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N=1 superconformal mode algebra in NS and Ramond sectors

Facts & Assumptions

Given: Work over C. The modes Lm (m∈Z) and C are even (parity 0), and Gr is odd (parity 1); C is central, meaning its bracket with every mode is zero. The bracket of two odd modes is denoted by braces; in any representation it acts by the operator anticommutator ST+TS. In the Neveu–Schwarz (NS) sector r∈Z+12; in the Ramond (R) sector r∈Z.

Here a complex Lie superalgebra means a complex vector space in the sense of Vector space over a field, graded as g=g0ˉ⊕g1ˉ, with a parity-preserving bilinear bracket satisfying [A,B]=−(−1)∣A∣∣B∣[B,A] and, for homogeneous A,B,D, the graded Jacobi identity (−1)∣A∣∣D∣[A,[B,D]]+(−1)∣B∣∣A∣[B,[D,A]]+(−1)∣D∣∣B∣[D,[A,B]]=0. A representation means a complex vector space V=V0ˉ⊕V1ˉ with this Z/2-grading and a parity-preserving linear map ρ:g→End⁡C(V) satisfying ρ([A,B])=[ρ(A),ρ(B)]s for homogeneous A,B; here End⁡C(V) is the set of complex-linear maps V→V, with [S,T]s=ST−(−1)∣S∣∣T∣TS. For the algebra defined below, it has central charge c when ρ(C)=c id⁡V.

An algebra ∗-structure is a parity-preserving conjugate-linear involution A↦A∗ satisfying [A,B]∗=[B∗,A∗] for homogeneous elements. The convention specified below is the ∗-structure used here.

An algebraic ∗-representation here means such a representation on a nonzero graded complex vector space H=H0ˉ⊕H1ˉ with a positive-definite sesquilinear form ⟨⋅,⋅⟩ satisfying ⟨v,u⟩=⟨u,v⟩‾ (conjugate-linear in the first variable and linear in the second), together with a graded dense linear domain D=D0ˉ⊕D1ˉ⊆H for the norm ∥u∥=⟨u,u⟩, invariant under every mode. The adjoint condition is the formal identity ⟨ρ(A)u,v⟩=⟨u,ρ(A∗)v⟩ for every generator A and u,v∈D. It is an identity on this common domain; no operator closure or essential self-adjointness is included.

[F1]

Virasoro algebra in the Lm convention: The Virasoro bracket is [Lm,Ln]=(m−n)Lm+n+m3−m12δm+n,0C, and its cubic central term satisfies the Lie-algebra Jacobi identity.

[F2]
[A1]

The N=1 super-Virasoro normalization used here is the standard one in Gaberdiel, §3.7.6 and §4.1, and Ginsparg, §5.4. It is distinct from an extended super-W algebra.

Definition

For either index set I=Z+12 (NS) or I=Z (R), take g0ˉ=(⨁m∈ZCLm)⊕CC and g1ˉ=⨁r∈ICGr. Thus all displayed mode symbols and C form a linearly independent homogeneous basis of g=g0ˉ⊕g1ˉ; vectors are finite linear combinations, with coefficientwise operations and no completion. On this carrier define the N=1 superconformal mode algebra by complex-bilinear and super-skew extension of [Lm,Gr]=(m2−r)Gm+r,{Gr,Gs}=2Lr+s+r2−143 δr+s,0C, the Virasoro brackets in [F1], and [C,Lm]=[C,Gr]=0. Brackets not forced by these rules and super-skew symmetry vanish. In a representation with C=cI, the displayed central terms carry the scalar c.

The algebraic adjoint convention for a real central charge is Lm∗=L−m, Gr∗=G−r and C∗=C. A ∗-representation must have c∈R; this definition does not assert a positive-energy spectrum or classify representations.

A full N=(1,1) mode system has a second, antiholomorphic copy Lˉm,Gˉr,Cˉ with the same formulas and its own charge cˉ. All barred generators supercommute with the unbarred generators. This product construction does not identify the two charges.

Proof

1.1givenF1F2A1

The field [F2] supplies the coefficient scalars for the bilinear brackets. For triples containing only L modes, Jacobi is exactly the Virasoro Jacobi identity supplied by [F1]. Centrality makes every Jacobi expression containing C vanish.

1.2givenA1algebra

For (Lm,Ln,Gr), put a(m,r)=m/2−r. The only coefficient identity required by super-Jacobi is a(n,r)a(m,n+r)−a(m,r)a(n,m+r)=(m−n)a(m+n,r). Expanding both products and cancelling the quadratic terms gives this identity, so the Gm+n+r coefficients agree.

2.1givenA1step 1.2algebra

For (Lm,Gr,Gs), the Lm+r+s coefficients on the two sides of [Lm,{Gr,Gs}]={[Lm,Gr],Gs}+{Gr,[Lm,Gs]} are both 2(m−r−s). If m+r+s≠0, all central terms vanish. If m+r+s=0, setting b(x)=(x2−14)/3 reduces equality of central terms to a(m,r)b(m+r)+a(m,s)b(r)=m3−m6,s=−m−r. Substituting s=−m−r gives a(m,r)b(m+r)+a(m,s)b(r)=(m/2−r)((m+r)2−1/4)+(3m/2+r)(r2−1/4)3=m3−m6, which is the central contribution from 2[Lm,Lr+s].

3.1givenA1step 1.1step 1.2step 2.1algebra

For three odd modes, super-Jacobi reduces to the cyclic sum of [Gr,{Gs,Gt}]. Its coefficient of Gr+s+t is (2r−s−t)+(2s−t−r)+(2t−r−s)=0. These cases exhaust triples by the number of odd entries, proving the graded Jacobi identity.

4.1givenA1step 1.1step 2.1step 3.1algebra

For real c, reversing order in the adjoint of [Lm,Gr] gives a(m,r)G−m−r=[G−r,L−m]; for {Gr,Gs} it gives the same symmetric expression with indices −r,−s. For the LL bracket, the adjoint of its central coefficient is unchanged, while [L−n,L−m]=(m−n)L−m−n+(−n)3−(−n)12δm+n,0C. On the support m+n=0, (−n)3−(−n)=m3−m, so this is exactly [Lm,Ln]∗=[Ln∗,Lm∗], including the cubic central term. Thus the stated operation is an involutive anti-linear anti-automorphism. In a nonzero ∗-representation with ρ(C)=cI, the adjoint identity for C=C∗ gives cˉ⟨u,u⟩=c⟨u,u⟩ for nonzero u∈D, hence c∈R.

5.1givenA1step 1.1step 1.2step 2.1step 3.1step 4.1algebra∎

The antiholomorphic bracket is a copy of the same algebra, so its internal Jacobi identities follow from the preceding steps. Since all cross-copy superbrackets are zero, any mixed Jacobi expression has each nested term zero. This verifies the independent N=(1,1) product convention.

Copy conventions

The N=1 super-Virasoro algebra is only the subalgebra generated by the stress tensor and one supercurrent. It is not the extended SW(3/2,5/2) algebra used for the exceptional (E6,D8) target below.

Depends on

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