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The 3-cycle filter for ν=(3,2) on S_8
Example
For and the filter The -cycle virtual character filter gives the virtual character of because the four partitions with a removable -border strip are (height ), (height ), (height ) and (height ), with signs . It vanishes on every class of whose cycle type has no part ; the computations below verify this on the classes without -cycles that are displayed in the statement: the identity class, where has degree , the class of -cycles, where all four characters vanish because none of the four shapes is a hook (The value of an irreducible character on a full cycle is supported on hooks), and the class , where the rule gives , , , , so that .
Facts & Assumptions
Given: The partitions and , and for every partition of an integer the character of the complex Specht module (Column antisymmetrizers, polytabloids, and Specht modules).
Filter proposition: is the outer product with , and it vanishes on every class of whose cycle type has no part ; vanishes off the class of -cycles, so (The -cycle virtual character filter).
Removable border strip: a removable -strip of is a connected, -free skew diagram with nodes and ; its height is its number of rows minus one, equivalently where is its number of columns (Removable border strips and their height, Hook, arm, leg, and hook length of a box).
Murnaghan–Nakayama rule: for a cycle of length on a specified set of points fixed by (a specified fixed point for length ), summed over the removable -strips of (The Murnaghan–Nakayama character rule).
Full-cycle values: for an -cycle , if , and otherwise; in particular whenever contains a block (The value of an irreducible character on a full cycle is supported on hooks).
Dimensions by the hook length formula: , , , (The hook length formula).
Class language: a class contains a -cycle exactly when its cycle type has a part , and the identity class is the class of cycle type (Support, fixed points, disjoint cycles, cycle length, disjoint-cycle decompositions, and cycle type).
Verification
A partition contains exactly when and , leaving the eleven candidates ; among their skew differences , which all have nodes, exactly four are edge-connected and contain no block, namely the horizontal strip with columns in , the corners and with in and , and the vertical strip with in ; the other seven differences are disconnected, for instance , where the node is not adjacent to or . The heights are , namely , so the four signs and the displayed expression for follow.
The four dimensions of [F5] give ; equivalently by [F1] and because the identity of is not a -cycle, so the degree vanishes.
On the class of -cycles each of the four shapes contains a block (rows and , columns and ), so none is a hook and on that class for all four by the full-cycle lemma [F4]; hence vanishes there.
On the class the rule [F3] gives: , since the unique -strip takes to with height and has no -strip; from the strips to (height ) and to (height ), with and ; from the strips to and to , both of height , with ; and because has no -strip. Hence on the class , whose cycle type has no part .
Steps 2.1, 2.2 and 2.3 verify the vanishing predicted by [F1] on the identity class, the class of -cycles and the class , all of which are classes of without a -cycle, confirming the displayed value there.
Remarks
- Consistency of the four shapes with the hook-length list. The removable -strips found in step 1.1 correspond to the hook lengths of the four shapes: for instance the strip to is the hook of the node , of length ; the full hook-length multiset of is , and the other strips arise from further hooks of length in the respective shapes.
Depends on
- The $r$-cycle virtual character filter
- Removable border strips and their height
- The value of an irreducible character on a full cycle is supported on hooks
- The Murnaghan–Nakayama character rule
- The hook length formula
- Hook, arm, leg, and hook length of a box
- Support, fixed points, disjoint cycles, cycle length, disjoint-cycle decompositions, and cycle type
- Column antisymmetrizers, polytabloids, and Specht modules
Used by
Nothing in the library uses this result yet.
Dependency tree · two levels
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Sources
- G. D. James, The Representation Theory of the Symmetric Groups, Lecture Notes in Mathematics 682, Springer 1978 (complete author-hosted scan, 161 pp.) (standard reference, not scraped)
- I. G. Macdonald, Symmetric Functions and Hall Polynomials, 2nd ed., Oxford Mathematical Monographs, 1995 (complete author-hosted scan, 486 pp.) (standard reference, not scraped)