Alternative experimental evidence for chiral restoration in excited baryons

Given existing empirical spectral patterns of excited hadrons it has been suggested that chiral symmetry is approximately restored in excited hadrons at zero temperature/density (effective symmetry restoration). If correct, this implies that mass generation mechanisms and physics in excited hadrons is very different as compared to the lowest states. One needs an alternative and independent experimental information to confirm this conjecture. Using very general chiral symmetry arguments it is shown that strict chiral restoration in a given excited nucleon forbids its decay into the N \pi channel. Hence those excited nucleons which are assumed from the spectroscopic patterns to be in approximate chiral multiplets must only "weakly" decay into the N \pi channel, (f_{N^*N\pi}/f_{NN\pi})^2 << 1. However, those baryons which have no chiral partner must decay strongly with a decay constant comparable with f_{NN\pi}. Decay constants can be extracted from the existing decay widths and branching ratios. It turnes out that for all those well established excited nucleons which can be classified into chiral doublets N_+(1440) - N_-(1535), N_+(1710) - N_-(1650), N_+(1720) - N_-(1700), N_+(1680) - N_-(1675), N_+(2220) - N_-(2250), N_+(?) - N_-(2190), N_+(?) - N_-(2600), the ratio is (f_{N^*N\pi}/f_{NN\pi})^2 ~ 0.1 or much smaller for the high-spin states. In contrast, the only well established excited nucleon for which the chiral partner cannot be identified from the spectroscopic data, N(1520), has a decay constant into the N\pi channel that is comparable with f_{NN\pi}. This gives an independent experimental verification of the chiral symmetry restoration scenario.Comment: 4 pp. A new footnote with an alternative proof of impossibility of parity doublet decay into pi + N is added. To appear in Phys. Rev. Let

Nuclear Forces and Few-Nucleon Studies Based on Chiral Perturbation Theory

After a brief review on the status of few--nucleon studies based on conventional nuclear forces, we sketch the concepts of the effective field theory approach constrained by chiral symmetry and its application to nuclear forces. Then first results for few--nucleon observables are discussed.Comment: 8 pages, presented by W. Gloeckle at the International Symposium on "A New Era of Nuclear Structure Physics", Kurokawa Village (Niigata Pref.), Japan, Nov. 19-22, 200

Few-Nucleon Systems with Two-Nucleon Forces from Chiral Effective Field Theory

Nucleon-nucleon (NN) forces from chiral perturbation theory at next-to-leading (NLO) and next-to-next-to-leading order (NNLO) are applied to systems with two, three and four nucleons. At NNLO, we consider two versions of the chiral potential which differ in the strength of the two-pion-exchange (TPE) but describe two nucleon observables equally well. The NNLO potential leads to unphysical deeply bound states in the low partial waves and effects of the 3N forces, which appear first at this order, are expected to be large. We provide arguments for a reduction of the TPE potential and introduce the NNLO* version of the NN forces. We calculate nd scattering observables as well as various properties of 3H and 4He with the NNLO* potential and find good agreement with the data and with predictions based upon the standard high-precision potentials. We find an improved description of the 3H and 4He binding energies.Comment: 34 pages, 25 figure

XLI.— On the genus Mermis

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Crystallographic disorder and electron scattering on structural two-level systems in ZrAs1.4Se0.5

Single crystals of ZrAs1.4Se0.5 (PbFCl type structure) were grown by chemical vapour transport. While their thermodynamic and transport properties are typical for ordinary metals, the electrical resistivity exhibits a shallow minimum at low temperatures. Application of strong magnetic fields does not influence this anomaly. The minimum of the resistivity in ZrAs1.4Se0.5 apparently originates from interaction between the conduction electrons and structural two-level systems. Significant disorder in the As-Se substructure is inferred from X-ray diffraction and electron microprobe studies

Parity violation in deuteron photo-disintegration

We analyze the energy dependence for two types of parity-non-conserving (PNC) asymmetries in the reaction $\gamma D\to np$ in the near-threshold region. The first one is the asymmetry in reaction with circularly polarized photon beam and unpolarized deuteron target. The second one corresponds to those with an unpolarized photon beam and polarized target. We find that the two asymmetries have quite different energy dependence, and their shapes are sensitive to the PNC-meson exchange coupling constants. The predictions for the future possible experiments to provide definite constraints for the PNC-coupling constants are discussed.Comment: 22 pages, 12 figures. Submitted to Phys.Rev.C 10Oct.0

Chiral condensate thermal evolution at finite baryon chemical potential within Chiral Perturbation Theory

We present a model independent study of the chiral condensate evolution in a hadronic gas, in terms of temperature and baryon chemical potential. The meson-meson interactions are described within Chiral Perturbation Theory and the pion-nucleon interaction by means of Heavy Baryon Chiral Perturbation Theory, both at one loop, and nucleon-nucleon interactions can be safely neglected within our hadronic gas domain of validity. Together with the virial expansion, this provides a systematic expansion at low temperatures and chemical potentials, which includes the physical quark masses. This can serve as a guideline for further studies on the lattice. We also obtain estimates of the critical line of temperature and chemical potential where the chiral condensate melts, which systematically lie somewhat higher than recent lattice calculations but are consistent with several hadronic models. We have also estimated uncertainties due to chiral parameters, heavier hadrons and higher orders through unitarized Chiral Perturbation Theory.Comment: 15 pages, 15 figures, 3 tables, ReVTeX. Version to appear in Phys. Rev. D. References added. More conservative estimate of applicability domain, with new figure. More detailed explanation of final results with two more figures. Results unchange

Phycomyces

This monographic review on a fungus is not addressed to mycologists. None of the authors has been trained or has otherwise acquired a general proficiency in mycology. They are motivated by a common interest in the performances of signal handling exhibited by the sense organs of all organisms and by the desire to attack these as yet totally obscure aspects of molecular biology by the study of a microorganism with certain desirable properties. The sporangiophore of the fungus Phycomyces is a gigantic, single-celled, erect, cylindrical, aerial hypha. It is sensitive to at least four distinct stimuli: light, gravity, stretch, and some unknown stimulus by which it avoids solid objects. These stimuli control a common output, the growth rate, producing either temporal changes in growth rate or tropic responses. We are interested in the output because it gives us information about the reception of the various signals. In the absence of external stimuli, the growth rate is controlled by internal signals keeping the network of biochemical processes in balance. The external stimuli interact with the internal signals. We wish to inquire into the early steps of this interaction. For light, for instance, the cell must have a receptor pigment as the first mediator. What kind of a molecule is this pigment? Which organelle contains it? What chemical reaction happens after a light quantum has been absorbed? And how is the information introduced by this primary photochemical event amplified in a controlled manner and processed in the next step? How do a few quanta or a few molecules trigger macroscopic responses? Will we find ourselves confronted with devices wholly distinct from anything now known in biology

Effective dynamics of the closed loop quantum cosmology

In this paper we study dynamics of the closed FRW model with holonomy corrections coming from loop quantum cosmology. We consider models with a scalar field and cosmological constant. In case of the models with cosmological constant and free scalar field, dynamics reduce to 2D system and analysis of solutions simplify. If only free scalar field is included then universe undergoes non-singular oscillations. For the model with cosmological constant, different behaviours are obtained depending on the value of $\Lambda$. If the value of $\Lambda$ is sufficiently small, bouncing solutions with asymptotic de Sitter stages are obtained. However if the value of $\Lambda$ exceeds critical value $\Lambda_{\text{c}} =\frac{\sqrt{3}m^2_{\text{Pl}}}{2\pi\gamma^3} \simeq 21 m^2_{\text{Pl}}$ then solutions become oscillatory. Subsequently we study models with a massive scalar field. We find that this model possess generic inflationary attractors. In particular field, initially situated in the bottom of the potential, is driven up during the phase of quantum bounce. This subsequently leads to the phase of inflation. Finally we find that, comparing with the flat case, effects of curvature do not change qualitatively dynamics close to the phase of bounce. Possible effects of inverse volume corrections are also briefly discussed.Comment: 18 pages, 11 figure

The Nucleon Anapole Moment and Parity-Violating ep Scattering

Parity-violating (PV) interactions among quarks in the nucleon induce a PV $\gamma NN$ coupling, or anapole moment (AM). We compute electroweak gauge-independent contributions to the AM through {\cal O}(1/\lamchis) in chiral perturbation theory. We estimate short-distance PV effects using resonance saturation. The AM contributions to PV electron-proton scattering slightly enhance the axial vector radiative corrections, R_A^p, over the scale implied by the Standard Model when weak quark-quark interactions are neglected. We estimate the theoretical uncertainty associated with the AM contributions to R_A^p to be large, and discuss the implications for the interpretation PV of ep scattering.Comment: RevTex 29 pages + 8 PS figures, references and discussions added, to appear in Phys. Rev.