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Riccardo Benedetti

Publications and source records attributed to Riccardo Benedetti.

31 records · Page 2Linked to original sources
arXiv2004

3D Quantum Hyperbolic Field Theory

We construct a new family of exact quantum field theories modeled on hyperbolic geometry, called {\it quantum hyperbolic field theories} (QHFTs). The QHFTs are defined for a $(2+1)$-bordism category based on the set of compact oriented 3-manifolds $Y$, equipped with properly embedded framed links $L_\Ff$ and with flat connections $ρ$ of principal $PSL(2,\C)$-bundles over $Y \setminus L_\Ff$, with arbitrary holonomy at the link meridians. A main point is the introduction of new parameters for the space of all $PSL(2,\C)$-characters of a punctured surface. Each QHFT associates to a triple $(Y,L_\Ff,ρ)$ as above with parametrized boundary components a tensor, which is generically holomorphic w.r.t. the parameters for the restriction of $ρ$ to $\partial Y \setminus L_\Ff$. This gives new numerical invariants of 3-manifolds, such as Chern-Simons invariants of $PSL(2,\mc)$-characters of arbitrary link complements, or quantum invariants of compact hyperbolic cone manifolds. Also, for any $PSL(2,\mc)$-character of a surface of finite topological type, we obtain new conjugacy classes of linear representations of the mapping class group. Finally, we discuss some evidences showing that the QHFTs are pertinent to 3D gravity.

math.GT↗
arXiv2002

QHI Theory, II: Dilogarithmic and Quantum Hyperbolic Invariants of 3-Manifolds with PSL(2,C)-Characters

We give parallel constructions of an invariant R(W,f), based on the classical Rogers dilogarithm, and of quantum hyperbolic invariants (QHI), based on the Faddeev-Kashaev quantum dilogarithms, for flat PSL(2,C)-bundles f over closed oriented 3-manifolds W. All these invariants are explicitely computed as a sum or state sums over the same hyperbolic ideal tetrahedra of the idealization of any fixed simplicial 1-cocycle description of (W,f) of a special kind, called a D-triangulation. R(W,f) recovers the volume and the Chern-Simons invariant of f, and we conjecture that it determines the semi-classical limit of the QHI.

math.GT↗
arXiv2002

On the Dynamics of G-Solenoids. Applications to Delone Sets

A G-solenoid is a laminated space whose leaves are copies of a single Lie group G, and whose transversals are totally disconnected sets. It inherits a G-action and can be considered as dynamical system. Free Z^d-actions on the Cantor set as well as a large class of tiling spaces possess such a structure of G-solenoid. We show that a G-solenoid can be seen as a projective limit of branched manifolds modeled on G. This allows us to give a topological description of the transverse invariant measures associated with a G-solenoid in terms of a positive cone in the projective limit of the dim(G)-homology groups of these branched manifolds. In particular we exhibit a simple criterion implying unique ergodicity. A particular attention is paid to the case when the Lie group $G$ is the group of affine orientation preserving isometries of the Euclidean space or its subgroup of translations.

math.DS↗
arXiv2001

Spaces of tilings, finite telescopic approximations and gap-labelling

For a large class of tilings, including the Penrose tiling in two dimension as well as the icosahedral ones in 3 dimension, the continuous hull of such a tiling inherits a minimal lamination structure with flat leaves and a transversal which is a Cantor set. In this case, we show that the continuous hull can be seen as the projective limit of a suitable sequence of branched, oriented and flat compact manifolds.The algebraic topological features related to this sequence reflect the dynamical properties of the action on the continuous hull. In particular the set of positive invariant measures of this action turns to be a convex cone, canonically associated with the orientation, in the projective limit of the top homology groups of the branched manifolds. As an application of this construction we prove a gap-labelling theorem.

math.DS↗
arXiv2001

Cosmological Time in (2+1) - Gravity

We consider maximal globally hyperbolic flat (2+1) spacetimes with compact space S of genus g>1. For any spacetime M of this type, the length of time that the events have been in existence is M defines a global time, called the cosmological time CT of M, which reveals deep intrinsic properties of spacetime. In particular, the past/future asymptotic states of the cosmological time recover and decouple the linear and the translational parts of the ISO(2,1)-valued holonomy of the flat spacetime. The initial singularity can be interpreted as an isometric action of the fundamental group of S on a suitable real tree. The initial singularity faithfully manifests itself as a lack of smoothness of the embedding of the CT level surfaces into the spacetime M. The cosmological time determines a real analytic curve in the Teichmuller space of Riemann surfaces of genus g, which connects an interior point (associated to the linear part of the holonomy) with a point on Thurston's natural boundary (associated to the initial singularity).

gr-qc↗
arXiv2001

Quantum Hyperbolic State Sum Invariants of 3-Manifolds

Any triple $(W,L,ρ)$, where $W$ is a compact closed oriented 3-manifold, $L$ is a link in $W$ and $ρ$ is a flat principal $B$-bundle over $W$ ($B$ is the Borel subgroup of upper triangular matrices of $SL(2,\mc)$), can be encoded by suitable {\it distinguished} and {\it decorated} triangulations ${\cal T}=(T,H,{\cal D})$. For each $\cal T$, for each odd integer $N\geq 3$, one defines a state sum $K_N({\cal T})$, based on the Faddeev-Kashaev quantum dilogarithm at $ω=\exp(2πi/N)$, such that $K_N(W,L,ρ)=K_N({\cal T})$ is a well-defined complex valued invariant. The purely topological, conjectural invariants $K_N(W,L)$ proposed earlier by Kashaev correspond to the special case of the {\it trivial} flat bundle. Moreover, we extend the definition of these invariants to the case of flat bundles on $W\setminus L$ with non necessarily trivial holonomy along the meridians of the link's components, and also to 3-manifolds endowed with a $B$-flat bundle and with \emph{arbitrary} non-spherical parametrized boundary components. We point out some remarkable specializations of the invariants; among these, the so called {\it Seifert-type} invariants, when $W=S^3$: these seem to be good candidates in orther to fully reconduct the Jones polynomials in the main stream of quantum hyperbolic invariants. Finally, we try to set our results against the heuristic backgroud of the Euclidean analytic continuation of (2+1)-quantum gravity with negative cosmological constant, regarded as a gauge theory with the {\it non compact} group SO(3,1) as gauge group.

math.GT↗
arXiv2000

Geometric Cone Surfaces and (2+1)- Gravity coupled to Particles

We introduce the (2+1)-spacetimes with compact space of genus g and with r gravitating particles which arise by ``Minkowskian suspensions of flat or hyperbolic cone surfaces'', by ``distinguished deformations'' of hyperbolic suspensions and by ``patchworking'' of suspensions. Similarly to the matter-free case, these spacetimes have nice properties with respect to the canonical Cosmological Time Function. When the values of the masses are sufficiently large and the cone points are suitably spaced, the distinguished deformations of hyperbolic suspensions determine a relevant open subset of the full parameter space; this open subset is homeomorphic to the product of an Euclidean space of dimension 6g-6+2r with an open subset of the Teichmüller Space of Riemann surfaces of genus g with r punctures. By patchworking of suspensions one can produce examples of spacetimes which are not distinguished deformations of any hyperbolic suspensions, although they have the same masses; in fact, we will guess that they belong to different connected components of the parameter space.

gr-qc↗
arXiv2000

Reidemeister Torsion of 3-Dimensional Euler Structures with Simple Boundary Tangency and Pseudo-Legendrian Knots

We generalize Turaev's definition of torsion invariants of pairs (M,x), where M is a 3-dimensional manifold and x is an Euler structure on M (a non-singular vector field up to homotopy relative to bM and local modifications in int(M). Namely, we allow M to have arbitrary boundary and x to have simple (convex and/or concave) tangency circles to the boundary. We prove that Turaev's H_1(M)-equivariance formula holds also in our generalized context. Our torsions apply in particular to (the exterior of) pseudo-Legendrian knots (i.e. knots transversal to a given vector field), and hence to Legendrian knots in contact 3-manifolds. We show that torsion, as an absolute invariant, contains a lifting to pseudo-Legendrian knots of the classical Alexander invariant. We also precisely analyze the information carried by torsion as a relative invariant of pseudo-Legendrian knots which are framed-isotopic. Using branched standard spines to describe vector fields we show how to explicitly invert Turaev's reconstruction map from combinatorial to smooth Euler structures, thus making the computation of torsions a more effective one. As an example we work out a specific calculation.

math.GT↗
arXiv2000

Combed 3-Manifolds with Concave Boundary, Framed Links, and Pseudo-Legendrian Links

We provide combinatorial realizations, according to the usual objects/moves scheme, of the following three topological categories: (1) pairs (M,v) where M is a 3-manifold (up to diffeomorphism) and v is a (non-singular vector) field, up to homotopy; here possibly the boundary of M is non-empty and v may be tangent to the boundary, but only in a concave fashion, and homotopy should preserve tangency type; (2) framed links L in M, up to framed isotopy; (3) triples (M,v,L), with (M,v) as above and L transversal to v, up to pseudo-Legendrian isotopy (transversality-preserving simultaneous homotopy of v and isotopy of L). All realizations are based on the notion of branched standard spine, and build on results previously obtained. Links are encoded by means of diagrams on branched spines, where the diagram is smooth with respect to the branching. Several motivations for being interested in combinatorial realizations of the topological categories considered in this paper are given in the introduction. The encoding of links is suitable for the comparison of the framed and the pseudo-Legendrian categories, and some applications are given in connection with contact structures, torsion and finite-order invariants. An estension of Trace's notion of winding number of a knot diagram is introduced and discussed.

math.GT↗
arXiv1999

Reidemeister Torsion of 3-Dimensional Euler Structures with Simple Boundary Tangency and Legendrian Knots

We generalize Turaev's definition of torsion invariants of pairs $(M,ξ)$, where $M$ is a 3-dimensional manifold and $ξ$ is an Euler structure on $M$ (a non-singular vector field up to homotopy relative to the boundary of $M$ and local modifications in the interior of $M$). Namely, we allow $M$ to have arbitrary boundary and $ξ$ to have simple (convex and/or concave) tangency circles to the boundary. We prove that Turaev's $H_1(M)$-equivariance formula holds also in our generalized context. Our torsions apply in particular to (the exterior of) Legendrian links (in particular, knots) in contact 3-manifolds, and we prove that they can distinguish knots which are isotopic as framed knots but not as Legendrian knots. Using the combinatorial encoding of vector fields based on branched standard spines we show how to explicitly invert Turaev's reconstruction map from combinatorial to smooth Euler structures, thus making the computation of torsions a more effective one. As an example we work out a specific computation.

math.GT↗
arXiv1998

Branched Spines and Contact Structures on 3-manifolds

We introduce and analyze the characteristic foliation induced by a contact structure on a branched surface, in particular a branched standard spine of a 3-manifold. We extend to (fairly general) singular foliations of branched surfaces the local existence and uniqueness results which hold for genuine surfaces. Moreover we show that global uniqueness holds when restricting to tight structures. We establish branched versions of the elimination lemma. We prove a smooth version of the Gillman-Rolfsen PL-embedding theorem, deducing that branched spines can be used to construct contact structures in a given homotopy class of plane fields.

math.GT↗
arXiv1998

Torsion Invariants of Combed 3-Manifolds with Boundary Pattern and Legendrian Links

We extend Turaev's definition of torsion invariants of 3-dimensional manifolds equipped with non-singular vector fields, by allowing (suitable) tangency circles to the boundary, and manifolds with non-zero Euler characteristic. We show that these invariants apply in particular to (the exterior of) Legendrian links in contact 3-manifolds. Our approach uses a combinatorial encoding of vector fields, based on standard spines. In this paper we extend this encoding from closed manifolds to manifolds with boundary.

math.GT↗