Cosmology branaire

In Cosmologie and Théorie of the cords, the cosmology branaire is a cosmological Modèle whose principal idea is that our universe, and all that it contains, is imprisoned in a 3-brane.

Introduction

Cosmology branaire is a whole of cosmological scenarios inspired by the ideas of the second revolution in Théorie of the cords of which the goal is to solve the famous Problème of the hierarchy. In these models, the observable universe with four dimensions is a under-part of the total universe which has additional dimensions. The observable matter particles (described by the standard Model) are confined in the four dimensions obervées by a mechanism not described explicitly but presumedly similar to that of the theory of the cords in the models having of the D-branes (these last being by definition the place of the ends of the opened cords, and the matter particles in these models of open cords are precisely described by such ends). The Gravité, as for it, is propagated in all dimensions and it is thus only by its intermediary that these additional dimensions would be observable.

Motivation, models

The first models of cosmology branaire go back to work of LISA Randall and Raman Sundrum in 1999 inspired by work of Arkhani-Hamed, Dimopoulos and Dvali in 1998. The principal idea is to try to explain the extraordinary weakness of the intensity of the force of gravitation in front of the other forces by the existence of additional size. Gravity living naturally in all dimensions, it is the constant giving its intensity in all dimensions which is then fundamental and selected of the same order of magnitude as the other fundamental scales. The gravitation observed in four dimensions is then governed by an effective constant , derived from this fundamental constant as well as scale length associated with additional dimensions.

Several descriptions of these additional dimensions compatible with this idea were proposed. First of all, they can be selected compact but of big size (model Randall-Sundrum I) in front of the électrofaible scale of the standard model (about 1 mm in order to remain compatible in practice with the current tests of the force of gravitation) or then of infinite size (Randall-Sundrum II) but having a Courbure given by a cosmological Constante in the Bulbe (which is distinct from a possible cosmological constant in four visible dimensions) which fixes it also a scale returning the Constante of small gravitation effective at four dimensions in front of the intensity of the other forces.

Difference compared to the reduction of Kaluza-Klein

In the models of compactification with the Kaluza-Klein, one also finds a total geometry having of additional dimensions but of which only four are indeed visible. However in a model of compactification, no mechanism of containment of the particles of the standard model is considered what thus imposes that these last are compact and of very small size in order to be compatible with the experimental data which are extremely precise (cf measures gyromagnetic Constante) and thus impose a four-dimensional physics of the particles. Unfortunately low-size additional do not allow to solve the problem of the hierarchy concerning the gravitation.

Contrary, the models branaires make use owing to the fact that, relative with the data concerning physics of the particles, the experiments concerning the tests of gravity at small distances are only far from precise, the best given being available only on a tenth scale of millimetre (cf tests of the Newtonian gravitation). It is thus in theory possible to put up with the presence of large additional dimensions (“large” in front of the scale of the standard model) but smaller than the tenth of millimetre.

Observational aspects

New ways of testing the existence of possible additional dimensions will be accessible with the startup LHC since its field of energy about the TeV corresponds to a size of these dimensions about the millimetre.

See too

Internal bonds

External bonds

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- original Paper of the model commonly called Raman-Sundrum I.
- original Paper of the model commonly called Raman-Sundrum II.
- teaching Review of the cosmological consequences of a model branaire.
- These notes (32 pages) are an introduction to cosmology branaire.
- Notes (24 pages) of a course presents to First Aegean Summer School one Cosmology, Samos, September 2001.

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