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mitchell porter
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- TL;DR Summary
- Latest version of Blanchet's theory of dark matter as gravitational dipoles
A dielectric is a substance made of electric dipoles which, when placed in an external electric field, reduces the electric field because its constituent dipoles line up and contribute their own opposing field.
For some years, the astrophysicist Luc Blanchet has proposed to explain MOND via a gravitational counterpart of this effect.
"Gravitational polarization and the phenomenology of MOND"
This would require dark matter to be made of "gravitational dipoles" that polarize along the gravitational field lines of galaxies (and which enhance, rather than reduce, the net field). In one version of this idea, one end of the dipole has positive mass and the other end has negative mass. In another version, there are two forces of gravity (an idea known elsewhere as "bimetric gravity" or just "bigravity"), and the ends of the dipole both have positive mass, but with respect to different gravities.
In this week's paper
"Dipolar dark matter theory based on a non-Abelian Yang-Mills field"
based on the earlier paper
"Effective field theory reproducing the MOND phenomenology based on a non-Abelian Yang-Mills graviphoton"
Blanchet and the PhD student Emeric Semaille describe a version of this "dipolar dark matter" in which there is a multiplet of negative and positive mass particles which are also charged under a new SU(2) gauge field. This new SU(2) force is what actually holds the "gravitational dipoles" together.
This idea has some intrinsic interest as a dark matter theory that gives rise to a MOND relation. But what really catches my eyes is the appearance of SU(2) charges, since the well-known Ashtekar variables re-express gravity itself as an SU(2) gauge field. I have to wonder if there's a version of this theory in which the dipolar dark matter is held together by gravity too!
For some years, the astrophysicist Luc Blanchet has proposed to explain MOND via a gravitational counterpart of this effect.
"Gravitational polarization and the phenomenology of MOND"
This would require dark matter to be made of "gravitational dipoles" that polarize along the gravitational field lines of galaxies (and which enhance, rather than reduce, the net field). In one version of this idea, one end of the dipole has positive mass and the other end has negative mass. In another version, there are two forces of gravity (an idea known elsewhere as "bimetric gravity" or just "bigravity"), and the ends of the dipole both have positive mass, but with respect to different gravities.
In this week's paper
"Dipolar dark matter theory based on a non-Abelian Yang-Mills field"
based on the earlier paper
"Effective field theory reproducing the MOND phenomenology based on a non-Abelian Yang-Mills graviphoton"
Blanchet and the PhD student Emeric Semaille describe a version of this "dipolar dark matter" in which there is a multiplet of negative and positive mass particles which are also charged under a new SU(2) gauge field. This new SU(2) force is what actually holds the "gravitational dipoles" together.
This idea has some intrinsic interest as a dark matter theory that gives rise to a MOND relation. But what really catches my eyes is the appearance of SU(2) charges, since the well-known Ashtekar variables re-express gravity itself as an SU(2) gauge field. I have to wonder if there's a version of this theory in which the dipolar dark matter is held together by gravity too!
