International Journal of Modern Physics E

This public lecture is about 100 years of research on elementary particles and fundamental forces, beginning with the identification of the electron about 1900 and extending to the astonishing discovery of Dark Matter in the late 1900s. I talk about the elementary particle concept; the discoveries of leptons, quarks and force carrying particles; and some of the experimental technology used. I tell of my own research, our discovery of the tau lepton, our long, inconclusive search for fractional charged particles, and my new involvement in astronomical research on Dark Matter. I conclude by looking ahead to old unsolved puzzles and new questions on the fundamental nature of matter and force that face us in the 21st Century.

In this talk, I will describe results on 1,220 electron pairs produced from a ²⁰⁷Pb beam at 160A GeV in a nuclear experiment EMU 11 conducted at the CERN SPS. These electron pairs were produced at a distance of more than 50 μm from the primary interactions, which eliminates contamination due to Dalitz pairs. Results on electron pairs with invariant mass Q ranging between 1 and 100 MeV and life-time τ between 10⁻¹⁵ s and 10⁻¹² s were analyzed. After subtracting background pairs from the materialization of photons and from the decays of π₀ to photons from the data, they exhibit an enhancement at low mass Q = 6 – 20 MeV with narrow peaks at 7 ± 1 MeV, 19 ± 1 MeV and τ ≤ 10⁻¹³s.

The status of the physics of heavy ion collisions is reviewed based on measurements over the past 6 years from the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. The dense nuclear matter produced in Au+Au collisions with nucleon-nucleon c.m. energy at RHIC corresponds roughly to the density and temperature of the universe a few microseconds after the ‘big-bang’ and has been described as “a perfect liquid” of quarks and gluons, rather than the gas of free quarks and gluons, “the quark-gluon plasma” as originally envisaged. The measurements and arguments leading to this description will be presented.

In this contribution, we describe an investigation of the fractal nature of non-statistical fluctuations in the density distribution of singly charged secondary particles produced in ³²S-Ag/Br interactions in emulsion target at incident energy of 200A GeV. The experimental results have been compared with those obtained from an event sample simulated by the Lund Monte Carlo code FRITIOF. Besides obtaining the fractal dimensions and a smooth multifractal spectrum, show that the results can be used to determine universal parameters such as the Levy index, and the multifractal specific heat.

We are living in a Golden Age of Astronomy. Cosmological Parameters are found with an unprecedented accuracy comparable to high energy physics. Yet, the known form of matter forms only a small fraction of the total energy density of the universe. Also, a mysterious dark energy dominates the universe and causes acceleration in the rate of expansion. These findings raise new questions concerning the ultimate constitution of matter in the universe.

I discuss the motivations for, and the status of, precision calculations for the Large Hadron Collider (LHC) and the planned International Linear Collider (ILC).

Selected applications of perturbative Quantum chromodynamics (QCD) to predictions of the Standard Model for processes at high energy colliders are reviewed with emphasis on past successes and future problems.

Hawking radiation can be thought of as resulting from the breakdown of the vacuum into photon pairs due to the strong gravitational field at the bounding surface of black holes. We show how this argument can be made quantitative and obtain Hawking's result.

A brief review of the Bakamjian–Thomas method for constructing Poincaré invariant models of few-particle systems is presented. An application of the method to a simple model of the coupled N – πN – ππN system is outlined. This three-particle model contains vertex interactions as well as renormalization contributions.

I discuss the current status of inflationary cosmology in light of the recent WMAP 3-year data release. The basic predictions of inflation are all supported by the data. Inflation also makes predictions which are have not been well tested by current data but can be by future experiments, most notably a deviation from a scale-invariant power spectrum and the production of primordial gravitational waves. A scale-invariant spectrum is disfavored by current data, but not conclusively. Tensor modes are currently poorly constrained, and slow-roll inflation does not make an unambiguous prediction of the expected amplitude of primordial gravitational waves. A tensor/scalar ratio of r ≃ 0.01 is within reach of near-future measurements.

When a monkey is presented simultaneously two stimuli in the receptive field of a neuron in the visual cortex area V4, the neuron firing rate response is intermediate between the neuron response when both stimuli are presented alone. This phenomenon is called stimulus competition. To study its basic underlying neural mechanisms, we calculate the neuron firing rate response to different stimulus configurations. We find that stimulus competition can arise from the neuron's response properties alone, but only for a limited set of stimulus pair parameters. Furthermore, network properties may be important in modifying the inputs so that competition may occur for much wider sets of stimulus pairs.

We propose that a battle between two conflicting entities can be modeled as a kinematic problem on a lattice. We examine the parameters relevant to such simulations, and describe global patterns emerging from a lattice model of a conflict with a few simple rules. We conclude that models of this type display interesting and relevant properties and warrant more in-depth analysis. The focus in this work is on the role of knowledge of the “neighborhood” in winning a battle.

Multiple sclerosis (MS) is a chronic disabling disease of the central nervous system (CNS) that is characterized by lesions with inflammatory cells, axons with the insulating myelin sheath damaged, and axonal loss. The causes of MS are not known and there is as yet no cure. The purpose of this research was to evaluate a physically motivated network model for lesion formation in the brain. The parsimonious network model contained two elements: (i) a spatially spreading pathological process causing cell damage and death leading to neuro-degeneration and, (ii) generation of alarm signals by the damaged cells that lead to activation of programmed death of cells surrounding the lesions in an attempt to contain the spatial spread of the pathologic process. Simulation results with a range of network geometries indicated that the model was capable of describing lesion progression and arrest. The modeling results also demonstrated dynamical complexity with sensitivity to initial conditions.

A Feynman diagram generator, named FeynChois, is described. It provides the user with a full GUI (Graphical User Interface) environment which enables the generation diagrams automatically with several mouse operations. The diagram generator is built on an Application Programming Interface (API) called ViewableBeans which provides a framework for programming graphically representable objects. We also present a means for describing Feynman rules in a computer friendly manner using the XML (Extensible Markup Language) format.