Annual Review of Nuclear and Particle Science - Volume 60, 2010

Electromagnetic form factors have long been used to probe the underlying charge and magnetization densities of hadrons and nuclei. Traditional three-dimensional Fourier transform methods are not rigorously applicable for systems with constituents that move relativistically. The use of the transverse charge density is a new, rigorously defined way to analyze electromagnetic form factors of hadrons. This review is concerned with the following issues: what a transverse charge density is, how one is extracted from elastic scattering data, the existing results, its relationship with other observable quantities, and future prospects.

Reheating is an important part of inflationary cosmology. It describes the production of Standard Model particles after the phase of accelerated expansion. We review the reheating process with a focus on an in-depth discussion of the preheating stage, which is characterized by exponential particle production due to a parametric resonance or tachyonic instability. We give a brief overview of the thermalization process after preheating and end with a survey of some applications to supersymmetric theories and to other issues in cosmology, such as baryogenesis, dark matter, and metric preheating.

Nuclear astrophysics strives for a comprehensive picture of the nuclear reactions responsible for synthesizing chemical elements and for powering the stellar evolution engine. Deep underground in the Gran Sasso National Laboratory, the cross sections of the key reactions of the proton-proton chain and of the carbon-nitrogen-oxygen cycle have been measured right down to the energies of astrophysical interest. The salient features of underground nuclear astrophysics are summarized here. We review the main results obtained by LUNA during the past 20 years and discuss their influence on our understanding of the properties of the neutrino, the Sun, and the universe itself. Future directions of underground nuclear astrophysics toward the study both of helium and carbon burning and of stellar neutron sources in stars are outlined.

Recent breakthroughs in the field of numerical relativity have led to dramatic progress in understanding the predictions of general relativity for the dynamical interactions of two black holes in the regime of very strong gravitational fields. Such black-hole binaries are important astrophysical systems and are a key target of current and developing gravitational-wave detectors. The waveform signature of strong gravitational radiation emitted as the black holes fall together and merge provides a clear, observable record of the process. After decades of slow progress, these mergers and the gravitational-wave signals they generate can now be routinely calculated using the methods of numerical relativity. We review recent advances in understanding the predicted physics of events and the consequent radiation and discuss some of the impacts of this new knowledge in various areas of astrophysics.

The electron-proton collider HERA at DESY in Hamburg, Germany, delivered luminosity from 1992 to 2007. The center-of-mass energy was a factor of ten higher compared to previous lepton-nucleon scattering experiments. The research at HERA emphasized precision analyses of the proton structure at small x and high Q². In addition, precision tests of QCD provided significant new insights into the strong force. Diffractive scattering plays an important role in hard interactions. Many searches for new physics were performed at the electron-proton energy frontier. Additionally, two fixed-target experiments that used only the electron and proton beams of HERA, respectively, studied the spin structure of the nucleon and the production of strangeness, charm, and bottom in high-energy proton collisions. This review summarizes key results obtained by the four experiments at HERA: H1, ZEUS, HERMES, and HERA-B.

We review the search for astrophysical neutrinos. We begin by summarizing the various theoretical predictions that correlate the expected neutrino flux with data from other messengers, specifically γ rays and ultrahigh-energy cosmic rays. We then review the status and results of neutrino telescopes both in operation and decommissioned as well as the methods used for data analysis and background discrimination. Particular attention is devoted to the challenge enforced by the highly uncertain atmospheric muon and neutrino backgrounds in relation to searches of diffuse neutrino fluxes. Next, we examine the impact of existing limits on neutrino fluxes on studies of the chemical composition of cosmic rays. After that, we show not only that neutrinos have the potential to discover astrophysical sources, but also that the huge statistics of atmospheric muons can be a powerful tool. We end by discussing the prospects for indirect detection of dark matter with neutrino telescopes.

A new laboratory for astroparticle physics has been created in the Creighton Mine near Sudbury, Ontario, Canada. The laboratory is located at a great depth to provide shielding from the cosmic-ray backgrounds, and it has been constructed as a clean room to protect experiments from radioactive dust contamination. In this review, we discuss the motivation for the establishment of the laboratory and the design and construction process. We also introduce the initial suite of experiments.

We present an overview of recent developments, based on on-shell techniques, in the calculation of multiparton scattering amplitudes at one loop that are relevant for phenomenological studies at hadron colliders. These new on-shell methods make efficient use of the physical properties of the hard scattering, such as unitarity and factorization.

Particles with resonant short-range interactions have universal properties that do not depend on the details of their structure or their interactions at short distances. In the three-body system, these properties include the existence of a geometric spectrum of three-body Efimov states and a discrete scaling symmetry, which leads to log-periodic dependence of observables on the scattering length. Similar universal properties appear in the four-body system and possibly higher-body systems as well. For example, universal four-body states have recently been predicted and observed in experiments. These phenomena are often referred to as Efimov physics. We review their theoretical description and discuss applications in different areas of physics with a special emphasis on nuclear and particle physics.

We review recent progress in realizing Grand Unified Theories (GUTs) in a strongly coupled formulation of type IIB string theory known as F-theory. This review's main emphasis is on the expected low-energy phenomenology of a minimal class of F-theory GUTs. We introduce the primary ingredients in such constructions, then present qualitative features of GUT models in this framework such as GUT breaking, doublet-triplet splitting, and proton decay. Next, we review proposals for realizing flavor hierarchies in the quark and lepton sectors. We discuss possible supersymmetry-breaking scenarios and their consequences for experiments, as well as geometrically minimal realizations of F-theory GUTs that incorporate most of these features.

Jets have been used to verify the theory of quantum chromodynamics (QCD), measure the structure of the proton, and search for physics beyond the Standard Model. In this article, we review the current status of jet physics at the Tevatron, a TeV collider at the Fermi National Accelerator Laboratory. We report on recent measurements of the inclusive jet production cross section, dijet production measurements, and the results of searches for physics beyond the Standard Model using jets.

The ultimate goal of neutrino oscillation physics is the search for leptonic CP violation, which will require neutrino beams that are much more intense and pure than those used in present experiments. Beta beams are an attractive innovative possibility in this direction. Neutrinos are generated by the beta decays of radioactive nuclei and are accelerated at very high energies. The resulting neutrino beam consists of only one easily predictable flavor of neutrinos (ve or ). A realistic beta beam design, which has already been demonstrated by the Eurisol Design Study, is based on CERN's PS and SPS accelerators. The beta beam concept has also been extended in several other directions, including high energy, high Q, electron capture, and low energy. Both the accelerator complex and the physics potential of a neutrino experiment are reviewed here. We emphasize the beta beam design based on the CERN PS and SPS, but we also discuss other possibilities.

A new generation of experiments is studying muon capture on hydrogen, deuterium, and ³He with significantly improved precision using a novel active-target method. At the same time, chiral effective field theories (EFTs) allow the calculation of low-energy electroweak observables on protons and the simplest nuclei within a rigorous quantum chromodynamics (QCD)-based framework. This experimental and theoretical progress significantly enhances our understanding of the axial current. In the case of the nucleon, the unambiguous experimental determination of the pseudoscalar coupling gP clarifies a long-standing puzzle and provides a basic test of QCD at low energies. In the case of deuterium and ³He, the new precision data allow a comprehensive test of EFT calculations of weak few-body reactions and determine an essential low-energy constant relevant for related astrophysics reactions of fundamental interest.

Over the past decade, much progress in experimentally measuring and theoretically understanding flavor physics has been achieved. Specifically, the accuracy of the determination of the CKM elements has been greatly improved, and a large number of (a) flavor-changing neutral-current processes involving b→d, b→s, and c→u transitions and (b) CP-violating asymmetries have been measured. No evidence for new physics has been established. Consequently, strong constraints on new physics at a high scale apply. In particular, the flavor structure of new physics at the teraelectronvolt scale is strongly constrained. We review these constraints and discuss future prospects to better understand the flavor structure of physics beyond the Standard Model.

New experimental methods and techniques, combined with the development of new theoretical tools, have opened new avenues to explore nuclear reactions of significance for nucleosynthesis at or near the actual temperatures of stellar burning. In particular, many reactions of the cold and hot CNO cycles have been investigated in recent years to provide a complete understanding of this critical hydrogen-burning mechanism in stars and stellar explosions. This has led to new interpretations of or new signatures for a number of critical hydrogen-burning environments and events. This article provides a summary of the most recent discoveries and results associated with CNO reactions, and it identifies existing shortcomings in the data as well as needs and opportunities for additional future experiments.

Most embeddings of the Standard Model into a more unified theory, in particular those based on supergravity or superstrings, predict the existence of a hidden sector of particles that have only very weak interactions with visible-sector Standard Model particles. Some of these exotic particle candidates [for instance, axions, axion-like particles, and hidden U(1) gauge bosons] may be very light, with masses in the subelectronvolt range, and may have very weak interactions with photons. Correspondingly, these very weakly interacting subelectronvolt particles (WISPs) may lead to observable effects in experiments (as well as in astrophysical and cosmological observations) searching for light shining through a wall, for changes in laser polarization, for nonlinear processes in large electromagnetic fields, and for deviations from Coulomb's law. We present the physics case and a status report of this emerging low-energy frontier of fundamental physics.

The diffuse supernova neutrino background (DSNB) is the weak glow of megaelectronvolt neutrinos and antineutrinos from distant core-collapse supernovae. The DSNB has not been detected yet, but the Super-Kamiokande (SK) 2003 upper limit on the flux is close to predictions, now quite precise, that are based on astrophysical data. If SK is modified with dissolved gadolinium to reduce detector backgrounds and increase the energy range for analysis, then it should detect the DSNB at a rate of a few events per year, providing a new probe of supernova neutrino emission and the cosmic core-collapse rate. If the DSNB is not detected, then new physics will be required. Neutrino astronomy, although uniquely powerful, has proven extremely difficult—only the Sun and the nearby Supernova 1987A have been detected to date—so the promise of detecting new sources soon is exciting indeed.

We provide a broad overview of the theoretical status and phenomenological applications of the color glass condensate effective field theory, which describes universal properties of saturated gluons in hadron wave functions that are extracted from deep-inelastic scattering and hadron-hadron collision experiments at high energies.

We review recent works on supersymmetry breaking and gauge mediation. We survey our current understanding of dynamical supersymmetry-breaking mechanisms and describe new model-building tools that use duality, metastability, and stringy construction. We discuss phenomenological constraints and their solutions, paying particular attention to gaugino masses and electroweak symmetry breaking.

Particle physics experiments at the intensity frontier aim to probe nature through precision studies of the properties and interactions of its basic constituents, using intense particle beams and innovative detectors. We review the physics potential of several of these experiments, especially those that can be very effectively pursued at Fermilab in the near and intermediate future, assuming that a new intense proton source—Project X—will be available. We concentrate on flavor-violating phenomena that have been identified as the main particle physics drivers for Project X: the study of neutrino masses and mixing through long-baseline neutrino oscillations; searches for rare, flavor-violating muon processes; and precision measurements of kaon decays into neutrinos, . We also comment on other opportunities, such as measurements of the anomalous magnetic moment of muon and neutrino-matter scattering.