Fermionic isocurvature perturbations

Chung, Daniel J. H.; Yoo, Hojin; Zhou, Peng

doi:10.1103/physrevd.91.043516

Cited by 16 publications

(19 citation statements)

References 139 publications

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“…There are many models for gravitationally produced dark matter with different mass ranges and different types of interactions [50][51][52][53][54][55][56][57]. One may ask if it is possible to determine some properties of such dark matter independently of the details of these models.…”

Section: Introductionmentioning

confidence: 99%

Gravitational production of superheavy dark matter and associated cosmological signatures

Nakama

Sou

et al. 2019

J. High Energ. Phys.

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We study the gravitational production of super-Hubble-mass dark matter in the very early universe. We first review the simplest scenario where dark matter is produced mainly during slow roll inflation. Then we move on to consider the cases where dark matter is produced during the transition period between inflation and the subsequent cosmological evolution. The limits of smooth and sudden transitions are studied, respectively. The relic abundances and the cosmological collider signals are calculated.

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Section: Introductionmentioning

confidence: 99%

Gravitational production of superheavy dark matter and associated cosmological signatures

Nakama

Sou

et al. 2019

J. High Energ. Phys.

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“…Physical effects of free fermionic fields viewed as perturbations propagating in a flat cosmology, both during inflation and in other epochs of the Universe, have been discussed in several works, treating them as test fields in the framework of quantum field theory [6][7][8][9][10][11][12][13]. The first analyses that studied fermions in quantum cosmology, that is, assuming that the cosmological homogeneous background is as well a quantum entity, can be traced back to the 70's [14,15].…”

Section: Introductionmentioning

confidence: 99%

Fermions in hybrid loop quantum cosmology

2017

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This work pioneers the quantization of primordial fermion perturbations in hybrid Loop Quantum Cosmology (LQC). We consider a Dirac field coupled to a spatially flat, homogeneous, and isotropic cosmology, sourced by a scalar inflaton, and treat the Dirac field as a perturbation. We describe the inhomogeneities of this field in terms of creation and annihilation variables, chosen to admit a unitary evolution if the Dirac fermion were treated as a test field. Considering instead the full system, we truncate its action at quadratic perturbative order and construct a canonical formulation. In particular this implies that, in the global Hamiltonian constraint of the model, the contribution of the homogeneous sector is corrected with a quadratic perturbative term. We then adopt the hybrid LQC approach to quantize the full model, combining the loop representation of the homogeneous geometry with the Fock quantization of the inhomogeneities. We assume a Born-Oppenheimer ansatz for physical states and show how to obtain a Schrödinger equation for the quantum evolution of the perturbations, where the role of time is played by the homogeneous inflaton. We prove that the resulting quantum evolution of the Dirac field is indeed unitary, despite the fact that the underlying homogeneous geometry has been quantized as well. Remarkably, in such evolution, the fermion field couples to an infinite sequence of quantum moments of the homogeneous geometry. Moreover, the evolved Fock vacuum of our fermion perturbations is shown to be an exact solution of the Schrödinger equation. Finally, we discuss in detail the quantum backreaction that the fermion field introduces in the global Hamiltonian constraint. For completeness, our quantum study includes since the beginning (gauge-invariant) scalar and tensor perturbations, that were studied in previous works.

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“…where the subscript p stands for physical quantities, so k p = k/a, w p = w/a. Also the piece in the product coming from the initial vacuum and an oscillatory term has been discarded, as it has been done as well in [52,53]; in the literature this is called normal ordering or renormalization of the product. In this way we can obtain the expectation value for a massive fermion during Inflation as a function of its mass as shown in Figure 3…”

Section: Massive Fermion Productionmentioning

confidence: 99%

Gravitationally produced top quarks and the stability of the electroweak vacuum during inflation

Roman

Fairbairn

2019

Phys. Rev. D

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In the standard model the (Brout-Englert-)Higgs quartic coupling becomes negative at high energies rendering our current electroweak vacuum metastable, but with an instability timescale much longer than the age of the Current Universe. During cosmological Inflation, unless there is a non-minimal coupling to gravity, the Higgs field is pushed away from the origin of its potential due to quantum fluctuations. It is therefore a mystery how we have remained in our current vacuum if we went through such a period of Inflation. In this work we study the effect of top quarks created gravitationally during Inflation and their effect upon the Higgs potential using only General Relativity with minimal couplings and Standard Model particle physics. We show how the evolution of the Higgs field during Inflation is modified coming to the conclusion that this effect is non negligible for scales of Inflation close to or larger than the stability scale but small for scales where the Higgs is stable. Also, we briefly discuss the effect of other fermions to the Higgs instability.

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Fermionic isocurvature perturbations

Cited by 16 publications

References 139 publications

Gravitational production of superheavy dark matter and associated cosmological signatures

Gravitational production of superheavy dark matter and associated cosmological signatures

Fermions in hybrid loop quantum cosmology

Gravitationally produced top quarks and the stability of the electroweak vacuum during inflation

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