Recent studies show that for central collisions the rising of the incident energy from AGS to RHIC decreases the value of the chemical potential in the Hadron-QGP phase diagram. Thus, the formation of QGP at RHIC energies in central collisions may be expected to occur at very small values of the chemical potential. Using many different relativistic mean-field hadronic models (RMF) at this regime we show that the critical temperature for the Hadron-QGP transition is hadronic model independent. We have traced back the reason for this and conclude that it comes from the fact that the QGP entropy is much larger than the hadronic entropy obtained in all the RMF models. We also find that almost all of these models present a strong entropy enhancement in the hadronic sector coming from the baryonic phase transition to a nucleon-antinucleon plasma. This result is in agreement with the recent data obtained in the STAR collaboration at RHIC where it was found a rich proton-antiproton matter.

We study the two point-function for the scalar mesons σ, κ, f0(980) and a0(980) as diquakantidiquark states. We also study the decays of these mesons into ππ, Kπ and KK. We found that the couplings are consistent with existing experimental data, pointing in favor of the four-quark structure for the light scalar mesons.PACS numbers: 11.55. Hx, 12.38.Lg , It is known that the identification of scalar mesons is difficult experimentally, and that the underlying structure of them is not well stablished theoretically, due to the complications of the nonperturbative strong interactions. Actually, the observed light scalar states below 1.5 GeV are too numerous [1] to be accommodated in a single qq multiplet.The experimental proliferation of light scalar mesons is consistent with two nonets, one below 1 GeV region and another one near 1.5 GeV. If the light scalars (the isoscalars σ(500), f 0 (980), the isodoublet κ and the isovector a 0 (980)) form an SU(3) flavor nonet, in the naive quark model the flavor structure of these scalars would be:Although with this model it is difficult to understand the mass degeneracy of f 0 (980) and a 0 (980), and it is hard to explain why σ and κ are broader than f 0 (980) and a 0 (980), its use is not yet discarded [2,3,4,5,6]. Some alternative models allow a mixing between the isoscalars. However, different experimental data lead to different mixing angle [7,8,9]. By the other hand, the scalar mesons in the 1.3 − 1.7 GeV mass region (the isoscalars f 0 (1370)), f 0 (1500), the isodoublet K * 0 (1430) and the isovector a 0 (1450)) may be easily accommodated in an SU(3) flavor nonet. Therefore, theory and data are now converging that QCD forces are at work but with different dynamics dominating below and above 1 GeV mass. Below 1 GeV the phenomena point clearly towards an S−wave attraction among two quarks and two anti-quarks, while above 1 GeV it is the P −wave qq that is manifested. [10].Below 1 GeV the inverted structure of the four-quark dynamics in S-wave is revealed with f 0 (980), a 0 (980), κ and σ symbolically given by [11] This is supported by a recent lattice calculation [12]. In this four-quark scenario for the light scalars, the mass degeneracy of f 0 (980) and a 0 (980) is natural, and the mass hierarchy pattern of the nonet is understandable. Besides, it is easy to explain why σ and κ are broader than f 0 and a 0 . The decays σ → ππ, κ → Kπ and f 0 , a 0 → KK are OZI superallowed without the need of any gluon exchange, while f 0 → ππ and a 0 → ηπ are OZI allowed as it is mediated by one gluon exchange. Since f 0 (980) and a 0 (980) are very close to theKK threshold, the f 0 (980) is dominated by the ππ state and a 0 (980) is governed by the ηπ state. Consequently, their widths are narrower than σ and κ.In the four-quark scenario it is also easier to understand why, in some three-body decays of charmed mesons, the intermediate light scalar meson accounts for the main contribution to the total decay rate.

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The D * Dπ form factor is evaluated in a QCD sum rule calculation for both D and π off-shell mesons. We study the Borel sum rule for the three point function of one pseudoscalar, one axial and one vector meson currents. We find that the momentum dependence of the form factors is very different if the D or the π meson is off-shell, but they lead to the same coupling constant in the D * Dπ vertex. PACS numbers 14.40.Lb, 14.40.Nd, 12.38.Lg, 11.55.Hx In a very recent measurement by the CLEO collaboration [1], the total width of D * meson was obtained: Γ tot (D * ) = 96 ± 4 ± 22 keV. This measurement yields the strong D * Dπ coupling, g D * Dπ = 17.9 ± 0.3 ± 1.9, which is defined as [2]

We review the calculations of form factors and coupling constants in vertices with charm mesons in the framework of QCD sum rules. We first discuss the motivation for this work, describing possible applications of these form factors to heavy ion collisions and to B decays. We then present an introduction to the method of QCD sum rules and describe how to work with the three-point function. We give special attention to the procedure employed to extrapolate results obtained in the deep euclidean region to the poles of the particles, located in the time-like region. We present a table of ready-to-use parametrizations of all the form factors, which are relevant for the processes mentioned in the introduction. We discuss the uncertainties in our results. We also give the coupling constants and compare them with estimates obtained with other methods. Finally we apply our results to the calculation of the cross section of the reaction $J/\psi + \pi \rightarrow D + \bar{D^*}$.Comment: 43 pages, 26 figures, 10 table

We suggest that the recently observed charmed scalar mesons D Due to its low mass, the structure of the meson D + sJ (2317) has been extensively debated. It has been interpreted as a cs state [8,9,10,11,12], two-meson molecular state [13,14], D − K-mixing [15], four-quark states [16,17,18] or a mixture between two-meson and four-quark states [19]. The same analyses would also apply to the meson D 0 0 (2308). In the light sector the idea that the scalar mesons could be four-quark bound states is not new [20] and, therefore, it is natural to consider analogous states in the charm sector.We propose that the resonances observed by BELLE [6] and FOCUS [7] Collaborations be considered as two different resonances. In this work we use the method of QCD sum rules (QCDSR) [21] to study the two-point functions of the scalar mesons, D sJ (2317), D 0 (2308) and D 0 (2405) considered as four-quark states. The use of the QCD sum rules to study the charmed scalar mesons was already done in refs. [8,11,12], but in these calculations they were interpreted as two-quark states.In a recent calculation [22] some of us have considered that the lowest lying scalar mesons are S-wave bound states of a diquark-antidiquark pair. As suggested in ref.[23] the diquark was taken to be a spin zero colour anti-triplet. We extend this prescription to the charm sector and, therefore, the corresponding interpolating fields containing zero, one and two strange quarks are:where a, b, c, ... are colour indices, C is the charge conjugation matrix and q represents the quark u or d according to the charge of the meson. Since D sJ has ones quark, we choose the j s current to have the same quantum numbers of D sJ , which is supposed to be an isoscalar. However, since we are working in the SU(2) limit, the isoscalar and isovector states are mass degenerate and, therefore, this particular choice has no relevance here. The QCDSR for the charmed scalar mesons are constructed from the two-point correlation functionThe coupling of the scalar meson, S, to the scalar current, j S , can be parametrized in terms of the meson decay constant f S as [22]: 0|j S |S = √ 2f S m 4 S , therefore, the phenomenological side of Eq. (2) can be written aswhere the dots denote higher resonance contributions that will be parametrized, as usual, through the introduction of the continuum threshold parameter s 0 [24].In the OPE side we work at leading order and consider condensates up to dimension six. We deal with the strange quark as a light one and consider the diagrams up to order m s . To keep the charm quark mass finite, we use the momentum-space expression for the charm quark propagator. We follow ref. [25] and calculate the light

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