Gravitational waves in ghost free bimetric gravity

Mohseni, Morteza

doi:10.1088/1475-7516/2012/11/023

Cited by 19 publications

(14 citation statements)

References 89 publications

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“…It is very illustrative to study the wavefront-coordinate sum-separable solutions to the decoupled exact excitations (22). This procedure provides a quick integration and, more importantly, reveals the d.o.f.…”

Section: Separable Configurationsmentioning

confidence: 99%

“…Let us return to the most general case in which the effective mass is not trivial and the AdS waves are described by the decoupled exact excitations (21) obeying the system (22). Once again, in order to exhibit the decomposition in the prevailing modes we will search for decoupled solutions that are sum separable with respect to the wavefront coordinates, i.e., ℱðu; y; xÞ ¼ X 1 ðu; xÞ þ Y 1 ðu; yÞ and ℋðu; y; xÞ ¼ X 2 ðu; xÞ þ Y 2 ðu; yÞ.…”

Section: B Massive Profilesm ≠mentioning

confidence: 99%

“…[22] under the restriction that both metrics have the same profile. As we will see in the next section, the interaction terms inherently include cosmological constants for both metrics; hence, it is natural to search for wave solutions that can be interpreted as being propagated over (anti-)de Sitter [(A)dS] backgrounds.…”

Section: Introductionmentioning

confidence: 99%

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Exact ghost-free bigravitational waves

et al. 2018

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We study the propagation of exact gravitational waves in the ghost-free bimetric theory. Our focus is on type-N spacetimes compatible with the cosmological constants provided by the bigravity interaction potential, and particularly in the single class known by allowing at least a Killing symmetry: the AdS waves. They have the advantage of being represented by a generalized Kerr-Schild transformation from AdS spacetime. This entails a notorious simplification in bigravity by allowing to straightforwardly compute any power of its interaction square root matrix, opening the door to explore physically meaningful exact configurations. For these exact gravitational waves the complex dynamical structure of bigravity decomposes into elementary exact massless or massive excitations propagating on AdS. We use a complexified formulation of the Euler-Darboux equations to provide for the first time the general solutions to the massive version of the Siklos equation which rules the resulting AdS-wave dynamics, using an integral representation originally due to Poisson. Inspired by this progress, we tackle the subtle problem of how matter couples to bigravity and, more concretely, if this occurs through a composite metric, which is hard to handle in a general setting. Surprisingly, the Kerr-Schild ansatz brings again a huge simplification in how the related energy-momentum tensors are calculated. This allows us to explicitly characterize AdS waves supported by either a massless free scalar field or a wavefront-homogeneous Maxwell field. Considering the most general allowed Maxwell source instead is a highly nontrivial task, which we accomplish by again exploiting the complexified Euler-Darboux description and taking advantage of the classical Riemann method. In fact, this eventually allows us to find the most general configurations for any matter source.

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Section: Separable Configurationsmentioning

confidence: 99%

Section: B Massive Profilesm ≠mentioning

confidence: 99%

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Exact ghost-free bigravitational waves

et al. 2018

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“…If = 0, we can nonholonomically induce a nontrivial μ ϒ. Inverse nonlinear transforms are possible if we change mutually the left labels μ with f . It should be noted that above classes of metrics can be extended to describe exact solutions with nonholonomically ( 18) and take instead of (17) the value w i = ∂ i / . It is possible to re-write all coefficients in terms of the generating function , or in terms ofˇ .…”

Section: Exact Off-diagonal Solutions In Mgftmentioning

confidence: 99%

“…[14,15] for possible effective actions). Cosmological implications of massive gravity were also analyzed in the framework of modified gravity theories, MGT, [16][17][18][19][20][21][22][23], and also cosmological models related to bi-metric gravity [24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Ghost-free massive $$f(R)$$ f ( R ) theories modeled as effective Einstein spaces and cosmic acceleration

Vacaru

2014

Eur. Phys. J. C

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We study how massive ghost-free gravity f (R)-modified theories, MGFTs, can be encoded into generic off-diagonal Einstein spaces. Using "auxiliary" connections completely defined by the metric fields and adapted to nonholonomic frames with associated nonlinear connection structure, we decouple and integrate in certain general forms the field equations in MGFT. Imposing additional nonholonomic constraints, we can generate Levi-Civita, LC, configurations and mimic MGFT effects via off-diagonal interactions of effective Einstein and/or Einstein-Cartan gravity with nonholonomically induced torsion. We show that imposing nonholonomic constraints it is possible reproduce very specific models of massive f (R) gravity studied in Cai et al. (arXiv:1307.7150, 2013, Klusoňet al. (Phys Lett B 726:918, 2013), Nojiri and Odintov (Phys Lett B 716:377, 2012) and Nojiri et al. (JCAP 1305:020, 2013. The cosmological evolution of ghost-free off-diagonal Einstein spaces is investigated. Certain compatibility of MGFT cosmology to small off-diagonal deformations of CDM models is established.

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Prospects for domestic biofuels for transport in Sweden 2030 based on current production and future plans

Grahn

Hansson

2014

WIREs Energy & Environment

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Currently, Sweden has the largest share of renewable fuels for transport in the EU. The ambition of the Swedish Government for 2030 is for a vehicle fleet independent of fossil fuels. This paper assesses the potential future contribution of domestically produced biofuels for transport in Sweden to 2030, based on a mapping of the prospects from the actual and potential Swedish biofuel producers. There are plans for cellulose-based ethanol, methanol, DME (dimethyl ether), methane, and the biodiesel option HVO (hydrotreated vegetable oil). Continued domestic production of biofuels at current levels and the realization of all the ongoing mapped plans for additional biofuels production result in potential domestic biofuels production of 18 TWh fuel in 2023. When assuming a continued expansion of biofuels production capacity, the potential domestic biofuels production reaches about 26 TWh fuel in 2030. If the realization of the mapped biofuels plans is delayed by 5 years and the pace of continued implementation of additional biofuel capacity is also reduced, the potential domestic biofuels production is reduced to about 8 TWh fuel and 20 TWh fuel biofuels in 2020 and 2030, respectively. These two scenarios correspond to a share of biofuels of the total future energy demand for road transport in Sweden at about 10-30% in 2020 and 26-79% in 2030, depending on which official energy demand scenario is used. The actual contribution of biofuels for road transport will depend on, e.g., policies, the global development for fossil fuels and biofuels, the competition for biomass and biofuels, and future energy demand in the road transport sector.

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Gravitational waves in ghost free bimetric gravity

Cited by 19 publications

References 89 publications

Exact ghost-free bigravitational waves

Exact ghost-free bigravitational waves

Ghost-free massive $$f(R)$$ f ( R ) theories modeled as effective Einstein spaces and cosmic acceleration

Prospects for domestic biofuels for transport in Sweden 2030 based on current production and future plans

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