On Infravacua and Superselection Theory

In the DHR theory of superselection sectors, one usually considers states which are local excitations of some vacuum state. Here, we extend this analysis to local excitations of a class of "infravacuum" states appearing in models with massless particles. We show that the corresponding superselection structure, the statistics of superselection sectors and the energy-momentum spectrum are the same as with respect to the vacuum state. (The latter result is obtained with a novel method of expressing the shape of the spectrum in terms of properties of local charge transfer cocycles.) These findings provide evidence to the effect that infravacua are a natural starting point for the analysis of the superselection structure in theories with long-range forces.Comment: LaTeX, 18 pages, spelling errors correcte

On Infravacua and the Localisation of Sectors

A certain class of superselection sectors of the free massless scalar field in 3 space dimensions is considered. It is shown that these sectors, which cannot be localised with respect to the vacuum, acquire a much better localisation, namely in spacelike cones, when viewed in front of suitable ``infravacuum'' backgrounds. These background states coincide, essentially, with a class of states introduced by Kraus, Polley and Reents as models for clouds of infrared radiation.Comment: LaTeX, 18 pages, minor corrections in order to conform with published versio

Renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking

The renormalization of supersymmetric Yang-Mills theories with soft supersymmetry breaking is presented using spurion fields for introducing the breaking terms. It is proven that renormalization of the fields and parameters in the classical action yields precisely the correct counterterms to cancel all divergences. In the course of the construction of higher orders additional independent parameters appear, but they can be shown to be irrelevant in physics respects. Thus, the only parameters with influence on physical amplitudes are the supersymmetric and the well-known soft breaking parameters.Comment: 29 pages, published in The European Physical Journal

A probabilistic and information theoretic interpretation of quantum evolutions

In quantum mechanics, outcomes of measurements on a state have a probabilistic interpretation while the evolution of the state is treated deterministically. Here we show that one can also treat the evolution as being probabilistic in nature and one can measure `which unitary' happened. Likewise, one can give an information-theoretic interpretation to evolutions by defining the entropy of a completely positive map. This entropy gives the rate at which the informational content of the evolution can be compressed. One cannot compress this information and still have the evolution act on an unknown state, but we demonstrate a general scheme to do so probabilistically. This allows one to generalize super-dense coding to the sending of quantum information. One can also define the ``interaction-entanglement'' of a unitary, and concentrate this entanglement.Comment: 9 page

Chiral black hole in three-dimensional gravitational Chern-Simons

A chiral black hole can be defined from the three-dimensional pure gravitational Chern-Simons action as an independent gravitational theory. The third order derivative of the Cotton tensor gives a dimensional constant which plays a role of the cosmological constant. The handedness of angular momentum depends on the signature of the Chern-Simons coefficient. Even in the massless black hole which corresponds to the static black hole, it has a nonvanishing angular momentum. We also study statistical entropy and thermodynamic stability.Comment: 6 pages, a reference added, minor changes to introductio