Fortschritte Der Physik-Progress of Physics最新文献

Many quantum gravitational frameworks, such as DBI inflation, k-essence, and effective field theories obtained by integrating out heavy modes, can lead to a non-trivial sound speed. Meanwhile, universe can be described as an open system. Under the non-trivial sound speed, the method of open quantum systems combined with Arnoldi iterations is employed to study the Krylov complexity throughout the early universe, including the inflationary, radiation-dominated, and matter-dominated epochs. A key ingredient in the analysis is the open two-mode squeezed state formalism and the generalized Lanczos algorithm. To numerically compute the Krylov complexity, the evolution equations for the parameters $�r_k$ and $�{\varphi }_k$ are derived for the first time within an open two-mode squeezed state. The results indicate that the Krylov complexity exhibits a similar trend in both the standard case and the case with non-trivial sound speed. To distinguish between these two scenarios, the Krylov entropy for completeness is also investigated. The evolution of the Krylov entropy shows a clear difference between the standard case and the non-trivial sound speed case. Furthermore, based on the behavior of the Lanczos coefficients, the case of non-trivial sound speed behaves as a maximally chaotic system. However, the numerical results suggest that the Krylov complexity does not saturate to a constant value due to the huge expansion of spacetime background. This study offers a new perspective for exploring the early universe through the quantum information.

The accelerated expansion of the Universe remains a fundamental challenge in cosmology, motivating model-independent methods to reconstruct its expansion history without relying on specific dark energy models. Cosmography, which employs series expansions of cosmological observables around the present epoch, provides a powerful kinematic framework rooted in the cosmological principle. However, standard Taylor expansions suffer from limited convergence at high redshift, prompting the exploration of alternative expansions. In this work, logarithmic polynomial cosmography is investigated, which expands observables in powers of the logarithm of redshift, thereby enhancing convergence over a broad redshift range while maintaining physical insight. The logarithmic polynomial parameters are constrained using recent datasets, including gravitational-wave standard sirens, DESI DR2, cosmic chronometers, and multiple Type Ia supernova compilations (DES-SN5YR, Union3, Pantheon+SH0ES). The analysis demonstrates the efficacy of the logarithmic approach in accurately modeling the cosmic expansion history, providing an interpretable alternative to traditional cosmographic techniques.

Over the last seventy years, many Finsler-type geometric and modified gravity theories (MGTs) have been elaborated. They have been formulated in terms of different classes of Finsler generating functions, metric and nonmetric structures, nonlinear and linear connections, and various sets of postulated fundamental geometric objects with corresponding nonholonomic dynamical or evolution equations. In several approaches, the resulting gravitational and matter field equations were not completely defined geometrically, or were developed only for restricted models. A progress report with historical remarks and a summary of new results on Finsler–Lagrange–Hamilton (FLH) geometric flow and gravity theories is presented. Such theories can be constructed in an axiomatic form on (co)tangent Lorentz bundles as nontrivial modifications of Einstein gravity. They are characterized by nonlinear dispersion relations and may encode nonassociative and noncommutative corrections from string theory, quantum effects, or other MGTs. To generate exact and physically relevant solutions of the FLH–modified Einstein equations, the anholonomic frame and connection deformation method is developed. A proof of the general integrability of such FLH geometric flows and MGTs is provided, and new classes of generic off-diagonal solutions determined by generating functions and effective sources that, in general, depend on all spacetime and (co)fiber coordinates are analyzed. In general, such off-diagonal configurations do not exhibit horizon/hypersurface duality or holographic structures and thus lie outside the Bekenstein–Hawking thermodynamic paradigm. Instead, by extending G. Perelman's entropy concept to relativistic FLH geometric flows, new classes of geometric thermodynamic variables that characterize different FLH theories and their associated solution spaces are introduce and computed.

The accelerated expansion of the Universe remains a fundamental challenge in cosmology, motivating model-independent methods to reconstruct its expansion history without relying on specific dark energy models. Cosmography, which employs series expansions of cosmological observables around the present epoch, provides a powerful kinematic framework rooted in the cosmological principle. However, standard Taylor expansions suffer from limited convergence at high redshift, prompting the exploration of alternative expansions. In this work, logarithmic polynomial cosmography is investigated, which expands observables in powers of the logarithm of redshift, thereby enhancing convergence over a broad redshift range while maintaining physical insight. The logarithmic polynomial parameters are constrained using recent datasets, including gravitational-wave standard sirens, DESI DR2, cosmic chronometers, and multiple Type Ia supernova compilations (DES-SN5YR, Union3, Pantheon+SH0ES). The analysis demonstrates the efficacy of the logarithmic approach in accurately modeling the cosmic expansion history, providing an interpretable alternative to traditional cosmographic techniques.

In this article I consider type II superstring in the pure spinor formulation with constant background fields in the context of T-dualization. First, I prove that bosonic and fermionic T-dualization commute using already known T-dual transformation laws for bosonic and fermionic T-dualization. Consequently, the T-dual transformation laws of the full T-dualization are obtained. At the end, the full T-dualization is realized in double space and it is showed that Buscher procedure and double space approach are equivalent in this specific case.

The propagation of a massive scalar field and a massless Dirac field in the geometry of a dilaton–de Sitter black hole is investigated. Starting from the covariant perturbation equations, the corresponding effective potentials are presented and their dependence on the dilaton charge, field mass, and cosmological constant is analyzed. Using the WKB approximation, the grey-body factors are computed and the associated absorption cross-sections are studied. The results show that increasing the field mass or dilaton charge raises the effective potential barrier, leading to a suppression of transmission at low frequencies, while a larger cosmological constant lowers the barrier and enhances transmission. The partial absorption cross-sections for different multipole numbers display the expected oscillatory structure, with the lowest multipoles dominating at small frequencies. After summation over multipoles, the oscillations average out and the total cross-section interpolates between strong suppression in the infrared regime and the geometric capture limit at high frequencies. These findings provide a systematic description of scattering and absorption properties of dilaton–de Sitter black holes for both scalar and fermionic perturbations.

In this work, the interaction of circularly polarized gravitational waves (GWs) with electromagnetic (EM) fields. Circular perturbations of spacetime are assumed and the perturbed Maxwell equations are used as the starting point for all governing relations. Within this framework, modified evolution equations for the electric and magnetic fields, charge density, and the EM stress–energy tensor are derived. The results show that the GW amplitude $�h_c$ plays a central role. It determines the strength of oscillations in the charge density, controls the redistribution of stored EM energy, and modifies the flux of energy through both electric and magnetic sectors. The charge density acquires synchronized oscillations with the GW, while circular polarization produces a helical modulation pattern that directly reflects the GW helicity. The electric and magnetic fields show both static amplifications and oscillatory modulations, and the energy flux exhibits variations that depend on polarization. As $�h_c$ increases, the deviations from the unperturbed fields become more pronounced, leading to enhanced oscillations, stronger non-linear growth, and richer sideband structures in polarization dynamics. In general, this study provides a consistent and extended framework for understanding how GWs leave signatures on EM systems. The results suggest that even weak GWs imprint detectable modulations, while stronger perturbations reshape EM energy flow in a distinctive way. Such GW and EM couplings open up complementary possibilities for probing spacetime perturbations, with relevance to both astrophysical environments and controlled laboratory experiments designed for precision measurements.