Transcript Slide 1
Lecture 4 Before Christmas… 1.2 SUSY Algebra (N=1) From the Haag, Lopuszanski and Sohnius extension of the Coleman-Mandula theorem we need to introduce fermionic operators as part of a “graded Lie algebra” or “superalgerba” introduce spinor operators and Weyl representation: Note Q is Majorana General Superfield Scalar field Scalar field spinor Vector field spinor (where we have suppressed spinor indices) spinor Scalar field Total derivative Action Chiral Superfields - Irreducible multiplet, - Describes lepton / slepton, quark / squark and Higgs / Higgsino multiplets In the “symmetric” representation. Scalar field Fermion field Auxilliary field Chiral Superfields - Irreducible multiplet, - Describes lepton / slepton, quark / squark and Higgs / Higgsino multiplets Chiral representation scalar spinor scalar Auxilliary fields Switch between representations change of variables: Chiral Superfields - Irreducible multiplet, - Describes lepton / slepton, quark / squark and Higgs / Higgsino multiplets scalar spinor scalar Auxilliary fields Four-divergence, yields invariant action under SUSY F-terms provide contributions to the Lagrangian density Boson ! fermion Fermion ! boson Action Lagrangian density from Chiral superfields The F-terms from products of chiral superfields will also contribute to the Lagrangian density: Another SUSY invariant contribution to the action Similarly from the triple product we can pick out the F-term: Moreover: The F-term of any polynomial of chiral superfields contributes to the SUSY invariant action! The Superpotential is a polynomial function of chiral superfields, Truncated at cubic term to keep only renormalisable terms From which the F-term contributions to the SUSY Lagrangian density can be extracted. We can now extract the F-terms for the SUSY lagrangian density, The superpotential can also be a function of only the scalar components, Allowing the Lagrangian density terms to be extracted via the recipe As well as polonomials of chiral superfields we can also take the combination of , Invariant D-term Note: 1) not a chiral superfield so the F-term (µµ term) does not transform as a total derivative, as can be checked by performing a SUSY transform or by comparison with a general superfield. 2) the D-term however does transform as a four divergence, and provides contributions to the SUSY Lagrangian density 3) the auxilliary fields Fi do not have a kinetic term (with derivatives) and hence are not really dynamical degrees of freedom, and will be fixed by their E-L eqn. 4) these terms are not present in the superpotential , but instead appear in the Kahler Potential, K(©1 … ©n, ©1y … ©ny) We can now extract the F-terms for the SUSY lagrangian density, And obtain the kinetic parts from (Vector superfields) Are not dynamical degrees of freedom, eliminated by E-L eqns: We can now extract the F-terms for the SUSY lagrangian density, And obtain the kinetic parts from (Vector superfields) Are not dynamical degrees of freedom, eliminated by E-L eqns: Sfermions (another glimpse) Recall in Lecture 1 we constructed states : (via SUSY generators) And showed new states were spin zero: (using SUSY algebra) SUSY chiral supermultiplet with electron + selectron Superpotential only a function of left chiral superfields! Use: (only renormalisable superpotential term allowed by charge conservation!) SUSY mass relation! Higgs + electron top chiral supermultiplets and Assume a superpotential Higgs + electron top chiral supermultiplets and Assume a superpotential Higgs + electron top chiral supermultiplets and Assume a superpotential SM-like Yukawa coupling H-f-f Higgs-squark-quark couplings with same Yukawa coupling! Higgs + electron top chiral supermultiplets and Assume a superpotential Quartic scalar couplings again from the same Yukawa coupling SUSY gauge theory But in SUSY Phase transform superfield! Abelian gauge transformation Abelian supergauge transformation 2.6 Vector Superfields A Vector superfield obeys the constraint: Note: still more degrees of freedom than needed for a vector boson. Some not physical! Remember Vector bosons appears in gauge theories! Supergauge invariance of superfields means many excess degrees of freedom! Can fix gauge to Wess-Zumino gauge: Gauge boson Note: Gaugino Auxilliary D 1) Wess-Zumino gauge has only gauge boson, gaugino and auxilliary D degrees of freedom. 2) Wess-Zumino gauge does not fix the ordinary gauge freedom! 3) SUSY transforms will spoil Wess-Zumino gauge fixing constraints. Mainfest SUSY invariance lost in this gauge. 4) After each SUSY transform field dependent gauge transformation can restore us to Wess-Zumino gauge