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Particle physics model of inflation and the cosmological density perturbation
"... This is a review of models of inflation, and their predictions for the primordial curvature perturbation that is thought to be the origin of structure in the Universe. The spectral index n, specifying the scaledependence of the spectrum of the curvature perturbation, will be a powerful discriminato ..."
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Cited by 163 (7 self)
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This is a review of models of inflation, and their predictions for the primordial curvature perturbation that is thought to be the origin of structure in the Universe. The spectral index n, specifying the scaledependence of the spectrum of the curvature perturbation, will be a powerful discriminator between models, when it is measure with accuracy ∆n ∼ 0.01. The usual formula for n is derived, as well as its less familiar extension to the case of a multicomponent inflaton; in both cases the key ingredient is the separate evolution of causally disconnected regions of the Universe. Primordial gravitational waves will be an even more powerful discriminator if they are observed, since most models of inflation predict that they are completely negligible. We focus on the new wave of models, which are firmly rooted in modern particle theory and have supersymmetry as a crucial ingredient. The essential particle theory background is summarized, first at an elementary level and later at a more advanced one. The review is addressed to both astrophysicists and particle physicists, and each section is fairly homogeneous regarding the assumed background knowledge.
The holographic principle
 Rev. Mod. Phys
, 2002
"... There is strong evidence that the area of any surface limits the information content of adjacent spacetime regions, at 1.4 ×10 69 bits per square meter. We review the developments that have led to the recognition of this entropy bound, placing special emphasis on the quantum properties of black hole ..."
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Cited by 132 (9 self)
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There is strong evidence that the area of any surface limits the information content of adjacent spacetime regions, at 1.4 ×10 69 bits per square meter. We review the developments that have led to the recognition of this entropy bound, placing special emphasis on the quantum properties of black holes. The construction of lightsheets, which associate relevant spacetime regions to any
Electroweak baryon number nonconservation in the early universe and in highenergy collisions,”Uspekhi
 Fizicheskikh Nauk,
, 1996
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The prebig bang scenario in string cosmology
 Phys. Rept
, 2003
"... We review physical motivations, phenomenological consequences, and open problems of the socalled prebig bang scenario in superstring cosmology. Contents 1 ..."
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Cited by 89 (3 self)
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We review physical motivations, phenomenological consequences, and open problems of the socalled prebig bang scenario in superstring cosmology. Contents 1
Towards inflation in string theory
 JCAP
, 2003
"... We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one wellknown difficulty of braneantibrane scenarios. Careful consideration of the closed ..."
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Cited by 82 (9 self)
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We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one wellknown difficulty of braneantibrane scenarios. Careful consideration of the closed string moduli reveals a further obstacle: superpotential stabilization of the compactification volume typically modifies the inflaton potential and renders it too steep for inflation. We discuss the nongeneric conditions under which this problem does not arise. We conclude that brane inflation models can only work if restrictive assumptions about the method of volume stabilization, the warping of the internal space, and the source of inflationary energy are satisfied. We argue that this may not be a real problem, given the large range of available fluxes and background geometries in string theory.
Metricaffine f(R) theories of gravity
 J. Suppl. Ser
, 2007
"... Modified gravity theories have received increased attention lately due to combined motivation coming from highenergy physics, cosmology and astrophysics. Among numerous alternatives to Einstein’s theory of gravity, theories which include higher order curvature invariants, and specifically the parti ..."
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Cited by 69 (1 self)
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Modified gravity theories have received increased attention lately due to combined motivation coming from highenergy physics, cosmology and astrophysics. Among numerous alternatives to Einstein’s theory of gravity, theories which include higher order curvature invariants, and specifically the particular class of f(R) theories, have a long history. In the last five years there has
Computational capacity of the universe
 Physical Review Letters
"... Merely by existing, all physical systems register information. And by evolving dynamically in time, they transform and process that information. The laws of physics determine the amount of information that a physical system can register (number of bits) and the number of elementary logic operations ..."
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Cited by 55 (0 self)
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Merely by existing, all physical systems register information. And by evolving dynamically in time, they transform and process that information. The laws of physics determine the amount of information that a physical system can register (number of bits) and the number of elementary logic operations that a system can perform (number of ops). The universe is a physical system. This paper quantifies the amount of information that the universe can register and the number of elementary operations that it can have performed over its history. The universe can have performed no more than 10 120 ops on 10 90 bits. ‘Information is physical ’ 1. This statement of Landauer has two complementary interpretations. First, information is registered and processed by physical systems. Second, all physical systems register and process information. The description of physical systems in terms of information and information processing is complementary to the conventional description of physical system in terms of the laws of physics. A recent paper by the author2 put bounds on the amount of information processing that can be performed by physical systems. The first limit is on speed. The Margolus/Levitin theorem3 implies that the total
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
Inflationary scenarios from branes at angles
 JHEP 0207 (2002) 051 [arXiv:hepth/0203163
"... Abstract: We describe a simple mechanism that can lead to inflation within stringbased braneworld scenarios. The idea is to start from a supersymmetric configuration with two parallel static Dpbranes, and slightly break the supersymmetry conditions to produce a very flat potential for the field t ..."
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Cited by 48 (2 self)
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Abstract: We describe a simple mechanism that can lead to inflation within stringbased braneworld scenarios. The idea is to start from a supersymmetric configuration with two parallel static Dpbranes, and slightly break the supersymmetry conditions to produce a very flat potential for the field that parametrises the distance between the branes, i.e. the inflaton field. This breaking can be achieved in various ways: by slight relative rotations of the branes with small angles, by considering small relative velocities between the branes, etc. If the breaking parameter is sufficiently small, a large number of efolds can be produced within the Dbrane, for small changes of the configuration in the compactified directions. Such a process is local, i.e. it does not depend very strongly on the compactification space nor on the initial conditions. Moreover, the breaking induces a very small velocity and acceleration, which ensures very small slowroll parameters and thus an almost scale invariant spectrum of metric fluctuations, responsible for the observed temperature anisotropies in the microwave background. Inflation ends as in hybrid inflation, triggered by the negative curvature of the string tachyon potential. In this paper we elaborate on one of the simplest examples: two almost parallel D4branes in a flat compactified space. JHEP01(2002)036