A
bstract
Primordial SU(2) gauge fields with an isotropic background lead to the production of spin-2 particles during inflation. We provide a unified formalism to compute this effect in all of the ...inflation models with isotropic SU(2) gauge fields such as Gauge-flation and Chromo-Natural inflation with and without spectator axion fields or the mass of the gauge field from the Higgs mechanism. First, we calculate the number and energy densities of the spin-2 particles. We then obtain exact analytical formulae for their backreaction on the background equations of motion of SU(2) and axion fields in (quasi) de Sitter expansion, which were calculated only numerically for one particular model in the literature. We show that the backreaction is directly related to the number density of the spin-2 field. Second, we relate the number density of the spin-2 particles to the power spectrum and the energy density of the gravitational waves sourced by them. Finally, we use the size of the backreaction to constrain the parameter space of the models. We find that the tensor-to-scalar ratio of the sourced gravitational waves can at most be on the order of that of the vacuum contribution to avoid a large backreaction on slow-roll dynamics of the gauge ssand axion fields in quasi-de Sitter expansion.
Inflationary models are usually based on dynamics of one or more scalar fields coupled to gravity. In this work we present a new class of inflationary models, gauge-flation or non-Abelian gauge field ...inflation, where slow-roll inflation is driven by a non-Abelian gauge field. This class of models is based on a gauge field theory with a generic non-Abelian gauge group minimally coupled to gravity. We then focus on a particular gauge-flation model by specifying the action for the gauge theory. This model has two parameters which can be determined using the current cosmological data and has the prospect of being tested by Planck satellite data. Moreover, the values of these parameters are within the natural range of parameters in generic grand unified theories of particle physics.
A
bstract
Non-Abelian gauge fields may exist during inflation. We study the Schwinger effect by an SU(2) gauge field coupled to a charged scalar doublet in a (quasi) de Sitter background and the ...possible backreaction of the generated charged particles on the homogeneous dynamics. Contrary to the Abelian U(1) case, we find that both the Schwinger pair production and the induced current decrease as the interaction strength increases. The reason for this suppression is the isotropic vacuum expectation value of the SU(2) field which generates a (three times) greater effective mass for the scalar field than the U(1). In the weak interaction limit, the above effect is negligible and both the SU(2) and U(1) cases exhibit a linear increase of the current and a constant conductivity with the interaction strength. We conclude that the Schwinger effect does not pose a threat to the dynamics of inflationary models involving an SU(2) gauge field.
In this work we revisit Wald's cosmic no-hair theorem R. M. Wald, Phys. Rev. D 28, 2118 (1983) (http://dx.doi.org/10.1103/PhysRevD.28.2118). in the context of accelerating Bianchi cosmologies for a ...generic cosmic fluid with nonvanishing anisotropic stress tensor and when the fluid energy-momentum tensor is of the form of a cosmological constant term plus a piece which does not respect strong or dominant energy conditions. Such a fluid is the one appearing in inflationary models. We show that for such a system anisotropy may grow, in contrast to the cosmic no-hair conjecture. In particular, for a generic inflationary model we show that there is an upper bound on the growth of anisotropy. For slow-roll inflationary models, our analysis can be refined further and the upper bound is found to be of the order of slow-roll parameters. We examine our general discussions and our extension of Wald's theorem for three classes of slow-roll inflationary models, generic multiscalar field driven models, anisotropic models involving U(1) gauge fields and the gauge-flation scenario.
Gauge fields and inflation Maleknejad, A.; Sheikh-Jabbari, M.M.; Soda, J.
Physics reports,
07/2013, Letnik:
528, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The isotropy and homogeneity of the cosmic microwave background (CMB) favors “scalar driven” early Universe inflationary models. However, gauge fields and other non-scalar fields are far more common ...at all energy scales, in particular at high energies seemingly relevant to inflation models. Hence, in this review we consider the role and consequences, theoretical and observational, that gauge fields can have during the inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main classes of models with gauge fields in the background, models which show violation of the cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era.
Primordial SU(2) gauge fields with an isotropic background lead to the
production of spin-2 particles during inflation. We provide a unified formalism
to compute this effect in all of the inflation ...models with isotropic SU(2)
gauge fields such as Gauge-flation and Chromo-Natural inflation with and
without spectator axion fields or the mass of the gauge field from the Higgs
mechanism. First, we calculate the number and energy densities of the spin-2
particles. We then obtain exact analytical formulae for their backreaction on
the background equations of motion of SU(2) and axion fields in (quasi) de
Sitter expansion, which were calculated only numerically for one particular
model in the literature. We show that the backreaction is directly related to
the number density of the spin-2 field. Second, we relate the number density of
the spin-2 particles to the power spectrum and the energy density of the
gravitational waves sourced by them. Finally, we use the size of the
backreaction to constrain the parameter space of the models. We find that the
tensor-to-scalar ratio of the sourced gravitational waves can at most be on the
order of that of the vacuum contribution to avoid a large backreaction on
slow-roll dynamics of the gauge and axion fields in quasi-de Sitter expansion.
In this work, we study a new quintessence model associated with non-Abelian gauge fields, minimally coupled to Einstein gravity. This gauge theory has been recently introduced and studied as an ...inflationary model, called gauge-flation. Here, however, we are interested in the late time cosmology of the model in the presence of matter and radiation to explain the present time accelerating Universe. During the radiation and matter eras, the gauge field tracks radiation and basically acts like a dark radiation sector. As we approach lower redshifts, the dark component takes the form of a dark energy source which eventually becomes the dominate part of the energy budget of the Universe. Due to the tracking feature of our model, solutions with different initial values are attracted to a common trajectory. The existence of early dark radiation is a robust prediction of our model which contributes to the effective number of relativistic species, \(N_{\rm eff}\) and has its own interesting observational features.
Primordial SU(2) gauge fields with an isotropic background lead to the production of spin-2 particles during inflation. We provide a unified formalism to compute this effect in all of the inflation ...models with isotropic SU(2) gauge fields such as Gauge-flation and Chromo-Natural inflation with and without spectator axion fields or the mass of the gauge field from the Higgs mechanism. First, we calculate the number and energy densities of the spin-2 particles. We then obtain exact analytical formulae for their backreaction on the background equations of motion of SU(2) and axion fields in (quasi) de Sitter expansion, which were calculated only numerically for one particular model in the literature. We show that the backreaction is directly related to the number density of the spin-2 field. Second, we relate the number density of the spin-2 particles to the power spectrum and the energy density of the gravitational waves sourced by them. Finally, we use the size of the backreaction to constrain the parameter space of the models. We find that the tensor-to-scalar ratio of the sourced gravitational waves can at most be on the order of that of the vacuum contribution to avoid a large backreaction on slow-roll dynamics of the gauge and axion fields in quasi-de Sitter expansion.
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