Study of non-canonical scalar field model using various parametrizations of dark energy equation of state

In this present work, we try to build up a cosmological model using a non-canonical scalar field within the framework of a spatially flat FRW space-time. In this context, we have considered four different parametrizations of the equation of state parameter of the non-canonical scalar field. Under this scenario, analytical solutions for various cosmological parameters have been found out. It has been found that the deceleration parameter shows a smooth transition from a positive value to some negative value which indicates that the universe was undergoing an early deceleration followed by late time acceleration which is essential for the structure formation of the universe. With these four parametrizations, the future evolution of the models are also discussed. It has been found that one of the models (Generalized Chaplygin gas model, GCG) mimics the concordance $\Lambda$CDM in the near future, whereas two other models (CPL and JBP) diverge due to future singularity. Finally, we have studied these theoretical models with the latest datasets from SN Ia $+$ $H(z)$ $+$ BAO/CMB.Comment: 25 pages, 20 figures, accepted for publication in European Physical Journal

Observational constraints on the jerk parameter with the data of the Hubble parameter

We study the accelerated expansion phase of the universe by using the {\textit{kinematic approach}}. In particular, the deceleration parameter $q$ is parametrized in a model-independent way. Considering a generalized parametrization for $q$, we first obtain the jerk parameter $j$ (a dimensionless third time derivative of the scale factor) and then confront it with cosmic observations. We use the latest observational dataset of the Hubble parameter $H(z)$ consisting of 41 data points in the redshift range of $0.07 \leq z \leq 2.36$, larger than the redshift range that covered by the Type Ia supernova. We also acquire the current values of the deceleration parameter $q_0$, jerk parameter $j_0$ and transition redshift $z_t$ (at which the expansion of the universe switches from being decelerated to accelerated) with $1\sigma$ errors ($68.3\%$ confidence level). As a result, it is demonstrate that the universe is indeed undergoing an accelerated expansion phase following the decelerated one. This is consistent with the present observations. Moreover, we find the departure for the present model from the standard $\Lambda$CDM model according to the evolution of $j$. Furthermore, the evolution of the normalized Hubble parameter is shown for the present model and it is compared with the dataset of $H(z)$.Comment: 9 pages, 4 figures, 1 table, new references added, version accepted for publication in the European Physical Journal

A parametric reconstruction of the deceleration parameter

The present work is based on a parametric reconstruction of the deceleration parameter $q(z)$ in a model for the spatially flat FRW universe filled with dark energy and non-relativistic matter. In cosmology, the parametric reconstruction technique deals with an attempt to build up a model by choosing some specific evolution scenario for a cosmological parameter and then estimate the values of the parameters with the help of different observational datasets. In this paper, we have proposed a logarithmic parametrization of $q(z)$ to probe the evolution history of the universe. Using the type Ia supernova (SNIa), baryon acoustic oscillation (BAO) and the cosmic microwave background (CMB) datasets, the constraints on the arbitrary model parameters $q_{0}$ and $q_{1}$ are obtained (within $1\sigma$ and $2\sigma$ confidence limits) by $\chi^{2}$-minimization technique. We have then reconstructed the deceleration parameter, the total EoS parameter $\omega_{tot}$, the jerk parameter and have compared the reconstructed results of $q(z)$ with other well-known parametrizations of $q(z)$. We have also shown that two model selection criteria (namely, Akaike information criterion and Bayesian Information Criterion) provide the clear indication that our reconstructed model is well consistent with other popular models.Comment: v2:substantially revised, refs added, Accepted for publication in European Physical Journal

The effects of normal ageing and processing style on explicit and implicit memory

Explicit memory (e.g. recognition) declines with age, but there is disagreement about whether implicit memory (e.g. priming) declines or remains intact with age. Processing style is one primary factor that may explain this discrepancy: there is evidence that ageing does not affect conceptual (meaning-based) and perceptual (feature-based) processing equally, yet processing demands have varied in prior studies. The aim of this thesis is to understand how the type of cognitive processing affects the magnitude of age effects on implicit memory. Five experiments were conducted (four online and one lab-based) to compare the performance of young (18-30 years) and older (+65 years) adults on a range of implicit tests while varying conceptual /perceptual processing at encoding (Experiments 1A, 1B and 2), and both encoding and test (Experiments 3-4). In Experiments 1A and 1B a perceptual implicit memory task (Continuous Identification Task with Recognition; CID-R) was used, while in Experiment 2 a conceptual implicit task (Category Exemplar Generation; CEG) was used, and a recognition task was also included to assess explicit memory. In Experiment 3 both conceptual and perceptual tasks were used in a within-subjects design, and the conceptual implicit task was changed to Category Verification with Recognition (CV-R). Experiment 4 replicated Experiment 3 but was performed in person after COVID-19 restrictions ended. The results showed an age-related decline in explicit memory in all experiments except Experiment 3, and the key finding in relation to implicit memory is that age differences were affected by the type of processing. In most cases, priming was reduced by age when items were encoded conceptually and the test phase involved perceptual processing. These new findings challenge the widely held view that implicit memory remains stable with age and suggest that age differences in implicit memory are mediated by the type of processing at encoding and test

Generalized Second Law of Thermodynamics for Non-canonical Scalar Field Model with Corrected-Entropy

In this work, we have considered a non-canonical scalar field dark energy model in the framework of flat FRW background. It has also been assumed that the dark matter sector interacts with the non-canonical dark energy sector through some interaction term. Using the solutions for this interacting non-canonical scalar field dark energy model, we have investigated the validity of generalized second law (GSL) of thermodynamics in various scenarios using first law and area law of thermodynamics. For this purpose, we have assumed two types of horizons viz apparent horizon and event horizon for the universe and using first law of thermodynamics, we have examined the validity of GSL on both apparent and event horizons. Next, we have considered two types of entropy-corrections on apparent and event horizons. Using the modified area law, we have examined the validity of GSL of thermodynamics on apparent and event horizons under some restrictions of model parameters.Comment: 15 pages, 8 figures, Accepted for publication in EPJ