|  Quantum Theory of Cosmological Perturbations | 
Quantization of Cosmological Perturbations
  > s.a. quantum cosmology; quantum-gravity effects on cosmology.
  * Idea: In the quantum
    theory of cosmological perturbations one normally assumes that the
    pre-inflationary state of the universe was the vacuum of a (scalar)
    field coupled to gravity, and the observed cosmic microwave background
    fluctuations are then interpreted as due to quantum fluctuations turned
    into classical perturbations; The quantum theory itself is trivial, but
    it is used to give a framework for choosing as initial conditions an
    appropriate vacuum, like the Bunch-Davies vacuum, a local attractor
    (because deviations are redshifted away) which gives Gaussian fluctuations.
  @ General references: Giovannini CQG(03)ht;
    Peter et al JCAP(05)ht [including quantum backgrounds];
    Pinho & Pinto-Neto PRD(07);
    Campo & Parentani PRD(08)-a0805 [decoherence and entropy];
    Prokopec & Rigopoulos PRD(10) [inflation, path-integral formulation];
    Vitenti et al PRD(13)-a1206;
    Guth a1312-proc [and the multiverse];
    Kanno JCAP(14)-a1405 [effect of entanglement];
    Castelló et al JCAP(15)-a1503 [gauge-invariant];
    Armendáriz-Picón & Şengör JCAP(16)-a1606 [BRST quantization];
    Han et al PRD(20)-a2005 [from lqg].
  @ Coherence: 
    Giovannini CQG(17)
    + CQG+ [and Glauber theory];
    Giovannini MPLA(17)-a1709.
    @ Phenomenology: 
    Mukhanov EPJC(13)-a1303 [predictions and observations];
    Kuntz & da Rocha EPJC(19)-a1903 [instability due to runaway modes].
  @ Types of matter: Peter et al PRD(16)-a1510 [multiple fluids].
 In
  theories of quantum gravity: see perturbations in quantum cosmology.
 In
  theories of quantum gravity: see perturbations in quantum cosmology.
From Quantum Fluctuations to Classical Perturbations
  > s.a. decoherence phenomenology;
  quantum-to-classical transition.
  * Idea: The collapse
    approach uses physics beyond the established paradigm, possibly associated
    with a quantum-gravity effect à la Penrose, in which the collapse
    of the state function of the inflaton field would be responsible for the
    emergence of the primordial inhomogeneities.
  @ And observation: Green & Porto PRL(20) [distinguishing classical and quantum initial states].
  @ General references: Kiefer et al IJMPD(98)gq;
    Kiefer & Polarski AdP(98)gq [emergence from the quantum state];
    Lombardo PhD(98)gq;
    Martin LNP(05)ht/04;
    Pérez et al CQG(06)gq/05;
    Lyth & Seery PLB(08)ap/06 [after horizon exit];
    Armendáriz-Picón et al CQG(09)-a0805 [limits];
    Bojowald & Skirzewski ASL(08)-a0808 [effective theory];
    Kiefer & Polarski ASL(09)-a0810 [rev];
    Sudarsky IJMPD(11)-a0906,
    IJMPD(11);
    Dimopoulos JPCS(11)-a1009 [rev];
    Malik a1011-conf;
    Berkhahn et al PRL(11);
    Martin & Vennin PRD(16)-a1510 [how to prove the quantum-mechanical nature of perturbations];
    Ryssens a1907-MS [pilot-wave approach];
    Green & Porto a2001
      [distinguishing quantum and classical primordial fluctuations];
    Berjon et al PRD-a2009;
    > s.a. early-universe cosmology; inflation.
  @ And entanglement: Genovese ASL(09)-a0904;
    Nelson & Riedel a1704
      [squeezing of the quantum state for super-horizon modes]
  @ Semiclassical theory: Aslanyan et al JCAP(13)-a1301 [limits on semiclassical fluctuations];
    Donà & Marcianò PRD(16)-a1605 [and Dirac fermions].
  @ And de Broglie-Bohm quantum theory:
    Pinto-Neto et al PRD(12)-a1110,
    PRD(14)-a1309;
    Goldstein et al a1508
      [structure formation and Boltzmann brains].
  @ Inflation: Diez-Tejedor et al GRG(12)-a1106 [and loss of symmetries];
    Martin et al PRD(12)-a1207 [and the quantum measurement problem];
    Singh a1607-fs
      [model, evolution of the classicality parameter];
    Martin Univ-a1904 [and quantum information theory].
  @ Collapse of the wave function:
    De Unánue & Sudarsky PRD(08)-a0801;
    Diez-Tejedor & Sudarsky JCAP(12)-a1108 [details of approach];
    Landau et al PRD(12)-a1112;
    Das et al PRD(13)-a1304 [continuous spontaneous localization];
    León & Sudarsky JCAP(15)-a1503 [statistical characterization];
    León et al PRD(15)-a1509 ["self-induced collapse" and primordial gravitational waves];
    Stargen & Sreenath a1605.
  @ Quantum corrections to correlations:
    Weinberg PRD(06);
    van der Meulen & Smit JCAP(07)-a0707.
  @ Approaches: de Alwis a1504
      [replacing the quantum vacuum with a classical statistical distribution].
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