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25
Towards a Systematic Construction of Realistic Dbrane Models on a del Pezzo Singularity,” JHEP 1110
, 2011
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TASI Lectures: Particle Physics from Perturbative and Nonperturbative Effects in Dbraneworlds
, 2011
"... In these notes we review aspects of semirealistic particle physics from the point of view of type II orientifold compactifications. We discuss the appearance of gauge theories on spacetime filling Dbranes which wrap nontrivial cycles in the CalabiYau. Chiral matter can appear at their intersect ..."
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In these notes we review aspects of semirealistic particle physics from the point of view of type II orientifold compactifications. We discuss the appearance of gauge theories on spacetime filling Dbranes which wrap nontrivial cycles in the CalabiYau. Chiral matter can appear at their intersections, with a natural interpretation of family replication given by the topological intersection number. We discuss global consistency, including tadpole cancellation and the generalized GreenSchwarz mechanism, and also the importance of related global U(1) symmetries for superpotential couplings. We review the basics of Dinstantons, which can generate superpotential corrections to charged matter couplings forbidden by the global U(1) symmetries and may play an important role in moduli stabilization. Finally, for the purpose of studying the landscape, we discuss certain advantages of studying quiver gauge theories which arise from type II orientifold compactifications rather than globally defined models. We utilize the type IIa geometric picture and CFT techniques to illustrate the main physical points, though sometimes we supplement the discussion from the type IIb perspective using complex algebraic geometry.
Sequestering in String Compactifications
 JHEP
"... We study the mediation of supersymmetry breaking in string compactifications whose moduli are stabilized by nonperturbative effects. We begin with a critical review of arguments for sequestering in supergravity and in string theory. We then show that geometric isolation, even in a highly warped spa ..."
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We study the mediation of supersymmetry breaking in string compactifications whose moduli are stabilized by nonperturbative effects. We begin with a critical review of arguments for sequestering in supergravity and in string theory. We then show that geometric isolation, even in a highly warped space, is insufficient to achieve sequestering: in type IIB compactifications, nonperturbative superpotentials involving the Kähler moduli introduce crosscouplings between wellseparated visible and hidden sectors. The scale of the resulting soft terms depends on the moduli stabilization scenario. In the Large Volume Scenario, nonperturbative superpotential contributions to the soft trilinear A terms can introduce significant flavor violation, while in KKLT compactifications their effects are negligible. In both cases, the contributions to the µ and Bµ parameters cannot be ignored in general. We conclude that sequestered supersymmetry breaking is possible in nonperturbativelystabilized compactifications only if a mechanism in addition to bulk locality suppresses superpotential crosscouplings.
SU(5) orientifolds, Yukawa couplings, Stringy Instantons and Proton Decay
, 909
"... Abstract: We construct a large class of SU(5) orientifold vacua with tadpole cancellation both for the standard and the flipped case. We give a general analysis of superpotential couplings up to quartic order in orientifold vacua and identify the properties of needed Yukawa couplings as well as the ..."
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Abstract: We construct a large class of SU(5) orientifold vacua with tadpole cancellation both for the standard and the flipped case. We give a general analysis of superpotential couplings up to quartic order in orientifold vacua and identify the properties of needed Yukawa couplings as well as the baryon number violating couplings. We point out that successful generation of the perturbatively forbidden Yukawa couplings entails a generically disastrous rate for proton decay from an associated quartic term in the superpotential, generated from the same instanton effects. We search for the appropriate instanton effects that generate the missing Yukawa couplings in the SU(5) vacua we constructed and find them in a small subset of them. On leave of absence from APC, Université Paris 7, (UMR du CNRS 7164). – 1 –
FCNC Processes from Dbrane Instantons
"... Low string scale models might be tested at the LHC directly by their Regge resonances. For such models it is important to investigate the constraints of Standard Model precision measurements on the string scale. It is shown that highly suppressed FCNC processes like K0K 0 oscillations or leptonic ..."
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Low string scale models might be tested at the LHC directly by their Regge resonances. For such models it is important to investigate the constraints of Standard Model precision measurements on the string scale. It is shown that highly suppressed FCNC processes like K0K 0 oscillations or leptonic decays of the D0meson provide nonnegligible lower bounds on both the perturbatively and surprisingly also nonperturbatively induced string theory couplings. We present both the Dbrane instanton formalism to compute such amplitudes and discuss various possible scenarios and their constraints on the string scale for (softly broken) supersymmetric intersecting Dbrane models. 1 ar
0 1 1
, 2010
"... SU(5) Dbrane realizations, Yukawa couplings and proton stability ..."
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On the computation of nonperturbative effective potentials in the string theory landscape  IIB/Ftheory perspective
, 2010
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Global Ftheory models . . .
, 2011
"... We elucidate certain aspects of Ftheory gauge dynamics, due to quantum splitting of certain brane stacks, which are absent in the Type IIB limit. We also provide a working implementation of an algorithm for computing cohomology of line bundles on arbitrary toric varieties. This should be of genera ..."
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We elucidate certain aspects of Ftheory gauge dynamics, due to quantum splitting of certain brane stacks, which are absent in the Type IIB limit. We also provide a working implementation of an algorithm for computing cohomology of line bundles on arbitrary toric varieties. This should be of general use for studying the physics of global Type IIB and Ftheory models, in particular for the explicit counting of zero modes for rigid Ftheory instantons which contribute to charged matter couplings. We illustrate the discussion by constructing and analyzing in detail a compact Ftheory GUT model in which a Dbrane instanton generates the top Yukawa coupling nonperturbatively.