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Special Issue "Fundamental Constants in Cosmology and Cosmological Parameters"

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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: 31 January 2024 | Viewed by 3008

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Prof. Dr. Rajendra Gupta

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Guest Editor

Department of Physics, University of Ottawa, Ottawa, ON, Canada
Interests: cosmology; CMB; BBN; varying physical constants; stellar evolution; pulsars; gravitational lensing
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Dear Colleagues,

Despite the stunning success of the standard ΛCDM model in explaining various cosmological observations, many gaps remain which require new physics. One needs to examine the foundations of physics developed over centuries, from local observations extrapolated to the universe at large. One such foundation is that constants relating various observables remain constant everywhere and all times. This is especially significant because attempts to measure their variations have led to very tight constraints on their potential variation. One may ask if the tight constraints are due to the extremely high constancy of the constants or due to the limitations of the tools used for their measurement.

Since Dirac suggested the possibility of the variability of Newton’s gravitational constant derived from his large numbers theory in 1937, there has been a great deal of interest not only in its variability but also in the potential of the variability of other fundamental constants, such as the speed of light, the fine structure constant, and proton to electron mass ratio. Since each fundamental constant is considered to represent a physical symmetry through Noether’s theorem, Symmetry has decided to produce a Special Issue comprising a collection of diverse and innovative research papers on the fundamental constants in cosmology.

Prof. Dr. Rajendra Gupta
Guest Editor

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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. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). 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.

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Research

Open AccessArticle

Dynamical Analysis of the Covarying Coupling Constants in Scalar–Tensor Gravity

Rodrigo R. Cuzinatto

Rajendra P. Gupta

and

Pedro J. Pompeia

Symmetry 2023, 15(3), 709; https://doi.org/10.3390/sym15030709 - 12 Mar 2023

Cited by 5 | Viewed by 1023

Abstract

A scalar–tensor theory of gravity was considered, wherein the gravitational coupling G and the speed of light c were admitted as space–time functions and combined to form the definition of the scalar field

ϕ

. The varying c participates in the definition of [...] Read more.

ϕ

. The varying c participates in the definition of the variation of the matter part of the action; it is related to the effective stress–energy tensor, which is a result of the requirement of symmetry under general coordinate transformations in our gravity model. The effect of the cosmological coupling

Λ

is accommodated within a possible behavior of

ϕ

. We analyzed the dynamics of

ϕ

in the phase space, thereby showing the existence of an attractor point for reasonable hypotheses on the potential

V (ϕ)

and no particular assumption on the Hubble function. The phase space analysis was performed both with the linear stability theory and via the more general Lyapunov method. Either method led to the conclusion that the condition

\dot{G} / G = σ (\dot{c} / c)

, where

σ = 3

must hold for the rest of cosmic evolution after the system arrives at the globally asymptotically stable fixed point and the dynamics of

ϕ

ceases. This result realized our main motivation: to provide a physical foundation for the phenomenological model admitting

(G / G_{0}) = {(c / c_{0})}^{3}

, used recently to interpret cosmological and astrophysical data. The thus covarying couplings G and c impact the cosmic evolution after the dynamical system settles to equilibrium. The secondary goal of our work was to investigate how this impact occurs. This was performed by constructing the generalized continuity equation in our scalar–tensor model and considering two possible regimes for the varying speed of light—decreasing c and increasing c—while solving our modified Friedmann equations. The solutions to the latter equations make room for radiation- and matter-dominated eras that progress to a dark-energy-type of accelerated expansion. Full article

(This article belongs to the Special Issue Fundamental Constants in Cosmology and Cosmological Parameters)

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Open AccessArticle

Analytical Solutions and a Clock for Orbital Progress Based on Symmetry of the Ellipse

Robert E. Criss

and

Anne M. Hofmeister

Symmetry 2023, 15(3), 641; https://doi.org/10.3390/sym15030641 - 03 Mar 2023

Viewed by 750

Abstract

Kepler’s discoveries were permitted by his remarkable insight to place the Sun at the focus of an elliptical planetary orbit. This coordinate system reduces a 2-dimensional orbit to a single spatial dimension. We consider an alternative coordinate system centered on the “image focus,” which is the symmetrical (mirror) counterpart of the “real focus” occupied by the Sun. Our analytical approach provides new purely geometric formulae and an exact relationship for the dynamic property of orbital time. In addition, considering the mirror symmetry of the ellipse leads to a simple approximation: the radial hand of an orbital clock rotates counterclockwise at a nearly steady angular velocity 2π/T about the “image focus,” where T is the orbital period. This approximation is a useful pedagogic tool and has good accuracy for orbits with low to moderate eccentricities, since the deviation from the exact result goes as eccentricity squared. Planetary comparisons are made. In particular, the angular speeds of Mercury and Jupiter are highly variable in the geocentric and heliocentric reference frames, but are nearly constant in the image focus reference frame. Our findings resolve whether the image focus is the location for observing uniform motion of an elliptical orbit, and pertain to their stability. Full article

(This article belongs to the Special Issue Fundamental Constants in Cosmology and Cosmological Parameters)

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Figure 1

Open AccessArticle

Constraining Coupling Constants’ Variation with Supernovae, Quasars, and GRBs

Rajendra P. Gupta

Symmetry 2023, 15(2), 259; https://doi.org/10.3390/sym15020259 - 17 Jan 2023

Cited by 4 | Viewed by 967

Abstract

Dirac, in 1937, proposed the potential variation of coupling constants derived from his large numbers hypothesis. Efforts have continued since then to constrain their variation by various methods, including astrophysical and cosmological observations. We briefly discuss several methods used for the purpose while focusing primarily on the use of supernovae type 1a, quasars, and gamma-ray bursts as cosmological probes for determining cosmological distances. Supernovae type Ia (SNeIa) are considered the best standard candles since their intrinsic luminosity can be determined precisely from their light curves. However, they have only been observed up to about redshift

z = 2.3

, mostly at

z \leq 1.5

. Quasars are the brightest non-transient cosmic sources in the Universe. They have been observed up to

z = 7.5

. Certain types of quasars can be calibrated well enough for their use as standard candles but with a higher degree of uncertainty in their intrinsic luminosity than SNeIa. Gamma-ray bursts (GRBs) are even brighter than quasars, and they have been observed up to

z = 9.4

. They are sources of highly transient radiation lasting from tens of milliseconds to several minutes and, in rare cases, a few hours. However, they are even more challenging to calibrate as standard candles than quasars. Both quasars and GRBs use SNeIa for distance calibration. What if the standard candles’ intrinsic luminosities are affected when the coupling constants become dynamic and depend on measured distances? Assuming it to be constant at all cosmic distances leads to the wrong constraint on the data-fitted model parameters. This paper uses our earlier finding that the speed of light

c,

the gravitational constant

G

, the Planck constant

h

, and the Boltzmann constant

k

vary in such a way that their variation is interrelated as

G ~ c^{3} ~ h^{3} ~ k^{3 / 2}

with

\dot{G} / G = 3 \dot{c} / c = 3 \dot{h} / h = 1.5 \dot{k} / k

= 3.90 (\pm 0.04) \times 10^{- 10} {yr}^{- 1}

and corroborates it with SNeIa, quasars, and GRBs observational data. Additionally, we show that this covarying coupling constant model may be better than the standard

Λ

CDM model for using quasars and GRBs as standard candles and predict that the mass of the GRBs scales with

z

({(1 + z)}^{1 / 3} - 1)

. Noether’s symmetry on the coupling constants is now transferred effectively to the constant in the function relating to their variation. Full article

(This article belongs to the Special Issue Fundamental Constants in Cosmology and Cosmological Parameters)

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