International Journal of Modern Physics A

Velocity-dependent interactions in a fundamental-string dominated universe lead quite naturally, with reasonable assumptions on initial conditions, to an accelerating expanding universe without assuming the existence of a cosmological constant. Using a mean-field approximation, exact solutions are obtained for various string/brane cosmological toy models. A multi-body model is also investigated. It is also shown that the repulsive velocity-dependent force arises in more general contexts and can lead to cosmic structure formation. Finally, we discuss a toy model including both ordinary and extremal matter, in which the latter accounts for dark matter while simultaneously acting as effective dark energy. Eternal acceleration is once more seen to arise in this case.

We study the relation of the spin-statistics theorem to the geometric structures on phase space, which are introduced in quantization procedures (namely a U(1) bundle and connection). The relation can be proved in both the relativistic and the nonrelativistic domain (in fact for any symmetry group including internal symmetries) by requiring that the exchange can be implemented smoothly by a class of symmetry transformations that project in the phase space of the joint system system. We discuss the interpretation of this requirement, stressing the fact that any distinction of identical particles comes solely from the choice of coordinates — the exchange then arises from suitable change of coordinate system. We then examine our construction in the geometric and the coherent-state-path-integral quantization schemes. In the appendix we apply our results to exotic systems exhibiting continuous "spin" and "fractional statistics." This gives novel and unusual forms of the spin-statistics relation.

We give a detailed analysis of the oscillation formula within the context of the wave packet formalism. Particular attention is made to insure flavor eigenstate creation in the physical cases (Δp≠0). This requirement imposes noninstantaneous particle creation in all frames. It is shown that the standard formula is not only exact when the mass wave packets have the same velocity, but it is a good approximation when minimal slippage occurs. For more general situations the oscillation formula contains additional arbitrary parameters, which allows for the unknown form of the wave packet envelope.

We formulate Dirac–Kähler fermion action by introducing a new Clifford product with noncommutative differential form on a lattice. Hermiticity of the Dirac–Kähler action requires to choose the lattice structure having both orientabilities on a link. The Kogut–Susskind fermion and the staggered fermion actions are derived directly from the Dirac–Kähler fermion formulated by the Clifford product. The lattice QCD action with Dirac–Kähler matter fermion is also derived via an inner product defined by the Clifford product.

We propose a superfield formalism of Lagrangian BRST–anti-BRST quantization of arbitrary gauge theories in general coordinates with the base manifold of fields and antifields described in terms of both bosonic and fermionic variables.

In this paper we apply a Schrödinger picture description of the minisuperspace approach to the closed string tachyon condensation. We will calculate the rate of produced closed string and we will show that the density of high massive closed string modes reaches the string density in time of order one in string units.

An algorithm for numerical computation of the barrier transparency for the potentials surrounding Schwarzschild black holes is described for massive spinor particles. It is then applied to calculate the total (including electronic neutrino and the contributions of twisted field configurations connected with Dirac monopoles) luminosity for the electron–positron Hawking radiation from a Schwarzschild black hole with mass M=10¹⁵ g. It is found that the contribution due to monopoles can be of order 12% of the total electron–positron luminosity.

We discuss a description of Ω^- two body nonleptonic decays based on possible, albeit tiny, admixtures of mirror matter in ordinary hadrons. The |ΔI|=1/2 rule enhancement is obtained as a result of isospin symmetry and, more importantly, the rather large observed deviations from this rule result from small isospin breaking. This analysis lends support to the possibility that the enhancement phenomenon observed in low energy weak interactions may be systematically described by mirror matter admixtures in ordinary hadrons.