Gravitational collapse of a homogeneous scalar field in deformed phase space

Rasouli, S. M. M.; Ziaie, Amir Hadi; Marto, João; Moniz, Paulo Vargas

doi:10.1103/physrevd.89.044028

Cited by 31 publications

(31 citation statements)

References 196 publications

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“…Let us therefore employ a specific type of a canonical noncommutativity, which is obtained by means of an appropriate deformation on the classical phase space variables. Our choice has been seldom [20] used in the literature, namely in inflationary settings but has computational advantages. We will explain that the corresponding equations of motion (associated to the deformed scenario) can still be obtained by employing the Hamiltonian (4), being evaluated on variables which satisfy the deformed Poisson bracket.…”

Section: Noncommutative Cosmological Scenariomentioning

confidence: 99%

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Inflationary universe in deformed phase space scenario

et al. 2018

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We consider a noncommutative (NC) inflationary model with a homogeneous scalar field minimally coupled to gravity. The particular NC inflationary setting herein proposed, produces entirely new consequences as summarized in what follows. We first analyze the free field case and subsequently examine the situation where the scalar field is subjected to a polynomial and exponential potentials. We propose to use a canonical deformation between momenta, in a spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) universe, and while the Friedmann equation (Hamiltonian constraint) remains unaffected the Friedmann acceleration equation (and thus the Klein-Gordon equation) is modified by an extra term linear in the NC parameter. This concrete noncommutativity on the momenta allows interesting dynamics that other NC models seem not to allow. Let us be more precise. This extra term behaves as the sole explicit pressure that under the right circumstances implies a period of accelerated expansion of the universe. We find that in the absence of the scalar field potential, and in contrast with the commutative case, in which the scale factor always decelerates, we obtain an inflationary phase for small negative values of the NC parameter. Subsequently, the period of accelerated expansion is smoothly replaced by an appropriate deceleration phase providing an interesting model regarding the graceful exit problem in inflationary models. This last property is present either in the free field case or under the influence of the scalar field potentials considered here. Moreover, in the case of the free scalar field, we show that not only the horizon problem is solved but also there is some resemblance between the evolution equation of the scale factor associated to our model and that for the R 2 (Starobinsky) inflationary model. Therefore, our herein NC model not only can be taken as an appropriate scenario to get a successful kinetic inflation, but also is a convenient setting to obtain inflationary universe possessing the graceful exit when scalar field potentials are present.

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Section: Noncommutative Cosmological Scenariomentioning

confidence: 99%

“…In addition, one evident but very pertinent impact of the NC deformation studied in this work is that the NC dependent terms in Eqs. (16)- (20) are, at least, proportional to the inverse square of the scale factor a(t). Therefore, it is expected that the NC effect should be noticeable at the initial stage of inflation and very residual at its end.…”

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confidence: 99%

Inflationary universe in deformed phase space scenario

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“…In addition, there are higher-order gravities including the special case f (R) gravity [13][14][15][16][17][18][19], the induced gravity [20,21], the scalar-tensor theories with the special case of Brans-Dicke theory [22][23][24][25][26][27][28], higher-dimensional theories, e.g., the Kaluza-Klein theories [29] and the braneworld scenarios [30]. Also, there are theories that introduce some modifications in the matter component [31,32] or change the geometrical structure, e.g., the non-commutative theories [33][34][35][36][37][38].…”

Section: Introductionmentioning

confidence: 99%

Cosmological and solar system consequences off(R,T)gravity models

2014

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To find more deliberate f (R, T ) cosmological solutions, we proceed our previous paper further by studying some new aspects of the considered models via investigation of some new cosmological parameters/quantities to attain the most acceptable cosmological results. Our investigations are performed by applying the dynamical system approach. We obtain the cosmological parameters/quantities in terms of some defined dimensionless parameters that are used in constructing the dynamical equations of motion. The investigated parameters/quantities are the evolution of the Hubble parameter and its inverse, the "weight function", the ratio of the matter density to the dark energy density and its time variation, the deceleration, the jerk and the snap parameters, and the equation-of-state parameter of the dark energy. We numerically examine these quantities for two general models R + αR −n + √ −T and R log [αR] q + √ −T . All considered models have some inconsistent quantities (with respect to the available observational data), except the model with n = −0.9 which has more consistent quantities than the other ones. By considering the ratio of the matter density to the dark energy density, we find that the coincidence problem does not refer to a unique cosmological event, rather, this coincidence also occurred in the early universe. We also present the cosmological solutions for an interesting model R+c1 √ −T in the non-flat FLRW metric. We show that this model has an attractor solution for the late times, though with w (DE) = −1/2. This model indicates that the spatial curvature density parameter gets negligible values until the present era, in which it acquires the values of the order 10 −4 or 10 −3 . As the second part of this work, we consider the weak-field limit of f (R, T ) gravity models outside a spherical mass immersed in the cosmological fluid. We have found that the corresponding field equations depend on the both background values of the Ricci scalar and the background cosmological fluid density. As a result, we attain the parametrized post-Newtonian (PPN) parameter for f (R, T ) gravity and show that this theory can admit the experimentally acceptable values of this parameter. As a sample, we present the PPN gamma parameter for general minimal power law models, in particular, the model R + c1 √ −T .

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“…In fact, the scalar field in the chameleon cosmology, similar to in some other contexts, see, e.g., Refs. [78]- [91]. In addition, some efforts have been devoted to explain the standard model of particle physics in the framework of noncommutative spectral geometry and the cosmological consequences of such an approach [92,93].…”

Section: Introductionmentioning

confidence: 99%

Noncommutative universe and chameleon field dynamics

Saba

Farhoudi

2018

Annals of Physics

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We consider a noncommutative standard model with a minimal coupling scalar field and a dynamical deformation between the canonical momenta of its scale factor and scalar field, and a chameleon model with a non-minimally coupling scalar field. We indicate that there is a correspondence between these two models, more specific, actually between the noncommutative parameter and the chameleon coupling strength, and also between the matter density of the chameleon model and the noncommutative geometry. In addition, the analogy constrains the type of the matter field in the chameleon model to be nearly a cosmic string-like during the inflation. Thus, the scenario enables the evolution of the universe being described by one single scalar field. That is, the effects of the chameleon and the inflaton can be described by one single scalar field which plays the role of inflaton in the very early universe and then, acts as a chameleon field. Moreover, the proposed correspondence procedure not only sets some constraints on the noncommutative parameter and the chameleon coupling constant, but also nearly specifies functions of the scalar field and its potential.the quintessence models [44]- [49], provides a dynamical alternative to the static cosmological constant. Due to the coupling of the scalar and the matter fields with the gravitational strength, the chameleon field acquires a density-dependent mass and consequently, its property changes depending on the environmental situations. Because of such a dependence, its mass is very light in the cosmological scales, wherein it may play the role of dark energy and causes the cosmic late time acceleration. Although, in the regions of high density, such as on the earth, the chameleon field acquires a large mass that makes its effects being short-ranged and hence, becomes invisible in search for the EPviolation and fifth force in the current experimental and observational tests.However, in Refs. [50,51] by proving two theorems, it has been claimed that the effect of chameleonlike scalar fields is negligible on density perturbations considering the linear scales and also, its influence may not be regarded for the observed cosmic acceleration except as some form of dark energy. Also, in Ref.[52], we considered a coupling between the chameleon field and an unknown matter scalar field, and analyzed a possibility of an influence of the chameleon field on a cosmological acceleration of the universe inflation. In the context of the slow-roll approximations, by employing the potential usually used in this issue in the literature, we evaluated the number of e-folding of the model in order to verify its viability during the inflation. We examined the model for different ranges of the free parameters, however, the results of analysis showed that there is not much chance of having the viable chameleonic universe inflation. That is, as expected for the extreme case, the exponential term (entered due to the conformal factor describing the interaction of the chameleon field with an ambient matter)...

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Gravitational collapse of a homogeneous scalar field in deformed phase space

Cited by 31 publications

References 196 publications

Inflationary universe in deformed phase space scenario

Inflationary universe in deformed phase space scenario

Cosmological and solar system consequences off(R,T)gravity models

Noncommutative universe and chameleon field dynamics

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