Duality and scale invariant magnetic fields from bouncing universes

Chowdhury, Debika; Sriramkumar, L.; Jain, Rajeev Kumar

doi:10.1103/physrevd.94.083512

Cited by 22 publications

(25 citation statements)

References 147 publications

(247 reference statements)

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“…We are interested in considering the fruitful sourced fluctuations idea with the contracting background. Deviating from the scalar field(s) framework of bouncing models, and considering sourced fluctuations, the above stated predictions change considerably [31][32][33][34][35]. In [35] it was demonstrated for the first time that even in a bouncing model, a nearly scale invariant tensor spectrum can be generated due to sourced fluctuations.…”

Section: Introductionmentioning

confidence: 97%

Sourced scalar fluctuations in bouncing cosmology

Ben-Dayan

Kupferman

2019

J. Cosmol. Astropart. Phys.

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We calculate the scalar power spectrum generated by sourced fluctuations due to coupling between the scalar field, which holds most of the energy density of the universe, and a gauge field for a general FLRW metric. For this purpose we calculate the curvature perturbation to second order in the presence of gauge fields, and show that the gauge fields behave like an additional potential term. We then apply the analysis to the case of slow-contraction. Due to the interaction between the scalar field and gauge fields additional 'sourced' tensor and scalar spectra are generated. The resulting spectra are chiral, slightly blue and arbitrarily close to scale invariance. The only difference between the tensor and scalar spectra is the coupling constant with an O(1) numerical coefficient, and some momentum space polarization vectors. As a result the tilt of the spectra are the same. For the nearly scale invariant case, the momentum integration gives the same leading contribution. Hence, r 1 where the deviation from unity is controlled by the deviation from scale invariance, and is not in agreement with CMB observations. Deviating considerably from near scale invariance, and considering a bluer tilt with n T > 0.12, the model cannot account for CMB observations, but can be detected by LIGO and/or LISA in the future.

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Section: Introductionmentioning

confidence: 97%

Sourced scalar fluctuations in bouncing cosmology

Ben-Dayan

Kupferman

2019

J. Cosmol. Astropart. Phys.

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“…We can now analytically evaluate the power spectrum after the bounce at η = β η 0 . We find that the power spectrum of the magnetic field retains its scale dependence across the bounce [65]. In the scale invariant case corresponding toγ = 3, the amplitude of the power spectrum for k/(α k 0 ) ≪ 1 can be determined to be…”

Section: This Equation Can Be Integrated Twice To Yield [65]mentioning

confidence: 77%

“…Further, the corresponding consistency relation is violated in the bouncing model. It should be noted that the bouncing scenario that we have considered here suffers from considerable backreaction in the vicinity of the bounce [64,65], which can possibly be responsible for the large non-Gaussianities that we encounter. This issue of circumventing the backreaction in the proximity of the bounce is non-trivial and needs to be investigated in more detail.…”

Section: Discussionmentioning

confidence: 94%

“…Under these conditions, we have J ′′ /J ≃γ (γ − 1)/η 2 , which is of the same form as in the inflationary case that we had discussed in the previous sub-section. Therefore, in the first domain, we can express the electromagnetic modesĀ k in terms of the Hankel function H (1) ν (x) as follows [64,65]:…”

Section: The Bouncing Scenariosmentioning

confidence: 99%

“…In these models, the universe goes through a period of contraction followed by an expanding phase, with a 'bounce' connecting the two epochs. Lately, there have been some efforts towards understanding the generation of magnetic fields in the bouncing scenarios [62][63][64][65][66][67][68].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Cross-correlations between scalar perturbations and magnetic fields in bouncing universes

Chowdhury

Sriramkumar

Kamionkowski

2019

J. Cosmol. Astropart. Phys.

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Bouncing scenarios offer an alternative to the inflationary paradigm for the generation of perturbations in the early universe. Recently, there has been a surge in interest in examining the issue of primordial magnetogenesis in the context of bouncing universes. As in the case of inflation, the conformal invariance of the electromagnetic action needs to be broken in bouncing scenarios in order to generate primordial magnetic fields which correspond to observed strengths today. The non-minimal coupling, which typically depends on a scalar field that possibly drives the homogeneous background, leads to a cross-correlation at the level of the three-point function between the perturbation in the scalar field and the magnetic fields. This has been studied in some detail in the context of inflation and, specifically, it has been established that the three-point function satisfies the so-called consistency relation in the squeezed limit. In this work, we study the cross-correlation between the magnetic fields and the perturbation in an auxiliary scalar field in a certain class of bouncing scenarios. We consider couplings that lead to scale invariant spectra of the magnetic field and evaluate the corresponding cross-correlation between the magnetic field and the perturbation in the scalar field. We find that, when compared to de Sitter inflation, the dimensionless non-Gaussianity parameter that characterizes the amplitude of the cross-correlations proves to be considerably larger in bouncing scenarios. We also show that the aforementioned consistency condition governing the cross-correlation is violated in the bouncing models. We discuss the implications of our results.

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Primordial magnetic fields from gravitationally coupled electrodynamics in nonsingular bounce cosmology

Chen

et al. 2018

Sci. China Phys. Mech. Astron.

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We in this paper study the generation of primordial magnetic field (PMF) in the non-singular bouncing scenario, through the coupling of the electromagnetic field to gravity. We adopt an electrodynamic model with a coupling coefficient as a function of the scale factor a, i.e. f = 1 + (a/a ) −n , with a and n > 0 being constants. The result implies that in this mechanism, the power spectrum of PMF today is always blue tilted on large scales from 1 Mpc to the Hubble length, and the observational constraints favor the ekpyrotic-bounce scenario. Furthermore, the back reaction of the energy density of PMF at the bouncing point yields theoretical constraints on the bouncing model.

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Duality and scale invariant magnetic fields from bouncing universes

Cited by 22 publications

References 147 publications

Sourced scalar fluctuations in bouncing cosmology

Sourced scalar fluctuations in bouncing cosmology

Cross-correlations between scalar perturbations and magnetic fields in bouncing universes

Primordial magnetic fields from gravitationally coupled electrodynamics in nonsingular bounce cosmology

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