Chameleon cosmology
Open accessAbstract
The evidence for the accelerated expansion of the Universe and the time dependence of the fine-structure constant suggests the existence of at least one scalar field with a mass of order ${H}_{0}.$ If such a field exists, then it is generally assumed that its coupling to matter must be tuned to unnaturally small values in order to satisfy the tests of the equivalence principle (EP). In this paper, we present an alternative explanation which allows scalar fields to evolve cosmologically while having couplings to matter of order unity. In our scenario, the mass of the fields depends on the local matter density: the interaction range is typically of order 1 mm on Earth (where the density is high) and of order $10--{10}^{4}\mathrm{AU}$ in the solar system (where the density is low). All current bounds from tests of general relativity are satisfied. Nevertheless, we predict that near-future experiments that will test gravity in space will measure an effective Newton's constant different by order unity from that on Earth, as well as EP violations stronger than currently allowed by laboratory experiments. Such outcomes would constitute a smoking gun for our scenario.
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The chameleon solution is valid under the thin shell condition.
“This solution is valid under the thin shell condition (Khoury and Weltman 2004a),293”
From Testing general relativity in cosmology (2019) · cites this paper as Khoury and Weltman 2004a
The gravitational potential profile from a dense region to a less dense region matters rather than the dense region alone.
“This brings us to an important point stressed in Khoury and Weltman (2004a) and Koyama (2016) which is the gravitational potential profile from a dense region to a less dense region that matters rather than the dense region alone.”
From Testing general relativity in cosmology (2019) · cites this paper as Khoury and Weltman 2004a
Under the thin shell condition, only the mass within the thin shell contributes to the fifth force outside the shell because in the interior the scalar field mass is large and the fifth force is suppressed by the Yukawa exponential.
“In such a case, only the mass within the thin-shell defined by contributes to the fifth force outside the shell because in the interior of the source the scalar field mass is large and the fifth force is suppressed by the Yukawa exponential realizing the chamelon mechanism.”
From Testing general relativity in cosmology (2019) · cites this paper as Khoury and Weltman 2004a
The chameleon field is an example of a field whose mass depends on the environment.
“An example of a field with such a behavior is the aptly named chameleon field (Khoury and Weltman 2004b, a).”
From Testing general relativity in cosmology (2019) · cites this paper as Khoury and Weltman 2004a
Taking the sun density and the Milky Way density, the scalar field in the vicinity of the sun is suppressed compared to the galaxy.
“For example, taking the sun density as g cm and the Milky way density as g cm, one can conclude that the scalar field in the vicinity of the sun is suppressed compared to the galaxy.”
From Testing general relativity in cosmology (2019) · cites this paper as Khoury and Weltman 2004a
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- Authors
- Khoury, J., & Weltman, A.
- Affiliations
- Columbia University (US)
- Venue
- Physical Review D
- Publisher
- American Physical Society (APS)
- Published
- 2004-02-27
- Volume
- 69
- Issue
- 4
- ISSN
- 0556-2821 (ISSN-L)
- 1550-7998
- 1550-2368
- OpenAlex
- W3037060671
- Cited by
- 1,634
- References
- 5
- Citations by year
- 2026: 55 · 2025: 72 · 2024: 88 · 2023: 70 · 2022: 83 · 2021: 95 · 2020: 74 · 2019: 97 · 2018: 125 · 2017: 81 · 2016: 93 · 2015: 97 · 2014: 82 · 2013: 93 · 2012: 105
- FWCI
- 14.55
- Type
- journal article
- Language
- en
- Open access
- green
- arxiv.org
- Locations
- Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields (publishedVersion)
- arXiv (Cornell University) (submittedVersion)
- CERN Document Server (European Organization for Nuclear Research) (submittedVersion)
- arXiv (Cornell University)
- Topics
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Cosmology and Gravitation Theories
- Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Noncommutative and Quantum Gravity Theories
- Physical Sciences › Physics and Astronomy › Astronomy and Astrophysics › Relativity and Gravitational Theory
- Keywords
- chameleon mechanism, scalar field, cosmic acceleration, fine-structure constant variation, equivalence principle, modified gravity, effective Newton's constant, tests of general relativity, scalar field coupling to matter, local matter density
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