In the present study, we have described the accelerated cosmological models of the universe in f(Q) gravity. In f(Q) gravity, the gravitational field equations are modified by a function of the non-metricity tensor, which characterizes the deviation of the affine connection from the metric compatibility condition. We have considered two different forms of f(Q) gravity as f(Q) = beta + alpha , Q^{(n+1)} and f(Q) = beta , Q + alpha , Q^{n} to explain the dynamics of the expanding universe. We have discussed the dynamics of the universe through graphical representation by considering the power law ( $a = k t^m$). The free parameters of {color{red}the} models are fitted {color{red}with} the latest observational data set of {color{red} Observational Hubble Data} (OHD), consisting of 57 points, using statistical analysis based on the MCMC method. The best-fitted values for the model’s parameter are estimated as H_0 = 67.3 pm 1.1, m = 1.0213 pm 0.0071, and k = 65.4 pm 1.1. The parameters of the derived model, like energy density, isotropic pressure, EoS parameter, and jerk parameter, are discussed. We have described the energy conditions to explain the viability of the considered models. We have also verified the stability of the derived model through perturbation analysis.
{"title":"Stability of Power Law cosmological model in f(Q) gravity","authors":"Priyanka Garg, Vinod Kumar Bhardwaj","doi":"10.1139/cjp-2023-0113","DOIUrl":"https://doi.org/10.1139/cjp-2023-0113","url":null,"abstract":"In the present study, we have described the accelerated cosmological models of the universe in f(Q) gravity. In f(Q) gravity, the gravitational field equations are modified by a function of the non-metricity tensor, which characterizes the deviation of the affine connection from the metric compatibility condition. We have considered two different forms of f(Q) gravity as f(Q) = beta + alpha , Q^{(n+1)} and f(Q) = beta , Q + alpha , Q^{n} to explain the dynamics of the expanding universe. We have discussed the dynamics of the universe through graphical representation by considering the power law ( $a = k t^m$). The free parameters of {color{red}the} models are fitted {color{red}with} the latest observational data set of {color{red} Observational Hubble Data} (OHD), consisting of 57 points, using statistical analysis based on the MCMC method. The best-fitted values for the model’s parameter are estimated as H_0 = 67.3 pm 1.1, m = 1.0213 pm 0.0071, and k = 65.4 pm 1.1. The parameters of the derived model, like energy density, isotropic pressure, EoS parameter, and jerk parameter, are discussed. We have described the energy conditions to explain the viability of the considered models. We have also verified the stability of the derived model through perturbation analysis.
","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135728532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ben Niu, Yizhuo Zhang, Jihui Chen, Shiyan Meng, Ke Yao, Yaming Zou, Jiguang Li, Zhencen He, Ju Meng
This work reported the investigation of optical spectra of Rh-like Xe9+ and Ru-like Xe10+ ions at a low-energy electron beam ion trap. The line from 4d92D3/2 - 2D5/2M1 transition of Xe9+ ions was remeasured, the wavelength of which was determined to be 598.365(5) nm, and the uncertainty was significantly improved. In the region of 200 - 700 nm, four spectral lines emitted from Xe10+ ions were directly observed for the first time. The relativistic many-body perturbation method was adopted for the investigation of fine structure in Xe10+ ions. The theoretical and experimental results were in good agreement within 2%, and the four observed lines of Xe10+ ions were identified.
{"title":"Optical lines of Xe<sup>9+</sup> and Xe<sup>10+</sup> ions measured at a low-energy electron beam ion trap.","authors":"Ben Niu, Yizhuo Zhang, Jihui Chen, Shiyan Meng, Ke Yao, Yaming Zou, Jiguang Li, Zhencen He, Ju Meng","doi":"10.1139/cjp-2023-0231","DOIUrl":"https://doi.org/10.1139/cjp-2023-0231","url":null,"abstract":"This work reported the investigation of optical spectra of Rh-like Xe<sup>9+</sup> and Ru-like Xe<sup>10+</sup> ions at a low-energy electron beam ion trap. The line from 4<i>d</i><sup>9</sup> <sup>2</sup>D<sub>3/2</sub> - <sup>2</sup>D<sub>5/2</sub> <i>M</i>1 transition of Xe<sup>9+</sup> ions was remeasured, the wavelength of which was determined to be 598.365(5) nm, and the uncertainty was significantly improved. In the region of 200 - 700 nm, four spectral lines emitted from Xe<sup>10+</sup> ions were directly observed for the first time. The relativistic many-body perturbation method was adopted for the investigation of fine structure in Xe<sup>10+</sup> ions. The theoretical and experimental results were in good agreement within 2%, and the four observed lines of Xe<sup>10+</sup> ions were identified.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"54 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135729426","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, we investigate the influence of the angular momentum of the charged particle around non-extremal and extremal charged Taub–NUT black holes on Lyapunov exponent, and find spatial regions where chaos bound is violated. The exponent is determined by the effective potential. When the particle’s charge is fixed, circular orbits gradually move away from the event horizons with the angular momentum’s increases. We find that the bound is always violated at a certain distance from the horizons when the angular momentum is greater than a certain value. Especially when the black holes’ charges are small enough, the Lyapunov exponent’s violation always exists for any value of the particle’s angular momentum.
{"title":"Violation of the chaos bound in charged Taub–NUT black holes","authors":"Jian Tang","doi":"10.1139/cjp-2023-0082","DOIUrl":"https://doi.org/10.1139/cjp-2023-0082","url":null,"abstract":"In this paper, we investigate the influence of the angular momentum of the charged particle around non-extremal and extremal charged Taub–NUT black holes on Lyapunov exponent, and find spatial regions where chaos bound is violated. The exponent is determined by the effective potential. When the particle’s charge is fixed, circular orbits gradually move away from the event horizons with the angular momentum’s increases. We find that the bound is always violated at a certain distance from the horizons when the angular momentum is greater than a certain value. Especially when the black holes’ charges are small enough, the Lyapunov exponent’s violation always exists for any value of the particle’s angular momentum.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135993537","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, I have investigated the two-body pure penguin decays of [Formula: see text] and [Formula: see text], that these were collected with the LHCb detector, and the branching fractions were measured to be [Formula: see text] and [Formula: see text]. I have studied these decay modes within the framework of the factorization approach by using three different energy scales; while in calculating the amplitude of these decays, the multiplications of four vectors of the polarization vectors, such as [Formula: see text], [Formula: see text], and [Formula: see text] appear. These parameters have been calculated based on helicity amplitudes [Formula: see text]; the results obtained for branching fractions in the μ = m b /2 scale are [Formula: see text] and [Formula: see text]. I have also estimated the fractions of longitudinal polarizations in [Formula: see text] and [Formula: see text] decay modes by considering the transverse amplitudes [Formula: see text]; at the μ = m b /2 scale the results are obtained to be [Formula: see text] and [Formula: see text], which are comparable to the experimental results, 0.724 ± 0.051 ± 0.016 and 0.694 ± 0.016 ± 0.012, respectively, reported by the LHCb collaboration.
在本文中，我研究了[公式:见文]和[公式:见文]的两体纯企鹅衰变，这些都是用LHCb探测器收集的，分支分数测量为[公式:见文]和[公式:见文]。我通过使用三种不同的能量尺度在分解方法的框架内研究了这些衰变模式;在计算这些衰减的幅度时，出现了四个偏振矢量的乘法，如[公式:见文]、[公式:见文]和[公式:见文]。这些参数是根据螺旋幅值计算的[公式:见文];μ = m b /2尺度下分支分数的计算结果为[公式:见文]和[公式:见文]。我还通过考虑横向振幅[公式:见文本]估算了[公式:见文本]和[公式:见文本]衰减模式中纵向极化的分量;在μ = m b /2尺度下得到的结果为[公式:见文]和[公式:见文]，与LHCb合作报告的实验结果相当，分别为0.724±0.051±0.016和0.694±0.016±0.012。
{"title":"Calculations of branching ratios and longitudinal polarization fractions in B 0 → K * 0 K ¯ * 0 and B s 0 → K * 0 K ¯ * 0 decays","authors":"Behnam Mohammadi","doi":"10.1139/cjp-2023-0041","DOIUrl":"https://doi.org/10.1139/cjp-2023-0041","url":null,"abstract":"In this paper, I have investigated the two-body pure penguin decays of [Formula: see text] and [Formula: see text], that these were collected with the LHCb detector, and the branching fractions were measured to be [Formula: see text] and [Formula: see text]. I have studied these decay modes within the framework of the factorization approach by using three different energy scales; while in calculating the amplitude of these decays, the multiplications of four vectors of the polarization vectors, such as [Formula: see text], [Formula: see text], and [Formula: see text] appear. These parameters have been calculated based on helicity amplitudes [Formula: see text]; the results obtained for branching fractions in the μ = m b /2 scale are [Formula: see text] and [Formula: see text]. I have also estimated the fractions of longitudinal polarizations in [Formula: see text] and [Formula: see text] decay modes by considering the transverse amplitudes [Formula: see text]; at the μ = m b /2 scale the results are obtained to be [Formula: see text] and [Formula: see text], which are comparable to the experimental results, 0.724 ± 0.051 ± 0.016 and 0.694 ± 0.016 ± 0.012, respectively, reported by the LHCb collaboration.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"36 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136113175","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Muhammad Rizwan, Muhammad Moin, Hafiz Muhammad Naeem Ullah, Abdul Waheed Anwar, Uzma Mushtaq, Tariq Mahmood
In this study, we used density functional theory to examine how the wide band gap optoelectronic properties of pure, silver-, and cadmium-doped LaAlO 3 perovskites changed. Structural, electrical, elastic, and mechanical properties were calculated using generalized gradient approximation. Silver and cadmium incorporated at Al site demonstrated a decreasing trend in the band gap. Both impurities showed the reduction in band gap from 2.98 to 0.468 eV and from 2.98 to 2.0238 eV. The density of states was examined for pristine and doped structures to understand behavioral change of LaAlO 3 . It was observed that p states in upper valance band and d states in lower conduction band were contributing toward the reduction of band gap. Elastic properties were computed. Elastic parameters were used to calculate Born’s stability and it is predicted that the material is stable mechanically for both pristine and doped forms. Mechanical properties were also predicted and brittle nature was found for both pristine and doped materials. Optical responses such as dielectric function, absorption, and refractive index were also predicted. The impurity inclusion in pristine structure not only reduces the bad gap but also alters the optical behavior. Absorption edge shifted toward lower energy shows a clear redshift, whereas refractive index also reduces from 2.4 to 1.9, making the material more transparent. The absorption spectrum as well as electronic band gap makes this material more useful for solar cell application as well as photocatalytic applications.
{"title":"Investigations of electronic, elastic, and optical properties of (Ag, Cd)-doped LaAlO<sub>3</sub>: a computational insight","authors":"Muhammad Rizwan, Muhammad Moin, Hafiz Muhammad Naeem Ullah, Abdul Waheed Anwar, Uzma Mushtaq, Tariq Mahmood","doi":"10.1139/cjp-2023-0040","DOIUrl":"https://doi.org/10.1139/cjp-2023-0040","url":null,"abstract":"In this study, we used density functional theory to examine how the wide band gap optoelectronic properties of pure, silver-, and cadmium-doped LaAlO 3 perovskites changed. Structural, electrical, elastic, and mechanical properties were calculated using generalized gradient approximation. Silver and cadmium incorporated at Al site demonstrated a decreasing trend in the band gap. Both impurities showed the reduction in band gap from 2.98 to 0.468 eV and from 2.98 to 2.0238 eV. The density of states was examined for pristine and doped structures to understand behavioral change of LaAlO 3 . It was observed that p states in upper valance band and d states in lower conduction band were contributing toward the reduction of band gap. Elastic properties were computed. Elastic parameters were used to calculate Born’s stability and it is predicted that the material is stable mechanically for both pristine and doped forms. Mechanical properties were also predicted and brittle nature was found for both pristine and doped materials. Optical responses such as dielectric function, absorption, and refractive index were also predicted. The impurity inclusion in pristine structure not only reduces the bad gap but also alters the optical behavior. Absorption edge shifted toward lower energy shows a clear redshift, whereas refractive index also reduces from 2.4 to 1.9, making the material more transparent. The absorption spectrum as well as electronic band gap makes this material more useful for solar cell application as well as photocatalytic applications.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"42 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135720219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present a simple model of a metal in a gravitational field in order to show some physical features that help in understanding how the metal holds itself up against gravity. The nuclei are held up against gravity by their bound electron(s) as well as the electric field due to all the gravitationally induced electric dipoles at other lattice sites; these dipoles result from the bound electrons sinking, in response to the gravitational field, by a smaller distance than the nuclei. We also consider the conduction electrons to be held up by Fermi pressure. We use the model to estimate the magnitude of the gravitationally induced electric field in a metal and to establish its direction. We work in the low temperature limit.
{"title":"Model of a Metal in a Gravitational Field","authors":"Mark R.A. Shegelski, Jerad Shaw, Mitchell Hawse","doi":"10.1139/cjp-2023-0183","DOIUrl":"https://doi.org/10.1139/cjp-2023-0183","url":null,"abstract":"We present a simple model of a metal in a gravitational field in order to show some physical features that help in understanding how the metal holds itself up against gravity. The nuclei are held up against gravity by their bound electron(s) as well as the electric field due to all the gravitationally induced electric dipoles at other lattice sites; these dipoles result from the bound electrons sinking, in response to the gravitational field, by a smaller distance than the nuclei. We also consider the conduction electrons to be held up by Fermi pressure. We use the model to estimate the magnitude of the gravitationally induced electric field in a metal and to establish its direction. We work in the low temperature limit.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"49 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135769780","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We calculate the Big Bang nucleosynthesis abundances for helium-4 and deuterium for a range of neutron lifetimes, τ n = 840–1050 s, using the state-of-the-art Python package PRyMordial. We show the results for two different nuclear reaction rates, calculated by NACRE II and the PRIMAT collaborations.
我们使用最先进的Python软件包PRyMordial计算了在中子寿命τ n = 840 - 1050s范围内氦-4和氘的大爆炸核合成丰度。我们展示了两种不同的核反应速率的结果，由NACRE II和PRIMAT合作计算。
{"title":"Neutron Lifetime Anomaly and Big Bang Nucleosynthesis","authors":"Tammi Chowdhury, Seyda Ipek","doi":"10.1139/cjp-2023-0188","DOIUrl":"https://doi.org/10.1139/cjp-2023-0188","url":null,"abstract":"We calculate the Big Bang nucleosynthesis abundances for helium-4 and deuterium for a range of neutron lifetimes, τ n = 840–1050 s, using the state-of-the-art Python package PRyMordial. We show the results for two different nuclear reaction rates, calculated by NACRE II and the PRIMAT collaborations.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"82 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136307058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV metric [M.C. Durgapal, J. Phys. A 15 2637 (1982)]. In this work, we investigate the effects of the scale parameter k on the local matter distribution.
Here, we have chosen the compact star candidate SMC X-1 with observed values of mass =(1.29 ± 0.05)M⊙ and radius = 8.831_{-0.09}^{+0.09} km. respectively, to analyze our results analytically as well as graphically. For smaller values of k, we get the stiff (or hard) equation of state (EoS). Here we solve the modified Einstein's field equations in presence of the background metric gamma_{mu nu}. Due to this constant curvature background, the density and pressure terms are modified by adding an extra term, which affects the EoS. For r ll k, the background de Sitter space-time reduces into Minkowski form and the coupling vanishes. We discuss certain physical quantities of our obtained solution such as density, isotropic pressure, sound speed, pressure-density gradients, compactness, and surface redshift to claim the physical viability of our model.
It is found that our model clearly satisfies all the energy conditions, the causality condition, and the dynamical equilibrium via modified TOV equation. Finally, we can conclude that our proposed model is physically realistic and well-behaved.
{"title":"Isotropic Durgapal IV fluid sphere in bigravity","authors":"PRAMIT REJ","doi":"10.1139/cjp-2023-0205","DOIUrl":"https://doi.org/10.1139/cjp-2023-0205","url":null,"abstract":"We analyze an isotropic uncharged fluid sphere model within bigravity considering the Durgapal IV metric [M.C. Durgapal, J. Phys. A <b>15</b> 2637 (1982)]. In this work, we investigate the effects of the scale parameter k on the local matter distribution.
 Here, we have chosen the compact star candidate SMC X-1 with observed values of mass =(1.29 ± 0.05)M⊙ and radius = 8.831_{-0.09}^{+0.09} km. respectively, to analyze our results analytically as well as graphically. For smaller values of k, we get the stiff (or hard) equation of state (EoS). Here we solve the modified Einstein's field equations in presence of the background metric gamma_{mu nu}. Due to this constant curvature background, the density and pressure terms are modified by adding an extra term, which affects the EoS. For r ll k, the background de Sitter space-time reduces into Minkowski form and the coupling vanishes. We discuss certain physical quantities of our obtained solution such as density, isotropic pressure, sound speed, pressure-density gradients, compactness, and surface redshift to claim the physical viability of our model.
 It is found that our model clearly satisfies all the energy conditions, the causality condition, and the dynamical equilibrium via modified TOV equation. Finally, we can conclude that our proposed model is physically realistic and well-behaved.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"25 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136307909","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Surendra Singh, Leishingam Kumrah, Md Khurshid Alam, L. Kapil Singh, Lambamayum Anjana Devi
In this work, the authors examine the dynamics of viscous Universe in the Sáez–Ballester theory of gravity. The solutions of the Friedmann–Robertson–Walker field equations have been derived within the framework of full causal theories presented by Israel and Stewart using simple parametrization of scale factor a( t), i.e., power law relation a( t) = a 0 t α and exponential law a( t) = b 0 e β t . The power law cosmological model shows that the Universe transitioned from early cosmic deceleration to the present cosmic acceleration, and the exponential cosmological model shows the accelerated expansion of the Universe. It has been discovered that as time passes, energy density and viscosity decrease while temperature rises. Energy conditions are also investigated in which the strong energy condition is violated. The behaviour of the cosmological parameters such as the Hubble parameter, energy density, pressure, coefficient of viscosity, and state-finder parameter has been presented graphically.
在这项工作中，作者研究了Sáez-Ballester重力理论中粘性宇宙的动力学。在Israel和Stewart提出的全因果理论框架内，利用尺度因子a(t)的简单参数化，即幂律关系a(t) = a 0 t α和指数律a(t) = b 0 e β t，推导出了friedman - robertson - walker场方程的解。幂律宇宙学模型表明宇宙从早期的宇宙减速过渡到现在的宇宙加速，指数宇宙学模型表明宇宙的加速膨胀。人们发现，随着时间的推移，能量密度和粘度随着温度的升高而降低。还研究了违反强能条件的能量条件。宇宙学参数，如哈勃参数、能量密度、压力、粘度系数和状态探测参数的行为已经用图形表示出来。
{"title":"Causal Viscous Universe in Sáez-Ballester Theory","authors":"S. Surendra Singh, Leishingam Kumrah, Md Khurshid Alam, L. Kapil Singh, Lambamayum Anjana Devi","doi":"10.1139/cjp-2022-0342","DOIUrl":"https://doi.org/10.1139/cjp-2022-0342","url":null,"abstract":"In this work, the authors examine the dynamics of viscous Universe in the Sáez–Ballester theory of gravity. The solutions of the Friedmann–Robertson–Walker field equations have been derived within the framework of full causal theories presented by Israel and Stewart using simple parametrization of scale factor a( t), i.e., power law relation a( t) = a 0 t α and exponential law a( t) = b 0 e β t . The power law cosmological model shows that the Universe transitioned from early cosmic deceleration to the present cosmic acceleration, and the exponential cosmological model shows the accelerated expansion of the Universe. It has been discovered that as time passes, energy density and viscosity decrease while temperature rises. Energy conditions are also investigated in which the strong energy condition is violated. The behaviour of the cosmological parameters such as the Hubble parameter, energy density, pressure, coefficient of viscosity, and state-finder parameter has been presented graphically.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"2018 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135059621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Many models have been proposed to minimize the dark matter (DM) content in various astronomical objects at every scale in the Universe. The most widely known model is MOdified Newtonian dynamics (MOND). MOND was first published by Mordehai Milgrom in 1983. A second concurrent model is modified gravity, which is a covariant scalar–tensor–vector extension of general relativity. Other theories also exist but have not been broadly applied to a large list of astronomical objects. Eventually, we can also mention the Newtonian fractional-dimension gravity, a gravity theory based on spaces with fractional (i.e., non-integer) dimension. A new model, called κ-model, based on very elementary phenomenological considerations, has recently been proposed in the astrophysics field. This model shows that the presence of DM can be considerably minimized with regard to the dynamics of galaxies. The κ-model belongs to the general family of theories descended from MOND. Under this family of theories, there is no need to develop a highly uncertain DM sector of physics to explain the observations.
{"title":"A comparative study of MOND and MOG theories versus 
 κ-model: An application to galaxy clusters","authors":"G. Pascoli","doi":"10.1139/cjp-2023-0159","DOIUrl":"https://doi.org/10.1139/cjp-2023-0159","url":null,"abstract":"Many models have been proposed to minimize the dark matter (DM) content in various astronomical objects at every scale in the Universe. The most widely known model is MOdified Newtonian dynamics (MOND). MOND was first published by Mordehai Milgrom in 1983. A second concurrent model is modified gravity, which is a covariant scalar–tensor–vector extension of general relativity. Other theories also exist but have not been broadly applied to a large list of astronomical objects. Eventually, we can also mention the Newtonian fractional-dimension gravity, a gravity theory based on spaces with fractional (i.e., non-integer) dimension. A new model, called κ-model, based on very elementary phenomenological considerations, has recently been proposed in the astrophysics field. This model shows that the presence of DM can be considerably minimized with regard to the dynamics of galaxies. The κ-model belongs to the general family of theories descended from MOND. Under this family of theories, there is no need to develop a highly uncertain DM sector of physics to explain the observations.","PeriodicalId":9413,"journal":{"name":"Canadian Journal of Physics","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135059618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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