Turning very long tensor perturbations into effective gravitational waves: An estimate of the gravitons’ back reaction

Maia, M. R. de Garcia; Carvalho, J. C.; Alcaniz, J. S.

doi:10.1103/physrevd.56.6351

Cited by 4 publications

(14 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We will denote by α 1 , β 1 the coeficients associated with the first transition from an arbitrary phase to the radiation dominated era, and by α 2 , β 2 those related with the transition from the radiation to the matter dominated epoch. These coefficents have been obtained in references [3,4] (see also [1]). The coefficient β is then given by [2]…”

Section: Basic Equationsmentioning

confidence: 96%

“…As the inequivalence of vacua appear at different instants of time, we will focus on the time-dependent amplitude of the tensor perturbations µ(k, η), which obeys [1,3,4]…”

Section: Basic Equationsmentioning

confidence: 99%

“…Full details of this approach can be found in Ref. [1] where the equation for a(t) was numerically solved for a model in which the universe evolves from an arbitrary initial phase to a radiation dominated era. It was found that, if the barotropic index γ of the equation of state in the first epoch is close to 2/3, the back reaction of the effective gravitational waves makes a(t) deviate appreciably from the standard behavior a(t) ∝ t 1/2 .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Cosmological gravitons and the expansion dynamics during the matter age

Maia¹,

Carvalho²,

Alcaniz

1999

Phys. Rev. D

Self Cite

View full text Add to dashboard Cite

Extending previous results [Phys. Rev.D 56, 6351 (1997)], we estimate the back reaction of cosmological gravitons in the expansion dynamics, during the matter age. Tensor perturbations with scales larger than the Hubble radius are created due to the inequivalence of vacua at different times. During noninflationary phases these perturbations become effective gravitational waves as they enter the Hubble radius, adding new contributions to the energy density of the subhorizon waves. During the radiation epoch the creation of these effective gravitons may lead to a departure from the standard behaviour a(t) ∝ t 1/2 , with possible consequences to several cosmic processes, such as primordial nucleosynthesis. We examine the implications of this phenomenom during the matter dominated era, assuming an initial inflationary period. The dynamical equation obeyed by the scale factor is derived and numerically solved for different values of the relevant parameters involved. PACS number(s): 04.30. Nk, 04.30.Db, 04.62.+v, 98.80.Cq

show abstract

Section: Basic Equationsmentioning

confidence: 96%

“…As the inequivalence of vacua appear at different instants of time, we will focus on the time-dependent amplitude of the tensor perturbations µ(k, η), which obeys [1,3,4]…”

Section: Basic Equationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Cosmological gravitons and the expansion dynamics during the matter age

Maia¹,

Carvalho²,

Alcaniz

1999

Phys. Rev. D

Self Cite

View full text Add to dashboard Cite

show abstract

“…It is usually assumed that modes with wavelengths larger than the temporary Hubble radius can be discarded, since they are unobservable and not true waves [20], have no appreciable influence on the local wave energy density [21], [22], [23], or appear locally as gauge transformation [24], [18]. The relations (52) and (53) allow a definite answer.…”

Section: B Stress Tensor Evolution In a Fixed Backgroundmentioning

confidence: 99%

“…The general solution of the algebraic constraints (23,24) for the spectral densities contains four complex functions of k and η, which describe polarized background radiation in general. The stochastic background of gravitational waves expected from pre-galactic stages of the Universe could be polarized due to strong anisotropies expected at Planck time.…”

Section: Averaging the Field Equationsmentioning

confidence: 99%

Classical back reaction of low-frequency cosmic gravitational radiation

Dautcourt

1999

Phys. Rev. D

View full text Add to dashboard Cite

We study in a Brill-Hartle type of approximation the back reaction of a superposition of linear gravitational waves on its own mean gravitational field up to second order in the wave amplitudes. The background field is taken as a spatially flat Einstein-de Sitter geometry. In order to follow inflationary scenarios, the wavelengths are allowed to exceed the temporary Hubble distance. As in optical coherence theory, the wave amplitudes are considered as random variables, which form a homogeneous and isotropic stochastic process, sharing the symmetries of the background metric. A segregation of the field equations into equations for the wave amplitudes and equations for the background field is performed by averaging the field equations and interpreting the averaging process as a stochastic (ensemble) average. The spectral densities satisfy a system of ordinary differential equations. The effective stress-energy tensor for the random gravity waves is calculated in terms of correlation functions and covers subhorizon as well as superhorizon modes, where superhorizon modes give in many cases negative contributions to energy density and pressure. We discuss solutions of the second-order equations including pure gravitational radiation universes.

show abstract

Cosmological Gravitons Back Reaction and the Primordial Nucleosynthesis

Maia¹,

Carvalho²,

Alcaniz³

et al. 2000

Symp. - Int. Astron. Union

Self Cite

View full text Add to dashboard Cite

Abstract. The back reaction of effective gravitons created during noninflationary epochs due to the inequivalence of vacuum states at different eras is examined in the context of primordial nucleosynthesis. Our final purpose is to obtain limits on the model employed to study such a process.The inequivalence of vacuum states at different eras of the history of the universe determines the production of gravitational waves in scales larger than the Hubble lengh. During noninflationary periods of expansion, these very long tensor perturbations (VLTP's) enter the Hubble radius, thus becoming effective gravitational waves (EGW's) (Allen 1988). Such an effect adds new contributions to the gravitons energy density Pg within the horizon, the modes energetically meningful, and can be described by using a macroscopic approach to matter creation (see de Garcia Maia et al., 1997 an references therein). This is done by introducing a creation pressure term in the balance equation for Pg and the EWG's back reaction leads to the following dynamical equation for the scale factor a(t) during the radiation era (for the flat case):where H is the Hubble parameter, "[r is the barotropic parameter related to the dominant component of the era denote by the subscript r and the whole R.H.S. is due to the effective gravitons creation process. It can be shown (de Garcia Maia et al. 1997) that given Ir-l, "[r and H (t r ), the explicit expression for Ps is univocally determined in terms of a(t) and o'(t), so that a(t) can be determined.Here, we will consider that a transition occurred between a phase denoted by r = 0, for example an inflationary period, to the radiation era (r = 1). In such a case,where I(t) accounts for the graviton creation and is given by (Carvalho et al. 2000)I(t) = ( 2m o + 1)2r

show abstract

Turning very long tensor perturbations into effective gravitational waves: An estimate of the gravitons’ back reaction

Cited by 4 publications

References 63 publications

Cosmological gravitons and the expansion dynamics during the matter age

Cosmological gravitons and the expansion dynamics during the matter age

Classical back reaction of low-frequency cosmic gravitational radiation

Cosmological Gravitons Back Reaction and the Primordial Nucleosynthesis

Contact Info

Product

Resources

About