Comment on "Dirac fermions in Som-Raychaudhuri space-time with scalar and vector potential and the energy momentum distributions"

Gravitational non-commutativity and Gödel-like spacetimes

We derive general conditions under which geodesics of stationary spacetimes resemble trajectories of charged particles in an electromagnetic field. For large curvatures (analogous to strong magnetic fields), the quantum mechanicical states of these particles are confined to gravitational analogs of {\it lowest Landau levels}. Furthermore, there is an effective non-commutativity between their spatial coordinates. We point out that the Som-Raychaudhuri and Gödel spacetime and its generalisations are precisely of the above type and compute the effective non-commutativities that they induce. We sh…

Comment on ``Quantization of Diffeomorphism-Invariant Theories with Fermions''

In the comment to the article by J.Baez and K.Krasnov (hep-th/9703112) are discussed some topics related with application of certain constructions to non-trivial principal bundles.

Towards a geometrical interpretation of rainbow geometries for quantum gravity phenomenology

In the literature, there are several papers establishing a correspondence between a deformed kinematics and a nontrivial (momentum dependent) metric. In this work, we study in detail the relationship between the trajectories given by a deformed Hamiltonian and the geodesic motion obtained from a geometry in the cotangent bundle, finding that both trajectories coincide when the Hamiltonian is identified with the squared distance in momentum space. Moreover, following the natural structure of the cotangent bundle geometry, we construct the space-time curvature tensor, from which we obtain genera…

Some Comments on Wheeler De Witt Equation for Gravitational Collapse and the Problem of Time

We write the Hamiltonian for a gravitational spherically symmetric scalar field collapse with massive scalar field source, and we discuss the application of Wheeler De Witt equation as well as the appearence of time in this context. Using an Ansatz for Wheeler De Witt equation, solutions are discussed including the appearence of time evolution.

The energy-momentum tensor on noncommutative spaces - some pedagogical comments

We present the discussion of the energy-momentum tensor of the scalar $ϕ^4$- theory on a noncommutative space. The Noether procedure is performed at the operator level. Additionally, the broken dilatation symmetry will be considered in a Moyal-Weyl deformed scalar field theory at the classical level.

关于弦动力学的一些评论

Some Comments On String Dynamics

本文讨论了三个问题：IIB超弦理论中出现在${\rm K3}$模空间中IIA理论具有扩展规范对称性的点上的自对偶非临界弦;共形场论在这样的点上的奇点，它可能表明即使在弱耦合下也存在量子效应;以及紧致化下现实世界的丰富动力学，这可能与一些试图解释宇宙学常数消失的尝试有关。

Comment on ``Dimensional and dynamical aspects of the Casimir effect: understanding the reality and significance of vacuum energy''

In [hep-th/0009173] Milton has presented a brief review of some interesting aspects of the theory of the Casimir effect. This comment is aimed at correcting some imprecise statements in that work with respect to the relevance of the Casimir effect for explaining the phenomenon of sonoluminescence.

Some Comments on the Holographic Heavy Quark Potential in a Thermal Bath

The heavy quark potential of a thermal Yang-Mills theory in strong coupling limit is explored in terms of the holographic principle. With a fairly general AdS/QCD metric the heavy quark potential displays a kink-like screening in the plasma phase. This behavior may conflict the causality of a field theory that is mathematically equivalent to the thermal Yang-Mills.