Fortschritte Der Physik-Progress of Physics最新文献

In this work, gravastars-like structures are investigated in spherically symmetric and static space-time within the $��f�\left(�Q�\right)�$ gravity framework, coupled with conformal symmetry. The conventional gravastar model is modified by introducing a strongly interacting quark matter shell, which maintains the apex of causal limit through the EoS, $��p�=�\rho �-�2�B_g�$, where, $�B_g$ is the bag constant. Non-singular and non-vanishing solutions for the interior and shell regions are obtained, respectively. The Israel junction condition is used to evaluate the mass of the thin shell for different choices of characteristic radii. Interestingly, the mass of the shell is independent of the matter distribution in the shell region. For radii 9.009, 10.009, and 11.009 Km, the mass increases to $��1.80�,��1.95�$, and $��2.28��M_{\odot }�$, respectively. The physical features associated with the gravastars, such as, proper length, energy, and entropy of the shell region are studied within the parameter space. Surface redshift calculations were used to validate the proposed model.

A generalized entropy functional for $��f�\left(�Q�\right)�$ gravity is derived by adapting the Noether charge formalism to the nonmetricity-based gravitational Lagrangian. The resulting functional, $��S�=�\frac{1}{4}�{\int }_H�d^2�x��h��f��\left(�Q�\right)��$ generalizes the Bekenstein–Hawking law and is shown to be consistent with the first law of entanglement thermodynamics. This consistency establishes a direct link between the modification of the gravitational action and the entanglement structure of spacetime, providing a robust thermodynamic and quantum information–theoretic interpretation for $��f�\left(�Q�\right)�$ gravity.

In this paper, a new definition of temperature is proposed for the FRW(Friedmann–Robertson–Walker) universe, i.e., the effective temperature $��T_{�e�f�f�}�:�=�d�E�/�d�S�$, where $�E$ is the energy and $�S$ is the entropy of the FRW universe. Based on this definition, the effective temperature is derived for the $�N$-dimensional FRW universe in Einstein gravity, Gauss–Bonnet gravity, and Lovelock gravity. For the 4-dimensional FRW universe, the effective temperature is found to be $��T_{�e�f�f�}�=�1�/��\left(�4�\pi �R_A�\right)��$, which is exactly the same form with the Hawking temperature of the Schwarzschild black hole. In higher-dimensional FRW universe, the form of the effective temperature depends on the choices of the gravitational theories or the corresponding coupling constants. The free energy of the FRW universe in the three theories of gravity is also obtained.

The recent applications of Euclidean path integrals to the black hole information problem are discussed. In calculations with replica wormholes as the next-to-leading order correction to the Gibbons–Hawking saddlepoint, the radiation density matrix approaches a pure state at late times, following the Page curve. The unitary evaporation of black holes (in real time), mediated by calculable quantum hair effects, are compared with the replica wormhole results. Both the replica wormhole and quantum hair approaches imply that radiation states are macroscopic superpositions of spacetime backgrounds, invalidating firewall and monogamy of entanglement constructions. Importantly, identification of modes inside the horizon with radiation modes (i.e., large-scale nonlocality across the horizon) is not required to provide a physical picture of unitary evaporation. Radiation modes can encode the interior information while still remaining independent degrees of freedom.

A model is presented that provides an explanation for the presence of (Dark Matter and) Dark Energy in the universe. A key idea is to express the volume form of the Lorentzian metric on space–time in terms of a positive function of a new scalar field multiplying a certain four-form given by the wedge product of the differential of the mimetic scalar field and a certain closed three-form. An ansatz for this three-form related to one commonly used to determine the winding number of a map from a three-dimensional hypersurface to a three-sphere is discussed. An action functional depending on the space–time metric, the new scalar field, the mimetic scalar and the three-form is proposed, and the field equations are derived. Special solutions of these equations for a Friedmann–Lemaître universe are presented.

A conformally extended Standard Model with a hidden scalar $�\varphi$ is investigated. It is shown that due to non-perturbative dynamics in the hidden sector, $�\varphi$ develops a vacuum expectation value (vev) in the form of a mass gap which triggers the electroweak symmetry breaking (EWSB) and dynamically generates the SM Higgs boson mass. To estimate the non-perturbatively generated mass scale, a hierarchy of Dyson–Schwinger equations is solved in form of partial differential equations using the exact solution known via a novel technique developed by Bender, Milton, and Savage. A Jacobi Elliptic function is employed as exact background solution and show that the mass gap that arises in the hidden sector can be transmuted to the EW sector, expressed in terms of Higgs-portal mixed quartic coupling $�\beta$ and self interaction quartic coupling $�{\lambda }_{\varphi }$ of $�\varphi$. The suitable parameter space where the observed SM Higgs boson can be successfully generated is identified. Finally, the idea of non-perturbative EW scale generation can serve as a new starting point for better realistic model building in the context of resolving the hierarchy problem in the Standard Model is discussed.

We define a metric $�G$ on the KBc-subalgebra modulo gauge and describe the worldsheet RG-flow as the gradient flow of the action of cubic open string field theory, where the flow lines are kink-solitons. In particular, for a constant tachyon the gradient flow equations are equivalent to the RG-equations. Additionally, a more general family of gradient flow lines is presented, which describes the RG-flow from the conformal manifold of the D-brane under tachyon condensation. We also derive the stability operator of our solution and show that the zero-modes reflect the invariance of the flow under such marginal perturbations. In fact, the beta function is colinear to our solution such that it describes geodesics from the conformal manifold to the tachyon vacuum with respect to $�G$.