Phenomenology of effective geometries from quantum gravity

Torromé, Ricardo Gallego; Letizia, Marco; Liberati, Stefano

doi:10.1103/physrevd.92.124021

Cited by 6 publications

(13 citation statements)

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“…These kinds of corrections are typical of rainbow gravity scenarios [31] (see also [17]). Similar results where also found in [23,24] where the propagation of particle in a quantum geometry was analyzed and the deviations from the classical results were given in terms of a dimensionless non-classicality parameter β, involving expectation values of the geometrical operators over a state of the quantum geometry, and functions of p/m, without an explicit dependence on any fundamental scale. In the framework presented here, the analogous parameter would be represented by the dimensionless combination ℓm, which makes manifest the presence of a fundamental scale.…”

Section: B Finsler Spacetime From the Q-de Sitter Mass Casimirsupporting

confidence: 74%

Deformed relativity symmetries and the local structure of spacetime

Letizia¹,

Liberati²

2017

Phys. Rev. D

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A spacetime interpretation of deformed relativity symmetry groups was recently proposed by resorting to Finslerian geometries, seen as the outcome of a continuous limit endowed with first order corrections from the quantum gravity regime. In this work we further investigate such connection between deformed algebras and Finslerian geometries by showing that the Finsler geometries associated to the generalisation of the Poincar\'{e} group (the so called $\kappa$-Poincar\'{e} Hopf algebra) are maximally symmetric spacetimes which are also of the Berwald type: Finslerian spacetimes for which the connections are substantially Riemannian, belonging to the unique class for which the weak equivalence principle still holds. We also extend this analysis by considering a generalization of the de Sitter group (the so called $q$-de Sitter group) and showing that its associated Finslerian geometry reproduces locally the one from the $\kappa$-Poincar\'{e} group and that itself can be recast in a Berwald form in an appropriate limit.Comment: 20 page

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Section: B Finsler Spacetime From the Q-de Sitter Mass Casimirsupporting

confidence: 74%

Deformed relativity symmetries and the local structure of spacetime

Letizia¹,

Liberati²

2017

Phys. Rev. D

Self Cite

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“…Several previous papers have investigated various aspects of the phenomenology of Rainbow Gravity (see for example [67,68,69,70]). As a much expected consequence of quantum gravity the effects of Lorentz Violation should also be investigated.…”

Section: Discussionmentioning

confidence: 99%

Energy scale of Lorentz violation in Rainbow Gravity

Nilsson

Dąbrowski

2017

Physics of the Dark Universe

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We modify the standard relativistic dispersion relation in a way which breaks Lorentz symmetry -the effect is predicted in a high-energy regime of some modern theories of quantum gravity. We show that it is possible to realise this scenario within the framework of Rainbow Gravity which introduces two new energy-dependent functions f 1 (E) and f 2 (E) into the dispersion relation. Additionally, we assume that the gravitational constant G and the cosmological constant Λ also depend on energy E and introduce the scaling function h(E) in order to express this dependence. For cosmological applications we specify the functions f 1 and f 2 in order to fit massless particles which allows us to derive modified cosmological equations. Finally, by using Hubble+SNIa+BAO(BOSS+Lyman α)+CMB data, we constrain the energy scale E LV to be at least of the order of 10 16 GeV at 1σ which is the GUT scale or even higher 10 17 GeV at 3σ. Our claim is that this energy can be interpreted as the decoupling scale of massless particles from spacetime Lorentz violating effects.

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“…In fact, strong experimental bounds exist for particles moving faster than gravitons (based on Cerenkov radiation), but not much can be said for particles moving slower than gravitons. According to [9], the current bounds for this case are |β| 10 −2 , giving δV 10 −1 which fits for a semiclassicality parameter. Finally, a note about evolution: one might expect that, while today β is tiny, in the far past (when the universe was supposedly in a much more "quantum" state) such parameter was large.…”

Section: Evaluation Of β In Isotropic Lqcmentioning

confidence: 96%

“…Finally, it is not clear whether this deformation would be measurable even in principle, as it simply amounts to a rescaling of the speed of light, and hence -if β is the same for all matter species in the universe -it would have no physical significance. On the other hand, the situation is different if each matter type had its own parameter β: for example, in [9] it is suggested that gravitons might travel at the bare speed of light, in which case one expects (detectable) Cerenkov effect. As of now we cannot tell for sure, since the only system we explicitly studied is the massive scalar field.…”

Section: Summary and Commentsmentioning

confidence: 99%

“…In Section 2, the quantization of the theory is performed (note that, for all intents and purposes, this step is completely general: in no way we are limiting ourselves to a specific theory of quantum gravity), and a system of equations is found, whose solutions correspond to compatible dressed metrics. Section 3 is dedicated to the analysis of dispersion relations: following [9], we observe that it is not necessary to know the complete dressed metric solution in order to extract the exact dispersion relation for the scalar field (in fact, only the low-energy limit is required). This intuition allows us to find the explicit form of the Lorentz-deformed dispersion relation in the Bianchi case which -as already said -turns out to be controlled by a unique parameter.…”

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Rainbow metric from quantum gravity: Anisotropic cosmology

Assanioussi

Dapor

2017

Phys. Rev. D

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In this paper we present a construction of effective cosmological models which describe the propagation of a massive quantum scalar field on a quantum anisotropic cosmological spacetime. Each obtained effective model is represented by a rainbow metric in which particles of distinct momenta propagate on different classical geometries. Our analysis shows that upon certain assumptions and conditions on the parameters determining such anisotropic models, we surprisingly obtain a unique deformation parameter β in the modified dispersion relation of the modes. Hence inducing an isotropic deformation despite the general starting considerations. We then ensure the recovery of the dispersion relation realized in the isotropic case, studied in [1], when some proper symmetry constraints are imposed, and we estimate the value of the deformation parameter for this case in loop quantum cosmology context.How to recover classical spacetime from a fundamentally quantum description of geometry is a longstanding question in quantum gravity. A promising idea is that classical gravity could be a collective phenomenon emerging from quantum degrees of freedom [2,3], not unlike fluid dynamics emerges from microscopic molecular interactions. Taking a pragmatic point of view, we note that what an observer really measures is matter, not geometry: through matter propagation, she infers the geometry. Thus, given a certain dynamics for the matter content, every geometry which is consistent with such dynamics is equally good. In light of this fact, in [4] the authors derived the dynamics of a quantum scalar field (the matter) propagating on a quantum cosmological spacetime (the geometry), and looked for classical spacetimes which would produce the same dynamics for such a scalar field. It turns out that a possible effective spacetime exists, whose metric is given by certain expectation values of geometric operators on the quantum state of geometry (for this reason, it was called "dressed metric"). This fact -i.e., the possibility of giving an equivalent description of QFT on quantum spacetime in terms of QFT on a classical spacetime -simplifed the treatment of quantum spacetime in several scenarios, such as preinflationary cosmological perturbations [5], particle creation in primordial cosmology [6] and Hawking radiation from quantum spherical black holes [7]. From a purely theoretical perspective, however, we must point out that the effective spacetime proposed in [4] is not unique, unless the scalar field is free and massless. In particular, in [1] we focused on the massive free scalar field case, finding an alternative dressed metric for the same underlying quantum system. The peculiarity of this result lies in the fact that such metric depends on the energy of the field quanta under consideration (despite having explicitly made use of the test-field approximation [8], in which one disregards the backreaction of matter on geometry), which in turn leads to an apparent Lorentz-symmetry violation. This was confirmed in [9], where the ...

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Phenomenology of effective geometries from quantum gravity

Cited by 6 publications

References 29 publications

Deformed relativity symmetries and the local structure of spacetime

Deformed relativity symmetries and the local structure of spacetime

Energy scale of Lorentz violation in Rainbow Gravity

Rainbow metric from quantum gravity: Anisotropic cosmology

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