The cell, as the most fundamental unit of life, is a microcosm of biology in which the confluence of nearly all aspects of classical physics (mechanics, statistical physics, condensed matter, and electromagnetism) plays out. This leads to a rich and complex emergent behavior that determines the entire gamut of biological functions. Specifically, at the cellular scale, mechanical forces and deformations are inextricably linked to electrical fields (and, to a lesser degree, magnetic fields). This in turn is responsible for phenomenology such as cell-cell communication, morphological evolution, cell fusion, self-assembly, cell fission, magnetoreception, endocytosis, and adhesion, among others. From the viewpoint of biomedicine, cellular response to the combined influence of electrical, magnetic, and mechanical fields has applications in cancer treatment, targeted transfer of medicine, gene therapy, and wound amelioration. As an example of the profound influence of the combined electrical-mechanical coupling, one needs to take cognizance only of the operation of ion channels that form the basis for our sensing system (such as hearing, sight, and tactile sense). The coupled mechanical and electromagnetic behavior of a cell is a highly interdisciplinary endeavor and this review provides a distillation of both the theoretical underpinnings of the subject and the pertinent biological interpretation. The key developments pertaining to this topic are reviewed, a unified mathematical framework that couples nonlinear deformation and electromagnetic behavior as germane for soft biological entities is summarized, gaps in current knowledge are pointed out, and the central issues that are pertinent to future research are commented upon.

Interfacial thermal resistance (ITR) is the main obstacle for heat flows from one material to another. Understanding ITR becomes essential for the removal of redundant heat from fast and powerful electronic and photonic devices, batteries, etc. In this review, a comprehensive examination of ITR is conducted. Particular focus is placed on the theoretical, computational, and experimental developments in the 30 years after the last review given by Swartz and Pohl in 1989. To be self-consistent, the fundamental theories, such as the acoustic mismatch model, the diffuse mismatch model, and the two-temperature model, are reviewed. The most popular computational methods, including lattice dynamics, molecular dynamics, the Green’s function method, and the Boltzmann transport equation method, are discussed in detail. Various experimental tools in probing ITR, such as the time-domain thermoreflectance, the thermal bridge method, the $3\omega$ method, and the electron-beam self-heating method, are illustrated. This review covers ITR (also known as the thermal boundary resistance or Kapitza resistance) of solid-solid, solid-liquid, and solid-gas interfaces. Such fundamental challenges as how to define the interface, temperature, etc. when the materials scale down to the nanoscale or atomic scale and the opportunities for future studies are also pointed out.

The new era of gravitational wave astronomy truly began on September 14, 2015, with the detection of GW150914, the sensational first direct observation of gravitational waves from the inspiral and merger of two black holes by the two Advanced LIGO detectors. In the subsequent first three observing runs of the LIGO-Virgo network, gravitational waves from $\sim 50$ compact binary mergers have been announced, with more results to come. The events have mostly been produced by binary black holes, but two binary neutron star mergers have been observed thus far, as well as the mergers of two neutron star–black hole systems. Furthermore, gravitational waves emitted by core-collapse supernovae, pulsars, and the stochastic gravitational wave background are within the LIGO-Virgo-KAGRA sensitivity band and are likely to be observed in future observation runs. Beyond signal detection, a major challenge has been the development of statistical and computational methodology for estimating the physical waveform parameters and quantifying their uncertainties in order to accurately characterize the emitting system. These methods depend on the sources of the gravitational waves and the gravitational waveform model that is used. This review examines the main waveform models and parameter estimation methods used to extract physical parameters from gravitational wave signals detected to date by LIGO and Virgo and from those expected to be observed in the future, which will include KAGRA, and how these methods interface with various aspects of LIGO-Virgo-KAGRA science. Also presented are the statistical methods used by LIGO and Virgo to estimate detector noise, test general relativity, and draw conclusions about the rates of compact binary mergers in the Universe. Furthermore, a summary of major publicly available gravitational wave parameter estimation software packages is given.

The rich and diverse dynamics of particle-based systems ultimately originates from the coupling of their degrees of freedom via internal interactions. To arrive at a tractable approximation of such many-body problems, coarse graining is often an essential step. Power functional theory provides a unique and microscopically sharp formulation of this concept. The approach is based on an exact one-body variational principle to describe the dynamics of both overdamped and inertial classical and quantum many-body systems. In equilibrium, density-functional theory is recovered, and hence spatially inhomogeneous systems are described correctly. The dynamical theory operates on the level of time-dependent one-body correlation functions. Two- and higher-body correlation functions are accessible via the dynamical test-particle limit and the nonequilibrium Ornstein-Zernike route. The structure of this functional approach to many-body dynamics is described, including much background as well as applications to a broad range of dynamical situations, such as the van Hove function in liquids, flow in nonequilibrium steady states, motility-induced phase separation of active Brownian particles, lane formation in binary colloidal mixtures, and both steady and transient shear phenomena.

The Monte Carlo evaluation of path integrals is one of a few general purpose methods to approach strongly coupled systems. It is used in all branches of physics, from QCD and nuclear physics to the correlated electron systems. However, many systems of great importance (dense matter inside neutron stars, the repulsive Hubbard model away from half filling, and dynamical and nonequilibrium observables) are not amenable to the Monte Carlo method as it currently stands due to the so-called sign problem. A new set of ideas recently developed to tackle the sign problem based on the complexification of field space and the Picard-Lefshetz theory accompanying it is reviewed. The mathematical ideas underpinning this approach, as well as the algorithms developed thus far, are described together with nontrivial examples where the method has already been proved successful. Directions of future work, including the burgeoning use of machine learning techniques, are delineated.

The ongoing transition to renewable energy supply comes with a restructuring of power grids, changing their effective interaction topologies, more and more strongly decentralizing them and substantially modifying their input, output, and response characteristics. All of these changes imply that power grids become increasingly affected by collective, nonlinear dynamic phenomena, structurally and dynamically more distributed and less predictable in space and time, more heterogeneous in its building blocks, and as a consequence less centrally controllable. Here cornerstone aspects of data-driven and mathematical modeling of collective dynamical phenomena emerging in real and model power grid networks by combining theories from nonlinear dynamics, stochastic processes and statistical physics, anomalous statistics, optimization, and graph theory are reviewed. The mathematical background required for adequate modeling and analysis approaches is introduced, an overview of power system models is given, and a range of collective dynamical phenomena are focused on, including synchronization and phase locking, flow (re)routing, Braess’s paradox, geometric frustration, and spreading and localization of perturbations and cascading failures, as well as the nonequilibrium dynamics of power grids, where fluctuations play a pivotal role.

A universal fault-tolerant quantum computer that can efficiently solve problems such as integer factorization and unstructured database search requires millions of qubits with low error rates and long coherence times. While the experimental advancement toward realizing such devices will potentially take decades of research, noisy intermediate-scale quantum (NISQ) computers already exist. These computers are composed of hundreds of noisy qubits, i.e., qubits that are not error corrected, and therefore perform imperfect operations within a limited coherence time. In the search for achieving quantum advantage with these devices, algorithms have been proposed for applications in various disciplines spanning physics, machine learning, quantum chemistry, and combinatorial optimization. The overarching goal of such algorithms is to leverage the limited available resources to perform classically challenging tasks. In this review, a thorough summary of NISQ computational paradigms and algorithms is provided. The key structure of these algorithms and their limitations and advantages are discussed. A comprehensive overview of various benchmarking and software tools useful for programming and testing NISQ devices is additionally provided.

The study of lepton flavor universality violation (LFUV) in semitauonic $b$-hadron decays has become increasingly important in light of long-standing anomalies in their measured branching fractions, and the large datasets anticipated from the LHC experiments and Belle II. In this review, a comprehensive survey of the experimental environments and methodologies for semitauonic LFUV measurements at the $B$ factories and LHCb is undertaken, along with an overview of the theoretical foundations and predictions for a wide range of semileptonic decay observables. The future prospects of controlling systematic uncertainties down to the percent level, matching the precision of standard model (SM) predictions, are examined. Furthermore, new perspectives and caveats on combinations of the LFUV data are discussed and the world averages for the $\mathcal{R}(D^{(*)})$ ratios are revisited. Here it is demonstrated that different treatments for the correlations of uncertainties from $D^{**}$ excited states can vary the current $3\sigma$ tension with the SM within a $1\sigma$ range. Prior experimental overestimates of $D^{**}\tau \nu$ contributions may further exacerbate this. The precision of future measurements is also estimated; their power to exploit full differential information, and solutions to the inherent difficulties in self-consistent new physics interpretations of LFUV observables, are explored.

Nucleons (protons and neutrons) are the building blocks of atomic nuclei and are responsible for more than 99% of the visible matter in the Universe. Despite decades of efforts in studying its internal structure, there are still a number of puzzles surrounding the proton such as its spin and charge radius. Accurate knowledge about the proton charge radius is not only essential for understanding how QCD works in the nonperturbative region but also important for bound state QED calculations of atomic energy levels. It also has an impact on the Rydberg constant, one of the most precisely measured fundamental constants in nature. This review examines the latest situation concerning the proton charge radius in light of the new experimental results from both atomic hydrogen spectroscopy and electron-scattering measurements, with particular focus on the latter. Theoretical backgrounds and recent developments concerning the determination of the proton charge radius using different experimental techniques are also presented. Upcoming experiments are discussed, and the deuteron charge radius puzzle is mentioned at the end.

The second law of thermodynamics implies a relationship between the net entropy export by Earth and its internal irreversible entropy production. The application of this constraint for the purpose of understanding Earth’s climate is reviewed. Both radiative processes and material processes are responsible for irreversible entropy production in the climate system. With a focus on material processes, an entropy budget for the climate system is derived that accounts for the multiphase nature of the hydrological cycle. The entropy budget facilitates a heat-engine perspective of atmospheric circulations that has been used to propose theories for convective updraft velocities, tropical cyclone intensity, and the atmospheric meridional heat transport. Such theories can be successful, however, only if they properly account for the irreversible entropy production associated with water in all its phases in the atmosphere. Irreversibility associated with such moist processes is particularly important in the context of global climate change, for which the concentration of water vapor in the atmosphere is expected to increase, and recent developments toward understanding the response of the atmospheric heat engine to climate change are discussed. Finally, the application of variational approaches to the climate and geophysical flows is reviewed, including the use of equilibrium statistical mechanics to predict the behavior of long-lived coherent structures and the controversial maximum entropy production principle.

The theory of entanglement provides a fundamentally new language for describing interactions and correlations in many-body systems. Its vocabulary consists of qubits and entangled pairs, and the syntax is provided by tensor networks. How matrix product states and projected entangled pair states describe many-body wave functions in terms of local tensors is reviewed. These tensors express how the entanglement is routed, act as a novel type of nonlocal order parameter, and the manner in which their symmetries are reflections of the global entanglement patterns in the full system is described. The manner in which tensor networks enable the construction of real-space renormalization group flows and fixed points is discussed, and the entanglement structure of states exhibiting topological quantum order is examined. Finally, a summary of the mathematical results of matrix product states and projected entangled pair states, highlighting the fundamental theorem of matrix product vectors and its applications, is provided.

Water vapor is a greenhouse gas that dominates Earth’s terrestrial radiation absorption. As the planetary temperature warms, forced by increasing ${\mathrm{CO}}_2$ and other greenhouse gases, water vapor content of the atmosphere increases, thereby producing the strongest positive feedback in the climate system. At the same time, the rate at which atmospheric temperature drops with height (the “lapse rate”) is expected to decrease with warming. This represents a smaller, but significant, negative feedback since it enables the planet to radiate more effectively to space. The two feedbacks are closely coupled to each other, and the combined result represents the foundational net positive feedback in the climate system, mandating substantial global warming in response to increased greenhouse gases. This review summarizes the published work that has provided an ever deepening understanding of these critical feedbacks. The historical context, beginning with the 19th century awakening to the importance of water vapor in the climate, is outlined before the review’s focus shifts to the theoretical, observational, and modeling work in recent decades that has transformed our understanding of the feedbacks’ role in climate change. It is shown that the evidence is now overwhelming that combined water vapor and lapse rate processes indeed provide the strongest positive feedback in the climate system. However, important challenges remain. This review provides physicists with a deeper understanding of these feedbacks and stimulates engagement with the climate research community. Together the scientific community can facilitate further rigor, understanding, and confidence in these most fundamental Earth system processes.

The distinctive electronic properties of quasicrystals stem from their long-range structural order, with invariance under rotations and under discrete scale change, but without translational invariance. $d$-dimensional quasicrystals can be described in terms of lattices of higher dimension ($D>d$), and many of their properties can be simply derived from analyses that take into account the extra “hidden” dimensions. In particular, as recent theoretical and experimental studies have shown, quasicrystals can have topological properties inherited from the parent crystals. These properties are discussed here for the simplest of quasicrystals, the one-dimensional (1D) Fibonacci chain. The Fibonacci noninteracting tight-binding Hamiltonians are characterized by the multifractality of the spectrum and states, which is manifested in many of its physical properties, most notably in transport. Perturbations due to disorder and reentrance phenomena are described, along with the crossover to strong Anderson localization. Perturbations due to boundary conditions also give information on the spatial and topological electronic properties, as is shown for the superconducting proximity effect. Related models including phonon and mixed Fibonacci models are discussed, as are generalizations to other quasiperiodic chains and higher-dimensional extensions. Interacting quasiperiodic systems and the case for many body localization are discussed. Some experimental realizations of the 1D quasicrystal and their potential applications are described.

Recent progress in utilizing ultrafast light-matter interaction to control the macroscopic properties of quantum materials is reviewed. Particular emphasis is placed on photoinduced phenomena that do not result from ultrafast heating effects but rather emerge from microscopic processes that are inherently nonthermal in nature. Many of these processes can be described as transient modifications to the free energy landscape resulting from the redistribution of quasiparticle populations, the dynamical modification of coupling strengths, and the resonant driving of the crystal lattice. Other pathways result from the coherent dressing of a material’s quantum states by the light field. A selection of recently discovered effects leveraging these mechanisms, as well as the technological advances that led to their discovery, is discussed. A road map for how the field can harness these nonthermal pathways to create new functionalities is presented.

In this Colloquium recent advances in the field of quantum heat transport are reviewed. This topic has been investigated theoretically for several decades, but only during the past 20 years have experiments on various mesoscopic systems become feasible. A summary of the theoretical basis for describing heat transport in one-dimensional channels is first provided. The main experimental investigations of quantized heat conductance due to phonons, photons, electrons, and anyons in such channels are then presented. These experiments are important for understanding the fundamental processes that underlie the concept of a heat conductance quantum for a single channel. An illustration of how one can control the quantum heat transport by means of electric and magnetic fields, and how such tunable heat currents can be useful in devices, is first given. This lays the basis for realizing various thermal device components such as quantum heat valves, rectifiers, heat engines, refrigerators, and calorimeters. Also of interest are fluctuations of quantum heat currents, both for fundamental reasons and for optimizing the most sensitive thermal detectors; at the end of the Colloquium the status of research on this topic is given.

Entropy production is a key quantity in any finite-time thermodynamic process. It is intimately tied with the fundamental laws of thermodynamics, embodying a tool to extend thermodynamic considerations all the way to nonequilibrium processes. It is also often used in attempts to provide the quantitative characterization of logical and thermodynamic irreversibility, stemming from processes in physics, chemistry, and biology. Notwithstanding its fundamental character, a unifying theory of entropy production valid for general processes, both classical and quantum, has not yet been formulated. Developments pivoting around the frameworks of stochastic thermodynamics, open quantum systems, and quantum information theory have led to substantial progress in such endeavors. This has culminated in the unlocking of a new generation of experiments able to address stochastic thermodynamic processes and the impact of entropy production on them. This review aims to provide a compendium on the current framework for the description, assessment, and manipulation of entropy production. Formal aspects of its formulation and the implications stemming from the potential quantum nature of a given process, including a detailed survey of recent experiments, are both presented.

The annihilation of dark matter into neutrinos over a range of dark matter masses from $\mathrm{MeV}/c^2$ to $\mathrm{ZeV}/c^2$ is reviewed. Thermally produced models of dark matter are expected to self-annihilate to standard model products. As no such signal has yet been detected, neutrino detectors are turned to in order to constrain the “most invisible channel.” The experimental techniques that are used to detect neutrinos are reviewed, and the expected contributions to the neutrino flux at current and upcoming neutrino experiments is revisited. Updated constraints are placed on the dark matter self-annihilation cross section to neutrinos $⟨\sigma v⟩$ using the most recent data, and the sensitivity of upcoming experiments such as Hyper-Kamiokande, Deep Underground Neutrino Experiment (DUNE), and IceCube Gen2 is forecasted. Where possible, limits and projections are scaled to a single set of dark matter halo parameters for consistent comparison. Galactic and extragalactic signals of $s$-, $p$-, and $d$-wave annihilation processes directly into neutrino pairs are considered, yielding constraints that range from $⟨\sigma v⟩\sim 2.5\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $30\mathrm{MeV}/c^2$ to ${10}^{-17}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at ${10}^{11}\mathrm{Ge}\mathrm{V}/c^2$. Experiments that report directional and energy information of their events provide much stronger constraints, outlining the importance of making such data public.

Spin-polarized atoms have applications in many areas, including biological magnetic resonance imaging, optical magnetometry, atomic clocks, and fundamental symmetry studies. Polarized atoms are often held in a container, most commonly a glass cell. Their interactions with the walls of the container during their collisions with the walls are often the main cause of spin relaxation, which determines the ultimate attainable polarization, and frequency shift, which affects the long-term frequency stability in atomic clocks. A critical review of studies of wall interactions of spin-polarized atoms done in the past six decades is presented, including the hydrogen atom, alkali metal atoms, and diamagnetic atoms with ${}^1{S}_0$ ground states such as mercury, cadmium, and noble gas atoms. The review summarizes the progress that has been made in understanding the nature of wall interactions and the physical mechanisms of spin relaxation and frequency shift due to wall collisions. It also points out those issues, particularly in connection with the widely used antirelaxation coatings, that are not yet understood.

Since the parton model was introduced by Feynman more than 50 years ago, much has been learned about the partonic structure of the proton through a large body of high-energy experimental data and dedicated global fits. However, limited progress has been made in calculating partonic observables such as the parton distribution function (PDFs) from the fundamental theory of strong interactions, quantum chromodynamics (QCD). Recently some advocated for a formalism, large-momentum effective theory (LaMET), through which one can extract parton physics from the properties of the proton traveling at a moderate boost factor such as $\gamma \sim 2–5$. The key observation behind this approach is that Lorentz symmetry allows the standard formalism of partons in terms of light-front operators to be replaced by an equivalent one with large-momentum states and time-independent operators of a universality class. With LaMET, the PDFs, generalized PDFs or generalized parton distributions, transverse-momentum-dependent PDFs, and light-front wave functions can all be extracted in principle from lattice simulations of QCD (or other nonperturbative methods) through standard effective field theory matching and running. Future lattice QCD calculations with exascale computational facilities could help one to understand the experimental data related to the hadronic structure, including those from the upcoming electron-ion colliders dedicated to exploring the partonic landscape of the proton. Here the progress made in the past few years in the development of the LaMET formalism and its applications is reviewed, with an emphasis on a demonstration of its effectiveness from initial lattice QCD simulations.

The current status of baryogenesis is reviewed, with an emphasis on electroweak baryogenesis and leptogenesis. The first detailed studies were carried out for $\mathrm{SU}(5)$ grand unified theory (GUT) models where $CP$-violating decays of leptoquarks generate a baryon asymmetry. These GUT models were excluded by the discovery of unsuppressed, ($B+L$)-violating sphaleron processes at high temperatures. Yet a new possibility emerged: electroweak baryogenesis. Here sphaleron processes generate a baryon asymmetry during a strongly first-order phase transition. This mechanism has been studied in detail in many extensions of the standard model. However, constraints from the LHC and from low-energy precision experiments exclude most of the known models, leaving composite Higgs models of electroweak symmetry breaking as an interesting possibility. Sphaleron processes are also the basis of leptogenesis, where $CP$-violating decays of heavy right-handed neutrinos generate a lepton asymmetry that is partially converted to a baryon asymmetry. This mechanism is closely related to that of GUT baryogenesis, and simple estimates based on GUT models can explain the order of magnitude of the observed baryon-to-photon ratio. In the one-flavor approximation an upper bound on the light-neutrino masses has been derived that is consistent with the cosmological upper bound on the sum of neutrino masses. For quasidegenerate right-handed neutrinos the leptogenesis temperature can be lowered from the GUT scale down to the weak scale, and $CP$-violating oscillations of GeV sterile neutinos can also lead to successful leptogenesis. Significant progress has been made in developing a full field-theoretical description of thermal leptogenesis, which demonstrated that interactions with gauge bosons of the thermal plasma play a crucial role. Finally, recent ideas on how the seesaw mechanism and $B-L$ breaking at the GUT scale can be probed by gravitational waves are discussed.