Modern Physics Letters A

Ultra high energy observational data collected during the last decade indicate an anomalous interaction of the particles emitted by some point sources in the sky. We briefly review the evidence and discuss possible explanations of the observed anomalies. The most likely interpretation is that at energies of the order of a few TeV in the Center of Mass, new phenomena begin to take place which cannot be explained within the framework of the Standard Model. Implications of such an explanation are briefly discussed.

We discuss how recapture of an object from debris spewed at the early stage of formation by the millisecond pulsar whose signals where observed briefly in the remnant of SN1987A may have caused its subsequent collapse into a black hole, by damping the rapid rotation which is believed to have contributed to its stability. The mass of the object sufficient to bring this about in the two week interval between observation and next search is calculated to be up to 1/20 of a Jupiter mass.

We show that the significant Tolman-Bondi metrics originated by a synchronous big bang can be divided, according to the initial conditions, into three classes. The elements of one of these classes give the dynamical description of the formation of a black hole in the background of an expanding universe.

A general model of the piecewise-smooth spacetime whose smooth regions are the Kerr space pieces is constructed. The model includes three arbitrary constants and one arbitrary function depending on the coordinates. The Einstein tensor does not vanish only on the common boundary of the smooth regions and contains the δ-function as a factor, so that this boundary is interpreted as an infinitesimally thin rotating disk. The shape of the Einstein tensor indicates the absence of the pressure and motion of the source matter in the direction normal to the disk.

We describe the canonical quantization of Einstein gravity for space-times with one killing vector field. We use the new canonical variables introduced by Ashtekar. Both the connection and loop space representations for the quantum theory are considered. We find that the physical state space has a characterization in terms of equivalence classes of Eulerian graphs.

Constraints on the masses of possible fourth generation quarks (a, υ) are obtained from measurements of the ρ parameter and the elements of the quark mixing matrix. Stringent mass limits are found when the off-diagonal elements V_tυ and V_ab are large. For example, with m_t=90 GeV and |V_tυ|≃0.5 we find m_a,v≤ 300 GeV. Stronger constraints are obtained as m_t or |V_tυ| increase.

We study the K_l3 decays and show that a large isospin breaking effect is present in experimental data of K_µ3. From the K_µ3 and K_e3 rates, we determine the following weighted averages values: with being the vector charge of the weak transition K→π.

Perturbative approach to two-dimensional gravity and supergravity is considered. One-loop renormalization of the central charge of SL(2, R) Kac-Moody algebra is calculated perturbatively by functional integration and by explicit calculations of the Feynman diagrams. Also the wavefunction renormalization and the anomalous dimensions in the presence of gravity are calculated.

We discuss a new method for measuring the critical exponent γ for the partition function of the bosonic string. The statistics seems very good and the fit to γconsistent with the assumed asymptotic form for the partition function for dimensions d=1–6. The results are in agreement with analytical results when the target space dimension is d=0, but disagree when d=1. We conjecture that this is due to the appearance of logarithmic corrections to the asymptotic form of the partition function. These corrections might persist for d>1 and might render the determination of γquite difficult.

The critical properties of Ising model on the dynamical triangulated random surface embedded in D-dimensional Euclidean space are investigated. The strong coupling expansion method is used. The transition to thermodynamical limit is performed by means of continuous fractions.