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Radu A. Ionas

Publications and source records attributed to Radu A. Ionas.

9 recordsLinked to original sources
arXiv2023

Revisiting Atiyah-Hitchin manifold in the generalized Legendre transform

We revisit construction of the Atiyah-Hitchin manifold in the generalized Legendre transform approach. This is originally studied by Ivanov and Rocek and is subsequently investigated more by Ionas, in the latter of which the explicit forms of the Kähler potential and the Kähler metric are calculated. There is a difference between the former and the latter. In the generalized Legendre transform approach, a Kähler potential is constructed from the contour integration of one function with holomorphic coordinates. The choice of the contour in the latter is different from the former's one, whose difference may yield a discrepancy in the Kähler potential and eventually in the Kähler metric. We show that the former only gives the real Kähler potential, which is consistent with its definition, while the latter yields the complex one. We derive the Kähler potential and the metric for the Atiyah-Hitchin manifold in terms of holomorphic coordinates for the contour considered by Ivanov and Roček for the first time.

hep-th↗
arXiv2019

An analogue of the Gibbons-Hawking Ansatz for quaternionic Kähler spaces

We show that the geometry of $4n$-dimensional quaternionic Kähler spaces with a locally free $\mathbb{R}^{n+1}$-action admits a Gibbons-Hawking-like description based on the Galicki-Lawson notion of quaternionic Kähler moment map. This generalizes to higher dimensions a four-dimensional construction, due to Calderbank and Pedersen, of self-dual Einstein manifolds with two linearly independent commuting Killing vector fields. As an application, we use this new Ansatz to give an explicit equivariant completion of the twistor space construction of the local c-map proposed by Roček, Vafa and Vandoren.

math.DG↗
arXiv2019

Twisted hyperkähler symmetries and hyperholomorphic line bundles

In this paper we propose and investigate in full generality new notions of (continuous, non-isometric) symmetry on hyperkähler spaces. These can be grouped into two categories, corresponding to the two basic types of continuous hyperkähler isometries which they deform: tri-Hamiltonian isometries, on one hand, and rotational isometries, on the other. The first category of deformations gives rise to Killing spinors and generate what are known as hidden hyperkähler symmetries. The second category gives rise to hyperholomorphic line bundles over the hyperkähler manifolds on which they are defined and, by way of the Atiyah-Ward correspondence, to holomorphic line bundles over their twistor spaces endowed with meromorphic connections, generalizing similar structures found in the purely rotational case by Haydys and Hitchin. Examples of hyperkähler metrics with this type of symmetry include the c-map metrics on cotangent bundles of affine special Kähler manifolds with generic prepotential function, and the hyperkähler constructions on the total spaces of certain integrable systems proposed by Gaiotto, Moore and Neitzke in connection with the wall-crossing formulas of Kontsevich and Soibelman, to which our investigations add a new layer of geometric understanding.

math.DG↗
arXiv2008

A note on conformal symmetry in projective superspace

We describe a sufficient condition for actions constructed in projective superspace to possess an SU(2) R-symmetry. We check directly that this condition implies that the corresponding hyperkahler varieties, constructed by means of the generalized Legendre transform, have a Swann bundle structure.

hep-th↗
arXiv2008

Quaternionic Kahler spaces with large toric symmetry

We consider a general 4n-dimensional quaternionic Kahler geometry with a free action of the torus T^(n+1). The toric action lifts onto the Swann bundle of the quaternionic Kahler space to a tri-holomorphic action that commutes with the standard H* action on the bundle. By matching Pedersen and Poon's generalized Gibbons-Hawking Ansatz description of the total space with the Swann picture we extract the local geometry of the quaternionic Kahler base. Specifically, we obtain explicit expressions for the quaternionic Kahler metric and Sp(1) connection in terms of a set of reduced Higgs fields and connection 1-forms that satisfy a reduced Bogomol'nyi-type equation. We find, moreover, that these Higgs fields can be derived from a single function V satisfying a system of linear second-order partial differential constraints. In four dimensions, corresponding to the case of self-dual Einstein manifolds with two commuting Killing vector fields, our formulas coincide with those obtained through a different approach by Calderbank and Pedersen. Finally, we show how to construct explicit solutions to the reduced Bogomol'nyi and V equations by means of Lindstrom and Rocek's generalized Legendre transform construction for a large class of quaternionic Kahler manifolds related to the c-map.

math.DG↗
arXiv2007

Elliptic constructions of hyperkaehler metrics I: The Atiyah-Hitchin manifold

This is the first in a series of papers in which we develop a twistor-based method of constructing hyperkaehler metrics from holomorphic functions and elliptic curves. As an application, we revisit the Atiyah-Hitchin manifold and derive in an explicit holomorphic coordinate basis closed-form formulas for, among other things, the metric, the holomorphic symplectic form and all three Kaehler potentials.

math.DG↗
arXiv2007

Elliptic constructions of hyperkaehler metrics II: The quantum mechanics of a Swann bundle

The generalized Legendre transform method of Lindstrom and Rocek yields hyperkaehler metrics from holomorphic functions. Its main ingredients are sections of ${\cal O}(2j)$ bundles over the twistor space satisfying a reality condition with respect to antipodal conjugation on the hyperkaehler sphere of complex structures. Formally, the structure of the real ${\cal O}(2j)$ sections is identical to that of quantum-mechanical wave functions describing the states of a particle with spin $j$ in the spin coherent representation. We analyze these sections and their SO(3) invariants and illustrate our findings with two Swann bundle constructions.

math.DG↗
arXiv2007

Elliptic constructions of hyperkaehler metrics III: Gravitons and Poncelet polygons

In the generalized Legendre approach, the equation describing an asymptotically locally Euclidean space of type $D_n$ is found to admit an algebraic formulation in terms of the group law on a Weierstrass cubic. This curve has the structure of a Cayley cubic for a pencil generated by two transversal plane conics, that is, it takes the form $Y^2 = \det ({\cal A}+X{\cal B})$, where ${\cal A}$ and ${\cal B}$ are the defining $3 \times 3$ matrices of the conics. In this light, the equation can be interpreted as the closure condition for an elliptic billiard trajectory tangent to the conic ${\cal B}$ and bouncing into various conics of the pencil determined by the positions of the monopoles. Poncelet's porism guarantees then that once a trajectory closes to a star polygon, any trajectory will close, regardless of the starting point and after the same number of steps.

math.DG↗