Modern Physics Letters A

We show that the cosmic bulk viscosity estimated in our previous works is sufficient to bridge the $H_0$ value inferred from observations of the early universe with the value inferred from the local (late) universe.

We consider general relativity as a limit case of the scalar–tensor theory with Barbero–Immirzi (BI) field when the field tends to a constant. We use Shapiro time delay experimental value of $1/w(x)=(2.1\pm 2.3)10^{-5}$ provided by the Cassini spacecraft to find the present BI parameter value.

To address fermion mass hierarchy and flavor mixings in the quark and lepton sectors, a minimal flavor structure without any redundant parameters beyond phenomenological observables is proposed via decomposition of the Standard Model Yukawa mass matrix into a bi-unitary form. After reviewing the roles and parameterization of the factorized matrix $M_0^f$ and $F_L^f$ in fermion masses and mixings, we generalize the mechanism to up- and down-type fermions to unify them into a universal quark/lepton Yukawa interaction. In the same way, a unified form of the description of the quark and lepton Yukawa interactions is also proposed, which shows a similar picture as the unification of gauge interactions.

Various proposals for gravitational entropy densities have been constructed from the Weyl tensor. In almost all cases, though, these studies have been restricted to general relativity, and little has been done in modified theories of gravity. However, in this paper, we investigate the simplest proposal for an entropy density constructed from the Weyl tensor in five-dimensional Gauss–Bonnet gravity and find that it fails to reproduce the expected entropy of a black hole.

The criteria for thermal stability of a most general quantum black hole derived by us appeared in the form of a series of inequalities connecting second-order derivatives of black hole mass with respect to its parameters, which determine the mass of the black hole. These nullify the concept of positivity of specific heat as the sole criteria for thermal stability. Using this most general stability criterion, we prove here that AdS Schwarzschild black holes are no longer stable anywhere in their parameter space if cosmological constant is allowed to vary. We also calculate the fluctuations of both horizon area and cosmological constant of this black hole. We calculate specific heat of it and compare this with Hawking’s prediction.

Within the background field formalism of quantum gravity, I show that if the quantum fluctuations are limited to diffeomorphic gauge transformations rather than the physical degrees of freedom, as in conventional quantum field theory, all the quantum corrections vanish on shell and the effective action is equivalent to the classical action. In principle, the resulting theory is finite and unitary, and requires no renormalization. I also show that this is the unique parameterization that renders the path integral independent of the on-shell condition for the background field, a form of background independence. Thus, a connection is established between background independence and renormalizability and unitarity.

Gauge field theory with rank-one field $T_{\mu }$ is a quantum field theory that describes the interaction of elementary spin-1 particles, of which being massless to preserve gauge symmetry. In this paper, we give a generalized, extended study of abelian gauge field theory under successive rotor model in general $D$-dimensional flat spacetime for spin-1 particles in the context of higher-order derivatives. We establish a theorem that $n$ rotor contributes to the ${\square }^n{T}^{\mu }$ fields in the integration-by-parts formalism of the action. This corresponds to the transformation of gauge field $T^{\mu }\to {\square }^n{T}^{\mu }$ and gauge field strength $G_{\mu \nu }\to {\square }^n{G}_{\mu \nu }$ in the action. The $n=0$ case restores back to the standard abelian gauge field theory. The equation of motion and Noether’s conserved current of the theory are also studied.