Cascade production in heavy-ion collisions at SIS energies

Production of the doubly strange $\Xi$ baryon in heavy-ion collisions at \textrm{SIS} energies is studied in a relativistic transport model that includes perturbatively the strangeness-exchange reactions $\bar{K}\Lambda \to \pi \Xi$ and $\bar{K}\Sigma \to \pi \Xi$. Taking the cross sections for these reactions from the predictions of a hadronic model, we find that the $\Xi$ yield is about $10^{-4}$ in central collisions of $$Ni + $^{58}$Ni at $E/A=1.93$ \textrm{GeV}. The $\Xi$ yield is further found to be more sensitive to the magnitude of the cross sections for strangeness-exchange reactions than to the medium effects due to modified kaon properties. We have also made predictions for $\Xi$ production in Au+Au collisions at energies from 1 to 2 GeV/nucleon.Comment: 13 pages, 5 figures, typos fixed and discussions added, to appear in PL

Enhancement of low-mt{m_t} kaons in AGS heavy-ion collisions

In the relativistic transport model, we show that the recently observed enhancement of low-$m_t$ kaons ($K^+$ and $K^-$) in Si+Pb collisions at AGS can be explained if a density isomer is introduced in the nuclear equation-of-state.Comment: 12 pages, RevTex, 6 figs on request to [email protected]

Spinodal Instabilities of Baryon-Rich Quark-gluon Plasma in the PNJL Model

Using the Polyakov-Nambu-Jona-Lasinia (PNJL) model, we study the spinodal instability of a baryon-rich quark-gluon plasma in the linear response theory. We find that the spinodal unstable region in the temperature and density plane shrinks with increasing wave number of the unstable mode and is also reduced if the effect of Polyakov loop is not included. In the small wave number or long wavelength limit, the spinodal boundaries in both cases of with and without the Polyakov loop coincide with those determined from the isothermal spinodal instability in the thermodynamic approach. Also, the vector interactions among quarks is found to suppress unstable modes of all wave numbers. Moreover, the growth rate of unstable modes initially increases with the wave number but is reduced when the wave number becomes large. Including the collisional effect from quark scattering via the linearized Boltzmann equation, we further find that it decreases the growth rate of unstable modes of all wave numbers. Relevance of these results to relativistic heavy ion collisions is discussed.Comment: 13 pages, 9 figure

Production and rescattering of strange baryons at SPS energies in a transport model with hadron potentials

A mean-field potential version of the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) model is used to investigate the production of strange baryons, especially the $\Lambda$s and $\overline{\Lambda}$s, from heavy ion collisions at SPS energies. It is found that, with the consideration of both formed and pre-formed hadron potentials in UrQMD, the transverse mass and longitudinal rapidity distributions of experimental data of both $\Lambda$s and $\overline{\Lambda}$s can be quantitatively explained fairly well. Our investigation also shows that both the production mechanism and the rescattering process of hadrons play important roles in the final yield of strange baryons.Comment: 15 pages, 7 figure

The Predictability of REIT Returns and Market Segmentatio

Recent research suggests that real estate returns are more predictable than the returns of other assets and that the real estate market is segmented from the general stock market. This study examines these two issues empirically using a multifactor asset pricing model that allows for time-varying risk premiums. The results indicate that, in a general two-factor asset pricing framework, the REIT market is integrated with the general stock market. Furthermore, no evidence can be found that REIT returns are more predictable than the returns of other stocks.

Characterizing Higgs portal dark matter models at the ILC

We study the Dark Matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with $\sqrt{s} = 500$ GeV. In such models, the DM pair is produced in association with a $Z$ boson. In case the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying $Z$ boson provides a better search sensitivity than the signal with leptonically decaying $Z$ boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling $g_\chi$ is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator $H_2$. And the spin discriminating from scalar DM is always promising while it is difficult to discriminate from vector DM. As for $g_\chi$ approaching the perturbative limit, benchmark points with the mediator $H_2$ in the full mass region of interest are discoverable. And the spin discriminating from both the scalar and fermion DM are quite promising.Comment: 26 pages, 9 figures, version accepted for publication in EPJ

Antikaon flow in heavy-ion collisions: the effects of absorption and mean fields

We study antikaon flow in heavy-ion collisions at SIS energies based on the relativistic transport model (RVUU 1.0). The production of antikaons from both baryon-baryon and pion-baryon collisions are included. Taking into account only elastic and inelastic collisions of the antikaon with nucleons and neglecting its mean-field potential as in the cascade model, a strong antiflow or anti-correlation of antikaons with respect to nucleons is seen as a result of the strong absorption of antikaons by nucleons. However, the antiflow of antikaons disappears after including also their propagation in the attractive mean-field potential. The experimental measurement of antikaon flow in heavy-ion collision will be very useful in shedding lights on the relative importance of antikaon absorption versus its mean-field potential.Comment: 12 pages, 2 postscript figures omitted in the original submission are included, to appear in Phys. Rev.