Helical magnetic fields from Riemann coupling

Kushwaha, Ashu; Shankaranarayanan, S.

doi:10.1103/physrevd.102.103528

Cited by 16 publications

(14 citation statements)

References 74 publications

(93 reference statements)

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“…This leads to the following crucial question: Is there a set of unique signatures that distinguish MG theories from GR? This section investigates this issue by considering three specific cases: Testing MG theories using gravitational wave (GW) observations [112][113][114][115][116], low-energy observational signatures in cosmological observations [117] and non-minimal coupling of electromagnetic fields leading to observable signatures [118][119][120].…”

Section: What Are the Observational Consequences?mentioning

confidence: 99%

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Modified theories of Gravity: Why, How and What?

Shankaranarayanan,

Johnson

2022

Preprint

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General Relativity (GR) was proven via the direct detection of gravitational waves from the mergers of the binary black holes and binary neutron stars by the Advanced LIGO and Advanced Virgo detectors. These detections confirmed the prediction of GR and provided the first direct evidence of the existence of stellar-mass black holes (BHs). However, the occurrence of singularities at the centers of BHs suggests that GR is inapplicable because of the breakdown of the equivalence principle at the singularities. The fact that these singularities exist indicates that GR cannot be a universal theory of space-time. In the low-energy limit, the theoretical and observational challenges faced by the ΛCDM model also indicate that we might have to look beyond GR as the underlying theory of gravity. Unlike GR, whose field equations contain only up to second-order derivatives, the modified theories with higher derivative Ricci/Riemann tensor gravity models include higher derivatives. Therefore, one expects significant differences between GR and modified theories. Since there are many ways of modifying GR in the strong-gravity and cosmological distances, each model has unique features. This leads to the following crucial question: Are there a set of unique signatures that distinguish GR from modified gravity (MG) theories? This review discusses three aspects of MG theories: (1) Why do we need to consider MG theories? (2) How to modify GR? and (3) What are the observational consequences? The review is written in a pedagogical style with the expectation that it will serve as a useful reference for theorists and observers and those interested in bridging the divide between theory and observations.

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Section: What Are the Observational Consequences?mentioning

confidence: 99%

“…Since both require physics beyond the standard model, there is a tantalizing possibility that the same physics can solve both problems. Recently, it was shown that non-minimal coupling of the electromagnetic field with the Riemann tensor could potentially explain magnetogenesis and baryogenesis [118,119].…”

Section: What Are the Observational Consequences?mentioning

confidence: 99%

Modified theories of Gravity: Why, How and What?

Shankaranarayanan,

Johnson

2022

Preprint

Self Cite

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“…One of the first works along these lines was [125], suggesting the creation of a left-handed PMF due to a change of the Chern-Simons number. Other possible mechanisms include extra dimensions [126], the coupling to the cosmic axion field [127] or an axion-like coupling [128], the Riemann tensor [129], a spectator field [84], or an inherently helical coupling [130] during Inflation in the first place. Recently, also the possibility of helicity generation via a chiral cosmological medium around the EWPT has been considered [131], however the authors found the effect to be suppressed due to the value of the baryon to entropy ratio.…”

Section: Post-inflationarymentioning

confidence: 99%

The Gamma-ray Window to Intergalactic Magnetism

Batista

Saveliev

2021

Universe

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One of the most promising ways to probe intergalactic magnetic fields (IGMFs) is through gamma rays produced in electromagnetic cascades initiated by high-energy gamma rays or cosmic rays in the intergalactic space. Because the charged component of the cascade is sensitive to magnetic fields, gamma-ray observations of distant objects such as blazars can be used to constrain IGMF properties. Ground-based and space-borne gamma-ray telescopes deliver spectral, temporal, and angular information of high-energy gamma-ray sources, which carries imprints of the intervening magnetic fields. This provides insights into the nature of the processes that led to the creation of the first magnetic fields and into the phenomena that impacted their evolution. Here we provide a detailed description of how gamma-ray observations can be used to probe cosmic magnetism. We review the current status of this topic and discuss the prospects for measuring IGMFs with the next generation of gamma-ray observatories.

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“…where it may be observed that m4 obeys a first order differential Eq. (39). With these choice of EFT parameters, the scalar Mukhanov-Sasaki equation takes the following form, ṽ (k, η)…”

Section: Solving For the Electromagnetic Mode Function And Metric Per...mentioning

confidence: 99%

“…[1], the observable quantities like scalar spectral index and tensor to scalar ratio are indeed compatible with the Planck constraints in the present EFT context where the EFT coefficients satisfy Eq. (39). Thereby using the viable value(s) of n s and A s , in particular we will consider n s = 0.9649 and ln [10 10 A s ] = 3.044 (i.e the central values of n s and A s in respect to the Planck constraints), one can determine Ḣ * and Ḧ * from Eq.…”

Section: B Reheating With Time Independent Equation Of State: Evoluti...mentioning

confidence: 99%

Effective Theory of Inflationary Magnetogenesis and Constraints on Reheating

Maity,

Pal,

Paul

2021

Preprint

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Effective theory framework based on symmetry has recently gained widespread interest in the field of cosmology. In this paper, we apply the same idea on the genesis of the primordial magnetic field and its evolution throughout the cosmological universe. Given the broken time-diffeomorphism symmetry by the cosmological background, we considered the most general Lagrangian of electromagnetic and metric fluctuation up to second order, which naturally breaks conformal symmetry in the electromagnetic (EM) sector. We also include parity violation in the electromagnetic sector with the motivation that has potential observational significance. In such a set-up, we explore the evolution of EM, scalar, and tensor perturbations considering different observational constraints. In our analysis we emphasize the role played by the intermediate reheating phase which has got limited interest in all the previous studies. Assuming the vanishing electrical conductivity during the entire period of reheating, the well-known Faraday electromagnetic induction has been shown to play a crucial role in enhancing the strength of the present-day magnetic field. We show how such physical effects combined with the PLANCK and the large scale magnetic field observation makes a large class of models viable and severely restricts the reheating equation of state parameter within a very narrow range of 0.01 < ω eff < 0.27, which is nearly independent of reheating scenarios we have considered.

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Helical magnetic fields from Riemann coupling

Cited by 16 publications

References 74 publications

Modified theories of Gravity: Why, How and What?

Modified theories of Gravity: Why, How and What?

The Gamma-ray Window to Intergalactic Magnetism

Effective Theory of Inflationary Magnetogenesis and Constraints on Reheating

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