Hamiltonian analysis of nonlocal F(R) gravity models

Joshi, Pawan; Panda, Sukanta

doi:10.1140/epjc/s10052-022-10557-w

Cited by 4 publications

(3 citation statements)

References 75 publications

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“…It can be observed that M s value is increasing with the rise in the Cu 2+ ions concentration due to the successive reduction in the particle size. This is mainly due to the imbalance in the super exchange interaction between the spins on the surface of the ultrafine nanoparticles or spins get canted on the surface and accounting towards spin canting phenomena [53].…”

Section: Ferroelectric Analysismentioning

confidence: 99%

Advancements in multiferroic, dielectric, and impedance properties of copper–yttrium co-doped cobalt ferrite for hydroelectric cell applications

Jain,

Shankar,

Thakur

2024

J. Phys.: Condens. Matter

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This paper explores yttrium and copper co-doped cobalt ferrite [Co1-xCuxFe1.85Y0.15O4] synthesized via the sol-gel auto combustion route (0.0 ≤ x ≤ 0.08). Investigating the impact of co-dopants on CoFe2O4, the study reveals altered cation distribution affecting structure, multiferroic, and electrical properties. XRD studies show nanocrystalline co-doped cobalt ferrites with lattice expansion and smaller grains due to Cu-Y co-doping. FTIR confirms inverse spinel family classification with tetrahedral lattice shrinkage. FESEM indicates a grain size of approximately 0.12 μm. Ferroelectric analysis reveals a peak saturation polarization of 23.42 μC/cm2 for 8% copper doping, attributed to increased Fe3+ ions at tetrahedral sites. Saturation magnetization peaks at 54.4706 emu/g for 2% Cu2+ ion substitution [Co0.98Cu0.02Fe1.85Y0.15O4] and decreases to 37.09 emu/g for 4% Cu substitution due to irregular iron atom distribution at tetrahedral sites. Dielectric studies uncover Maxwell-Wagner Polarization and high resistance in grain and grain boundaries using Impedance Spectroscopy. Fabricated hydroelectric cells exhibit improved ionic diffusion, suggesting potential applications.

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Section: Ferroelectric Analysismentioning

confidence: 99%

Advancements in multiferroic, dielectric, and impedance properties of copper–yttrium co-doped cobalt ferrite for hydroelectric cell applications

Jain,

Shankar,

Thakur

2024

J. Phys.: Condens. Matter

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“…Apart from these, there have been several propositions that hold the Standard Model of particle physics to be fundamental and intend not to modify that and instead propose modifications on the gravity side. These modifications may include the inclusion of higher derivative terms such as Starobinsky model [28][29][30][31][32][33] or Horndeski theories [34][35][36], and Gauss-Bonnet gravity [37,38], or nonlocal terms [39][40][41][42] which attempt to get rid of issues that plague Einstein-Hilbert gravity. There are also models that incorporate both these features simultaneously in order to fix the problems encountered in one model with features from another, for example the Scalaron-Higgs models [29,32,[43][44][45][46][47][48][49][50][51], which shall be the topic of interest in this work.…”

Section: Introductionmentioning

confidence: 99%

Ultraviolet unitarity violations in non-minimally coupled scalar-Starobinsky inflation

Panda

Altafhussain

Vidyarthi

2023

J. Cosmol. Astropart. Phys.

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We perform the calculation for tree-level ultraviolet unitarity violation scales for scalar-R 2 inflation models by including an additional R 2|Φ|2-type term. Due to certain constraints, we resort to the Einstein frame for our calculations, where we separate our analysis between metric and Palatini formulations. We follow recent works in this line that debunk the naive predictions for unitarity violations in Higgs' inflation models to determine how to accurately estimate the behaviour of scattering amplitudes in the UV limit. Later, we work out different cases by assuming potentials corresponding to known inflation scenarios so we could predict the range of coupling parameters for which the theories would remain unitary up to the Planckian regime. We also try to find the behaviour of the scattering amplitudes for these theories during the transition from inflationary to reheating epoch.

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“…Mostly these theories include terms involving a curvature tensor in the linear order coupled with higher derivatives of the scalar field. The instability can be identified either in the Lagrangian with higher-order derivatives, or through the associated Hamiltonian with the linear momenta [5][6][7][8]. However, there exist stable theories with a Lagrangian containing higher derivatives where the ghosts are avoided by ensuring that the higher derivatives are not a part of the equations of motion.…”

Section: Introductionmentioning

confidence: 99%

Ghost free theory in unitary gauge: a new candidate

Joshi

Panda

Vidyarthi

2023

J. Cosmol. Astropart. Phys.

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We propose an algebraic analysis using a 3+1 decomposition to identify conditions for a clever cancellation of the higher derivatives, which plagued the theory with Ostrogradsky ghosts, by exploiting some existing degeneracy in the Lagrangian. We obtain these conditions as linear equations (in terms of coefficients of the higher derivative terms) and demand that they vanish, such that the existence of nontrivial solutions implies that the theory is degenerate. We find that, for the theory under consideration, no such solutions exist for a general inhomogeneous scalar field, but that the theory is degenerate in the unitary gauge. We, then, find modified FLRW equations and narrow down conditions for which there could exist a de Sitter inflationary epoch. We further find constraints on the coefficients of the remaining higher-derivative interaction terms, based on power-counting renormalizability and tree-level unitarity up to the Planck scale.

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Hamiltonian analysis of nonlocal F(R) gravity models

Abstract: We construct a Hamiltonian for the nonlocal F(R) theory in the present work. By this construction, we demonstrate the nature of the ghost degrees of freedom. Finally, we find conditions that give rise to ghost-free theories.

Cited by 4 publications

References 75 publications

Advancements in multiferroic, dielectric, and impedance properties of copper–yttrium co-doped cobalt ferrite for hydroelectric cell applications

Advancements in multiferroic, dielectric, and impedance properties of copper–yttrium co-doped cobalt ferrite for hydroelectric cell applications

Ultraviolet unitarity violations in non-minimally coupled scalar-Starobinsky inflation

Ghost free theory in unitary gauge: a new candidate

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