The Common Origin of Linear and Nonlinear Chiral

Multiplets in Mechanics

F. Delduc, E. Ivanov,

a)Laboratoire de Physique de l’ENS Lyon, CNRS UMR 5672,

46, allée d’Italie, 69364 Lyon Cedex 07, France

b)Bogoliubov Laboratory of Theoretical Physics, JINR,

141980 Dubna, Moscow region, Russia

Elaborating on previous work (hep-th/0605211, 0611247), we show how the linear and nonlinear chiral multiplets of supersymmetric mechanics with the off-shell content (2,4,2) can be obtained by gauging three distinct two-parameter isometries of the “root” (4,4,0) multiplet actions. In particular, two different gauge groups, one abelian and one non-abelian, lead, albeit in a disguised form in the second case, to the same (unique) nonlinear chiral multiplet. This provides an evidence that no other nonlinear chiral multiplets exist. General sigma model type actions are discussed, together with the restricted potential terms coming from the Fayet-Iliopoulos terms associated with abelian gauge superfields. As in our previous work, we use the manifestly supersymmetric language of harmonic superspace. A novel point is the necessity to use in parallel the and gauge frames, with the “bridges” between these two frames playing a crucial role. It is the harmonic analyticity which, though being non-manifest in the frame, gives rise to both linear and nonlinear chirality constraints.

PACS: 11.30.Pb, 11.15.-q, 11.10.Kk, 03.65.-w

Keywords: Supersymmetry, gauging, isometry, superfield

## 1 Introduction

The one-dimensional supersymmetry and related models of supersymmetric (quantum) mechanics reveal many specific surprising features and, at the same time, have a lot of links with higher-dimensional theories of current interest (see e.g. [1, 2] and refs. therein). This motivates many research groups towards thorough study and further advancing of this subject (see e.g. [2, 3]).

Recently, we argued [4, 5] that the plethora of relationships between various supermultiplets with the same number of fermionic fields, but different divisions of the bosonic fields into physical and auxiliary ones (so called “ automorphic dualities” [6]), can be adequately understood in the approach based on the gauging of isometries of the invariant actions of some basic (“root”) multiplets by non-propagating (“topological”) gauge multiplets (these isometries should commute with supersymmetry, i.e. be triholomorphic). The key merit of our approach is the possibility to study these relationships in a manifestly supersymmetric superfield manner, including the choice of supersymmetry-preserving gauges. Previous analysis [6, 7] was basically limited to the component level and used some “ad-hoc” substitutions of the auxiliary fields. In the framework of the gauging procedure, doing this way corresponds to making use of the Wess-Zumino-type gauges.

In [4, 5] we focused on the case of supersymmetric mechanics and showed that the actions of the multiplets with the off-shell contents , and can be obtained by gauging certain isometries of the general actions of the “root” multiplet in the harmonic superspace. Based on this, we argued that the latter is the underlying superspace for all mechanics models. Here we confirm this by studying, along the same line, the remaining multiplets, the chiral and nonlinear chiral off-shell multiplets with the field content . They prove to naturally arise as a result of gauging some two-parameter isometry groups admitting a realization on the harmonic analytic superfield which describes the multiplet . The origin of the difference between these two versions of the multiplet is attributed to the fact that they emerge from gauging two essentially different isometries: the linear multiplet is associated with gauging of some purely shift isometries, while the nonlinear one corresponds to gauging the product of two “rotational” isometries, viz. the target space rescalings and a subgroup of the Pauli-Gürsey group. We also recover the same nonlinear version of this multiplet, though in disguise, by gauging a mixture of the rescaling and shift isometries. It is the last possible two-parameter symmetry implementable on . Thus we show that two known off-shell forms of the multiplet , the linear and nonlinear ones, in fact exhaust all possibilities.

It should be emphasized that the existence of non-linear cousins of the basic supermultiplets is one of the most amazing features of extended supersymmetry. In superspace they are described by superfields satisfying some nonlinear versions of the standard constraints (e.g. of chirality constraints). As a result, the realization of the corresponding off-shell supersymmetry on the component fields of such supermultiplets is intrinsically nonlinear. The list of such multiplets known to date includes the nonlinear analogs of the multiplets [8, 9, 10, 4, 11], [12, 13], [13], as well as of the multiplets [14] and [15]. As shown in [4], within the approach based on the gauging procedure the difference between linear and nonlinear multiplets originates from the fact that the first multiplet is related to the gauging of the shift or rotational symmetries, and the second one to the gauging of the target space rescalings. In the case of the multiplets we find an analogous intimate relation between the type of multiplet and the two-parameter symmetry group which has to be gauged to generate it.

## 2 Brief preliminaries

Throughout the paper we use the same harmonic superspace (HSS) techniques, conventions and notation as in [12, 4, 5]. The “root” multiplet is described by the harmonic analytic superfield which is subjected to the Grassmann harmonic and bosonic harmonic constraints

(2.1) |

Here are coordinates of the harmonic analytic superspace [12], , , they are related to the standard superspace (central basis) coordinates as

(2.2) |

Respectively, the covariant spinor derivatives and their harmonic projections are defined by

(2.3) | |||

(2.4) |

In the analytic basis, the derivatives and are short,

(2.5) |

so the conditions (2.1a) become the harmonic Grassmann Cauchy-Riemann conditions stating that does not depend on the coordinates in this basis. The analyticity-preserving harmonic derivative and its conjugate in the analytic basis are given by

(2.6) |

and are reduced to the pure harmonic partial derivatives in the central basis. They satisfy the commutation relations

(2.7) |

where is the operator counting external harmonic charges. In the analytic basis it is given by

(2.8) |

while in the central basis it coincides with its pure harmonic part. On the extra doublet index of the superfield the so-called Pauli-Gürsey group is realized. It commutes with the supersymmetry generators, as distinct from the -symmetry group which acts on the doublet indices of the Grassmann and harmonic coordinates, spinor derivatives and supercharges.

The free action of can be written either in the analytic, or the central superspace

(2.9) |

where and the integration measures are defined as

(2.10) |

The general sigma model-type action of (with a non-trivial bosonic target space metric) is given by

(2.11) |

The constraint (2.1) possesses a seven-parameter group of rigid symmetries commuting with supersymmetry (it includes as a subgroup) [5]. One can single out the appropriate subclasses of the general action (2.11) (including the free action (2.9)) which are invariant with respect to one or another symmetry of this sort. For further use we give here the full list of non-equivalent two-parameter symmetries.

Abelian symmetries

(2.12) |

Nonabelian symmetry

(2.13) |

Here the constant triplet is normalized as ^{1}^{1}1We use the same notation for the
unrelated constant triplets in (2.12a) and (2.12b), hoping that this will not give rise
to any confusion.

(2.14) |

The algebra of the transformations (2.13) provides an example of two-generator solvable algebra. All other possible two-parameter symmetry groups listed in [5] can be reduced to (2.12), (2.13) by a redefinition of .

In what follows we shall gauge these symmetries and show that this gauging gives rise to three versions of the multiplet , with the corresponding general actions arising from the appropriate invariant subclasses of the general action (2.11). It turns out that the standard linear chiral multiplet emerges as the result of gauging purely shift isometry (2.12a) while the two alternative gaugings give rise to two nonlinear versions of this multiplet. The nonlinear multiplet obtained from gauging the group (2.12b) is identical to the one discovered in [13]. The multiplet obtained from gauging (2.13), although looking different, can be identified with the previous one after suitable redefinitions.

## 3 Chiral multiplet

We start with the gauged version of the transformations (2.12a)

(3.1) |

where and are now charge-zero analytic superfields. The gauge covariantization of the harmonic constraint (2.1b) is given by

(3.2) |

where and are analytic gauge superfield transforming as

(3.3) |

In the cases considered here (as distinct from the cases treated in [4, 5]), it is convenient to make use of the “bridge” representation of the gauge superfields [16, 17].

The analytic superfields and may be represented as

(3.4) |

where and are non-analytic harmonic superfields which may be interpreted as “bridges” between the analytic and central superspace gauge groups (called the and gauge groups, see [17]). They transform under local shifts as

(3.5) |

where and are non-analytic gauge superparameters bearing no dependence on the harmonic variables

(3.6) |

We now define the non-analytic doublet superfield by

(3.7) |

As a consequence of (3.2), (3.4), it satisfies the simple harmonic constraint

(3.8) |

which implies

(3.9) |

where the superfields are independent of the harmonic variables and form a real quartet. We also have

(3.10) |

where

(3.11) |

and

(3.12) |

From (3.10) and (3.12) one can find the gauge transformation law of the non-analytic harmonic superfield :

(3.13) |

Now it is easy to determine how the superfields introduced in (3.7), (3.10) transform under the local shift symmetries. They are inert under the gauge transformations and have the following gauge transformation law

(3.14) |

As a consequence of the Grassmann analyticity constraints (2.1), the superfield satisfies the following fermionic constraints

(3.15) |

It is important that, due to the analyticity of the gauge superfields , , the fermionic connections , depend linearly on the harmonic variables. We shall use the notations

(3.16) |

Using (3.9) and (3.16), one can rewrite (3.15) in the following equivalent form with no harmonic dependence at all:

(3.17) |

Now let us more closely inspect the transformation laws (3.14). We start by choosing a frame in which the matrix has only one non-vanishing component:

(3.18) |

In this frame the transformations (3.14) look as

(3.19) |

or, in terms of the superfields defined in (3.9),

(3.20) |

It is then convenient to choose the unitary-type gauge

(3.21) |

Now the constraints (3.17) determine the spinor connection superfields and their conjugate in terms of the remaining superfield and its complex conjugate

(3.22) |

simultaneously with imposing the constraints on these superfields

(3.23) |

These constraints may be interpreted as twisted chirality conditions. They can be given the standard form
of the chirality conditions by relabelling the spinor derivative in such
a way that the -symmetry acting on the indices gets hidden, while another
(which rotates through ), gets manifest ^{2}^{2}2Both these
-symmetry are manifest in the quartet notation
, .. Thus we have succeeded in deriving
the linear chiral multiplet from the analytic multiplet
by gauging two independent shift isometries realized on the latter.

Let us now examine this correspondence on the level of the invariant actions. We start with the gauge covariantization of the free action (2.9) of the analytic superfield . In the full superspace the covariantized action reads

(3.24) |

It is gauge invariant up to a total harmonic derivative in the integrand, i.e. it is of the Chern-Simons type. It may be equivalently rewritten in terms of the superfield and the bridges ,

(3.25) |

In this form it is invariant under both the and gauge transformations. In fact, the action can be written as a sum of two terms, the first of which transforms only under the gauge group, and the second only under the group

(3.26) | |||

(3.27) |

To check the invariance of we use the following transformation laws :

(3.28) |

It is worthwhile to note that all three terms in the action are singlets (independent of harmonic variables), so that the harmonic integral is in fact not necessary. After some simple algebra, making use of the integration by parts with respect to the harmonic derivatives, the constraint (3.2) and the definitions (3.4), (3.11) and (3.12), one can show that, up to a total harmonic derivative,

(3.29) |

whence one obtains the representation of the gauge-covariantized action (3.24) solely in terms of the superfields :

(3.30) |

Now, the gauge condition (3.21) simply amounts to

(3.31) |

and in this gauge the action (3.30) takes the standard form of the free action of the (twisted) chiral multiplet

(3.32) |

Thus the free action of the chiral multiplet arises as a particular gauge of the properly gauge-covariantized free action of the analytic multiplet . Note that this equivalence, like in other cases [4, 5], was shown here in a manifestly supersymmetric superfield approach, without any need to pass to the components. It is interesting to note that there exist two more equivalent useful forms of the action (3.24) in terms of the original superfields :

(3.33) |

Checking the gauge invariance of the action in the second form is especially simple: one uses the transformation law (3.13) and the fact that is analytic in virtue of the relation

(3.34) |

Let us now comment on the general sigma-model type action. The only invariant of the gauge transformations (3.1), (3.13) which one can construct from and is the quantity defined as follows

(3.35) |

where

It admits the equivalent representation, in which its gauge invariance becomes manifest

(3.36) |

(the remaining relations in (3.35) preserve their form modulo the replacements ). The subclass of the general sigma-model type action (2.11) invariant under the gauge transformations (3.1), (3.13) is then defined as follows

(3.37) |

In the gauge (3.21) and in the frame (3.18) we have

(3.38) |

and, after integration over harmonics, the action (3.37) is reduced to the most general action of the twisted chiral superfields . Note the relation

(3.39) |

The free action (3.24) can also be expressed through the universal invariant :

(3.40) |

This relation can be proved, starting from the form of the free action (3.30) and integrating by parts with respect to the harmonic derivatives. Another way to see this is to compare both sides in the original frame representation (i.e. in terms of ) by choosing the Wess-Zumino gauge for the superfields and

Finally, we address the issue of the Fayet-Iliopoulos (FI) terms. In the present case one can define two independent gauge invariant FI terms

(3.41) |

Let us consider the first one. Rewriting it in the full harmonic superspace

(3.42) |

expressing from the relation (3.7), integrating by parts with using the analyticity property of and and performing in the end the integration over harmonics, this term in the gauge (3.21) and frame (3.18) can be transformed to the expression

(3.43) |

It is a particular case of twisted chiral superpotential term. Analogously,

(3.44) |

It is unclear whether a general chiral superpotential can be generated from some gauge invariant action.

## 4 Nonlinear chiral multiplet

Let us now consider the gauging of the two-parameter abelian symmetry (2.12b)

(4.1) |

The harmonic constraint (2.1b) is now covariantized as

(4.2) |

The analytic potentials , possess the same gauge transformation laws (3.3) and are expressed through the bridges with the mixed transformation rules (3.5) by the same relations (3.4). However, since now transforms homogeneously under the gauge transformations, the relation (3.7) between the and world objects has to be modified:

(4.3) |

or, in another form,

(4.4) |

A direct calculation shows that the constraint (4.2) entails, for ,

(4.5) |

whence, in the central basis,

(4.6) |

(cf. (3.9)). Also, using the transformation laws (3.5) and (4.1), it is easy to find

(4.7) |

In what follows it will be convenient to choose the frame (3.18) in which

(4.8) |

(4.9) |

Like in the previous Section, the analyticity of implies the “covariant analyticity” for :

(4.10) |

(4.11) |

From the analyticity of it follows that the gauge connections in (4.10), (4.11) are linear in harmonics

(4.12) |

Now it is time to properly fix the gauge freedom (4.9). Assuming that possesses a non-zero constant background, a convenient gauge is

(4.13) |

Substituting this gauge into the covariant analyticity conditions for in (4.11), taking into account the relations (4.6), (4.12), and equating to zero the coefficients of three independent products of harmonics ( and ), we obtain

(4.14) |

where , .

Thus the only independent object that remains in the gauge (4.13) is a complex superfield