International Journal of Modern Physics A

Recent progress in the understanding of the nucleon is presented. The unpolarized structure functions are obtained with unprecedented precision from the combined H1 and ZEUS data and are used to extract proton parton distribution functions via NLO QCD fits. The obtained parametrization displays an improved precision, in particular at low Bjorken x, and leads to precise predictions of cross-sections for LHC phenomena. Recent data from proton–antiproton collisions at Tevatron indicate further precise constraints at large Bjorken x. The flavor content of the proton is further studied using final states with charm and beauty in DIS ep and collisions. Data from polarized DIS or proton–proton collisions are used to test the spin structure of the proton and to constrain the polarized parton distributions.

We reconsider the question of the relative importance of single particle effects and correlations in the solvable interacting neutrino models introduced by Friedland and Lunardini and by Bell, Rawlinson and Sawyer. We show, by an exact calculation, that the two particle correlations are not "small," and that they dominate the time evolution in these models, in spite of indications to the contrary from the rate of equilibration. The failure of the Boltzmann single particle approximation in this model is tentatively attributed to the simplicity of the model, in particular the restriction to two-flavor mixing, and the neglect of the position dependence of the interaction.

The standard model of strong interactions invokes the quantum chromodynamics (QCD) of quarks and gluons interacting within a fluid. At sufficiently small length scales, the effective interactions between the color charged particles within the fluid are thought to be weak. Short distance asymptotic freedom provides the perturbation theory basis for comparisons between QCD theory and laboratory high energy scattering experiments. It is here shown that the asymptotically free vacuum has negative dissipation implicit in the color electrical conductivity. Negative dissipation implies an asymptotically free QCD negative temperature excited state amplifier unstable to decay. The qualitative experimental implications of this instability are explored.

The framework of large extra dimensions provides a way to explain why gravity is weaker than the other forces in nature. A consequence of this model is the possible production of D-dimensional black holes in high energy p–p collisions at the Large Hadron Collider. The present work uses the CATFISH black hole generator to study quantitatively how these events could be observed in the hadronic channel at midrapidity using a particle-tracking detector.

We study a class of constant scalar invariant (CSI) space–times which belong to the higher-dimensional Kundt class and which are solutions of supergravity. We review the known CSI supergravity solutions in this class and we explicitly present a number of new exact CSI supergravity solutions, some of which are Einstein.

We introduce a numerical procedure to investigate the spectrum of massive modes and its contribution for gravity localization on thick branes. After considering a model with an analytically known Schrödinger potential, we present the method and discuss its applicability. With this procedure we can study several models even when the Schrödinger potential is not known analytically. We discuss both the occurrence of localization of gravity and the correction to the Newtonian potential given by the massive modes.

Within a quark combination model, we study systematically the yields and rapidity spectra of various hadrons in central Au + Au collisions at . We find that considering the difference in rapidity between net quarks and newborn quarks, the data of multiplicities, rapidity distributions for π^±, K^±, and, in particular, the ratios of charged antihadron to hadron as a function of rapidity, can be well described. The effects of net quarks on various hadrons are analyzed, and the rapidity distributions for , , , and are predicted. We discuss the rapidity distribution of net baryons, and find that it reflects exactly the energy loss of colliding nuclei.

The unification of quantum mechanics and general relativity remains the primary goal of theoretical physics, with string theory appearing as the only plausible unifying scheme. In the present work, in a search of the conceptual foundations of string theory, we analyze the relational logic developed by C. S. Peirce in the late 19th century. The Peircean logic has the mathematical structure of a category with the relation R_ij among two individual terms S_i and S_j, serving as an arrow (or morphism). We introduce a realization of the corresponding categorical algebra of compositions, which naturally gives rise to the fundamental quantum laws, thus indicating category theory as the foundation of quantum mechanics. The same relational algebra generates a number of group structures, among them W_∞. The group W_∞ is embodied and realized by the matrix models, themselves closely linked with string theory. It is suggested that relational logic and in general category theory may provide a new paradigm, within which to develop modern physical theories.

The quantum field model of unstable particles with a smeared mass is suggested to describe the finite-width effects. Within the framework of this model, we derive the convolution formula for a width and factorized formula for a cross-section. The phenomenological consequences of the mass smearing is discussed in the various fields of particle physics.

In this paper we imitate the traditional method which is used customarily in the general relativity and some mathematical literatures to derive the Gauss–Codazzi–Ricci equations for dimensional reduction. It would be more distinct concerning geometric meaning than the vielbein method. Especially, if the lower-dimensional metric is independent of reduced dimensions the counterpart of the symmetric extrinsic curvature is proportional to the antisymmetric Kaluza–Klein gauge field strength. For isometry group of internal space, the SO(n) symmetry and SU(n) symmetry are discussed. And the Kaluza–Klein instanton is also enquired.

Cherenkov gluons may be responsible for the asymmetry of dilepton mass spectra near ρ-meson observed in experiment. They can be in charge only for dileptons in the low-mass wing of the resonance. Therefore the dilepton mass spectra are flattened there and their peak is slightly shifted to lower masses compared with the in-vacuum ρ-meson mass. This feature must be common for all resonances.