arXiv subjects

Julieth Saavedra

Publications and source records attributed to Julieth Saavedra.

7 recordsLinked to original sources

arXiv2026

Geometric Reductions of the $G_2$-Hilbert Functional via Circle Actions

In this paper, we study critical points and gradient flows of the $G_2$--Hilbert functional on a manifolds with free $\mathbb S^1$--actions. We analyze $\mathbb S^1$--invariant $G_2$--structures under the constant fiber-length non-K\"ahler transverse ansatz, reducing the variational problem to the $6$--dimensional quotient and we also consider a Gibbons--Hawking-type ansatz with varying fiber length and derive the formal negative $L^2$--gradient flow. We conclude that the unnormalized flow admits only trivial stationary configurations: flat connection, scalar-flat base metric, and constant fiber length.

math.DG↗

arXiv2026

Symmetries and the First Laplace Eigenvalue of Lawson Surfaces

In this paper, we study the first eigenvalue of the Laplace--Beltrami operator on the Lawson minimal surfaces $\xi_{m,k}$ embedded in the unit three-sphere $\mathbb{S}^3$. Motivated by Yau's conjecture on the first eigenvalue of closed embedded minimal hypersurfaces in the sphere, we develop a symmetry-based approach to the equality $\lambda_1(\xi_{m,k})=2$ for the family of Lawson surfaces with $m$ and $k$ even. Our method exploits the discrete reflection symmetries intrinsic to Lawson's construction, together with the algebraic structure of the associated reflection group, Courant's nodal domain theorem, and the coordinate eigenfunctions arising from Takahashi's theorem. More precisely, we show that the equality $\lambda_1(\xi_{m,k})=2$ follows once a natural topological obstruction for invariant nodal sets in the fundamental patch is verified.

math.DG↗

arXiv2024

Laplacian coflows of $G_2$-structures on contact Calabi--Yau 7-manifolds

We explore three versions of the Laplacian coflow of $G_2$-structures on circle fibrations over Calabi--Yau 3-folds, interpreting their dimensional reductions to the K\"ahler geometry of the base. Precisely, we reduce Ans\"atze for the Laplacian coflow, modified or not by de Turck's trick, both on trivial products $CY^3\times S^1$ and on contact Calabi--Yau 7-manifolds, obtaining in each case a natural modification of the K\"ahler--Ricci flow.

math.DG↗

arXiv2024

Riemannian Geometry of $G_2$-type Real Flag Manifolds

In this paper, we investigate homogeneous Riemannian geometry on real flag manifolds of the split real form of $\mathfrak{g}_2$. We characterize the metrics that are invariant under the action of a maximal compact subgroup of $G_2.$ Our exploration encompasses the analysis of g.o. metrics and equigeodesics on the $\mathfrak{g}_2$-type flag manifolds. Additionally, we explore the Ricci flow for the case where the isotropy representation has no equivalent summands, employing techniques from the qualitative theory of dynamical systems.

math.DG↗

arXiv2023

On the Laplacian coflow of invariant $G_2$-structures and its solitons

In this work, we approach the Laplacian coflow of a coclosed $G_2$-structure $\varphi$ using the formulae for the irreducible $G_2$-decomposition of the Hodge Laplacian and the Lie derivative of the Hodge dual $4$-form of $\varphi$. In terms of this decomposition, we characterise the conditions for a vector field as an infinitesimal symmetry of a coclosed $G_2$-structure, as well as the soliton condition for the Laplacian coflow. More specifically, we provide an easier proof for the absence of compact shrinking solitons of the Laplacian coflow. Moreover, we revisit the Laplacian coflow of coclosed $G_2$-structures on almost Abelian Lie groups addressed by Fino-Bagaglini (2018). However, our approach is based on the bracket flow point of view. Notably, by showing that the norm of the Lie bracket is strictly decreasing, we prove that we have long-time existence for any coclosed Laplacian coflow solution.

math.DG↗

arXiv2021

Flows of $\mathrm{G}_2$-structures on contact Calabi--Yau $7$-manifolds

We study the Laplacian flow and coflow on contact Calabi-Yau $7$-manifolds. We show that the natural initial condition leads to an ancient solution of the Laplacian flow with a finite time Type I singularity which is not a soliton, whereas it produces an immortal (though not eternal and not self-similar) solution of the Laplacian coflow which has an infinite time singularity, that is Type IIb unless the transverse Calabi--Yau geometry is flat. The flows in each case collapse (after normalising the volume) to a lower-dimensional limit, which is either $\mathbb{R}$ for the Laplacian flow or standard $\mathbb{C}^3$ for the Laplacian coflow. We also study the Hitchin flow in this setting, which we show coincides with the Laplacian coflow up to reparametrisation of time, and defines an (incomplete) Calabi--Yau structure on the spacetime track of the flow.

math.DG↗

arXiv2021

Harmonic $Sp(2)$-invariant $G_2$-structures on the $7$-sphere

We describe the $10$-dimensional space of $Sp(2)$-invariant $G_2$-structures on the homogeneous $7$-sphere $S^7=Sp(2)/Sp(1)$ as $\mathbb{R}^+\times Gl^+(3,\mathbb{R})$. In those terms, we formulate a general Ansatz for $G_2$-structures, which realises representatives in each of the $7$ possible isometric classes of homogeneous $G_2$-structures. Moreover, the well-known nearly parallel round and squashed metrics occur naturally as opposite poles in an $S^3$-family, the equator of which is a new $S^2$-family of coclosed $G_2$-structures satisfying the harmonicity condition $div T=0$. We show general existence of harmonic representatives of $G_2$-structures in each isometric class through explicit solutions of the associated flow and describe the qualitative behaviour of the flow. We study the stability of the Dirichlet gradient flow near these critical points, showing explicit examples of degenerate and nondegenerate local maxima and minima, at various regimes of the general Ansatz. Finally, for metrics outside of the Ansatz, we identify families of harmonic $G_2$-structures, prove long-time existence of the flow and study the stability properties of some well-chosen examples.

math.DG↗