177 research outputs found
Smeared versus localised sources in flux compactifications
We investigate whether vacuum solutions in flux compactifications that are
obtained with smeared sources (orientifolds or D-branes) still survive when the
sources are localised. This seems to rely on whether the solutions are BPS or
not. First we consider two sets of BPS solutions that both relate to the GKP
solution through T-dualities: (p+1)-dimensional solutions from
spacetime-filling Op-planes with a conformally Ricci-flat internal space, and
p-dimensional solutions with Op-planes that wrap a 1-cycle inside an everywhere
negatively curved twisted torus. The relation between the solution with smeared
orientifolds and the localised version is worked out in detail. We then
demonstrate that a class of non-BPS AdS_4 solutions that exist for IASD fluxes
and with smeared D3-branes (or analogously for ISD fluxes with anti-D3-branes)
does not survive the localisation of the (anti) D3-branes. This casts doubts on
the stringy consistency of non-BPS solutions that are obtained in the limit of
smeared sources.Comment: 23 pages; v2: minor corrections, added references, version published
in JHE
An Introduction to Extra Dimensions
Models that involve extra dimensions have introduced completely new ways of
looking up on old problems in theoretical physics. The aim of the present notes
is to provide a brief introduction to the many uses that extra dimensions have
found over the last few years, mainly following an effective field theory point
of view. Most parts of the discussion are devoted to models with flat extra
dimensions, covering both theoretical and phenomenological aspects. We also
discuss some of the new ideas for model building where extra dimensions may
play a role, including symmetry breaking by diverse new and old mechanisms.
Some interesting applications of these ideas are discussed over the notes,
including models for neutrino masses and proton stability. The last part of
this review addresses some aspects of warped extra dimensions, and graviton
localization.Comment: 39 pages. Two figures. Comments and references added. Lectures given
at the XI Mexican School of Particles and Fields. Xalapa, Mexico, August
1-13, 200
Hypermoduli Stabilization, Flux Attractors, and Generating Functions
We study stabilization of hypermoduli with emphasis on the effects of
generalized fluxes. We find a class of no-scale vacua described by ISD
conditions even in the presence of geometric flux. The associated flux
attractor equations can be integrated by a generating function with the
property that the hypermoduli are determined by a simple extremization
principle. We work out several orbifold examples where all vector moduli and
many hypermoduli are stabilized, with VEVs given explicitly in terms of fluxes.Comment: 45 pages, no figures; Version submitted to JHE
Modelling the orbital modulation of ultraviolet resonance lines in high-mass X-ray binaries
The stellar-wind structure in high-mass X-ray binaries (HMXBs) is
investigated through modelling of their ultraviolet (UV) resonance lines. For
the OB supergiants in two systems, Vela X-1 and 4U1700-37, high-resolution UV
spectra are available; for Cyg X-1, SMC X-1, and LMC X-4 low-resolution spectra
are used. In order to account for the non-monotonic velocity structure of the
stellar wind, a modified version of the Sobolev Exact Integration (SEI) method
by Lamers et al. (1987) is applied. The orbital modulation of the UV resonance
lines provides information on the size of the Stroemgren zone surrounding the
X-ray source. The amplitude of the observed orbital modulation (known as the
Hatchett-McCray effect), however, also depends on the density- and velocity
structure of the ambient wind. Model profiles are presented that illustrate the
effect on the appearance of the HM effect by varying stellar-wind parameters.
The q parameter of Hatchett & McCray (1977), as well as other parameters
describing the supergiant's wind structure, are derived for the 5 systems. The
X-ray luminosity needed to create the observed size of the Stroemgren zone is
consistent with the observed X-ray flux. The derived wind parameters are
compared to those determined in single OB supergiants of similar spectral type.
Our models naturally explain the observed absence of the HM effect in
4U1700-37. The orbital modulation in Vela X-1 indicates that besides the
Stroemgren zone other structures are present in the stellar wind (such as a
photo-ionization wake). The ratio of the wind velocity and the escape velocity
is found to be lower in OB supergiants in HMXBs than in single OB supergiants
of the same effective temperature.Comment: 29 pages, good quality figures 11, 12, 13, A2 & B1 available upon
request from JvL. Accepted for publication in Astronomy & Astrophysic
Factorization Properties of Soft Graviton Amplitudes
We apply recently developed path integral resummation methods to perturbative
quantum gravity. In particular, we provide supporting evidence that eikonal
graviton amplitudes factorize into hard and soft parts, and confirm a recent
hypothesis that soft gravitons are modelled by vacuum expectation values of
products of certain Wilson line operators, which differ for massless and
massive particles. We also investigate terms which break this factorization,
and find that they are subleading with respect to the eikonal amplitude. The
results may help in understanding the connections between gravity and gauge
theories in more detail, as well as in studying gravitational radiation beyond
the eikonal approximation.Comment: 35 pages, 5 figure
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
At Least Ten Genes Define the Imprinted Dlk1-Dio3 Cluster on Mouse Chromosome 12qF1
Background: Genomic imprinting is an exception to Mendelian genetics in that imprinted genes are expressed monoallelically, dependent on parental origin. In mammals, imprinted genes are critical in numerous developmental and physiological processes. Aberrant imprinted gene expression is implicated in several diseases including Prader-Willi/ Angelman syndromes and cancer. Methodology/Principal Findings: To identify novel imprinted genes, transcription profiling was performed on two uniparentally derived cell lines, androgenetic and parthenogenetic primary mouse embryonic fibroblasts. A maternally expressed transcript termed Imprinted RNA near Meg3/Gtl2 (Irm) was identified and its expression studied by Northern blotting and whole mounts in situ hybridization. The imprinted region that contains Irm has a parent of origin effect in three mammalian species, including the sheep callipyge locus. In mice and humans, both maternal and paternal uniparental disomies (UPD) cause embryonic growth and musculoskeletal abnormalities, indicating that both alleles likely express essential genes. To catalog all imprinted genes in this chromosomal region, twenty-five mouse mRNAs in a 1.96Mb span were investigated for allele specific expression. Conclusions/Significance: Ten imprinted genes were elucidated. The imprinting of three paternally expressed protein coding genes (Dlk1, Peg11, and Dio3) was confirmed. Seven noncoding RNAs (Meg3/Gtl2, Anti-Peg11, Meg8, Irm/ââRianââ
Analyses and localization of pectin-like carbohydrates in cell wall and mucilage of the green alga Netrium digitus
The unicellular, simply shaped desmid Netrium digitus inhabiting acid bog ponds grows in two phases. Prior to division, the cell elongates at its central zone, whereas in a second phase, polar tip growth occurs. Electron microscopy demonstrates that Netrium is surrounded by a morphologically homogeneous cell wall, which lacks pores. Immunocytochemical and biochemical analyses give insight into physical wall properties and, thus, into adaptation to the extreme environment. The monoclonal antibodies JIM5 and JIM7 directed against pectic epitopes with different degrees of esterification label preferentially growing wall zones in Netrium. In contrast, 2F4 marks the cell wall only after experimental de-esterification. Electron energy loss spectroscopy reveals Ca-binding capacities of pectins and gives indirect evidence for the degree of their esterification. An antibody raised against Netrium mucilage is not only specific to mucilage but also recognizes wall components in transmission electron microscopy and dot blots. These results indicate a smooth transition between mucilage and the cell wall in Netrium
Search for low-scale gravity signatures in multi-jet final states with the ATLAS detector at âs=8 TeV
A search for evidence of physics beyond the Standard Model in final states with multiple high-transverse-momentum jets is performed using 20.3 fbâ1 of proton-proton collision data at âs=8 TeV recorded by the ATLAS detector at the LHC. No significant excess of events beyond Standard Model expectations is observed, and upper limits on the visible cross sections for non-Standard Model production of multi-jet final states are set. A wide variety of models for black hole and string ball production and decay are considered, and the upper limit on the cross section times acceptance is as low as 0.16 fb at the 95% confidence level. For these models, excluded regions are also given as function of the main model parameters
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