346 research outputs found
Non-Perturbative Corrections and Modularity in N=1 Type IIB Compactifications
Non-perturbative corrections and modular properties of four-dimensional type
IIB Calabi-Yau orientifolds are discussed. It is shown that certain
non-perturbative alpha' corrections survive in the large volume limit of the
orientifold and periodically correct the Kahler potential. These corrections
depend on the NS-NS two form and have to be completed by D-instanton
contributions to transform covariantely under symmetries of the type IIB
orientifold background. It is shown that generically also the D-instanton
superpotential depends on the two-form moduli as well as on the complex
dilaton. These contributions can arise through theta-functions with the dilaton
as modular parameter. An orientifold of the Enriques Calabi-Yau allows to
illustrate these general considerations. It is shown that this compactification
leads to a controlled four-dimensional N=1 effective theory due to the absence
of various quantum corrections. Making contact to the underlying topological
string theory the D-instanton superpotential is proposed to be related to a
specific modular form counting D3, D1, D(-1) degeneracies on the Enriques
Calabi-Yau.Comment: 35 page
Four-modulus "Swiss Cheese" chiral models
We study the 'Large Volume Scenario' on explicit, new, compact, four-modulus
Calabi-Yau manifolds. We pay special attention to the chirality problem pointed
out by Blumenhagen, Moster and Plauschinn. Namely, we thoroughly analyze the
possibility of generating neutral, non-perturbative superpotentials from
Euclidean D3-branes in the presence of chirally intersecting D7-branes. We find
that taking proper account of the Freed-Witten anomaly on non-spin cycles and
of the Kaehler cone conditions imposes severe constraints on the models.
Nevertheless, we are able to create setups where the constraints are solved,
and up to three moduli are stabilized.Comment: 40 pages, 10 figures, clarifying comments added, minor mistakes
correcte
From ten to four and back again: how to generalize the geometry
We discuss the four-dimensional N=1 effective approach in the study of warped
type II flux compactifications with SU(3)x SU(3)-structure to AdS_4 or flat
Minkowski space-time. The non-trivial warping makes it natural to use a
supergravity formulation invariant under local complexified Weyl
transformations. We obtain the classical superpotential from a standard
argument involving domain walls and generalized calibrations and show how the
resulting F-flatness and D-flatness equations exactly reproduce the full
ten-dimensional supersymmetry equations. Furthermore, we consider the effect of
non-perturbative corrections to this superpotential arising from gaugino
condensation or Euclidean D-brane instantons. For the latter we derive the
supersymmetry conditions in N=1 flux vacua in full generality. We find that the
non-perturbative corrections induce a quantum deformation of the internal
generalized geometry. Smeared instantons allow to understand KKLT-like AdS
vacua from a ten-dimensional point of view. On the other hand, non-smeared
instantons in IIB warped Calabi-Yau compactifications 'destabilize' the
Calabi-Yau complex structure into a genuine generalized complex one. This
deformation gives a geometrical explanation of the non-trivial superpotential
for mobile D3-branes induced by the non-perturbative corrections.Comment: LaTeX, 47 pages, v2, references, hyperref added, v3, correcting small
inaccuracies in eqs. (2.6a) and (5.16
On 'Light' Fermions and Proton Stability in 'Big Divisor' D3/D7 Swiss Cheese Phenomenology
Building up on our earlier work [1,2], we show the possibility of generating
"light" fermion mass scales of MeV-GeV range (possibly related to first two
generations of quarks/leptons) as well as eV (possibly related to first two
generations of neutrinos) in type IIB string theory compactified on
Swiss-Cheese orientifolds in the presence of a mobile space-time filling
D3-$brane restricted to (in principle) stacks of fluxed D7-branes wrapping the
"big" divisor \Sigma_B. This part of the paper is an expanded version of the
latter half of section 3 of a published short invited review [3] written up by
one of the authors [AM]. Further, we also show that there are no SUSY GUT-type
dimension-five operators corresponding to proton decay, as well as estimate the
proton lifetime from a SUSY GUT-type four-fermion dimension-six operator to be
10^{61} years. Based on GLSM calculations in [1] for obtaining the geometric
Kaehler potential for the "big divisor", using further the Donaldson's
algorithm, we also briefly discuss in the first of the two appendices,
obtaining a metric for the Swiss-Cheese Calabi-Yau used, that becomes Ricci
flat in the large volume limit.Comment: v2: 1+25 pages, Title modified and text thoroughly expanded including
a brief discussion on obtaining Ricci-flat Swiss Cheese Calabi-Yau metrics
using the Donaldson's algorithm, references added, to appear in EPJ
Axion Stabilization in Type IIB Flux Compactifications
A scenario for stabilization of axionic moduli fields in the context of type
IIB Calabi-Yau flux compactifications is discussed in detail. We consider the
case of a Calabi-Yau orientifold with h^{1,1}_- \neq 0 which allows for the
presence of B_2 and C_2-moduli. In an attempt to generalize the KKLT and the
Large Volume Scenario, we show that these axions can also be stabilized - some
already at tree level, and others when we include perturbative
\alpha'-corrections to the Kaehler potential K and nonperturbative D3-instanton
contributions to the superpotential W. At last, we comment on the possible
influence of worldsheet instantons on the process of moduli stabilization.Comment: 34 pages, 1 figure; improved referencing, published versio
Cost calculation and prediction in adult intensive care: A ground-up utilization study
Publisher's copy made available with the permission of the publisherThe ability of various proxy cost measures, including therapeutic activity scores (TISS and Omega) and cumulative daily severity of illness scores, to predict individual ICU patient costs was assessed in a prospective “ground-up” utilization costing study over a six month period in 1991. Daily activity (TISS and Omega scores) and utilization in consecutive admissions to three adult university associated ICUs was recorded by dedicated data collectors. Cost prediction used linear regression with determination (80%) and validation (20%) data sets. The cohort, 1333 patients, had a mean (SD) age 57.5 (19.4) years, (41% female) and admission APACHE III score of 58 (27). ICU length of stay and mortality were 3.9 (6.1) days and 17.6% respectively. Mean total TISS and Omega scores were 117 (157) and 72 (113) respectively. Mean patient costs per ICU episode (1991 6801 (2534, range 95,602. Dominant cost fractions were nursing 43.3% and overheads 16.9%. Inflation adjusted year 2002 (mean) costs were AUS). Total costs in survivors were predicted by Omega score, summed APACHE III score and ICU length of stay; determination R2, 0.91; validation 0.88. Omega was the preferred activity score. Without the Omega score, predictors were age, summed APACHE III score and ICU length of stay; determination R2, 0.73; validation 0.73. In non-survivors, predictors were age and ICU length of stay (plus interaction), and Omega score (determination R2, 0.97; validation 0.91). Patient costs may be predicted by a combination of ICU activity indices and severity scores.J. L. Moran, A. R. Peisach, P. J. Solomon, J. Martinhttp://www.aaic.net.au/Article.asp?D=200403
Moduli Stabilisation versus Chirality for MSSM like Type IIB Orientifolds
We investigate the general question of implementing a chiral MSSM like
D-brane sector in Type IIB orientifold models with complete moduli
stabilisation via F-terms induced by fluxes and space-time instantons,
respectively gaugino condensates. The prototype examples are the KKLT and the
so-called large volume compactifications. We show that the ansatz of first
stabilising all moduli via F-terms and then introducing the Standard Model
module is misleading, as a chiral sector notoriously influences the structure
of non-perturbative effects and induces a D-term potential. Focusing for
concreteness on the large volume scenario, we work out the geometry of the
swiss-cheese type Calabi-Yau manifold P_[1,3,3,3,5][15]_(3,75) and analyse
whether controllable and phenomenologically acceptable Kaehler moduli
stabilisation can occur by the combination of F- and D-terms.Comment: 43 pages, 4 figures, v2: refs. adde
Non-perturbative effects and wall-crossing from topological strings
We argue that the Gopakumar-Vafa interpretation of the topological string
partition function can be used to compute and resum certain non-perturbative
brane instanton effects of type II CY compactifications. In particular the
topological string A-model encodes the non-perturbative corrections to the
hypermultiplet moduli space metric from general D1/D(-1)-brane instantons in 4d
N=2 IIB models. We also discuss the reduction to 4d N=1 by fluxes and/or
orientifolds and/or D-branes, and the prospects to resum brane instanton
contributions to non-perturbative superpotentials. We argue that the connection
between non-perturbative effects and the topological string underlies the
continuity of non-perturbative effects across lines of BPS stability. We also
confirm this statement in mirror B-model matrix model examples, relating matrix
model instantons to non-perturbative D-brane instantons. The computation of
non-perturbative effects from the topological string requires a 3d circle
compactification and T-duality, relating effects from particles and instantons,
reminiscent of that involved in the physical derivation of the
Kontsevich-Soibelmann wall-crossing formula.Comment: 44 pages, 5 figures. Major revisions, new results added, previous
results unchanged, refs adde
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