strength and type of species interactions within a trophic level. We demonstrate that host-associated bacteria alter host growth rates and carrying capacity. This did not change the type but frequently changed the strength of host interspecific interactions by facilitating host growth in the presence of an established species. These findings indicate that microbiomes can regulate their host species' interspecific interactions. As between-species interaction strength impacts their ability to coexist, our findings show that microbiomes have the potential to modulate eukaryotic species diversity and community composition.IMPORTANCE Description of the Earth's microbiota has recently undergone a phenomenal expansion that has challenged basic assumptions in many areas of biology, including hominid evolution, human gastrointestinal and neurodevelopmental disorders, and plant adaptation to climate change. By using the classic model system of freshwater phytoplankton that has been drawn upon for numerous foundational theories in ecology, we show that microbiomes, by facilitating their host population, can also influence between-species interactions among their eukaryotic hosts. Between-species interactions, including competition for resources, has been a central tenet in the field of ecology because of its implications for the diversity and composition of communities and how this in turn shapes ecosystem functioning
Exact solutions for supersymmetric stationary black hole composites
Four dimensional N=2 supergravity has regular, stationary, asymptotically
flat BPS solutions with intrinsic angular momentum, describing bound states of
separate extremal black holes with mutually nonlocal charges. Though the
existence and some properties of these solutions were established some time
ago, fully explicit analytic solutions were lacking thus far. In this note, we
fill this gap. We show in general that explicit solutions can be constructed
whenever an explicit formula is known in the theory at hand for the
Bekenstein-Hawking entropy of a single black hole as a function of its charges,
and illustrate this with some simple examples. We also give an example of
moduli-dependent black hole entropy.Comment: 13 pages, 1 figur
Constructive Wall-Crossing and Seiberg-Witten
We outline a comprehensive and first-principle solution to the wall-crossing
problem in D=4 N=2 Seiberg-Witten theories. We start with a brief review of the
multi-centered nature of the typical BPS states and recall how the
wall-crossing problem thus becomes really a bound state formation/dissociation
problem. Low energy dynamics for arbitrary collections of dyons is derived,
from Seiberg-Witten theory, with the proximity to the so-called marginal
stability wall playing the role of the small expansion parameter. We find that,
surprisingly, the low energy dynamics of n+1 BPS dyons cannot
be consistently reduced to the classical moduli space, \CM, yet the index can
be phrased in terms of \CM. We also explain how an equivariant version of
this index computes the protected spin character of the underlying field
theory, where SO(3)_\CJ isometry of \CM turns out to be the diagonal
subgroup of spatial rotation and R-symmetry. The so-called
rational invariants, previously seen in the Kontsevich-Soibelman formalism of
wall-crossing, are shown to emerge naturally from the orbifolding projection
due to Bose/Fermi statistics.Comment: 25 pages, conference proceeding contribution for "Progress of Quantum
Field Theory and String Theory," Osaka, April 201
Bubbling solutions, entropy enhancement and the fuzzball proposal
In this short note we explain the main idea of the work done in
arXiv:0804.4487[hep-th] and arXiv:0812.2942[hep-th]. We present a family of
black hole microstates, the bubbling solutions. We then explain how supertubes
placed in such backgrounds have their entropy enhanced by the presence of the
background dipole charges. This indicates this could account for a large amount
in the entropy of the three charge black hole.Comment: 2 pages, contribution to the Cargese 2008 proceedings: Theory and
Particle Physics: the LHC perspective and beyon
Type IIB Flux Vacua from M-theory via F-theory
We study in detail some aspects of duality between type IIB and M-theory. We
focus on the duality between type IIB string theory on K3 x T^2/Z_2 orientifold
and M-theory on K3 x K3, in the F-theory limit. We give the explicit map
between the fields and in particular between the moduli of compactification,
studying their behavior under the F-theory limit. Turning on fluxes generates a
potential for the moduli both in type IIB and in M-theory. We verify that the
type IIB analysis gives the same results of the F-theory analysis. In
particular, we check that the two potentials match.Comment: 24 pages; reference correcte
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