Simulating Relic Gravitational Waves from Inflationary Magnetogenesis

Brandenburg, Axel; Sharma, Ramkishor

doi:10.3847/1538-4357/ac1599

Cited by 10 publications

(16 citation statements)

References 80 publications

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“…We should further note that, since the electromagnetic field possesses anisotropic stress, apart from inducing secondary scalar perturbations, they will also generate secondary tensor perturbations (in this context, see, for example, Refs. [36,[95][96][97][98][99][100]). Such a tensor mode will also contribute to the B-mode polarization of the CMB, apart from the contributions to the temperature and E-mode polarizations.…”

Section: B Contributions Due To the Induced Curvature Perturbationsmentioning

confidence: 99%

Circumventing the challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

et al. 2023

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As is well known, in order to generate magnetic fields of observed amplitudes during inflation, the conformal invariance of the electromagnetic field has to be broken by coupling it either to the inflaton or to the scalar curvature. Couplings to scalar curvature pose certain challenges even in slow roll inflation and it seems desirable to consider couplings to the inflaton. It can be shown that, in slow roll inflation, to generate nearly scale invariant magnetic fields of adequate strengths, the nonconformal coupling to the inflaton has to be chosen specifically depending on the inflationary model at hand. In a recent work, we had found that, when there arise sharp departures from slow roll inflation leading to strong features in the scalar power spectra, there inevitably arise sharp features in the spectra of the electromagnetic fields, unless the nonconformal coupling functions are extremely fine tuned. In particular, we had found that, if there occurs an epoch of ultra slow roll inflation (that is often required either to lower scalar power on large scales or to enhance power on small scales), then the strength of the magnetic field over large scales can be severely suppressed. In this work, we examine whether these challenges can be circumvented in models of inflation involving two fields. We show that the presence of the additional scalar field allows us to construct coupling functions that lead to magnetic fields of required strengths even when there arise intermediate epochs of ultra slow roll inflation. However, we find that the features in the spectra of the magnetic fields that are induced due to the departures from slow roll inflation cannot be completely ironed out. We make use of the code MagCAMB to calculate the effects of the magnetic fields on the anisotropies in the cosmic microwave background and investigate if the spectra with features are broadly consistent with the current constraints.

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Section: B Contributions Due To the Induced Curvature Perturbationsmentioning

confidence: 99%

Circumventing the challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

et al. 2023

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“…We should further note that, since the electromagnetic field possesses anisotropic stress, apart from inducing secondary scalar perturbations, they will also generate secondary tensor perturbations (in this context, see, for example, Refs. [35,[90][91][92][93][94][95]). Such a tensor mode will also contribute to the B-mode polarization of the CMB, apart from the contributions to the temperature and E-mode polarizations.…”

Section: B Contributions Due To the Induced Curvature Perturbationsmentioning

confidence: 99%

Challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

et al. 2022

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Primordial magnetic fields are generated during inflation by considering actions that break the conformal invariance of the electromagnetic field. To break the conformal invariance, the electromagnetic fields are coupled either to the inflaton or to the scalar curvature. Also, a parity violating term is often added to the action in order to enhance the amplitudes of the primordial electromagnetic fields. In this work, we examine the effects of deviations from slow roll inflation on the spectra of nonhelical as well as helical electromagnetic fields. We find that, in the case of the coupling to the scalar curvature, there arise certain challenges in generating electromagnetic fields of the desired shapes and strengths even in slow roll inflation. When the field is coupled to the inflaton, it is possible to construct model-dependent coupling functions that lead to nearly scale invariant magnetic fields in slow roll inflation. However, we show that sharp features in the scalar power spectrum generated due to departures from slow roll inflation inevitably lead to strong features in the power spectra of the electromagnetic fields. Moreover, we find that such effects can also considerably suppress the strengths of the generated electromagnetic fields over the scales of cosmological interest. We illustrate these aspects with the aid of inflationary models that have been considered to produce specific features in the scalar power spectrum. Further, we find that, in such situations, if the strong features in the electromagnetic power spectra are to be undone, the choice of the coupling function requires considerable fine tuning. We discuss wider implications of the results we obtain.

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“…( 1), and the magnetic field initial conditions are all chosen in line with Refs. [55,56]. For series A and B, we choose α = 2 to avoid the backreaction problem [57], and β ∈ {7.3, 2.7}, corresponding to reheating temperatures of T r ∈ {100, 0.15} GeV, i.e., the energy levels of EW and QCD phase transitions.…”

Section: A Choice Of Parametersmentioning

confidence: 99%

“…We are interested in studying the leading-order nonlinear term producing gravitational radiation, for which we require strong sources. For this reason, we consider in this work the production of GWs by reheating magnetogeneses, which yield electromagnetic (EM) strengths that depend only on the initial field and can grow several orders of magnitude [55,56]. For simplicity, we defer the study of the nonlinear effect produced by hydromagnetic turbulence from cosmological phase transitions to future work, since it requires a fully relativistic framework to reach plasma and/or Alfvén velocities near speed of light, as expected for very strong sources.…”

Section: Introductionmentioning

confidence: 99%

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Leading-order nonlinear gravitational waves from reheating magnetogeneses

He,

Pol,

Brandenburg

2021

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We study the leading-order nonlinear gravitational waves (GWs) produced by an electromagnetic (EM) stress in reheating magnetogenesis scenarios. Both nonhelical and helical magnetic fields are considered. By numerically solving the linear and leading-order nonlinear GW equations, we find that the GW energy from the latter is usually larger. We compare their differences in terms of the GW spectrum and parameterize the GW energy difference due to the nonlinear term, ∆EGW, in terms of EM energy EEM as ∆EGW = (pEEM/k * ) 3 , where k * is the characteristic wave number, p = 0.84 and 0.88 are found in the nonhelical and helical cases, respectively, with reheating around the QCD energy scale, while p = 0.45 is found at the electroweak energy scale. We also compare the polarization spectrum of the linear and nonlinear cases and find that adding the nonlinear term usually yields a decrease in the polarization that is proportional to the EM energy density. We parameterize the fractional polarization suppression as |∆PGW/PGW| = rEEM/k * and find r = 1.2 × 10 −1 , 7.2 × 10 −4 , and 3.2 × 10 −2 for the helical cases with reheating temperatures Tr = 300 TeV, 8 GeV, and 120 MeV, respectively. Prospects of observation by pulsar timing arrays, space-based interferometers, and other novel detection proposals are also discussed.

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Simulating Relic Gravitational Waves from Inflationary Magnetogenesis

Cited by 10 publications

References 80 publications

Circumventing the challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

Circumventing the challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

Challenges in the choice of the nonconformal coupling function in inflationary magnetogenesis

Leading-order nonlinear gravitational waves from reheating magnetogeneses

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