Cosmological bounce and the cosmological constant problem

Pavlović, Petar; Sossich, Marko

doi:10.48550/arxiv.2112.09523

Cited by 3 publications

(7 citation statements)

References 35 publications

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“…A variety of studies bear relation in different ways with these investigations, see e.g. [63][64][65][66][67][68][69][70][71][72][73][74][75][76] and corresponding references. However, it was only recently, in the aforementioned work [57], where an explicit form of the RVM vacuum density could be derived within the QFT context.…”

Section: Introductionmentioning

confidence: 99%

Renormalizing the vacuum energy in cosmological spacetime: implications for the cosmological constant problem

Moreno-Pulido,

Peracaula

2022

Preprint

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The renormalization of the vacuum energy in quantum field theory (QFT) is usually plagued with theoretical conundrums related not only with the renormalization procedure itself, but also with the fact that the final result leads usually to very large (finite) contributions incompatible with the measured value of Λ in cosmology. As a consequence, one is bound to extreme fine-tuning of the parameters and so to sheer unnaturalness of the result and of the entire approach. We may however get over this adversity using a different perspective. Herein, we compute the zero-point energy (ZPE) for a nonminimally coupled (massive) scalar field in FLRW spacetime using the off-shell adiabatic renormalization technique employed in previous work. The on-shell renormalized result first appears at sixth adiabatic order, so the calculation is rather cumbersome. The general off-shell result yields a smooth function ρ vac (H) made out of powers of the Hubble rate and/or of its time derivatives involving different (even) adiabatic orders ∼ H N (N = 0, 2, 4, 6, ...), i.e. it leads, remarkably enough, to the running vacuum model (RVM) structure. We have verified the same result from the effective action formalism and used it to find the β-function of the running quantum vacuum. No undesired contributions ∼ m 4 from particle masses appear and hence no fine-tuning of the parameters is needed in ρ vac (H). Furthermore, we find that the higher power ∼ H 6 could naturally drive RVM-inflation in the early universe. Our calculation also elucidates in detail the equation of state of the quantum vacuum: it proves to be not exactly −1 and is moderately dynamical. The form of ρ vac (H) at low energies is also characteristic of the RVM and consists of an additive term (the so-called 'cosmological constant') together with a small dynamical component ∼ νH 2 (|ν| ≪ 1). Finally, we predict a slow (∼ ln H) running of Newton's gravitational coupling G(H). The physical outcome of our semiclassical QFT calculation is revealing: today's cosmic vacuum and the gravitational strength should be both mildly dynamical.

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Section: Introductionmentioning

confidence: 99%

Renormalizing the vacuum energy in cosmological spacetime: implications for the cosmological constant problem

Moreno-Pulido,

Peracaula

2022

Preprint

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“…It was also demonstrated that the problem of magnetogenesis has a simple possible solution in the model-independent approach to bouncing cosmology [38]. Recently, we proposed a model-independent approach to bouncing cosmology in which we proposed a simple solution of the cosmological constant problem and also studied the effects of quantum fluctuations of the spacetime geometry [39]. We will use some of the obtained conclusion in the present study of wormholes created during the cosmological bounce.…”

Section: Introductionmentioning

confidence: 87%

“…model independent) description of bouncing cosmological solutions. Here we follow the steps discussed in [39]. With this aim we introduce the following action for gravity (c = 1):…”

Section: General Approach To Bouncing Cosmologymentioning

confidence: 99%

“…Although the collection of terms G mod μν can in principle be some arbitrary complicated function of the curvature invariants and their combinations (such as Ricci scalar, contractions of Riemann and Ricci tensors, their higher powers and derivatives), the only cosmological coordinate on which components of this collection on terms can depend is -due to the homogeneous and isotropic nature of the considered spacetime -the time coordinate. Therefore, despite the arbitrary nature of such corrections, on the FLRW spacetime the field equations must take the following form [39]:…”

Section: General Approach To Bouncing Cosmologymentioning

confidence: 99%

“…From this, one easily obtains the approximation for H (t) around the bounce valid for any possible type of bouncing cosmology. This approximate form of S(t) around the bounce is given by [39] S(t…”

Section: General Approach To Bouncing Cosmologymentioning

confidence: 99%

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Creation of wormholes during the cosmological bounce

Pavlović

Sossich

2023

Eur. Phys. J. C

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In this work we demonstrate that wormholes can in principle be naturally created during the cosmological bounce without the need for the exotic matter or any kind of additional modifications of the gravitational sector, apart from the one enabling the cosmological bounce. This result is general and does not depend on the details of the modifications of gravitational equations needed to support the bounce. To study the possible existence of wormholes around the cosmological bounce we introduce general modifications of Einstein’s field equations need to support the bouncing solutions. In this regime we show that it is possible to construct a cosmological wormhole solution supported by matter, radiation and vacuum energy, satisfying the Weak Energy Condition (WEC), which asymptotically approaches the Friedmann–Lemaître–Robertson–Walker (FLRW) metric. However, at a specific cosmological time, which depends on the parameters of the bouncing cosmological model, the WEC describing the matter needed to support such wormholes is spontaneously violated. This means that such wormholes could potentially exist in large numbers during some period around the bounce, significantly changing the causal structure of space-time, and then vanish afterwards.

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Geodesically complete cyclic cosmologies and entropy

Pavlović,

Sossich

2024

Eur. Phys. J. C

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We demonstrate that there exists a class of cyclic cosmological models, such that these models can in principle solve the problem of the entropy growth, and are at the same time geodesically complete. We thus show that some recently stated conclusions, according to which cyclic cosmologies solving the problem of entropy growth can not be geodesically complete due to the Borde–Guth–Vilenkin (BGV) theorem, are not justified. We also add a short conceptual discussion on entropy and cyclic cosmology, and present a detailed analysis of entropy density growth during periodic and non-periodic evolution for cyclic cosmologies.

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Cosmological bounce and the cosmological constant problem

Cited by 3 publications

References 35 publications

Renormalizing the vacuum energy in cosmological spacetime: implications for the cosmological constant problem

Renormalizing the vacuum energy in cosmological spacetime: implications for the cosmological constant problem

Creation of wormholes during the cosmological bounce

Geodesically complete cyclic cosmologies and entropy

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