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Quantum Grav."],"published-print":{"date-parts":[[2018,4,12]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>We rederive the equations of motion for relativistic strings, that is, one-dimensional elastic bodies whose internal energy depends only on their stretching, and use them to study circular string loops rotating in the equatorial plane of flat and black hole spacetimes. We start by obtaining the conditions for equilibrium, and find that: (i) if the string\u2019s longitudinal speed of sound does not exceed the speed of light then its radius when rotating in Minkowski\u2019s spacetime is always larger than its radius when at rest; (ii) in Minkowski\u2019s spacetime, equilibria are linearly stable for rotation speeds below a certain threshold, higher than the string\u2019s longitudinal speed of sound, and linearly unstable for some rotation speeds above it; (iii) equilibria are always linearly unstable in Schwarzschild\u2019s spacetime. Moreover, we study interactions of a rotating string loop with a Kerr black hole, namely in the context of the weak cosmic censorship conjecture and the Penrose process. We find that: (i) elastic string loops that satisfy the null energy condition cannot overspin extremal black holes; (ii) elastic string loops that satisfy the dominant energy condition cannot increase the maximum efficiency of the usual particle Penrose process; (iii) if the dominant energy condition (but not the weak energy condition) is violated then the efficiency can be increased. This last result hints at the interesting possibility that the dominant energy condition may underlie the well known upper bounds for the efficiencies of energy extraction processes (including, for example, superradiance).<\/jats:p>","DOI":"10.1088\/1361-6382\/aaaeaf","type":"journal-article","created":{"date-parts":[[2018,2,12]],"date-time":"2018-02-12T11:15:25Z","timestamp":1518434125000},"page":"075003","update-policy":"https:\/\/doi.org\/10.1088\/crossmark-policy","source":"Crossref","is-referenced-by-count":8,"title":["Rotating elastic string loops in flat and black hole spacetimes: stability, cosmic censorship and the Penrose process"],"prefix":"10.1088","volume":"35","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0885-9867","authenticated-orcid":false,"given":"Jos\u00e9","family":"Nat\u00e1rio","sequence":"first","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0166-8542","authenticated-orcid":false,"given":"Leonel","family":"Queimada","sequence":"additional","affiliation":[]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3150-9315","authenticated-orcid":false,"given":"Rodrigo","family":"Vicente","sequence":"additional","affiliation":[]}],"member":"266","published-online":{"date-parts":[[2018,2,28]]},"reference":[{"key":"cqgaaaeafbib001","doi-asserted-by":"publisher","first-page":"936","DOI":"10.1119\/1.14795","type":"journal-article","article-title":"On traveling round without feeling it and uncurving curves","volume":"54","author":"Abramowicz","year":"1986","journal-title":"Am. 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