Modern Physics Letters A

By taking into account both quantum mechanical and general relativistic effects, an equation that describes some limitations on the measurability of space-time distances can be derived. We then discuss possible features of quantum gravity which are suggested by this equation.

A universal parametrization for possible quark and lepton substructure is advocated in terms of quark and lepton form factors. It is emphasized that the lower bounds on compositeness scale, Λ_c, to be determined experimentally depend strongly on their definitions in composite models. From the recent HERA data, it is estimated to be Λ_c>50 GeV, 0.4 TeV and 10 TeV, depending on the parametrizations with a single-pole form factor, a contact interaction and a logarithmic form factor, respectively.

We consider classical Yang-Mills-Dirac equations on Minkowski space, with gauge group SU(2), and look for solutions invariant (up to a gauge transformation) under a four-dimensional subgroup of the conformal group. In each of the four different cases that we analyze, the equations admit non-Abelian solutions, but these cannot be obtained analytically. In addition, some cases admit solutions with chiral spinors that may be physically relevant. All these solutions are singular.

In the superspace z^M=(x^μ, θ_R, θ_L) the global symmetries for d=10 superparticle model with kinetic terms for both Bose and Fermi variables are shown to form a superalgebra, which includes the Poincaré superalgebra as a subalgebra. The subalgebra is realized in the space of variables of the theory by a nonstandard way. The local version of this model with off-shell closed Lagrangian algebra of gauge symmetries and off-shell global supersymmetry are presented. It is shown that the resulting model is dynamically equivalent to the Siegel superparticle.

A thermodynamical bag model is proposed to study the parton distribution functions and nucleon structure functions in the deep inelastic scattering (DIS) of leptons on nucleons. Equations of state for the thermodynamical bag are deduced and solved self-consistently. The theory explains all the observed features in DIS and gives a good fit to the experimental data.

The flat phase space (R²ⁿ, ω) with a symmetry group G generated by quadratic first class constraints is considered. We analyze the quantization of this constrained system in terms of the Fock bundle , where S=Sp(2n, R)/U(n) is the space of positive translationally invariant complex structures J on (R²ⁿ, ω) and fibers H_J are the Hilbert spaces of quantization associated with the space (R²ⁿ, ω, J).

The oscillator quantum algebra is extended, through a general approach, in order to put in evidence new q-Hermite polynomials and to discuss the already known ones. Such an approach constraints possible brackets. New sets of corresponding q-bosonic operators are pointed out, reducing for specific values of the subtended parameters to the parabosonic operators.

Using the proper definition¹ of the massless 2D-propagator – depending on an arbitrary ir-scale μ – we check Elitzur’s conjecture on the ir finiteness of O(N)-invariant Green functions.

Explicit computations to the second order in the coupling constant show that non-invariant correlators become finite but μ-dependent objects, whereas the correlators of invariant operators, which are possible candidates for “physical” observables, do not depend on the ir-scale.

We present a formulation of the correlation problem in the transverse plane of high-energy nuclear collisions. The correlation variable is the azimuthal angle between two transverse momenta. We assume that the effects of quark-hadron phase transition are manifested in the existence of a coherence angle χ and a parameter ε characterizing the irreducible correlation. We then derive the consequences on the observable two-particle correlation function.

On the ambiguity arising in the derivation of the critical dimension of bosonic string in the covariant gauge shown by the present authors, there appears a critical paper by Mödritsch. A reply to this criticism is made by pointing out his misunderstanding about how the ambiguity arises.