Fortschritte Der Physik-Progress of Physics最新文献

In this study, the features of a charged gravastar are investigated within the framework of $��f�\left(�Q�\right)�$ gravity ($�Q$ represents nonmetricity) using the Finch–Skea metric. This metric is applied to both the interior and shell regions of the charged gravastar and the field equations are derived accordingly. For the exterior regions, various black holes are considered, i.e., Reissner–Nordström, Bardeen, and Hayward regular black holes. The interior and exterior layers are matched using the Israel junction conditions, which help to determine the surface energy density and surface pressure for these black holes. Some physical properties such as proper length, entropy, energy, and the equation of state parameter are examined. The stability of the developed gravastar model is discussed through the effective potential, the causality condition and adiabatic index. It is concluded that the compact gravastar structure could be a viable alternative to black holes within this framework.

The simultaneous twisting of the Courant bracket by a 2-form $�B$ and a bi-vector $�\theta$ is investigated, with the generalized fluxes obtained in Courant algebroid relations explored. The twisted Lie bracket is defined and it is demonstrate that the generalized $�H$-flux can be expressed as the field strength defined on this Lie algebroid. Similarly, it is shown that the $�f$-flux is a direct consequence of simultaneous twisting, which arises in the twisted Lie bracket relations between holonomic partial derivatives. The generalized $�Q$ flux is obtained in terms of the twisted Koszul bracket, which is identified as a quasi-Lie algebroid bracket. The action of an exterior derivative related to the twisted Koszul bracket on a bi-vector produces the generalized $�R$-flux. It is shown that the generalized $�R$-flux is also the twisted Schouten–Nijenhuis bracket, i.e., the natural graded bracket on multi-vectors defined with the twisted Lie bracket.

Symmetry Theories (SymThs) provide a flexible framework for analyzing the global categorical symmetries of a $�D$-dimensional $�{\text{QFT}}_D$ in terms of a $��(�D�+�1�)�$-dimensional bulk system $�{\text{SymTh}}_{�D�+�1�}$. In QFTs realized via local string backgrounds, these SymThs naturally arise from dimensional reduction of the linking boundary geometry. To track possible time dependent effects we introduce a celestial generalization of the standard “boundary at infinity” of a SymTh. As an application of these considerations we revisit large $�N$ quiver gauge theories realized by spacetime filling D3-branes probing a non-supersymmetric orbifold $��R^6�/�\Gamma �$. Comparing the imprint of symmetry breaking on the celestial geometry at small and large ‘t Hooft coupling we find evidence for an intermediate symmetry preserving conformal fixed point.

The authors present a new method to analytically prove global stability in ghost-ridden dynamical systems. The proposal encompasses all prior results and consequentially extends them. In particular, it is shown that stability can follow from a conserved quantity that is unbounded from below, contrary to expectation. Novel examples illustrate all of the results. The findings take root on a careful examination of the literature, here comprehensively reviewed for the first time. This work lays the mathematical basis for ulterior extensions to field theory and quantization, and it constitutes a gateway for inter-disciplinary research in dynamics and integrability.

The integrability of two-dimensional theories that are obtained by a dimensional reduction of certain four-dimensional gravitational theories describing the coupling of Maxwell fields and neutral scalar fields to gravity in the presence of a potential for the neutral scalar fields is studied. For a certain solution subspace, partial integrability is demonstrated by showing that a subset of the equations of motion in two dimensions are the compatibility conditions for a linear system. Subsequently, the integrability of these two-dimensional models is studied from a complementary one-dimensional point of view, framed in terms of Liouville integrability. In this endeavor, various machine learning techniques are employed to systematize our search for numerical Lax pair matrices for these models, as well as conserved currents expressed as functions of phase space variables.

A model is presented where a GeV axion-like-particle (ALP) is predicted in a large portion of the parameter space due to the presence of explicit Peccei–Quinn (PQ) symmetry-breaking terms in an exotic leptonic sector. The latter provides a solution to the muon $��g�-�2�$ anomaly, within the framework of the Linear Seesaw neutrino mechanism. The spectrum is extended by a complex scalar singlet only transforming under the PQ symmetry, which generates the ALP. Its couplings with fermions can continuously span over many orders of magnitude, which constitutes a specific feature of this model in contrast to generic ultraviolet constructions. Interestingly, these couplings are suppressed by the ALP characteristic scale that can be as low as the TeV scale, which represents a novel feature of the model and opens up to several phenomenological consequences.

The Kerr metric is a vacuum solution of the Einstein equations outside of a rotating black hole (BH), but what interior matter is actually rotating and sourcing the Kerr geometry? Here, a rotating exotic matter is described, which can source the Kerr geometry for the entire acceptable range of its spin parameter and be shown to saturate the radial null-energy condition at every point in the interior, while being free of any obvious pathologies. The rotating frozen star is introduced, whose compactness is controlled by a perturbative parameter and whose outer surface can be arbitrarily close to the horizon of a Kerr BH. The interior geometry modifies Kerr's such that there is neither an inner ergosphere nor an inner horizon. The geometry of each radial slice of the interior is a nearly null surface with the same geometry, but different radial size, as that of the would-be horizon on the outermost slice. The integral of the energy density leads to a rest mass that is equal to the irreducible mass of a Kerr BH, and the integral of the angular-momentum density confirms that the ratio of the angular momentum to the mass is equal to the Kerr spin parameter. Including the rotational energy in the standard way, the total gravitational mass and angular momentum of a Kerr BH with the same mass and spin parameters are obtained.

Current observations show that a significant fraction of the Universe is composed of dark energy and dark matter. In this paper, the simultaneous effects of these dark sectors on the Euler–Heisenberg black hole are investigated, using the quintessence matter field and perfect fluid to model them. In particular, the black hole's thermodynamics, shadows, and quasinormal modes are studied, and detailed discussions are provided on how these properties change with relatively large or small dark sector components.

A relation between dark energy and the scale of new physics in weakly coupled string theory is motivated. This mixing between infrared and ultraviolet physics leads to a unique corner for real-world phenomenology: barring fine-tunings, the authors are naturally led to the “dark dimension” scenario, a single mesoscopic extra dimension of micron size with the standard model localized on D-branes. Our explicit top-down worldsheet derivation establishes it on a more solid grounding. Allowing some fine-tuning, such that the vacuum energy only arise at higher orders in string perturbation theory, the “little string theory” scenario with a very weakly coupled string is an alternative possibility. In this case, the string scale lies at the edge of detectability of particle accelerators.