Expanding Universe and Dynamical Compactification Using Yang-Mills Instantons

We consider an eight-dimensional Einstein-Yang-Mills theory to explore whether Yang-Mills instantons formed in extra dimensions can induce the dynamical instability of our four-dimensional spacetime. We show that the Yang-Mills instantons in extra dimensions can trigger the expansion of our universe in four-dimensional spacetime as well as the dynamical compactification of extra dimensions. We also discuss a possibility to realize a reheating mechanism via the quantum back-reaction from the contracting tiny internal space with a smeared instanton.Comment: v3; 26 pages, 6 figures, version to be published in JHE

Magnetic moments of the pentaquarks

We present in this talk a recent analysis for the magnetic moments of the baryon antidecuplet within the framework of the chiral quark-soliton model with linear $m_s$ corrections considered. We take into account the mixing of higher representations to the collective magnetic moment operator, which comes from the SU(3) symmetry breaking. Dynamical parameters of the model are fixed by experimental data for the magnetic moments of the baryon octet as well as by the masses of the octet, decuplet and of $\Theta^{+}$. The magnetic moment of $\Theta^{+}$ is rather sensitive to the pion-nucleon sigma term and ranges from $-1.19 {\rm n.m.}$ to $-0.33 {\rm n.m.}$ as the sigma term is varied from $\Sigma_{\pi N} = 45$ to 75 MeV, respectively. On top of them, we obtained that the strange magnetic moment of the nucleon has the value of $\mu^{(s)}_N =+0.39$ n.m. within this scheme and turns out to be almost independent of the sigma term.Comment: 7 pages, 1 figure, A talk given at International Workshop on PENTAQUARK04, SPring-8, Hyogo, Japan, 20-23 Jul 200

Strong decays of exotic and non-exotic heavy baryons in the chiral quark-soliton model

In the large $N_c$ limit both heavy and light baryons are described by the universal mean field, which allows us to relate the properties of heavy baryons to light ones. With the only input from the decays of light octet baryons (due to the universality of the chiral mean field), excellent description of strong decays of both charm and bottom sextets is obtained. The parameter-free prediction for the widths of exotic anti-decapentaplet ($\overline{\boldsymbol{15}}$) baryons is also made. The exotic heavy baryons should be anomalously narrow despite of large phase space available. In particular, the widths of $\Omega_c(3050)$ and $\Omega_c(3119)$, interpreted as members of $\overline{\boldsymbol{15}}$-plet, are very small: 0.48~MeV and 1.12~MeV respectivly. This result is in very good agreement with the measurements of the LHCb Collaboration and provides natural and parameter free explanation of the LHCb observation that $\Omega_c(3050)$ and $\Omega_c(3119)$ have anomalously small widths among five recently observed states.Comment: 13 pages, 3 figures. Discussion on large Nc limit of the decay couplings added. Acknowledgment added. Version to appear in Physics. Rev.