A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

In quantum field theory, an effective action is a modified version of the action which takes into account quantum mechanical corrections. The effective action action is a generating functional of the …
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Absolute units, or natural units, are a system of units where certain dimensionful constants are set to 1. This often simplifies various formulae.
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A transition by which the energy of at least one photon is completely transferred to a material.
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The rate of change of velocity of a body per unit of time.
is appropriate for questions dealing with the physics of beams in accelerators (synchrotrons, cyclotrons, linacs, betatrons and other types of accelerators); the ways in which beams are generated; the…
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An accretion disk is the disk around a compact star that accumulates matter from e.g. a companion star by the Roche lobe overflow or stellar wind transfer.
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Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. Applications of acoust…
The action is the integral of the Lagrangian over time, or the integral of the Lagrangian Density over both time and space.
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Thermodynamic processes that occur without exchanging heat between the system and its environment.
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Adinkras are a type of diagram on lattices, encoding equations of supersymmetry.
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contains questions relating to ADM formalism i.e., Arnowitt-Deser-Misner formalism which is a Hamiltonian formulation of General Relativity that plays an important role in canonical quantum …
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AdS/CFT is a special case of the holographic principle. It states that a quantum gravitating theory in Anti-de-Sitter (AdS) space is exactly equivalent to the gauge theory/Conformal Field Theory (CFT…
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concerning primarily forces such as lift and drag generated on bodies as they move through gasses or as gasses move through the body (typically air).
Aether (or ether) relates to the material which supposedly fills the entire universe. It is a concept used to understand action at a distance. Aether was described by Huygens as an "omnipresent, perfe…
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not to be confused with the [lie-algebra] tag.
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The Aharonov–Bohm effect is a quantum mechanical phenomenon in which an electrically charged particle is affected by a non-zero electromagnetic gauge potential despite there being a zero electromagnet…
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Earth's atmosphere is a layer of gases that surround it, permitting life and protecting life by absorbing ultraviolet solar radiation, warming the surface by retaining the heat and mitigating the temp…
Aircraft are man-made vehicles intended to operate while flying through Earth's atmosphere.
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Use for questions about algebraic geometry as it applies to physics. Purely mathematical questions should NOT go here, instead, they belong on Math Stack Exchange.
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Algebraic topology is a branch of mathematics that uses tools from abstract algebra to study topological spaces. The basic goal is to find algebraic invariants that classify topological spaces up to h…
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For questions about an algorithm as it relates to physics. DO NOT ask how to implement an algorithm, questions like that belong on Stack Overflow or Computational Science. DO NOT ask about the efficie…
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An amorphous solid is a condensed matter system with the mechanical properties of a solid, but lacking the long-range order characteristic of crystals. Examples of amorphous solids are glasses and gel…
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A geometric object whose volume is conjectured to be related to scattering amplitudes. It is used mostly in string theory.
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