604 research outputs found
Reversing the paradigm on the urgency of acute retinal detachments defined by their foveal status: when off may be more urgent than on
D3-brane Potentials from Fluxes in AdS/CFT
We give a comprehensive treatment of the scalar potential for a D3-brane in a
warped conifold region of a compactification with stabilized moduli. By
studying general ultraviolet perturbations in supergravity, we systematically
incorporate `compactification effects' sourced by supersymmetry breaking in the
compact space. Significant contributions to the D3-brane potential, including
the leading term in the infrared, arise from imaginary anti-self-dual (IASD)
fluxes. For an arbitrary Calabi-Yau cone, we determine the most general IASD
fluxes in terms of scalar harmonics, then compute the resulting D3-brane
potential. Specializing to the conifold, we identify the operator dual to each
mode of flux, and for chiral operators we confirm that the potential computed
in the gauge theory matches the gravity result. The effects of four-dimensional
curvature, including the leading D3-brane mass term, arise directly from the
ten-dimensional equations of motion. Furthermore, we show that gaugino
condensation on D7-branes provides a local source for IASD flux. This flux
precisely encodes the nonperturbative contributions to the D3-brane potential,
yielding a promising ten-dimensional representation of four-dimensional
nonperturbative effects. Our result encompasses all significant contributions
to the D3-brane potential discussed in the literature, and does so in the
single coherent framework of ten-dimensional supergravity. Moreover, we
identify new terms with irrational scaling dimensions that were inaccessible in
prior works. By decoupling gravity in a noncompact configuration, then
systematically reincorporating compactification effects as ultraviolet
perturbations, we have provided an approach in which Planck-suppressed
contributions to the D3-brane effective action can be computed.Comment: 70 page
On Loops in Inflation II: IR Effects in Single Clock Inflation
In single clock models of inflation the coupling between modes of very
different scales does not have any significant dynamical effect during
inflation. It leads to interesting projection effects. Larger and smaller modes
change the relation between the scale a mode of interest will appear in the
post-inflationary universe and will also change the time of horizon crossing of
that mode. We argue that there are no infrared projection effects in physical
questions, that there are no effects from modes of longer wavelength than the
one of interest. These potential effects cancel when computing fluctuations as
a function of physically measurable scales. Modes on scales smaller than the
one of interest change the mapping between horizon crossing time and scale. The
correction to the mapping computed in the absence of fluctuations is enhanced
by a factor N_e, the number of e-folds of inflation between horizon crossing
and reheating. The new mapping is stochastic in nature but its variance is not
enhanced by N_e.Comment: 13 pages, 1 figure; v2: JHEP published version, added minor comments
and reference
Predictive Association of Pre-Operative Defect Areas in the Outer Retinal Layers With Visual Acuity in Macular Hole Surgery
Purpose: The purpose of this study was to develop methods to model the external limiting membrane (ELM) and ellipsoid zone (EZ) within the elevated cuff surrounding a macular hole (MH) to determine if the predicted size of the defect in these layers after virtual flattening was associated with the actual postoperative defect and best corrected visual acuity (BCVA). Methods: Patients were included who had undergone successful MH surgery. The defects in the ELM and EZ after virtual flattening were modeled using in-house software. Main outcomes were postoperative defects in ELM and EZ at 2 months and BCVA at 12 months. Results: Fifty-eight patients were included. BCVA improved from 0.87 (0.31) logMAR pre-operatively to 0.26 (0.21) at 12 months (P < 0.001). For both the ELM and EZ, the predicted virtually flattened pre-operative defects were associated with the actual postoperative defects at 2 months (R-2 = 0.33, P < 0.01 and R-2 = 0.50, P < 0.01, respectively). There was a significant association of BCVA at 12 months (adjusted R-2 = 0.85) with the pre-operative modeled area of the defect in the ELM (P < 0.01) and to a lesser extent with the defect in the EZ (P < 0.01) and base of the MH (P < 0.01). Conclusions: Virtually flattening of the pre-operative defect in the ELM provides important predictive information of visual acuity. Incorporation of tools into commercially available optical coherence tomography (OCT) devices to facilitate such measurements would provide the clinician with important prognostic information. Translational Relevance: We have developed methodology that can potentially be used to predict the postoperative state of the outer retinal layers and the associated visual outcome in patients undergoing surgery for MH
Non-supersymmetric Conifold
We find a new family of non-supersymmetric numerical solutions of IIB
supergravity which are dual to the N=1 cascading "conifold" theory perturbed by
certain combinations of relevant single trace and marginal double trace
operators with non infinitesimal couplings. The SUSY is broken but the
resulting ground states, and their gravity duals, remain stable, at least
perturbatively.Despite the complicated field theory dynamics the gravity
solutions have a simple structure. They feature the Ricci-flat non-Kahler
metric on the deformed conifold and the imaginary self-dual three-form flux
accompanied by a constant dilaton.Comment: 27 pages, 6 figures; v2: minor corrections; v3: comments adde
Anomalous Dimensions and Non-Gaussianity
We analyze the signatures of inflationary models that are coupled to strongly
interacting field theories, a basic class of multifield models also motivated
by their role in providing dynamically small scales. Near the squeezed limit of
the bispectrum, we find a simple scaling behavior determined by operator
dimensions, which are constrained by the appropriate unitarity bounds.
Specifically, we analyze two simple and calculable classes of examples:
conformal field theories (CFTs), and large-N CFTs deformed by relevant
time-dependent double-trace operators. Together these two classes of examples
exhibit a wide range of scalings and shapes of the bispectrum, including nearly
equilateral, orthogonal and local non-Gaussianity in different regimes. Along
the way, we compare and contrast the shape and amplitude with previous results
on weakly coupled fields coupled to inflation. This signature provides a
precision test for strongly coupled sectors coupled to inflation via irrelevant
operators suppressed by a high mass scale up to 1000 times the inflationary
Hubble scale.Comment: 40 pages, 10 figure
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
The backreaction of anti-D3 branes on the Klebanov-Strassler geometry
We present the full numerical solution for the 15-dimensional space of
linearized deformations of the Klebanov-Strassler background which preserve the
SU(2) X SU(2) X Z_2 symmetries. We identify within this space the solution
corresponding to anti-D3 branes, (modulo the presence of a certain subleading
singularity in the infrared). All the 15 integration constants of this solution
are fixed in terms of the number of anti-D3 branes, and the solution differs in
the UV from the supersymmetric solution into which it is supposed to decay by a
mode corresponding to a rescaling of the field theory coordinates. Deciding
whether two solutions that differ in the UV by a rescaling mode are dual to the
same theory is involved even for supersymmetric Klebanov-Strassler solutions,
and we explain in detail some of the subtleties associated to this.Comment: 41 pages, 5 figures, LaTe
D-brane potentials in the warped resolved conifold and natural inflation
In this paper we obtain a model of Natural Inflation from string theory with
a Planckian decay constant. We investigate D-brane dynamics in the background
of the warped resolved conifold (WRC) throat approximation of Type IIB string
compactifications on Calabi-Yau manifolds. When we glue the throat to a compact
bulk Calabi-Yau, we generate a D-brane potential which is a solution to the
Laplace equation on the resolved conifold. We can exactly solve this equation,
including dependence on the angular coordinates. The solutions are valid down
to the tip of the resolved conifold, which is not the case for the more
commonly used deformed conifold. This allows us to exploit the effect of the
warping, which is strongest at the tip. We inflate near the tip using an
angular coordinate of a D5-brane in the WRC which has a discrete shift
symmetry, and feels a cosine potential, giving us a model of Natural Inflation,
from which it is possible to get a Planckian decay constant whilst maintaining
control over the backreaction. This is because the decay constant for a wrapped
brane contains powers of the warp factor, and so can be made large, while the
wrapping parameter can be kept small enough so that backreaction is under
control.Comment: 41 pages, 3 appendices, 1 figure, PDFLaTex; various clarifications
added along with a new appendix on b-axions and wrapped D5 branes;version
matches the one published in JHE
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
- …