The art of the state

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Quantum field theory on curved spacetimes lacks an obvious distinguished vacuum state. We review a recent no-go theorem that establishes the impossibility of finding a preferred state in each globally hyperbolic spacetime, subject to certain natural conditions. The result applies in particular to the free scalar field, but the proof is model-independent and therefore of wider applicability. In addition, we critically examine the recently proposed `SJ states', that are determined by the spacetime geometry alone, but which fail to be Hadamard in general. We describe a modified construction that can yield an infinite family of Hadamard states, and also explain recent results that motivate the Hadamard condition without direct reference to ultra-high energies or ultra-short distance structure.
Original languageEnglish
Number of pages27
JournalInternational Journal of Modern Physics D
Early online date13 Mar 2018
Publication statusPublished - 20 Apr 2018
EventIV Amazonian Symposium on Physics - Pará University, Belém, Brazil
Duration: 18 Sep 201722 Sep 2017

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