Particle Physics and Inflationary Cosmology - Linde (pdf document) free file download at fliiby.com

"arXiv:hep-th/0503203 v1 26 Mar 2005 PARTICLE PHYSICS AND INFLATIONARY COSMOLOGY1 Andrei Linde Department of Physics, Stanford University, Stanford CA 94305-4060, USA This is the LaTeX version of my book “Particle Physics and Inﬂationary Cosmology” (Harwood, Chur, Switzerland, 1990). 1 vi Abstract This is the LaTeX version of my book “Particle Physics and Inﬂationary Cosmology” (Harwood, Chur, Switzerland, 1990). I decided to put it to hep-th, to make it easily available. Many things happened during the 15 years since the time when it was written. In particular, we have learned a lot about the high temperature behavior in the electroweak theory and about baryogenesis. A discovery of the acceleration of the universe has changed the way we are thinking about the problem of the vacuum energy: Instead of trying to explain why it is zero, we are trying to understand why it is anomalously small. Recent cosmological observations have shown that the universe is ﬂat, or almost exactly ﬂat, and conﬁrmed many other predictions of inﬂationary theory. Many new versions of this theory have been developed, including hybrid inﬂation and inﬂationary models based on string theory. There was a substantial progress in the theory of reheating of the universe after inﬂation, and in the theory of eternal inﬂation. It s clear, therefore, that some parts of the book should be updated, which I might do sometimes in the future. I hope, however, that this book may be of some interest even in its original form. I am using it in my lectures on inﬂationary cosmology at Stanford, supplementing it with the discussion of the subjects mentioned above. I would suggest to read this book in parallel with the book by Liddle and Lyth “Cosmological Inﬂation and Large Scale Structure,” with the book by Mukhanov “Physical Foundations of Cosmology,” which is to be published soon, and with my review article hep-th/0503195, which contains a discussion of some (but certainly not all) of the recent developments in inﬂationary theory. Contents Preface to the Series Introduction CHAPTER 1 Overview of Uniﬁed Theories of Elementary Particles and the Inﬂationary Universe Scenario 1.1 The scalar ﬁeld and spontaneous symmetry breaking 1.2 Phase transitions in gauge theories 1.3 Hot universe theory 1.4 Some properties of the Friedmann models 1.5 Problems of the standard scenario 1.6 A sketch of the development of the inﬂationary universe scenario 1.7 The chaotic inﬂation scenario 1.8 The self-reproducing universe 1.9 Summary Scalar Field, Eﬀective Potential, and Spontaneous Symmetry Breaking 2.1 Classical and quantum scalar ﬁelds 2.2 Quantum corrections to the eﬀective potential V(ϕ) 2.3 The 1/N expansion and the eﬀective potential in the λϕ4 /N theory 2.4 The eﬀective potential and quantum gravitational eﬀects Restoration of Symmetry at High Temperature 3.1 Phase transitions in the simplest models with spontaneous symmetry breaking 3.2 Phase transitions in realistic theories of the weak, strong, and electromagnetic interactions 3.3 Higher-order perturbation theory and the infrared problem in the thermodynamics of gauge ﬁelds Phase Transitions in Cold Superdense Matter 4.1 Restoration of symmetry in theories with no neutral currents x xi 1 1 6 9 13 16 25 29 42 49 50 50 53 59 64 67 67 72 74 78 78 CHAPTER 2 CHAPTER 3 CHAPTER 4 CONTENTS viii 4.2 Enhancement of symmetry breaking and the condensation of vector mesons in theories with neutral currents 79 82 82 86 90 94 94 99 108 108 109 113 120 126 CHAPTER 5 Tunneling Theory and the Decay of a Metastable Phase in a FirstOrder Phase Transition 5.1 General theory of the formation of bubbles of a new phase 5.2 The thin-wall approximation 5.3 Beyond the thin-wall approximation Phase Transitions in a Hot Universe 6.1 Phase transitions with symmetry breaking between the weak, strong, and electromagnetic interactions 6.2 Domain walls, strings, and monopoles General Principles of Inﬂationary Cosmology 7.1 Introduction 7.2 The inﬂationary universe and de Sitter space 7.3 Quantum ﬂuctuations in the inﬂationary universe 7.4 Tunneling in the inﬂationary universe 7.5 Quantum ﬂuctuations and the generation of adiabatic density perturbations 7.6 Are scale-free adiabatic perturbations suﬃcient to produce the observed large scale structure of the universe? 7.7 Isothermal perturbations and adiabatic perturbations with a nonﬂat spectrum 7.8 Nonperturbative eﬀects: strings, hedgehogs, walls, bubbles, . . . 7.9 Reheating of the universe after inﬂation 7.10 The origin of the baryon asymmetry of the universe CHAPTER 6 CHAPTER 7 136 139 145 150 154 CHAPTER 8 The New Inﬂationary Universe Scenario 160 8.1 Introduction. The old inﬂationary universe scenario 160 8.2 The Coleman–Weinberg SU(5) theory and the new inﬂationary universe scenario (initial simpliﬁed version) 162 8.3 Reﬁnement of the new inﬂationary universe scenario 165 8.4 Primordial inﬂation in N = 1 supergravity 170 8.5 The Shaﬁ–Vilenkin model 171 8.6 The new inﬂationary universe scenario: problems and prospects176 The Chaotic Inﬂation Scenario 9.1 Introduction. Basic features of the scenario. The question of initial conditions 179 179 CHAPTER 9 CONTENTS ix 9.2 9.3 9.4 9.5 The simplest model based on the SU(5) theory Chaotic inﬂation in supergravity The modiﬁed Starobinsky model and the combined scenario Inﬂation in Kaluza–Klein and superstring theories 182 184 186 189 195 195 207 213 221 223 232 234 243 245 CHAPTER 10 Inﬂation and Quantum Cosmology 10.1 The wave function of the universe 10.2 Quantum cosmology and the global structure of the inﬂationary universe 10.3 The self-reproducing inﬂationary universe and quantum cosmology 10.4 The global structure of the inﬂationary universe and the problem of the general cosmological singularity 10.5 Inﬂation and the Anthropic Principle 10.6 Quantum cosmology and the signature of space-time 10.7 The cosmological constant, the Anthropic Principle, and reduplication of the universe and life after inﬂation CONCLUSION REFERENCES Preface to the Series The series of volumes, Contemporary Concepts in Physics, is addressed to the professional physicist and to the serious graduate student of physics. The subjects to be covered will include those at the forefront of current research. It is anticipated that the various volumes in the series will be rigorous and complete in their treatment, supplying the intellectual tools necessary for the appreciation of the present status of the areas under consideration and providing the framework upon which future developments may be based. Introduction With the invention and development of uniﬁed gauge theories of weak and electromagnetic interactions, a genuine revolution has taken place in elementary particle physics in the last 15 years. One of the basic underlying ideas of these theories is that of spontaneous symmetry breaking between diﬀerent types of interactions due to the appearance of constant classical scalar ﬁelds ϕ over all space (the so-called Higgs ﬁelds). Prior to the appearance of these ﬁelds, there is no fundamental diﬀerence between strong, weak, and electromagnetic interactions. Their spontaneous appearance over all space essentially signiﬁes a restructuring of the vacuum, with certain vector (gauge) ﬁelds acquiring high mass as a result. The interactions mediated by these vector ﬁelds then become shortrange, and this leads to symmetry breaking between the various interactions described by the uniﬁed theories. The ﬁrst consistent description of strong and weak interactions was obtained within the scope of gauge theories with spontaneous symmetry breaking. For the ﬁrst time, it became possible to investigate strong and weak interaction processes using high-order perturbation theory. A remarkable property of these theories — asymptotic freedom — also made it possible in principle to describe interactions of elementary particles up to center-of-mass energies E ∼ MP ∼ 1019 GeV, that is, up to the Planck energy, where quantum gravity eﬀects become important. Here we will recount only the main stages in the development of gauge theories, rather than discussing their properties in detail. In the 1960s, Glashow, Weinberg, and Salam proposed a uniﬁed theory of the weak and electromagnetic interactions [1], and real progress was made in this area in 1971–1973 after the theories were shown to be renormalizable [2]. It was proved in 1973 that many such theories, with quantum chromodynamics in particular serving as a description of strong interactions, possess the property of asymptotic freedom (a decrease in the coupling constant with increasing energy [3]). The ﬁrst uniﬁed gauge theories of strong, weak, and electromagnetic interactions with a simple symmetry group, the so-called grand uniﬁed theories [4], were proposed in 1974. The ﬁrst theories to unify all of the fundamental interactions, including gravitation, were proposed in 1976 within the context of supergravity theory. This was followed by the development of Kaluza–Klein theories, which maintain that our four-dimensional space-time results from the spontaneous compactiﬁcation of a higher-dimensional space [6]. Finally, our most recent hopes for a uniﬁed theory of all interactions have been invested in superstring theory [7]. Modern theories of elementary particles are covered in a number of PARTICLE PHYSICS AND INFLATIONARY COSMOLOGY xii excellent reviews and monographs (see [8–17], for example). The rapid development of elementary particle theory has not only led to great advances in our understanding of particle interactions at superhigh energies, but also (as a consequence) to signiﬁcant progress in the theory of superdense matter. Only ﬁfteen years ago, in fact, the term superdense matter meant matter with a density somewhat higher than nuclear values, ρ ∼ 1014 –1015 g · cm−3 and it was virtually impossible to conceive of how one might describe matter with ρ ≫ 1015 g · cm−3 . The main problems involved strong-interaction theory, whose typical coupling constants at ρ > 1015 g · cm−3 ∼ were large, making standard perturbation-theory predictions of the properties of such matter unreliable. Because of asymptotic freedom in quantum chromodynamics, however, the corresponding coupling constants decrease with increasing temperature (and density). This enables one to describe the behavior of matter at temperatures approaching T ∼ MP ∼ 1019 GeV, which corresponds to a density ρP ∼ M4 ∼ 1094 g · cm−3 . P Present-day elementary particle theories thus make it possible, in principle, to describe the properties of matter more than 80 orders of magnitude denser than nuclear matter! The study of the properties of superdense matter described by uniﬁed gauge theories began in 1972 with the work of Kirzhnits [18], who showed that the classical scalar ﬁeld ϕ responsible for symmetry breaking should disappear at a high enough temperature T. This means that a phase transition (or a series of phase transitions) occurs at a suﬃciently high temperature T > Tc , after which symmetry is restored between various types of interactions. When this happens, elementary particle properties and the laws governing their interaction change signiﬁcantly. This conclusion was conﬁrmed in many subsequent publications [19–24]. It was found that similar phase transitions could also occur when the density of cold matter was raised [25–29], and in the presence of external ﬁelds and currents [22, 23, 30, 33]. For brevity, and to conform with current terminology, we will hereafter refer to such processes as phase transitions in gauge theories. Such phase transitions typically take place at exceedingly high temperatures and densities. The critical temperature for a phase transition in the Glashow–Weinberg– Salam theory of weak and electromagnetic interactions [1], for example, is of the order of 102 GeV ∼ 1015 K. The temperature at which symmetry is restored between the strong and electroweak interactions in grand uniﬁed theories is even higher, Tc ∼ 1015 GeV ∼ 1028 K. For comparison, the highest temperature attained in a supernova explosion is about 1011 K. It is therefore impossible to study such phase transitions in a laboratory. However, the appropriate extreme conditions could exist at the earliest stages of the evolution of the universe. According to the standard version of the hot universe theory, the universe could have expanded from a state in which its temperature was at least T ∼ 1019 GeV [34, 35], cooling all the while. This means that in its earliest stages, the symmetry between the strong, weak, and electromagnetic interactions should have been intact. In cooling, the universe would have gone through a number of phase transitions, breaking the symmetry between the diﬀerent interactions [18–24]. This result comprised the ﬁrst evidence for the importance of uniﬁed theories of ele- PARTICLE PHYSICS AND INFLATIONARY COSMOLOGY xiii mentary particles and the theory of superdense matter for the development of the theory of the evolution of the universe. Cosmologists became particularly interested in recent theories of elementary particles after it was found that grand uniﬁed theories provide a natural framework within which the observed baryon asymmetry of the universe (that is, the lack of antimatter in the observable part of the universe) might arise [36–38]. Cosmology has likewise turned out to be an important source of information for elementary particle theory. The recent rapid development of the latter has resulted in a somewhat unusual situation in that branch of theoretical physics. The reason is that typical elementary particle energies required for a direct test of grand uniﬁed theories are of the order of 1015 GeV, and direct tests of supergravity, Kaluza–Klein theories, and superstring theory require energies of the order of 1019 GeV. On the other hand, currently planned accelerators will only produce particle beams with energies of about 104 GeV. Experts estimate that the largest accelerator that could be built on earth (which has a radius of about 6000 km) would enable us to study particle interactions at energies of the order of 107 GeV, which is typically the highest (center-of-mass) energy encountered in cosmic ray experiments. Yet this is twelve orders of magnitude lower than the Planck energy EP ∼ MP ∼ 1019 GeV. The diﬃculties involved in studying interactions at superhigh energies can be highlighted by noting that 1015 GeV is the kinetic energy of a small car, and 1019 GeV is the kinetic energy of a medium-sized airplane. Estimates indicate that accelerating particles to energies of the order of 1015 GeV using present-day technology would require an accelerator approximately one light-year long. It would be wrong to think, though, that the elementary particle theories currently being developed are totally without experimental foundation — witness the experiments on a huge scale which are under way to detect the decay of the proton, as predicted by grand uniﬁed theories. It is also possible that accelerators will enable us to detect some of the lighter particles (with mass m ∼ 102 –103 GeV) predicted by certain versions of supergravity and superstring theories. Obtaining information solely in this way, however, would be similar to trying to discover a uniﬁed theory of weak and electromagnetic interactions using only radio telescopes, detecting radio waves with an energy Eγ no greater EP EW than 10−5 eV (note that ∼ , where EW ∼ 102 GeV is the characteristic energy in EW Eγ the uniﬁed theory of weak and electromagnetic interactions). The only laboratory in which particles with energies of 1015 –1019 GeV could ever exist and interact with one another is our own universe in the earliest stages of its evolution. At the beginning of the 1970s, Zeldovich wrote that the universe is the poor man’s accelerator: experiments don’t need to be funded, and all we have to do is collect the experimental data and interpret them properly [39]. More recently, it has become quite clear that the universe is the only accelerator that could ever produce particles at energies high enough to test uniﬁed theories of all fundamental interactions directly, and in that sense it is not just the poor man’s accelerator but the richest man’s as well. These days, most new elementary particle theories must ﬁrst take a “cosmological validity” test — and only a very few pass. PARTICLE PHYSICS AND INFLATIONARY COSMOLOGY xiv It might seem at ﬁrst glance that it would be diﬃcult to glean any reasonably deﬁnitive or reliable information from an experiment performed more than ten billion years ago, but recent studies indicate just the opposite. It has been found, for instance, that phase transitions, which should occur in a hot universe in accordance with the grand uniﬁed theories, should produce an abundance of magnetic monopoles, the density of which ought to exceed the observed density of matter at the present time, ρ ∼ 10−29 g · cm−3 , by approximately ﬁfteen orders of magnitude [40]. At ﬁrst, it seemed that uncertainties inherent in both the hot universe theory and the grand uniﬁed theories, being very large, would provide an easy way out of the primordial monopole problem. But many attempts to resolve this problem within the context of the standard hot universe theory have not led to ﬁnal success. A similar situation has arisen in dealing with theories involving spontaneous breaking of a discrete symmetry (spontaneous CP-invariance breaking, for example). In such models, phase transitions ought to give rise to supermassive domain walls, whose existence would sharply conﬂict with the astrophysical data [41–43]. Going to more complicated theories such as N = 1 supergravity has engendered new problems rather than resolving the old ones. Thus it has turned out in most theories based on N = 1 supergravity that the decay of gravitinos (spin = 3/2 superpartners of the graviton) which existed in the early stages of the universe leads to results diﬀering from the observational data by about ten orders of magnitude [44, 45]. These theories also predict the existence of so-called scalar Polonyi ﬁelds [15, 46]. The energy density that would have been accumulated in these ﬁelds by now diﬀers from the cosmological data by ﬁfteen orders of magnitude [47, 48]. A number of axion theories [49] share this diﬃculty, particularly in the simplest models based on superstring theory [50]. Most Kaluza–Klein theories based on supergravity in an 11-dimensional space lead to vacuum energies of order −M4 ∼ P −1094 g · cm−3 [16], which diﬀers from the cosmological data by approximately 125 orders of magnitude. . . This list could be continued, but as it stands it suﬃces to illustrate why elementary particle theorists now ﬁnd cosmology so interesting and important. An even more general reason is that no real uniﬁcation of all interactions including gravitation is possible without an analysis of the most important manifestation of that uniﬁcation, namely the existence of the universe itself. This is illustrated especially clearly by Kaluza–Klein and superstring theories, where one must simultaneously investigate the properties of the space-time formed by compactiﬁcation of “extra” dimensions, and the phenomenology of the elementary particles. It has not yet been possible to overcome some of the problems listed above. This places important constraints on elementary particle theories currently under development. It is all the more surprising, then, that many of these problems, together with a number of others that predate the hot universe th..."

You need to upgrade your Flash Player , or try to enable javascript in order see this document properly.