Iso-curvature fluctuations through axion trapping by cosmic string wakes

We consider wake-like density fluctuations produced by cosmic strings at the quark-hadron transition in the early universe. We show that low momentum axions which are produced through the radiation from the axionic string at an earlier stage, may get trapped inside these wakes due to delayed hadronization in these overdense regions. As the interfaces, bordering the wakes, collapse, the axions pick-up momentum from the walls and finally leave the wake regions. These axions thus can produce large scale iso-curvature fluctuations. We have calculated the detailed profile of these axionic density fluctuations and discuss its astrophysical consequences.Comment: 23 pages, 4 figures, RevTe

Azimuthal flow of decay photons in relativistic nuclear collisions

An overwhelming fraction of photons from relativistic heavy ion collisions has its origin in the decay of $\pi^0$ and $\eta$ mesons. We calculate the azimuthal asymmetry of the decay photons for several azimuthally asymmetric pion distributions. We find that the $k_T$ dependence of the elliptic flow parameter$v_2$ for the decay photons closely follows the elliptic flow parameter $v_2^{\pi^0}$ evaluated at $p_T \approx k_T+\delta$, where $\delta\approx$ 0.1 -- 0.2 GeV, for typical pion distributions measured in nucleus-nucleus collisions at relativistic energies. Similar results are obtained for photons from the 2-$\gamma$ decay of $\eta$ mesons. Assuming that the flow of $\pi^0$ is similar to those for $\pi^+$ and $\pi^-$ for which independent measurements would be generally available, this ansatz can help in identifying additional sources for photons. Taken along with quark number scaling suggested by the recombination model, it may help to estimate $v_2$ of the parton distributions in terms of azimuthal asymmetry of the decay photons at large $k_T$.Comment: 6 pages, figures added, references added, with more elaborate discussion

Baryon Inhomogeneity Generation in the Quark-Gluon Plasma Phase

We discuss the possibility of generation of baryon inhomogeneities in a quark-gluon plasma phase due to moving Z(3) interfaces. By modeling the dependence of effective mass of the quarks on the Polyakov loop order parameter, we study the reflection of quarks from collapsing Z(3) interfaces and estimate resulting baryon inhomogeneities in the context of the early universe. We argue that in the context of certain low energy scale inflationary models, it is possible that large Z(3) walls arise at the end of the reheating stage. Collapse of such walls could lead to baryon inhomogeneities which may be separated by large distances near the QCD scale. Importantly, the generation of these inhomogeneities is insensitive to the order, or even the existence, of the quark-hadron phase transition. We also briefly discuss the possibility of formation of quark nuggets in this model, as well as baryon inhomogeneity generation in relativistic heavy-ion collisions.Comment: 11 pages, 2 figures, revtex4, more detailed discussion added about formation and evolution of Z(3)domain walls in the univers

Strings with a confining core in a Quark-Gluon Plasma

We consider the intersection of N different interfaces interpolating between different $Z_N$ vacua of an SU(N) gauge theory using the Polyakov loop order parameter. Topological arguments show that at such a string-like junction, the order parameter should vanish, implying that the core of this string (i.e. the junction region of all the interfaces) is in the confining phase. Using the effective potential for the Polyakov loop proposed by Pisarski for QCD, we use numerical minimization technique and estimate the energy per unit length of the core of this string to be about 2.7 GeV/fm at a temperature about twice the critical temperature. For the parameters used, the interface tension is obtained to be about 7 GeV/fm$^2$. Lattice simulation of pure gauge theories should be able to investigate properties of these strings. For QCD with quarks, it has been discussed in the literature that this $Z_N$ symmetry may still be meaningful, with quark contributions leading to explicit breaking of this $Z_N$ symmetry. With this interpretation, such {\it QGP} strings may play important role in the evolution of the quark-gluon plasma phase and in the dynamics of quark-hadron transition.Comment: 18 pages, 6 figures, RevTe

Excited hadrons as a signal for quark-gluon plasma formation

At the quark-hadron transition, when quarks get confined to hadrons, certain orbitally excited states, namely those which have excitation energies above the respective $L = 0$ states of the same order as the transition temperature $T_c$, may form easily because of thermal velocities of quarks at the transition temperature. We propose that the ratio of multiplicities of such excited states to the respective $L = 0$ states can serve as an almost model independent signal for the quark-gluon plasma formation in relativistic heavy-ion collisions. For example, the ratio $R^*$ of multiplicities of $D_{SJ}^{*\pm}(2317)(J^P = 0^+)$ and $D_S^{*\pm}(2112)(J^P = 1^-)$ when plotted with respect to the center of mass energy of the collision $\sqrt{s}$ (or vs. centrality/number of participants), should show a jump at the value of $\sqrt{s}$ beyond which the QGP formation occurs. This should happen irrespective of the shape of the overall plot of $R^*$ vs. $\sqrt{s}$. Recent data from RHIC on $\Lambda^*/\Lambda$ vs. N$_{part}$ for large values of N$_{part}$ may be indicative of such a behavior, though there are large error bars. We give a list of several other such candidate hadronic states.Comment: 19 pages, RevTex, no figures, minor change