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Participant |
Bluhm, Robert | |||||||
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Institution |
Colby College - Mayflower Hill 5862 - Waterville - ME - USA | |||||||
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Session |
AT1 |
Accepted |
Yes |
Order |
99 |
Time |
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Talk |
Poster abstract |
Title |
Background Fields and Explicit Diffeomorphism Breaking in Gravity | |||||
| Coauthors | Bluhm, Robert | |||||||
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Abstract |
When a fixed background field appears in the action describing an effective gravitational theory in Riemann spacetime, diffeomorphism invariance and local Lorentz invariance are explicitly broken. However, to maintain observer independence it is still necessary that the action be invariant under general coordinate transformations. This sets up a potential inconsistency between the requirements of covariant energy-momentum conservation, the Bianchi identities, and the dynamical equations of motion. This talk looks at how these conflicts arise, how they are evaded in some theories, and what the consequences are when explicit-breaking backgrounds are present. In contrast, if the symmetry breaking is spontaneous, then the background fields arise dynamically as vacuum expectation values, and no potential conflicts occur. Examples of gravitational theories with background fields include Chern-Simons gravity, massive gravity, and the gravity sector of the Standard-Model Extension (or SME), which is used in phenomenological tests of Lorentz violation. |
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Pdf file |
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