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Published on: November 15, 2013
No-go theorems for generalized chameleon field theories
Junpu Wang1, Lam Hui, Justin Khoury
1Physics Department and Institute for Strings, Cosmology and Astroparticle Physics, Columbia University, New York, NY 10027, USA.
Physical Review Letters
|February 2, 2013
Summary
Chameleon scalar fields, which interact with matter gravitationally, have their effects screened in dense environments. This study proves their cosmological impact is limited, ruling out self-acceleration and genuine modified gravity effects for cosmic acceleration.
Area of Science:
- Cosmology
- Theoretical Physics
- Particle Physics
Background:
- Chameleon scalar fields are hypothetical light particles that couple to matter with gravitational strength.
- Their observable effects depend on the ambient matter density due to a screening mechanism.
- Generalizations of chameleon theories include symmetron and dilaton models.
Purpose of the Study:
- To mathematically prove the cosmological impact limitations of chameleon scalar fields.
- To investigate whether chameleon fields can explain cosmic acceleration through modified gravity.
- To analyze the implications for theories involving chameleon, symmetron, and dilaton fields.
Main Methods:
- Proving two general theorems concerning the cosmological impact of chameleon scalar fields.
- Analyzing the Compton wavelength of the scalar field at present cosmic density.
- Examining the constancy of the conformal factor over the last Hubble time.
Main Results:
- The Compton wavelength of chameleon scalars is restricted to at most 1 Megaparsec (MPc) at present cosmic density, limiting their effects to nonlinear scales.
- The conformal factor remains nearly constant over the last Hubble time, precluding self-acceleration.
- Chameleonlike scalar fields have a negligible impact on the linear-scale growth history of the universe.
Conclusions:
- Chameleonlike scalar fields do not provide a genuine modified gravity explanation for cosmic acceleration.
- Theories invoking these fields for cosmic acceleration likely rely on a form of dark energy.
- The findings apply broadly to chameleon, symmetron, and dilaton theories.
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