{"work":{"id":"62b74acc-6456-4fb5-8136-5250426062b9","openalex_id":null,"doi":null,"arxiv_id":"0811.2197","raw_key":null,"title":"The galileon as a local modification of gravity","authors":null,"authors_text":"A","year":2008,"venue":"hep-th","abstract":"In the DGP model, the ``self-accelerating'' solution is plagued by a ghost instability, which makes the solution untenable. This fact as well as all interesting departures from GR are fully captured by a four-dimensional effective Lagrangian, valid at distances smaller than the present Hubble scale. The 4D effective theory involves a relativistic scalar \\pi, universally coupled to matter and with peculiar derivative self-interactions. In this paper, we study the connection between self-acceleration and the presence of ghosts for a quite generic class of theories that modify gravity in the infrared. These theories are defined as those that at distances shorter than cosmological, reduce to a certain generalization of the DGP 4D effective theory. We argue that for infrared modifications of GR locally due to a universally coupled scalar, our generalization is the only one that allows for a robust implementation of the Vainshtein effect--the decoupling of the scalar from matter in gravitationally bound systems--necessary to recover agreement with solar system tests. Our generalization involves an internal ``galilean'' invariance, under which \\pi's gradient shifts by a constant. This symmetry constrains the structure of the \\pi Lagrangian so much so that in 4D there exist only five terms that can yield sizable non-linearities without introducing ghosts. We show that for such theories in fact there are ``self-accelerating'' deSitter solutions with no ghost-like instabilities. In the presence of compact sources, these solutions can support spherically symmetric, Vainshtein-like non-linear perturbations that are also stable against small fluctuations. [Short version for arxiv]","external_url":"https://arxiv.org/abs/0811.2197","cited_by_count":null,"metadata_source":"pith","metadata_fetched_at":"2026-05-25T18:36:08.337033+00:00","pith_arxiv_id":"0811.2197","created_at":"2026-05-09T06:10:40.492901+00:00","updated_at":"2026-06-05T21:23:00.469572+00:00","title_quality_ok":true,"display_title":"The galileon as a local modification of gravity","render_title":"The galileon as a local modification of gravity"},"hub":{"state":{"work_id":"62b74acc-6456-4fb5-8136-5250426062b9","tier":"hub","tier_reason":"10+ Pith inbound or 1,000+ external citations","pith_inbound_count":14,"external_cited_by_count":null,"distinct_field_count":4,"first_pith_cited_at":"2019-06-21T19:25:20+00:00","last_pith_cited_at":"2026-05-08T14:17:06+00:00","author_build_status":"not_needed","summary_status":"needed","contexts_status":"needed","graph_status":"needed","ask_index_status":"not_needed","reader_status":"not_needed","recognition_status":"not_needed","updated_at":"2026-06-19T19:17:47.220254+00:00","tier_text":"hub"},"tier":"hub","role_counts":[{"context_role":"background","n":9},{"context_role":"method","n":1}],"polarity_counts":[{"context_polarity":"background","n":9},{"context_polarity":"use_method","n":1}],"runs":{},"summary":{},"graph":{},"authors":[]}}