# Superconformal algebra

In theoretical physics, the superconformal algebra is a graded Lie algebra or superalgebra that combines the conformal algebra and supersymmetry. In two dimensions, the superconformal algebra is infinite-dimensional. In higher dimensions, superconformal algebras are finite-dimensional and generate the superconformal group (in two Euclidean dimensions, the Lie superalgebra does not generate any Lie supergroup).

## Superconformal algebra in dimension greater than 2

The conformal group of the $(p+q)$-dimensional space $\mathbb {R} ^{p,q}$ is $SO(p+1,q+1)$ and its Lie algebra is ${\mathfrak {so}}(p+1,q+1)$. The superconformal algebra is a Lie superalgebra containing the bosonic factor ${\mathfrak {so}}(p+1,q+1)$ and whose odd generators transform in spinor representations of ${\mathfrak {so}}(p+1,q+1)$. Given Kac's classification of finite-dimensional simple Lie superalgebras, this can only happen for small values of $p$ and $q$. A (possibly incomplete) list is
* ${\mathfrak {osp}}^{*}(2N|2,2)$ in 3+0D thanks to ${\mathfrak {usp}}(2,2)\simeq {\mathfrak {so}}(4,1)$;
* ${\mathfrak {osp}}(N|4)$ in 2+1D thanks to ${\mathfrak {sp}}(4,\mathbb {R} )\simeq {\mathfrak {so}}(3,2)$;
* ${\mathfrak {su}}^{*}(2N|4)$ in 4+0D thanks to ${\mathfrak {su}}^{*}(4)\simeq {\mathfrak {so}}(5,1)$;
* ${\mathfrak {su}}(2,2|N)$ in 3+1D thanks to ${\mathfrak {su}}(2,2)\simeq {\mathfrak {so}}(4,2)$;
* ${\mathfrak {sl}}(4|N)$ in 2+2D thanks to ${\mathfrak {sl}}(4,\mathbb {R} )\simeq {\mathfrak {so}}(3,3)$;
* real forms of $F(4)$ in five dimensions
* ${\mathfrak {osp}}(8^{*}|2N)$ in 5+1D, thanks to the fact that spinor and fundamental representations of ${\mathfrak {so}}(8,\mathbb {C} )$ are mapped to each other by outer automorphisms.

## Superconformal algebra in 3+1D

According to the superconformal algebra with ${\mathcal {N}}$ supersymmetries in 3+1 dimensions is given by the bosonic generators $P_{\mu }$, $D$, $M_{\mu \nu }$, $K_{\mu }$, the U(1) R-symmetry $A$, the SU(N) R-symmetry $T_{j}^{i}$ and the fermionic generators $Q^{\alpha i}$, ${\overline {Q}}_{i}^{\dot {\alpha }}$, $S_{i}^{\alpha }$ and ${\overline {S}}^{{\dot {\alpha }}i}$. Here, $\mu ,\nu ,\rho ,\dots$ denote spacetime indices; $\alpha ,\beta ,\dots$ left-handed Weyl spinor indices; ${\dot {\alpha }},{\dot {\beta }},\dots$ right-handed Weyl spinor indices; and $i,j,\dots$ the internal R-symmetry indices.
The Lie superbrackets of the bosonic conformal algebra are given by
    $[M_{\mu \nu },M_{\rho \sigma }]=\eta _{\nu \rho }M_{\mu \sigma }-\eta _{\mu \rho }M_{\nu \sigma }+\eta _{\nu \sigma }M_{\rho \mu }-\eta _{\mu \sigma }M_{\rho \nu }$
    $[M_{\mu \nu },P_{\rho }]=\eta _{\nu \rho }P_{\mu }-\eta _{\mu \rho }P_{\nu }$
    $[M_{\mu \nu },K_{\rho }]=\eta _{\nu \rho }K_{\mu }-\eta _{\mu \rho }K_{\nu }$
    $[M_{\mu \nu },D]=0$
    $[D,P_{\rho }]=-P_{\rho }$
    $[D,K_{\rho }]=+K_{\rho }$
    $[P_{\mu },K_{\nu }]=-2M_{\mu \nu }+2\eta _{\mu \nu }D$
    $[K_{n},K_{m}]=0$
    $[P_{n},P_{m}]=0$
where η is the Minkowski metric; while the ones for the fermionic generators are:
    $\left\{Q_{\alpha i},{\overline {Q}}_{\dot {\beta }}^{j}\right\}=2\delta _{i}^{j}\sigma _{\alpha {\dot {\beta }}}^{\mu }P_{\mu }$
    $\left\{Q,Q\right\}=\left\{{\overline {Q}},{\overline {Q}}\right\}=0$
    $\left\{S_{\alpha }^{i},{\overline {S}}_{{\dot {\beta }}j}\right\}=2\delta _{j}^{i}\sigma _{\alpha {\dot {\beta }}}^{\mu }K_{\mu }$
    $\left\{S,S\right\}=\left\{{\overline {S}},{\overline {S}}\right\}=0$
    $\left\{Q,S\right\}=$
    $\left\{Q,{\overline {S}}\right\}=\left\{{\overline {Q}},S\right\}=0$
The bosonic conformal generators do not carry any R-charges, as they commute with the R-symmetry generators:
    $[A,M]=[A,D]=[A,P]=[A,K]=0$
    $[T,M]=[T,D]=[T,P]=[T,K]=0$
But the fermionic generators do carry R-charge:
    $[A,Q]=-{\frac {1}{2}}Q$
    $[A,{\overline {Q}}]={\frac {1}{2}}{\overline {Q}}$
    $[A,S]={\frac {1}{2}}S$
    $[A,{\overline {S}}]=-{\frac {1}{2}}{\overline {S}}$
    $[T_{j}^{i},Q_{k}]=-\delta _{k}^{i}Q_{j}$
    $[T_{j}^{i},{\overline {Q}}^{k}]=\delta _{j}^{k}{\overline {Q}}^{i}$
    $[T_{j}^{i},S^{k}]=\delta _{j}^{k}S^{i}$
    $[T_{j}^{i},{\overline {S}}_{k}]=-\delta _{k}^{i}{\overline {S}}_{j}$
Under bosonic conformal transformations, the fermionic generators transform as:
    $[D,Q]=-{\frac {1}{2}}Q$
    $[D,{\overline {Q}}]=-{\frac {1}{2}}{\overline {Q}}$
    $[D,S]={\frac {1}{2}}S$
    $[D,{\overline {S}}]={\frac {1}{2}}{\overline {S}}$
    $[P,Q]=[P,{\overline {Q}}]=0$
    $[K,S]=[K,{\overline {S}}]=0$

## Superconformal algebra in 2D

There are two possible algebras with minimal supersymmetry in two dimensions; a Neveu–Schwarz algebra and a Ramond algebra. Additional supersymmetry is possible, for instance the N = 2 superconformal algebra.