CONFERENCE PAPER | doi:10.20944/preprints201612.0045.v2
Subject: Physical Sciences, General & Theoretical Physics Keywords: Sunyaev-Zeldovich effect, galaxy clusters, dark energy models
Online: 10 December 2016 (08:24:22 CET)
The Sunyaev-Zeldovich effect (SZe) is a global distortion of Cosmic Microwave Bckground (CMB) spectrum as result of its interaction with a hot electron plasma in the intracluster medium for large gravitational virialized structures such as galaxy clusters. Furthermore, this hot gas of electrons emits X-Rays due to its fall in the gravitational potential well of the cluster. The analysis of SZe and X-Ray data, provide a method for calculating distances to galaxy clusters at any redshift (Angular diameter distance (dA) and gas mass fraction (fgas)). On the other side, many of these galaxy clusters produce a Strong Gravitational Lens effect (SGL), which has become an useful astrophysical tool for cosmology. We use these cosmological tests, in addition to the more traditional ones (SNIa, CMB, BAO), to constraint alternative models of dark energy (ωCDM, CPL, IDE, EDE) and study the history of expansion through the cosmographic parameters (H(z), q(z), j(z)). Using Akaike and Bayesian Information Criterion (AIC, BIC) we find that the ωCDM and ΛCDM models are the most favored by the observational data. In addition, we found that at low redshift appears an peculiar behavior of slowdown of aceleration, which occurs only on dynamical dark energy models using only galaxy clusters (dA,clusters + fgas).
ARTICLE | doi:10.20944/preprints201801.0018.v1
Subject: Keywords: reaction-diffusion equations; Newell-Whitehead-Segel equation; Zeldovich equation; exact solution; traveling wave solution
Online: 3 January 2018 (03:34:43 CET)
Complex and real valued exact solutions to some reaction-diffusion equations are suggested by using homogeneous balance and Sine-Gordon equation expansion method. The predicted solution of finite series of some hyperbolic functions are determined by using some relations between the hyperbolic functions and trigonometric functions based on Sine-Gordon equation and traveling wave transform. The Newel-Whitehead-Segel and Zeldovich equations are solved explicitly. Some real valued solutions are depicted for some particular choice of parameters.
ARTICLE | doi:10.20944/preprints201806.0349.v2
Subject: Physical Sciences, Particle & Field Physics Keywords: MacDowell-Mansouri formalism; Bjorken-Zeldovich scale; Gauss-Bonnet term; Einstein-Cartan formalism; Big Bang Nucleosynthesis; cosmological constant; Kodama wavefunctions
Online: 2 August 2018 (08:57:01 CEST)
We discuss a possible scale of gravitational origin at around 10 MeV, or 10−12 cm, which arises in the MacDowell-Mansouri formalism of gravity due to the topological Gauss-Bonnet term in the action, as pointed out by Bjorken several years ago.~A length scale of the same size emerges also in the Kodama solution in gravity, which is known to be closely related to the MacDowell-Mansouri formulation. We particularly draw attention to the intriguing incident that existence of six compact extra dimensions originated from TeV-scale quantum gravity as well points to a length scale of 10−12 cm, as the compactification scale. The presence of six such extra dimensions is also in remarkable consistency with the MacDowell-Mansouri formalism; it provides a possible explanation for the factor of ~10120 multiplying the Gauss-Bonnet term in the action. We also comment on the relevant implications of such a scale regarding the thermal history of the universe motivated by the fact that it is considerably close to 1–2 MeV below which the weak interactions freeze out, leading to Big Bang Nucleosynthesis.