Late time cosmology in f(R,G)- gravity with interacting fluids

Cosmological models are obtained in a $f(R)$ modified gravity with a coupled Gauss-Bonnet (GB) terms in the gravitational action. The dynamical role of the GB terms is explored with a coupled dilaton field in two different cases (I) $f(R)= R + \gamma R^2- \lambda \left( \frac{R}{3m_s^2} \right)^{\delta}$ where $\gamma$, $\lambda$ and $\delta$ are arbitrary constants and (II) $f(R)=R$ and estimate the constraints on the model parameters. In the first case we choose GB terms coupled with a free scalar field in the presence of interacting fluid and in the second case GB terms coupled with scalar field in a self interacting potential to compare the observed universe. The evolutionary scenario of the universe is obtained adopting a numerical technique as the field equations are highly non-linear. Defining a new density parameter $\Omega_{H}$, a ratio of the dark energy density to the present energy density of the non-relativistic matter, we look for a late accelerating universe. The state finder parameters $\Omega_{H}$, deceleration parameter ($q$), jerk parameter ($j$) are plotted. It is noted that a non-singular universe with oscillating cosmological parameters for a given strength of interactions is admitted in Model-I. The gravitational coupling constant $\lambda$ is playing an important role. The Lagrangian density of $f(R)$ is found to dominate over the GB terms when oscillating phase of dark energy arises. In Model-II, we do not find oscillation of the cosmological parameters as the universe evolves. In the presence of interaction the energy from radiation sector of matter cannot flow to the other two sectors of fluid. The range of values of the strengths of interaction of the fluids are estimated for a stable universe assuming the primordial gravitational wave speed equal to unity.

Generalized model of interacting dark energy and dark matter: Phase portrait analysis for evolving universe

The main aim of this work is to give a suitable explanation of present accelerating universe through an acceptable interactive dynamical cosmological model. A three-fluid cosmological model is introduced in the background of Friedmann–Lemaître–Robertson-Walker asymptotically flat spacetime. This model consists of interactive dark matter and dark energy with baryonic matter, taken as perfect fluid, satisfying barotropic equation of state. We consider dust as the candidate of dark matter. A scalar field [Formula: see text] represents dark energy with potential [Formula: see text]. Einstein’s field equations are utilized to construct a three-dimensional interactive autonomous system by choosing suitable interaction between dark energy and dark matter. We take the interaction kernel as [Formula: see text], where [Formula: see text] indicates the density of dark energy, [Formula: see text] is the interacting constant and [Formula: see text] is Hubble parameter. In order to explain the stability of this system, we obtain some suitable critical points. We analyze stability of obtained critical points to show the different phases of universe and cosmological implications. Surprisingly, we find some stable critical points which represent late-time dark energy-dominated era when a model parameter [Formula: see text] is equal to [Formula: see text]. We introduce a two-dimensional interactive autonomous system and after phase portrait analysis of it, we get several stable points which represent dark energy-dominated era and late-time cosmic acceleration simultaneously. Here, we also demonstrate the variation in interaction at vicinity of phantom barrier [Formula: see text]. From our work, we can also predict the future phase evolution of the universe.

Quantum cloud theory: Collapse expectations and superposition conservation

Most of metabolic processes are extremely complicated but occur spontaneously and steadily, the essential reason of which may be either a thermodynamic problem or related to some quantum properties. Here, collapse selection is interpreted with an analytical model of energy transfer, from which the concept of quantum cloud is defined as that during undetectable changes of a group of particles between its effective changes, particles are in the superposition of various energy states and the group is named as a cloud. It is deduced from a conservation notion of matter proportions that active cloud collapses have least-time expectation while passive collapses have matter-proportion expectation. As the results, quantum Zeno effect is a typical phenomenon of passive collapses while anti-Zeno effect is typical active collapses; moreover, the phenomenon of dark matter may be dark-cloud effect of normal matter while the phenomenon of accelerating universe may be induced by the luminescent asymmetries of bright celestial bodies.

The PAU survey: measurement of narrow-band galaxy properties with approximate bayesian computation

Narrow-band imaging surveys allow the study of the spectral characteristics of galaxies without the need of performing their spectroscopic follow-up. In this work, we forward-model the Physics of the Accelerating Universe Survey (PAUS) narrow-band data. The aim is to improve the constraints on the spectral coefficients used to create the galaxy spectral energy distributions (SED) of the galaxy population model in Tortorelli et al. 2020. In that work, the model parameters were inferred from the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) data using Approximate Bayesian Computation (ABC). This led to stringent constraints on the B-band galaxy luminosity function parameters, but left the spectral coefficients only broadly constrained. To address that, we perform an ABC inference using CFHTLS and PAUS data. This is the first time our approach combining forward-modelling and ABC is applied simultaneously to multiple datasets. We test the results of the ABC inference by comparing the narrow-band magnitudes of the observed and simulated galaxies using Principal Component Analysis, finding a very good agreement. Furthermore, we prove the scientific potential of the constrained galaxy population model to provide realistic stellar population properties by measuring them with the SED fitting code CIGALE. We use CFHTLS broad-band and PAUS narrow-band photometry for a flux-limited (i < 22.5) sample of galaxies up to redshift z ∼ 0.8. We find that properties like stellar masses, star-formation rates, mass-weighted stellar ages and metallicities are in agreement within errors between observations and simulations. Overall, this work shows the ability of our galaxy population model to correctly forward-model a complex dataset such as PAUS and the ability to reproduce the diversity of galaxy properties at the redshift range spanned by CFHTLS and PAUS.

Thermodynamic analysis for Non-linear system (Van-der-Waals EOS) with viscous cosmology

The following paper is motivated by the recent works of Kremer [Gen Relativ Gravit 36(6):1423–1432, 2004; Phys Rev D 68(12):123507, 2003], Vardiashvili (Inflationary constraints on the van Der Waals equation of state, arXiv:1701.00748, 2017), Jantsch (Int J Mod Phys D 25(03):1650031, 2016), Capozziello (Phys Lett A 299(5–6):494–498, 2002) on Van-Der-Waals EOS cosmology. The main aim of this paper is to analyze the thermodynamics of a Non-linear system which in this case is Van-Der-Waals fluid EOS (Capozziello et al., Quintessence without scalar fields, arXiv:astro-ph/0303041, 2003). We have investigated the Van-Der-Waals fluid system with the generalized EOS as $$p=w\left( \rho ,t \right) \rho +f\left( \rho \right) -3\eta \left( H,t \right) H$$ p = w ρ , t ρ + f ρ - 3 η H , t H (Brevik et al., Int J Geom Methods Mod Phys 15(09):1850150, 2018). The third term signifies viscosity which has been considered as an external parameter that only modifies pressure but not the density of the liquid. The $$w(\rho ,t)$$ w ( ρ , t ) and $$f(\rho )$$ f ( ρ ) are the two functions of energy density and time that are different for the 3 types of Vander Waal models namely one parameter model, two parameters model and three parameters model (Ivanov and Prodanov, Eur Phys J C 79(2):118, 2019; Elizalde and Khurshudyan, Int J Mod Phys D 27(04):1850037, 2018). The value of EOS parameter ($$w_{EOS})$$ w EOS ) (Capozziello et al., Quintessence without scalar fields, arXiv:astro-ph/0303041, 2003; Obukhov and Timoshkin, Russ Phys J 60(10):1705–1711, 2018) will showdifferent values for different models. We have studied the changes in the parameters for different cosmic phases [Kremer, Phys Rev D 68(12):123507, 2003; Capozziello et al., Phys Lett A 299(5–6):494–498, 2002; Capozziello et al., Quintessence without scalar fields, arXiv:astro-ph/0303041, 2003]. We have also studied the thermodynamics and the stability conditions for the three models in viscous condition [Obukhov and Timoshkin, Russ Phys J 60(10):1705–1711, 2018; Panigrahi and Chatterjee, Gen Relativ Gravit 49(3):35, 2017; Panigrahi and Chatterjee, J Cosmol Astropart Phys 2016(05):052, 2016; Chakraborty et al., Evolution of FRW Universe in Variable Modified Chaplygin Gas Model, arXiv:1906.12185, 2019]. We have discussed the importance of viscosity (Brevik and Grøn, Astrophys Space Sci 347(2):399–404, 2013) in explaining accelerating universe with negative pressure (Panigrahi and Chatterjee, Gen Relativ Gravit 49(3):35, 2017).Finally, we have resolved the finite time future singularity problems [Brevik et al., The effect of thermal radiation on singularities in the Dark Universe, arXiv:2103.08430, 2021; Odintsov and Oikonomou, Phys Rev D 98(2):024013, 2018; Odintsov and Oikonomou, Int J Mod Phys D 26(08):1750085, 2017; Frampton et al., Phys Rev D 85(8):083001, 2012; Frampton et al., Phys Lett B 708(1–2):204–211, 2012; Frampton et al., Phys Rev D 84(6):063003, 2011] and discussed the thermodynamics energy conditions [Visser and Barcelo, Energy conditions and their cosmological implications. In: Cosmo-99, pp 98–112, 2000; Chattopadhyay et al., Eur Phys J C 74(9):1–13, 2014; Arora et al., Phys. Dark Universe 31:100790, 2021; Sharma and Pradhan, Int J Geom Methods Mod Phys 15(01):1850014, 2018; Sahoo et al., AstronomischeNachrichten 342(1–2):89–95, 2021; Yadav et al., Mod Phys Lett A 34(19):1950145, 2019; Sharma et al., Int J Geom Methods Mod Phys 17(07):2050111, 2020, Moraes and Sahoo, Eur Phys J C 77(7):1–8, 2017; Hulke et al., New Astron 77:101357, 2020; Singla et al., Gravit Cosmol 26(2):144–152, 2020; Sharif et al., Eur Phys J Plus 128(10):1–11, 2013] with those models.

From Rindler fluid to dark fluid on the holographic cutoff surface

As an approximation to the near horizon regime of black holes, the Rindler fluid was proposed on an accelerating cutoff surface in the flat spacetime. The concept of the Rindler fluid was then generalized into a flat bulk with the cutoff surface of the induced de Sitter and FRW universe, such that an effective description of dark fluid in the accelerating universe can be investigated.

AS CARACTERÍSTICAS DOS TEXTOS DE DIVULGAÇÃO CIENTÍFICA QUE PROMOVEM O INTERESSE PELA CIÊNCIA EM UM PÚBLICO INFANTOJUVENIL

Neste artigo identificamos as principais características de textos de divulgação científica que têm o potencial de despertar o interesse pela ciência e facilitar a aprendizagem no público infantojuvenil. Para isso, escrevemos textos de divulgação conjugando técnicas de redação utilizadas por jornalistas científicos e informação científica dos pesquisadores brasileiros envolvidos no projeto J-PAS (Javalambre Physics of the Accelerating Universe Astrophysical Survey). Realizamos aplicações didáticas para turmas de 7º, 8º e 9º ano do Ensino Fundamental 2 e uma para uma turma do 1º Ano do Ensino Médio. Os resultados indicam que o uso de textos de divulgação científica podem ser uma estratégia eficaz não apenas para a difusão do conhecimento, mas também para o ensino de Astronomia na sala de aula. Este trabalho foi desenvolvido no contexto de um mestrado profissional em ensino de Astronomia, que teve como produto educacional uma rede de divulgação centrada na plataforma Wordpress e ligada às redes sociais Facebook, Twitter e Google Plus, além de um e-book voltado a professores com parâmetros de escolha de textos de divulgação científica para atividades didáticas e uma proposta de atividade didática com textos de divulgação científica.

Accelerating universe with binary mixture of bulk viscous fluid and dark energy

In this paper, we have proposed a model of accelerating universe with binary mixture of bulk viscous fluid and dark energy (DE) and probed the model parameters: present values of Hubble’s constant [Formula: see text], equation of state paper of DE [Formula: see text] and density parameter of DE [Formula: see text] with recent observational [Formula: see text] data (OHD) as well as joint Pantheon compilation of SN Ia data and OHD. Using cosmic chronometric technique, we obtain [Formula: see text] and [Formula: see text] by restricting our derived model with recent OHD and joint Pantheon compilation SN Ia data and OHD, respectively. The present age of the universe in derived model is estimated as [Formula: see text]. Also, we observe that derived model represents a model of transitioning universe with transition redshift [Formula: see text]. We have constrained the present value of jerk parameter as [Formula: see text] with joint OHD and Pantheon data. From this analysis, we observed that the model of the universe, presented in this paper, shows a marginal departure from [Formula: see text]CDM model.