Primordial Nucleosynthesis Constraints on Z' Properties

In models involving new TeV-scale Z' gauge bosons, the new U(1)' symmetry often prevents the generation of Majorana masses needed for a conventional neutrino seesaw, leading to three superweakly interacting ``right-handed'' neutrinos nu_R, the Dirac partners of the ordinary neutrinos. These can be produced prior to big bang nucleosynthesis by the Z' interactions, leading to a faster expansion rate and too much ^4He. We quantify the constraints on the Z' properties from nucleosynthesis for Z' couplings motivated by a class of E_6 models parametrized by an angle theta_E6. The rate for the annihilation of three approximately massless right-handed neutrinos into other particle pairs through the Z' channel is calculated. The decoupling temperature, which is higher than that of ordinary left-handed neutrinos due to the large Z' mass, is evaluated, and the equivalent number of new doublet neutrinos Delta N_nu is obtained numerically as a function of the Z' mass and couplings for a variety of assumptions concerning the Z-Z' mixing angle and the quark-hadron transition temperature T_c. Except near the values of theta_E6 for which the Z' decouples from the right-handed neutrinos, the Z' mass and mixing constraints from nucleosynthesis are much more stringent than the existing laboratory limits from searches for direct production or from precision electroweak data, and are comparable to the ranges that may ultimately be probed at proposed colliders. For the case T_c = 150 MeV with the theoretically favored range of Z-Z' mixings, Delta N_nu 4.3 TeV for any value of theta_E6. Larger mixing or larger T_c often lead to unacceptably large Delta N_nu except near the nu_R decoupling limit.Comment: 22 pages, 5 figures; two additional references adde

Measurement of the dijet invariant mass cross section in proton anti-proton collisions at sqrt{s} = 1.96 TeV

The inclusive dijet production double differential cross section as a function of the dijet invariant mass and of the largest absolute rapidity of the two jets with the largest transverse momentum in an event is measured in proton anti-proton collisions at sqrt{s} = 1.96 TeV using 0.7 fb^{-1} integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The measurement is performed in six rapidity regions up to a maximum rapidity of 2.4. Next-to-leading order perturbative QCD predictions are found to be in agreement with the data.Comment: Published in Phys. Lett. B, 693, (2010), 531-538, 8 pages, 2 figures, 6 table

Molecular dynamic studies of crack propagation. The role of the interatomic potential

We have used the molecular dynamic simulation technique in studying a variety of solid state problems, ranging from equation-of-state and shock wave propagation to epitaxy and various aspects of crack propagation. In these simulations, which are classical, Newton's equations-of-motion are solved for each particle at every step to yield positions, velocities, forces and energies. An important limitation of the technique is that one has to put an interatomic potential into the calculation. Within these restrictions the technique is exact and is very powerful in automatically incorporating many body and anharmonic effects into the calculation. For complicated processes, such as crack propagation, there is a practical limitation to two dimensions, simply by the availability of computing capabilities, if a large enough sample, representative of bulk processes is to be used

Theory of Point Defect Annealing in Metals

The kinetics of the annealing of point defects, either by migration to sinks or by recombination, is complicated by the occurrence of a variety of simultaneous reactions. An extensive theoretical study of anneallng processes is in progress based on the isolation and combination of simple kinetic steps. When analytic solutions could not be found, computer solutions were used to obtain useful approximations and to determine their regions of validity. Two migration reaction schemes were studied: the simultaneous annealing of single and di- vacancies and the annealing of single vacancies with impurity trapping. Three recombination reactions were investigated: vacancy-interstitial annihilation with interstitial migration to sinks, di-interstitial formation, and interstitial trapping at impurities. (auth

Thermal desorption spectroscopy (TDS) of hydrogen from niobium

Thermal desorption spectroscopy is often used to determine the activation energy of desorption of an adsorbate on a substrate as well as the order of the kinetics. In the case of flash desorption of an adsorbate from a surface obeying second order kinetics, a plot of Log(theta/sub o/T/sub p//sup 2/) vs 1/T/sub p/ (where theta/sub o/ is the initial surface coverage and T/sub P/ is the temperature of the maximum desorption rate, i.e., the desorption temperature) will yield a straight line, the slope of which is determined by the chemisorption energy. However, it is argued that in the case of a system with hydrogen absorbed into the bulk in quasiequilibrium with adsorption sites on the surface, a similar plot, where the coverage theta/sub o/ must now be replaced by the initial concentration x/sub o/, will yield a slope determined by the heat of solution. In the following experiments the functional dependence of the desorption temperature on hydrogen loading as outlined above is verified. Deviations from these theoretical predictions were observed, and numerical kinetic simulations were made to aid in understanding them