Enhancement of the Deuteron-Fusion Reactions in Metals and its Experimental Implications

Recent measurements of the reaction d(d,p)t in metallic environments at very low energies performed by different experimental groups point to an enhanced electron screening effect. However, the resulting screening energies differ strongly for divers host metals and different experiments. Here, we present new experimental results and investigations of interfering processes in the irradiated targets. These measurements inside metals set special challenges and pitfalls which make them and the data analysis particularly error-prone. There are multi-parameter collateral effects which are crucial for the correct interpretation of the observed experimental yields. They mainly originate from target surface contaminations due to residual gases in the vacuum as well as from inhomogeneities and instabilities in the deuteron density distribution in the targets. In order to address these problems an improved differential analysis method beyond the standard procedures has been implemented. Profound scrutiny of the other experiments demonstrates that the observed unusual changes in the reaction yields are mainly due to deuteron density dynamics simulating the alleged screening energy values. The experimental results are compared with different theoretical models of the electron screening in metals. The Debye-H\"{u}ckel model that has been previously proposed to explain the influence of the electron screening on both nuclear reactions and radioactive decays could be clearly excluded.Comment: 22 pages, 12 figures, REVTeX4, 2-column format. Submitted to Phys. Rev. C; accepte

Finite Nuclei in a Relativistic Mean-Field Model with Derivative Couplings

We study finite nuclei, at the mean-field level, using the Zimanyi-Moskowski model and one of its variations (the ZM3 model). We calculate energy levels and ground-state properties in nuclei where the mean-field approach is reliable. The role played by the spin-orbit potential in sorting out mean-field model descriptions is emphasized.Comment: 17 pages, 9 figures, 30 kbytes. Uses EPSF.TEX. To appear in Zeit. f. Phys. A (Hadrons and Nuclei

New order parameters in the Potts model on a Cayley tree

For the $q-$state Potts model new order parameters projecting on a group of spins instead of a single spin are introduced. On a Cayley tree this allows the physical interpretation of the Potts model at noninteger values q of the number of states. The model can be solved recursively. This recursion exhibits chaotic behaviour changing qualitatively at critical values of $q_0$ . Using an additional order parameter belonging to a group of zero extrapolated size the additional ordering is related to a percolation problem. This percolation distinguishes different phases and explains the critical indices of percolation class occuring at the Peierls temperature.Comment: 16 pages TeX, 5 figures PostScrip

Pion structure from improved lattice QCD: form factor and charge radius at low masses

The charge form factor of the pion is calculated in lattice QCD. The non-perturbatively improved Sheikholeslami-Wohlert action is used together with the $\mathcal{O}(a)$ improved vector current. Other choices for the current are examined. The form factor is extracted for pion masses from 970 MeV down to 360 MeV and for momentum transfers $Q^2 \leq 2 \mathrm{GeV}^2$. The mean square charge radius is extracted, compared to previous determinations and its extrapolation to lower masses discussed.Comment: 12 pages REVTeX, 15 figures. Designation of currents clarified. Details concerning extraction of parameters added. Version accepted by Phys. Rev.

Hot Nuclear Matter in the Quark Meson Coupling Model with Dilatons

We study hot nuclear matter in an explicit quark model based on a mean field description of nonoverlapping nucleon bags bound by the self-consistent exchange of scalar and vector mesons as well as the glueball field. The glueball exchange as well as a realization of the broken scale invariance of quantum chromodynamics is achieved through the introduction of a dilaton field. The calculations also take into account the medium-dependence of the bag constant. The effective potential with dilatons is applied to nuclear matter. The nucleon properties at finite temperature as calculated here are found to be appreciably different from cold nuclear matter. The introduction of the dilaton potential improves the shape of the saturation curve at T=0 and is found to affect hot nuclear matter significantly.Comment: LaTeX/TeX 12 pages (zak2), 13 figures in TeX forma

Towards a Realistic Equation of State of Strongly Interacting Matter

We consider a relativistic strongly interacting Bose gas. The interaction is manifested in the off-shellness of the equilibrium distribution. The equation of state that we obtain for such a gas has the properties of a realistic equation of state of strongly interacting matter, i.e., at low temperature it agrees with the one suggested by Shuryak for hadronic matter, while at high temperature it represents the equation of state of an ideal ultrarelativistic Stefan-Boltzmann gas, implying a phase transition to an effectively weakly interacting phase.Comment: LaTeX, figures not include

Modified Quark-Meson Coupling Model for Nuclear Matter

The quark-meson coupling model for nuclear matter, which describes nuclear matter as non-overlapping MIT bags bound by the self-consistent exchange of scalar and vector mesons, is modified by introducing medium modification of the bag constant. We model the density dependence of the bag constant in two different ways: one invokes a direct coupling of the bag constant to the scalar meson field, and the other relates the bag constant to the in-medium nucleon mass. Both models feature a decreasing bag constant with increasing density. We find that when the bag constant is significantly reduced in nuclear medium with respect to its free-space value, large canceling isoscalar Lorentz scalar and vector potentials for the nucleon in nuclear matter emerge naturally. Such potentials are comparable to those suggested by relativistic nuclear phenomenology and finite-density QCD sum rules. This suggests that the reduction of bag constant in nuclear medium may play an important role in low- and medium-energy nuclear physics.Comment: Part of the text is reordered, revised version to appear in Phys. Rev. C. 19 pages, ReVTeX, 4 figures embedde

Derivative-Coupling Models and the Nuclear-Matter Equation of State

The equation of state of saturated nuclear matter is derived using two different derivative-coupling Lagrangians. We show that both descriptions are equivalent and can be obtained from the sigma-omega model through an appropriate rescaling of the coupling constants. We introduce generalized forms of this rescaling to study the correlations amongst observables in infinite nuclear matter, in particular, the compressibility and the effective nucleon mass.Comment: 16 pages, 6 figures, 36 kbytes. To appear in Zeit. f. Phys. A (Hadrons and Nuclei

Finite-Width Effects in Top Quark Production at Hadron Colliders

Production cross sections for t\bar{t} and t\bar{t}j events at hadron colliders are calculated, including finite width effects and off resonance contributions for the entire decay chain, t --> bW --> b\ell\nu, for both top quarks. Resulting background rates to Higgs search at the CERN LHC are updated for inclusive H --> WW studies and for H --> \tau\tau and H --> WW decays in weak boson fusion events. Finite width effects are large, increasing t\bar{t}(j) rates by 20% or more, after typical cuts which are employed for top-background rejection.Comment: 32 pages, 11 figures, 7 tables; minor changes, reference added, to be published in Phys. Rev.