Approaches to understanding cosmic accel
➤ Gửi thông báo lỗi ⚠️ Báo cáo tài liệu vi phạmNội dung chi tiết: Approaches to understanding cosmic accel
Approaches to understanding cosmic accel
arXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel s and Kavli Institute for Astrophysics and Space Research, MIT. 77 Massachusetts Ave., Cambridge, MA 02139. USA.•Center for Particle Cosmology. Department of Physics ami Astronomy, David Rittenhouse Laboratories, University of Pennsylvania. Philadelphia, PA 19104, USA.E-mail: as ilvesfStn it.edu, tr Approaches to understanding cosmic accel oddcntiphyslcs.upenn.eduAbstract. Theoretical approaches to explaining the observed acceleration of the universe are reviewed. We briefly discuss theApproaches to understanding cosmic accel
evidence for cosmic acceleration, and the implications for standard General Relativity coupled to conventional sources of energy-momentum. We then addarXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel y of dark energy, and the associated challenges for fundamental physics; and the option that an infrared modification of general relativity may be responsible for the large-scale behavior of the universe.Approaches to Understanding Cosmic Acceleration21. IntroductionThe development of General Relati Approaches to understanding cosmic accel vity .almost 90 years ago provided not only a new way to understand gravity, but heralded the dawn of an entirely new branch of science - cosmology. OApproaches to understanding cosmic accel
f course, a discussion of the visible contents of the night sky was not a new development - these objects and phenomena have forever fascinated civiliarXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel ght - that space and time are themselves players in the cosmic drama. Hubble’s 1921 observation that distant galaxies are receding from ours at speeds proportional to their distances, in agreement with Friedmann’s corresponding solution to General Relativity, then provided the first experimental con Approaches to understanding cosmic accel firmation of this new science.Almost a century has passed since the beginning of this era, and in the intervening years increasingly accurate predictiApproaches to understanding cosmic accel
ons of this model of the cosmos, supplemented only by the presence of a dark matter component, have been confronted with, and spectacularly passed, a arXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel osynthesis (BBN); the formation of structure under gravitational instability; the small temperature anisotropies in the CMB: the structure of gravitational lensing maps; and many more. Many of these tests are highly nontrivial and provide remarkable support for the overall big bang model.All this he Approaches to understanding cosmic accel ld true until approximately a decade ago, when the first evidence for cosmic acceleration was reported by two groups using the lightcurves of type laApproaches to understanding cosmic accel
supernovae to construct an accurate Hubble diagram out to redshift greater than unity. As we will describe in some detail, the natural expectation is arXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel hould slow down as cosmic time unfolds. Amazingly, that initial data, supplemented over the last decade by dozens of further, independent observations, showed that the universe is speeding up - what we observe is not deceleration, but cosmic acceleration!The goal of this article is to provide an ove Approaches to understanding cosmic accel rview of what is meant by cosmic acceleration, some proposed theoretical approaches to understanding the phenomenon, and how upcoming observational daApproaches to understanding cosmic accel
ta may cast crucial light on these. We have not attempted to be completely comprehensive, but have tried to provide a flavor of the current research larXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel accelerating universe. There are a number of excellent recent review articles on dark energy, which the reader might find as a useful complement to the present paper [1, 2, 3. 4Ị,The article is organized as follows. In the next section we provide a brief introduction to the relevant cosmological so Approaches to understanding cosmic accel lutions to General Relativity, with perfect fluid sources. In section 3 we review the observational evidence, primarily fromApproaches to UnderstandinApproaches to understanding cosmic accel
g Cosmic Acceleration3observations made during the last decade or so, for an accelerating universe. In section I we then discuss the minimal possibiliarXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel arameter raises for particle physics. In 5 we then explore a class of dynamical dark energy models, in which the universe accelerates duo to the evolution of a new component of the cosmic energy budget, under the assumption that the cosmological constant is negligibly small. In a similar vein, in 6 Approaches to understanding cosmic accel wo then consider the possibility that rhe universe contains only standard model and dark matter sources of energy and momentum, but accelerates becausApproaches to understanding cosmic accel
e GR is modified al large distances, leading to new self-accelerating solutions. Finally, before concluding, in 7 wo then consider the challenge of diarXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel nd this phenomena.A note on conventions. 'Throughout this article wo use units in which h — c - 1, adopt the (—,+,+,+) signature and define the reduced Planck mass by—8wG.2. Essential Elements of Background CosmologyOur goal here is to lay out rhe bare minimum for understanding the background evolut Approaches to understanding cosmic accel ion of the universe. By background in this context, we mean the dynamics pertaining to the homogeneous ami isotropic description of spacetime, valid oApproaches to understanding cosmic accel
n the very largest scales, without reference to spatial perturbations of either the metric or matter fields]:.The most general homogeneous and isotroparXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel sections (slices at constant cosmic time) and a(t) is referred to as the scale factor or the universe. Without loss of generality, wo may normalize k so that k —1-1 corresponds to positively curved spatial sections (locally isometric to 3 spheres); k — 0 corresponds to local flatness, and k — — i co Approaches to understanding cosmic accel rresponds to negatively curved (locally hyperbolic) spatial sections. Those local definitions say nothing about the global topology of the spatial secApproaches to understanding cosmic accel
tions, which may be that of the covering spaces a 3 sphere, an infinite plane or a 3 hyperboloid but it need not be. as topological identifications unarXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel well to a 3-tonis as to an infinite plane.Noto that wo have not chosen a normalization such that flfl — 1. Wo are not free to do this and to simultaneously normalize |fc| — i, without including explicit factors of the current scale factor in the metric. In the fiat case, whore k — 0, wo can safely Approaches to understanding cosmic accel choose flo = 1.Ị Wo follow closely the brief discussion in [5]Approaches to Understanding Cosmic Acceleration4At cosmic time t, the physical distanceApproaches to understanding cosmic accel
from the origin to an object at radial coordinate r is given by d(t) = a(t)r. The recessional velocity of such an object due to the expansion of the uarXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of Physics Approaches to understanding cosmic accel day value of which we refer to as the Hubble constant Ho.The Hubble parameter is a useful function through which to parametrize the expansion rate of the universe. As we shall encounter later, it is convenient to define a second function, describing the rate at which the expansion rate is slowing d Approaches to understanding cosmic accel own or speeding up - the deceleration parameter, defined as<7(0 =.-32.1. Dynamics: The Friedmann EquationsThe FRW metric is merely an ansatz, arrivedApproaches to understanding cosmic accel
at by requiring homogeneity and isotropy of spatial sections. The unknown function a(t) is obtained by solving the differential equations obtained by arXiv:0904.0024v2 [astro-ph.CO] 28 Jun 2009Approaches to Understanding Cosmic AccelerationAlessandra Silvestri and Mark Trodden2’Department of PhysicsGọi ngay
Chat zalo
Facebook