In the simplest case, these are differential operators. Let be a field, and let be the ring of polynomials in one variable with coefficients in . Then the corresponding Weyl algebra consists of differential operators of form
This is the first Weyl algebra. The n-th Weyl algebra are constructed similarly.
Alternatively, can be constructed as the quotient of the free algebra on two generators, q and p, by the ideal generated by . Similarly, is obtained by quotienting the free algebra on 2n generators by the ideal generated bywhere is the Kronecker delta.
More generally, let be a partial differential ring with commuting derivatives . The Weyl algebra associated to is the noncommutative ring satisfying the relations for all . The previous case is the special case where and where is a field.
This article discusses only the case of with underlying field characteristic zero, unless otherwise stated.
The Weyl algebra arises naturally in the context of quantum mechanics and the process of canonical quantization. Consider a classical phase space with canonical coordinates . These coordinates satisfy the Poisson bracket relations:In canonical quantization, one seeks to construct a Hilbert space of states and represent the classical observables (functions on phase space) as self-adjoint operators on this space. The canonical commutation relations are imposed:where denotes the commutator. Here, and are the operators corresponding to and respectively. Erwin Schrödinger proposed in 1926 the following:[1]
with multiplication by .
with .
With this identification, the canonical commutation relation holds.
Constructions
The Weyl algebras have different constructions, with different levels of abstraction.
Representation
The Weyl algebra can be concretely constructed as a representation.
In the differential operator representation, similar to Schrödinger's canonical quantization, let be represented by multiplication on the left by , and let be represented by differentiation on the left by .
In the matrix representation, similar to the matrix mechanics, is represented by[2]
Generator
can be constructed as a quotient of a free algebra in terms of generators and relations.
One construction starts with an abstract vector spaceV (of dimension 2n) equipped with a symplectic formω. Define the Weyl algebra W(V) to be
where T(V) is the tensor algebra on V, and the notation means "the ideal generated by".
In other words, W(V) is the algebra generated by V subject only to the relation vu − uv = ω(v, u). Then, W(V) is isomorphic to An via the choice of a Darboux basis for ω.
The algebra W(V) is a quantization of the symmetric algebra Sym(V). If V is over a field of characteristic zero, then W(V) is naturally isomorphic to the underlying vector space of the symmetric algebra Sym(V) equipped with a deformed product – called the Groenewold–Moyal product (considering the symmetric algebra to be polynomial functions on V∗, where the variables span the vector space V, and replacing iħ in the Moyal product formula with 1).
The isomorphism is given by the symmetrization map from Sym(V) to W(V)
If one prefers to have the iħ and work over the complex numbers, one could have instead defined the Weyl algebra above as generated by qi and iħ∂qi (as per quantum mechanics usage).
Thus, the Weyl algebra is a quantization of the symmetric algebra, which is essentially the same as the Moyal quantization (if for the latter one restricts to polynomial functions), but the former is in terms of generators and relations (considered to be differential operators) and the latter is in terms of a deformed multiplication.
Stated in another way, let the Moyal star product be denoted , then the Weyl algebra is isomorphic to .[3]
In the case of exterior algebras, the analogous quantization to the Weyl one is the Clifford algebra, which is also referred to as the orthogonal Clifford algebra.[4][5]
The Weyl algebra is also referred to as the symplectic Clifford algebra.[4][5][6] Weyl algebras represent for symplectic bilinear forms the same structure that Clifford algebras represent for non-degenerate symmetric bilinear forms.[6]
D-module
The Weyl algebra can be constructed as a D-module.[7] Specifically, the Weyl algebra corresponding to the polynomial ring with its usual partial differential structure is precisely equal to Grothendieck's ring of differential operations .[7]
More generally, let be a smooth scheme over a ring . Locally, factors as an étale cover over some equipped with the standard projection.[8] Because "étale" means "(flat and) possessing null cotangent sheaf",[9] this means that every D-module over such a scheme can be thought of locally as a module over the Weyl algebra.
Let be a commutative algebra over a subring . The ring of differential operators (notated when is clear from context) is inductively defined as a graded subalgebra of :
Let be the union of all for . This is a subalgebra of .
In the case , the ring of differential operators of order presents similarly as in the special case but for the added consideration of "divided power operators"; these are operators corresponding to those in the complex case which stabilize , but which cannot be written as integral combinations of higher-order operators, i.e. do not inhabit . One such example is the operator .
Explicitly, a presentation is given by
with the relations
where by convention. The Weyl algebra then consists of the limit of these algebras as .[10]: Ch. IV.16.II
When is a field of characteristic 0, then is generated, as an -module, by 1 and the -derivations of . Moreover, is generated as a ring by the -subalgebra . In particular, if and , then . As mentioned, .[11]
Properties of An
Many properties of apply to with essentially similar proofs, since the different dimensions commute.
Under the representation, this equation is obtained by the general Leibniz rule. Since the general Leibniz rule is provable by algebraic manipulation, it holds for as well.
In particular, and .
Corollary — The center of Weyl algebra is the underlying field of constants .
Proof
If the commutator of with either of is zero, then by the previous statement, has no monomial with or .
By repeating the commutator relations, any monomial can be equated to a linear sum of these. It remains to check that these are linearly independent. This can be checked in the differential operator representation. For any linear sum with nonzero coefficients, group it in descending order: , where is a nonzero polynomial. This operator applied to results in .
This allows to be a graded algebra, where the degree of is among its nonzero monomials. The degree is similarly defined for .
The first relation is by definition. The second relation is by the general Leibniz rule. For the third relation, note that , so it is sufficient to check that contains at least one nonzero monomial that has degree . To find such a monomial, pick the one in with the highest degree. If there are multiple such monomials, pick the one with the highest power in . Similarly for . These two monomials, when multiplied together, create a unique monomial among all monomials of , and so it remains nonzero.
Suppose for contradiction that is a nonzero two-sided ideal of , with . Pick a nonzero element with the lowest degree.
If contains some nonzero monomial of form , then
contains a nonzero monomial of form
Thus is nonzero, and has degree . As is a two-sided ideal, we have , which contradicts the minimality of .
Similarly, if contains some nonzero monomial of form , then is nonzero with lower degree.
Theorem — The derivations of are in bijection with the elements of up to an additive scalar.[15]
That is, any derivation is equal to for some ; any yields a derivation ; if satisfies , then .
The proof is similar to computing the potential function for a conservative polynomial vector field on the plane.[16]
Proof
Since the commutator is a derivation in both of its entries, is a derivation for any . Uniqueness up to additive scalar is because the center of is the ring of scalars.
It remains to prove that any derivation is an inner derivation by induction on .
Base case: Let be a linear map that is a derivation. We construct an element such that . Since both and are derivations, these two relations generate for all .
Since , there exists an element such that
Thus, for some polynomial . Now, since , there exists some polynomial such that . Since , is the desired element.
For the induction step, similarly to the above calculation, there exists some element such that .
Similar to the above calculation, for all . Since is a derivation in both and , for all and all . Here, means the subalgebra generated by the elements.
Thus, ,
Since is also a derivation, by induction, there exists such that for all .
Since commutes with , we have for all , and so for all of .
In the case that the ground field F has characteristic zero, the nth Weyl algebra is a simpleNoetheriandomain.[17] It has global dimensionn, in contrast to the ring it deforms, Sym(V), which has global dimension 2n.
It has no finite-dimensional representations. Although this follows from simplicity, it can be more directly shown by taking the trace of σ(q) and σ(Y) for some finite-dimensional representation σ (where [q,p] = 1).
Since the trace of a commutator is zero, and the trace of the identity is the dimension of the representation, the representation must be zero dimensional.
In fact, there are stronger statements than the absence of finite-dimensional representations. To any finitely generated An-module M, there is a corresponding subvariety Char(M) of V × V∗ called the 'characteristic variety'[clarification needed] whose size roughly corresponds to the size[clarification needed] of M (a finite-dimensional module would have zero-dimensional characteristic variety). Then Bernstein's inequality states that for M non-zero,
An even stronger statement is Gabber's theorem, which states that Char(M) is a co-isotropic subvariety of V × V∗ for the natural symplectic form.
Positive characteristic
The situation is considerably different in the case of a Weyl algebra over a field of characteristicp > 0.
In this case, for any element D of the Weyl algebra, the element Dp is central, and so the Weyl algebra has a very large center. In fact, it is a finitely generated module over its center; even more so, it is an Azumaya algebra over its center. As a consequence, there are many finite-dimensional representations which are all built out of simple representations of dimension p.
For more details about this quantization in the case n = 1 (and an extension using the Fourier transform to a class of integrable functions larger than the polynomial functions), see Wigner–Weyl transform.
Weyl algebras and Clifford algebras admit a further structure of a *-algebra, and can be unified as even and odd terms of a superalgebra, as discussed in CCR and CAR algebras.
Affine varieties
Weyl algebras also generalize in the case of algebraic varieties. Consider a polynomial ring
Then a differential operator is defined as a composition of -linear derivations of . This can be described explicitly as the quotient ring
Dirac, P. A. M. (1926). "On Quantum Algebra". Mathematical Proceedings of the Cambridge Philosophical Society. 23 (4): 412–418. doi:10.1017/S0305004100015231. ISSN0305-0041.
Helmstetter, J.; Micali, A. (2008). Quadratic Mappings and Clifford Algebras. Basel ; Boston: Birkhäuser. ISBN978-3-7643-8605-4. OCLC175285188.
Lounesto, P.; Ablamowicz, R. (2004). Clifford Algebras. Boston: Springer Science & Business Media. ISBN0-8176-3525-4.
Micali, A.; Boudet, R.; Helmstetter, J. (1992). Clifford Algebras and their Applications in Mathematical Physics. Dordrecht: Springer Science & Business Media. ISBN0-7923-1623-1.
de Traubenberg, M. Rausch; Slupinski, M. J.; Tanasa, A. (2006). "Finite-dimensional Lie subalgebras of the Weyl algebra". J. Lie Theory. 16: 427–454. arXiv:math/0504224.
Traves, Will (2010). "Differential Operations on Grassmann Varieties". In Campbell, H.; Helminck, A.; Kraft, H.; Wehlau, D. (eds.). Symmetry and Spaces. Progress in Mathematics. Vol. 278. Birkhäuse. pp. 197–207. doi:10.1007/978-0-8176-4875-6_10. ISBN978-0-8176-4875-6.
Cannings, R.C.; Holland, M.P. (1994). "Right Ideals of Rings of Differential Operators". Journal of Algebra. 167 (1). Elsevier BV: 116–141. doi:10.1006/jabr.1994.1179. ISSN0021-8693.
Lebruyn, L. (1995). "Moduli Spaces for Right Ideals of the Weyl Algebra". Journal of Algebra. 172 (1). Elsevier BV: 32–48. doi:10.1006/jabr.1995.1046. ISSN0021-8693.
Bouvard e PécuchetTitolo originaleBouvard et Pécuchet Frontespizio della prima edizione AutoreGustave Flaubert 1ª ed. originale1881 1ª ed. italiana1927 Genereromanzo Lingua originalefrancese Modifica dati su Wikidata · Manuale Bouvard e Pécuchet (Bouvard et Pécuchet) è un romanzo incompiuto di Gustave Flaubert pubblicato postumo nel 1881. Il libro fu scritto da Flaubert negli ultimi cinque anni di vita, durante i quali assorbì sentimenti e idee contrastanti nei confronti degli acca…
Eclipse over North America 2024 solar eclipse redirects here. For the October eclipse, see Solar eclipse of October 2, 2024. Solar eclipse of April 8, 2024The solar eclipse during totality, seen from Dallas, TexasMapType of eclipseNatureTotalGamma0.3431Magnitude1.0566Maximum eclipseDuration268 s (4 min 28 s)LocationNazas, Durango, MexicoCoordinates25°18′N 104°06′W / 25.3°N 104.1°W / 25.3; -104.1Max. width of band198 km (123 mi)Ti…
Сельское поселение России (МО 2-го уровня)Новотитаровское сельское поселение Флаг[d] Герб 45°14′09″ с. ш. 38°58′16″ в. д.HGЯO Страна Россия Субъект РФ Краснодарский край Район Динской Включает 4 населённых пункта Адм. центр Новотитаровская Глава сельского посел…
2017 single by Liam PayneBedroom FloorSingle by Liam Paynefrom the album LP1 Released20 October 2017 (2017-10-20)GenreElectropop[1]Length3:08LabelCapitolSongwriter(s)Jacob Kasher HindlinCharlie PuthAmmar MalikSteve MacAaron JenningsNoel ZancanellaProducer(s)Steve MacBen RiceLiam Payne singles chronology Get Low (2017) Bedroom Floor (2017) For You (2018) Music videoBedroom Floor on YouTube Bedroom Floor is a song by English singer-songwriter Liam Payne. It was written by Ja…
SloveniaAssociationFootball Association of SloveniaConfederationUEFA (Europe)Head coachTomislav HorvatCaptainIgor OsredkarMost capsIgor Osredkar (187)[1]Top scorerIgor Osredkar (88)[1]FIFA codeSVNFIFA ranking24 (6 May 2024) Home colours Away colours First international Slovakia 1–1 Slovenia (Košice, Slovakia; 15 September 1995)Biggest win Slovenia 14–0 United States (Koper, Slovenia; 27 January 2016)Biggest defeat Spain 10–0 Slovenia (Caste…
В Википедии есть статьи о других людях с фамилией Эвен. Абба Эвенивр. אבא אבן 3-й Министр иностранных дел Израиля 1966 — 1974 Предшественник Голда Меир Преемник Игаль Алон 5-й Министр образования Израиля 1960 — 1963 Предшественник Залман Аран Преемник Залман Аран Рождение…
Classical approach to the many-body problem of astronomy The perturbing forces of the Sun on the Moon at two places in its orbit. The blue arrows represent the direction and magnitude of the gravitational force on the Earth. Applying this to both the Earth's and the Moon's position does not disturb the positions relative to each other. When it is subtracted from the force on the Moon (black arrows), what is left is the perturbing force (red arrows) on the Moon relative to the Earth. Because the …
Pride flag Asexual flagAdopted2010; 14 years ago (2010)DesignFour horizontal stripes colored respectively with black, grey, white, and purple Part of the LGBT seriesLGBT symbols Symbols Pink triangle Black triangle Labrys Lambda Handkerchief code Pride flags Rainbow Rainbow crossing Lesbian Gay Bisexual Transgender Pansexual Intersex Aromantic Asexual Non-binary Bear Leather vte The asexual flag was created in 2010 by a member of the Asexual …
Overview of crime in Alaska, U.S. Crime in Alaska has attracted significant attention, both within the state and nationally, due to its unique challenges and higher crime rates compared to the rest of the United States.[1] A sparsely populated state with vast wilderness areas, Alaska poses particular difficulties for law enforcement and social service agencies. Capital punishment is not applied in Alaska, having been abolished by the territorial legislature prior to statehood.[2]…
Естонії в Другій світовій війні Друга світова війна Дата: 1940-1945 Місце: Естонія Результат: радянська окупація Сторони СРСР Німеччина естонські призовники, допоміжна поліція, прикордонники та сили міліції Фінляндія (до вересня 1944) Естонські сили, орієнтовані на здобуття нез…
American talk show host and comedian (born 1974) Jimmy FallonFallon in 2013BornJames Thomas Fallon (1974-09-19) September 19, 1974 (age 49)New York City, U.S.EducationCollege of Saint Rose (BA)OccupationsComedianTV hostactorsingerwriterYears active1995–presentSpouse Nancy Juvonen (m. 2007)Children2Comedy careerMediumStand-uptelevisionfilmmusicbooksGenres Observational musical sketch surreal humor impressions satire Subject(s) American culture American p…
American political commentator This biography of a living person needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately from the article and its talk page, especially if potentially libelous.Find sources: William Arkin – news · newspapers · books · scholar · JSTOR (January 2019) (Learn how and when to remove this message)…
See also: Healthcare reform in the United States, Health care in the United States, and Health insurance coverage in the United States This article needs to be updated. Please help update this article to reflect recent events or newly available information. (March 2018) Healthcare in the United States Government health programs Federal Employees Health Benefits Program (FEHBP) Indian Health Service (IHS) Medicaid / State Health Insurance Assistance Program (SHIP) Medicare Prescription Assistance…
Druga liga 1958-1959Druga savezna liga FNRJ 1958-1959 Competizione 2. Savezna liga Sport Calcio Edizione 13ª Organizzatore FSJ Luogo Jugoslavia Partecipanti 24 Formula 2 gironi all'italiana Risultati Vincitore finale non disputata Promozioni Sloboda TuzlaOFK Belgrado Retrocessioni BorovoRudar KakanjRabotničkiLovćen Cronologia della competizione 1957-58 1959-60 Manuale La Druga savezna liga FNRJ[1] 1958-1959, conosciuta semplicemente come Druga liga 1958-1959, fu la 13ª edizione…
Indian actor This biography of a living person needs additional citations for verification. Please help by adding reliable sources. Contentious material about living persons that is unsourced or poorly sourced must be removed immediately from the article and its talk page, especially if potentially libelous.Find sources: Jai Jagadish – news · newspapers · books · scholar · JSTOR (April 2021) (Learn how and when to remove this message) Jai JagadishOccupati…
Jalan Tol Gedebage-Tasikmalaya-CilacapGedebage–Tasikmalaya–Cilacap Toll RoadJalan Tol GetaciAplikasi Pile Slab Sepanjang 9,12 kmInformasi ruteBagian dari Jalan Tol Trans JawaDikelola oleh BUJT (Dalam proses)Panjang:206.65 km (128,41 mi)Berdiri:Tahap 1(STA 00+000 – 108+300)Tahap 2(STA 108+300 – 206+650) – sekarangPersimpangan besarUjung Barat: Jalan Tol Padalarang–Cileunyi BIUTR/ Jalan Tol Dalam Kota Bandung Junction GedebageSimpang Susun MajalayaSimpang Susun NagregSimp…
Main article: Snowboarding at the 2014 Winter Olympics Snowboarding at the2014 Winter OlympicsQualification HalfpipemenwomenParallel giant slalommenwomenParallel slalommenwomenSlopestylemenwomenSnowboard crossmenwomenvte These are the qualification rules and the quota allocation for the snowboarding events at the 2014 Winter Olympics.[1] Qualification standard An athlete must have placed in the top 30 at a World Cup event after July 2012 or at the 2013 World Championships in that respect…
أوسكار موريلو (بالإسبانية: Óscar Murillo) معلومات شخصية الميلاد 18 أبريل 1988 (العمر 36 سنة)أرمينيا الطول 1.84 م (6 قدم 1⁄2 بوصة) مركز اللعب مدافع الجنسية كولومبيا معلومات النادي النادي الحالي باتشوكا الرقم 23 مسيرة الشباب سنوات فريق 2005–2006 بوكا جونيورز المسيرة الاحتر…