The Monte Carlo Program KORALZ, for the Lepton or Quark Pair Production at LEP/SLC Energies -- From version 4.0 to version 4.04

Brief information on new features of KORALZ version 4.04 with respect to version 4.0 is given. The main difference is that the new version could be used at LEP2 energies, i.e. up to 240 GeV centre-of-mass system energy. The possibility to switch on different classes of anomalous couplings is also included.Comment: 1+6 page

The Precision Monte Carlo Event Generator KK For Two-Fermion Final States In e+e- Collisions

We present the Monte Carlo event generator KK version 4.13 for precision predictions of the Electroweak Standard Model for the process $e^+e^-\to f\bar{f} +n\gamma$, $f=\mu,\tau,d,u,s,c,b$ at centre of mass energies from $\tau$ lepton threshold to 1TeV, that is for LEP, SLC, future Linear Colliders, $b,c,\tau$-factories etc. Effects due to photon emission from initial beams and outgoing fermions are calculated in QED up to second order, including all interference effects, within Coherent Exclusive Exponentiation (CEEX), which is based on Yennie-Frautschi-Suura exponentiation. Electroweak corrections are included in first order, with higher order extensions, using the DIZET 6.x library. Final state quarks hadronize according to the parton shower model using JETSET. Beams can be polarized longitudinally and transversely. Decay of the tau leptons is simulated using the TAUOLA library, taking into account spin polarization effects as well. In particular the complete spin correlations density matrix of the initial state beams and final state tau's is incorporated in an exact manner. Effects due to beamstrahlung are simulated in a realistic way. The main improvements with respect to KORALZ are: (a) inclusion of the initial-final state QED interference, (b) inclusion of the exact matrix element for two photons, and (c) inclusion of the transverse spin correlations in $\tau$ decays (as in KORALB).Comment: Source code available from http://home.cern.ch/jadac

Coherent Exclusive Exponentiation of 2f Processes in e+e- Annihilation

In the talk we present the Coherent Exclusive Exponentiation (CEEX) which is implemented in the KK MC event generator for the process e+e- to f bar f +n gamma, f=mu,tau,d,u,s,c,b for center of mass energies from tau lepton threshold to 1TeV, that is for LEP1, LEP2, SLC, future Linear Colliders, b,c,tau-factories etc. We will attempt a short discussion of the theoretical concepts necessary in our approach, in particular the relations between the rigorous calculation of spin amplitudes (perturbation expansion), phase space parametrisation and exponentiation. In CEEX effects due to photon emission from the initial beams and outgoing fermions are calculated in QED up to second-order, including all interference effects. Electroweak corrections are included in first-order, at the amplitude level. The beams can be polarised longitudinally and transversely, and all spin correlations are incorporated in an exact manner. Precision predictions, in particular the photon emission at LEP2 energies, are also shown.Comment: latex 9 pages, including 6 eps tables/figure

Global Positioning of Spin GPS Scheme for Half-Spin Massive Spinors

We present a simple and flexible method of keeping track of the complex phases and spin quantization axes for half-spin initial- and final-state Weyl spinors in scattering amplitudes of Standard Model high energy physics processes. Both cases of massless and massive spinors are discussed. The method is demonstrated and checked numerically for spin correlations in tau tau-bar production and decay. Its main application will be in the forthcoming work of combining effects due to multiple photon emission (exponentiation) and spin, embodied in the Monte Carlo event generators for production and decay of unstable fermions such as the tau lepton, t-quark and hypothetical new heavy particles.Comment: 13 pages, 1 eps figur

Inflation from Geometrical Tachyons

We propose an alternative formulation of tachyon inflation using the geometrical tachyon arising from the time dependent motion of a BPS $D3$-brane in the background geometry due to $k$ parallel $NS$5-branes arranged around a ring of radius $R$. Due to the fact that the mass of this geometrical tachyon field is $\sqrt{2/k}$ times smaller than the corresponding open-string tachyon mass, we find that the slow roll conditions for inflation and the number of e-foldings can be satisfied in a manner that is consistent with an effective 4-dimensional model and with a perturbative string coupling. We also show that the metric perturbations produced at the end of inflation can be sufficiently small and do not lead to the inconsistencies that plague the open string tachyon models. Finally we argue for the existence of a minimum of the geometrical tachyon potential which could give rise to a traditional reheating mechanism.Comment: Latex, 20 pages, 4 figures; correction of algebraic errors in section 5 concerning the tachyon potential near its minimum. Conclusions unchange

Emergent Phenomena in Spatially Confined Manganites

Rare earth manganites exhibit colossal magnetoresistance (CMR). There is evidence that alloyed single crystal materials in this class can display electronic inhomogeneity in which areas with vastly different electronic and magnetic properties can form and coexist in phase separated domains ranging in size from a few nanometers to micrometers. This phase separation (PS) is of particular interest, as it has been suggested that it is the central feature that leads to CMR in manganites, the Mott transition in VO2 and may play a role in high-TC superconductivity in cuprates. However there is debate as to its precise role. The purpose of my research is to answer fundamental questions about the specific role of PS in complex oxides. I reduce single crystal thin films of an electronically phase separated manganite to the scale of their inherent electronic phase domains near the metal-insulator transition. Unlike transport measurements done on bulk or thin films where the electrons follow only the metallic path of least resistance, this configuration forces electrons to travel through both the metallic and insulating regions residing in the material. This has led to observations of several new phenomena such as a reemergent metal-insulator transition, ultra-sharp jumps in resistivity at the metal-insulator transition, and the first high resolution observation of single domain electronic phase transitions in the time domain. While the manganites will be the primary focus throughout this dissertation, the spatial confinement techniques presented here are not limited to only these materials. They can be applied to any phase separated system to probe regions resistively hidden to transport measurements