http://www.icranet.org/misc/Scientific_Report_2009/Reports/08Xue_b.pdf

Electron-positron pairs in physics and astrophysics: from heavy nuclei to black holes

From the interaction of physics and astrophysics we are witnessing in these years a splendid synthesis of theoretical, experimental and observational results originating from three fundametal physical processes. They were originally proposed by Dirac, by Breit and Wheeler and by Sauter, Heisenberg, Euler and Schwinger. The vacuum polarization process in strong electromagnetic field, pioneered by Sauter, Heisenberg, Euler and Schwinger, introduced the concept of critical electric field. It has been searched without success for more than forty years by heavy-ion collisions in many of the leading particle accelerators worldwide. The novel situation today is that these same processes can be studied on a much more grandiose scale during the gravitational collapse leading to the formation of a black hole being observed in Gamma Ray Bursts. This report is dedicated to the scientific race in act. The theoretical and experimental work developed in Earth-based laboratories is confronted with the theoretical interpretation of space-based observations of phenomena originating on cosmological scales. What has become clear in the last ten years is that all the three above mentioned processes, duly extended in the general relativistic framework, are necessary for the understanding of the physics of the gravitational collapse to a black hole. Vice versa, the natural arena where these processes can be observed in mutual interaction and on an unprecedented scale, is indeed the realm of relativistic astrophysics.

/pdf/electron-positron-pairs-in-physics-and-astrophysics-from-4g79pe8o5i.pdf

This article is intended to give a review of the history of the classical aspects of unified field theories in the 20th century. It includes brief technical descriptions of the theories suggested, short biographical notes concerning the scientists involved, and an extensive bibliography. The present first installment covers the time span between 1914 and 1933, i.e., when Einstein was living and working in Berlin - with occasional digressions into other periods. Thus, the main theme is the unification of the electromagnetic and gravitational fields augmented by short-lived attempts to include the matter field described by Schrodinger's or Dirac's equations. While my focus lies on the conceptual development of the field, by also paying attention to the interaction of various schools of mathematicians with the research done by physicists, some prosopocraphical remarks are included.

/pdf/on-the-history-of-unified-field-theories-26kjp679te.pdf

On the History of Unified Field Theories.

Lovelock theory is a natural extension of Einstein theory of gravity to higher dimensions, and it is of great interest in theoretical physics as it describes a wide class of models. In particular, it describes string theory inspired ultraviolet corrections to Einstein–Hilbert action, while admits the Einstein general relativity and the so-called Chern–Simons theories of gravity as particular cases. Here, we give an introduction to the black hole solutions of Lovelock theory and analyze their most important properties. These solutions can be regarded as generalizations of the Boulware–Deser solution of Einstein–Gauss–Bonnet gravity, which we discuss in detail here. We briefly discuss some recent progress in understanding these and other solutions, like topological black holes that represent black branes of the theory, and vacuum thin-shell wormhole-like geometries that connect two different asymptotically de Sitter spaces. We also make some comments on solutions with time-like naked singularities.

The Lovelock Black Holes

Holographic superconductors in the Born–Infeld electrodynamics

Gravitational and Electromagnetic Mass in the Born-Infeld Electrodynamics

Noon-Midnight Red Shift

On the spherically symmetric field in relativity (iii)

In a recent series of articles Born, with Infeld, has developed a theory of the electromagnetic field in which the self-energy of the electron is finite. In II the theory is based upon an unsymmetric fundamental tensor of which the symmetric and antisymmetric parts are identified respectively with the gravitational potentials and the electromagnetic field strengths. The Lagrangian is built up in terms of the determinants of the fundamental unsymmetric tensor and its symmetric part, but field equation of the Lagrangian with respect to the field strengths. One must first assume that these field strengths form the curl of a potential vector, and one must then perform the variation with respect to this vector. Again, though the gravitational gab enter the Lagrangian, variation with respect to them does not lead to adequate field equations for the gravitational field, so that Born and Infeld have suggested the arbitrary addition of the Riemannian curvature scalar density R√- g to their Lagrangian. In view of these two points it seems desirable to discuss the possible modification of the Born-Infeld theory in terms of the projective theory of relativity since in this way the difficulties mentioned above will be automatically overcome.

Banesh Hoffmann

Papers

Gravitational and Electromagnetic Mass in the Born-Infeld Electrodynamics

Noon-Midnight Red Shift

On the spherically symmetric field in relativity (iii)

On the new field theory

The Vector Meson Field and Projective Relativity