The strange quark mass from QCD sum rules

The strange quark mass is calculated from QCD sum rules for the divergence of the vector as well as axialvector current in the next-next-to-leading logarithmic approximation. The determination for the divergence of the axial-vector current is found to be unreliable due to large uncertainties in the hadronic parametrisation of the two-point function.From the sum rule for the divergence of the vector current, we obtain a value of (1 GeV)=189±32 MeV, where the error is dominated by the unknown perturbativeO( _s ³ ) correction. Assuming a continued geometric growth of the perturbation series, we findm _s =178±18 MeV. Using both determinations ofm _s , together with quark-mass ratios from chiral perturbation theory, we also give estimates of the light quark massesm _u andm _d.     

Strangeness in paradise: The strange quark as a probe of QCD

I review the arguments for considering the strange quark as a probe of changes in the QCD vacuum, and of the formation of a quark-gluon plasma, in particular. I survey existing data showing enhanced production of strange hadrons in relativistic heavy ion collisions and analyse their implications in the context of thermal and microscopic reaction models. My lecture closes with some remarks on strange quark matter and hypernuclei.     

Duality and the phases of massive gauge-invariant QCD

I discuss the phase structure of massive gauge invariant QCD (the gauged non-linear sigma model) using an operator formalism proposed by 't Hooft. The dual variables for this system are determined and the 't Hooft loop operator is constructed from these dual field variables. Its equal time commutation relations with the Wilson loop operator is explicitly verified. The system possesses two possible phases. In the semi-classical approximation (weak coupling), magnetic confinement as indicated by an area law for the expectation value of 't Hooft loops is observed. If above a certain critical coupling a condensate of vortices is formed, then the expectation value of the 't Hooft loop in the dilute vortex approximation shows a perimeter law indicating electric confinement.     

QCD phase transition with strange quark in wilson formalism for fermions

The nature of QCD phase transition is studied with massless up and down quarks and a light strange quark, using the Wilson formalism for quarks on a lattice with the temporal direction extensionN _t=4. We find that the phase transition is of first order for the physical strange quark mass.     

Lattice QCD with a twisted mass term and a strange quark

There are three quarks with masses at or below the characteristic scale of QCD dynamics: up, down and strange. However, twisted mass lattice QCD relies on quark doublets. Various options for including three quark flavors within the twisted mass approach are explored by studying the kaon masses, both analytically (through chiral Lagrangians) and numerically (through lattice simulations). Advantages and disadvantages are revealed for each “strange and twisted” option.     

QCD phase transition with strange quark in wilson formalism for fermions

The nature of QCD phase transition is studied with massless up and down quarks and a light strange quark, using the Wilson formalism for quarks on a lattice with the temporal direction extensionN _t=4. We find that the phase transition is of first order for the physical strange quark mass.     

A QCD relation between electromagnetic mass differences of charmed mesons and strange baryons

Relations between hadron mass splittings are obtained from the assumption that the ratio of the electromagnetic and strong contributions to hardon spin splittings depends only upon the ratio of the electromagnetic to the strong couplings of the quark-quark or quark-antiquark pairs involved. This ratio is the same in charmed mesons and strange baryons when the values of color and electric charges of the standard colored quark model are used. Predictions for D¹⁺?D¹⁰ and ∑^1?-∑¹⁺ mass splittings obtained are in good agreement with present experimental data and can be tested much better when better data on D and D¹ masses become available.     

Determination of the strange quark content of the nucleon from a next-to-leading-order QCD analysis of neutrino charm production

We present the first next-to-leading-order QCD analysis of neutrino charm production, using a sample of 6090 ^– and -induced opposite-sign dimuon events observed in the CCFR detector at the Fermilab Tevatron. We find that the nucleon strange quark content is suppressed with respect to the non-strange sea quarks by a factor =0.477 _–0.053 ^+0.063 , where the error includes statistical, systematic and QCD scale uncertainties. In contrast to previous leading order analyses, we find that the strange seax-dependence is similar to that of the non-strange sea, and that the measured charm quark mass,m _c =1.70±0.19 GeV/c², is larger and consistent with that determined in other processes. Further analysis finds that the difference inx-distributions betweenxs(x) and is small. A measurement of the Cabibbo-Kobayashi-Maskawa matrix element |V _cd |=0.232 _–0.020 ^+0.018 is also presented.     

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.     

Next-to-Leading order QCD corrections to charged current charm production and the unpolarized and polarized strange sea at HERA

We discuss fixed target and ISR inclusive photon production and attempt a comparison between theory and experiments. The dependence of the theoretical predictions on the structure functions, and on the renormalization and factorization scales is investigated. The main result of this study is that the data cannot be simultaneously fitted with a single set of scales and structure functions. On the other hand, there is no need for an additional primordial to force the agreement between QCD predictions and experiments, with the possible exception of one data set. Since the data cover almost overlapping kinematical ranges this raises the question of consistency among data sets. A comparative discussion of some possible sources of experimental uncertainties is sketched. Received: 23 November 1998 / Published online: 22 March 1999     

Higher power QCD mechanisms for largep T strange or charmed baryon production in polarized proton-proton collisions

We investigate potential higher power mechanisms for strange or charmed baryon production of large transverse momentum and calculate the corresponding helicity asymmetries, which turn out to be large and significantly different to those obtained from the leading power mechanism.     

The strange behavior of entangled photons

An experiment is discussed in which a conflict between the wave like and nonlocal properties of photons leads to an apparent paradox. Possible ways of circumventing this contradiction are suggested. The experiment allows us to prove a Bell’s theorem for two particles without using an inequality and to test local realism against quantum mechanics introducing additional assumptions weaker than nonenhancement.     

The strange backbending behaviour in the Yb isotopes

The rotational energies and the backbending behaviour of ^166,168,170Yb are calculated utilizing angular momentum and particle number projected deformed BCS trial wave functions. The anomaly of the moment of inertia can be reproduced quantitatively with the moment of inertia of an inert core as the only free parameter. A possible explanation for the strange behaviour in the Yb isotopes is given.     

The three-gluon vertex of QCD

We show how the Q² evolution of gluon jets can be used to provide indirect but strong evidence for the three-gluon vertex of QCD. We propose looking for this evolution in the $Q\overline{Q}\to 3G\to$ hadrons decay of successive 1 ³S₁ quarkonium states. The results apply to other processes if G-jets can be isolated.     

The strange eigenmode in Lagrangian coordinates

For a distribution advected by a simple chaotic map with diffusion, the "strange eigenmode" is investigated from the Lagrangian (material) viewpoint and compared to its Eulerian (spatial) counterpart. The eigenmode embodies the balance between diffusion and exponential stretching by a chaotic flow. It is not strictly an eigenmode in Lagrangian coordinates, because its spectrum is rescaled exponentially rapidly.     

The Fundamental Scale of QCD

Physics of Atomic Nuclei - There are several scales in the QCD as the theory of strong interaction: the vacuum gluonic condensate (as the divergence of the dilatation current), the nucleon mass as...