R-parity

The general superpotential of MSSM contains terms where the baryon and the lepton numbers are violated. In order to cure this, a new symmetry, called R-parity is introduced. It is a multiplicative quantum number where all the particles of the Standard Model have positive R-parity, while their superpartners have negative R-parity, where the quantum number is given by

R=(-1)^3(B-L)+2S (6)

for a particle with spin S and baryon- and lepton number B and L. This symmetry has a great influence of the phenomenology of the MSSM, since it requires that supersymmetric particles always are produced in pairs. Otherwise this would lead to results in conflict with observation, for instance flavour changing neutral currents. In addition to that, the conservation of R-parity, means that the Lightest Supersymmetric Particle (LSP) is absolutely stable. This could turn out to be a good candidate for cold dark matter [17].

Table: Particle content and notation in the Minimal Supersymmetric Standard Model (MSSM). Arrows indicate particles that mix due to the Yukawa interactions, and the corresponding physical particles that results. From Ref. [15].

Quarks				Squarks
(spin-$1\over2$)	$\left({u\atop d}\right)_L$	uR , dR		(spin-0)	$\left({\tilde u\atop\tilde d}\right)_L$	$\tilde u_R$ , $\tilde d_R$
	$\left({c\atop s}\right)_L$	cR , sR			$\left({\tilde c\atop\tilde s}\right)_L$	$\tilde c_R$ , $\tilde s_R$
	$\left({t\atop b}\right)_L$	tR , bR			$\left({\tilde t\atop\tilde b}\right)_L$	$\tilde t_R$ , $\tilde b_R$
						$\longrightarrow$ $\tilde t_{1,2}\,,\tilde b_{1,2}$
Leptons				Sleptons
(spin-$1\over2$)	$\left({e\atop \nu_e}\right)_L$	eR		(spin-0)	$\left({\tilde e\atop\tilde \nu_e}\right)_L$	$\tilde e_R$
	$\left({\mu\atop \nu_\mu}\right)_L$	$\mu_R$			$\left({\tilde \mu\atop\tilde \nu_\mu}\right)_L$	$\tilde \mu_R$
	$\left({\tau\atop\nu_\tau}\right)_L$	$\tau_R$			$\left({\tilde \tau\atop\tilde \nu_\tau}\right)_L$	$\tilde t_R$
						$\longrightarrow$ $\tilde \tau_{1,2}$
Gauge bosons				Gauginos
(spin-1)	g			(spin-$1\over2$)	$\tilde g$
	$\gamma$				$\tilde{\gamma}$	Neutralinos
	$\z$				$\widetilde Z$	$\longrightarrow$ $\chi^0_{1,2,3,4}$
	$W^\pm$				$\widetilde W^\pm$	$\{\tilde\gamma,\widetilde Z,\widetilde H^0_{1,2}\}$
Higgs bosons				Higgsinos		Charginos
(spin-0)	h,H,A			(spin-$1\over2$)	$\widetilde H^0_{1,2}$	$\longrightarrow$ $\chi^\pm_{1,2}$
	$H^\pm$				$\widetilde H^\pm$	$\{\widetilde W^\pm,\widetilde H^\pm\}$