Parton distribution functions (PDFs) describe the structure of hadrons as composed of quarks and gluons. They are needed to make predictions for short-distance processes in high-energy collisions and are determined by fitting to cross section data. We review definitions of the PDFs and their relations to high-energy cross sections. We focus on the PDFs in protons, but also discuss PDFs in nuclei. We

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This article reviews experiments on elasticity, plasticity and ow of solid 4He and 3He, focusing on dislocations and other defects that are responsible for the unusual mechan-ical behavior of such quantum crystals. Heliums zero point motion prevents it from freezing unless pressure is applied, and makes the solid extremely compressible, with elastic constants orders of magnitude smaller than those

The statistical mechanical description of small systems staying in thermal equilibrium with an environment can be achieved by means of the Hamiltonian of mean force. In clear contrast to the reduced density matrix of an open quantum system, or the reduced phase space probability density function of a classical open system, the Hamiltonian of mean force does not only characterize the reduced state but

A few decades ago, quantum optics stood out as a new domain of physics by exhibiting states of light with no classical equivalent. The first investigations concerned single photons, squeezed states, twin beams and EPR states, that involve only one or two modes of the electromagnetic field. The study of the properties of quantum light then evolved in the direction of more and more complex and rich situations

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This paper is occasioned by the passing (in 2019) of the three decades that have followed the rst spectroscopic identication of the H+3 molecular ion outside of the laboratory, in the auroral atmosphere of the giant planet Jupiter. These decades have seen the astronomy related to this simple molecular ion expand enormously such that, in order to do justice to this being a review paper, we have had

The Sun is our nearest star; it is also the most important star that determines life on Planet Earth. A great variety of phenomena observed on the Sun’s surface, with potential impact on the Earth, is thought to arise from turbulent convection in Sun’s interior, this being the dominant mode of heat transport within the outer envelope at r & 0:715R. However, convection in the Sun dirs in nearly all

Quantum crystallization of 4He is a first-order phase transition from a superfluid liquid and can proceed extremely quickly at very low temperatures. The entropy difference between the two quantum phases, the quantum crystal and superfluid liquid, is small and atoms are carried to the crystal surface via a dissipationless superflow. A limiting process of the transition near absolute zero temperature

Fluid flows hosting electrical phenomena make the subject of a fascinating and highly interdisciplinary scientific field. In recent years, the extraordinary success of electrospinning and solution blowing technologies for the generation of polymer nanofibers has motivated vibrant research aiming at rationalizing the behavior of viscoelastic jets under applied electric fields or other stretching fields

Electronic transport properties of single-molecule junctions have been widely measured by several techniques, including mechanically controllable break junctions, electromigration break junctions or by means of scanning tunneling microscopes. In parallel, many theoretical tools have been developed and refined for describing such transport properties and for obtaining numerical predictions. Most prominent

The climate system is a forced, dissipative, nonlinear, complex and heterogeneous system that is out of thermodynamic equilibrium. The system exhibits natural variability on many scales of motion, in time as well as space, and it is subject to various external forcings, natural as well as anthropogenic. This paper reviews the observational evidence on climate phenomena and the governing equations of

This review article discusses the present status and development of strong-field nanooptics, an emerging field of nonlinear optics. An exciting non-perturbative regime of light-matter interactions is reached when the amplitude of the external electromagnetic fields that are driving a material approach or exceed the field strengths that bind the electrons inside the medium. In this strong-field regime

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Bell’s Theorem rules out many potential reformulations of quantum mechanics, but within a generalized framework, it does not exclude all locally-mediated models. Such models describe the correlations between entangled particles as mediated by intermediate parameters which track the particle world-lines and respect Lorentz covariance. These locally-mediated models require the relaxation of an arrow-of-time

In principle, quantum key distribution (QKD) offers information-theoretic security based on the laws of physics. In practice, however, the imperfections of realistic devices might introduce deviations from the idealized models used in security analyses. Can quantum code-breakers successfully hack real systems by exploiting the side channels? Can quantum code-makers design innovative counter-measures

The nuclear physics landscape has been redesigned as} a sequence of effective field theories (EFTs) connected to the Standard Model through symmetries and lattice simulations of Quantum Chromodynamics (QCD). EFTs in this sequence are expansions around different low-energy limits of QCD, each with its own characteristics, scales, and ranges of applicability regarding energy and number of nucleons. We

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Many biological functions are executed by molecular machines, which like man made motors consume energy and convert it into mechanical work. Biological machines have evolved to transport cargo, facilitate folding of proteins and RNA, remodel chromatin and replicate DNA. A common aspect of these machines is that their functions are driven by fuel provided by hydrolysis of ATP or GTP, thus driving them

Angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) have become indispensable tools in the study of correlated quantum materials. Both probe complementary aspects of the single-particle excitation spectrum. Taken together, ARPES and STM have the potential to explore properties of the electronic Green function, a central object of many-body theory. In this article

DOI:https://doi.org/10.1103/RevModPhys.91.049902

One of the most promising suggested applications of quantum computing is solving classically intractable chemistry problems. This may help to answer unresolved questions about phenomena like: high temperature superconductivity, solid-state physics, transition metal catalysis, or certain biochemical reactions. In turn, this increased understanding may help us to re ne, and perhaps even one day design

DOI:https://doi.org/10.1103/RevModPhys.91.049901

In this Colloquium, the wavefunction-based {M}ulticonfigurational {T}ime-{D}ependent {H}artree approaches to the dynamics of indistinguishable particles (MCTDH-F for {F}ermions and MCTDH-B for {B}osons) are reviewed. MCTDH-B and MCTDH-F or, together, MCTDH-X are methods for describing correlated quantum systems of identical particles by solving the time-dependent Schrdinger equation from first principles

For over 40 years, physicists have considered possible uses for neutrino detectors in nuclear nonproliferation, arms control, and fissile materials security. Neutrinos are an attractive fission signature because they readily pass through matter. The same property makes neutrinos challenging to detect in systems that would be practical for nuclear security applications. This colloquium presents a broad

Recent experiments have demonstrated that light and matter can mix together to an extreme degree, and previously uncharted regimes of light-matter interactions are currently being explored in a variety of settings. The so-called ultrastrong coupling (USC) regime is established when the light-matter interaction energy is a comparable fraction of the bare frequencies of the uncoupled systems. Furthermore

The fundamental coherent radiation emission processes from a bunched charged particles beam are outlined. In contrast to spontaneous emission of radiation from a random electron beam that is proportional to the number of particles, a prebunched electron beam can emit spontaneously coherent radiation proportional to the number of particles—squared, through the process of (spontaneous) superradiance

Ion transport through nanopores permeates through many areas of science and technology, from cell behavior to sensing and separation to catalysis and batteries. Two-dimensional materials, such as graphene, molybdenum disulfide (MoS2), and hexagonal boron nitride (hBN), are recent additions to these fields. Low-dimensional materials present new opportunities to develop filtration, sensing, and power

A theory of fractional electricity and magnetism is presented here which is capable of describing phenomena as disparate as the nonlocality of the Pippard kernel in superconductivity and anomalous dimensions for conserved currents in holographic dilatonic models. While it is a standard result in field theory that the scaling dimension of conserved currents and their associated gauge fields are determined

This review covers the modern era of experimental kaonic atom studies, encompassing 20 years of activity, defined by breakthroughs in technological developments which allowed performing a series of long-awaited precision measurements. Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing the strange quark, which interacts in the lowest orbits with the

Recently, many Earth-sized planets have been discovered around stars other than the Sun that might possess appropriate conditions for life. The development of theoretical methods for assessing the putative habitability of these worlds is of paramount importance, since it serves the dual purpose of identifying and quantifying what types of biosignatures may exist and determining the selection of optimal

Memory formation in matter is a theme of broad intellectual relevance; it sits at the interdisciplinary crossroads of physics, biology, chemistry, and computer science. Memory connotes the ability to encode, access, and erase signatures of past history in the state of a system. Once the system has completely relaxed to thermal equilibrium, it is no longer able to recall aspects of its evolution. The

Hybrid systems of laser-cooled trapped ions and ultracold atoms combined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics. This paper reviews the theoretical and experimental progress in research on cold hybrid ion-atom systems which aim to combine the best features of the two well-established fields. A broad overview is provided of

DOI:https://doi.org/10.1103/RevModPhys.91.030502

DOI:https://doi.org/10.1103/RevModPhys.91.030501

Spin-orbit coupling in inversion-asymmetric magnetic crystals and structures has emerged as a powerful tool to generate complex magnetic textures, interconvert charge and spin under applied current, and control magnetization dynamics. Current-induced spin-orbit torques mediate the transfer of angular momentum from the lattice to the spin system, leading to sustained magnetic oscillations or switching

Protein is matter of dual nature. As a physical object, a protein molecule is a folded chain of amino acids with diverse biochemistry. But it is also a point along an evolutionary trajectory determined by the function performed by the protein within a hierarchy of interwoven interaction networks of the cell, the organism, and the population. A physical theory of proteins therefore needs to unify both

Magnetism at low dimensions is a thriving field of research with exciting opportunities in technology. This Colloquium focuses on the properties of 1D magnetic systems on solid surfaces. From the emulation of 1D quantum phases to the potential realization of Majorana edge states, spin chains are unique systems to study. The advent of scanning tunneling microscope (STM) based techniques has permitted