Rho Meson Broadening in Hot and Dense Hadronic Matter

In this write-up we summarize main result of our recent analysis on the mixing between transverse $\rho$ and $a_1$ mesons through a set of $\omega\rho a_1$-type interactions in dense baryonic matter. In the analysis, we showed that a clear enhancement of the vector spectral function appears below $\sqrt{s}=m_\rho$ for small three-momenta of the $\rho$ meson, and thus the vector spectrum exhibits broadening.

A detailed study of the analytic structure of 1-loop self energy graphs for neutral and charged $\rho$ mesons is presented at finite temperature and arbitrary magnetic field using the real time formalism of thermal field theory. The imaginary part of the self energy is obtained from the discontinuities of these graphs across the Unitary and Landau cuts, which is seen to be different for $\rho^0$ and $\rho^\pm$. The magnetic field dependent vacuum contribution to the real part...

We study the behavior of the rho vector mass in the context of the almost baryon-free environment of an ultra-relativistic heavy-ion collision. We show that rho scattering within the hadronic phase of the collision leads to a temperature dependent, decrease of its intrinsic mass at rest, compared to the value in vacuum. The main contributions arise from s-channel scattering with pions through the formation of a1 resonances as well as with nucleons through the formation of eve...

We explore the range of values of the in-medium width of a $\rho$-meson at rest which is compatibale with the QCD sum rule approach in a nuclear medium assuming vector meson dominance and a Brown-Rho scaling law of the $\rho$-meson mass with the chiral condensate. The lower and upper bounds for the in-medium width are found to be strongly increasing with the decreasing mass of the $\rho$-meson (increasing nuclear density). We also study the bounds for the in-medium width in m...

Vector Meson Dominance ideas together with a Finite Energy QCD sum rule allows for the determination of the $q^{2}$- and the $T$- dependence of the effective hadronic coupling constant $g_{\rho \pi \pi}$ in the space-like region. It turns out that $g_{\rho \pi \pi}(q^{2},T)$ vanishes at the critical temperature $T_{c}$, independently of $q^{2}$. A comparison with a previous independent QCD determination of the electromagnetic pion form factor at finite temperature supports th...

Recent developments on medium modifications of hadron properties in dense and hot hadronic matter are discussed. I will focus in particular on the behavior of spectral functions associated to collective scalar-isoscalar modes, kaons and vector mesons from ordinary nuclear matter to highly excited matter produced in relativistic heavy-ion collisions from SIS to SPS energies. Various theoretical approaches are presented in connection with the interpretation of experimental data...

We discuss medium modification of the rho meson originating from its coupling to in medium quasi-pions and delta-hole states. This medium effect leads to a marked structure of the rho meson strength function in the $500 MeV$ invariant mass region. We suggest that this effect may provide an explanation of the structure observed by the DLS collaboration in the $Ca+Ca/C+C$ ratio at $1 GeV/u$.

The couplings and decay widths of the proceses (1^+,2^+)->(0^-,1^-)+rho are studied with ligh-cone QCD sum rules in the leading order of heavy quark effective theory. These processes are employed to estimate the two pion transition widths of the (1^+,2^+) doublet through the low mass tail of the rho resonance. Our calculation shows that the two pion decay widths are much smaller than the single pion decay widths. However, B_1 and B_2^* mesons should also have significant two ...

We present an alternative method for calculating amplitudes for correlated pi pi exchange in the ``sigma'' and rho channel in piN scattering. Starting from a fixed mass meson exchange potential, we introduce the width of the exchanged particles by integrating over a mass spectral function. The spectral functions are constructed from the pseudoempirical N\bar{N} -> pi pi data. Using this approach we develop a prescription for resolving ambiguities of the correlated pi pi excha...

There is currently enormous interest in the investigation of how hadron properties may be altered by immersion in matter. There is strong evidence of a reduction in the mass of the rho meson from relativistic heavy ion collisions as well as a hint from a recent experiment on photoproduction in light nuclei. We briefly review the main theoretical ideas which lead one to expect the mass of a hadron to change in matter, including the various QCD-based methods, notably the QCD su...