Fortschritte Der Physik-Progress of Physics最新文献

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.

The present work discusses the topic of cosmic evolution in an intriguing framework of $��f�\left(�Q�\right)�$ theory of gravity (with $�Q$ as a non-metricity (NM) scalar which controls the gravitational interaction) by using some recently proposed holographic dark energy (HDE) models. To achieve this goal, the dynamical equations for locally rotationally symmetric (LRS) Bianchi type-I (BI) geometry are formulated with matter contents as a mixture of dust and anisotropic fluids. By assuming that the time-redshift relation follows a Lambert function, the cosmological model is constructed by using Rényi HDE (RHDE), Sharma–Mittal HDE (SMHDE) and Generalized HDE (GHDE) as separate cases where Hubble horizon is taken as an infrared (IR) cutoff. Cosmological characteristics of these models are then examined through graphs of energy densities, skewness parameter $��\left(�\gamma �\right)�$, deceleration, and EoS parameters. The evolution of the EoS parameter is also studied, i.e., $�{\omega }^{{}^{\prime }}$ to discuss the dynamical characteristics of constructed DE models and assess the stability of models via the squared speed of sound parameter. It is found that the $��\omega �-�{\omega }^{{}^{\prime }}�$ plane shows the freezing region for RHDE and GHDE models while the thawing region for the SMHDE case. Also, it is concluded that all constructed models exhibit cosmologically viable and stable behavior.

The concepts of microstates and statistical ensembles form a fundamental starting point for various statistical physics theories that address thermodynamic and phase transition behaviors of correlated many-body systems. In this paper, we propose microstate sequence (MSS) theory built on a novel idea of arranging all microstates of a discrete thermodynamic system into a sequence with monotonically increasing property of key parameters and strict “smooth structure variation” property. Because of the properties, it obtains better analytical ability to express the derivation with the essential parameter change (in the cubic Ising model, the parameter is the dimensionality) at any micro-structure to figure out the qualitative issues like the relationship between phase transition order and dimensionality. With this idea in mind, the microstate sequence (MSS) of the Ising model in arbitrary dimension is constructed through a nontrivial iteration method based on a series of number-theoretic transformation tricks. After obtaining the complete form of the MSS for the Ising model, we provide a concise proof of the second-order phase transition nature for the Ising model in all n $�>$ 2 dimensions starting from the well-known exact result for the two-dimensional Ising model, as a test of the qualitative issue of MSS theory. Finally, we discuss the MSS theory in other lattice models like the Potts model and temperature derivation model to explore the correlations of number theory and phase trajectory in an extended range of discrete thermodynamic systems.

The quantum phase transition of the hardcore boson model on a Lieb lattice by quantum Monte Carlo simulations is studied. Considering nearest-neighbor interchain hopping, the phase diagram of the Bose-Hubbard model on the Lieb lattice contains solid phases with average density $�\rho$ = 2/3, and superfluid phases between solid phases.Two ways of controlling quantum states are discussed: to add an alternating on-site $�\mu$ potential, and to add an alternating hopping amplitude in the X- and Y-directions. For the above cases, there exists a new filling state, $�\rho$ = 1/3. Adding an alternating on-site potential to the Hamiltonian, the phase transition from $��\rho �=�1�/�3�$ to $��\rho �=�2�/�3�$ is sharp and discontinuous, featuring the nature of a first order. Considering a dimerization term, for large V, it is expected that there is a direct transition from the valence-bond insulator to the CDW as the interaction is strengthened. For the three cases, upper boundary for $��\rho �=�0�$ and lower boundary for $��\rho �=�1�$ are calculated.

A renormalization group approach based on the idea that the primary contribution to the Schwarzschild-like black hole spacetime arises from the value of the gravitational coupling is considered. The latter depends on the distance from the origin and approaches its classical value in the far zone. However, at some stage, this approach introduces an arbitrariness in choosing an identification parameter. There are three approaches to the identification: the modified proper length (the Bonanno–Reuter metric), the Kretschmann scalar (the Hayward metric), and an iterative, and, in a sense, coordinate-independent procedure (Dymnikova solution). Using the Wentzel–Kramers–Brillouin method, gray-body factors are calculated for the Standard Model massless test fields and their corresponding energy emission rates. For all of these solutions, it is found that the intensity of Hawking radiation of massless fields is significantly suppressed by several or more orders once the quantum correction is taken into consideration. This indicates that the effect of suppression of the Hawking radiation may be appropriate to the quantum corrected black holes in asymptotically safe gravity in general and is independent on the particular choice of the identification parameter.

The non-minimally coupled global monopole is a point like topological defect that may have been created during the phase transitions in the early universe. It is argued that topological defects are responsible for the structure formation of the galaxies and monopole could be the galactic dark matter in the spiral galaxies. In this article, the deflection of massive particle by the global monopole is studied. This basically makes sense as global monopole produces strong gravitational field due to enormous energy density allied with the Nambu–Goldstone field adjoining the monopole. The energy density of the monopole is decreasing with distance as $��r^{�-�2�}�+�0��\left(�r^{�-�2�}�\right)��$ and as a result global monopole structure plays an important role to explain the flatness of rotation curves of the outer region of various galaxies.