175,294 research outputs found
Noncommutative resolutions of ADE fibered Calabi-Yau threefolds
No full textIn this paper we construct noncommutative resolutions of a certain class of Calabi-Yau threefolds studied by F. Cachazo, S. Katz and C. Vafa. The threefolds under consideration are fibered over a complex plane with the fibers being deformed Kleinian singularities. The construction is in terms of a noncommutative algebra introduced by V. Ginzburg, which we call the "N=1 ADE quiver algebra"
Calabi–Yau threefolds and moduli of abelian surfaces I
No full textWe describe birational models and decide the rationality/unirationality of moduli spaces d (and levd) of (1, d)-polarized Abelian surfaces (with canonical level structure, respectively) for small values of d. The projective lines identified in the rational/unirational moduli spaces correspond to pencils of Abelian surfaces traced on nodal threefolds living naturally in the corresponding ambient projective spaces, and whose small resolutions are new Calabi–Yau threefolds with Euler characteristic zero
Microscopic Calabi-Yau Black Holes in String Theory
No full textIn this thesis we study microscopic aspects of Calabi-Yau black holes in string theory.
We compute the absorption cross-section of the space-time massless scalars by the world-volume
of D2-branes, wrapped on the S2 of an AdS_2 x S^2 x CY_3 geometry of a four-dimensional
D4-D0 Calabi-Yau black hole. The D2-brane can also have a generic D0
probe-brane charge. However, we restrict ourselves to D2-branes with small D0-charge
so that the perturbation theory is applicable. According to the proposed AdS_2/QM correspondence
the candidate for the dual theory is the quantum mechanics of a set of probe
D0-branes in the AdS2 geometry. For small but non-zero probe D0-charge we find the quantum
mechanical absorption cross-section seen by an asymptotic anti-de Sitter observer. We
repeat the calculations for vanishing probe D0-charge as well and discuss our result by
comparing with the classical absorption cross-section. In other project, for a given four-dimensional
Calabi-Yau black hole with generic D6-D4-D2-D0 charges we identify a set of
supersymmetric branes, which are static or stationary in the global coordinates, of the corresponding
eleven-dimensional near horizon geometry. The set of these BPS states, which
include the branes partially or fully wrap the horizon, should play a role in understanding
the partition function of black holes with D6-charge
Special Lagrangian Cycles and Calabi-Yau Transitions
No full textAbstract
We construct special Lagrangian 3-spheres in non-Kähler compact threefolds equipped with the Fu–Li–Yau geometry. These non-Kähler geometries emerge from topological transitions of compact Calabi-Yau threefolds. From this point of view, a conifold transition exchanges holomorphic 2-cycles for special Lagrangian 3-cycles
Superpotentials, Calabi–Yau algebras, and PBW deformations
No full textThe paper [9] by Bocklandt, Schedler and Wemyss considers path algebras with relations given by the higher derivations of a superpotential, giving a condition for such an algebra to be Calabi–Yau. In particular they show that the algebra C[V]⋊G, for V a finite dimensional C vector space and G a finite subgroup of GL(V), is Morita equivalent to a path algebra with relations given by a superpotential, and is Calabi–Yau for G<SL(V). In this paper we extend these results, giving a condition for a PBW deformation of a Calabi–Yau, Koszul path algebra with relations given by a superpotential to have relations given by a superpotential, and proving these are Calabi–Yau in certain cases.We apply our methods to symplectic reflection algebras, where we show that every symplectic reflection algebra is Morita equivalent to a path algebra whose relations are given by the higher derivations of an inhomogeneous superpotential. In particular we show these are Calabi–Yau regardless of the deformation parameter.Also, for G a finite subgroup of GL2(C) not contained in SL2(C), we consider PBW deformations of a path algebra with relations which is Morita equivalent to C[x,y]⋊G. We show there are no non-trivial PBW deformations when G is a small subgroup
Evaluation of Weed Management Practices for Rain‐Fed Safflower Production in a Semiarid Mediterranean Environment
No full textSince safflower (Carthamus tinctorius L.) has slow early growth, effective early weed control is essential. The objective of this study was to investigate the effectiveness of various nonchemical and chemical practices for weed management in rain-fed safflower. Field experiments were performed for three production years in the Bekaa Valley of Lebanon. Six weed management practices were tested: delayed sowing, delayed sowing with interrow cultivation, normal sowing with interrow cultivation, preermergence herbicide, hand weeding, and the normal sowing weedy check. Averaged over 1999-2000 and 2000-2001, weeds were absent with herbicide application and there were as few as andlt;4 weed plants m-2 in delayed sowing with interrow cultivation and hand weeding. Interrow cultivation under normal sowing, herbicide application, and hand weeding gave higher safflower seed and straw yields than the weedy check. Over the three production years, only interrow cultivation under normal sowing and hand weeding produced higher safflower seed and straw yields than the weedy check. In conclusion, interrow cultivation under normal sowing could be considered the best practice; application of pendimethalin and pronamide was also superior to delay sowing. Copyright © 2008 by the American Society of Agronomy. All rights reserved.BEG A, 1993, STATUS POTENTIAL SOM; HAIDAR MA, 2000, 7 AR C PLANT PROT 22, P31; KAFTKA SR, 1998, PUBL U CALIFORNIA; Knowles P. F., 1976, Evolution of crop plants., P31; MCINTOSH MS, 1983, AGRON J, V75, P153; MONTEMURRO P, 1997, SAFFLOWER MULTIPURPO, P132; Mundel HH, 1992, SAFFLOWER PRODUCTION, P35; RYAN J, 1980, PUBL AM U BEIRUT, V64; SALERA E, 1997, SAFFLOWER MULTIPURPO, P136; Yau SK, 2007, EUR J AGRON, V26, P249, DOI 10.1016-j.eja.2006.10.004; Yau SK, 2004, EXP AGR, V40, P453, DOI 10.1017-S0014479704002121; Yau SK, 2003, AGRON J, V95, P821; Yau S.K., 1999, SESAME SAFFLOWER NEW, V14, P9722
Poly-instanton inflation
No full textWe propose a new inflationary scenario in type IIB Calabi-Yau compactifications, where the inflaton is a Kahler modulus parameterising the volume of an internal four-cycle. The inflaton potential is generated via poly-instanton corrections to the superpotential which give rise to a naturally flat direction due to their double exponential suppression. Given that the volume mode is kept stable during inflation, all the inflaton-dependent higher dimensional operators are suppressed. Moreover, string loop effects can be shown to be negligible throughout all the inflationary dynamics for natural values of the underlying parameters.
The model is characterised by a reheating temperature of the order 10^6 GeV which requires about 54 e-foldings of inflation. All the inflationary observables are compatible with current observations since the spectral index is around 0.96, while the tensor-to-scalar ratio is
of order 10^{−5}. The volume of the Calabi-Yau is of order 10^3 in string units, corresponding to an inflationary scale around 10^15 GeV
A free boundary Monge-Amp\`ere equation and applications to complete Calabi-Yau metrics
No full textLet be a convex body containing the origin in its interior. We study a
real Monge-Amp\`ere equation with singularities along \del P which is
Legendre dual to a certain free boundary Monge-Amp\`ere equation. This is
motivated by the existence problem for complete Calabi-Yau metrics on log
Calabi-Yau pairs with an ample, simple normal crossings divisor.
We prove the existence of solutions in , and establish the strict convexity of the free
boundary. When is a polytope, we obtain an asymptotic expansion for the
solution near the interior of the codimension faces of \del P
Boron Toxicity Tolerance in Crops: A Viable Alternative to Soil Amelioration
No full textResearch on the problems of excessive soil B has increased considerably in the past two decades, especially in the dry areas of the world such as the Mediterranean region and parts of Australia. The objectives of this review are to promote awareness of the widespread occurrence and importance of B toxicity (BT) in dry areas, and to review the availability of BT-tolerant germplasm and progress in breeding cultivars with BT tolerance. The importance of BT was not adequately recognized until the 1980s, when scientists discovered that BT caused significant crop yield reductions in South Australia. We offer several reasons for this belated awareness before describing the areas reported to have high-B soils in the world and reviewing the occurrence of two contrasting types of BT symptoms. In the field, BT in crops usually is more prominent after drought, indicating that both BT and drought tolerance are needed in crops for dry areas having high levels of subsoil B. The interaction of BT with salinity and the levels of other nutrients such as Zn and N are also discussed. As it is neither practical nor easy to detoxify high-B soil by agronomic means in most circumstances, selecting or breeding crop cultivars with high BT tolerance is the only practical approach to increase yields on high-B soils. Extensive surveys of germplasm in different crops have been performed, and a list of some BT-tolerant lines or cultivars is presented. Finally, we review the progress in breeding for BT tolerance, which has been achieved with varying success in several common crops. We believe that the shift from soil intervention to plant adaptation to solve an intractable crop nutrition constraint represents a new paradigm in the agronomic sciences. © Crop Science Society of America. 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