International Journal of Modern Physics A

Diffusive TeV gamma-ray emissions have been recently discovered extending beyond the pulsar wind nebulae of a few middle-aged pulsars, implying that energetic electron/ positron pairs are escaping from the pulsar wind nebulae and radiating in the ambient interstellar medium. It has been suggested that these extended emissions constitute a distinct class of nonthermal sources, termed “pulsar halos”. In this paper, I will review the research progress on pulsar halos and discuss our current understanding on their physics, including the multiwavelength observations, different theoretical models, as well as implications for the origin of cosmic-ray positron excess and Galactic diffuse gamma-ray emission.

In this paper, we make a close comparison of a covariant definition of an energy/ entropy in general relativity, recently proposed by a collaboration including the present authors, with existing definitions of energies such as the one from the pseudo-tensor and the quasi-local energy. We show that existing definitions of energies in general relativity are conserved charges from Noether’s second theorem for the general coordinate transformation, whose conservations are merely identities implied by the local symmetry and always hold without using equations of motion. Thus, none of the existing definitions in general relativity reflects the dynamical properties of the system, and the need for a physical definition of an energy. In contrast, our new definition of the energy/ entropy in general relativity is generically a conserved non-Noether charge and gives physically sensible results for various cases such as the black hole mass, the gravitational collapse and the expanding universe, while existing definitions sometimes lead to unphysical ones including zero and infinity. We conclude that our proposal is more physical than existing definitions of energies. Our proposal makes it possible to define almost uniquely the covariant and conserved energy/ entropy in general relativity, which brings some implications to future investigations.

In this paper, we investigate the influence of the extended uncertainty principle (EUP) on the thermodynamics of a charged rotating Bañados, Teitelboim and Zanelli (BTZ) black hole in ($2+1$)-dimensional anti-de Sitter (AdS) space–time. To this end, we derive EUP-corrected Hawking temperature, pressure, entropy, Gibbs free energy and heat capacity functions. We observe that EUP-based quantum corrections decrease pressure and entropy functions in AdS space–time. Such decreases show up itself only in physically meaningful region for Gibbs free energy and specific heat functions.

Axion like particles (ALPs) and right-handed neutrinos (RHNs) are two well-motivated dark matter (DM) candidates. However, these two particles have a completely different origin. Axion was proposed to solve the strong CP problem, whereas RHNs were introduced to explain light neutrino masses through seesaw mechanisms. We study the case of ALP portal RHN DM (Majorana DM) taking into account existing constraints on ALPs. We consider the leading effective operators mediating interactions between the ALP and Standard Model (SM) particles and three RHNs to generate light neutrino masses through type-I seesaw. Further, ALP-RHN neutrino coupling is introduced to generalize the model which is restricted by the relic density and indirect detection constraint.

Fractals are the fundamental characteristics of the universe. In this research, the Lagrangian formulation of the de Broglie–Proca (dBP) field for space with noninteger dimension is examined. Based on the Laplace of the dBP’s equations in noninteger space, the solutions of these equations are found where the dimensionality of the space is $\alpha >2$. Also, we obtain the wave equation for the electric field and the wave equation for the magnetic field in noninteger space.

We derive thermodynamic quantities such as the Hawking temperature, mass, entropy, heat capacity and study the thermodynamic phase transitions of rotating Bardeen black holes surrounded by quintessence-like matter. Interpreting the cosmological parameter as thermodynamic pressure and its conjugate variable as volume, the first law of black hole thermodynamics has been modified in the Anti-de Sitter (AdS) space. It then has been used to investigate the thermodynamics of the rotating Bardeen–AdS black hole with quintessence matter. Properties of the thermodynamic volume have also been analyzed through the study of compressibility and sound speed of the black hole. The black hole sound speed is associated with the adiabatic compressibility, and it equals the light speed for nonrotating black holes and decreases with increasing angular momentum. The nonrotating black holes are adiabatically incompressible, and as the angular momentum attains a maximum value in the extremal case, the compressibility grows maximum. We further derive the equation of state in the extended phase space and explore the critical behaviors of the black hole in the canonical ensemble. Graphs of phase transitions and critical behaviors show an accentuated influence of quintessence matter on the thermodynamic phase transitions and stability of the black holes and support the van der Waals-like phase transition behavior.

We present a new asymptotically flat black hole solution in Null Aether Theory (NAT) by applying Newman–Janis process. For this purpose, we study the asymptotically flat NAT black hole solution in Newman–Janis algorithm and then compute the tunneling radiation for NAT black hole. The Hawking temperature for NAT black hole depends upon the rotation parameter and charge of the black hole. The Hawking temperature describes a black hole with extremal event horizon. Furthermore, we analyze the graphical interpretation of Hawking temperature with respect to event horizon and check the stability of black hole under the influence of different parameters associated with black hole temperature.

The temperature behavior of the pion width in the hadronic phase is investigated in the framework of the Nambu–Jona–Lasinio (NJL) model. The contribution to the width from the pion–pion collision is considered with a scalar sigma-meson as an intermediate state. It is shown that the pion width significantly broadens at $T>0.1$GeV. Using the two-step iteration method, suggested by Kadanoff and Baym, the pion spectral function in a hot pion gas is calculated at different temperatures.

In this work, we develop the quantum theory of gravity in the gravitational compressed space. The equivalence of spatial compression to the Lorentz contraction of special relativity, supported by the relative gravitational red-shift using the black hole clock, leads to the brane potential and gives the minimum length at which the extra dimensions become dominant, comparable to that of the Schwarzschild radius. For Planck mass the minimum length is almost Planck’s length. When doing the quantization of the theory, we find that those responsible for the evolution of time for luminous matter, graviton and for dark matter, the axion, have the property that in compressed gravitational space, naked and dressed propagators are equal and coincide with the corresponding naked propagators.

Cold dark matter (DM) is conceived as a gas of massive particles that undergo collisions, interact gravitationally and exchange quanta of energy. A new nonrelativistic quantum theory is presented for this model of DM, based on a recently discovered equation for a spinless, no charge and free particle. This theory describes the quantum processes undergoing by the particles, specifies the required characteristic wavelength of the quanta of energy, gives constraints on the mass of DM particles, and predicts a detectable gravitational wave background associated with DM halos.

Motivated by Aoki et al.’s recent research on conserved charges and entropy current, we reinvestigated the conservation of relativistic Ertel’s current, which has received little attention outside the field of geophysical fluid dynamics. Ertel’s charge is an important indicator of the correlation between vortex vectors and entropy gradient fields in Earth’s meridional heat transport. We first show that in the generalized Hamiltonian structure of baroclinic fluids, the duality between the total energy and the Casimir as a function of Ertel’s charge plays an important role in the nonrelativistic case. Then, by extending the result to relativistic cases, we show that this finding has far-reaching implications not only for space–time issues in cosmology but also for the foundation of quantum field theory. An especially important finding is that, as an unreported dual form of the Einstein field equation, we identify a special equation satisfied not only by the vortex tensor field generated by the conserved charge but also by the Weyl tensor in interpreting the physical nature of the metric tensor $g^{\mu \nu }$, which appears in the cosmological term $\mathrm{\Lambda }{g}^{\mu \nu }$.