Modern Physics Letters A

The core–cusp problem remains a challenging discrepancy between observations and simulations in the standard $\mathrm{\Lambda }$CDM model for the formation of galaxies. The problem is that $\mathrm{\Lambda }$CDM simulations predict a steep power-law mass density profile at the center of galactic dark matter halos. However, observations of dwarf galaxies in the Local Group reveal a density profile consistent with a nearly flat distribution of dark matter near the center. A number of solutions to this dilemma have been proposed. Here, we summarize investigations into the possibility that the dark matter particles themselves self interact and scatter. Such self-interacting dark matter (SIDM) particles can smooth out the dark-matter profile in high-density regions. We also review the theoretical proposal that self-interacting dark matter may arise as an additional Higgs scalar in the 3–3–1 extension of the Standard Model (SM). We present new simulations of galaxy formation and evolution for this formulation of self-interacting dark matter. Current constraints on this self-interacting dark matter are then summarized.

In this paper, under the framework of generalized uncertainty principle (GUP), based on the quantum tunneling radiation, we discuss the influence of dark matter on thermodynamics and phase transition from the X-cold dark matter (XCDM) black hole in Braneworld. It turns out that the existence of the dark matter can give rise to some new relations such as local temperature–mass, heat capacity–mass and local free energy–local temperature, and dark matter can play an important role in phase transitions. It is worth emphasizing that the first-order phase transition, second-order and Hawking–Page-like phase transitions can be observed from the new phase diagrams, and the novel and interesting thermodynamics behavior has been presented under the influence of GUP and dark matter.

Based on a higher energy scale, the dispersion relation might be corrected. Correspondingly, the Hamilton–Jacobi equation should also be modified. In this paper, we use the correction to study the fermion tunneling radiation for a Gibbons–Maeda–Garfinkle-Horowitz–Strominger (GMGHS) black hole, a Kerr–NUT black hole, and an Einstein–Maxwell–Dilaton–Axion (EMDA) black hole. The result shows that compared to the charged GMGHS black hole and the rotating Kerr–NUT black hole, the Hawking temperate and the entropy of the rotating charged EMDA black hole not only are related to the correction parameter $\sigma$ and particle mass $m$ but also depend on the angle parameter $𝜃$ of the black hole coordinates.

Hawking radiation presents a mechanism how a black hole decreases its energy. We would like to discuss the mesoscopic effect of the temperature of the blackbody by applying the analysis of particle’s self-gravitation by Parikh and Wilczek to the blackbody radiation without the heat bath. We then obtain an interesting result that the temperature of the system depends on photon energies by analyzing a gedanken experiment. We propose an experiment to examine the effect.

Quantum gravitational effects suggest a minimal length, or spacetime interval, of order of the Planck length. This in turn suggests that Hilbert space itself may be discrete rather than continuous. One implication is that quantum states with norm below some very small threshold do not exist. The exclusion of what Everett referred to as maverick branches is necessary for the emergence of the Born Rule in no collapse quantum mechanics. We discuss this in the context of quantum gravity, showing that discrete models (such as simplicial or lattice quantum gravity) indeed suggest a discrete Hilbert space with minimum norm. These considerations are related to the ultimate level of fine-graining found in decoherent histories (of spacetime geometry plus matter fields) produced by quantum gravity.

In this paper, we focused our attention to find Ricci solitons of spherically symmetric static spacetimes. It is shown that special classes of such spacetime metrics admit shrinking, expanding or steady Ricci solitons. It is found that the dimensions of the Ricci soliton vector fields are four, five, eight, ten or eleven. It is observed that non-Einstein metrics also exist with shrinking or expanding Ricci soliton vector fields. In all the cases, the obtained Ricci soliton vector fields are proved to be gradient and concircular potential fields.

Quantum theory sets a bound on the minimal time it takes for a system to evolve from initial state to target state. This bound is called the quantum speed limit (QSL) time. The quantum speed limit time is used to quantify the maximal speed of the quantum evolution. The quantum evolution will be faster if the quantum speed limit time decreases. In this work, we study the quantum speed limit time for an open quantum system in the presence of disturbance in an environment. We use the model which is provided by Ban [Phys. Rev. A 99, 012116 (2019)]. In this model, two quantum systems ${𝒜}$ and ${𝒮}$ interact with environment sequentially. At first, quantum system ${𝒜}$ interacts with the environment ${ℰ}$ as an auxiliary system, then quantum system ${𝒮}$ starts its interaction with disturbed environment immediately. In this work, we consider the dephasing coupling with two types of environment that has different spectral density: Ohmic and Lorentzian. We observe that, non-Markovian effects will appear in the dynamics of the second quantum system ${𝒮}$ due to the interaction of the first quantum system ${𝒜}$ with the environment. Given the fact that the quantum speed limit time reduces due to the non-Markovian feature of quantum evolution, we show that disturbance effects will reduce the quantum speed limit time for the dynamics of the second quantum system ${𝒮}$.

Recent studies have emphasized the important role that a shape deformability of scalar-field models pertaining to the same class with the standard ${\varphi }^4$ field, can play in controlling the production of a specific type of breathing bound states so-called oscillons. In the context of cosmology, the built-in mechanism of oscillons suggests that they can affect the standard picture of scalar ultra-light dark matter. In this paper, kink scatterings are investigated in a parametrized model of bistable system admitting the classical ${\varphi }^4$ field as an asymptotic limit, with focus on the formation of long-lived low-amplitude almost harmonic oscillations of the scalar field around a vacuum. The parametrized model is characterized by a double-well potential with a shape-deformation parameter that changes only the steepness of the potential walls, and hence the flatness of the hump of the potential barrier, leaving unaffected the two degenerate minima and the barrier height. It is found that the variation of the deformability parameter promotes several additional vibrational modes in the kink-phonon scattering potential, leading to suppression of the two-bounce windows in kink–antikink scatterings and the production of oscillons. Numerical results suggest that the anharmonicity of the potential barrier, characterized by a flat barrier hump, is the main determinant factor for the production of oscillons in double-well systems.

In this work, we investigate the bipartite entanglement of decohered mixed states generated from maximally entangled cluster states of $n$ qubits physical system. We introduce the disconnected cluster states for an ensemble of $n$ non-interacting qubits and we give the corresponding separable density matrices. The maximally entangled states can be generated from disconnected cluster states, by assuming that the dynamics of the multi-qubit system is governed by a quadratic Hamiltonian of Ising type. When exposed to a local noisy interaction with the environment, the multi-qubit system evolves from its initial pure maximally entangled state to a decohered mixed state. The decohered mixed states generated from bipartite, tripartite and multipartite maximally entangled cluster states are explicitly expressed and their bipartite entanglements are investigated.