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Field and gauge theories
Field and gauge theories

... loop and momentum is not uniquely defined (off-the-shell)  Closely related to failures of classical EM, like infinite selfenergy of electron , and to vacuum polarization  Solution: problem is purely mathematical, create a cutoff for high energy quanta (quantize space, forbidding short distances), ...
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... Most notably, the f ields that carry the three fundamental forces of the standard model of particle physics are gauge f ields: 1. Ordinary electromagnetism–considered without any magnetic charges– is a gauge theory of U (1)-symmetry-principal bundles with connection. 2. The f ields in the Yang-Mills ...


... the Lagrangian approach [14, 10, 11, 16, 4]. The Hamiltonian formalism gives rise to the canonical quantization, while the Lagrangian approach is used in the path-integral quantization. Usually, in classical mechanics, there is a transformation that relates these two approaches. However, for a repar ...
Physics 722, Spring 2007 Final Exam Due Friday, May 11, 5pm
Physics 722, Spring 2007 Final Exam Due Friday, May 11, 5pm

... are not asked to prove (but it is not difficult). This means that the variation of the variation of any field vanishes. For example, varying the antighost field once gives a term proportional to B a , and varying again, δB a =0. The existence of BRST invariance is helpful in proving renormalizabilit ...
A path towards quantum gravity
A path towards quantum gravity

... (sections of vector bundles in classical FT, operator-valued distributions in QFT) but rather on extended objects such as strings. • The various string theories are different aspects of a more fundamental theory, called M-theory. ...
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Document

... the parameter that gives the infinitesimal change is a vector field. Hence these constraints must multiply a vector field, without using a metric. Thus these constraints are the components of a one form. It should also be invariant under ordinary gauge transformations, as they commute with differomo ...
Title: Physics of gauge field and topology in spintronics, graphene
Title: Physics of gauge field and topology in spintronics, graphene

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BRST quantization

In theoretical physics, BRST quantization (where the BRST refers to Becchi, Rouet, Stora and Tyutin) denotes a relatively rigorous mathematical approach to quantizing a field theory with a gauge symmetry. Quantization rules in earlier QFT frameworks resembled ""prescriptions"" or ""heuristics"" more than proofs, especially in non-abelian QFT, where the use of ""ghost fields"" with superficially bizarre properties is almost unavoidable for technical reasons related to renormalization and anomaly cancellation. The BRST global supersymmetry introduced in the mid-1970s was quickly understood to rationalize the introduction of these Faddeev–Popov ghosts and their exclusion from ""physical"" asymptotic states when performing QFT calculations. Crucially, this symmetry of the path integral is preserved in loop order, and thus prevents introduction of counterterms which might spoil renormalizability of gauge theories. Work by other authors a few years later related the BRST operator to the existence of a rigorous alternative to path integrals when quantizing a gauge theory.Only in the late 1980s, when QFT was reformulated in fiber bundle language for application to problems in the topology of low-dimensional manifolds, did it become apparent that the BRST ""transformation"" is fundamentally geometrical in character. In this light, ""BRST quantization"" becomes more than an alternate way to arrive at anomaly-cancelling ghosts. It is a different perspective on what the ghost fields represent, why the Faddeev–Popov method works, and how it is related to the use of Hamiltonian mechanics to construct a perturbative framework. The relationship between gauge invariance and ""BRST invariance"" forces the choice of a Hamiltonian system whose states are composed of ""particles"" according to the rules familiar from the canonical quantization formalism. This esoteric consistency condition therefore comes quite close to explaining how quanta and fermions arise in physics to begin with.In certain cases, notably gravity and supergravity, BRST must be superseded by a more general formalism, the Batalin–Vilkovisky formalism.
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