Philipp Gubler

Charmonium Spectra at Finite Temperature from QCD Sum Rules with the Maximum Entropy Method

Charmonia spectral functions at finite temperature are studied using QCD sum rules in combination with the maximum entropy method. This approach enables us to directly obtain the spectral function from the sum rules, without having to introduce any specific assumption about its functional form. As a result, it is found that while J/ψ and η(c) manifest themselves as significant peaks in the spectral function below the deconfinement temperature T(c), they quickly dissolve into the continuum and almost completely disappear at temperatures between 1.0T(c) and 1.1T(c).

A Bayesian Approach to QCD Sum Rules

QCD sum rules are analyzed with the help of the Maximum Entropy Method. We develop a new technique based on the Bayesion inference theory, which allows us to directly obtain the spectral function of a given correlator from the results of the operator product expansion given in the deep euclidean 4-momentum region. The most important advantage of this approach is that one does not have to make any a priori assumptions about the functional form of the spectral function, such as the “pole + continuum” ansatz that has been widely used in QCD sum rule studies, but only needs to specify the asymptotic values of the spectral function at high and low energies as an input. As a first test of the applicability of this method, we have analyzed the sum rules of the ρ-meson, a case where the sum rules are known to work well. Our results show a clear peak structure in the region of the experimental mass of the ρ-meson. We thus demonstrate that the Maximum Entropy Method is successfully applied and that it is an efficient tool in the analysis of QCD sum rules. Subject Index: 167

Thermal modification of bottomonium spectra from QCD sum rules with the maximum entropy method

Abstract The bottomonium spectral functions at finite temperature are analyzed by employing QCD sum rules with the maximum entropy method. This approach enables us to extract the spectral functions without any phenomenological parametrization, and thus to visualize deformation of the spectral functions due to temperature effects estimated from quenched lattice QCD data. As a result, it is found that ϒ and η b survive in hot matter of temperature up to at least 2.3 T c and 2.1 T c , respectively, while χ b 0 and χ b 1 will disappear at T 2.5 T c . Furthermore, a detailed analysis of the vector channel shows that the spectral function in the region of the lowest peak at T = 0 contains contributions from the excited states, ϒ ( 2 S ) and ϒ ( 3 S ) , as well as the ground states ϒ ( 1 S ) . Our results at finite T are consistent with the picture that the excited states of bottomonia dissociate at lower temperature than that of the ground state. Assuming this picture, we find that ϒ ( 2 S ) and ϒ ( 3 S ) disappear at T = 1.5 – 2.0 T c .

Constraining the strangeness content of the nucleon by measuring the ϕ meson mass shift in nuclear matter

The behavior of the

Dmeson mass increase by restoration of chiral symmetry in nuclear matter

\ensuremath{\phi}

D mesons in a magnetic field

meson at finite density is studied, making use of a QCD sum rule approach in combination with the maximum entropy method. It is demonstrated that a possible mass shift of the

Parity projection of QCD sum rules for the nucleon

\ensuremath{\phi}

Moments of ϕ meson spectral functions in vacuum and nuclear matter

in nuclear matter is strongly correlated to the strangeness content of the nucleon, which is proportional to the strange sigma term,

A Bayesian analysis of the nucleon QCD sum rules

{\ensuremath{\sigma}}_{sN}={m}_{s}⟨N|\overline{s}s|N⟩

Mass of heavy-light mesons in a constituent quark picture with partially restored chiral symmetry

. Our results furthermore show that, depending on the value of