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Register a new userRho-meson properties in medium
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Joao Pacheco B. C. de Melo Dr.
Publication date
2018
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and research's language is
English
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Properties of $rho$-meson in symmetric nuclear matter are investigated in a light-front constituent quark model (LFCQM), using the in-medium inputs calculated by the quark-meson coupling (QMC) model. The LFCQM used in this study was already applied for the studies of the electromagnetic properties of $rho$-meson in vacuum, namely, the charge~$G_0$, magnetic~$G_1$, and quadrupole~$G_2$ form factors, electromagnetic charge radius, and electromagnetic decay constant. We predict that the electromagnetic decay constant, charge radius, and quadrupole moment are enhanced as increasing the nuclear matter density, while the magnetic moment is slightly quenched. Furthermore, we predict that the value $Q^2_{rm zero}$, which crosses zero of the charge form factor, $G_0(Q^2_{rm zero})=0$ ($Q^2 = -q^2 > 0$ with $q$ being the four-momentum transfer), decreases as increasing the nuclear matter density.
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Properties of r{ho}-meson in symmetric nuclear matter are investigated within a light-front constituent quark model (LFCQM), using the in-medium input calculated by the quark-meson coupling (QMC) model. The LFCQM used here was previously applied in vacuum to calculate the r{ho}-meson electromagnetic properties, namely, charge G 0 , magnetic G 1 , and quadrupole G 2 form factors, as well as the electromagnetic radius and decay constant. We predict the in-medium modifications of the r{ho}-meson electromagnetic form factors in symmetric nuclear matter.
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 of the self energy, which is usually ignored, is found to be appreciable. A significant effect of temperature and magnetic field is seen in the self energy, spectral function, effective mass and dispersion relation of $rho^0$ as well as of $rho^pm$ relative to its trivial Landau shift. However, for charged $rho$ mesons, on account of the dominance of the Landau term, the effective mass appears to be independent of temperature. The trivial coupling of magnetic moment of $rho^pm$ with external magnetic field, when incorporated in the calculation, makes the $rho^pm$ to condense at high magnetic field.
The one loop self energy of the neutral $rho$ meson is obtained for the effective $rhopipi$ and $rho NN$ interaction at finite temperature and density in the presence of a constant background magnetic field of arbitrary strength. In our approach, the eB-dependent vacuum part of the self energy is extracted by means of dimensional regularization where the ultraviolet divergences corresponding to the pure vacuum self energy manifest as the pole singularities of gamma as well as Hurwitz zeta functions. This improved regularization procedure consistently reproduces the expected results in the vanishing magnetic field limit and can be used quite generally in other self energy calculations dealing with arbitrary magnetic field strength. In presence of the external magnetic field, the general Lorentz structure for the in-medium vector boson self energy is derived which can also be implemented in case of the gauge bosons such as photons and gluons. It has been shown that with vanishing perpendicular momentum of the external particle, essentially two form factors are sufficient to describe the self energy completely. Consequently, two distinct modes are observed in the study of the effective mass, dispersion relations and the spectral function of $rho^0$ where one of the modes possesses two fold degeneracy. For large baryonic chemical potential, it is observed that the critical magnetic field required to block the $rho^0rightarrowpi^+pi^-$ decay channel increases significantly with temperature. However, in case of smaller values reaching down to vanishing chemical potential, the critical field follows the opposite trend.
We present a calculation of the electromagnetic form factors of the $rho^+$ meson. Our formalism is based on the point-form of relativistic quantum mechanics. Electron-$rho$-meson scattering is formulated as a coupled-channel problem for a Bakamjian-Thomas mass operator, such that the dynamics of the exchanged photon is taken explicitly into account. The $rho$-meson current is extracted from on-shell matrix elements of the optical potential of the scattering process. As a consequence of the violation of cluster separability in the Bakamjian-Thomas framework, our current includes additional, unphysical contributions, which can be separated from the physical ones uniquely. Our results for the form factors are in good agreement with other approaches.
In-medium properties of the low-lying baryons are studied in the quark-meson coupling (QMC) model, focusing on the $Sigma_b$ and $Xi_b$ baryons. It is predicted that the Lorentz-scalar effective mass of $Sigma_b$ becomes smaller than that of $Xi_b$ at moderate nuclear matter density, and as the density increases, namely, $m^*_{Sigma_b} < m^*_{Xi_b}$, although in vacuum $m_{Sigma_b} > m_{Xi_b}$. We also study the effects of the repulsive Lorentz-vector potentials on the excitation energies of these bottom baryons.
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