604 research outputs found
Gravity waves and the LHC: Towards high-scale inflation with low-energy SUSY
It has been argued that rather generic features of string-inspired
inflationary theories with low-energy supersymmetry (SUSY) make it difficult to
achieve inflation with a Hubble scale H > m_{3/2}, where m_{3/2} is the
gravitino mass in the SUSY-breaking vacuum state. We present a class of
string-inspired supergravity realizations of chaotic inflation where a simple,
dynamical mechanism yields hierarchically small scales of post-inflationary
supersymmetry breaking. Within these toy models we can easily achieve small
ratios between m_{3/2} and the Hubble scale of inflation. This is possible
because the expectation value of the superpotential relaxes from large to
small values during the course of inflation. However, our toy models do not
provide a reasonable fit to cosmological data if one sets the SUSY-breaking
scale to m_{3/2} < TeV. Our work is a small step towards relieving the apparent
tension between high-scale inflation and low-scale supersymmetry breaking in
string compactifications.Comment: 21+1 pages, 5 figures, LaTeX, v2: added references, v3: very minor
changes, version to appear in JHE
Universal de Sitter solutions at tree-level
Type IIA string theory compactified on SU(3)-structure manifolds with
orientifolds allows for classical de Sitter solutions in four dimensions. In
this paper we investigate these solutions from a ten-dimensional point of view.
In particular, we demonstrate that there exists an attractive class of de
Sitter solutions, whose geometry, fluxes and source terms can be entirely
written in terms of the universal forms that are defined on all SU(3)-structure
manifolds. These are the forms J and Omega, defining the SU(3)-structure
itself, and the torsion classes. The existence of such universal de Sitter
solutions is governed by easy-to-verify conditions on the SU(3)-structure,
rendering the problem of finding dS solutions purely geometrical. We point out
that the known (unstable) solution coming from the compactification on SU(2)x
SU(2) is of this kind.Comment: 20 pages, 3 figures, v2: added reference
Stability Constraints on Classical de Sitter Vacua
We present further no-go theorems for classical de Sitter vacua in Type II
string theory, i.e., de Sitter constructions that do not invoke
non-perturbative effects or explicit supersymmetry breaking localized sources.
By analyzing the stability of the 4D potential arising from compactification on
manfiolds with curvature, fluxes, and orientifold planes, we found that
additional ingredients, beyond the minimal ones presented so far, are necessary
to avoid the presence of unstable modes. We enumerate the minimal setups for
(meta)stable de Sitter vacua to arise in this context.Comment: 18 pages; v2: argument improved, references adde
The problematic backreaction of SUSY-breaking branes
In this paper we investigate the localisation of SUSY-breaking branes which,
in the smeared approximation, support specific non-BPS vacua. We show, for a
wide class of boundary conditions, that there is no flux vacuum when the branes
are described by a genuine delta-function. Even more, we find that the smeared
solution is the unique solution with a regular brane profile. Our setup
consists of a non-BPS AdS_7 solution in massive IIA supergravity with smeared
anti-D6-branes and fluxes T-dual to ISD fluxes in IIB supergravity.Comment: 27 pages, Latex2e, 5 figure
Flux moduli stabilisation, Supergravity algebras and no-go theorems
We perform a complete classification of the flux-induced 12d algebras
compatible with the set of N=1 type II orientifold models that are T-duality
invariant, and allowed by the symmetries of the T^6/(Z_2 x Z_2) isotropic
orbifold. The classification is performed in a type IIB frame, where only H_3
and Q fluxes are present. We then study no-go theorems, formulated in a type
IIA frame, on the existence of Minkowski/de Sitter (Mkw/dS) vacua. By deriving
a dictionary between the sources of potential energy for the three moduli (S, T
and U) in types IIA and IIB, we are able to combine algebra results and no-go
theorems. The outcome is a systematic procedure for identifying
phenomenologically viable models where Mkw/dS vacua may exist. We present a
complete table of the allowed algebras and the viability of their resulting
scalar potential, and we point at the models which stand any chance of
producing a fully stable vacuum.Comment: Version published in JHE
Charting the landscape of N=4 flux compactifications
We analyse the vacuum structure of isotropic Z_2 x Z_2 flux
compactifications, allowing for a single set of sources. Combining algebraic
geometry with supergravity techniques, we are able to classify all vacua for
both type IIA and IIB backgrounds with arbitrary gauge and geometric fluxes.
Surprisingly, geometric IIA compactifications lead to a unique theory with four
different vacua. In this case we also perform the general analysis allowing for
sources compatible with minimal supersymmetry. Moreover, some relevant examples
of type IIB non-geometric compactifications are studied. The computation of the
full N=4 mass spectrum reveals the presence of a number of non-supersymmetric
and nevertheless stable AdS_4 vacua. In addition we find a novel dS_4 solution
based on a non-semisimple gauging.Comment: Minor corrections and references added. Version published in JHE
Exceptional Flux Compactifications
We consider type II (non-)geometric flux backgrounds in the absence of brane
sources, and construct their explicit embedding into maximal gauged D=4
supergravity. This enables one to investigate the critical points, mass spectra
and gauge groups of such backgrounds. We focus on a class of type IIA geometric
vacua and find a novel, non-supersymmetric and stable AdS vacuum in maximal
supergravity with a non-semisimple gauge group. Our construction relies on a
non-trivial mapping between SL(2) x SO(6,6) fluxes, SU(8) mass spectra and
gaugings of E7(7) subgroups.Comment: 51 pages, 2 figures and 4 tables. v3: change of SO(6,6) spinorial
conventions, published versio
Moduli Stabilization and Cosmology of Type IIB on SU(2)-Structure Orientifolds
We consider type IIB flux compactifications on six-dimensional
SU(2)-structure manifolds with O5- and O7-planes. These six-dimensional spaces
allow not only for F_3 and H_3 fluxes but also for F_1 and F_5 fluxes. We
derive the four-dimensional N=1 scalar potential for such compactifications and
present one explicit example of a fully stabilized AdS vacuum with large volume
and small string coupling. We then discuss cosmological aspects of these
compactifications and derive several no-go theorems that forbid dS vacua and
slow-roll inflation under certain conditions. We also study concrete examples
of cosets and twisted tori and find that our no-go theorems forbid dS vacua and
slow-roll inflation in all but one of them. For the latter we find a dS
critical point with \epsilon numerically zero. However, the point has two
tachyons and eta-parameter \eta \approx -3.1.Comment: 35 pages + appendices, LaTeX2e; v2: numerical dS extremum added,
typos corrected, references adde
PubChem3D: Similar conformers
<p>Abstract</p> <p>Background</p> <p>PubChem is a free and open public resource for the biological activities of small molecules. With many tens of millions of both chemical structures and biological test results, PubChem is a sizeable system with an uneven degree of available information. Some chemical structures in PubChem include a great deal of biological annotation, while others have little to none. To help users, PubChem pre-computes "neighboring" relationships to relate similar chemical structures, which may have similar biological function. In this work, we introduce a "Similar Conformers" neighboring relationship to identify compounds with similar 3-D shape and similar 3-D orientation of functional groups typically used to define pharmacophore features.</p> <p>Results</p> <p>The first two diverse 3-D conformers of 26.1 million PubChem Compound records were compared to each other, using a shape Tanimoto (ST) of 0.8 or greater and a color Tanimoto (CT) of 0.5 or greater, yielding 8.16 billion conformer neighbor pairs and 6.62 billion compound neighbor pairs, with an average of 253 "Similar Conformers" compound neighbors per compound. Comparing the 3-D neighboring relationship to the corresponding 2-D neighboring relationship ("Similar Compounds") for molecules such as caffeine, aspirin, and morphine, one finds unique sets of related chemical structures, providing additional significant biological annotation. The PubChem 3-D neighboring relationship is also shown to be able to group a set of non-steroidal anti-inflammatory drugs (NSAIDs), despite limited PubChem 2-D similarity.</p> <p>In a study of 4,218 chemical structures of biomedical interest, consisting of many known drugs, using more diverse conformers per compound results in more 3-D compound neighbors per compound; however, the overlap of the compound neighbor lists per conformer also increasingly resemble each other, being 38% identical at three conformers and 68% at ten conformers. Perhaps surprising is that the average count of conformer neighbors per conformer increases rather slowly as a function of diverse conformers considered, with only a 70% increase for a ten times growth in conformers per compound (a 68-fold increase in the conformer pairs considered).</p> <p>Neighboring 3-D conformers on the scale performed, if implemented naively, is an intractable problem using a modest sized compute cluster. Methodology developed in this work relies on a series of filters to prevent performing 3-D superposition optimization, when it can be determined that two conformers cannot possibly be a neighbor. Most filters are based on Tanimoto equation volume constraints, avoiding incompatible conformers; however, others consider preliminary superposition between conformers using reference shapes.</p> <p>Conclusion</p> <p>The "Similar Conformers" 3-D neighboring relationship locates similar small molecules of biological interest that may go unnoticed when using traditional 2-D chemical structure graph-based methods, making it complementary to such methodologies. The computational cost of 3-D similarity methodology on a wide scale, such as PubChem contents, is a considerable issue to overcome. Using a series of efficient filters, an effective throughput rate of more than 150,000 conformers per second per processor core was achieved, more than two orders of magnitude faster than without filtering.</p
Cryptosporidium Priming Is More Effective than Vaccine for Protection against Cryptosporidiosis in a Murine Protein Malnutrition Model
Cryptosporidium is a major cause of severe diarrhea, especially in malnourished children. Using a murine model of C. parvum oocyst challenge that recapitulates clinical features of severe cryptosporidiosis during malnutrition, we interrogated the effect of protein malnutrition (PM) on primary and secondary responses to C. parvum challenge, and tested the differential ability of mucosal priming strategies to overcome the PM-induced susceptibility. We determined that while PM fundamentally alters systemic and mucosal primary immune responses to Cryptosporidium, priming with C. parvum (106 oocysts) provides robust protective immunity against re-challenge despite ongoing PM. C. parvum priming restores mucosal Th1-type effectors (CD3+CD8+CD103+ T-cells) and cytokines (IFNÎł, and IL12p40) that otherwise decrease with ongoing PM. Vaccination strategies with Cryptosporidium antigens expressed in the S. Typhi vector 908htr, however, do not enhance Th1-type responses to C. parvum challenge during PM, even though vaccination strongly boosts immunity in challenged fully nourished hosts. Remote non-specific exposures to the attenuated S. Typhi vector alone or the TLR9 agonist CpG ODN-1668 can partially attenuate C. parvum severity during PM, but neither as effectively as viable C. parvum priming. We conclude that although PM interferes with basal and vaccine-boosted immune responses to C. parvum, sustained reductions in disease severity are possible through mucosal activators of host defenses, and specifically C. parvum priming can elicit impressively robust Th1-type protective immunity despite ongoing protein malnutrition. These findings add insight into potential correlates of Cryptosporidium immunity and future vaccine strategies in malnourished children
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