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{{distinguish|Harish-Chandra homomorphism}} | |||
In [[mathematics]], the '''Harish-Chandra isomorphism''', introduced by {{harvs|txt|last=Harish-Chandra|year=1951}}, | |||
is an [[isomorphism]] of commutative rings constructed in the theory of [[Lie algebra]]s. The isomorphism maps the [[center (algebra)|center]] ''Z''(''U''(''g'')) of the [[universal enveloping algebra]] ''U''(''g'') of a [[reductive Lie algebra]] ''g'' to the elements ''S''(''h'')<sup>''W''</sup> of the [[symmetric algebra]] ''S''(''h'') of a [[Cartan subalgebra]] ''h'' that are invariant under the [[Weyl group]] ''W''. | |||
==Fundamental invariants== | |||
Let ''n'' be the '''rank''' of ''g'', which is the dimension of the Cartan subalgebra ''h''. [[H. S. M. Coxeter]] observed that ''S''(''h'')<sup>''W''</sup> is a [[polynomial ring|polynomial algebra]] in ''n'' variables (see [[Chevalley–Shephard–Todd theorem]] for a more general statement). Therefore, the center of the universal enveloping algebra of a reductive Lie algebra is a polynomial algebra. The degrees of the generators are the degrees of the fundamental invariants given in the following table. | |||
{| class="wikitable" style="text-align:center" | |||
|- | |||
! Lie algebra || [[Coxeter number]] ''h'' || [[Dual Coxeter number]] || Degrees of fundamental invariants | |||
|- | |||
| '''R'''</sub> || 0 || 0 || 1 | |||
|- | |||
| A<sub>''n''</sub> || ''n'' + 1 || ''n'' + 1 || 2, 3, 4, ..., ''n'' + 1 | |||
|- | |||
| B<sub>''n''</sub> || 2''n'' || 2''n'' − 1 || 2, 4, 6, ..., 2''n'' | |||
|- | |||
| C<sub>''n''</sub> || 2''n'' || ''n'' + 1 || 2, 4, 6, ..., 2''n'' | |||
|- | |||
| D<sub>''n''</sub> || 2''n'' − 2 || 2''n'' − 2 || ''n''; 2, 4, 6, ..., 2''n'' − 2 | |||
|- | |||
| E<sub>6</sub> || 12 || 12 || 2, 5, 6, 8, 9, 12 | |||
|- | |||
| E<sub>7</sub> || 18 || 18 || 2, 6, 8, 10, 12, 14, 18 | |||
|- | |||
| E<sub>8</sub> || 30 || 30 || 2, 8, 12, 14, 18, 20, 24, 30 | |||
|- | |||
| F<sub>4</sub> || 12 || 9 || 2, 6, 8, 12 | |||
|- | |||
| G<sub>2</sub> || 6 || 4 || 2, 6 | |||
|} | |||
For example, the center of the universal enveloping algebra of ''G''<sub>2</sub> is a polynomial algebra on generators of degrees 2 and 6. | |||
==Examples== | |||
*If ''g'' is the Lie algebra ''sl''(2, '''R'''), then the center of the universal enveloping algebra is generated by the [[Casimir invariant]] of degree 2, and the Weyl group acts on the Cartan subalgebra, which is isomorphic to '''R''', by negation, so the invariant of the Weyl group is simply the square of the generator of the Cartan subalgebra, which is also of degree 2. | |||
== Introduction and setting == | |||
Let ''g'' be a [[semisimple Lie algebra]], ''h'' its [[Cartan subalgebra]] and λ, μ ∈ ''h''* be two elements of the [[weight space]] and assume that a set of [[Positive root#Positive roots and simple roots|positive roots]] Φ<sup>+</sup> have been fixed. Let ''V''<sub>λ</sub>, resp. ''V''<sub>μ</sub> be [[highest weight module]]s with highest weight λ, resp. μ. | |||
=== Central characters === | |||
The ''g''-modules ''V''<sub>λ</sub> and ''V''<sub>μ</sub> are representations of the [[universal enveloping algebra]] ''U''(''g'') and its [[center (algebra)|center]] acts on the modules by scalar multiplication (this follows from the fact that the modules are generated by a highest weight vector). So, for ''v'' in ''V''<sub>λ</sub> and ''x'' in ''Z''(''U''(''g'')), | |||
:<math>x\cdot v:=\chi_\lambda(x)v</math> | |||
and similarly for ''V''<sub>μ</sub>. | |||
The functions <math>\chi_\lambda, \,\chi_\mu</math> are homomorphims to scalars called ''central characters''. | |||
==Statement of Harish-Chandra theorem== | |||
For any λ, μ ∈ ''h''*, the characters <math>\chi_\lambda=\chi_\mu</math> if and only if λ+δ and μ+δ are on the same [[orbit (group theory)|orbit]] of the [[Weyl group]] of ''h''*, where δ is the half-sum of the [[positive root]]s.<ref>Humphreys (1972), p.130</ref> | |||
Another closely related formulation is that the [[Harish-Chandra homomorphism]] from the center of the [[universal enveloping algebra]] ''Z''(''U''(''g'')) to ''S''(''h'')<sup>''W''</sup> (the elements of the symmetric algebra of the Cartan subalgebra fixed by the Weyl group) is an [[isomorphism]]. | |||
== Applications == | |||
The theorem may be used to obtain a simple algebraic proof of [[Weyl's character formula]] for finite dimensional representations. | |||
Further, it is a necessary condition for the existence of a nonzero homomorphism of some highest weight modules (a homomorphism of such modules preserves central character). A simple consequence is that for [[Verma module]]s or [[generalized Verma module]]s ''V''<sub>λ</sub> with highest weight λ, there exist only finitely many weights μ such that a nonzero homomorphism ''V''<sub>λ</sub> → ''V''<sub>μ</sub> exists. | |||
==See also== | |||
* [[Translation functor]] | |||
* [[Universal enveloping algebra]] | |||
* [[Infinitesimal character]] | |||
== Notes == | |||
{{reflist}} | |||
==References== | |||
*{{Citation | last1=Harish-Chandra | title=On some applications of the universal enveloping algebra of a semisimple Lie algebra | jstor=1990524 | mr=0044515 | year=1951 | journal=[[Transactions of the American Mathematical Society]] | issn=0002-9947 | volume=70 | pages=28–96}} | |||
*{{cite isbn|0387900535}} | |||
*{{Citation | last1=Humphreys | first1=James E. | author1-link=James Humphreys (mathematician) | title=Representations of semisimple Lie algebras in the BGG category O | publisher=AMS | year=2008 | isbn=978-0-8218-4678-0 | page=26}} | |||
*{{Citation | last1=Knapp | first1=Anthony W. | first2=David A. |last2=Vogan| title=Cohomological induction and unitary representations | publisher=[[Princeton University Press]] | series=Princeton Mathematical Series | isbn=978-0-691-03756-1 | mr=1330919 | year=1995 | volume=45}} | |||
*Knapp, Anthony, ''Lie groups beyond an introduction'', Second edition, pages 300–303. | |||
[[Category:Lie algebras]] | |||
[[Category:Representation theory of Lie algebras]] | |||
[[Category:Theorems in algebra]] |
Revision as of 21:44, 19 September 2013
Template:Distinguish In mathematics, the Harish-Chandra isomorphism, introduced by Template:Harvs, is an isomorphism of commutative rings constructed in the theory of Lie algebras. The isomorphism maps the center Z(U(g)) of the universal enveloping algebra U(g) of a reductive Lie algebra g to the elements S(h)W of the symmetric algebra S(h) of a Cartan subalgebra h that are invariant under the Weyl group W.
Fundamental invariants
Let n be the rank of g, which is the dimension of the Cartan subalgebra h. H. S. M. Coxeter observed that S(h)W is a polynomial algebra in n variables (see Chevalley–Shephard–Todd theorem for a more general statement). Therefore, the center of the universal enveloping algebra of a reductive Lie algebra is a polynomial algebra. The degrees of the generators are the degrees of the fundamental invariants given in the following table.
Lie algebra | Coxeter number h | Dual Coxeter number | Degrees of fundamental invariants |
---|---|---|---|
R | 0 | 0 | 1 |
An | n + 1 | n + 1 | 2, 3, 4, ..., n + 1 |
Bn | 2n | 2n − 1 | 2, 4, 6, ..., 2n |
Cn | 2n | n + 1 | 2, 4, 6, ..., 2n |
Dn | 2n − 2 | 2n − 2 | n; 2, 4, 6, ..., 2n − 2 |
E6 | 12 | 12 | 2, 5, 6, 8, 9, 12 |
E7 | 18 | 18 | 2, 6, 8, 10, 12, 14, 18 |
E8 | 30 | 30 | 2, 8, 12, 14, 18, 20, 24, 30 |
F4 | 12 | 9 | 2, 6, 8, 12 |
G2 | 6 | 4 | 2, 6 |
For example, the center of the universal enveloping algebra of G2 is a polynomial algebra on generators of degrees 2 and 6.
Examples
- If g is the Lie algebra sl(2, R), then the center of the universal enveloping algebra is generated by the Casimir invariant of degree 2, and the Weyl group acts on the Cartan subalgebra, which is isomorphic to R, by negation, so the invariant of the Weyl group is simply the square of the generator of the Cartan subalgebra, which is also of degree 2.
Introduction and setting
Let g be a semisimple Lie algebra, h its Cartan subalgebra and λ, μ ∈ h* be two elements of the weight space and assume that a set of positive roots Φ+ have been fixed. Let Vλ, resp. Vμ be highest weight modules with highest weight λ, resp. μ.
Central characters
The g-modules Vλ and Vμ are representations of the universal enveloping algebra U(g) and its center acts on the modules by scalar multiplication (this follows from the fact that the modules are generated by a highest weight vector). So, for v in Vλ and x in Z(U(g)),
and similarly for Vμ.
The functions are homomorphims to scalars called central characters.
Statement of Harish-Chandra theorem
For any λ, μ ∈ h*, the characters if and only if λ+δ and μ+δ are on the same orbit of the Weyl group of h*, where δ is the half-sum of the positive roots.[1]
Another closely related formulation is that the Harish-Chandra homomorphism from the center of the universal enveloping algebra Z(U(g)) to S(h)W (the elements of the symmetric algebra of the Cartan subalgebra fixed by the Weyl group) is an isomorphism.
Applications
The theorem may be used to obtain a simple algebraic proof of Weyl's character formula for finite dimensional representations.
Further, it is a necessary condition for the existence of a nonzero homomorphism of some highest weight modules (a homomorphism of such modules preserves central character). A simple consequence is that for Verma modules or generalized Verma modules Vλ with highest weight λ, there exist only finitely many weights μ such that a nonzero homomorphism Vλ → Vμ exists.
See also
Notes
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References
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To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Template:Cite isbn
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010
- Many property agents need to declare for the PIC grant in Singapore. However, not all of them know find out how to do the correct process for getting this PIC scheme from the IRAS. There are a number of steps that you need to do before your software can be approved.
Naturally, you will have to pay a safety deposit and that is usually one month rent for annually of the settlement. That is the place your good religion deposit will likely be taken into account and will kind part or all of your security deposit. Anticipate to have a proportionate amount deducted out of your deposit if something is discovered to be damaged if you move out. It's best to you'll want to test the inventory drawn up by the owner, which can detail all objects in the property and their condition. If you happen to fail to notice any harm not already mentioned within the inventory before transferring in, you danger having to pay for it yourself.
In case you are in search of an actual estate or Singapore property agent on-line, you simply should belief your intuition. It's because you do not know which agent is nice and which agent will not be. Carry out research on several brokers by looking out the internet. As soon as if you end up positive that a selected agent is dependable and reliable, you can choose to utilize his partnerise in finding you a home in Singapore. Most of the time, a property agent is taken into account to be good if he or she locations the contact data on his website. This may mean that the agent does not mind you calling them and asking them any questions relating to new properties in singapore in Singapore. After chatting with them you too can see them in their office after taking an appointment.
Have handed an trade examination i.e Widespread Examination for House Brokers (CEHA) or Actual Property Agency (REA) examination, or equal; Exclusive brokers are extra keen to share listing information thus making certain the widest doable coverage inside the real estate community via Multiple Listings and Networking. Accepting a severe provide is simpler since your agent is totally conscious of all advertising activity related with your property. This reduces your having to check with a number of agents for some other offers. Price control is easily achieved. Paint work in good restore-discuss with your Property Marketing consultant if main works are still to be done. Softening in residential property prices proceed, led by 2.8 per cent decline within the index for Remainder of Central Region
Once you place down the one per cent choice price to carry down a non-public property, it's important to accept its situation as it is whenever you move in – faulty air-con, choked rest room and all. Get round this by asking your agent to incorporate a ultimate inspection clause within the possibility-to-buy letter. HDB flat patrons routinely take pleasure in this security net. "There's a ultimate inspection of the property two days before the completion of all HDB transactions. If the air-con is defective, you can request the seller to repair it," says Kelvin.
15.6.1 As the agent is an intermediary, generally, as soon as the principal and third party are introduced right into a contractual relationship, the agent drops out of the image, subject to any problems with remuneration or indemnification that he could have against the principal, and extra exceptionally, against the third occasion. Generally, agents are entitled to be indemnified for all liabilities reasonably incurred within the execution of the brokers´ authority.
To achieve the very best outcomes, you must be always updated on market situations, including past transaction information and reliable projections. You could review and examine comparable homes that are currently available in the market, especially these which have been sold or not bought up to now six months. You'll be able to see a pattern of such report by clicking here It's essential to defend yourself in opposition to unscrupulous patrons. They are often very skilled in using highly unethical and manipulative techniques to try and lure you into a lure. That you must also protect your self, your loved ones, and personal belongings as you'll be serving many strangers in your home. Sign a listing itemizing of all of the objects provided by the proprietor, together with their situation. HSR Prime Recruiter 2010 - Knapp, Anthony, Lie groups beyond an introduction, Second edition, pages 300–303.
- ↑ Humphreys (1972), p.130