1,309 research outputs found
Fractional branes, warped compactifications and backreacted orientifold planes
The standard extremal p-brane solutions in supergravity are known to allow
for a generalisation which consists of adding a linear dependence on the
world-volume coordinates to the usual harmonic function. In this note we
demonstrate that remarkably this generalisation goes through in exactly the
same way for p-branes with fluxes added to it that correspond to fractional
p-branes. We relate this to warped orientifold compactifications by trading the
Dp-branes for Op-planes that solve the RR tadpole condition. This allows us to
interpret the worldvolume dependence as due to lower-dimensional scalars that
flow along the massless directions in the no-scale potential. Depending on the
details of the fluxes these flows can be supersymmetric domain wall flows. Our
solutions provide explicit examples of backreacted orientifold planes in
compactifications with non-constant moduli.Comment: 20 pages, incl. references. v2: small changes required for JHEP
publication. v3: few equation typos correcte
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
Echocardiography of isolated subacute left heart tamponade in a patient with cor pulmonale and circumferential pericardial effusion
Patients with advanced idiopathic pulmonary artery hypertension have often a chronic pericardial effusion. It is the result of increased transudation and impaired re-absorption due to elevated venous pressure. These patients have pre-existent symptoms and signs of chronic right heart failure. High degree of suspicion is required to detect of development of an atypical form of tamponade with isolated compression of left heart chambers as shown in present case report. Transthoracic echocardiography provides a rapid access to the correct diagnosis, a prompt relief of symptoms following the ultrasound guided pericardiocentesis and important diagnostic tool for regular follow up of patients thereafter as shown in our case report
New families of interpolating type IIB backgrounds
We construct new families of interpolating two-parameter solutions of type
IIB supergravity. These correspond to D3-D5 systems on non-compact
six-dimensional manifolds which are T^2 fibrations over Eguchi-Hanson and
multi-center Taub-NUT spaces, respectively. One end of the interpolation
corresponds to a solution with only D5 branes and vanishing NS three-form flux.
A topology changing transition occurs at the other end, where the internal
space becomes a direct product of the four-dimensional surface and the
two-torus and the complexified NS-RR three-form flux becomes imaginary
self-dual. Depending on the choice of the connections on the torus fibre, the
interpolating family has either N=2 or N=1 supersymmetry. In the N=2 case it
can be shown that the solutions are regular.Comment: 20 page
Nearly K\"ahler heterotic compactifications with fermion condensates
We revisit AdS_4 heterotic compactifications on nearly K\"ahler manifolds in
the presence of H-flux and certain fermion condensates. Unlike previous
studies, we do not assume the vanishing of the supersymmetry variations.
Instead we determine the full equations of motion originating from the
ten-dimensional action, and subsequently we provide explicit solutions to them
on nearly K\"ahler manifolds at first order in alpha'. The Bianchi identity is
also taken into account in order to guarantee the absence of all anomalies. In
the presence of H-flux, which is identified with the torsion of the internal
space, as well as of fermion condensates in the gaugino and dilatino sectors,
new solutions are determined. These solutions provide a full classification of
consistent backgrounds of heterotic supergravity under our assumptions. All the
new solutions are non-supersymmetric, while previously known supersymmetric
ones are recovered too. Our results indicate that fully consistent
(supersymmetric or not) heterotic vacua on nearly K\"ahler manifolds are
scarce, even on AdS_4, and they can be completely classified.Comment: 1+17 pages, 1 figure; v2: remark and two references added, published
versio
Dynamical Cobordisms in General Relativity and String Theory
We describe a class of time-dependent solutions in string- or M-theory that
are exact with respect to alpha-prime and curvature corrections and interpolate
in physical space between regions in which the low energy physics is
well-approximated by different string theories and string compactifications.
The regions are connected by expanding "domain walls" but are not separated by
causal horizons, and physical excitations can propagate between them. As
specific examples we construct solutions that interpolate between oriented and
unoriented string theories, and also between type II and heterotic theories.
Our solutions can be weakly curved and under perturbative control everywhere
and can asymptote to supersymmetric at late times.Comment: 35 pages, 5 figures, LaTeX v2: reference adde
Single-molecule imaging to characterise the transport mechanism of the Nuclear Pore Complex
In the eukaryotic cell, a large macromolecular channel, known as the Nuclear Pore
Complex (NPC), mediates all molecular transport between the nucleus and cytoplasm.
In recent years, single-molecule fluorescence (SMF) imaging has emerged as a
powerful tool to study the molecular mechanism of transport through the NPC. More
recently, techniques such as Single-Molecule Localisation Microscopy (SMLM) have
enabled the spatial and temporal distribution of cargos, transport receptors and even
structural components of the NPC to be determined with nanometre accuracy. In this
protocol, we describe a method to study the position and/or motion of individual
molecules transiting through the NPC with high spatial and temporal precision
Soft branes in supersymmetry-breaking backgrounds
We revisit the analysis of effective field theories resulting from
non-supersymmetric perturbations to supersymmetric flux compactifications of
the type-IIB superstring with an eye towards those resulting from the
backreaction of a small number of anti-D3-branes. Independently of the
background, we show that the low-energy Lagrangian describing the fluctuations
of a stack of probe D3-branes exhibits soft supersymmetry breaking, despite
perturbations to marginal operators that were not fully considered in some
previous treatments. We take this as an indication that the breaking of
supersymmetry by anti-D3-branes or other sources may be spontaneous rather than
explicit. In support of this, we consider the action of an anti-D3-brane
probing an otherwise supersymmetric configuration and identify a candidate for
the corresponding goldstino.Comment: 36+5 pages. References added, minor typos correcte
Long Wavelength Anomalous Diffusion Mode in the 2D XY Dipole Magnet
In 2D XY ferromagnet the dipole force induces a strong interaction between
spin-waves in the long-wavelength limit. The major effect of this interaction
is the transformation of a propagating spin-wave into a diffusion mode. We
study the anomalous dynamics of such diffusion modes. We find that the
Janssen-De Dominics functional, which governs this dynamics, approaches the
non-Gaussian fixed-point. A spin-wave propagates by an anomalous anisotropic
diffusion with the dispersion relation: and
, where and
. The low-frequency response to the external magnetic field
is found.Comment: 34 pages, RevTeX, 2 .ps figures, the third figure is available upon
reques
Moduli Stabilisation in Heterotic Models with Standard Embedding
In this note we analyse the issue of moduli stabilisation in 4d models
obtained from heterotic string compactifications on manifolds with SU(3)
structure with standard embedding. In order to deal with tractable models we
first integrate out the massive fields. We argue that one can not only
integrate out the moduli fields, but along the way one has to truncate also the
corresponding matter fields. We show that the effective models obtained in this
way do not have satisfactory solutions. We also look for stabilised vacua which
take into account the presence of the matter fields. We argue that this also
fails due to a no-go theorem for Minkowski vacua in the moduli sector which we
prove in the end. The main ingredient for this no-go theorem is the constraint
on the fluxes which comes from the Bianchi identity.Comment: 20 pages, LaTeX; references adde
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