arXiv subjects
Publications and source records attributed to Milutin Blagojević.
It is shown that the Lorentz invariant $f(T)$ gravity, defined by the coframe-connection-multiplier form of the Lagrangian, can be gauge-fixed to the pure coframe form. After clarifying basic aspects of the problem in the Lagrangian formalism, a more detailed analysis of this gauge equivalence is given relying on the Dirac Hamiltonian approach.
It is shown that energy, entropy and the first law of the Martinez-Troncoso black hole with electric charge and scalar hair (2006) can be consistently described in a general Hamiltonian approach to black hole thermodynamics.
The Hamiltonian approach to black hole entropy, recently proposed in the framework of Poincaré gauge theory, is extended by including the scalar matter. The improved approach is used to analyse asymptotic charges and entropy of a typical black hole with scalar hair in two complementary dynamical settings, in GR and in the teleparallel gravity. In both cases, the results confirm the validity of the first law.
During the last five decades, gravity, as one of the fundamental forces of nature, has been formulated as a gauge theory of the Weyl-Cartan-Yang-Mills type. The present text offers commentaries on the articles from the most prominent proponents of the theory. In the early 1960s, the gauge idea was successfully applied to the Poincaré group of spacetime symmetries and to the related conserved energy-momentum and angular momentum currents. The resulting theory, the Poincaré gauge theory, encompasses Einstein's general relativity as well as the teleparallel theory of gravity as subcases. The spacetime structure is enriched by Cartan's torsion, and the new theory can accommodate fermionic matter and its spin in a perfectly natural way. This guided tour starts from special relativity and leads, in its first part, to general relativity and its gauge type extensions à la Weyl and Cartan. Subsequent stopping points are the theories of Yang-Mills and Utiyama and, as a particular vantage point, the theory of Sciama and Kibble. Later, the Poincaré gauge theory and its generalizations are explored and special topics, such as its Hamiltonian formulation and exact solutions, are studied. This guide to the literature on classical gauge theories of gravity is intended to be a stimulating introduction to the subject.
The canonical approach to black hole entropy in Poincaré gauge theory without matter is extended to include Maxwell field as a matter source. The new formalism is used to calculate asymptotic charges and entropy of Kerr--Newmann--AdS black holes with torsion. The result implies that the first law, with a nontrivial contribution of the Maxwell field, takes the same form as in general relativity.
In Poincaré gauge theory, black hole entropy is defined canonically by the variation of a boundary term $Γ_H$, located at horizon. For a class of static and spherically symmetric black holes in vacuum, the explicit formula reads $δΓ_H=TδS$, where $T$ is black hole temperature and $S$ entropy. Here, we analyze a new member of the same class, the Reissner-Nordström-like black hole with torsion [1], where the electric charge of matter is replaced by a gravitational parameter, induced by the existence of torsion. This parameter affects $δΓ_H$ in a way that ensures the validity of the first law.
In the literature on $f(T)$ gravity, the status of local Lorentz invariance and the number of physical degrees of freedom have been controversial issues. Relying on a detailed Hamiltonian analysis, we show that there are several scenarios describing how local Lorentz invariance can be broken, but in the generic case, the number of physical degrees of freedom is found to be $N^*=5$; in $D$ dimensions, this number is $N^*=D(D-3)/2+(D-1)$. As expected, the theory is vulnerable to having problematical propagating modes. We compare our results with those existing in the literature. As a byproduct of our analysis, the diffeomorphysm invariance is explicitly confirmed.
A Hamiltonian variational approach is used to study asymptotic charges and entropy of Kerr-AdS black holes in the general Poincaré gauge theory, with both even and odd parity modes. The results turn out to be the same as those found earlier in the sector of parity invariant Lagrangians.
A Hamiltonian approach to black hole entropy is used to study Riemannian Kerr-AdS solutions in the general, parity-violating Poincaré gauge theory. Entropy and the asymptotic charges are entirely determined by the parity-even sector of the theory, whereas the parity-odd contributions vanish. Entropy is found to be proportional to the horizon area, and the first law of black hole thermodynamics is confirmed.
Using a Hamiltonian approach, we introduce black hole entropy for Kerr-AdS spacetimes with torsion as the canonical charge on horizon. In spite of a completely different geometric setting with respect to GR, the resulting thermodynamic variables, energy, angular momentum and entropy, are shown to be proportional to the corresponding GR expressions. The validity of the first law is confirmed.
A general Hamiltonian approach to black hole thermodynamics is used to study entropy and conserved charges for Kerr-AdS solutions in general relativity. These thermodynamic variables are first consistently defined by choosing suitable boundary conditions, and then, they are shown to satisfy the first law of black hole dynamics
Black hole thermodynamics of the Kerr-AdS spacetime in three-dimensional general relativity is analyzed using a Hamiltonian approach. The values of the conserved charges and entropy, obtained by a proper treatment of the AdS asymptotic conditions, are shown to satisfy the first law of black hole dynamics.
The canonical generator $G$ of local symmetries in Poincaré gauge theory is constructed as an integral over a spatial section $Σ$ of spacetime. Its regularity (differentiability) on the phase space is ensured by adding a suitable surface term, an integral over the boundary of $Σ$ at infinity, which represents the asymptotic canonical charge. For black hole solutions, $Σ$ has two boundaries, one at infinity and the other at horizon. It is shown that the canonical charge at horizon defines entropy, whereas the regularity of $G$ implies the first law of black hole thermodynamics.
Basic aspects of the Hamiltonian structure of the parity-violating Poincaré gauge theory are studied. We found all possible primary constraints, identified the corresponding critical parameters, and constructed the generic form of the canonical Hamiltonian. In addition to being important in their own right, these results offer dynamical information that is essential for a proper understanding of the particle spectrum of the theory, calculated in the weak field approximation around the Minkowski background.
A family of exact vacuum solutions, representing generalized plane waves propagating on the (anti-)de Sitter background, is constructed in the framework of Poincaré gauge theory. The wave dynamics is defined by the general Lagrangian that includes all parity even and parity odd invariants up to the second order in the gauge field strength. The structure of the solution shows that the wave metric significantly depends on the spacetime torsion.
General criteria for the existence of conformally flat Riemannian solutions in 3D Poincaré gauge theory without matter are formulated. Using these criteria, we show that the Oliva-Tempo-Troncoso black hole, a solution of the Bergshoeff-Hohm-Town\-send gravity, is also an exact vacuum solution of the Poincaré gauge theory. The related conserved charges, calculated from the Hamiltonian boundary term, are shown to satisfy the first law of black hole thermodynamics. The form of the boundary term is verified by using the covariant Hamiltonian approach.
Basic aspects of the AdS/CFT correspondence are studied in the framework of 3-dimensional gravity with torsion. After choosing a consistent holographic ansatz, we formulate an improved approach to the Noether--Ward identities for the boundary theory. The method is applied first to the topological Mielke--Baekler model, and then to the more interesting (parity-preserving) 3-dimensional gravity with propagating torsion. In both cases, we find the finite holographic energy-momentum and spin currents and obtain the associated (anomalous) Noether--Ward identities.
We study the general parity-preserving model of three-dimensional gravity with propagating torsion, with a focus on its nonlinear dynamics in the AdS sector. The model is shown to posses the black hole with torsion as a vacuum solution, provided we adopt certain restrictions on its coupling constants. The canonical analysis in the AdS asymptotic region yields the conserved charges of the black hole and the central charges of the asymptotic conformal symmetry.