The Trigger System of the ARGO-YBJ detector

The ARGO-YBJ experiment has been designed to detect air shower events over a large size scale and with an energy threshold of a few hundreds GeV. The building blocks of the ARGO-YBJ detector are single-gap Resistive Plate Counters (RPCs). The trigger logic selects the events on the basis of their hit multiplicity. Inclusive triggers as well as dedicated triggers for specific physics channels or calibration purposes have been developed. This paper describes the architecture and the main features of the trigger system.Comment: 4 pages, to be published in the Proceedings of the 28th International Cosmic Ray Conference (Tsukuba, Japan 2003

Non-Fermi liquid behavior in transport through Co doped Au chains

We calculate the conductance as a function of temperature $G(T)$ through Au monoatomic chains containing one Co atom as a magnetic impurity, and connected to two conducting leads with a 4-fold symmetry axis. Using the information derived from {\it ab initio} calculations, we construct an effective model \Heff that hybridizes a 3d$^7$ quadruplet at the Co site with two 3d$^8$ triplets through the hopping of 5d$_{xz}$ and 5d$_{yz}$ electrons of Au. The quadruplet is split by spin anisotropy due to spin-orbit coupling. Solving \Heff with the numerical renormalization group (NRG) % Wb: reverted my own change we find that at low temperatures $G(T)=a-b \sqrt{T}$ and the ground state impurity entropy is $\ln(2)/2$, a behavior similar to the two-channel Kondo model. Stretching the chain leads to a non Kondo phase, with the physics of the underscreened Kondo model at the quantum critical point.Comment: Accepted in Physical Review Letter

Quantum Deconstruction of 5D SQCD

We deconstruct the fifth dimension of 5D SCQD with general numbers of colors and flavors and general 5D Chern-Simons level; the latter is adjusted by adding extra quarks to the 4D quiver. We use deconstruction as a non-stringy UV completion of the quantum 5D theory; to prove its usefulness, we compute quantum corrections to the SQCD_5 prepotential. We also explore the moduli/parameter space of the deconstructed SQCD_5 and show that for |K_CS| < N_F/2 it continues to negative values of 1/(g_5)^2. In many cases there are flop transitions connecting SQCD_5 to exotic 5D theories such as E0, and we present several examples of such transitions. We compare deconstruction to brane-web engineering of the same SQCD_5 and show that the phase diagram is the same in both cases; indeed, the two UV completions are in the same universality class, although they are not dual to each other. Hence, the phase structure of an SQCD_5 (and presumably any other 5D gauge theory) is inherently five-dimensional and does not depends on a UV completion.Comment: LaTeX+PStricks, 108 pages, 41 colored figures. Please print in colo

Unusual Kondo physics in a Co impurity atom embedded in noble-metal chains

We analyze the conduction bands of the one dimensional noble-metal chains that contain a Co magnetic impurity by means of ab initio calculations. We compare the results obtained for Cu and Ag pure chains, as well as O doped Cu, Ag and Au chains with those previously found for Au pure chains. We find similar results in the case of Cu and Au hosts, whereas for Ag chains a different behavior is obtained. Differences and similarities among the different systems are analyzed by comparing the electronic structure of the three noble-metal hosts. The d-orbitals of Cu chains at the Fermi level have the same symmetry as in the case of Au chains. These orbitals hybridize with the corresponding ones of the Co impurity, giving rise to the possibility of exhibiting a two-channel Kondo physics.Comment: Accepted in IEEE Trans. Magn. - April 201

High-performance functional renormalization group calculations for interacting fermions

We derive a novel computational scheme for functional Renormalization Group (fRG) calculations for interacting fermions on 2D lattices. The scheme is based on the exchange parametrization fRG for the two-fermion interaction, with additional insertions of truncated partitions of unity. These insertions decouple the fermionic propagators from the exchange propagators and lead to a separation of the underlying equations. We demonstrate that this separation is numerically advantageous and may pave the way for refined, large-scale computational investigations even in the case of complex multiband systems. Furthermore, on the basis of speedup data gained from our implementation, it is shown that this new variant facilitates efficient calculations on a large number of multi-core CPUs. We apply the scheme to the $t$,$t'$ Hubbard model on a square lattice to analyze the convergence of the results with the bond length of the truncation of the partition of unity. In most parameter areas, a fast convergence can be observed. Finally, we compare to previous results in order to relate our approach to other fRG studies.Comment: 26 pages, 9 figure

Chiral Rings of Deconstructive [SU(n_c)]^N Quivers

Dimensional deconstruction of 5D SQCD with general n_c, n_f and k_CS gives rise to 4D N=1 gauge theories with large quivers of SU(n_c) gauge factors. We construct the chiral rings of such [SU(n_c)]^N theories, off-shell and on-shell. Our results are broadly similar to the chiral rings of single U(n_c) theories with both adjoint and fundamental matter, but there are also some noteworthy differences such as nonlocal meson-like operators where the quark and antiquark fields belong to different nodes of the quiver. And because our gauge groups are SU(n_c) rather than U(n_c), our chiral rings also contain a whole zoo of baryonic and antibaryonic operators.Comment: 93 pages, LaTeX, PSTricks macros; 1 reference added in v