Cosmic Microwave Background Anisotropy numerical solution (CMBAns). Part I. An introduction toClcalculation

Das, Santanu; Phan, Anh Huy

doi:10.1088/1475-7516/2020/05/006

Cited by 6 publications

(1 citation statement)

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“…We therefore conclude that the VcGΛ model deserves to be considered seriously for further work which needs collaboration to study more difficult cosmological problems such as fitting the power spectrum of CMB temperature anisotropies. Current codes such as CAMB 46 , CLASS 47 and CMBAns 48 are unable to handle background based on VPC models and it is challenging undertaking to modify them 49,50 .…”

Section: Discussionmentioning

confidence: 99%

Cosmology with Relativistically Varying Physical Constants

Gupta

2020

Preprint

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We have shown that our varying physical constant model is consistent with the recently published variational approach wherein Einstein equations are modified to include the variation of the speed of light c, gravitational constant G and cosmological constant Λ using the Einstein-Hilbert action. The general constraint resulting from satisfying the local conservation laws and contracted Bianchi identities provides the freedom to choose the form of the variation of the constants as well as how their variations are related. When we choose dG/Gdt=3dc/cdt, ̇the same as in our quasi-phenomenological model, c=c0 exp⁡(aα-1), G=G0 exp⁡[3(aα-1)] and Λ=Λ0 exp⁡[(a-α-1)], where a is the scale factor and α=1.8, we are able to confirm the success of our the model in explaining three astrometric anomalies and the null results on the variation of G and the fine structure constant. We show that the model: (a) fits the supernovae 1a observational data better than the ΛCDM model; (b) determines the first peak in the power spectrum of the cosmic microwave background temperature anisotropies at multipole value of l=217.3; (c) calculates the age of the universe as 14.1 Gyr; and (d) finds the BAO acoustic scale to be 145.2 Mpc. These numbers are within less than 3% percent of the observed values and the values obtained by the ΛCDM model. Surprisingly we find that the dark-energy density is negative in a universe that has significant negative curvature and whose expansion is accelerating at a faster rate than predicted by the ΛCDM model.

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Section: Discussionmentioning

confidence: 99%

Cosmology with Relativistically Varying Physical Constants

Gupta

2020

Preprint

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Aspects of Everpresent Λ. Part II. Cosmological tests of current models

Das,

Nasiri,

Yazdi

2024

J. Cosmol. Astropart. Phys.

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This paper investigates Everpresent Λ, a stochastic dark energy model motivated by causal set theory and unimodular gravity, and confronts it with two key observational data sets, Supernova Ia (SN Ia) and Cosmic Microwave Background (CMB) data. A key feature of this model is that Λ fluctuates over time and on average the magnitude of its fluctuations is of the order of the dominant energy density (be it radiation or matter) for the given epoch. In particular, we focus on a phenomenological implementation of Everpresent Λ known as Model 1. The random fluctuations in Everpresent Λ realizations are generated using seed numbers, and we find that for a small fraction of seeds Model 1 is capable of producing realizations that fit SN Ia data better than ΛCDM. We further investigate what features distinguish these realizations from the more general behaviour, and find that the “good” realizations have relatively small fluctuations at low redshifts (z < 1.5), which do not closely track the matter density. We find that Model 1 struggles to improve on ΛCDM at describing the CMB data. However, by suppressing the values of Λ near the last scattering surface, as suggested in [1], we find a large improvement in the best fit of the model, though still with a χ 2 value much larger than that of ΛCDM. We also study the allowed variation of the dark energy density by the CMB constraints in a more model-independent manner, and find that some variation (especially prior to recombination) is possible and in fact can lead to improvement over ΛCDM and reduce the Hubble tension, in line with some early dark energy proposals. However, for the kinds of variations considered, the favoured fluctuations are smaller in magnitude than is typical in current Everpresent Λ models.

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