Alipurduar College

This investigation examines the dynamical characteristics of various soliton-type solutions of the (2+1)-dimensional non-autonomous perturbed Gardner-Kadomtsev-Petviashvili (NAPGKP) equation. Using its bilinear form, multi-soliton solutions are derived through Hirota's approach. Intensive study on soliton propagation, soliton interaction, and complex hybrid solutions are performed. Breathers are explored from a multi-soliton solution by selecting a suitable complex conjugate relation in the wave vector. The significant impact of different parameters on the characteristic line of the breather is examined. Along with the group velocity, the phase velocity of the breather is presented explicitly. Positon solution of higher order and the interaction of other waveforms are exhibited by selecting suitable values of parameters.

This article investigates the propagation of different types of nonlinear ion-acoustic waves, including periodic waves, solitons, and breathers in non-Maxwellian magnetized plasma. The plasma model consists of inertial cold ions, inertialess cold electrons that obey a Boltzmann distribution, and inertialess non-Maxwellian hot electrons that follow the generalized (r, q) distribution. The reductive perturbation technique is utilized to obtain the Korteweg–de Vries–Zakharov–Kuznetsov equation (KdV-ZK) from the fluid equations that govern plasma dynamics. Furthermore, the modified KdV-ZK equation is derived due to the limited capability of the KdV-ZK model to represent the dynamics of the nonlinear structures at specific critical values of the relevant physical variables in the investigated system. The periodic solutions to the two models (KdV-ZK and mKdV-ZK models) are derived using Jacobi elliptic functions. This approach directly links periodic waves (cnoidal waves) and soliton solutions. Hirota's bilinear method generates breathers for both models. Finally, we examine the quantitative understanding of the effects of several physical parameters replicated by the Swedish satellite Viking incorporated in the model. The findings reported in this study enhance our comprehension of the properties of the electron distribution function's high- and low-energy segments and the development of periodic, soliton, multi-soliton, and breather phenomena in space and astrophysical plasmas.

In this paper, the emergent universe model (EU) is explored (as per Mukherjee 𝑒𝑡 𝑎𝑙. ) in a flat scenario with equation of state (EoS) p=Bρ -Aρ ^1/2 (where A and B are constants). Here, the temperature function is evaluated in terms of the EoS parameters and redshift under the conditions of balanced particle creation and annihilation. To examine the thermodynamic evolution and find a viable EU model, constraints on its EoS parameters are determined. First, constraints on A_s , and B (where A_s = A/ρ _eu0^1/2 and ρ _eu0 is the present energy density) are obtained from the acceptable transition redshift limit z_tr and decoupling temperature limit T_d as A_s ≈ (0.84-1.07) and B ≈ (0.38-0.42) for the general EU model. Finally, stricter constraints on z_tr are drawn from recent T(z)-z and observed Hubble data (OHD). These z_tr and T_d values are then utilized to obtain acceptable limits on A_s , and B . On average, the acceptable limits on z_tr , A_s , and B are 0.79± 0.03 (in the 1 σ error limit), ≈ (1.11-1.15) and ≈ (0.41-0.43) , respectively, for the general EU model. In the B=1/3 model, obtained value z_tr= 0.71± 0.01 (at the 1 σ level). The present values of the EoS parameters are determined, and the viability of the models is examined with plots of the deceleration parameter ( q ), equation of state ( ω ) and squared adiabatic sound speed ( c^2_s ) with redshift ( z ). The distance modulus ( μ ) of this EU model is compared with the HIIG and Union2.1 data. The models with B (= -1/3, 0) , are not suitable at all according to the present analysis, whereas, the B=1/3 model is quite similar to the observations.

This work discuses the effect of the QCD coupling constant (α_c) on various physical properties of compact stars in the framework of the Tolman IV potential admitting the equation of state of MIT bag model with nonzero value of mass of strange quark mass (m_s). The internal matter, consisting of the deconfined phase of the 3-flavour quark, is overall charge neutral due to the presence of electrons and is assumed to be strongly interacting. Interestingly, it is noted that the coupling constant α_c has an upper limit due to thermodynamic consistency and affects the stability of the stellar structure in terms of energy per baryon (E_B). Present model is suitable to study the properties of stars with mass of approximately ≤ 2.00 M_⊙. The predicted radii of a few known stars from our model are in good agreement with the estimated values of radius obtained from the observations. Necessary energy conditions are obeyed inside the stellar configuration. Various stability conditions are carried out and it is found that within the range of parameter space used here the model is stable.

Abstract A class of strange stars is analysed in the present article in hydrostatic equilibrium, whose state is defined by a CFL phase equation of state. We have compared our results with those obtained from the MIT equation of state for strange quark matter, which is regarded as free particles. We have noted that if we consider quarks to form a cooper pair and if their description is made by the CFL equation of state, the maximum mass of strange star reaches a value as high as 3.61 $$M_{\odot }$$ M ⊙ . This value is well above the value of 2.03 $$M_{\odot }$$ M ⊙ obtained by using the MIT bag equation of state for massless free quarks. Both the maximum masses are determined by solving the TOV equation for different values of the strange quark mass $$m_s$$ m s . Thus, the inclusion of the possibility of quark pair formation in the theory permits us to accommodate a wider class of compact objects such as PSR J1614-2230, PSR J0740+6620, PSR J0952-0607 etc. and the mass of the companion star in the GW190814 event in our model. The consideration of such a high value of mass is hardly theoretically obtainable from normal strange star models in general relativity even with a fast rotation effect. The object PSR J0952-0607 is found to be the fastest and heaviest pulsar in the disk of Milky Way Galaxy, having a mass of 2.35 $$M_{\odot }$$ M ⊙ , which may be predicted in our model, as observational evidence supports the existence of strange quark matter in its composition.