Optical response of small carbon clusters

We apply the time-dependent local density approximation (TDLDA) to calculate dipole excitations in small carbon clusters. A strong low-frequency mode is found which agrees well with observation for clusters C_n with n in the range 7-15. The size dependence of the mode may be understood simply as the classical resonance of electrons in a conducting needle. For a ring geometry, the lowest collective mode occurs at about twice the frequency of the collective mode in the linear chain, and this may also be understood in simple terms.Comment: 19 pages, Latex(Revtex), and 7 figures Postscript; to be published in Zeit. Phys. D; contact is [email protected]

Why there is no crisis of the "spin crisis"

In a recent eprint [1] it is argued that the experimental determinations of the spin-dependent structure function g1 have been done incorrectly and that a reanalysis of those data suggests that the original motivation to argue fora "spin crisis", namely the small contribution of quark spins to the nucleon spin, is invalid. In a subsequent note [2] the theoretical understanding, as it has evolved from almost 30 years of theoretical and experimental scrutiny, has been shortly summarised. In this short note, arguments are presented that the line of reasoning in Ref. [1] does not apply, at least not for the Compass data.Comment: 2 pages, no figure

Time-Dependent Local Density Approximation for Collective Excitations of Atomic Clusters

We discuss the calculation of collective excitations in atomic clusters using the time-dependent local density approximation. In principle there are many formulations of the TDLDA, but we have found that a particularly efficient method for large clusters is to use a coordinate space mesh and the algorithms for the operators and the evolution equations that had been developed for the nuclear time-dependent Hartree-Fock theory. The TDLDA works remarkably well to describe the strong excitations in alkali metal clusters and in carbon clusters. We show as an example the benzene molecule, which has two strong features in its spectrum. The systematics of the linear carbon chains is well reproduced, and may be understood in rather simple terms.Comment: 12 pages in Postscrip

Thin KAPTON polyimide films vacuum formed at high temperature retain their shape at temperatures to 450 K

Purpose of investigation was to identify candidate materials for self-evacuating multilayer insulation systems to be used on liquid hydrogen tanks on space shuttle, which would survive re-entry temperatures and mechanical and thermal cycling of one hundred flights

On the Hamilton-Jacobi equation for second class constrained systems

We discuss a general procedure for arriving at the Hamilton-Jacobi equation of second-class constrained systems, and illustrate it in terms of a number of examples by explicitely obtaining the respective Hamilton principal function, and verifying that it leads to the correct solution to the Euler-Lagrange equations.Comment: 17 pages, to appear in Ann. Phy

Leading QCD-induced four-loop contributions to the β\beta-function of the Higgs self-coupling in the SM and vacuum stability

We present analytical results for the leading top-Yukawa and QCD contribution to the $\beta$-function for the Higgs self-coupling $\lambda$ of the Standard Model at four-loop level, namely the part $\propto y_t^4 g_s^6$ independently confirming a result given in [1]. We also give the contribution $\propto y_t^2 g_s^6$ of the anomalous dimension of the Higgs field as well as the terms $\propto y_t g_s^8$ to the top-Yukawa $\beta$-function which can also be derived from the anomalous dimension of the top quark mass. We compare the results with the RG functions of the correlators of two and four scalar currents in pure QCD and find a new relation between the anomalous dimension $\gamma_0$ of the QCD vacuum energy and the anomalous dimension $\gamma_m^{SS}$ appearing in the RG equation of the correlator of two scalar currents. Together with the recently computed top-Yukawa and QCD contributions to $\beta_{g_s}$ [2,3] the $\beta$-functions presented here constitute the leading four-loop contributions to the evolution of the Higgs self-coupling. A numerical estimate of these terms at the scale of the top-quark mass is presented as well as an analysis of the impact on the evolution of $\lambda$ up to the Planck scale and the vacuum stability problem.Comment: v2: This is the version accepted by JHEP; extended discussion of the numerics and vacuum stability analysis; references added; plot adde