Two-center resonant photo ionization

Photoionization of an atom $A$, in the presence of a neighboring atom $B$, can proceed via resonant excitation of $B$ with subsequent energy transfer to $A$ through two-center electron-electron correlation. We demonstrate that this two-center mechanism can strongly outperform direct photoionization at nanometer internuclear distances and possesses characteristic features in its time development and the spectrum of emitted electrons.Comment: 4 pages, 3 figure

A Gauge-fixed Hamiltonian for Lattice QCD

We study the gauge fixing of lattice QCD in 2+1 dimensions, in the Hamiltonian formulation. The technique easily generalizes to other theories and dimensions. The Hamiltonian is rewritten in terms of variables which are gauge invariant except under a single global transformation. This paper extends previous work, involving only pure gauge theories, to include matter fields.Comment: 7 pages of LaTeX, RU-92-45 and BUHEP-92-3

Possible Resolutions of the D-Paradox

We propose possible ways of explaining the net charge event-by-event fluctuations in Au+Au collisions at the Relativistic Heavy Ion Collider within a quark recombination model. We discuss various methods of estimating the number of quarks at recombination and their implications for the predicted net charge fluctuations. We also discuss the possibility of diquark and quark-antiquark clustering above the deconfinement temperature.Comment: 5 pages, 2 figure

Kilohertz laser ablation for doping helium nanodroplets

A new setup for doping helium nanodroplets by means of laser ablation at kilohertz repetition rate is presented. The doping process is characterized and two distinct regimes of laser ablation are identified. The setup is shown to be efficient and stable enough to be used for spectroscopy, as demonstrated on beam-depletion spectra of lithium atoms attached to helium nanodroplets. For the first time, helium droplets are doped with high temperature refractory materials such as titanium and tantalum. Doping with the non-volatile DNA basis Guanine is found to be efficient and a number of oligomers are detected

Generalized Parton Distributions of ^3He

A realistic microscopic calculation of the unpolarized quark Generalized Parton Distribution (GPD) $H_q^3$ of the $^3He$ nucleus is presented. In Impulse Approximation, $H_q^3$ is obtained as a convolution between the GPD of the internal nucleon and the non-diagonal spectral function, describing properly Fermi motion and binding effects. The proposed scheme is valid at low values of $\Delta^2$, the momentum transfer to the target, the most relevant kinematical region for the coherent channel of hard exclusive processes. The obtained formula has the correct forward limit, corresponding to the standard deep inelastic nuclear parton distributions, and first moment, giving the charge form factor of $^3He$. Nuclear effects, evaluated by a modern realistic potential, are found to be larger than in the forward case. In particular, they increase with increasing the momentum transfer when the asymmetry of the process is kept fixed, and they increase with the asymmetry at fixed momentum transfer. Another relevant feature of the obtained results is that the nuclear GPD cannot be factorized into a $\Delta^2$-dependent and a $\Delta^2$-independent term, as suggested in prescriptions proposed for finite nuclei. The size of nuclear effects reaches 8 % even in the most important part of the kinematical range under scrutiny. The relevance of the obtained results to study the feasibility of experiments is addressed.Comment: 23 pages, 8 figures; Discussion in section II enlarged; discussion in section IV shortened. Final version accepted by Phys. Rev.

Inhomogeneous holographic thermalization

The sudden injection of energy in a strongly coupled conformal field theory and its subsequent thermalization can be holographically modeled by a shell falling into anti-de Sitter space and forming a black brane. For a homogeneous shell, Bhattacharyya and Minwalla were able to study this process analytically using a weak field approximation. Motivated by event-by-event fluctuations in heavy ion collisions, we include inhomogeneities in this model, obtaining analytic results in a long wavelength expansion. In the early-time window in which our approximations can be trusted, the resulting evolution matches well with that of a simple free streaming model. Near the end of this time window, we find that the stress tensor approaches that of second-order viscous hydrodynamics. We comment on possible lessons for heavy ion phenomenology.Comment: 53 pages, 10 figures; v2: references adde