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1
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GABRIEL SOUZA BRILHANTE DE ARAUJO
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Goos-Hänchen Shift Associated Wwith Guided Wave Excitation in a Silicon Slab
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Leader : THOMAS DUMELOW
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MEMBRES DE LA BANQUE :
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FRANCISCO FRANCINÉ MAIA JÚNIOR
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JOSÉ ALZAMIR PEREIRA DA COSTA
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THOMAS DUMELOW
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Data: 3 mars 2023
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Afficher le Résumé
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When a beam of electromagnetic radiation is incident on a surface, the reflected beam may undergo a lateral displacement. This effect is not predicted by geometric optics and is known as the Goos-Hänchen effect, which, in the case of the present work, is due to guided wave excitation, in which the displacement will be dependent on the frequency of the incident radiation. The configuration studied consists of a Si prism, with the angle of incidence within the prism greater than the critical angle for total internal reflection, an air layer and a Si slab with defined thickness. Computer simulations were performed with this geometry and interesting results were obtained. The first one is that, for the frequency band used (255-295 GHz), from calculations assuming a wide beam, we observed that the beam displacement presents different values, presenting maximum and minimum for certain established frequencies coresponding to guided wave excitations. Apart from this result we consider how, for a Gaussian beam of finite width, the intensities of the incident and reflected beam present a displacement. We examine how, when we modify parameters such as the beam width and the thickness of the air layer between the prism and the Si plate, the displacements are greater for wider beams and a larger prism-slab distance.
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2
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WILLYAM THOMPSON SOARES DE FREITAS
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Magneto-Optical Effects in InSb at THz Frequencies
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Leader : THOMAS DUMELOW
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MEMBRES DE LA BANQUE :
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SUBENIA KARINE DE MEDEIROS
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JOSÉ ALZAMIR PEREIRA DA COSTA
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THOMAS DUMELOW
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Data: 13 mars 2023
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Afficher le Résumé
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We investigate the magneto-optical eff ects in refl ection for radiation in oblique incidence in InSb in the THz frequency range, through numerical simulations. The eff ects of interest occur in the reststrahl region, these eff ects being linked to the surface polaritons and the surface resonances that appear as an extension of the surface polaritons in the region where |k x | < k 0 . Our refl ection simulations for InSb considered room temperature and an undoped sample. We demonstrate some interesting eff ects for an external magnetic fi eld small in relation to those present in the literature. The most valuable results were obtained for the external magnetic fi eld of +0.05 T. In terms of the Goos-Hänchen eff ect, we obtained a clear shift in the upper reststrahl region. As for refl ectivity, we also had minima in its values in the upper reststrahl region that follow the line of surface resonances. We also demonstrate the non-reciprocal eff ects due to the external magnetic fi eld, in addition to the antisymmetry and non-symmetry of some parameters.
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3
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ADRIEL DE OLIVEIRA AQUINO
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Model of 𝜙CDM for Phantom Dark Energy from 1 − α Generalized Logarithm
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Leader : FÁBIO CABRAL CARVALHO
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MEMBRES DE LA BANQUE :
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EDESIO MIGUEL BARBOZA JUNIOR
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FÁBIO CABRAL CARVALHO
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HIDALYN THEODORY CLEMENTE MATTOS DE SOUZA
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Data: 15 mai 2023
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Afficher le Résumé
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From the 20th century, with the beginning of modern cosmology, there were extensive studies on the hypothesis of dark energy, a form of energy present in space that accele- rates the expansion of our universe. Among the many theories that explain this concept, we chose to work with Quintessence, a theory in which dark energy is described in terms of a scalar field 𝜙CDM . More specifically, we will work with a type of energy called phantom, which is characterized by the state parameter ω < −1. For this, we will use the 𝜙CDM model, an alternative to the standard model ΛCDM, exploring its scalar field and its energy-momentum tensor. Therefore, we sought to test the phantom field statistically using the χ2 method and verify its accuracy against observational data.
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4
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ADRIEL DE OLIVEIRA AQUINO
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Model of 𝜙CDM for Phantom Dark Energy from 1 − α Generalized Logarithm
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Leader : FÁBIO CABRAL CARVALHO
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MEMBRES DE LA BANQUE :
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EDESIO MIGUEL BARBOZA JUNIOR
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FÁBIO CABRAL CARVALHO
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HIDALYN THEODORY CLEMENTE MATTOS DE SOUZA
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Data: 15 mai 2023
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Afficher le Résumé
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From the 20th century, with the beginning of modern cosmology, there were extensive studies on the hypothesis of dark energy, a form of energy present in space that accele- rates the expansion of our universe. Among the many theories that explain this concept, we chose to work with Quintessence, a theory in which dark energy is described in terms of a scalar field 𝜙CDM . More specifically, we will work with a type of energy called phantom, which is characterized by the state parameter ω < −1. For this, we will use the 𝜙CDM model, an alternative to the standard model ΛCDM, exploring its scalar field and its energy-momentum tensor. Therefore, we sought to test the phantom field statistically using the χ2 method and verify its accuracy against observational data.
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5
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ADLAN DA SILVA FREITAS
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Magnetocaloric effect on clusters of ferromagnetic nanoparticles
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Leader : ARTUR DA SILVA CARRIÇO
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MEMBRES DE LA BANQUE :
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ARTUR DA SILVA CARRIÇO
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IDALMIR DE SOUZA QUEIROZ JÚNIOR
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GUSTAVO DE OLIVEIRA GURGEL REBOUÇAS
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Data: 26 oct. 2023
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Afficher le Résumé
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The magnetocaloric effect (MCE) is a relevant subject of study due to its potential in areas like biotechnology, medicine, and materials engineering. When a magnetic material is subjected to an external magnetic field, its entropy changes. Upon removal of the field, the material undergoes a temperature change, referred to as the magnetocaloric effect. This phenomenon has several innovative applications, such as magnetic refrigeration, magnetic hyperthermia, and data storage.
Magnetic refrigeration is a promising application of the EMC effect due to its eco-friendly nature. It offers a sustainable and efficient alternative to traditional refrigeration methods that rely on harmful gases. This technology has a significant impact, and with increasing concerns about the environment, it provides an excellent solution to the refrigeration needs of various sectors.
Currently, research is focused on discovering new materials and magnetic structures that efficiently present Electromagnetic Compatibility (EMC). Therefore, it is crucial to comprehend the interactions among magnetic moments, temperature, and external fields, as well as the magnetic order of magnetic materials concerning intrinsic and extrinsic parameters, to develop new structures that meet the demands of modern society.
This study aims to investigate the magnetocaloric effect on clusters of ferromagnetic gadolinium (Gd) nanoparticles with ellipsoidal geometry. Additionally, the study will explore the influence of the dipolar field on the thermal stabilization of the magnetic moments of the nanoparticles.
This study analyzed micrometric elliptical clusters of Gd nanoparticles with varying eccentricities, nanoparticle densities, and diameters ranging from 30 nm to 200 nm. The dipolar interaction in the clusters depends upon their anisotropy, which is influenced by their geometry. The analysis was conducted at a fixed magnetic field in the preferred direction of anisotropy (i.e., the ellipse's major axis) in a temperature range of 200 K to 450 K. The isothermal magnetic entropy variation DSM was calculated under an applied external magnetic field, revealing the normal EMC and the inverse magnetocaloric effect (EMCI) due to the competition between the Zeeman and dipolar interaction energies. Transitional phrases were used to indicate the sequence of the analysis. The technical terms planar susceptibility and out-of-plane angle were also utilized.
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6
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MIKAEL JAKSON SILVA GOMES
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Constraining cosmographic parameters with RSD data
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Leader : EDESIO MIGUEL BARBOZA JUNIOR
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MEMBRES DE LA BANQUE :
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CORNELIO RODRIGUES FILHO
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EDESIO MIGUEL BARBOZA JUNIOR
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HIDALYN THEODORY CLEMENTE MATTOS DE SOUZA
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MARIA ALDINÊZ DANTAS
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Data: 12 déc. 2023
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Afficher le Résumé
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The Hubble constant $H_0$, the deceleration parameter $q_0$ and and the jerk $j_0$ are between some of most searched parameters in cosmology. These parameters gives information about the expansion rate, the acceleration and the acceleration rate of universe, respectively. In the final years of 20th century, supernova Ia distance measurements revealed that $q_0<0$ meaning that the universe is accelerating currently. The model which better explain the cosmic acceleration is the so-called $\Lambda$CDM model. However, the global estimate of $H_0$ (which use the $\Lambda$CDM as background model) and the local estimate of $H_0$ (which is model independent) presents a discrepancy of approximately $4\sigma$. This discrepancy puts problems on the $\Lambda$CDM model. In this scenario, the jerk parameter becomes an important piece for the validation of the $\Lambda$CDM model for which $j_0=1$. In this paper we perform a series expansion of $f\sigma_8$ and use the differential equation which provide the time evolution of $f\sigma_8$ as recurrence formula to write the series coefficients in terms of the kinematic parameters $q_0$ and $j_0$. From this process $f_0\sigma_{8,0}$, $q_0$, $j_0$, $\Omega_{{\rm m},0}$ and $\sigma_{8,0}$ emerges as free parameters. Then we use the $f\sigma_8$ data to constraining the free parameters. The Planck 2018 bounds on $\Omega_{{\rm m},0}$ and $\sigma_{8,0}$ are used to break the parameters degeneracy. We obtain that $j_0\neq1$ at $1\sigma$. Although the $\Lambda$CDM model is not the preferred model it can not be ruled out by the data used in our analysis.
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7
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ADIVAN CARLOS DE OLIVEIRA SANTOS JUNIOR
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Comparison of flux distribution moments from light curves for stars with planets and without planets
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Leader : BRAULIO BATISTA SOARES
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MEMBRES DE LA BANQUE :
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ANTONIO CARLOS DA SILVA MIRANDA
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BRAULIO BATISTA SOARES
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MACKSON MATHEUS FRANÇA NEPOMUCENO
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Data: 21 déc. 2023
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Afficher le Résumé
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Since the beginning of humanity we have been instigated by questions about our existence and our place in the cosmos, based on questions like this and hypotheses, a new area to be studied by stellar astrophysics, the study of exoplanets gives us before nothing more is the certainty that our planetary system is not unique and that a wide range of Possibilities arise as new discoveries are made in this area of study. This one work aims to provide a historical overview of exoplanetology in addition to publicize the advances made in the area, from the first discoveries to future perspectives, show some basic concepts within this area of study such as the definition of what would be exoplanets and present the most used exoplanet detection methods and responsible for the most recent discoveries. A study was also carried out with 20 curves of light, obtained from the Exoplanet Archive, consisting of 10 stars with planets already confirmed by other studies and 10 stars without confirmed planets. For each of these stars the light curve and probability density graph was created in the R studio program, as well as studied the first four moments of statistical distribution for the flow of this star. In the results we obtained expected patterns for the light curves being eclipsed with periods very close to those found in the literature, and constant flows in the light curves of planetless stars. for statistical moments were also expected patterns were found, considering the limitations of the R studio program and the Kepler telescope.
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Thèses |
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1
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FRANCISCO GOMES DE QUEIROZ
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Field and Temperature Effect on the Magnetic Phases of bulk and Films of the Rare Earths Dysprosium and Holmium.
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Leader : VAMBERTO DIAS DE MELLO
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MEMBRES DE LA BANQUE :
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MANOEL SILVA DE VASCONCELOS
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DORY HÉLIO AIRES DE LIMA ANSELMO
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FRANCISCO CESAR DE MEDEIROS FILHO
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MARIA DAS GRAÇAS DIAS DA SILVA
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VAMBERTO DIAS DE MELLO
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Data: 1 mars 2023
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Afficher le Résumé
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Rare earth materials in their volumetric form without the presence of external field, only by thermal effects, present a rich diversity of magnetic configurations for certain temperature ranges, specific to each element. The construction of artificial systems, such magnetic thin films and multilayer, in which rare earth elements are part of at least one of the constituents, has promoted the discovery of new magnetic patterns.
In this work we present two investigations, one in collaboration with the experimental group of the magnetism laboratory of the Department of Physics of the Moscow State University M.V.Lomonosov in which we modeled the experimental results of ultrapure samples of the rare earth Dysprosium and the investigation of the thermal hysteresis cycles in holmium thin films of various dimensions, aiming to find different magnetic phases in these cycles.
The theoretical method used to obtain the equilibrium phases consists of a system, where the contributions of the exchange energies, anisotropy energy and zeeman energy are calculated in a set of nonequivalent magnetic spins, and the magnetic phases, from the temperature of Curie to the temperature of Nèel, are determined by self-consistent manner, resulting in a vanishing torque in the magnetic spins.
Our modeling reproduced the experimental measures of magnetization and magnetic phases obtained for the bulk Dysprosium. In the study for holmium thin films with dimensions of 7, 10, 12, 15, 18, 21 and 24 atomic planes, a width of thermal hysteresis is verified, varying from a value close to 18 K to approximately 100 K, depending on the intensity of the applied external magnetic field and the thickness of the film. For holmium thin films with dimensions less than 7 atomic planes thermal hysteresis is not observed.
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2
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LAZARO LIMA DE SALES
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Non-Gaussian Effects in Cosmology and Gravitation, Determination of Primordial Plasma Acceleration and Evolution of Chemical Potentials During Recombination
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Leader : FÁBIO CABRAL CARVALHO
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MEMBRES DE LA BANQUE :
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RAFAEL DA COSTA NUNES
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CARLOS ALEXANDRE WUENSCHE DE SOUZA
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FÁBIO CABRAL CARVALHO
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MARIA ALDINÊZ DANTAS
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RAIMUNDO SILVA JÚNIOR
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Data: 13 juil. 2023
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Afficher le Résumé
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This thesis aims to revisit and innovate the understanding of some phenomena of the primordial Universe from a non-Gaussian perspective. The research is divided into three main topics: non-Gaussian effects in Big Bang nucleosynthesis, hydrogen recombi- nation, particle-antiparticle excess, and Rindler space; primordial plasma acceleration; and evolution of primordial chemical potentials. In the first topic, we determined the non-Gaussian Saha ionization equation for recombination. We defined new binding energy and established new chemical equilibrium conditions. As an application in cosmology, we showed that there is a value q ≠ 1 that provides the same result as the usual case for the nucleosynthesis temperature and the fractional ionization equi- librium temperature, and that recombination necessarily occurs in excited states in a non-Gaussian context. Furthermore, we developed a correction strategy for the Saha ionization equation, allowing the reproduction of the same results for recombination as predicted by the Boltzmann kinetic approach. We derived non-Gaussian expressions for the particle-antiparticle excess in relativistic and non-relativistic limits and analyzed their effects. As an application in gravitation, we showed that the non-Gaussian binding energy in Rindler space has a quadratic dependence on the gravitational field and derived a constraint for this field. Besides, we demonstrated that photoionization and pair production are more intensely suppressed in regions with strong gravitational fields compared to results obtained with classical statistics and derived a constraint im- posed on the electron and positron chemical potentials. Regarding the second topic, we determined the plasma acceleration via the Saha ionization equation in the primordial Universe. We derived the plasma acceleration at the beginning of nucleosynthesis and showed that there is a transition in acceleration around the nucleosynthesis temperature. We also demonstrated that when the deuterium bottleneck is overcome, the plasma acceleration is much higher than the acceleration of the Universe. We showed that the plasma acceleration is negative at the time of recombination, and for z < 380.23 the primordial plasma begins to accelerate. We investigated the possible physical reasons underlying this occurrence. Finally, in the third topic, we revisited the hydrogen recom- bination history from an innovative perspective: the evolution of chemical potentials. We derived expressions for these potentials, which are dependent on the thermal bath temperature and the ionization degree of the Universe. This novel approach revealed a constraint between the chemical potentials of hydrogen and the proton at z ≈ 1200, when the free electron fraction is Xe ≈ 1/3.
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