58 Chapter 3. <strong>Gauge</strong>More matter representations. To study sqcd we add chiral matter superfield living inrepresentations of G = U(N). <strong>The</strong> representation theory for this group is clearly richer thanthat of U(1), but we are only interested in three representations, two of which we have alreadyencountered.As before, the fundamental representation is the defining representation of U(N) actingon C N . Hence, fundamental matter fields consist of N components and transform under supergauge transformations asΦ f ↦−→ e iΛ Φ f ,or, in terms of the component chiral superfields,Φ n f↦−→ ( e iΛ) nn ′ Φn′ f .Since the fundamental representation of U(N) is N-dimensional, it is sometimes denoted by N.Fundamental matter fields in sqcd are the super-version of quarks, and its dynamical componentfields can be interpreted as quarks ψ ± and squarks φ.<strong>The</strong> anti-fundamental representation is conjugate to N and is indicated by ¯N or N ∗ . Wecan think of ¯Φ¯f as a row vector containing N complex chiral superfields, and super gaugetransformations act as¯Φ¯f ↦−→ ¯Φ¯f e −iΛ or ¯Φ¯f,n ↦−→ ¯Φ¯f,n ′(e−iΛ ) n ′ n .<strong>The</strong>se fields correspond to anti-quarks and their superpartners.<strong>The</strong> third representation is the adjoint representation. (Perhaps a better notation wouldbe the ‘Adjoint’ representation.) A superfield Φ a in this representation is G-valued and theircomponent fields can be viewed as matrices in G. <strong>The</strong>y transform asΦ a ↦−→ e iΛ Φ a e −iΛ or (Φ a ) n m ↦−→ ( e iΛ) nn ′(Φ′ a) n′ m ′ (e−iΛ ) m ′ m .Since this combines the transformations from the fundamental and anti-fundamental representations,we can view a adjoint field as a field in the bifundamental representation (N, ¯N).Antifundamental fields are like the W -bosons in electroweak theory.<strong>The</strong> kinetic terms for fundamentals and anti-fundamentals looks like before. In order to geta scalar quantity the kinetic term for Φ a involves a trace. 5Vacuum structure. <strong>The</strong> set-up is as follows: we consider U(N) G sym with nonabelian superfield strength Σ. We include massive matter, L f flavours of fundamental fields Φ l f(each of whichconsists of N component superfields), L¯f anti-fundamentals ¯Φ¯f,k , and L a adjoint fields Φ j a. <strong>The</strong>global flavour symmetry group H max = ( U(L f ) × U(L¯f) × U(L a ) ) /U(N) G is broken by thecorresponding twisted mass terms with parameters ˜m l f , ˜mk¯f and ˜m j a. Since the matter fields areU(N) G -multiplets, each of the twisted masses is the tensor product of this parameter with theidentity in the G-representation.<strong>The</strong>re might be a gauge invariant superpotential W compatible with the values of theseparameters. <strong>The</strong> tree-level twisted superpotential ˜Wtree = iτ trΣ contains the complex couplingτ = ir + ϑ/2π.<strong>The</strong> procedure is the same as in the abelian case. <strong>The</strong> crucial observation is that the bosonicpotential contains the term tr ( [σ, ¯σ] 2) from (3.66). For ground states this term has to vanish,forcing σ to be diagonalizable. Thus we may restrict our attention to the maximal torus U(1) Nof U(N) G . In particular, both V and Σ are diagonal, and the component expansion of thematter kinetic terms consists of N copies of the Lagrangian (3.49). We denote the correspondingdiagonal elements of Σ by Σ n , so that the vacuum structure depends on the N complex scalarcomponent fields σ n . (In general, if we do not diagonalize the gauge fields, the σ n are theeigenvalues of σ.)<strong>The</strong> vacuum structure has more possible branches than in the abelian case. Again there areHiggs and Coulomb branches, but there are also branches of mixed type. For a discussion of5 Notice that our Φ f , Φ¯f and Φ a correspond to Q, ˜Q and Φ from [1], respectively.
3.5. <strong>The</strong> nonabelian case 59the case L a = 0 we refer to §2.2 of [15]; see also §2.2 of [2]. As before, we are interested in thevacuum structure on the Coulomb branch in which all of the φ’s have to be integrated out.Vacuum equation. <strong>The</strong> ϑ-term (3.67) shows that the periodicity of ϑ can be accounted for inseveral ways: we can independently shift of each of the σ n in W tree (σ) by an amount −im n σ n ,for m n ∈ Z. This leads us to consider the shifted twisted superpotential ˜W ⃗m = ˜W − i ∑ m n σ n .<strong>The</strong> same steps as in the abelian case yield a system of N coupled vacuum equations:(exp 2π ∂ ˜W)eff∂σ n = 1 , 1 ≤ n ≤ N . (3.69)We see that the vacuum structure of our theory on the Coulomb branch is once more determinedby the effective twisted superpotential. By the decoupling and non-renormalization theorems,˜W eff can be found by integrating out the matter scalar fields, and we may assume that thesuperpotential W vanishes.Effective twisted superpotential. Let’s start with the fields in the fundamental representationand consider integrating out the field Φ l fwith twisted mass parameter ˜m l f. <strong>The</strong> multipletΦ l f contains N chiral superfields (Φl f )n whose mass terms contain σ n and are given by |σ n − ˜m l f |.We can find the resulting contribution to ˜W eff from (3.62):δ ˜W l eff,f = 12πN∑ ((σ n − ˜m l f ) log σn − ˜m l fµn=1Similarly, the result for ¯Φ¯f,k isδ ˜W k eff,¯f = 12πN∑((−σ n − ˜m k¯f ) log σn − ˜m k¯fµn=1<strong>The</strong> contribution due to Φ a turns out to beδ ˜W j eff,a = 12πm≠n)− 1 . (3.70))− 1 . (3.71)N∑((σ m − σ n − ˜m j a) log σm − σ n − ˜m j )a− 1 . (3.72)µSumming up all these contributions, we arrive at the following total effective twisted superpotentialis˜W eff (σ) = i τN∑n=1σ n + 12π+ 12π+ 12πN∑ ∑L f(σ n − ˜m l f )n=1 l=1N∑ ∑L¯f(−σ n − ˜m k¯f )n=1 k=1N∑ ∑L a(σ m − σ n − ˜m j a)m,n j=1m≠n(log σn − ˜m l fµ)− 1(log −σn − ˜m k¯fµ)− 1(log σm − σ n − ˜m j )a− 1µ(3.73)Conclusion: the vacuum equation. In conclusion, plugging (3.73) into the vacuum equations(3.69), we get the following set of equations:∏ Lfl=1 (σn − ˜m l f∏ )L¯fk=1 (σn + ˜m k¯f ) = ∏NµL f−L¯f (−1) L¯f−L ae 2πiτ∏L am≠n j=1σ n − σ m + ˜m j aσ n − σ m − ˜m j a, 1 ≤ n ≤ N (3.74)<strong>The</strong>se are the equations that we were after, and conclude this chapter.