Fortschritte Der Physik-Progress of Physics最新文献

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.

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.

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.

S. Gukov and C. Vafa proposed a characterization of rational $��N�=�(�1�,�1�)�$ superconformal field theories (SCFTs) in $��1�+�1�$ dimensions with Ricci-flat Kähler target spaces in terms of the Hodge structure of the target space, extending an earlier observation by G. Moore. The idea is refined, and a conjectural statement on necessary and sufficient conditions for such SCFTs to be rational is obtained, which is indeed proven to be true in the case the target space is $�T^4$. In the refined statement, the algebraicity of the geometric data of the target space turns out to be essential, and the Strominger–Yau–Zaslow fibration in the mirror correspondence also plays a vital role.

Field theories with kinematic Lie algebras, such as field theories featuring color–kinematics duality, possess an underlying algebraic structure known as BV^■-algebra. If, additionally, matter fields are present, this structure is supplemented by a module for the BV^■-algebra. The authors explain this perspective, expanding on our previous work and providing many additional mathematical details. The authors also show how the tensor product of two metric BV^■-algebras yields the action of a new syngamy field theory, a construction which comprises the familiar double copy construction. As examples, the authors discuss various scalar field theories, Chern–Simons theory, self-dual Yang–Mills theory, and the pure spinor formulations of both M2-brane models and supersymmetric Yang–Mills theory. The latter leads to a new cubic pure spinor action for 10-dimensional supergravity. A homotopy-algebraic perspective on colour–flavour-stripping is also given, obtain a new restricted tensor product over a wide class of bialgebras, and it is also show that any field theory (even one without colour–kinematics duality) comes with a kinematic $�L_{\infty }$-algebra.

It is recalled how relationality arises as the core insight of general-relativistic gauge field theories from the articulation of the generalized hole and point-coincidence arguments. Hence, a compelling case for a manifestly relational framework ensues naturally. A formulation for such a framework is proposed, based on a significant development of the dressing field method of symmetry reduction. A version for the group $��Aut�\left(�P�\right)�$ of automorphisms of a principal bundle $�P$ over a manifold $�M$ is first developed, as it is the most natural and elegant, and as $�P$ hosts all the mathematical structures relevant to general-relativistic gauge field theory. However, as the standard formulation is local, on $�M$, the relational framework for local field theory is then developed. The generalized point-coincidence argument is manifestly implemented, whereby the physical field-theoretical degrees of freedoms co-define each other and define, coordinatize, the physical spacetime itself. Applying the framework to General Relativity, relational Einstein equations are obtained, encompassing various notions of “scalar coordinatization” à la Kretschmann–Komar and Brown–Kuchař.