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A global perspective to connections on principal 2-bundles

  • Konrad Waldorf EMAIL logo
Published/Copyright: October 17, 2017

Abstract

For a strict Lie 2-group, we develop a notion of Lie 2-algebra-valued differential forms on Lie groupoids, furnishing a differential graded-commutative Lie algebra equipped with an adjoint action of the Lie 2-group and a pullback operation along Morita equivalences between Lie groupoids. Using this notion, we define connections on principal 2-bundles as Lie 2-algebra-valued 1-forms on the total space Lie groupoid of the 2-bundle, satisfying a condition in complete analogy to connections on ordinary principal bundles. We carefully treat various notions of curvature, and prove a classification result by the non-abelian differential cohomology of Breen–Messing. This provides a consistent, global perspective to higher gauge theory.

MSC 2010: 53C08; 22A22; 55R65

Communicated by Karl-Hermann Neeb


Award Identifier / Grant number: WA 3300/1-1

Funding statement: This work was supported by the German Research Foundation under project code WA 3300/1-1.

A Formulary for calculations in strict Lie 2-algebras

The formulas presented here are valid for a strict Lie 2-algebra consisting of Lie algebras 𝔤 and 𝔥, a Lie algebra homomorphism t*:𝔥𝔤, and a bilinear map α*:𝔤×𝔥𝔥. The axioms are

α*([X1,X2],Y)=α*(X1,α*(X2,Y))-α*(X2,α*(X1,Y)),
α*(X,[Y1,Y2])=[α*(X,Y1),Y2]+[Y1,α*(X,Y2)],
α*(t*(Y1),Y2)=[Y1,Y2],
t*α*(X,Y)=[X,t*(Y)].

Formulas involving the adjoint action are

t*Adh=Adt(h)t*,
Ada(α*(X,Y))=α*(Adt(a)(X),Ada(Y)).

Formulas involving the map αg:HH defined by αg(h):=α(g,h) are

Adgt*=t*(αg)*,
Adα(g,h)(αg)*=(αg)*Adh,
(αt(h))*=Adh,
α*(Adg(X),Y)=(αg)*(α*(X,(αg-1)*(Y))),
(αg)*(α*(X,Y))=α*(Adg(X),(αg)*(Y)).

Formulas involving the map α~h:GH defined by α~h(g):=h-1α(g,h) are

(α~h1h2)*=Adh2-1(α~h1)*+(α~h2)*,
(α~α(g,h))*=(αg)*(α~h)*Adg-1,
(α~h-1)*=-Adh(α~h)*,
t*((α~h)*(X))=Adt(h)-1(X)-X,
((α~h)*t*)(Y)=Adh-1(Y)-Y,
(α~h)*([X,Y])=[(α~h)*(X),(α~h)*(Y)]+α*(X,(α~h)*(Y))-α*(Y,(α~h)*(X)).

Formulas involving the exterior derivative are

dα*(ωη)=α*(dωη)+(-1)deg(ω)α*(ωdη),
d(αg)*(φ)=(αg)*(dφ)+α*(g*θ¯(αg)*(φ)),
dAdg-1(φ)=Adg-1(dφ)-[g*θAdg-1(φ)],
d(α~h)*(φ)=(α~h)*(dφ)+(-1)deg(φ)α*(φh*θ)-[h*θ(α~h)*(φ)].

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Received: 2017-05-03
Revised: 2017-08-28
Published Online: 2017-10-17
Published in Print: 2018-07-01

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