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A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Cosmology".

Deadline for manuscript submissions: closed (30 November 2023) | Viewed by 11463

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Special Issue Editors

Prof. Dr. Zhiqi Huang

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Guest Editor

School of Physics and Astronomy, Sun Yat-sen University, 2 Daxue Rd., Tangjia, Zhuhai 519082, China
Interests: cosmic microwave background; dark energy; inflation

Prof. Dr. Pedro Pina Avelino

E-Mail Website
Guest Editor

Department of Physics and Astronomy, Faculty of Sciences, University of Porto, and Institute of Astrophysics and Space Sciences (IA/CAUP), Rua das Estrelas, 4150-762 Porto, Portugal
Interests: cosmology; structure formation; cosmic defects; dark energy; dark matter; varying fundamental couplings; modified gravity

Special Issue Information

Dear Colleagues,

In the past three decades, measurements of temperature and polarization anisotropies of the cosmic microwave background (CMB) have played a key role in the development of precision cosmology and our understanding of the early universe. The B-mode polarization of CMB is considered to be the unique probe of primordial gravitational waves on cosmological scales, the “smoking gun” of the inflationary paradigm. CMB secondary anisotropies correlated with the late-universe large scale structures are potentially a very powerful probe that helps to reveal the nature of the dark components of the universe. CMB spectral distortion contains information about energy injection in the early universe, which places bounds on the primordial abundance of supermassive black holes and other energy sources.

This Special Issue will collect contributions on the challenges, cutting-edge progresses, and future prospects of CMB science. The aim is to invite scientists all over the world to discuss and share their new ideas on how to utilize CMB to explore the physical cosmos. All original contributions are welcome.

Prof. Dr. Zhiqi Huang
Prof. Dr. Pedro Pina Avelino
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

cosmic microwave background
primordial gravitational wave
early universe
inflation

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Published Papers (6 papers)

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Research

14 pages, 490 KiB

Open AccessArticle

Betti Functionals as Probes for Cosmic Topology

by Ralf Aurich and Frank Steiner

Universe 2024, 10(5), 190; https://doi.org/10.3390/universe10050190 - 24 Apr 2024

Cited by 1 | Viewed by 1147

Abstract

The question of the global topology of the Universe (cosmic topology) is still open. In the

Λ

CDM concordance model, it is assumed that the space of the Universe possesses the trivial topology of

R^{3}

, and thus that the Universe has [...] Read more.

The question of the global topology of the Universe (cosmic topology) is still open. In the

Λ

CDM concordance model, it is assumed that the space of the Universe possesses the trivial topology of

R^{3}

, and thus that the Universe has an infinite volume. As an alternative, in this paper, we study one of the simplest non-trivial topologies given by a cubic 3-torus describing a universe with a finite volume. To probe cosmic topology, we analyze certain structure properties in the cosmic microwave background (CMB) using Betti functionals and the Euler characteristic evaluated on excursions sets, which possess a simple geometrical interpretation. Since the CMB temperature fluctuations

δ T

are observed on the sphere

S^{2}

surrounding the observer, there are only three Betti functionals

β_{k} (ν)

k = 0, 1, 2

. Here,

ν = δ T / σ_{0}

denotes the temperature threshold normalized by the standard deviation

σ_{0}

δ T

. The analytic approximations of the Gaussian expectations for the Betti functionals and an exact formula for the Euler characteristic are given. It is shown that the amplitudes of

β_{0} (ν)

and

β_{1} (ν)

decrease with an increasing volume

V = L^{3}

of the cubic 3-torus universe. Since the computation of the

β_{k}

’s from observational sky maps is hindered due to the presence of masks, we suggest a method that yields lower and upper bounds for them and apply it to four Planck 2018 sky maps. It is found that the

β_{k}

’s of the Planck maps lie between those of the torus universes with side-lengths

L = 2.0

and

L = 3.0

in units of the Hubble length and above the infinite

Λ

CDM case. These results give a further hint that the Universe has a non-trivial topology. Full article

(This article belongs to the Special Issue Cosmic Microwave Background)

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13 pages, 862 KiB

Open AccessArticle

Discord in Concordance Cosmology and Anomalously Massive Early Galaxies

by Stacy S. McGaugh

Universe 2024, 10(1), 48; https://doi.org/10.3390/universe10010048 - 19 Jan 2024

Cited by 6 | Viewed by 2072

Abstract

Cosmological parameters are constrained by a wide variety of observations. We examine the concordance diagram for modern measurements of the Hubble constant, the shape parameter from the large-scale structure, the cluster baryon fraction, and the age of the universe, all from non-CMB data. [...] Read more.

H_{0} = 73.24 \pm 0.38 km s^{- 1} {Mpc}^{- 1}

and

Ω_{m} = 0.237 \pm 0.015

. This concordance value is indistinguishable from the WMAP3 cosmology but is not consistent with that of Planck: there is a tension in

Ω_{m}

as well as

H_{0}

. These tensions have emerged as progressively higher multipoles have been incorporated into CMB fits. This temporal evolution is suggestive of a systematic effect in the analysis of CMB data at fine angular scales and may be related to the observation of unexpectedly massive galaxies at high redshift. These are overabundant relative to

Λ

CDM predictions by an order of magnitude at

z > 7

. Such massive objects are anomalous and could cause gravitational lensing of the surface of last scattering in excess of the standard calculation made in CMB fits, potentially skewing the best-fit cosmological parameters and contributing to the Hubble tension. Full article

(This article belongs to the Special Issue Cosmic Microwave Background)

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14 pages, 705 KiB

Open AccessArticle

CMB Power Spectrum in the Emergent Universe with K-Essence

by Qihong Huang, Kaituo Zhang, He Huang, Bing Xu and Feiquan Tu

Universe 2023, 9(5), 221; https://doi.org/10.3390/universe9050221 - 6 May 2023

Cited by 5 | Viewed by 1410

Abstract

The emergent universe provides a possible method to avoid the Big Bang singularity by considering that the universe stems from a stable Einstein static universe rather than the singularity. Since the Einstein static universe exists before inflation, it may leave some relics in the CMB power spectrum. In this paper, we analyze the stability condition for the Einstein static universe in general relativity with k-essence against both the scalar and tensor perturbations. Furthermore, we find the emergent universe can be successfully realized by constructing a scalar potential and an equation of state parameter. Solving the curved Mukhanov–Sasaki equation, we obtain the analytical approximation for the primordial power spectrum, and then depict the TT-spectrum of the emergent universe. The results show that both the primordial power spectrum and CMB TT-spectrum are suppressed on large scales. Full article

(This article belongs to the Special Issue Cosmic Microwave Background)

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9 pages, 399 KiB

Open AccessEditor’s ChoiceArticle

The Galactic Interstellar Medium Has a Preferred Handedness of Magnetic Misalignment

by Zhiqi Huang

Universe 2022, 8(8), 423; https://doi.org/10.3390/universe8080423 - 17 Aug 2022

Cited by 3 | Viewed by 2080

Abstract

The Planck mission detected a positive correlation between the intensity (T) and B-mode polarization of the Galactic thermal dust emission. The

T B

correlation is a parity-odd signal, whose statistical mean vanishes in models with mirror symmetry. Recent work has [...] Read more.

The Planck mission detected a positive correlation between the intensity (T) and B-mode polarization of the Galactic thermal dust emission. The

T B

correlation is a parity-odd signal, whose statistical mean vanishes in models with mirror symmetry. Recent work has shown, with strong evidence, that local handedness of the misalignment between the dust filaments and the sky-projected magnetic field produces

T B

signals. However, it remains unclear whether the observed global

T B

signal is caused by statistical fluctuations of magnetic misalignment angles or whether some parity-violating physics in the interstellar medium sets a preferred misalignment handedness. The present work aims to make a quantitative statement about how confidently the statistical fluctuation interpretation is ruled out by filament-based simulations of polarized dust emission. We use the publicly available DUSTFILAMENTS code to simulate the dust emission from filaments whose magnetic misalignment angles are symmetrically randomized and construct the probability density function of

ξ_{p}

, a weighted sum of the

T B

power spectrum. We find that the Planck data have a ≳

10 σ

tension with the simulated

ξ_{p}

distribution. Our results strongly support the idea that the Galactic filament misalignment has a preferred handedness, whose physical origin is yet to be identified. Full article

(This article belongs to the Special Issue Cosmic Microwave Background)

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13 pages, 543 KiB

Open AccessArticle

Stringy Signals from Large-Angle Correlations in the Cosmic Microwave Background?

by Miguel-Angel Sanchis-Lozano

Universe 2022, 8(8), 396; https://doi.org/10.3390/universe8080396 - 28 Jul 2022

Cited by 1 | Viewed by 1510

Abstract

We interpret the lack of large-angle temperature correlations and the even-odd parity imbalance observed in the cosmic microwave background (CMB) by COBE, WMAP and Planck satellite missions as a possible stringy signal ultimately stemming from a composite inflaton field (e.g., a fermionic condensate). [...] Read more.

k_{\min}^{even, odd}

(satisfying

k_{\min}^{even} ≃ 2 k_{\min}^{odd}

) are introduced to the CMB power spectrum associated, respectively, with periodic and antiperiodic boundary conditions of the fermionic constituents (echoing the Neveu–Schwarz–Ramond model in superstring theory), without resorting to any particular model. Full article

(This article belongs to the Special Issue Cosmic Microwave Background)

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8 pages, 2353 KiB

Open AccessArticle

Measuring the Modified Gravitational Wave Propagation beyond General Relativity from CMB Observations

by Jun Li

Universe 2022, 8(7), 367; https://doi.org/10.3390/universe8070367 - 3 Jul 2022

Cited by 3 | Viewed by 1796

Abstract

In modified gravity theories, gravitational wave propagations are presented in nonstandard ways. We consider a friction term different from GR and constrain the modified gravitational waves propagation from observations. The modified gravitational waves produce anisotropies and polarization, which generate measurable tensor power spectra. [...] Read more.

A_{t}

) when

ν_{0}

is allowed to vary in the Monte Carlo analyses from Planck+BK18 datasets. If we assume the result of the scalar perturbations is unchanged, the inflation consistency relation alters with the friction term. In the

Λ

CDM+r+

ν_{0}

model, the tensor-to-scalar ratio and the amplitude of the tensor spectrum are obviously influenced. Full article

(This article belongs to the Special Issue Cosmic Microwave Background)

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