Nucleon propagator at finite temperature

We study the nucleon propagator at finite temperature in the framework of finite energy QCD sum rules. We find that the nucleon mass is approximately constant over a wide range of temperature, increasing sharply near the critical temperature for deconfinementT _c . The coupling of the nucleon to quarks is a monotonically decreasing function ofT, vanishing atT=T _c .     

Quark-Model Nucleon–Nucleon Interaction Applied to Nucleon-Deuteron Scattering

We have examined the neutron-deuteron low-energy effective-range parameters, differential cross sections and spin polarization observables of the elastic nucleon-deuteron scattering up to the incident nucleon energy E _N  = 65 MeV, using the quark-model nucleon–nucleon interaction fss2. These observables are consistently described without introducing three nucleon forces except for the nucleon analyzing power A _y (θ) and the deuteron vector analyzing power iT ₁₁(θ) in the low-energy region E _N  ≤ 25 MeV. The long-standing A _y puzzle is slightly improved, but still remains. We have incorporated the screened Coulomb force to the proton-deuteron scattering, modifying the Vincent–Phatak approach for the sharp cutoff Coulomb force. The Coulomb effect on the elastic scattering observables is discussed.     

Pion-nucleon vertex function with an off-shell nucleon

We present a model calculation for the π-N vertex function in the case in which there is a single off-mass-shell nucleon and a (nearly) on-mass-shell pion. We find very strong effects due to the P₁₁ resonance at 1470 MeV. We provide a simple parametrization of the vertex function in the case that at least one nucleon is on its mass shell.     

Nucleon recoil for low-energy antikaon-deuteron scattering

The effect of the nucleon recoil for antikaon-deuteron scattering is studied in the framework of effective field theory. In particular, we performed a calculation of the nucleon recoil effect for the double scattering process. It is shown that the leading correction to the static term that emerges at order ξ ^1/2, where ξ?=?m _K /M _N , vanishes due to a complete cancellation of individually large terms. The resulting recoil effect for the double scattering process is found to be of order of 10–15% compared to the static term. We also developed a method to include the nucleon recoil effect in the calculation of the multiple scattering diagrams.     

A minimal dark matter interpretation for the CRESST-II signal

We report on the possible interpretation of the two proposed dark matter mass values m _?? =11.6 GeV and m _?? =25.3 GeV from CRESST-II within the framework of the Higgs portal minimal dark matter model. We find that the higher mass value yields a suitable fit with a dark matter-Higgs coupling ??/2=0.157 and a recoil cross section which is compatible with contemporary estimates of the effective Higgs?Cnucleon coupling. On the other hand, the lower mass solution would require a large strangeness component in the nucleon to explain the corresponding nucleon recoil cross section reported by CRESST-II.     

Chiral Expansion of Nucleon PDF at x ~ m π /M N

Based on the chiral perturbation theory, we investigate the low-energy dynamics of nucleon parton distributions. We show that in different regions of the momentum fraction x the chiral expansion is significantly different. For nucleon parton distributions these regions are characterized by x ~ 1, x ~ m _π /M _N and \({x \sim (m_{\pi}/M_{N})^2}\) . We derive extended counting rules for each region and obtain model-independent results for the nucleon parton distributions down to \({x \gtrsim m^{2}_{\pi}/M^2_{N} \approx 10^{-2} }\) .     

Microscopic approach to nucleon spectra in hypernuclear non-mesonic weak decay

A consistent microscopic diagrammatic approach is applied for the first time to the calculation of the nucleon emission spectra in the non-mesonic weak decay of Λ-hypernuclei. We adopt a nuclear matter formalism extended to finite nuclei via the local density approximation, a one-meson exchange weak transition potential and a Bonn nucleon–nucleon strong potential. Ground state correlations and final state interactions, at second order in the nucleon–nucleon interaction, are introduced on the same footing for all the isospin channels of one- and two-nucleon induced decays. Single and double-coincidence nucleon spectra are predicted for ¹²_ΛC and compared with recent KEK and FINUDA data. The key role played by quantum interference terms allows us to improve the predictions obtained with intranuclear cascade codes. Discrepancies with data remain for proton emission.     

New limits on D0 (1.865) production in proton-nucleus collisions at 400 GeV/c

We present final results of a sensitive search for new particles in π^±K^? effective mass spectra observed in proton-nucleus collisions at 400 GeV/c. We establish a limit for D⁰ (1.865) production B_π⁺π^? dσ/dy < 360 nb/nucleon at y_cm^≈ ?0.4. For D?⁰ → π^?K⁺ the limit is 290 nb/nucleon.     

No-Core Shell Model for Nuclear Systems with Strangeness

We report on a novel ab initio approach for nuclear few- and many-body systems with strangeness. Recently, we developed a relevant no-core shell model technique (Navrátil et al. in J Phys G 36:083101, 2009) which we successfully applied in first calculations of the lightest Λ hypernuclei. The use of a translationally invariant finite harmonic oscillator basis allows us to employ large model spaces, compared to traditional shell model calculations, and use realistic nucleon–nucleon and nucleon–hyperon interactions [such as those derived from EFT (Polinder et al. in Nucl Phys A 779:244, 2006)]. We discuss formal aspects of the methodology, show first demonstrative results for _Λ ³ H, _Λ ⁴ H and ⁴ _Λ He, and give outlook.     

Derivation of the effective pion-nucleon Lagrangian within heavy baryon chiral perturbation theory

We develop a method for constructing the heavy baryon chiral perturbation theory (HBChPT) Lagrangian, to a given chiral order, within HBChPT. We work within SU(2) theory, with only the pion field interacting with the nucleon. The main difficulties, which are solved, are to develop techniques for implementing charge conjugation invariance, and for taking the nucleon on shell, both within the non-relativistic formalism. We obtain complete lists of independent terms in L_HBChPT through O(q³) for off-shell nucleons. Then, eliminating equation-of-motion (e.o.m.) terms at the relativistic and non-relativistic level (both within HBChPT), we obtain L_HBChPT for on-shell nucleons, through O(q³). The extension of the method (to obtain on-shell L_HBChPT within HBChPT) to higher orders is also discussed.     

Study of the γD → ppπ− reaction in the Δ(1236) region for well defined kinematical conditions

The γD → ppπ^? reaction cross section, in the Δ(1236) region, is measured in a counter experiment with high statistical accuracy. Particular emphasis is put on the accurate determination of the complete kinematics. For low values of the undetected nucleon momentum (p_r, ≈ 50 MeV/c), the validity of the spectator nucleon model is experimentally checked and the γn → pπ^? elementary reaction cross section is extracted and compared with other experimental data. When the recoiling nucleon momentum increases (p_r ≈ 150 MeV/c), significant departures from the spectator nucleon model are found. Presumably they are the signature of final state interaction effects.     

Superfluid nuclear matter calculations

We present a method to calculate nuclear matter properties in the superfluid phase. The method is based on the use of self-consistent off-shell nucleon propagators in the T-matrix equation. Such a complete treatment of the spectral function is required below and around T_c due to a pseudogap formation in the spectral function. In the superfluid phase we introduce the anomalous self-energy in the fermion propagators and in the T-matrix equation, consistently with the strong coupling BCS equations. The equations for the nucleon spectral function include both a contribution of condensed and scattering pairs. The method is illustrated by numerical calculations. Above T_c pseudogap formation is visible in the spectral function and below T_c a superfluid gap also appears.     

Spin structure of the nucleon—status and recent results

After the initial discovery of the so-called “spin crisis in the parton model” in the 1980s, a large set of polarization data in deep inelastic lepton-nucleon scattering was collected at labs like SLAC, DESY and CERN. More recently, new high precision data at large x and in the resonance region have come from experiments at Jefferson Lab. These data, in combination with the earlier ones, allow us to study in detail the polarized parton densities, the Q² dependence of various moments of spin structure functions, the duality between deep inelastic and resonance data, and the nucleon structure in the valence quark region. Together with complementary data from HERMES, RHIC and COMPASS, we can put new limits on the flavor decomposition and the gluon contribution to the nucleon spin. In this report, we provide an overview of our present knowledge of the nucleon spin structure and give an outlook on future experiments. We focus in particular on the spin structure functions g₁ and g₂ of the nucleon and their moments.     

Momentum distributions in nuclei measured with relativistic heavy ions

In a peripheral reaction between relativistic heavy ions, where one nucleon is knocked out of the projectile, the momentum distribution of the remaining fragment reflects the momentum distribution of the knocked out nucleon. This has been proven in a previous paper. Here we study how the final-state interaction between the knocked out nucleon and the observed fragment influences the result: The real part of the optical potential which describes the final-state interaction shifts the experimental momentum distribution by a value 〈k_∥〉 of a few tens of MeV/c and the imaginary part reduces the cross sections by a factor 2 roughly. We also derive the cross section for a proton as target.     

Study of the charge dependence of the pion–nucleon coupling constant on the basis of data on low-energy nucleon–nucleon interactions

The relation between quantities that characterize the pion–nucleon and nucleon–nucleon interactions is studied with allowance for the fact that, at low energies, nuclear forces in nucleon–nucleon systems are mediated predominantly by one-pion exchange. On the basis of the values currently recommended for the low-energy parameters of the proton–proton interaction, the charged pion–nucleon coupling constant is evaluated at g_π²±/4π = 14.55(13). This value is in perfect agreement with the experimental value of g_π²±/4π = 14.52(26) found by the Uppsala Neutron Research Group. At the same time, the value obtained for the charged pion–nucleon coupling constant differs sizably from the value of the pion–nucleon coupling constant for neutral pions, which is g_π² 0/4π = 13.55(13). This is indicative of a substantial charge dependence of the coupling constant.     

Probabilistic quark-model approach to proton fragmentation

A probabilistic approach is formulated to study the behaviour of the incident hadron quark flavours in the fragmentation process of high energy protons in lowp _T reactions. Analysis of available data onpp collisions, mainly on hyperon and antibaryon multiplicities, leads to estimates of the probabilities for the different ways in which the incident valence quarks recombine into final hadrons. We find that all three incident quarks emerge in one and the same outgoing nucleon (or nucleon resonance) with probabilityA ₃=0.35–0.4, that two of them emerge in one baryon and the third in another hadron (mostly a meson or meson resonance) with probabilityA ₂=0.6–0.5, and that they emerge in three distinct hadrons (mostly mesons or meson resonances) with probabilityA ₁=0.05–0.1. We find good support for a very simple probabilistic picture of the fragmentation process.     

Diquarks in nucleons

Under the assumption that a scalar diquark coexists in part of the time with a single quark within a nucleon, which is favored to describe the higher twist effects of both γ and ν induced nucleon structure functions consistently, we consider how its presence affects nucleon properties. It is shown that the sum rule and the magnetic moment constrain its contribution strongly and the asymmetry is quite sensitive to it. In particular, theR=σ _L /σ _T ratio can be explained in terms of the large transverse momentum of the diquark which arises from the consideration on the neutron charge radius value.     

The Reid93 Potential Triton in the Unitary Pole Approximation

The Reid93 potential provides a representation of the nucleon–nucleon (NN) scattering data that rivals that of a partial wave analysis. We present here a unitary pole approximation (UPA) for this contemporary NN potential that provides a rank one separable potential for which the wave function of the deuteron (³S₁-³D₁) and singlet anti-bound (¹S₀) state are exactly those of the original potential. Our motivation is to use this UPA potential to investigate the sensitivity of the electric dipole moment for the deuteron and ³H and ³He to the ground state nuclear wave function. We compare the Reid93 results with those for the original Reid (Reid68) potential to illustrate the accuracy of the bound state properties.     

Test of the validity of the adiabatic approximation in scattering theory

Exact solutions for the scattering of a fast projectile x on deuterium are compared with various versions of the fixed scatterers approximation. The content of the approximations for a nucleon and a different projectile is discussed. The calculations show the approximate agreement of angular distributions in forward direction and the amount of disagreement in the backward hemisphere. In the case of nucleon scattering the importance of nucleon exchange, neglected in the FSA, is explicitly demonstrated. As expected, the quality of the tested approximations rapidly improves with diminishing mass ratio M_x/M_N.