GLOBAL KNOWLEDGE ARK

Reference library

Foundations

Explore concepts, laws, equations and methods, with clear explanations of their use and sources. Choose an area of study or find a specific entry.

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Reference entries

Showing 271–300 of 365 reference entries

PhysicsQCD running, scale and scheme conventions

The strong coupling α_s depends on renormalization scale and scheme.

Model
PhysicsPrecision electroweak fits and nuisance parameters

A precision Standard Model fit compares predicted electroweak observables with correlated measurements, jointly propagating input-parameter, systematic and missing-order uncertainties.

Method
PhysicsMuon g−2 · Final detailed Fermilab report (2026)

The Muon g−2 Collaboration's June 2026 detailed report describes the final positive-muon anomaly measurement at 127 ppb precision, including precession frequency, calibrated magnetic field and beam-dynamics corrections.

Empirical finding
PhysicsMuon hadronic vacuum polarization · Competing inputs

Data-driven dispersion calculations and lattice QCD estimate the same hadronic contribution through different inputs and systematics.

Model
PhysicsHubbard interaction and competing approximations

A single-band Hubbard model combines hopping t_ij with on-site repulsion U n_i↑n_i↓.

Model
PhysicsDynamical mean-field method and locality

Single-site dynamical mean-field theory maps an interacting lattice problem to a self-consistent impurity problem with a frequency-dependent local self-energy.

Method
PhysicsChern number, Hall response and edge index

For a gapped noninteracting two-dimensional band system, the occupied-band Berry curvature integrates to an integer C=(2π)⁻¹∫_BZTrF_xy d²k.

Model
PhysicsTime-reversal topology and experimental signatures

Spinful time-reversal symmetry with T²=−1 permits a Z₂ band distinction even when total Chern number vanishes.

Model
PhysicsKitaev chain and Majorana boundary modes

An ideal spinless one-dimensional p-wave pairing chain has a gapped topological phase with boundary Majorana modes for nonzero pairing and |μ|<2|t| in the uniform nearest-neighbour model.

Model
PhysicsFloquet topological order · Processor study (2025)

Will, Cochran and collaborators reported signatures of non-equilibrium topological order in a periodically driven quantum-processor experiment published 10 September 2025.

Empirical finding
PhysicsMajorana versus Andreev interpretations

Liu, Sau and Das Sarma's 2018 nanowire calculations show how trivial Andreev bound states can generate local zero-bias peaks resembling topological Majorana signals.

Model
PhysicsKinetic equations and molecular-chaos closure

The Boltzmann equation evolves a dilute one-particle distribution with streaming, force and collision terms.

Model
PhysicsThermalization, ETH and generalized Gibbs ensembles

ETH proposes that suitable local-observable matrix elements in many chaotic energy eigenstates have thermal structure, allowing narrow-energy isolated preparations to approach thermal local expectations.

Model
PhysicsCausal linear response and transport inference

For perturbation H′(t)=−f(t)B, the retarded response of A is χ_AB(t)=(i/ħ)θ(t)⟨[A(t),B(0)]⟩ in an equilibrium reference state.

Method
PhysicsLow-energy quantum gravity as an effective theory

Expanding a diffeomorphism-invariant gravitational action in curvature and derivatives organizes low-energy quantum corrections without claiming a complete short-distance theory.

Model
PhysicsQuantum-gravity frameworks and unresolved tests

String theory organizes extended-object states and includes a massless spin-two excitation in appropriate constructions; loop approaches quantize geometric variables with spin-network/holonomy methods; asymptotic safety seeks a suitable ultraviolet renormalization-group fixed point.

Open question
PhysicsGravity-induced entanglement · What would it establish?

The 2017 Marletto–Vedral proposal links entanglement between two masses to nonclassical mediation under explicit subsystem and locality assumptions.

Model
PhysicsReynolds stresses and turbulence closure

For constant-density incompressible flow, averaging u=U+u′ adds the Reynolds stress R_ij=⟨u′_iu′_j⟩ to the mean momentum equation.

Method
PhysicsDNS, filtered models and convergence evidence

DNS aims to resolve the dynamically relevant viscous scales of a specified flow; LES filters resolved scales and models subfilter stress.

Method
PhysicsNonlinear optical polarization and phase matching

A nonlinear polarization drives new frequency components.

Model
PhysicsKerr envelopes, dispersion and soliton limits

In a lossless scalar narrowband Kerr envelope convention, i∂_zA=−D∂²_tA+δ|A|²A represents second-order dispersion and self-phase modulation.

Model
PhysicsFDTD stability, boundaries and physical validation

Yee FDTD staggers electric/magnetic fields in space and time to approximate Maxwell curl evolution.

Method
PhysicsA mixing-layer benchmark and observable dependence

Nichols' worked compressible mixing-layer comparison specifies two streams, geometry, initial transients and statistical sampling before comparing RANS, LES and hybrid predictions with measurements downstream.

Method
PhysicsDisplacement, distance and average speed

Displacement compares endpoints; distance measures the travelled path.

Model
PhysicsConstant-acceleration kinematics

Closed formulas require constant acceleration over the interval.

Model
PhysicsInertial reference frames and inertia

Newtonian force balances need an inertial frame or explicit inertial terms.

Model
PhysicsCircular motion and centripetal acceleration

A constant speed can still have an acceleration.

Model
PhysicsMass, gravitational weight and apparent weight

Mass is in kilograms; gravitational weight is a force.

Model
PhysicsNormal forces and tension

Contact geometry determines the force direction.

Model
PhysicsFree-body diagrams and system boundaries

List forces on the selected body once.

Model