Modern Physics Letters A

Various recently developed connections between supersymmetric Yang–Mills theories in four dimensions and two-dimensional integrable systems serve as crucial ingredients in improving our understanding of the AdS/CFT correspondence. In this review, we highlight some connections between superconformal four-dimensional Yang–Mills theory and various integrable systems. In particular, we focus on the role of Yangian symmetries in studying the gauge theory dual of closed string excitations. We also briefly review how the gauge theory connects to Calogero models and open quantum spin chains through the study of the gauge theory duals of D3 branes and open strings ending on them. This invited review is based on a seminar given at the Institute of Advanced Study, Princeton.

In this letter we show that supersymmetry (like geometry) can be approximated using finite-dimensional matrix models and fuzzy manifolds. In particular, we propose a nonperturbative regularization of supersymmetric U(n) gauge action in 4D. In some planar large-N limits we recover exact SUSY together with the smooth geometry of .

The lowest order contribution of the amplitude of the Dirac–Coulomb scattering in de Sitter spacetime is calculated assuming that the initial and final states of the Dirac field are described by exact solutions of the free Dirac equation on de Sitter spacetime with a given momentum and helicity. One studies the difficulties that arises when one passes from the amplitude to cross section.

We address two questions about the past for infinitely cyclic cosmology. The first is whether it can contain an infinite length null geodesic into the past in view of the Borde–Guth–Vilenkin (BGV) "no-go" theorem, The second is whether, given that a small fraction of spawned universes fail to cycle, there is an adequate probability for a successful universe after an infinite time. We give positive answers to both questions and then show that in infinite cyclicity the total number of universes has been infinite for an arbitrarily long time.

We consider the possibility that the Ultra High Energy Cosmic Rays arriving to Earth might be neutrons instead of protons. We stress that in such case the argument for the GZK cutoff is weaker and that it is conceivable that neutrons would not be affected by it. This scenario would require the neutron to start with an energy larger than the observed one, in order to be able to travel the distances involved, within its proper lifetime. It must then lose most of the extra energy through interaction with the galactic dark matter or some other matter in the intergalactic medium.

The negative specific heat of a radiating black hole is indicative of a cataclysmic endpoint to the evaporation process. In this letter, we suggest a simple mechanism for circumventing such a dramatic outcome. The basis for our argument is a conjecture that was recently proposed by Arkani-Hamed and collaborators. To put it another way, we use their notion of "Gravity as the Weakest Force" as a means of inhibiting the process of black hole evaporation.

Using the Hamilton–Jacobi method, we discuss the Hawking radiation of the Kerr black hole. The result shows when the self-gravitational interaction as well as the conservation of energy and angular momentum are taken into account, the radiation spectrum deviates from the purely thermal one and the tunneling probability is related to the change of Bekenstein–Hawking entropy, which is in accordance with Parikh and Wilczek's result and gives a method to study the Hawking radiation of the black hole.