What Belongs Here vs Quantum Matter vs QFT.org

Many subjects in modern quantum physics can be described as many-body physics, condensed-matter physics, quantum information, computational physics, or quantum field theory depending on the question being asked. Those labels overlap scientifically. They must nevertheless be separated editorially if derivations, notation, and references are to have stable canonical homes.

This page is the routing contract for that separation. It answers:

where a topic receives its full definition or derivation;
where a model is introduced before its applications branch outward;
where an experimental realization, numerical implementation, or material phenomenon belongs;
when a many-body discussion should stop and hand the reader to QFT.org;
how to cross-link overlapping viewpoints without copying the same argument.

The rule is not that a subject may be mentioned in only one volume. The rule is that each well-defined scope has one canonical home, while every other appearance states its narrower purpose and links back.

The Short Routing Rule

Use the object and the question, not merely the vocabulary, to choose a home.

Primary question	Canonical owner
What is the generic ensemble, model, approximation, correlation function, phase concept, or many-body mechanism?	Many-Body and Quantum Statistical Mechanics
What physical phase, material class, device, or mesoscopic phenomenon realizes it?	Quantum Matter
What laboratory platform, trap, laser configuration, or spectroscopic protocol realizes it?	Atomic, Molecular, and Optical Physics
What algorithm, data structure, convergence test, or reusable implementation computes it?	Computational QM
What circuit, protocol, communication task, code, or information-processing resource uses it?	Quantum Information
What system–environment dynamics, channel, master equation, or decoherence mechanism governs it?	Measurement and Open Quantum Systems
What relativistic, renormalized, or fully field-theoretic framework develops it?	QFT.org
What interpretive, ontological, or foundations claim is at issue?	Foundations and Interpretations

The same physical system may therefore generate several pages. A Hubbard-model page belongs here; a material-specific Mott transition belongs in Quantum Matter; a sparse-matrix implementation belongs in Computational QM; and a cold-atom optical-lattice realization belongs in Atomic, Molecular, and Optical Physics. For model-by-model live destinations and planned-volume fallbacks, use the Model-to-Volume Cross-Link Index.

What This Volume Owns

Many-Body and Quantum Statistical Mechanics is the canonical home for the generic quantum mechanics of collective systems. Its central objects are Hamiltonians, ensembles, operators, correlations, response functions, phases, and emergent degrees of freedom considered independently of one particular material or implementation.

It owns the full treatments of:

equilibrium quantum ensembles and thermodynamic potentials;
Bose–Einstein, Fermi–Dirac, and Maxwell–Boltzmann statistics;
ideal and weakly interacting quantum gases;
indistinguishability, exchange symmetry, Fock space, and second-quantized operators and Hamiltonians;
generic lattice and spin Hamiltonians;
mean-field, Hartree–Fock, Bogoliubov, BCS, and related approximation frameworks;
correlation functions, spectral functions, structure factors, and linear response;
finite-temperature methods at the quantum-mechanical and bridge level;
order parameters, spontaneous symmetry breaking, quantum phase transitions, and universality as many-body concepts;
quasiparticles and collective modes as generic organizing ideas;
many-body entanglement, area laws, thermalization, ETH, scrambling, and nonequilibrium dynamics at their canonical introductory or graduate level;
the bridge from nonrelativistic many-body mechanics to field operators, path integrals, statistical field theory, and QFT.

A useful prototype is

H = \sum_i h_i + \sum_{i<j} V_{ij}.

Questions about how interaction, statistics, locality, system size, or temperature organize the states and observables of such a Hamiltonian belong here. Questions about which actual compound has parameters $h_i$ and $V_{ij}$ , how a laboratory engineers them, or how software diagonalizes the resulting matrix generally belong elsewhere.

Three Levels That Must Not Be Confused

Most apparent ownership conflicts disappear after separating three levels.

Object

The object is a definition or mathematical structure:

\rho_\beta = \frac{e^{-\beta H}}{Z}, \qquad Z = \operatorname{Tr}e^{-\beta H}.

The thermal density operator and its thermodynamic consequences belong here.

Method

The method is a controlled way to extract physics:

\delta\langle A(t)\rangle = \int_{-\infty}^{\infty} dt'\, \chi_{AB}^{R}(t-t')f(t').

The derivation and general interpretation of the Kubo response formula belong here.

Realization or use

The realization supplies material, platform, device, or protocol-specific content. Conductivity in graphene, Bragg spectroscopy of a cold gas, and an implementation of Krylov time evolution all use many-body objects and methods, but their canonical homes are different.

Cross-links should preserve this hierarchy: a generic object motivates a method, which supports a realization or implementation.

The arrow is conceptual, not a claim that every application is reducible to one simple model.

Interface with Composite Systems and Entanglement

Composite Systems and Entanglement supplies the grammar:

tensor products and subsystem structure;
partial traces and reduced states;
identical particles and exchange symmetry;
Fock space;
creation and annihilation operators;
the basic construction of second quantization.

This volume applies that grammar to systems with many active degrees of freedom:

interacting Hamiltonians;
quantum gases and lattice models;
thermodynamic ensembles;
correlations and response;
phases and collective excitations;
entanglement scaling and thermalization.

For example, the algebra

\{c_i,c_j^\dagger\} = \delta_{ij}

is foundational second-quantization material. The Hubbard Hamiltonian

\begin{aligned} H_{\mathrm{Hub}} ={}& -t \sum_{\langle i,j\rangle,\sigma} \left( c_{i\sigma}^\dagger c_{j\sigma} + c_{j\sigma}^\dagger c_{i\sigma} \right) \\ &+ U\sum_i n_{i\uparrow}n_{i\downarrow} \end{aligned}

is a many-body application of that algebra. The foundational page should not be copied into every model page; the model page states the convention and links back.

Interface with Measurement and Open Systems

Equilibrium statistical mechanics and open-system dynamics both use density operators, but they answer different questions.

An equilibrium page asks what state and thermodynamic relations follow from constraints:

\rho_\beta \propto e^{-\beta H}.

An open-system page asks how a reduced state changes under environmental coupling:

\begin{aligned} \dot\rho ={}& -\frac{i}{\hbar}[H,\rho] \\ &+ \sum_\alpha \left( L_\alpha\rho L_\alpha^\dagger - \frac{1}{2} \{L_\alpha^\dagger L_\alpha,\rho\} \right). \end{aligned}

The ownership split is:

Scope	Canonical home
Gibbs states, partition functions, ensembles, and equilibrium thermodynamics	Many-Body and Quantum Statistical Mechanics
Thermalization under closed many-body unitary dynamics and ETH	Many-Body and Quantum Statistical Mechanics
Baths, dynamical maps, Lindblad generators, decoherence, and system–environment approximations	Measurement and Open Quantum Systems
Quantum engines, work, heat, and entropy production for open driven systems	Measurement and Open Quantum Systems
Equilibrium many-body formulas used inside an open-system derivation	Link here; do not rederive

A Gibbs state can be a stationary state of a thermal master equation, but that fact does not merge the two canonical topics. The ensemble defines an equilibrium object; the master equation specifies a dynamical mechanism and its approximations.

Interface with Quantum Matter

The decisive distinction is generic model and method versus physical phase, material, or mesoscopic phenomenon.

Generic content here	Physical content in Quantum Matter
Hubbard model and its parameters	Mott materials and correlated-electron phenomenology
Heisenberg and spin models	Magnetism in specific materials
BCS mean-field framework	Superconductivity, electrodynamics, and material classes
Ideal or interacting Fermi gas	Metals, band structures, and Fermi-surface measurements
Generic topological-order preview	Quantum Hall systems and topological materials
Kubo formula	Transport in a concrete phase or device

The Hubbard Hamiltonian may predict a competition between kinetic energy and local repulsion. That mechanism belongs here. Whether a real compound realizes a one-band Hubbard description, what its effective $t/U$ is, and which probes reveal a Mott phase belong in Quantum Matter.

Likewise, the generic BCS gap equation

\Delta_k = -\sum_{k'} V_{kk'} \frac{\Delta_{k'}}{2E_{k'}} \tanh\left( \frac{\beta E_{k'}}{2} \right)

belongs in a many-body method page. The Meissner effect, flux quantization, pairing symmetries in material families, and experimental phase diagrams belong in Quantum Matter.

Interface with Atomic, Molecular, and Optical Physics

Many-Body owns generic gas and model theory. Atomic, Molecular, and Optical Physics owns experimental platforms and light–matter implementations.

Generic theory here	Platform-specific treatment in AMO
Ideal Bose gas and condensate thermodynamics	Trapped-gas preparation and condensate imaging
Ideal and interacting Fermi gases	Degenerate atomic Fermi-gas experiments
Bose–Hubbard model	Optical-lattice realization and calibration
Contact interactions and scattering-length parameterization	Feshbach-resonance control
Generic structure factors	Bragg or cavity spectroscopy protocols

For a trapped gas, the uniform-system Hamiltonian and its equation of state remain many-body topics. Trap geometry, laser detuning, imaging resolution, atom species, and experimental error budgets are AMO topics.

This split prevents an ideal-gas derivation from being repeated in every experimental platform page while still allowing each platform page to explain which assumptions it uses.

Interface with Computational QM

Many-Body defines the model, target observable, approximation, and physical interpretation. Computational QM owns reusable algorithms, software architecture, numerical error control, and implementation benchmarks.

Suppose the physics question is

\begin{gathered} H|\psi_n\rangle = E_n|\psi_n\rangle, \\ C_{ij} = \langle\psi_0| O_iO_j |\psi_0\rangle. \end{gathered}

The Hamiltonian, symmetry sectors, expected phases, and interpretation of $C_{ij}$ belong here. The following belong primarily in Computational QM:

sparse-matrix representations and memory layout;
Lanczos and Krylov implementations;
DMRG sweep algorithms and truncation diagnostics;
tensor-network contraction strategies;
quantum Monte Carlo updates and sign-problem diagnostics;
reproducible code, tests, data formats, and performance benchmarks.

Conceptual previews of exact diagonalization, DMRG, tensor networks, and quantum Monte Carlo may appear here because method choice depends on physical structure. A preview should explain what the method can represent and when it is appropriate, then link to the computational implementation.

The distinction is not analytic versus numerical. Finite-size scaling and numerical evidence can be central many-body physics. Ownership moves to Computational QM when the page’s main deliverable is the algorithm or implementation rather than the physical result.

Computational Many-Body QM routes a declared many-body problem to the appropriate numerical branch while preserving this ownership boundary. The Computational Many-Body Overview supplies the detailed method-selection, evidence-ledger, finite-size-inference, and reproducibility audit.

Interface with Quantum Information

Many-body entanglement and quantum information share entropy, correlations, channels, and tensor networks. Their canonical questions differ.

Many-Body owns:

entanglement scaling in ground states and dynamics;
area laws and volume laws;
entanglement near criticality;
operator spreading and scrambling as many-body phenomena;
ETH and relations between local equilibration and entanglement;
tensor networks as representations of many-body states.

Quantum Information owns:

qubit and gate models;
communication and cryptographic protocols;
quantum algorithms and complexity tasks;
error-correcting codes and fault tolerance;
resource theories;
operational discrimination, metrology, and channel-capacity questions.

For a spatial region $A$ ,

S_A = -\operatorname{Tr} \left( \rho_A\log\rho_A \right)

is used in both areas. A page about how $S_A$ scales with the boundary of $A$ belongs here. A page about using entanglement as a communication resource belongs in Quantum Information. The entropy definition itself should link to its canonical mathematical or composite-systems treatment rather than be rederived each time.

Interface with Foundations

Thermalization raises foundational questions, but not every thermalization page is a foundations page.

Nonequilibrium Overview owns the operational distinction among dephasing, equilibration, ensemble identification, retained memory, and recurrence. Interpretive questions about probability and irreversibility remain a separate scope.

This volume owns the physical mechanisms and testable structures:

dephasing under unitary many-body dynamics;
relaxation of local observables;
ETH ansatz and its limits;
integrability and generalized ensembles;
prethermalization, chaos, and localization previews;
comparisons of entanglement and thermodynamic entropy.

Foundations owns questions such as:

what probability or typicality means interpretively;
whether thermodynamic irreversibility requires additional assumptions;
how macroscopic definiteness relates to measurement;
what an emergent classical description claims about ontology.

A clean many-body page may state the dynamical result

\langle O(t)\rangle = \sum_{m,n} c_m^*c_n e^{i(E_m-E_n)t/\hbar} O_{mn},

then analyze dephasing and matrix elements. It should cross-link rather than settle an interpretation of probability or irreversibility by assertion.

Interface with QFT.org

This volume must build a real bridge to field theory without becoming a duplicate field-theory curriculum.

Why Many-Body QM Leads to QFT owns the conceptual distinction among exact nonrelativistic field reformulations, effective collective fields, and relativistic QFT.

Many-Body owns:

nonrelativistic field operators as a reformulation of many-particle mechanics;
continuum and lattice many-body Hamiltonians;
Green functions and finite-temperature notation needed for many-body calculations;
imaginary time and Matsubara frequencies at the bridge level;
path-integral previews for quantum statistical systems;
renormalization-group intuition in quantum critical and impurity examples;
the physical motivation for effective fields and collective modes.

QFT.org owns:

relativistic quantum fields and Lorentz-covariant dynamics;
canonical and path-integral quantization as full frameworks;
renormalization and the renormalization group in systematic depth;
gauge theories, anomalies, and nonperturbative field-theory structure;
full thermal QFT;
Schwinger–Keldysh and nonequilibrium effective field theory;
field-theoretic treatments whose central objects are no longer merely a reformulation of a fixed-particle quantum system.

The bridge can begin with

\begin{aligned} H ={}& H_0 + H_{\mathrm{int}}, \\ H_0 ={}& \int d^d x\, \psi^\dagger(x) \\ &\quad{}\times \left( -\frac{\hbar^2\nabla^2}{2m} \right) \psi(x) \\ H_{\mathrm{int}} ={}& \frac{1}{2} \int d^d x\,d^d y \\ &\quad{}\times \psi^\dagger(x) \psi^\dagger(y) \\ &\quad{}\times V(x-y) \psi(y)\psi(x). \end{aligned}

This Hamiltonian belongs here as nonrelativistic many-body quantum mechanics in field language. A systematic treatment of renormalized field theories, relativistic causality, or real-time contour methods belongs at the QFT destination.

The practical stopping rule is:

If field notation is serving a many-particle Hamiltonian, the discussion can remain here. If field theory itself is the object being constructed, renormalized, or classified, route to QFT.org.

Interface with the Reference

Reference pages and teaching pages have different jobs.

This volume owns motivations, derivations, assumptions, examples, failure modes, and exercises. The Many-Body and Quantum Statistical Mechanics Reference routes among volume-specific conventions, formula sheets, Hamiltonian summaries, glossaries, and ownership indexes. The site-wide Reference may own a compact cross-volume formula entry, definition index, notation table, or model card designed for lookup.

For example:

the Kubo derivation belongs here;
a concise retarded-susceptibility formula card may live in the Reference;
the Hubbard model’s physical interpretation belongs here;
a model index may list its Hamiltonian and route back here.

The reference entry should not silently become a second derivation. Conversely, a teaching page should not force a reader to reconstruct conventions from an isolated formula card.

Canonical Decision Table

Topic or artifact	Canonical home	Cross-linking role here
Tensor products and partial trace	Composite Systems and Entanglement	Prerequisite
Fock space and second-quantization basics	Composite Systems and Entanglement	Prerequisite and notation link
Thermal density operators and ensembles	Many-Body and Quantum Statistical Mechanics	Full treatment
Thermal master equations	Measurement and Open Systems	Equilibrium-state cross-link
Bose–Einstein and Fermi–Dirac statistics	Many-Body and Quantum Statistical Mechanics	Full treatment
Cold-atom BEC experiment	Atomic, Molecular, and Optical Physics	Theory cross-link
Hubbard and Heisenberg models	Many-Body and Quantum Statistical Mechanics	Canonical model pages
Mott phases and material magnetism	Quantum Matter	Model cross-link
Hartree–Fock theory	Many-Body and Quantum Statistical Mechanics	Derivation and validity
Hartree–Fock software	Computational QM	Physics cross-link
BCS mean-field theory	Many-Body and Quantum Statistical Mechanics	Generic method
Superconductivity phenomenology	Quantum Matter	Method cross-link
Kubo formula and generic response	Many-Body and Quantum Statistical Mechanics	Full derivation
Material transport coefficients	Quantum Matter	Response cross-link
Many-body entanglement scaling	Many-Body and Quantum Statistical Mechanics	Full treatment
Quantum circuits and error correction	Quantum Information	Context link only
ETH and closed-system thermalization	Many-Body and Quantum Statistical Mechanics	Full treatment
Decoherence and bath-induced relaxation	Measurement and Open Systems	Contrast and cross-link
Exact-diagonalization algorithm	Computational QM	Model and benchmark input
Nonrelativistic field bridge	Many-Body and Quantum Statistical Mechanics	Bridge treatment
Full thermal and relativistic QFT	QFT.org	Destination link

A Decision Procedure for New Pages

When a proposed page seems to fit several volumes, apply these tests in order.

1. State the page’s one-sentence deliverable

Bad:

Explain the Hubbard model, Mott insulators, optical lattices, DMRG, and field theory.

Good:

Derive the Hubbard Hamiltonian, define its parameters and symmetries, and explain its basic limiting regimes.

The good deliverable has a clear canonical home here. The other subjects become cross-links.

2. Identify the irreducible object

Ask what would remain if material names, apparatus details, and software choices were removed.

A Hamiltonian, ensemble, response function, phase concept, or emergent mode points here.
A material, device, or measured phase diagram points to Quantum Matter.
A trap, laser sequence, detector, or experimental protocol points to AMO.
An algorithm, implementation, convergence proof, or benchmark points to Computational QM.
A circuit, code, or information task points to Quantum Information.
A bath model, channel, or reduced dynamical law points to Open Systems.
A relativistic field theory or renormalization framework points to QFT.org.

3. Separate derivation from application

If a page needs a standard derivation already owned elsewhere, summarize only the assumptions and result, then link to the derivation. Add new material only for the local application.

4. Check whether the proposed scope has two nouns joined by “and”

Titles such as “Hubbard Models and Mott Materials” or “BEC Theory and Cold-Atom Experiments” often conceal two canonical homes. Split them unless the page is explicitly a short bridge.

5. Write the boundary sentence before writing the page

Every bridge or preview should be able to state:

This page develops X; the full treatment of Y belongs in Z.

If that sentence cannot be written precisely, the scope is still too broad.

6. Make the links asymmetric in content, not absent

The source page contains the full derivation. The destination application page contains only what is needed to use it and links back. Both pages may discuss the same symbol, but they do not repeat the same argument.

Worked Routing Cases

Kubo response and conductivity

The many-body page derives

\chi_{AB}^{R}(t) = -\frac{i}{\hbar} \Theta(t) \langle[A(t),B(0)]\rangle.

It explains causality, spectral representations, and the assumptions of linear response. A Quantum Matter page then specializes $A$ and $B$ to currents in a material, supplies band or scattering physics, and interprets the measured conductivity. A QFT page may later develop generating functionals or Ward identities. The commutator derivation remains here.

Bose–Hubbard physics in an optical lattice

The Bose–Hubbard Model page owns

\begin{aligned} H ={}& -J \sum_{\langle i,j\rangle} \left( b_i^\dagger b_j + b_j^\dagger b_i \right) \\ &+ \frac{U}{2} \sum_i n_i(n_i-1). \end{aligned}

It discusses number fluctuations, the $J/U$ competition, and generic phase structure. The AMO page explains how lattice depth determines $J$ and $U$ , how atoms are loaded, and how observables are measured. A Computational page owns the algorithm used to calculate a finite lattice.

Entanglement entropy in a spin chain

This volume owns the scaling question:

S_A(\ell) \sim \frac{c}{3} \log\ell + \text{constant}

for an appropriate one-dimensional critical setting, together with its assumptions and many-body meaning. Quantum Information owns protocols that consume entanglement as a resource. Computational QM owns a tensor-network implementation that extracts $S_A$ . QFT.org owns the full conformal-field-theory derivation when conformal symmetry is the central framework.

Renormalization near a quantum critical point

This volume may explain scale invariance, relevant perturbations, finite-size scaling, and why the renormalization group organizes critical behavior. It should hand off when the page’s objective becomes the systematic construction of RG flows, fixed-point field theories, operator products, or renormalized correlation functions.

Thermalization versus thermal contact

Closed-system thermalization asks why local observables in

|\psi(t)\rangle = e^{-iHt/\hbar} |\psi(0)\rangle

can approach values predicted by an ensemble despite globally unitary evolution. Open-system thermal contact asks how coupling to an environment drives $\rho(t)$ and which approximations yield a thermal stationary state. Similar late-time density operators do not make the dynamical questions identical.

Common Taxonomy Mistakes

Assigning by vocabulary alone

The word “field” does not automatically make a page QFT. Nonrelativistic field operators are often the natural language of many-body quantum mechanics. Conversely, a full renormalized field theory is not merely a notation appendix here.

Treating every phase as a model page

The Hamiltonian and generic mechanism may belong here while the physical phase and its phenomenology belong in Quantum Matter. “Hubbard model” and “Mott insulator” are related scopes, not synonyms.

Treating every numerical result as Computational QM

A phase diagram obtained numerically can be a many-body physics result. The algorithm, implementation, and error-control infrastructure remain computational topics.

Repeating second quantization

Many-body model pages use Fock-space notation but should not reproduce the foundational construction of Fock space or operator algebra.

Confusing equilibrium with relaxation

Writing $\rho_\beta$ does not explain how a state reaches equilibrium. Ensemble theory, closed-system thermalization, and bath-induced relaxation are three distinct scopes.

Turning a bridge into a destination

A bridge page introduces why another framework is needed, fixes a translation dictionary, and routes onward. It should not quietly expand into a second full curriculum.

Giving future volumes no canonical claim

The absence of a completed destination page is not permission to absorb its subject permanently. Use the appropriate roadmap or bridge link and keep the local treatment explicitly limited.

Duplicating formulas without assumptions

Even a familiar equation changes meaning with ensemble, boundary condition, normalization, or response convention. A local summary must state the assumptions and link to the canonical derivation.

Exercises

Route a topic bundle

A proposed page is titled “The Hubbard Model, Mott Insulators, and DMRG.” Split the proposal into canonical homes and state what the many-body page should contain.

Solution

The generic Hubbard Hamiltonian, its symmetries, parameters, limiting regimes, and basic correlation functions belong in Many-Body and Quantum Statistical Mechanics. Mott-insulator phenomenology, material realizations, and experimental signatures belong in Quantum Matter. The DMRG algorithm, implementation, truncation diagnostics, and benchmarks belong in Computational QM.

The many-body page may preview that DMRG is effective in one-dimensional low-entanglement settings and may show a result needed to explain the model. It should link to, rather than reproduce, the algorithm and the material phenomenology.

Distinguish three meanings of thermalization

Classify the following: deriving $\rho_\beta$ by maximum entropy, explaining ETH in an isolated chain, and deriving a thermal Lindblad equation for a weakly coupled bath.

Solution

The maximum-entropy derivation of the Gibbs state belongs in equilibrium quantum statistical mechanics here. ETH and the relaxation of local observables in an isolated chain belong in nonequilibrium many-body dynamics here. The thermal Lindblad derivation belongs in Measurement and Open Quantum Systems because its central object is a reduced dynamical generator obtained from system–bath assumptions.

The three pages should cross-link because they may predict related equilibrium observables, but they answer state-construction, closed-dynamics, and open-dynamics questions respectively.

Separate a cold-atom realization

An article derives the Bose–Hubbard model from a continuum bosonic Hamiltonian and then describes laser geometry, Feshbach tuning, time-of-flight imaging, and calibration uncertainties. Where should it be split?

Solution

The generic continuum-to-lattice reduction, Bose–Hubbard Hamiltonian, and interpretation of $J$ , $U$ , and filling belong here. The detailed optical-lattice construction, Feshbach protocol, imaging method, and uncertainty budget belong in Atomic, Molecular, and Optical Physics.

Each page can state the parameter map needed by its readers. The AMO page should link to the canonical model derivation; the model page should link to the platform as a realization.

Place a response calculation

A calculation derives the Kubo formula, evaluates a current–current correlator for a generic lattice model, and compares the result with conductivity data from a named material. Assign the components.

Solution

The Kubo derivation and the generic lattice-model correlator belong here. The material-specific parameter extraction, experimental comparison, and phase interpretation belong in Quantum Matter. If reusable numerical code performs the correlator calculation, its implementation and validation belong in Computational QM.

A concise formula card may also exist in the Reference, but it should link to the derivation rather than duplicate it.

Decide where the QFT bridge ends

A draft begins with nonrelativistic field operators, introduces an imaginary-time path integral, derives Matsubara frequencies, constructs a Wilsonian RG flow, and develops renormalized composite operators. Where should the handoff occur?

Solution

Nonrelativistic field operators, the motivation for imaginary time, and a bridge-level derivation of Matsubara frequencies can live here. A short RG preview may explain why integrating over scales is useful near a many-body critical point.

The systematic Wilsonian flow and renormalization of composite operators belong in QFT.org because field theory and renormalization have become the central objects rather than supporting language for a fixed many-body problem. The bridge page should announce that handoff before the full machinery begins.

Cross-Links

References

The ownership rules above are editorial conventions. The following sources support the scientific distinctions and interfaces used in the examples.

A. L. Fetter and J. D. Walecka, Quantum Theory of Many-Particle Systems, Dover (2003).
P. Coleman, Introduction to Many-Body Physics, Cambridge University Press (2015).
A. Altland and B. Simons, Condensed Matter Field Theory, 2nd ed., Cambridge University Press (2010).
S. Sachdev, Quantum Phase Transitions, 2nd ed., Cambridge University Press (2011).
H.-P. Breuer and F. Petruccione, The Theory of Open Quantum Systems, Oxford University Press (2002).
I. Bloch, J. Dalibard, and W. Zwerger, “Many-body physics with ultracold gases,” Reviews of Modern Physics 80, 885–964 (2008).
U. Schollwöck, “The density-matrix renormalization group in the age of matrix product states,” Annals of Physics 326, 96–192 (2011).
M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information, 10th anniversary ed., Cambridge University Press (2010).