Showing papers in "Annual Review of Nuclear and Particle Science in 2005"

Toward realistic intersecting d-brane models

Abstract: ▪ Abstract We provide a pedagogical introduction to a recently studied class of phenomenologically interesting string models known as Intersecting D-Brane Models. The gauge fields of the Standard Model are localized on D-branes wrapping certain compact cycles on an underlying geometry, whose intersections can give rise to chiral fermions. We address the basic issues and also provide an overview of the recent activity in this field. This article is intended to serve non-experts with explanations of the fundamental aspects of string phenomenology and also to provide some orientation for both experts and non-experts in this active field.

Leptogenesis as the origin of matter

Abstract: ▪ Abstract We explore in some detail the hypothesis that the generation of a primordial lepton-antilepton asymmetry (Leptogenesis) early on in the history of the Universe is the root cause for the origin of matter. After explaining the theoretical conditions for producing a matter-antimatter asymmetry in the Universe we detail how, through sphaleron processes, it is possible to transmute a lepton asymmetry—or, more precisely, a (B – L)-asymmetry—into a baryon asymmetry. Because Leptogenesis depends in detail on properties of the neutrino spectrum, we review briefly existing experimental information on neutrinos as well as the seesaw mechanism, which offers a theoretical understanding of why neutrinos are so light. The bulk of the review is devoted to a discussion of thermal Leptogenesis, and we show that for the neutrino spectrum suggested by oscillation experiments, one obtains the observed value for the baryon to photon density ratio in the Universe, independently of any initial boundary conditions. In ...

Femtoscopy in relativistic heavy ion collisions

Abstract: Analyses of two-particle correlations have provided the chief means for determining spatio-temporal characteristics of relativistic heavy ion collisions. We discuss the theoretical formalism behind these studies and the experimental methods used in carrying them out. Recent results from RHIC are put into context in a systematic review of correlation measurements performed over the past two decades. The current understanding of these results are discussed in terms of model comparisons and overall trends.

Little higgs theories

Abstract: ▪ Abstract Recently there has been renewed interest in the possibility that the Higgs particle of the Standard Model is a pseudo-Nambu-Goldstone boson. This development was spurred by the observation that if certain global symmetries are broken only by the interplay between two or more coupling constants, then the Higgs mass-squared is free from quadratic divergences at one loop. This collective symmetry breaking is the essential ingredient in little Higgs theories, which are weakly coupled extensions of the Standard Model with little or no fine tuning, describing physics up to an energy scale ∼10 TeV. Here we give a pedagogical introduction to little Higgs theories. We review their structure and phenomenology, focusing mainly on the SU(3) theory, the Minimal Moose, and the littlest Higgs as concrete examples.

Physics of Ultra-Peripheral Nuclear Collisions

Abstract: Moving highly-charged ions carry strong electromagnetic fields which act as a field of photons. In collisions at large impact parameters, hadronic interactions are not possible, and the ions interact through photon-ion and photon-photon collisions known as ultra-peripheral collisions (UPC). Hadron colliders like the Relativistic Heavy Ion Collider (RHIC), the Tevatron and the Large Hadron Collider (LHC) produce photonuclear and two-photon interactions at luminosities and energies beyond that accessible elsewhere; the LHC will reach a {gamma}p energy ten times that of the Hadron-Electron Ring Accelerator (HERA). Reactions as diverse as the production of anti-hydrogen, photoproduction of the {rho}{sup 0}, transmutation of lead into bismuth and excitation of collective nuclear resonances have already been studied. At the LHC, UPCs can study many types of ''new physics''.

ASCERTAINING THE CORE COLLAPSE SUPERNOVA MECHANISM: The State of the Art and the Road Ahead

Abstract: ▪ Abstract More than four decades have elapsed since modeling of the core collapse supernova mechanism began in earnest. To date, the mechanism remains elusive, at least in detail, although significant progress has been made in understanding these multiscale, multiphysics events. One-, two-, and three-dimensional simulations of or relevant to core collapse supernovae have shown that (a) neutrino transport, (b) fluid instabilities, (c) rotation, and (d) magnetic fields, together with proper treatments of (e) the sub- and super- nuclear density stellar core equation of state, (f) the neutrino interactions, and (g) gravity are all important. The importance of these ingredients applies to both the explosion mechanism and to phenomena directly associated with the mechanism, such as neutron star kicks, supernova neutrino and gravitational wave emission, and supernova spectropolarimetry. Not surprisingly, current two- and three-dimensional models have yet to include (a)–(d) with sufficient realism. One-dimension...

Blind Analysis in Nuclear and Particle Physics

Abstract: ▪ Abstract During the past decade, blind analysis has become a widely used tool in nuclear and particle physics measurements. A blind analysis avoids the possibility of experimenters biasing their result toward their own preconceptions by preventing them from knowing the answer until the analysis is complete. There is at least circumstantial evidence that such a bias has affected past measurements, and as experiments have become costlier and more difficult and hence harder to reproduce, the possibility of bias has become a more important issue than in the past. We describe here the motivations for performing a blind analysis, and give several modern examples of successful blind analysis strategies.

Study of the fundamental structure of matter with an electron-ion collider

Abstract: ▪ Abstract We present an overview of the scientific opportunities that would be offered by a high-energy electron-ion collider. We discuss the relevant physics of polarized and unpolarized electron-proton collisions and of electron-nucleus collisions. We also describe the current accelerator and detector plans for a future electron-ion collider. This review is dedicated to the memory of Professor Vernon W. Hughes.

SMALL-x PHYSICS: From HERA to LHC and Beyond

Abstract: ▪ Abstract We summarize the lessons learned from studies of hard scattering processes in high-energy electron-proton collisions at HERA and antiproton-proton collisions at the Tevatron, with the aim of predicting new strong interaction phenomena observable in next-generation experiments at the Large Hadron Collider (LHC). Processes reviewed include inclusive deep-inelastic scattering (DIS) at small x, exclusive and diffractive processes in DIS and hadron-hadron scattering, as well as color transparency and nuclear shadowing effects. A unified treatment of these processes is outlined on the basis of factorization theorems of quantum chromodynamics, and using the correspondence between the “parton” picture in the infinite-momentum frame and the “dipole” picture of high-energy processes in the target rest frame. The crucial role of the three dimensional quark and gluon structure of the nucleon is emphasized. A new dynamical effect predicted at high energies is the unitarity, or black disk, limit (BDL) in the...

Direct Photon Production in Relativistic Heavy-Ion Collisions

Abstract: ▪ Abstract We examine the uses of direct photons in diagnosing the highly excited state of nuclear matter created in high-energy nuclear collisions. The traditional focus has been on direct photons as thermal radiation from the excited state, but we also explore the many other roles direct photons can play. We review experimental and theoretical techniques as well as the history of direct photon measurements in heavy-ion collisions and their interpretation.

Fundamental neutron physics

Abstract: ▪ Abstract Experiments using slow neutrons address a growing range of scientific issues spanning nuclear physics, particle physics, astrophysics, and cosmology. The field of fundamental physics using neutrons has experienced a significant increase in activity over the last two decades. This review summarizes some of the recent developments in the field and outlines some of the prospects for future research.

Tools for the simulation of hard hadronic collisions

Abstract: ▪ Abstract This review gives a pedagogical introduction to the current status and ongoing progress in the development of QCD-based Monte Carlo tools for the calculation and simulation of high-Q2 processes in hadronic collisions.

FROM PIONS TO PROTON DECAY: Tales of the Unexpected

Abstract: ▪ Abstract This account recalls early observations of elementary particles from cosmic ray experiments, using the nuclear emulsion technique. Discoveries in this field in the 1940s and 50s led to the development of high energy particle accelerators and associated detectors, resulting eventually in the observation of the quark and lepton constituents of matter and of the fundamental interactions between them, as described in the Standard Model. The concept of unification of the fundamental interactions led to the prediction of proton decay, and although this has not been observed, the unwanted background due to atmospheric neutrino interactions led to the discovery of neutrino oscillations and neutrino mass, and the first indications of new physics beyond that of the Standard Model. In all this research, unexpected developments have often played an important role.