THE CHAMELEON MECHANISM IN THE BRANS-DICKE SCALAR TENSOR MODEL

• Main Author: Sutiono, Azwar
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/86506
• Institution: Institut Teknologi Bandung

An investigation was conducted on the chameleon mechanism within the scalar tensor Brans-Dicke theory. The fundamental concept of the standard chameleon mechanism is retained, wherein the field becomes massive in regions with high matter density but possesses a very small mass on the scale of the solar system, where matter density is extremely low. Thin-shell solutions are found for static and spherically symmetric objects, demonstrating the relevance of this model to observations on a local scale. To reinforce its role as an accelerator of universe expansion, the stability of the mechanism is explored. By analyzing the modified Friedmann equations, autonomous equations are formulated to determine the critical points for this mechanism. A constraint is defined on the Brans-Dicke parameter ?????? ? , identifying two stability groups, ?????? > ?????? ? and 0 < ???????????? < ???????????? ? . The first group achieves stability with both appropriate eigenvalues and density parameter characteristic consistent with dark energy dominance. The second exhibits eigenvalue stability but contradicts conditions for a stable universe. The impact of variations in the scalar field potential and matter coupling is explored by analyzing different parameter sets. Each unique set of parameters results in a distinct ?????? ? . These findings indicate that system stability is achieved when the kinetic term of the scalar field and its potential dominate, emphasizing the crucial role of this mechanism as an accelerator of universe expansion.