Jucys–Murphy element

In mathematics, the Jucys–Murphy elements in the group algebra $\mathbb{C} [S_n]$ of the symmetric group, named after Algimantas Adolfas Jucys and G. E. Murphy, are defined as a sum of transpositions by the formula:

$X_1=0, ~~~ X_k= (1 k)+ (2 k)+\cdots+(k-1\ k), ~~~ k=2,\dots,n.$

They play an important role in the representation theory of the symmetric group.

Properties

They generate a commutative subalgebra of $\mathbb{C} [ S_n]$. Moreover, X_n commutes with all elements of $\mathbb{C} [S_{n-1}]$.

The vectors of the Young basis are eigenvectors for the action of X_n. For any standard Young tableau U we have:

$X_k v_U =c_k(U) v_U, ~~~ k=1,\dots,n,$

where c_k(U) is the content b − a of the cell (a, b) occupied by k in the standard Young tableau U.

Theorem (Jucys): The center $Z(\mathbb{C} [S_n])$ of the group algebra $\mathbb{C} [S_n]$ of the symmetric group is generated by the symmetric polynomials in the elements X_k.

Theorem (Jucys): Let t be a formal variable commuting with everything, then the following identity for polynomials in variable t with values in the group algebra $\mathbb{C} [S_n]$ holds true:

$(t+X_1) (t+X_2) \cdots (t+X_n)= \sum_{\sigma \in S_n} \sigma t^{\text{number of cycles of }\sigma}.$

Theorem (Okounkov–Vershik): The subalgebra of $\mathbb{C} [S_n]$ generated by the centers

$Z(\mathbb{C} [ S_1]), Z(\mathbb{C} [ S_2]), \ldots, Z(\mathbb{C} [ S_{n-1}]), Z(\mathbb{C} [S_n])$

is exactly the subalgebra generated by the Jucys–Murphy elements X_k.

See also

• Representation theory of the symmetric group
• Young symmetrizer