Decoherence can relax cosmic acceleration

We consider the effect of the Gibbons-Hawking radiation on the inflaton in the situation where it is coupled to a large number of spectator fields. We argue that this will lead to two important effects -a thermal contribution to the potential and a gradual change in parameters in the Lagrangian which results from thermodynamic and energy conservation arguments. We present a scenario of hilltop inflation where the field starts trapped at the origin before slowly experiencing a phase transition during which the field extremely slowly moves towards its zero temperature expectation value. We show that it is possible to obtain enough e-folds of expansion as well as the correct spectrum of perturbations without hugely fine-tuned parameters in the potential (albeit with many spectator fields). We also comment on how initial conditions for inflation can arise naturally in this situation.

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“…During this epoch there is little dynamics in φ 2 and the two relevant limiting cases from the above are 15) which are separated by the threshold…”

Section: ∼ 0: Large Quantum Fluctuationsmentioning

confidence: 96%

“…In a first principle approach this can be achieved in a prescription where the energy-momentum tensor sourcing gravity is coarse grained to include only the observable degrees of freedom, i.e. those inside the cosmological horizon [11,15,16].…”

Section: Introductionmentioning

confidence: 99%

Horizon feedback inflation

2018

Self Cite

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“…Discrepancies between the quantum dispersion of the semiclassical universe and the present observations can be analyzed as descending [87] from the compensation between the decayment of the two-point correlation functions, which should compensate for the presence of tensor gravitational degrees of freedom at the quantum level. Such degrees of freedom can be also explained [84] to produce small fluctuation on the wave functional, which however do not produce anisotropies but only a decohered wavefunction, and [88] lead to the observed (almost flat) curvature of the universe. The quantum-mechanical fluctuations can also account for [89] short-wavelength degrees of freedom in the long-wavelength fluctuation analysis in the proper Hamiltonian description.…”

Section: Classicalization At the Hubble Radiusmentioning

confidence: 99%

Semiclassical Length Measure from a Quantum-Gravity Wave Function

Lecian

2017

Technologies

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Abstract:The definition of a length operator in quantum cosmology is usually influenced by a quantum theory for gravity considered. The semiclassical limit at the Planck age must meet the requirements implied in present observations. The features of a semiclassical wave-functional state are investigated, for which the modern measure(ment)s is consistent. The results of a length measurement at present times are compared with the same measurement operation at cosmological times. By this measure, it is possible to discriminate, within the same Planck-length expansion, the corrections to a Minkowski flat space possibly due to classicalization of quantum phenomena at the Planck time and those due to possible quantum-gravitational manifestations of present times. This analysis and the comparison with the previous literature can be framed as a test for the verification of the time at which anomalies at present related to the gravitational field, and, in particular, whether they are ascribed to the classicalization epoch. Indeed, it allows to discriminate not only within the possible quantum features of the quasi (Minkowski) flat spacetime, but also from (possibly Lorentz violating) phenomena detectable at high-energy astrophysical scales. The results of two different (coordinate) length measures have been compared both at cosmological time and as a perturbation element on flat Minkowski spacetime. The differences for the components of the corresponding classical(ized) metric tensor have been analyzed at different orders of expansions. The results of the expectation values of a length operator in the universe at the Planck time must be comparable with the same length measurements at present times, as far as the metric tensor is concerned. The comparison of the results of (straight) length measures in two different directions, in particular, can encode the pertinent information about the parameters defining the semiclassical wavefunctional for (semiclassicalized) gravitational field.

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“…The gravitational backreaction from the quantum energy momentum tensor T µν is crucial for understanding the low-energy description of QG and sometimes destabilize the background spacetime. For instance, the instability of de Sitter spacetime has been discussed based on the quantum particle creations of minimally coupled massless scalar or graviton and the thermal feature of cosmological horizon [33][34][35][36][37][38][39][40][41][42][43] The continuous particle production or purely thermodynamic description of de Sitter spacetime imply that de Sitter spacetime might not be stable. However, the instability of the de Sitter spacetime is inconsistent with the naive consideration and has been still under debate [44][45][46][47][48][49][50].…”

Section: Introductionmentioning

confidence: 99%