A mechanism for the production of baryons at large transverse momentum

The difference between the proton and the antiproton distributions and the charged pion distribution are compared at largeP _T and agreement is found with a model attributing baryons to final state rearrangement of hard scattered partons. The model contains a dual topological suppression of baryonic clusters at largeP _T which is partially balanced as the cluster decay distribution into baryons is peaked at higher values of the momentum fractionz. The model implies positive correlations between antiproton triggers and opposite side protons.     

Temperature fluctuations of cosmic microwave background induced by gravitational lensing

Adopting the accepted interpretation of the cosmic microwave background (CMBR) as a relic of the early hot universe we show that any angular intensity variations existing in the background at the “last scattering surface” at the redshift of ∼10³ will induce bright fluctuations through gravitational lensing by intervening masses. The resulting temperature variations ΔT are estimated for gravitating masses like distant galaxies (z ∼ 1) and local dark objects (e.g. population III stars) in our own Galaxy. It is found that the value of ΔT/T produced by the above mechanisms further constrains the theories of galaxy formation. The calculation also limits the amount of matter present in the form of population III objects in the galaxy.     

Baryon magnetic moments in a dynamical quark-diquark model

The magnetic moments of baryons are calculated in a dynamical quark-diquark model using current-quark masses as input. Except for theΞ ^? moment, results are in fairly good agreement with experiment.     

High transverse momentum Ξ baryon correlations in p+p collisions at √s=200 GeV

Angular correlations between produced high-p _TΞ^? baryons and unidentified charged and neutral particles are observed in high-tower triggered (on a large electromagnetic energy deposit) √s=200 GeV p+p collisions. This trigger favors events with higher average multiplicity than those in minimum bias. These events are likely to contain jets. The average multiplicity of a high-tower triggered event is similar to that of a minimum bias event containing a Ξ baryon, which implies that Ξ baryons are likely to be produced in jets. Ξ^? <p _T> is higher in the triggered data then in the minimum bias sample.     

Static hyperon properties in a linearizedSU(3)-Chiral Bag model

We use a linearized Chiral Bag model to describe the strange octet and decuplet baryons. The approach is canonically extended to spontaneously broken chiral SU(3)_L × SU(3)_R, and the corresponding Goldstone Bosons are identified with the pseudoscalar meson octet. We include explicit symmetry breaking corrections both for baryons and mesons. The linearized quark-meson intraction is applied in a self-consistent calculation of the masses and, for Δ, Σ^* and Ξ^*, of the decay widths. Our special interest is in the influence of theK- andη-cloud (in addition to theπ) on hyperon static properties. We show results for radii, masses, decay widths and renormalization constants as obtained by a fit to the experimental hyperon spectra. The effects of theK- andη-mesons are found to be non-negligible, although supressed by symmetry breaking effects. The effective gluon coupling α is reduced in comparison to the SU(2)_L × SU(2)_R case. In addition, we discuss the dependence on the bag constantB. It turns out that the lightest hyperon states, Λ and Σ are well described and stable for B^1/4 < 130 MeV. The heavier strange baryons have stable solutions also for larger values ofB. The bag radii determined at the minimal energies are R₀?1.15 fm for the octet and R₀?1.25 fm for the decuplet baryons.     

On the mechanisms of photogeneration of charge carriers in PEPC-C60 composites

Photogeneration of electric charge carriers at high strengths of the external electric field and the temperature of transition to the viscous-flow state (T _visc) of thin PEPC-C₆₀ composite films obtained by casting from a toluene solution have been studied. The rheology of the composite films has been investigated by the nondestructive optical method. The consistent correlated change in the values of T _visc and the effective temperature in the expression for the photogeneration quantum yield (T ₀) in the Meltz representation with variations in the C₆₀ concentration has been established. The difference between T _visc and T ₀ in thin composite films does not exceed 2–3% of T _visc (T ₀).     

Enhancement of heavy quarkonium production in hadron collisions at finite temperature

We estimate how the masses and wave functions of heavy quarkonium mesons change with temperature below the deconfining temperatureT _c . To do so we use simple, theoretically motivated parametrizations of the way the heavy quark potential and quark masses vary with temperature. The effect of these changes on the production of charmonium and bottonium in hadron-hadron collisions is estimated using a standard phenomenological model. We find, for example, that forT close toT _c enhancements by as much as a factor of 3 are possible for charmonium and bottonium highp _T production at SPS energies \(\sqrt s\) =20 GeV. Thep _T and energy dependence of this enhancement is non-trivial. We discuss the relevance of our results for the interpretation of recentJ/ψ data from heavy ion collisions.     

Meson screening masses from lattice QCD with two light quarks and one strange quark

We present results for screening masses of mesons built from light and strange quarks in the temperature range of approximately between 140 MeV to 800 MeV. The lattice computations were performed with 2+1 dynamical light and strange flavors of improved (p4) staggered fermions along a line of constant physics defined by a pion mass of about 220 MeV and a kaon mass of 500 MeV. The lattices had temporal extents N _τ =4, 6 and 8 and aspect ratios of N _s /N _τ ≥4. At least up to a temperature of 140 MeV the pseudo-scalar screening mass remains almost equal to the corresponding zero temperature pseudo-scalar (pole) mass. At temperatures around 3T _c (T _c being the transition temperature) the continuum extrapolated pseudo-scalar screening mass approaches very close to the free continuum result of 2πT from below. On the other hand, at high temperatures the vector screening mass turns out to be larger than the free continuum value of 2πT. The pseudo-scalar and the vector screening masses do not become degenerate even for a temperature as high as 4T _c . Using these mesonic spatial correlation functions we have also investigated the restoration of chiral symmetry and the effective restoration of the axial symmetry. We have found that the vector and the axial-vector screening correlators become degenerate, indicating chiral symmetry restoration, at a temperature which is consistent with the QCD transition temperature obtained in previous studies. On the other hand, the pseudo-scalar and the scalar screening correlators become degenerate only at temperatures larger than 1.3T _c , indicating that the effective restoration of the axial symmetry takes place at a temperature larger than the QCD transition temperature.     

Perturbative versus lattice QCD energy density correlators at high temperatures

Correlators of magnetic and electric field energy density are investigated for SU(N_c) gauge theory at high temperatures T. A separations z ⩽ 2/T the correlators are shown to be dominated by a power-law behavior even for finite gluon screening masses. This continuum behavior is well approximated on current 4 × 16³-lattices in the perturbative limit and leads to a considerable overestimate of screening masses deduced from fitting the lattice correlators with conventional exponential forms. The use of extended sources and sinks to enhance the signal improves the situation for screening masses m ⪢ T but leads to a largely uncontrolled error for masses less than T. In fact, we show that recent lattice QCD data of Grossmann et al., from which a magnetic screening mass m_M ∼ 2.9T was deduced, may even be consistent with a vanishing actual magnetic screening mass.     

Pentaquarks: Facts and puzzles

On the occasion of the celebration of the 70th birthday of Prof. Yu.A. Simonov, we contribute a brief review of the status of exotic baryons, which are most likely pentaquark states. We summarize the experimental status of exotic baryons, discuss the baryon antidecuplet to which exotic baryons possibly belong, and review theoretical expectations for the masses and widths of recently discovered Θ and Ξ_3/2 baryons which have come from studies of QCD sum rules, lattice QCD, and quark models. We also pay special attention to the dynamical calculation of pentaquark masses in a framework of the QCD string approach originally elaborated by Simonov for baryons and using the Jaffe-Wilczek \([ud]^2 \bar q\) approximation for the pentaquark states.     

The determination of the Lorenz number at high temperatures

In a conducting system consisting of a short fine wire carrying a current between two larges masses of the same metal, the maximum temperature attained depends only upon the properties of the material and the applied potential difference, provided the heat lost from the surface of the wire is negligible compared with that conducted. Measurement of the maximum temperature as a function of the potential difference allows the ratio of the thermal conductivityλ to the electrical conductivityχ, and hence the Lorenz numberλ/χ T whereT is the absolute temperature, to be determined over a wide range of temperature. Experiments with platinum in various gases at atmospheric pressure and also at low gas pressures to test the effect of heat losses due to the surrounding gas are described. Under the conditions of the experiments, these losses are very small except in the case of hydrogen, the results agreeing among themselves and with those previously published. Values of the Lorenz number for palladium from 1000 to 1550? C are given.     

Amplitude of photostructural changes in chalcogenide vitreous semiconductors

It is shown that a position of an optical absorption edge (OAE) of amorphous AsSe and As₂S₃ films irradiated by light up to saturation is independent on T_exp the temperature at which the sample is exposed, and the amplitude of a reversible photoinduced shift of OAE ΔE is determined by its thermal shift ΔE as it is heated from T_exp up to the glass-transition temperature T_g. So, in order to obtain maximum photoinduced changes we need to use materials with maximum thermal variations of the forbidden zone width, and to tend to a greater difference between T_g and T_exp. The obtained results are well explained within the scope of the local heating model.     

Solitons bound to heavy mesons

We improve the bound state approach of the Skyrme model applied to the heavy baryons by adopting a static heavy meson picture where the soliton moves around the fixed heavy meson. This allows to take into account the center of mass corrections in a more consistent way. The bound state masses so obtained are comparable to the experimentally observed Λ _c and Λ _c ^* masses. A loosely bound state of a soliton with an antiflavored heavy meson is found, which leaves a possibility of the nonstrange pentaquark baryon(s).     

The strong and weak interactions of coloured particles

A new form of the weak interaction in Han-Nambu theory is proposed consistent with recent data on the weak production of new particles. The existence is inferred of coloured baryons in an (8,8) representation of SU(3) X SU(3) with masses 2–3.5 GeV/c².     

Phase transition in anyon superconductivity at finite temperature

The magnetic response of the charged anyon fluid at temperatures higher than the fermion energy gap (T ⪢ ω_c) is investigated in the self-consistent field approximation. In this temperature region a new phase, characterized by an inhomogeneous magnetic penetration, is found. The inhomogeneity is linked to the existence of an imaginary magnetic mass which increases with the temperature. It is explicitly proved that the electromagnetic field magnetic masses and rest-energies are different in the (T ⪢ ω_c)-phase.