Is the number of photons conserved in an expanding universe?

This article provides a general study of the Hamiltonian stability and the hyperbolicity of vector field models involving both a general function of the Faraday tensor and its dual, f (F 2 , FF ), as well as a Proca potential for the vector field, V (A 2 ). In particular it is demonstrated that theories involving only f (F 2 ) do not satisfy the hyperbolicity conditions. It is then shown that in this class of models, the cosmological dynamics always dilutes the vector field. In the case of a nonminimal coupling to gravity, it is established that theories involving Rf (A 2 ) or Rf (F 2 ) are generically pathologic. To finish, we exhibit a model where the vector field is not diluted during the cosmological evolution, because of a nonminimal vector field-curvature coupling which maintains second-order field equations. The relevance of such models for cosmology is discussed.

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“…It should be underlined that the above conclusion only applies to kinetic terms of the form (53). As shown in Ref.…”

Section: -(45) the Equation Of Motion Gets An Extra Termmentioning

confidence: 85%

Vector theories in cosmology

2010

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“…The case q 1 = q 2 = 0 was investigated in [5,6]. For q 2 = q 3 = 0 one obtains a model considered in [15].…”

Section: General Formalismmentioning

confidence: 99%

“…ik is proportional to the corresponding term in [15], the part T (3) ik reproduces the stress-energy tensor of [16]. The tensor T (2) ik is new.…”

Section: Non-minimal Constitutive Equationsmentioning

confidence: 99%

“…Most of the investigations so far were devoted to the analysis of the nonminimally modified Maxwell equations on a given background. With the exceptions [8] and [15] the impact of the non-minimal coupling on the gravitational field has been outside the focus of interest. However, one may expect that the rich structure of such type of theories gives rise to novel features in the gravitational dynamics as well.…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic cosmological models with nonminimally coupled magnetic field

Balakin

Zimdahl

2005

Phys. Rev. D

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Motivated by the structure of one-loop vacuum polarization effects in curved spacetime we discuss a non-minimal extension of the EinsteinMaxwell equations. This formalism is applied to Bianchi I models with magnetic field. We obtain several exact solutions of the non-minimal system including those which describe an isotropization process. We show that there are inflationary solutions in which the cosmological constant is determined by the non-minimal coupling parameters. Furthermore, we find an isotropic de Sitter solution characterized by a "screening" of the magnetic field as a consequence of the non-minimal coupling.

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“…Refs. [28][29][30][31][32][33][34][35][36][37][38][39]. Reference 38 revived, as well, the interest in the paradigm: curvature coupling and equivalence principle, various aspects of which are being discussed (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Nonminimal Isotropic Cosmological Model With Yang–mills and Higgs Fields

Balakin

Dehnen

Zayats

2008

Int. J. Mod. Phys. D

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We establish a nonminimal Einstein-Yang-Mills-Higgs model, which contains six coupling parameters. The first three parameters relate to the nonminimal coupling of a non-Abelian gauge field and a gravity field, the next two parameters describe the so-called derivative nonminimal coupling of a scalar multiplet with a gravity field, and the sixth parameter introduces the standard coupling of a scalar field with a Ricci scalar. The formulated six-parameter nonminimal Einstein-Yang-Mills-Higgs model is applied to cosmology. We show that there exists a unique exact cosmological solution of the de Sitter type for a special choice of the coupling parameters. The nonminimally extended Yang-Mills and Higgs equations are satisfied for arbitrary gauge and scalar fields, when the coupling parameters are specifically related to the curvature constant of the isotropic space-time. Based on this special exact solution, we discuss the problem of a hidden anisotropy of the Yang-Mills field, and give an explicit example, when the nonminimal coupling effectively screens the anisotropy induced by the Yang-Mills field and thus restores the isotropy of the model.

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Is the number of photons conserved in an expanding universe?

Cited by 12 publications

References 13 publications

Vector theories in cosmology

Vector theories in cosmology

Anisotropic cosmological models with nonminimally coupled magnetic field

Nonminimal Isotropic Cosmological Model With Yang–mills and Higgs Fields

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