Examination of the H dibaryon within a chiral constituent quark model

We perform a coupled--channel calculation of the H dibaryon within a chiral constituent quark model. The problem is solved within a quark model constrained by the experimental data of strangeness --1 and --2 two--baryon systems. We examine in detail the role played by the different contributions of the interacting potential as well as the number of coupled channels considered. Special attention has been payed to the parameter dependence, flavor symmetry breaking and spatial configurations. The value extracted for the binding energy of the H dibaryon, being compatible with the restrictions imposed by the Nagara event, falls within a plausible extrapolation of recent lattice QCD results.Comment: 14 pages, 13 figure

Charmonium spectroscopy above thresholds

We present a systematic and selfconsistent analysis of four-quark charmonium states and applied it to study compact four-quark systems and meson-meson molecules. Our results are robust and should serve to clarify the situation of charmonium spectroscopy above the threshold production of charmed mesons.Comment: 4 pages, 2 figure

NDˉN\bar D system: A challenge for Pˉ\bar {\rm P}ANDA

We study the $N \bar D$ system by means of a chiral constituent quark model. This model, tuned in the description of the baryon and meson spectra as well as the $NN$ interaction, provides parameter-free predictions for the charm -1 two-hadron systems. The presence of a heavy antiquark makes the interaction rather simple. We have found sharp quark-Pauli effects in some particular channels, generating repulsion, due to lacking degrees of freedom to accommodate the light quarks. Our results point to the existence of an attractive state, the $\Delta \bar D^*$ with $(T,S)=(1,5/2)$, presenting a resonance close to threshold. It would show up in the scattering of $\bar D$ mesons on nucleons as a D wave state with quantum numbers $(T)J^P=(1)5/2^-$. This resonance resembles our findings in the $\Delta\Delta$ system, that offered a plausible explanation to the cross section of double-pionic fusion reactions through the so-called {\it ABC} effect. The study of the interaction of $D$ mesons with nucleons is a goal of the $\bar {\rm P}$ANDA Collaboration at the European facility FAIR and, thus, the present theoretical study is a challenge to be tested at the future experiments.Comment: 16 pages, 15 figures, accepted for publication in Phys. Rev.

Solutions for f(R) gravity coupled with electromagnetic field

In the presence of external, linear / nonlinear electromagnetic fields we integrate f(R) \sim R+2{\alpha}\surd(R+const.) gravity equations. In contrast to their Einsteinian cousins the obtained black holes are non-asymptotically flat with a deficit angle. In proper limits we obtain from our general solution the global monopole solution in f(R) gravity. The scale symmetry breaking term adopted as the nonlinear electromagnetic source adjusts the sign of the mass of the resulting black hole to be physical.Comment: 7 pages no figure, final version for publication in European Physical Journal

The molecular systems composed of the charmed mesons in the HSˉ+h.c.H\bar{S}+h.c. doublet

We study the possible heavy molecular states composed of a pair of charm mesons in the H and S doublets. Since the P-wave charm-strange mesons $D_{s0}(2317)$ and $D_{s1}(2460)$ are extremely narrow, the future experimental observation of the possible heavy molecular states composed of $D_s/D_s^\ast$ and $D_{s0}(2317)/D_{s1}(2460)$ may be feasible if they really exist. Especially the possible $J^{PC}=1^{--}$ states may be searched for via the initial state radiation technique.Comment: 42 pages, 4 tables, 31 figures. Improved numerical results and Corrected typos

Black hole solutions in F(R) gravity with conformal anomaly

In this paper, we consider $F(R)=R+f(R)$ theory instead of Einstein gravity with conformal anomaly and look for its analytical solutions. Depending on the free parameters, one may obtain both uncharged and charged solutions for some classes of $F(R)$ models. Calculation of Kretschmann scalar shows that there is a singularity located at $r=0$, which the geometry of uncharged (charged) solution is corresponding to the Schwarzschild (Reissner-Nordstr\"om) singularity. Further, we discuss the viability of our models in details. We show that these models can be stable depending on their parameters and in different epoches of the universe.Comment: 12 pages, one figur