{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,26]],"date-time":"2025-10-26T22:53:23Z","timestamp":1761519203047,"version":"build-2065373602"},"reference-count":68,"publisher":"MDPI AG","issue":"10","license":[{"start":{"date-parts":[[2017,10,16]],"date-time":"2017-10-16T00:00:00Z","timestamp":1508112000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Symmetry"],"abstract":"<jats:p>An overview is given of effective gravitational field theories with fixed background fields that break spacetime symmetry. The behavior of the background fields and the types of excitations that can occur depend on whether the symmetry breaking is explicit or spontaneous. For example, when the breaking is spontaneous, the background field is dynamical and massless Nambu\u2013Goldstone and massive Higgs excitations can appear. However, if the breaking is explicit, the background is nondynamical, and in this case additional metric or vierbein excitations occur due to the loss of local symmetry, or these excitations can be replaced by dynamical scalar fields using a St\u00fcckelberg approach. The interpretation of Noether identities that must hold in each case differs, depending on the type of symmetry breaking, and this affects the nature of the consistency conditions that must hold. The Noether identities also shed light on why the St\u00fcckelberg approach works, and how it is able to restore the broken spacetime symmetry in a theory with explicit breaking.<\/jats:p>","DOI":"10.3390\/sym9100230","type":"journal-article","created":{"date-parts":[[2017,10,16]],"date-time":"2017-10-16T11:11:09Z","timestamp":1508152269000},"page":"230","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":16,"title":["Gravity Theories with Background Fields and Spacetime Symmetry Breaking"],"prefix":"10.3390","volume":"9","author":[{"given":"Robert","family":"Bluhm","sequence":"first","affiliation":[{"name":"Colby College, Department of Physics and Astronomy, Mayflower Hill 5862, Waterville, Maine, 04901, USA"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2017,10,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"065034","DOI":"10.1103\/PhysRevD.91.065034","article-title":"Explicit versus spontaneous diffeomorphism breaking in gravity","volume":"91","author":"Bluhm","year":"2015","journal-title":"Phys. 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