arXiv subjects
Publications and source records attributed to W. Broniowski.
A calculation of the pion balance functions in a thermal model is presented. The total result consists of resonance and non-resonance parts. A satisfactory agreement with the data on Au+Au collisions at 130 GeV is found.
The pi+ pi- balance function in rapidity is computed in a thermal model with resonances. It is found that the correlations from the neutral-resonance decays are important, yielding about a half of the total contribution, which in general consist of resonance and non-resonance parts. The model yields the pionic balance function a few per cent wider that what follows from the recent data for the Au+Au collisions at 130GeV.
The behavior of nonperturbative parts of the isovector-vector and isovector and isosinglet axial-vector correlators at Euclidean momenta is studied in the framework of a covariant chiral quark model with nonlocal quark-quark interactions. The gauge covariance is ensured with the help of the P-exponents, with the corresponding modification of the quark-current interaction vertices taken into account. The low- and high-momentum behavior of the correlators is compared with the chiral perturbation theory and with the QCD operator product expansion, respectively. The V-A combination of the correlators obtained in the model reproduces quantitatively the ALEPH data on hadronic τdecays, transformed into the Euclidean domain via dispersion relations. The predictions for the electromagnetic π^\pm - π^0 mass difference and for the pion electric polarizability are also in agreement with the experimental values. The topological susceptibility of the vacuum is evaluated as a function of the momentum, and its first moment is predicted to be χ'(0)\approx (50 MeV)^2. In addition, the fulfillment of the Crewther theorem is demonstrated.
The single-freeze-out model of hadron production is used to describe the particle ratios and the transverse-momentum spectra from RHIC. The emphasis is put on the new measurements done at the highest beam energy of 200 GeV. An overall very good agreement is found between the data and the model predictions. The data for different centrality windows are analyzed separately. A simple scaling of the two expansion parameters of the model with the centrality is found. Interestingly, this scaling turns out to be equivalent to the scaling of hadron production with the number of wounded nucleons.
We describe the formation of solitons in NJL-type models and discuss the influence of the regularization scheme on the stability of the solution. We concentrate on models with non-local regulators in which stable solutions exist without introducing additional constraints.
We show, under general assumptions which are well satisfied in relativistic heavy-ion collisions, that the geometric relation of centrality c to the impact parameter b, namely c ~ pi b^2/sigma_inel, holds to a very high accuracy for all but most peripheral collisions. More precisely, if c(N) is the centrality of events with the multiplicity higer than N, then b is the value of the impact parameter for which the average multiplicity is equal to N. The corrections to this geometric formula are of the order (Delta n(b)/ )^2, where Delta n(b) is the width of the multiplicity distribution at a given value of b, hence are very small. In other words, the centrality effectively measures the impact parameter.
We show that the dynamical quark mass in effective nonlocal models can vanish at zero virtuality of the quark as $M(p^2)\propto p^2$. Our arguments follow from the constrained-instanton model of the QCD vacuum and from QCD sum rules calculations with nonlocal condensates. The discussed models also lead to analyticity of $M(p^2)$ in the vicinity of zero.
Two examples of ``exotic'' phenomena which become possible and important in the presence of nuclear matter are discussed: omega -> pi pi decay, and rho-omega mixing. Significance of these processes for the low-mass dilepton production in relativistic heavy-ion collisions is indicated.
We confront the hypothesis of chemical freeze-out in ultra-relativistic heavy-ion collisions with the hypothesis of large modifications of hadron masses in nuclear medium. We find that the thermal-model predictions for the ratios of particle multiplicities are sensitive to the values of in-medium hadronic masses. In particular, the $π^+/p$ ratio decreases by 35% when the masses of all hadrons (except for pseudo-Goldstone bosons) are scaled down by 30%.
We analyze subtracted dispersion relations for meson correlators at finite baryon density and temperature. Such relations are needed for QCD sum rules. We point out the importance of scattering terms, as well as finite, well-defined subtraction constants. Both are necessary for consistency, in particular for the equality of the longitudinal and transverse correlators in the limit of the vanishing three-momentum of mesons relative to the medium. We present detailed calculations in various mesonic channels for the case of the Fermi gas of nucleons.
We calculate the width for the omega -> pi pi decay in nuclear medium. Chiral dynamics and low-density approximation are used. At densities around twice the nuclear saturation density we estimate the partial width for the decay of the longitudinal mode to be of the order of a few tens of MeV, and for the transverse mode a few times less.
The effects of meson loops in the vacuum sector of the Nambu--Jona-Lasinio model are calculated. Using the effective action formalism we take consistently all next-to-leading-order $1 \over \Nc$ terms into account. This leads to a symmetry-conserving approach, in which all features of spontaneously broken chiral symmetry, such as the Goldstone theorem, the Gold\-ber\-ger--Treiman and the Gell-Mann--Oakes--Renner relations are preserved. Contributions to $\langle \overline{q}q \rangle$ and $F_π$ are calculated, and are shown to be substantial, at the level of $\sim 30\%$, consistent with the $1 \over \Nc$ expansion. The leading nonanalytic terms in the chiral expansion of $\langle \overline{q}q \rangle$, $F_π$ and $m_π$ agree have the same form as the one-loop results of chiral perturbation theory.
We analyze the analytic structure of meson propagators in the Nambu--Jona-Lasinio model with a proper-time regulator. We show that the regulator produces unphysical complex singularities. As a result the naive use of the Wick rotation is no longer allowed. Formulas involving integration over mesonic momenta, such as meson-loop contributions or dispersion relations for meson Green's functions, cannot be written in usual forms.
We show that in a uniform medium, the vanishing of a particular condensate along with spontaneously broken symmetry imply the existence of an anomalously light pseudo-Goldstone mode. The consequences for a vanishing chiral condensate in nuclear matter are discussed.
The large-$N_c$ consistency conditions for axial vector and isovector magnetic couplings of pions to baryons are discussed from the point of view of low-energy current-algebra sum rules (Adler-Weisberger, Cabibbo-Radicati). In particular, we show how the result that ratios of axial vector and isovector magnetic coupling constants get corrections only at the order $1/N_c^2$ follows from the $N_c$-counting of appropriate cross sections. This counting is performed using various approaches at the quark and hadronic level. Other implications of our method are also presented.
The electric polarizability of the nucleon is calculated in the soliton approach to the Nambu--Jona-Lasinio model. We analyze the leading-$N_c$ contributions, as well as the effects of rotational $1/N_c$ corrections and $Δ$-$N$ mass splitting. Our model prediction is substantially reduced compared to other soliton calculations, and is closer to the experimental value.
Instead of using a simple reggeon-exchange model, we provide a model-independent estimate of high-energy contribution to the Adler-Weisberger sum-rule. Results and conclusions of the paper remain unchanged.
Electromagnetic polarizabilities of the nucleon are analyzed in a hedgehog model with quark and meson degrees of freedom.