Null energy condition and superluminal propagation
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Cites background or methods from "Null energy condition and superlumi..."
...10)—whose structure is protected by the volume-preserving diff symmetry— features vanishing propagation speed for the transverse phonons [8, 9], as can be checked explicitly in (2....
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...Cosmological systems of this sort have been considered briefly in [8]....
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...On the other hand however, because of powerful conservation laws for vorticity, classically one can consistently set to zero the transverse excitations—the vortices—and be left with an EFT for the compressional modes only [8]....
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...Here instead we will review the equivalent construction of [8, 9] (see also [10]), whose notation we will follow....
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...But our EFT conforms to the hypotheses of the general theorem of [8], which links NEC violations to such pathologies as ghost- or gradient-instabilities and superluminality....
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Cites background from "Null energy condition and superlumi..."
...It is worth emphasizing that the NEC is usually taken for granted not due to lack of imagination, but because of its exceptional robustness—it is especially hard to construct consistent effective field theories that violate it [1]....
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...For these theories the usual relation between the violation of the NEC and the presence of pathological instabilities [1] is avoided, due to the presence of higher derivative interactions....
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References
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