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We consider the Higgs potential in generalizations of the Standard Model. The possibility of the potential to develop two almost degenerate minima is explored. This would imply that QCD matter at two distinct sets of quark masses is relevant for astrophysics and cosmology. If in the exotic minimum the QCD matter ground state is electromagnetically neutral, dark matter may consist of QCD matter and antimatter in bubbles of the Higgs field. We predict an abundance of gamma rays in the few MeV region as messengers of dark matter regions in space. In addition the ratio of dark matter to normal matter is expected to show a time dependence., 8 pages, five figures, published version

We consider the chiral Lagrangian with nucleon, isobar, and pion degrees of freedom. The baryon masses and the axial-vector form factor of the nucleon are derived at the one-loop level. We explore the impact of using on-shell baryon masses in the loop expressions. As compared to results from conventional chiral perturbation theory we find significant differences. An application to QCD lattice data is presented. We perform a global fit to the available lattice data sets for the baryon masses and the nucleon axial-vector form factor, and determine the low-energy constants relevant at N$^3$LO for the baryon masses and at N$^2$LO for the form factor. Partial finite-volume effects are considered. We point out that the use of on-shell masses in the loops results in non-analytic behavior of the baryon masses and the form factor as function of the pion mass, which becomes prominent for larger lattice volumes than presently used., 39 pages, 9 figures

We consider the quark-mass dependence of the baryon octet and decuplet ground state masses. It is predicted that QCD dynamics implies a first order transition when increasing the strange quark mass from its chiral limit towards its physical value. Our claim relies on a global fit to the available QCD lattice data on such baryon masses. Quantitative results based on an application of the chiral SU(3) Lagrangian at N$^3$LO are discussed. We predict an anomalous sector of QCD where stable baryonic matter would be composed of lambda or anti-lambda particles rather than nucleons and anti-nucleons., slight revision of 4 pages, two updated figures

We explore a general framework how to treat coupled-channel systems in the presence of overlapping left and right-hand cuts as well as anomalous thresholds. Such systems are studied in terms of a generalized potential, where we exploit the known analytic structure of t- and u-channel forces as the exchange masses get smaller approaching their physical values. Given an approximate generalized potential the coupled-channel reaction amplitudes are defined in terms of non-linear systems of integral equations. For large exchange masses, where there are no anomalous thresholds present, conventional $N/D$ methods are applicable to derive numerical solutions to the latter. At a formal level a generalization to the anomalous case is readily formulated by use of suitable contour integrations with amplitudes to be evaluated at complex energies. However, it is a considerable challenge to find numerical solutions to anomalous systems set up on a set of complex contours. By a suitable deformations of left-hand and right-hand cut lines we managed to establish a framework of linear integral equations defined for real energies. Explicit expressions are derived for the driving terms that hold for an arbitrary number of channels. Our approach is illustrated in terms of a schematic 3-channel systems. It is demonstrated that despite the presence of anomalous thresholds the scattering amplitude can be represented in terms of 3 phase shifts and 3 in-elasticity parameters, as one would expect from the coupled-channel unitarity condition., 49 pages, 17 figures, major revision of the published version, the updated framework is applicable also in the presence of overlapping anomalous cut structures

It is argued that the chiral partners of the lowest-lying hadrons are hadronic molecules and not three-quark or quark-antiquark states, respectively. As an example the case of a_1 as the chiral partner of the rho is discussed. Deconfinement -- or as a precursor large in-medium widths for hadronic states -- is proposed as a natural way to accommodate for the fact that at chiral restoration the respective in-medium spectra of chiral partners must become degenerate. Ingredients for a systematic and self-consistent in-medium calculation are presented with special emphasis on vector-meson dominance which emerges from a recently proposed systematic counting scheme for the mesonic sector including pseudoscalar and vector mesons as active degrees of freedom., Comment: revised version: more references added

The decays of light vector mesons into three pseudoscalar mesons are calculated to leading order in the recently proposed counting scheme that is based on the hadrogenesis conjecture. Fully differential as well as integrated decay widths are presented. Since the required parameters have been fixed by other processes, the considered three-body decays are predictions of the presented approach. The decay width of the omega meson into three pions agrees very well with experiment. The partial decay widths of the K^* into its three K-pi-pi channels are predicted., Comment: 7 pages

Analyzing final state interactions in scattering processes in the non-perturbative regime of quantum chromodynamics (QCD), such as the hadron resonance region, is difficult. Using the analytic structure of partial-wave amplitudes derived from u- and t-channel exchange diagrams in $2-g2$ scattering, the authors put forward a systematic procedure for understanding the final state interactions in hadron processes.

We study the spectral distributions of charmed meson with $J^P=0^-$ quantum numbers in cold nuclear matter applying a self-consistent and covariant many-body approach established previously for the nuclear dynamics of kaons. At leading orders the computation requires as input the free-space two-body scattering amplitudes only. Our results are based on the s-wave meson-nucleon amplitudes obtained recently in terms of a coupled-channel approach. The amplitudes are characterized by the presence of many resonances in part so far not observed. This gives rise to an intriguing dynamics of charmed mesons in nuclear matter. At nuclear saturation density we predict a pronounced two-mode structure of the $D^+$ mesons with a main branch pushed up by about 32 MeV. The lower branch reflects the coupling to two resonance-hole states that are almost degenerate. For the $D^-$ we obtain a single mode pushed up by about 18 MeV relative to the vacuum mode. Most spectacular are the results for the $D^+_s$ meson. The presence of an exotic resonance-hole state gives rise to a rather broad and strongly momentum dependent spectral distribution., 11 pages, 3 figures

We present results of a self-consistent calculation for the kaon and antikaon spectral functions in cold nuclear matter, using as input the kaon-nucleon and antikaon-nucleon scattering amplitudes of the vacuum. We investigate the effect of in-medium pion dressing on the antikaon-nucleon scattering amplitudes and antikaon spectral function. We find the influence of pion dressing to be minor on the antikaon spectral function and limited on the hyperon resonances causing only a small additional broadening. An exception is the \Sigma(1690). At nuclear saturation density an attractive mass shift of about 20 MeV and width of about 130 MeV is obtained. The kaon shows a repulsive mass increase of 36 MeV and a small width of the quasiparticle peak at saturation density., Comment: 8 pages, 4 figures, submitted to Heavy Ion Physics

We review the important role played by the chiral SU(3) symmetry in predicting the properties of antikaons and hyperon resonances in cold nuclear matter. Objects of crucial importance are the meson-baryon scattering amplitudes obtained within the chiral coupled-channel effective field theory. The formation of baryon resonances as implied by chiral coupled-channel dynamics is discussed. Results for antikaon and hyperon-resonance spectral functions are presented for isospin symmetric and asymmetric matter., invited talk presented by M.F.M.L. at the 18th Nishinomiya Yukawa Memorial Symposium, 21 pages, 12 figures

We evaluate the antikaon spectral density in isospin symmetric nuclear matter. The in-medium antikaon-nucleon scattering process and the antikaon propagation is treated in a self consistent and relativistic manner where a maximally scheme-independent formulation is derived by performing a partial density resummation in terms of the free-space antikaon-nucleon scattering amplitudes. The latter amplitudes are taken from a covariant and chiral coupled-channel SU(3) approach which includes s-, p- and d-waves systematically. Particular care is taken on the proper evaluation of the in-medium mixing of the partial waves. Our analysis establishes a rich structure of the antikaon spectral function with considerable strength at small energies. At nuclear saturation density we predict attractive mass shifts for the $\Lambda(1405)$, $\Sigma (1385)$ and $\Lambda(1520)$ of about 60 MeV, 60 MeV and 100 MeV respectively. The hyperon states are found to exhibit at the same time an increased decay width of about 120 MeV for the s-wave $\Lambda(1405)$, 70 MeV for the p-wave $\Sigma (1385)$ and 90 MeV for the d-wave $\Lambda(1520)$ resonance., Comment: 24 pages, 3 figures, corrected manuscript

We give a review of recent progress on the application of the relativistic chiral SU(3) Lagrangian to meson–baryon scattering. It is shown that a combined chiral and 1/Nc expansion of the Bethe–Salpeter interaction kernel leads to a good description of the kaon–nucleon, antikaon–nucleon and pion–nucleon scattering data typically up to laboratory momenta of p lab ≃500 MeV. We solve the covariant coupled channel Bethe–Salpeter equation with the interaction kernel truncated to chiral order Q 3 where we include only those terms which are leading in the large Nc limit of QCD.

A theoretical study of Goldstone boson scattering based on the chiral Lagrangian with vector meson fields is presented. In application of a recently developed novel approach we extrapolate subthreshold partial-wave amplitudes into the physical region. The constraints set by micro-causality and coupled-channel unitarity are kept rigourously. It is shown that already the leading order subthreshold amplitudes lead to s- and p-wave $\pi\pi$ and $\pi K$ phase shifts are in agreement with the experimental data up to about 1.2 GeV.

We consider the chiral Lagrangian with a nonet of Goldstone bosons and a nonet of light vector mesons. The mixing between the pseudoscalar mesons eta and eta-prime is taken into account. A novel counting scheme is suggested that is based on hadrogenesis, which conjectures a mass gap in the meson spectrum of QCD in the limit of a large number of colors. Such a mass gap would justify to consider the vector mesons and the eta-prime meson as light degrees of freedom. The complete leading order Lagrangian is constructed and discussed. As a first application it is tested against electromagnetic transitions of light vector mesons to pseudoscalar mesons. Our parameters are determined by the experimental data on photon decays of the omega, phi and eta-prime meson. In terms of such parameters we predict the corresponding decays into virtual photons with either dielectrons or dimuons in the final state., Comment: 17 pages, extended discussion on mixing

We study the reactions $\gamma\gamma\rightarrow \pi^0\pi^0$, $\pi^+\pi^-$, $K^0\bar{K}^0$, $K^+K^-$, $\eta \eta$ and $\pi^0\eta$ based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains 5 unknown parameters that are relevant for the photon fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon fusion data $\gamma\gamma\rightarrow \pi^0\pi^0$, $\pi^+\pi^-, \pi^0\eta$ and to the decay $\eta\rightarrow\pi^0\gamma\gamma$. In order to derive gauge invariant reaction amplitudes in the resonance region constraints from micro-causality and exact coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The $a_0$ meson in the $\pi^0\eta$ channel is dynamically generated and an accurate reproduction of the $\gamma\gamma\rightarrow \pi^0\eta$ data is achieved up to 1.2 GeV. Based on our parameter sets we predict the $\gamma\gamma\rightarrow $ $K^0\bar{K}^0$, $K^+K^-$, $\eta \eta$ cross sections., Comment: 17 pages, 10 figures, all assumptions used in our method are clarified

In our recent analysis of lattice data of the BMW, LHPC and PACS-CS groups we determined a parameter set of the chiral Lagrangian that allows a simultaneous description of the baryon octet and decuplet masses as measured by those lattice groups. The results on the baryon spectrum of the HSC group were recovered accurately without their inclusion into our 6 parameter fit. We show that the same parameter set provides an accurate reproduction of the recent results of the QCDSF-UKQCD group probing the baryon masses at quite different quark masses. This shows a remarkable consistency amongst the different lattice simulations. With even more accurate lattice data in the near future it will become feasible to determine all low-energy parameters relevant at N$^3$LO., 7 pages, 2 figures

Baryon masses of the flavour SU(3) octet and decuplet baryons are calculated in the framework of the Chiral Perturbations Theory - the effective field theory of the strong interaction. The chiral extrapolation to the higher meson (quark) masses is carried out. The comparison with the recent results on the baryon masses from lattice calculations are presented.

We consider the scattering of fermions off antifermions with spin 1/2 and 3/2. Starting from helicity partial-wave scattering amplitudes we derive transformations that eliminate all kinematical constraints. Such amplitudes are expected to satisfy partial-wave dispersion relations and therefore provide a suitable basis for data analysis and the construction of effective field theories. Our derivation relies on a decomposition of the various scattering amplitudes into suitable sets of invariant functions., 12 pages, 3 tables

The chiral $SU(3)$ Lagrangian with pseudoscalar and vector $D$ mesons and with the octet and decuplet baryons is considered. The leading two-body counter terms involving two baryon fields and two $D$ meson fields are constructed in the open-charm sector. There are 26 terms. A combined expansion in the inverse of the charm quark mass and in the inverse of the number of colors provides sum rules that reduce the number of free parameters down to 5 only. Our result shows the feasibility of a systematic computation of the open-charm baryon spectrum based on coupled-channel dynamics.

We consider the scattering of two-bosons with negative parity and spin 0 or 1. Starting from helicity partial-wave scattering amplitudes we derive transformations that eliminate all kinematical constraints. Such amplitudes are expected to satisfy partial-wave dispersion relations and therefore provide a suitable basis for data analysis and the construction of effective field theories. Our derivation relies on a decomposition of the various scattering amplitudes into suitable sets of invariant functions. A novel algebra was developed that permits the efficient computation of such functions in terms of computer algebra codes., 14 pages, 8 tables

Proton Compton scattering is analyzed with the chiral Lagrangian. Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes computed in chiral perturbation theory, where the constraints set by electromagnetic-gauge invariance, causality and unitarity are used to stabilize the extrapolation. We present and discuss predictions for various spin observables and polarizabilties of the proton. While for the transition polarizabilities $\gamma_{E1M2}, \gamma_{M1E2}$ we recover the results of strict chiral perturbation theory, for the diagonal $\gamma_{E1E1}, \gamma_{M1M1}$ elements we find significant effects from rescattering., Comment: 18 pages, 3 figures, revised version

The chiral SU(3) Lagrangian with the baryon octet and decuplet fields is considered. The Q^2 counterterms involving the decuplet fields are constructed. We derive the correlation of the chiral parameters implied by the 1/N_c expansion at leading order in QCD., 20 pages, 3 figures

Pion-nucleon scattering, pion photoproduction, and nucleon Compton scattering are analyzed within a scheme based on the chiral Lagrangian. Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes computed in chiral perturbation theory, where the constraints set by electromagnetic-gauge invariance, causality and unitarity are used to stabilize the extrapolation. Experimental data are reproduced up to energies $\sqrt{s}\simeq 1300$ MeV in terms of the parameters relevant at order $Q^3$. A striking puzzle caused by an old photon asymmetry measurement close to the pion production threshold is discussed., Invited plenary talk at Chiral 10 Workshop, Valencia (Spain), June 21-24, 2010

We report on a novel scheme based on the chiral Lagrangian. It is used to analyze pion-nucleon scattering, pion photoproduction, and nucleon Compton scattering. Subthreshold partial-wave amplitudes are calculated in chiral perturbation theory and analytically extrapolated with constraints imposed by electromagnetic-gauge invariance, causality and unitarity. Experimental quantities are reproduced up to energies $\sqrt{s}\simeq 1300$ MeV in terms of the parameters relevant at order $Q^3$., Comment: 4 pages, contribution to the proceedings of the MENU 2010 conference, May 31-June 4, 2010, Williamsburg VA, USA

We study photoproduction off nuclei based on a self consistent and covariant many body approach for the pion and isobar propagation in infinite nuclear matter. For the first time the t-channel exchange of an in-medium pion is evaluated in the presence of vertex correction effects consistently. In particular the interference pattern with the s-channel in-medium nucleon and isobar exchange contribution is considered. Electromagnetic gauge invariance is kept as a consequence of various Ward identities obeyed by the computation. Adjusting the set of Migdal parameters to the data set we predict an attractive mass shift for the isobar of about 50 MeV at nuclear saturation density., Comment: 10 pages, 6 figures

To study fundamental questions of hadron and nuclear physics in interactions of antiprotons with nucleons and nuclei, the universal PANDA detector will be built. Gluonic excitations, the physics of strange and charm quarks and nucleon structure studies will be performed with unprecedented accuracy thereby allowing high-precision tests of the strong interaction. The proposed PANDA detector is a state-of-the art internal target detector at the HESR at FAIR allowing the detection and identification of neutral and charged particles generated within the relevant angular and energy range. This report presents a summary of the physics accessible at PANDA and what performance can be expected.

A scheme based on the chiral Lagrangian, analyticity and unitarity is applied to spin observables in pion photoproduction and nucleon Compton scattering. Subthreshold partial-wave amplitudes are calculated in chiral perturbation theory and extrapolated beyond the threshold region imposing the micro-causality and the unitarity constraint. A reasonable description of various spin observables up to energies [Formula: see text] MeV is obtained in terms of the parameters relevant at order [Formula: see text] in the chiral Lagrangian. Nucleon spin-polarizabilities predicted in our scheme are consistent with recent measurements of double polarization asymmetries at MAMI.

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of hadronic nuclei is formed. We argue that chiral symmetry and large-$N_c$ considerations determine that part of the interaction which generates the spectrum. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes., Talk given at charm06

Charmed meson resonances with quantum numbers J^P=0^+ and J^P=1^+ are generated in terms of chiral coupled-channel dynamics. At leading order in the chiral expansion a parameter-free prediction is obtained for the scattering of Goldstone bosons off charmed pseudo-scalar and vector mesons. The recently announced narrow open charm states observed by the BABAR and CLEO collaborations are reproduced. We suggest the existence of states that form an anti-triplet and a sextet representation of the SU(3) group. In particular, so far unobserved narrow isospin-singlet states with negative strangeness are predicted., Comment: Presented at Hadron 03: 10th International Conference on Hadron Spectroscopy, Aschaffenburg, Germany, 31 Aug - 6 Sep 2003

In this talk we review recent progress on the systematic evaluation of the kaon and antikaon spectral functions in dense nuclear matter based on a chiral SU(3) description of the low-energy pion-, kaon- and antikaon-nucleon scattering data., 9 pages, 4 figures, invited talk given by M.F.M.L. at the SQM2001 conference

To study fundamental questions of hadron and nuclear physics in interactions of antiprotons with nucleons and nuclei, the universal PANDA detector will be built. Gluonic excitations, the physics of strange and charm quarks and nucleon structure studies will be performed with unprecedented accuracy thereby allowing high-precision tests of the strong interaction. The proposed PANDA detector is a state-of-the art internal target detector at the HESR at FAIR allowing the detection and identification of neutral and charged particles generated within the relevant angular and energy range. This report presents a summary of the physics accessible at PANDA and what performance can be expected.