The potential of a Super Flavor Factory (SFF) for searches of new physics is reviewed. While very high luminosity $B$ physics is assumed to be at the core of the program, its scope for extensive charm and $\tau$ studies are also emphasized. The possibility to run at the ${\rm Y}\left(5S\right)$ is also discussed; in principle, this could provide very clean measurements of $B_s$ decays. The strength and reach of a SFF are most notably due to the possibility of examining an impressive array of very clean observables. The angles and the sides of the unitarity triangle can be determined with unprecedented accuracy. These serve as a reference for new physics (NP) sensitive decays such as $B^{+}\to {\tau }^{+}{\nu }_{\tau }$ and penguin dominated hadronic decay modes, providing tests of generic NP scenarios with an accuracy of a few percent. Besides very precise studies of direct and time dependent $\mathit{CP}$ asymmetries in radiative $B$ decays and forward-backward asymmetry studies in $B\to X_s{\mathcal{l}}^{+}{\mathcal{l}}^{-}$ and numerous null tests using $B$, charm, and $\tau$ decays are also likely to provide powerful insights into NP. The dramatic increase in luminosity at a SFF will also open up entirely new avenues for probing NP observables, e.g., by allowing sensitive studies using theoretically clean processes such as $B\to X_s\nu \overline{\nu }$. The SFF is envisioned to be a crucial tool for essential studies of flavor in the CERN Large Hadron Collider era and will extend the reach of the Large Hadron Collider in many important ways.

The physical origin of the Casimir force is connected with the existence of zero-point and thermal fluctuations. The Casimir effect is very general and finds applications in various fields of physics. This review is limited to the rapid progress at the intersection of experiment and theory that has been achieved in the last few years. It includes a critical assessment of the proposed approaches to the resolution of the puzzles arising in the applications of the Lifshitz theory of the van der Waals and Casimir forces to real materials. All the primary experiments on the measurement of the Casimir force between macroscopic bodies and the Casimir-Polder force between an atom and a wall that have been performed in the last decade are reviewed, including the theory needed for their interpretation. The methodology for the comparison between experiment and theory in the force-distance measurements is presented. The experimental and theoretical results described here provide a deeper understanding of the phenomenon of dispersion forces in real materials and offer guidance for the application of the Lifshitz theory to the interpretation of the measurement results.

Effective field theory allows for a systematic and model-independent derivation of the forces between nucleons in harmony with the symmetries of quantum chromodynamics. The foundations of this approach are reviewed and its application for light nuclei at various resolution scales is discussed. The extension of this approach to many-body systems is sketched.

Recent progress in the field of a versatile and common system in soft matter physics, namely, star-shaped polyelectrolytes, is reviewed. These charged macromolecules combine in their properties aspects of polymer physics, colloidal science, and the rich physics of charged matter, rendering them into versatile building blocks for new materials as well as prototypes for studying the effects of softness in the behavior of colloidal suspensions. The approaches to the problem are manifold. Theoretical methods typically involve scaling theory, self-consistent field theory, and variational free-energy calculations, while computer simulations play an important role in enhancing our understanding of the physics involved. Experiments, based mostly on scattering, offer insights from a different point of view. Finally, the flexibility in the synthesis of novel types of macromolecules has added to the richness and the increased activity in the field in the last few years. This review puts emphasis on theory and simulation but takes into account the key experimental findings in critically discussing the merits and shortcomings of the former. The perspectives opened for the future, with emphasis on the possibilities to steer the behavior of novel materials, are also discussed.

This Colloquium examines the field of the Einstein, Podolsky, and Rosen (EPR) gedanken experiment, from the original paper of Einstein, Podolsky, and Rosen, through to modern theoretical proposals of how to realize both the continuous-variable and discrete versions of the EPR paradox. The relationship with entanglement and Bell’s theorem are analyzed, and the progress to date towards experimental confirmation of the EPR paradox is summarized, with a detailed treatment of the continuous-variable paradox in laser-based experiments. Practical techniques covered include continuous-wave parametric amplifier and optical fiber quantum soliton experiments. Current proposals for extending EPR experiments to massive-particle systems are discussed, including spin squeezing, atomic position entanglement, and quadrature entanglement in ultracold atoms. Finally, applications of this technology to quantum key distribution, quantum teleportation, and entanglement swapping are examined.

This Colloquium reviews statistical models for money, wealth, and income distributions developed in the econophysics literature since the late 1990s. By analogy with the Boltzmann-Gibbs distribution of energy in physics, it is shown that the probability distribution of money is exponential for certain classes of models with interacting economic agents. Alternative scenarios are also reviewed. Data analysis of the empirical distributions of wealth and income reveals a two-class distribution. The majority of the population belongs to the lower class, characterized by the exponential (“thermal”) distribution, whereas a small fraction of the population in the upper class is characterized by the power-law (“superthermal”) distribution. The lower part is very stable, stationary in time, whereas the upper part is highly dynamical and out of equilibrium.

Fluctuation theorems (FTs), which describe some universal properties of nonequilibrium fluctuations, are examined from a quantum perspective and derived by introducing a two-point measurement on the system. FTs for closed and open systems driven out of equilibrium by an external time-dependent force, and for open systems maintained in a nonequilibrium steady state by nonequilibrium boundary conditions, are derived from a unified approach. Applications to fermion and boson transport in quantum junctions are discussed. Quantum master equations and Green’s functions techniques for computing the energy and particle statistics are presented.

Accurate x-ray scattering techniques to measure the physical properties of dense plasmas have been developed for applications in high energy density physics. This class of experiments produces short-lived hot dense states of matter with electron densities in the range of solid density and higher where powerful penetrating x-ray sources have become available for probing. Experiments have employed laser-based x-ray sources that provide sufficient photon numbers in narrow bandwidth spectral lines, allowing spectrally resolved x-ray scattering measurements from these plasmas. The backscattering spectrum accesses the noncollective Compton scattering regime which provides accurate diagnostic information on the temperature, density, and ionization state. The forward scattering spectrum has been shown to measure the collective plasmon oscillations. Besides extracting the standard plasma parameters, density and temperature, forward scattering yields new observables such as a direct measure of collisions and quantum effects. Dense matter theory relates scattering spectra with the dielectric function and structure factors that determine the physical properties of matter. Applications to radiation-heated and shock-compressed matter have demonstrated accurate measurements of compression and heating with up to picosecond temporal resolution. The ongoing development of suitable x-ray sources and facilities will enable experiments in a wide range of research areas including inertial confinement fusion, radiation hydrodynamics, material science, or laboratory astrophysics.

Intermetallic compounds containing $f$-electron elements display a wealth of superconducting phases, which are prime candidates for unconventional pairing with complex order parameter symmetries. For instance, superconductivity has been found at the border of magnetic order as well as deep within ferromagnetically and antiferromagnetically ordered states, suggesting that magnetism may promote rather than destroy superconductivity. Superconducting phases near valence transitions or in the vicinity of magnetopolar order are candidates for new superconductive pairing interactions such as fluctuations of the conduction electron density or the crystal electric field, respectively. The experimental status of the study of the superconducting phases of $f$-electron compounds is reviewed.

The direct observation of spin structures with atomic-scale resolution, a long-time dream in condensed matter research, recently became a reality based on the development of spin-sensitive scanning probe methods, such as spin-polarized scanning-tunneling microscopy (SP-STM) and magnetic exchange force microscopy (MExFM). This article reviews the basic principles and methods of SP-STM and MExFM and describes recently achieved milestones in the application of these techniques to metallic and electrically insulating magnetic nanostructures. Discoveries of novel types of magnetic order at the nanoscale are presented as well as challenges for the future, including studies of local spin excitations based on spin-resolved inelastic tunneling spectroscopy and measurements of damping forces in MExFM experiments.

The structure and thermodynamic state of a system changes under the influence of external electric fields. Neutral systems are characterized by their dielectric constant $\epsilon$, while charged ones also by their charge distribution. In this Colloquium several phenomena occurring in soft-matter systems in spatially uniform and nonuniform fields are surveyed and the role of the conductivity $\sigma$ and the linear or nonlinear dependency of $\epsilon$ on composition are identified. Uniform electric fields are responsible for elongation of droplets, for destabilization of interfaces between two liquids, and for mixing effects in liquid mixtures. Electric fields, when acting on phases with mesoscopic order, also give rise to block-copolymer orientation, to destabilization of polymer-polymer interfaces, and to order-order phase transitions. The role of linear and nonlinear dependences of $\epsilon$ on composition will be elucidated in these systems. In addition to the dielectric anisotropy, existence of a finite conductivity leads to appearance of large stresses when these systems are subject to external fields and usually to a reduction in the voltages required for the instabilities or phase transitions to occur. Finally, phase transitions which occur in nonuniform fields are described and emphasis on the importance of $\epsilon$ and $\sigma$ is given.

Intergalactic space is filled with a pervasive medium of ionized gas, the intergalactic medium (IGM). A residual neutral fraction is detected in the spectra of quasistellar objects at both low and high redshifts, revealing a highly fluctuating medium with temperatures characteristic of photoionized gas. The statistics of the fluctuations are well reproduced by numerical gravity-hydrodynamics simulations within the context of standard cosmological structure formation scenarios. Thus, the study of the IGM offers an opportunity to probe the nature of the primordial density fluctuations on scales unavailable to other methods. The simulations also suggest that the IGM is the dominant reservoir of baryons produced by the Big Bang, and so the principal source of the matter from which galaxies formed. The detection of metal systems within the IGM shows that it was enriched by evolved stars early in its history, demonstrating an intimate connection between galaxy formation and the IGM. A comprehensive review of the current understanding of the structure and physical properties of the IGM and its relation to galaxies is presented, concluding with comments on prospects for furthering the study of the IGM using future ground-based facilities and space-based experiments.

Complex (dusty) plasmas are composed of a weakly ionized gas and charged microparticles and represent the plasma state of soft matter. Complex plasmas have several remarkable features: Dynamical time scales associated with microparticles are “stretched” to tens of milliseconds, yet the microparticles themselves can be easily visualized individually. Furthermore, since the background gas is dilute, the particle dynamics in strongly coupled complex plasmas is virtually undamped, which provides a direct analogy to regular liquids and solids in terms of the atomistic dynamics. Finally, complex plasmas can be easily manipulated in different ways—also at the level of individual particles. Altogether, this gives us a unique opportunity to go beyond the limits of continuous media and study—at the kinetic level—various generic processes occurring in liquids or solids, in regimes ranging from the onset of cooperative phenomena to large strongly coupled systems. In the first part of the review some of the basic and new physics are highlighted which complex plasmas enable us to study, and in the second (major) part strong coupling phenomena in an interdisciplinary context are examined. The connections with complex fluids are emphasized and a number of generic liquid and solid-state issues are addressed. In summary, application oriented research is discussed.

Quantum key distribution (QKD) is the first quantum information task to reach the level of mature technology, already fit for commercialization. It aims at the creation of a secret key between authorized partners connected by a quantum channel and a classical authenticated channel. The security of the key can in principle be guaranteed without putting any restriction on an eavesdropper’s power. This article provides a concise up-to-date review of QKD, biased toward the practical side. Essential theoretical tools that have been developed to assess the security of the main experimental platforms are presented (discrete-variable, continuous-variable, and distributed-phase-reference protocols).

After the fundamental structure of semicrystalline polymers—platelike crystallites with thicknesses in the nanometer range, embedded in a liquid matrix—was discovered in the late 1950s, attention turned to the mechanism of formation. After intense controversial discussions, an approach put forward by Hoffman and Lauritzen prevailed and was broadly accepted. The picture envisaged by the treatment—platelike crystallites with atomically smooth side faces and a surface occupied by chain folds, growing sideways layer by layer with a secondary nucleation as the rate-determining step—was easy to grasp and yielded simple relationships. The main control parameter is the supercooling below the equilibrium melting point of a macroscopic crystal $T_f^{\infty }$, which determines both the thickness of the crystallites and their lateral growth rate. The impression that the mechanism of polymer crystallization was understood and the issue essentially settled, however, was wrong. Experiments carried out during the last decade on various polymer systems provided new insights which are now completely changing our understanding of such systems. They revealed a number of laws that control polymer crystallization and melting in bulk, showing in particular that the crystal thickness is inversely proportional to the distance to a temperature $T_c^{\infty }$ which is located above the equilibrium melting point, and that crystal growth stops at a temperature $T_{\mathrm{zg}}$ which is below $T_f^{\infty }$. Observations indicate that the pathway followed in the growth of polymer crystallites includes an intermediate metastable phase. In a proposed model a thin layer with mesomorphic inner structure forms between the lateral crystal face and the melt. The first step in the growth process is attachment of the coiled chain sequences of the melt onto the mesomorphic layer, which subsequently is transformed into the crystalline state. The transitions between melt, mesomorphic layers, and lamellar crystallites can be described with the aid of a temperature-thickness phase diagram. $T_c^{\infty }$ and $T_{\mathrm{zg}}$ are identified with the temperatures of the (hidden) transitions between the mesomorphic and the crystalline phase, and between the liquid and the mesomorphic phase, respectively. Comparing predictions of the model theory with experimental results from small-angle x-ray scattering, optical microscopy, and calorimetry yields in addition to the three equilibrium transition temperatures latent heats of transition and surface free energies.

Laser-driven plasma-based accelerators, which are capable of supporting fields in excess of $100\mathrm{GV}∕\mathrm{m}$, are reviewed. This includes the laser wakefield accelerator, the plasma beat wave accelerator, the self-modulated laser wakefield accelerator, plasma waves driven by multiple laser pulses, and highly nonlinear regimes. The properties of linear and nonlinear plasma waves are discussed, as well as electron acceleration in plasma waves. Methods for injecting and trapping plasma electrons in plasma waves are also discussed. Limits to the electron energy gain are summarized, including laser pulse diffraction, electron dephasing, laser pulse energy depletion, and beam loading limitations. The basic physics of laser pulse evolution in underdense plasmas is also reviewed. This includes the propagation, self-focusing, and guiding of laser pulses in uniform plasmas and with preformed density channels. Instabilities relevant to intense short-pulse laser-plasma interactions, such as Raman, self-modulation, and hose instabilities, are discussed. Experiments demonstrating key physics, such as the production of high-quality electron bunches at energies of $0.1–1\mathrm{GeV}$, are summarized.

The $\mathrm{U}{\left(1\right)}^{\prime }$ symmetry associated with a possible heavy $Z^{\prime }$ would have profound implications for particle physics and cosmology. The motivations for such particles in various extensions of the standard model, possible ranges for their masses and couplings, and classes of anomaly-free models are discussed. Present limits from electroweak and collider experiments are briefly surveyed, as are prospects for discovery and diagnostic study at future colliders. Implications of a $Z^{\prime }$ are discussed, including an extended Higgs sector, extended neutralino sector, and solution to the $\mu$ problem in supersymmetry; exotic fermions needed for anomaly cancellation; possible flavor changing neutral current effects; neutrino mass; possible $Z^{\prime }$ mediation of supersymmetry breaking; and cosmological implications for cold dark matter and electroweak baryogenesis.

The dynamics and stability of thin liquid films have fascinated scientists over many decades: the observations of regular wave patterns in film flows down a windowpane or along guttering, the patterning of dewetting droplets, and the fingering of viscous flows down a slope are all examples that are familiar in daily life. Thin film flows occur over a wide range of length scales and are central to numerous areas of engineering, geophysics, and biophysics; these include nanofluidics and microfluidics, coating flows, intensive processing, lava flows, dynamics of continental ice sheets, tear-film rupture, and surfactant replacement therapy. These flows have attracted considerable attention in the literature, which have resulted in many significant developments in experimental, analytical, and numerical research in this area. These include advances in understanding dewetting, thermocapillary- and surfactant-driven films, falling films and films flowing over structured, compliant, and rapidly rotating substrates, and evaporating films as well as those manipulated via use of electric fields to produce nanoscale patterns. These developments are reviewed in this paper and open problems and exciting research avenues in this thriving area of fluid mechanics are also highlighted.