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25
Fourdimensional String Compactifications with DBranes, Orientifolds and Fluxes
"... This review article provides a pedagogical introduction into various classes of chiral string compactifications to four dimensions with Dbranes and fluxes. The main concern is to provide all necessary technical tools to explicitly construct fourdimensional orientifold vacua, with the final aim to ..."
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Cited by 147 (18 self)
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This review article provides a pedagogical introduction into various classes of chiral string compactifications to four dimensions with Dbranes and fluxes. The main concern is to provide all necessary technical tools to explicitly construct fourdimensional orientifold vacua, with the final aim to come as close as possible to the supersymmetric Standard Model. Furthermore, we outline the available methods to derive the resulting fourdimensional effective action. Finally, we summarize recent attempts to address the
The Cosmological Constant and the String Landscape
"... Theories of the cosmological constant fall into two classes, those in which the vacuum energy is fixed by the fundamental theory and those in which it is adjustable in some way. For each class we discuss key challenges. The string theory landscape is an example of an adjustment mechanism. We discuss ..."
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Cited by 49 (1 self)
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Theories of the cosmological constant fall into two classes, those in which the vacuum energy is fixed by the fundamental theory and those in which it is adjustable in some way. For each class we discuss key challenges. The string theory landscape is an example of an adjustment mechanism. We discuss the status of this idea, and future directions. Rapporteur talk at the 23rd Solvay Conference in Physics, December, 2005. 1 The cosmological constant I would like to start by drawing a parallel to an earlier meeting — not a Solvay conference, but the 1947 Shelter Island conference. In both cases a constant of nature was at the center of discussions. In each case theory gave an unreasonably large or infinite value for the constant, which had therefore been assumed to vanish for reasons not yet understood, but in each case experiment or observation had recently found a nonzero value. At Shelter
Proton decay, Yukawa couplings and underlying gauge symmetry in string theory, Nucl.Phys. B747
, 2006
"... In string theory, massless particles often originate from a symmetry breaking of a large gauge symmetry G to its subgroup H. The absence of dimension4 proton decay in supersymmetric theories suggests that ( ¯ D,L) are different from ¯ H(¯5) in their origins. In this article, we consider a possibil ..."
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Cited by 37 (14 self)
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In string theory, massless particles often originate from a symmetry breaking of a large gauge symmetry G to its subgroup H. The absence of dimension4 proton decay in supersymmetric theories suggests that ( ¯ D,L) are different from ¯ H(¯5) in their origins. In this article, we consider a possibility that they come from different irreducible components in g/h. Requiring that all the Yukawa coupling constants of quarks and leptons be generated from the super Yang–Mills interactions of G, we found in the context of Georgi–Glashow H =SU(5) unification that the minimal choice of G is E7 and E8 is the only alternative. This idea is systematically implemented in Heterotic String, M theory and F theory, confirming the absence of dimension 4 proton decay operators. Not only H = SU(5) but also G constrain operators of effective field theories, String theory is a wellformulated theory of quantum gravity, and it is also known to be able to (almost) realize the (supersymmetric) standard model of particle physics at lowenergies [1, 2, 3, 4, 5, 6]. Since 1990’s, the understanding of string theory has improved dramatically,
Landscape Predictions from Cosmological Vacuum Selection,” Phys
 Rev. D
"... In BP models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from l ..."
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Cited by 20 (6 self)
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In BP models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to "staggering", an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.
An Entropyweighted sum over nonperturbative vacua” hepth/0705.1130
"... We discuss how, in a Universe restricted to the causal region connected to the observer, General Relativity implies the quantum nature of physical phenomena and directly leads to a string theory scenario, whose dynamics is ruled by a functional that weights all configurations according to their entr ..."
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Cited by 13 (11 self)
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We discuss how, in a Universe restricted to the causal region connected to the observer, General Relativity implies the quantum nature of physical phenomena and directly leads to a string theory scenario, whose dynamics is ruled by a functional that weights all configurations according to their entropy. The most favoured configurations are those of minimal entropy. Along this class of vacua a fourdimensional spacetime is automatically selected; when, at large volume, a description of spacetime in terms of classical geometry can be recovered, the entropyweighted sum reduces to the ordinary Feynman’s path integral. What arises is a highly predictive scenario, phenomenologically compatible with the experimental observations and measurements, in which everything is determined in terms of the fundamental constants and the age of the Universe, with no room for freelyadjustable parameters. We discuss how this leads to the known spectrum of particles and interactions. Besides the computation of masses and couplings, CKM matrix elements, cosmological constant, expansion parameters of the Universe etc..., all resulting, within the degree of the approximation we used, in agreement with the experimental observations, we also discuss how this scenario passes the tests provided by cosmology and the constraints imposed by the physics of the primordial Universe.
Quantum Computation vs. Firewalls
 PREPARED FOR SUBMISSION TO JHEP
, 2013
"... In this paper we discuss quantum computational restrictions on the types of thought experiments recently used by Almheiri, Marolf, Polchinski, and Sully to argue against the smoothness of black hole horizons. We argue that the quantum computations required to do these experiments would take a time w ..."
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Cited by 7 (1 self)
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In this paper we discuss quantum computational restrictions on the types of thought experiments recently used by Almheiri, Marolf, Polchinski, and Sully to argue against the smoothness of black hole horizons. We argue that the quantum computations required to do these experiments would take a time which is exponential in the entropy of the black hole under study, and we show that for a wide variety of black holes this prevents the experiments from being done. We interpret our results as motivating a broader type of nonlocality than is usually considered in the context of black hole thought experiments, and claim that once this type of nonlocality is allowed there may be no need for firewalls. Our results do not threaten the unitarity of of black hole evaporation or the ability of advanced civilizations to test it.
Higgs Bundles and UV Completion in FTheory
, 904
"... Ftheory admits 7branes with exceptional gauge symmetries, which can be compactified to give phenomenological fourdimensional GUT models. Here we study general supersymmetric compactifications of eightdimensional YangMills theory. They are mathematically described by meromorphic Higgs bundles, a ..."
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Cited by 1 (0 self)
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Ftheory admits 7branes with exceptional gauge symmetries, which can be compactified to give phenomenological fourdimensional GUT models. Here we study general supersymmetric compactifications of eightdimensional YangMills theory. They are mathematically described by meromorphic Higgs bundles, and therefore admit a spectral cover description. This allows us to give a rigorous and intrinsic construction of local models in Ftheory. We use our results to prove a nogo theorem showing that local SU(5) models with three generations do not exist for generic moduli. However we show that threegeneration models do exist on the NoetherLefschetz locus. We explain how Ftheory models can be mapped to nonperturbative orientifold models using a scaling limit proposed by Sen. Further we address the construction of global models that do not have heterotic duals. We show how one may obtain a contractible worldvolume with a twocycle not inherited from the bulk, a necessary condition for implementing GUT breaking using fluxes. We also show that the complex structure moduli in global models can be arranged so that no dimension four or five proton decay can be generated. Contents 1
On the computation of nonperturbative effective potentials in the string theory landscape  IIB/Ftheory perspective
, 2010
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, 2007
"... Abstract: Recently, it has become clear that neighboring multiple vacua might have interesting consequences for the physics of the early universe. In this paper we investigate the topography of the string landscape corresponding to complex structure moduli of flux compactified type IIB string theory ..."
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Abstract: Recently, it has become clear that neighboring multiple vacua might have interesting consequences for the physics of the early universe. In this paper we investigate the topography of the string landscape corresponding to complex structure moduli of flux compactified type IIB string theory. We find that series of continuously connected vacua are common. The properties of these series are described, and we relate the existence of infinite series of minima to certain unresolved mathematical problems in group theory.
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"... 2.1 Finegrained multithreading (FGMT)............. 8 2.2 Coarsegrained multithreading (CGMT)............ 10 ..."
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2.1 Finegrained multithreading (FGMT)............. 8 2.2 Coarsegrained multithreading (CGMT)............ 10