**Abstract**

# Topical Collection "Modified Theories of Gravity and Cosmological Applications"

A topical collection in *Universe* (ISSN 2218-1997).

## Editors

**Interests:**modified gravity; cosmology; gravitational waves; Finsler cosmology; extended Friedmann equations; dark matter

Special Issues, Collections and Topics in MDPI journals

2. Department of Astronomy, School of Physical Sciences, University of Science and Technology of China, Hefei 230026, China

3. CAS Key Laboratory for Research in Galaxies and Cosmology, University of Science and Technology of China, Hefei 230026, China

**Interests:**dark energy formulation; modified theories of gravity; inflationary cosmology; brane cosmology; observational cosmology

Special Issues, Collections and Topics in MDPI journals

## Topical Collection Information

Dear Colleagues,

General relativity is a theory of gravity that describes with high accuracy some of the effects of gravity, such as solar system tests, gravitational lensing, gravitational waves, black holes, etc., in a definite framework of a homogeneous and isotropic space-time.

However, considering the abundance and nature of dark energy and dark matter, the nature of inflation, cosmological tensions such as the H0 and S8, the possible values of local anisotropy in the evolution of the Universe, as well as the theoretical problems of the cosmological constant and of non-renormalizability, the validity range of general relativity might be restricted. Modified theories of gravity extend the form of general relativity through various methods, leading to different field equations and thus to different cosmological implications. They play an essential role in and contribute to modern cosmology, providing a foundation for the current understanding of physical phenomena of the Universe.

Topics of interest for this Topical Collection include, but are not limited to:

- Alternative theories of gravity and general relativity;
- Scalar-tensor theories;
- Finsler cosmology;
- Modified Teleparallel gravity;
- Extra-dimensional theories of gravity;
- Early- and late-time applications of modified gravity;
- Effects of modified gravity on gravitational wave observations;
- Modified gravity and cosmological tensions;
- Dark matter and dark energy.

This Topical Collection wishes to contribute to these efforts; we invite colleagues to submit their manuscripts.

Prof. Dr. Panayiotis Stavrinos

Prof. Dr. Emmanuel N. Saridakis*Collection 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 collection 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

- modified gravity
- cosmology
- gravitational waves
- Finsler cosmology
- extended Friedmann equations
- dark matter
- inflation
- dark energy

# 2023

### Jump to: 2022

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*D*= 3 curve can still fit all the experimental data within their error bars. This confirms other studies indicating that the dynamics of this galaxy can be described almost entirely by the baryonic mass distribution alone. In the case of NGC 1052-DF2, we use an argument based on the NFDG extension of the virial theorem applied to the velocity dispersion of globular clusters showing that, in general, discrepancies between observed and predicted velocity dispersions can be attributed to an overall fractal dimension

*α*,

*β*)-Metrics and Their Isometries Cited by 1 | Viewed by 837

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*a*; in particular, we list all

*a*. Full article

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# 2022

### Jump to: 2023

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*Q*is the responsible candidate for gravitational interactions. In the present work, we consider a Friedmann–Lemâitre–Robertson–Walker cosmological model dominated by bulk viscous cosmic fluid in

*n*are free parameters of the model. We constrain our model with the Pantheon supernovae dataset of 1048 data points, the Hubble dataset of 31 data points, and the baryon acoustic oscillations dataset consisting of 6 data points. We find that our

*f*(

*R*) Gravity Cited by 4 | Viewed by 886

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*d*dimensional Riemann space-time. Theory of canonical transformations, which relates equivalent Hamiltonian formulations of the metric gravity, is investigated in detail. In particular, [...] Read more.

*d*dimensional Riemann space-time. Theory of canonical transformations, which relates equivalent Hamiltonian formulations of the metric gravity, is investigated in detail. In particular, we have formulated the conditions of canonicity for transformation between the two sets of dynamical variables used in our Hamiltonian formulations of the metric gravity. Such conditions include the ordinary condition of canonicity known in classical Hamilton mechanics, i.e., the exact coincidence of the Poisson (or Laplace) brackets which are determined for both the new and old dynamical Hamiltonian variables. However, in addition to this, any true canonical transformations defined in the metric gravity, which is a constrained dynamical system, must also guarantee the exact conservation of the total Hamiltonians

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*G*plays a central role in gravitational theory. Researchers have, since at least the 1980s, tried to see if the Newton gravitational constant can be expressed or replaced with more fundamental units, such as the Planck units. However, it [...] Read more.

*G*plays a central role in gravitational theory. Researchers have, since at least the 1980s, tried to see if the Newton gravitational constant can be expressed or replaced with more fundamental units, such as the Planck units. However, it was already pointed out in 1987 that this led to a circular problem; namely, that one must know

*G*to find the Planck units, and that it is therefore of little or no use to express

*G*through the Planck units. This is a view repeated in the literature in recent years, and is held by the physics’ community. However, we will claim that the circular problem was solved a few years ago. In addition, when one expresses the mass from the Compton wavelength formula, this leads to the conclusion that the three universal constants of

*G*,

*h*, and

*c*now can be replaced with only

*l*and

_{p}*c*to predict observable gravitational phenomena. While there have been several review papers on the Newton gravitational constant, for example, about how to measure it, we have not found a single review paper on the composite view of the gravitational constant. This paper will review the history of, as well as recent progress in, the composite view of the gravitational constant. This should hopefully be a useful supplement in the ongoing research for understanding and discussion of Newton’s gravitational constant. Full article

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