Aziza Altaibayeva

We investigate a unified dark-energy scenario based on the combined effects of Barrow entropy corrections and the QCD ghost mechanism, referred to as the BH-QCDGDE model. The dark-energy density is constructed in a generalized holographic form that incorporates both Barrow-deformed entropy corrections and low-energy QCD vacuum effects within a single framework. The cosmological dynamics are analyzed in a spatially flat Friedmann–Lemaître–Robertson–Walker background. The model exhibits a smooth transition from a decelerated matter-dominated era to a late-time accelerated phase without crossing the phantom divide, indicating a viable background evolution within suitable parameter ranges. An equivalent scalar-field description of the effective dark-energy sector is reconstructed and shown to admit a quintessence-like behavior. The thermodynamic behavior is examined by testing the generalized second law at the apparent horizon, which is found to be satisfied for the considered parameter choices. The classical stability of the model is further investigated through the squared speed of sound, indicating that stable cosmological regimes can arise for appropriate choices of the model parameters. Overall, the BH-QCDGDE framework can provide an effective and physically consistent description of late-time cosmic acceleration within the explored parameter space.

We investigate a unified dark-energy scenario based on the combined effects of Barrow entropy corrections and the QCD ghost mechanism, referred to as the BH--QCDGDE model. The dark-energy density is constructed in a generalized holographic form that incorporates both Barrow-deformed entropy corrections and low-energy QCD vacuum effects within a single framework. The cosmological dynamics are analyzed in a spatially flat Friedmann--Lemaître--Robertson--Walker background. The model exhibits a smooth transition from a decelerated matter-dominated era to a late-time accelerated phase without crossing the phantom divide, indicating a viable background evolution. An equivalent scalar-field description of the effective dark-energy sector is reconstructed and shown to admit a quintessence-like behavior. The thermodynamic viability is examined by testing the generalized second law at the apparent horizon, which is found to be satisfied throughout the parameter space. The classical stability of the model is further investigated through the squared speed of sound, revealing the role of model parameters in shaping stable cosmological regimes. Overall, the BH--QCDGDE framework provides a consistent and physically viable description of late-time cosmic acceleration.

Бұл жұмыста cызықты емес эволюциялық теңдеулердің бірі екі өлшемді кеңейтілген Калоджеро-Богоявленский-Шифф (КБШ) теңдеуінің жаңа қозғалмалы толқындық шешімдері зерттеледі. Сызықты емес физикалық құбылыстар ғылым мен оның түрлі қолдану салаларында -оптикалық талшықтарда, астрофизикада және дифференциалдық теңдеулер физикасы - аса маңызды рөл атқарып, оларды моделдеуге мүмкіндік береді. Калоджеро-Богоявленский-Шифф (КБШ) теңдеуі бастапқыда локальды емес түрде тұжырымдалғанымен, оны дифференциалдық теңдеулер жүйесі ретінде де зерттелуде. Мұндай теңдеулер плазма физикасы, сұйықтық динамикасы және кванттық өріс теориясы сияқты ғылымның түрлі салаларында қолданылады. Әсіресе сызықты емес әдістер стандартты симметрия әдістерімен алынбайтын шешімдерді анықтауда тиімді екенің көрсетті. Бұл мақалада алынған нәтижелер сызықты емес дисперсиялық толқындарды және күрделі динамикалық жүйелерді сипаттайтын физикалық процесстерді моделдеуде қолданылуы мүмкін сондай-ақ екіөлшемді теңдеулер теориясын тереңірек түсінуге үлес қосады. Мақалада екі өлшемді Калоджеро-Богоявленский-Шифф (КБШ) теңдеуінің толқындық шешімдері алынып, бағдарламалық жүйелерде графиктері тұрғызылады. Алынған нәтижелер бейсызық дисперсиялық толқындарды және күрделі динамикалық жүйелерді модельдеуде тиімді қолданыла алатыны cөзсіз. Бұл жұмыс екіөлшемді бейсызық жүйелердің динамикасын тереңірек түсінуге үлес қосады

In this work, we study the Barrow Holographic Dark Energy (BHDE) model (Phys Rev D 102:123525, 2020), which is based on Barrow’s modification of entropy. We show that this model is a special case of the more general Nojiri–Odintsov HDE (NO-HDE) framework (Eur Phys J C 77:528, 2017). In the same way, the Granda–Oliveros (GO) cutoff also appears as a particular case of the NO cutoff. After this, we reconstruct the dynamics of BHDE using a k-essence scalar field, which provides a field theory picture of its evolution. The results show how the Barrow deformation parameter and the infrared cutoff affect the kinetic term and the behaviour of the scalar field. Further, we test the thermodynamic consistency of the model by checking the generalized second law on cosmological horizons. Overall, the study confirms that both BHDE and the GO cutoff can be understood as limits of the NO-HDE framework, and that they are consistent with scalar field theory and the principles of thermodynamics. Also we confront the reconstructed BHDE–k-essence model with late-time cosmological data from cosmic chronometers and baryon acoustic oscillations. The features derived in the study the models under as viable models to explain the late-time cosmic acceleration.

In this paper, we investigate the late-time acceleration of the universe within the extended [ ] gravity framework, which unifies curvature, matter Lagrangian, and the trace of the energy–momentum tensor in a single gravitational action. Considering the simplest functional form [ ], we adopt a parametric form of the deceleration parameter [ ] to reconstruct the Hubble parameter [ ]. Using Markov Chain Monte Carlo methods with combined observational Hubble data (OHD) and type Ia supernovae (SNe Ia) datasets, we constrain the cosmological parameters [ ], [ ], and [ ], finding [ ], [ ], and [ ]. Our results indicate a current accelerated expansion and a deceleration-to-acceleration transition consistent with observations. The inferred [ ] value lies between Planck 2018 and local SH0ES measurements, suggesting the parametrization may alleviate the Hubble tension. We further explore the impact of coupling parameters [ ] and [ ] on the energy density, pressure, and equation of state parameter [ ], revealing a quintessence-like dark energy behavior without phantom crossing. These findings demonstrate the versatility of the [ ] model in explaining cosmic acceleration and provide a promising alternative to the standard [ ]CDM cosmology.

Barrow Holographic Dark Energy (BHDE), that modifies the standard holographic dark energy framework by incorporating quantum-gravity-induced deformation through a Barrow entropy measure, demonstrated in [E. N. Saridakis, Barrow holographic dark energy, Phys. Rev. D 102(12) (2020) 123525], is investigated and studied in the framework of the Chern–Simons modified gravity framework. We bring into focus the BHDE with two different IR cutoffs. The BHDE density is reconstructed in the Chern–Simons modified gravity framework and accordingly the equation of state parameter is reconstructed and studied for different ranges of [ ], which is the deformation parameter indicating the amount of the quantum gravitational deformation effects to the horizon structure associated with BHDE. The relevant expressions of the Hubble parameter [ ] and reconstructed BHDE density are also studied. Finally, the four energy conditions are analyzed for the reconstruction models.