Results on High p_T Particle Production from the PHENIX Experiment at RHIC

Transverse momentum (p_T) spectra of neutral pions and charged hadrons measured in Au+Au and d+Au collisions at sqrt{s_NN}=200 GeV by the PHENIX experiment at RHIC are compared to p+p reference spectra at the same sqrt{s_NN}. In central Au+Au collisions a factor 4-5 suppression for neutral pions and charged hadrons with p_T > 5 GeV/c is found relative to the p+p reference scaled by the nuclear overlap function . In contrast, such a suppression of high p_T particles is absent in d+Au collisions.Comment: To appear in the proceedings of the 8th International Conference on Nucleus-Nucleus Collisions (NN 2003), Moscow, Russia, 17-21 Jun 2003 (4 pages, 3 figures), V1: error fixed in caption of Fig.

Artificial electromagnetism for neutral atoms: Escher staircase and Laughlin liquids

We show how lasers may create fields which couple to neutral atoms in the same way that the electromagnetic fields couple to charged particles. These fields are needed for using neutral atoms as an analog quantum computer for simulating the properties of many-body systems of charged particles. They allow for seemingly paradoxical geometries, such as a ring where atoms continuously reduce their potential energy while moving in a closed path. We propose neutral atom experiments which probe quantum Hall effects and the interplay between magnetic fields and periodic potentials.Comment: 4 pages, 1 color figure, RevTeX 4; v2 Revised introduction, additional reference

Structurally constrained protein evolution: results from a lattice simulation

We simulate the evolution of a protein-like sequence subject to point mutations, imposing conservation of the ground state, thermodynamic stability and fast folding. Our model is aimed at describing neutral evolution of natural proteins. We use a cubic lattice model of the protein structure and test the neutrality conditions by extensive Monte Carlo simulations. We observe that sequence space is traversed by neutral networks, i.e. sets of sequences with the same fold connected by point mutations. Typical pairs of sequences on a neutral network are nearly as different as randomly chosen sequences. The fraction of neutral neighbors has strong sequence to sequence variations, which influence the rate of neutral evolution. In this paper we study the thermodynamic stability of different protein sequences. We relate the high variability of the fraction of neutral mutations to the complex energy landscape within a neutral network, arguing that valleys in this landscape are associated to high values of the neutral mutation rate. We find that when a point mutation produces a sequence with a new ground state, this is likely to have a low stability. Thus we tentatively conjecture that neutral networks of different structures are typically well separated in sequence space. This results indicates that changing significantly a protein structure through a biologically acceptable chain of point mutations is a rare, although possible, event.Comment: added reference, to appear on European Physical Journal

Charge and Isospin Fluctuations in High Energy pp-Collisions

Charge and isospin event-by-event fluctuations in high-energy pp-collisions are predicted within the Unitary Eikonal Model, in particular the fluctuation patterns of the ratios of charged-to-charged and neutral-to-charged pions. These fluctuations are found to be sensitive to the presence of unstable resonances, such as $\rho$ and $\omega$ mesons. We predict that the charge-fluctuation observable $D_{UEM}$ should be restricted to the interval $8/3\le D_{UEM}\le 4$ depending on the $\rho /\pi$ production ratio. Also, the isospin fluctuations of the DCC-type of the ratio of neutral-to-charged pions are suppressed if pions are produced together with $\rho$ mesons.Comment: Latex, 5 pages, no figures. To appear in the proceedings of 9th Adriatic Meeting, Dubrovnik, Croatia, 4 - 14 September 2003. Added reference into reference no.

Probing Higgs-sector CP Violation at a Photon Collider

In this review we demonstrate physics potential of a photon linear collider by studying the neutral Higgs-boson sector of the MSSM in which interesting CP-violating Higgs mixing could arise via radiative corrections.Comment: 18 pages, 8 figures, 1 table, invited article by Modern Physics Letters A (review section), added reference

Interference of Higgs boson resonances in mu^+ mu^- -> neutralino_i neutralino_j with longitudinal beam polarization

We study the interference of resonant Higgs boson exchange in neutralino production in \mu^+ \mu^- annihilation with longitudinally polarized beams. We use the energy distribution of the decay lepton in the process \neutralino_j \to \ell^\pm \slepton^\mp to determine the polarization of the neutralinos. In the CP conserving Minimal Supersymmetric Standard Model a non-vanishing asymmetry in the lepton energy spectrum is caused by the interference of Higgs boson exchange channels with different CP eigenvalues. The contribution of this interference is large if the heavy neutral bosons H and A are nearly degenerate. We show that the asymmetry can be used to determine the couplings of the neutral Higgs bosons to the neutralinos. In particular, the asymmetry allows to determine the relative phase of the couplings. We find large asymmetries and cross sections for a set of reference scenarios with nearly degenerate neutral Higgs bosons.Comment: 20 pages, 6 figures, minor typos corrected, to appear in Eur. Phys. J.