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16 votes
Accepted

Are there principal $G$-bundles whose holonomy group is $G$?

Then I claim that the holonomy group of this connection is all of $G$. … Thus, since $G$ is connected, the holonomy of $\alpha$ is all of $G$. …
Robert Bryant's user avatar
18 votes
Accepted

Does the curvature locally determine the connection?

In fact, one can find a solution $\alpha_1$ that has holonomy in the maximal torus and a solution $\alpha_2$ whose holonomy is all of $\mathrm{SO}(3)$: Let $$ F = \begin{pmatrix}0&\mathrm{d}x_1\wedge\ …
Robert Bryant's user avatar
9 votes
Accepted

A consequence of Ambrose-Singer theorem on holonomy

However, I claim that the holonomy of $\nabla$ is $\mathrm{SL}(2,\mathbb{R})$. To see this, note that the Lie algebra of the holonomy group must contain $\mathfrak{so}(2)$. … Nevertheless, the holonomy of $\nabla$ is $\mathrm{SL}(3,\mathbb{R})$, not $\mathrm{SO}(3)$. This follows from an argument very similar to the one given above above. …
Robert Bryant's user avatar
14 votes
Accepted

Holonomy group of Enriques surface

The holonomy $H$ of $g$ cannot be contained in $\mathrm{SU}(2)$ because the canonical bundle of $S$ is not trivial (though its square is trivial). … Meanwhile, the identity component of $H$ has to be equal to $\mathrm{SU}(2)$ because this is the holonomy of the (simply-connected, non-product) K3 surface that is the double cover of $S$ endowed with …
Robert Bryant's user avatar
18 votes
Accepted

English translation of paper: Sur les variétés riemanniennes à groupe d'holonomie G2 ou Spin(7)

Section 3: The author makes some general remarks about holonomy and parallel differential forms and states that any Riemannian $7$-manifold with holonomy in $G_2$ supports a (nonzero) parallel $3$-form … and a (nonzero) parallel $4$-form and that any Riemannian $8$-manifold with holonomy in $\mathrm{Spin}(7)$ supports a (nonzero) parallel $4$-form. …
Robert Bryant's user avatar
3 votes

Holonomy of a Warped Product Metric

In general, just knowing the holonomy of $M$ will not tell you much about the holonomy of $\tilde M$. … In general, you need to know more about the metric on $M$ than just its holonomy in order to compute the holonomy of $\tilde M$. …
Robert Bryant's user avatar
10 votes
Accepted

Minimum requirements for a Kähler manifold to be hyperkähler

Suppose that the metric on $M^n$ has irreducible holonomy, is simply connected (or, slightly more generally, that the restricted holonomy $H^0$ acts irreducibly), and that there exist two independent parallel … Since there is at least one parallel complex structure $I$, the holonomy group $H^0$ is a subgroup of $\mathrm{U}(n/2)$. …
Robert Bryant's user avatar
22 votes
Accepted

Algebraic characterization of the curvature operator of symmetric spaces

Conversely, if this invariance holds, then $R$ is the curvature of an irreducible $n$-dimensional symmetric space with holonomy $G$. … Your other question about characterizing curvature operators of Riemannian manifolds with reduced holonomy is not as easy to answer. …
Robert Bryant's user avatar
1 vote

Holonomy of a triangle in an affine symmetric space

In case one has a reasonably explicit formula for the map $\exp:{\frak{m}}\to G$ and its inverse, one can work out an explicit formula for the holonomy in that case. … . $$ Using this and a little spherical trigonometry, one sees that, for a geodesic triangle with vertices $A$, $B$, and $C$ (no pair antipodal), then the holonomy of the geodesic path $A\to B\to C\to A …
Robert Bryant's user avatar
2 votes
Accepted

Decomposition of forms on a Spin$(7)$ manifold

Observe that, in a $\mathrm{Spin}(7)$-manifold, since $\mathrm{Spin}(7)\subset\mathrm{SO}(8)$, the $\mathrm{Spin}(7)$ decomposition $\Lambda^4 = \Lambda^4_1\oplus \Lambda^4_7\oplus\Lambda^4_{27}\oplus …
Robert Bryant's user avatar
18 votes
Accepted

Why Yau's theorem implies the existence of hyperkähler metric on complex symplectic manifolds?

Berger's classification of the possible irreducibly acting holonomy groups then implies that the metric must have restricted holonomy equal to $\mathrm{Sp}(n)$, since no proper subgroup of this group can … act irreducibly and be the holonomy. …
Robert Bryant's user avatar
8 votes
Accepted

Holonomy of a Ricci-flat affine connection

When $n=2$, Ricci-flatness of a connection implies that it is flat, so, in that case, yes, you get holonomy reduction locally. … Thus, by the Ambrose-Singer Holonomy Theorem, the holonomy of $\nabla$ is $\mathrm{SL}(n,\mathbb{R})$. …
Robert Bryant's user avatar
3 votes
Accepted

Isomorphisms of Positive and Negative Spinor Bundles

You're really asking an algebra question about how the various representations of $\mathrm{Spin}(8)$ interact. There are lots of places where you can read about this, but here is a set of notes that …
Robert Bryant's user avatar
3 votes

Holonomy groups of Hermitian, and hyper-Hermitian, manifolds

For which of these are you asking about the holonomy? …
Robert Bryant's user avatar