Rho-omega mixing in asymmetric nuclear matter via QCD sum rule approach

We evaluate the operator product expansion (OPE) for a mixed correlator of the isovector and isoscalar vector currents in the background of the nucleon density with intrinsic isospin asymmetry [i.e. excess of neutrons over protons] and match it with its imaginary part, given by resonances and continuum, via the dispersion relation. The leading density-dependent contribution to $\rho-\omega$ mixing is due the scattering term, which turns out to be larger than any density dependent piece in the OPE. We estimate that the asymmetric density of $n_n-n_p \sim 2.5 \times 10^{-2} ~{\rm fm^3}$ induces the amplitude of $\rho-\omega$ mixing, equal in magnitude to the mixing amplitude in vacuum, with the constructive interference for positive and destructive for negative values of $n_n-n_p$. We revisit sum rules for vector meson masses at finite nucleon density to point out the numerical importance of the screening term in the isoscalar channel, which turns out to be one order of magnitude larger than any density-dependent condensates over the Borel window. This changes the conclusions about the density dependence of $m_\omega$, indicating $\sim 40$ MeV increase at nuclear saturation density.Comment: 8 pages, Revte

Aspects of meson properties in dense nuclear matter

We investigate the modification of meson spectral densities in dense nuclear matter at zero temperature. These effects are studied in a fully relativistic mean field model which goes beyond the linear density approximation and also includes baryon resonances. In particular, the role of N*(1520) and N*(1720) on the rho meson spectral density is highlighted. Even though the nucleon-nucleon loop and the nucleon-resonance loop contribute with the opposite sign, an overall reduction of rho meson mass is still observed at high density. Importantly, it is shown that the resonances cause substantial broadening of the rho meson spectral density in matter and also induces non-trivial momentum dependence. The spectral density of the a0 meson is also shown. We study the dispersion relations and collective oscillations induced by the rho meson propagation in nuclear matter together with the influence of the mixing of rho with the a0 meson. The relevant expression for the plasma frequency is also recovered analytically in the appropriate limit.Comment: 19 pages, 17 figure

Astrophysical S-factor of the 7^7Be(p,γ)8p,\gamma)^8B reaction from Coulomb dissociation of 8^8B

The Coulomb dissociation method to obtain the astrophysical S-factor, $S_{17}(0)$, for the $^7$Be($p,\gamma)^8$B reaction at solar energies is investigated by analysing the recently measured data on the breakup reaction $^{208}$Pb$(^8$B,$^7$Be$~p)^{208}$Pb at 46.5 MeV/A beam energy. Breakup cross sections corresponding to E1, $E2$ and $M1$ transitions are calculated with a theory of Coulomb excitation that includes the effects of the Coulomb recoil as well as relativistic retardation. The interplay of nuclear and Coulomb contributions to the breakup process is studied by performing a full quantum mechanical calculation within the framework of the distorted-wave Born Approximation. In the kinematical regime of the present experiment, both nuclear as well as Coulomb-nuclear interference processes affect the pure Coulomb breakup cross sections very marginally. The $E2$ cross sections are strongly dependent on the model used to describe the structure of $^8$B. The value of $S_{17}(0)$ is deduced with and without $E2$ and $M1$ contributions added to the $E1$ cross sections and the results are discussed.Comment: 10 pages, with 4 figures included with psfig; Physics Letters B, in pres

The effects of meson mixing on dilepton spectra

The effect of scalar and vector meson mixing on the dilepton radiation from hot and dense hadronic matter is estimated in different isospin channels. In particular, we study the effect of $\sigma$-$\omega$ and $\rho-a_0$ mixing and calculate the corresponding rates. Effects are found to be significant compared to standard $\pi$-$\pi$ and $K$-${\bar K}$ annihilations. While the mixing in the isoscalar channel mostly gives a contribution in the invariant mass range between the two-pion threshold and the $\omega$ peak, the isovector channel mixing induces an additional peak just below that of the $\phi$. Experimentally, the dilepton signals from $\rho$-$a_0$ mixing seem to be more tractable than those from $\sigma$-$\omega$ mixing.Comment: 10 pages, 9 figure

Dispersion relation of the ρ\rho meson in hot/dense nuclear matter

The dispersion relation of $\rho$ meson in both timelike and spacelike regimes in hot and dense nuclear medium is analyzed and compared with $\sigma$ meson based on the quantum hadrodynamics model. The pole and screening masses of $\rho$ and $\sigma$ are discussed. The behavior of screening mass of $\rho$ is different from that of $\sigma$ due to different Dirac- and Fermi-sea contributions at finite temperature and density.Comment: 4 pages, 3 figures, identical to published versio

Modifications to the pulsar kick velocity due to magnetic interactions in dense plasma

In this work we calculate pulsar kick velocity of magnetized neutronstar composed of degenerate quark matter core with non-Fermi liquid (NFL)correction. Both the leading order (LO) and next to leading order (NLO)corrections to the kick velocity have been incorporated. In addition, the NFLcorrections to the specific heat of magnetized quark matter have been presented.This has been taken into account to calculate the kick velocity of the neutronstar. Results show significant departure from the normal Fermi liquid estimates.The relation between radius and temperature has been shown with kick velocityof 100km/s with and without NFL corrections

The width of the omega meson in the nuclear medium

We evaluate the width of the omega meson in nuclear matter. We consider the free decay mode of the omega into three pions, which is dominated by rho IEuro decay, and replace the rho and pi propagators by their medium-modified ones. We also take into account the quasielastic and inelastic processes induced by a vector-baryon interaction dominated by vector meson exchange, as well as the contributions coming from the mechanism with medium-modified K , propagators. We obtain a substantial increase of the omega width in the medium, reaching a value of 121 +/- 10 MeV at normal nuclear matter density for an omega at rest, which comes mainly from omega N -> pi pi N, omega NN -> pi NN processes associated to the dominant omega -> rho IEuro decay mode. The value of the width increases moderately with momentum, reaching values of around 200MeV at 600MeV/c