W, Z and photon production in CMS

The production of electroweak bosons (photons, W and Z particles) in PbPb and pp collisions at sqrt(s) = 2.76 TeV per interacting nucleon pair has been measured with the CMS detector at the LHC. Direct photon production is studied using samples of isolated photons. W and Z bosons are reconstructed through their leptonic decay into muons. Their production rate in PbPb data is studied as a function of the centrality of the collision and compared to that in pp interactions, once normalized by the number of binary nucleon-nucleon interactions. The results are also compared to next-to-leading-order perturbative QCD calculations.Comment: Proceedings from Plenary Talk at 5th International Conference on Hard and Electromagnetic Probes of High-Energy Nuclear Collisions (Hard Probes 2012) at Cagliari (Italia

Challenges for Superstring Cosmology

We consider whether current notions about superstring theory below the Planck scale are compatible with cosmology. We find that the anticipated form for the dilaton interaction creates a serious roadblock for inflation and makes it unlikely that the universe ever reaches a state with zero cosmological constant and time-independent gravitational constant.Comment: 14 pages, 2 figures available as eps files on reques

Tachyon Condensates and String Theoretic Inflation

Cosmological solutions of the beta function equations for the background fields of the closed bosonic string are investigated at the one-loop level. Following recent work of Kostelecky and Perry, it is assumed that the spatial sections of the space-time are conformally flat. Working in the sigma-model frame, the non-trivial tachyon potential is utilized to determine solutions with sufficient inflation to solve the smoothness and flatness problems. The graceful exit and density perturbation constraints can also be successfully implemented.Comment: FERMI-PUB 93/074-T, harvmac, 16 page

Extended Inflation from Strings

We study the possibility of extended inflation in the effective theory of gravity from strings compactified to four dimensions and find that it strongly depends on the mechanism of supersymmetry breaking. We consider a general class of string--inspired models which are good candidates for successful extended inflation. In particular, the $\omega$--problem of ordinary extended inflation is automatically solved by the production of only very small bubbles until the end of inflation. We find that the inflaton field could belong either to the untwisted or to the twisted massless sectors of the string spectrum, depending on the supersymmetry breaking superpotential.Comment: 18p

Boron nitride nanotubes : pronounced resistance to oxidation

Boron nitride (BN) nanotubes have the same nanostructure as carbon nanotubes but are found to exhibit significant resistance to oxidation at high temperatures. Our systematic study has revealed that BN nanotubes are stable at 700 &deg;C in air and that some thin nanotubes (diameter less than 20 nm) with perfect multiwalled cylindrical structure can survive up to 900 &deg;C. Thermogravimetric analysis reveals an onset temperature for oxidation of BN nanotubes of 800 &deg;C compared with only 400 &deg;C for carbon nanotubes under the same conditions. This more pronounced resistance of BN nanotubes to oxidation is inherited from the hexagonal BN and also depends on the nanocrystalline structure. This high level of resistance to oxidation allows promising BN nanotube applications athigh temperatures<br /

Virtually Abelian Quantum Walks

We introduce quantum walks on Cayley graphs of non-Abelian groups. We focus on the easiest case of virtually Abelian groups, and introduce a technique to reduce the quantum walk to an equivalent one on an Abelian group with coin system having larger dimension. We apply the technique in the case of two quantum walks on virtually Abelian groups with planar Cayley graphs, finding the exact solution.Comment: 10 pages, 3 figure