100 years of mathematical cosmology: Models, theories, and problems, Part A

Cotsakis, Spiros; Yefremov, Alexander P.

doi:10.1098/rsta.2021.0191

Cited by 7 publications

(9 citation statements)

References 131 publications

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“…Modern cosmology has its origins in solutions to the Einstein field equations, which are horrendously difficult to analytically solve without symmetries 28 . Seen in this historic context, some assumption, FLRW or equivalent, is required even without observational data to analytically solve the field equations [12]. Given that maximally symmetric spacetimes with 10 isometries do not constitute realistic cosmologies, the next most-symmetric and cosmologically relevant family is FLRW.…”

Section: Prologuementioning

confidence: 99%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

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The Cosmological Principle (CP) -- the notion that the Universe is spatially isotropic and homogeneous on large scales -- underlies a century of progress in cosmology. It is conventionally formulated through the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) cosmologies as the spacetime metric, and culminates in the successful and highly predictive $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) model. Yet, tensions have emerged within the $\Lambda$CDM model, most notably a statistically significant discrepancy in the value of the Hubble constant, $H_0$. Since the notion of cosmic expansion determined by a single parameter is intimately tied to the CP, implications of the $H_0$ tension may extend beyond $\Lambda$CDM to the CP itself. This review surveys current observational hints for deviations from the expectations of the CP, highlighting synergies and disagreements that warrant further study. Setting aside the debate about individual large structures, potential deviations from the CP include variations of cosmological parameters on the sky, discrepancies in the cosmic dipoles, and mysterious alignments in quasar polarizations and galaxy spins. While it is possible that a host of observational systematics are impacting results, it is equally plausible that precision cosmology may have outgrown the FLRW paradigm, an extremely pragmatic but non-fundamental symmetry assumption.

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Section: Prologuementioning

confidence: 99%

Is the observable Universe consistent with the cosmological principle?

Aluri

Cea

Chingangbam

et al. 2023

Class. Quantum Grav.

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“…Let us note that taking into account early time properties of the decay rate is especially important in the case of models with extremely long lifetimes of the false vacuum because in such cases the early time phase, [t init 0 = 0, T 0 ), of the quantum decay process can be longer than a duration of the inflation process (see Figs. 2,3,4). So, it could therefore have happened that in such models the wrong false vacuum decay rate was used in the analysis of the inflation process.…”

Section: Final Remarksmentioning

confidence: 99%

“…To view a copy of this licence, visit http://creativecomm ons.org/licenses/by/4.0/. Funded by SCOAP 3 . SCOAP 3 supports the goals of the International Year of Basic Sciences for Sustainable Development.…”

Section: Conflict Of Interestmentioning

confidence: 99%

“…Various aspects of the problem of whether the Universe can live forever or whether sooner or later will have to decay (i. e. to die) was considered in mathematical cosmology based on solutions to Einstein's equations practically from the very beginning (see, e.g. [1,2] and also a great review works [3,4]). This discussion gained a new face and intensified after the publication of a seminal series of papers by Coleman et al [5][6][7], where the instability of a physical system, which is not at an absolute energy minimum, and which is separated from the absolute minimum by an effective potential barrier was discussed.…”

Section: Introductionmentioning

confidence: 99%

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A universe born in a metastable false vacuum state needs not die

Urbanowski

2023

Eur. Phys. J. C

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We try to find conditions, the fulfillment of which allows a universe born in a metastable false vacuum state to survive and not to collapse. The conditions found are in the form of inequalities linking the depending on time t instantaneous decay rate $${\varGamma }(t)$$ Γ ( t ) of the false vacuum state and the Hubble parameter H(t). Properties of the decay rate of a quantum metastable states are discussed and then the possible solutions of the conditions found are analyzed and discussed. Within the model considered it is shown that a universe born in the metastable vacuum state has a very high chance of surviving until very late times if the lifetime, $$\tau _{0}^{F}$$ τ 0 F , of the metastable false vacuum state is much shorter, than the duration of the inflation process. Our analysis shows that the instability of the electroweak vacuum does not have to result in the tragic fate of our Universe leading to its death.

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“…It is well-known that the conformal transformation approach between Jordan and Einstein frames recasts vacuum modified gravity, be it scalar-tensor or higher-order, in a useful, reduced-order form as general relativity plus a selfinteracting scalar field with a particular conformal potential (also true in the case of matter fields present in both frames with additional matter-scalar field couplings), cf. [1][2][3][4][5][6][7][8][9][10][11][12]. By a slightly more complicated but totally equivalent procedure, one may also first introduce the Legendre transform of higher-order gravity to express higher-order gravity in a scalar-tensor form with the Legendre transform of the theory regarded as potential term, and then conformally transformed the resulting scalar-tensor theory to obtain the a e-mail: skot@aegean.gr (corresponding author) b e-mail: jpmimoso@fc.ul.pt c e-mail: imyr@aegean.gr same result as before in the Einstein frame representation of the original lagrangian [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

Legendre scalarization in gravity and cosmology

2023

Self Cite

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We propose a new formulation of f(R) gravity, dubbed scalarized f(R) gravity, in which the Legendre transform is included as a dynamical term. This leads to a theory with second-order field equations that describes general relativity with a self-interacting scalar field, without requiring the introduction of conformal frames. We demonstrate that the quadratic version of scalarized f(R) gravity reduces to general relativity with a massive scalar field, and we explore its implications for Friedmann cosmology. Our findings suggest that scalarized f(R) gravity may lead to simplified descriptions of cosmological applications, while the proposed formulation could offer a new perspective on the relationship between f(R) gravity and scalar–tensor theories.

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100 years of mathematical cosmology: Models, theories, and problems, Part A

Cited by 7 publications

References 131 publications

Is the observable Universe consistent with the cosmological principle?

Is the observable Universe consistent with the cosmological principle?

A universe born in a metastable false vacuum state needs not die

Legendre scalarization in gravity and cosmology

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