Search Talks

The emergence of cooperation among selfish agents that have no incentive to cooperate is a non-trivial phenomenon that has long intrigued biologists, social scientists and physicists. The iterated Prisoner’s Dilemma (IPD) game provides a natural framework for investigating this phenomenon. The spatial version of IPD, where each agent interacts only with their nearest neighbors on a specified connection topology, has been used to  study the evolution of cooperation under conditions of bounded rationality. This talk will explorehow the collective behavior that arises from the simultaneous actions of the agents (implemented by synchronous update) is affected by the connection topology among the interacting agents. The system exhibits three types of collective states, viz., a pair of absorbing states (corresponding to all agents cooperating or defecting, respectively) and a fluctuating state characterized by agents switching intermittently between cooperation and defection. We show that the system exhibits a transition from one state to another simply by altering the connection topology from regular to random, without altering any of the parameters govering the game dynamics, such as temptation payoff or noise. Such topological phase transitions in collective behavior of strategic agents suggest important role that social structure may play in promoting cooperation.

Beginning with the intimate relationship between recursive algorithms and dynamical systems, I shall describe some common dynamics that serve as templates for `stateless' learning. This will be followed by reinforcement learning for dynamic systems, using Markov decision processes as a test case.

We depict harmonic map ray structures on Teichmüller space as a geometric transition between Teichmüller ray structures and Thurston geodesic ray structures

As an application, while there may be many Thurston metric geodesics between a pair of points in Teichmüller space, we find that by imposing an additional energy minimization constraint on the geodesics, thought of as limits of harmonic map rays, we select a unique Thurston geodesic through those points. There are applications to the envelopes of Thurston geodesics between a pair of points.

Anosov representations can be considered a generalization of convex-cocompact representations for groups of higher-rank. In this talk we are considering connected components of Anosov representations from the fundamental group of a closed hyperbolic manifold N, and which contains Fuchsian representations, and their associated domains of discontinuity. We will prove that the quotient of these domains of discontinuity are always smooth fiber bundles over N. Determining the topology of the fiber is hard in general, but we are able to describe it for representations in Sp(4,C), and for the domain of discontinuity in the space of complex Lagrangians in C^4 by using the classification of smooth 4-manifolds. This is joint work with Daniele Alessandrini, Nicolas Tholozan and Anna Wienhard.

Amenability of a group action is a dynamical generalisation of amenability for groups, with interesting applications in geometry and topology. Many (non-amenable) groups, like the Gromov hyperbolic groups, relatively hyperbolic groups (with suitable parabolic subgroups), mapping class groups of surfaces and outer automorphism groups of free groups admit amenable actions.

In this talk we will define amenable action of a group and outline two constructions of amenable actions for (i) acylindrically hyperbolic groups and (ii) hierarchically hyperbolic groups, which generalise some of the above classes of groups, and thereby giving a new proof of amenable action for the mapping class groups. This is based on a joint work with Partha Sarathi Ghosh.

A hyperbolic quasifuchsian (or more generally convex co-compact) manifold $M$ contains a smallest non-empty geodesically convex subset, its convex core. The boundary of this convex core has a hyperbolic induced metric, and is pleated along a measured geodesic lamination. Thurston asked whether the induced metric, or the the measured pleating lamination, uniquely determine $M$. In the first part, we will explain why the answer is positive for the measured pleating lamination (joint w/ Bruno Dular). In the second part, we will put this problem in a more general frramework concerning the boundary data of convex subsets in hyperbolic manifolds or in hyperbolic space.

We depict harmonic map ray structures on Teichmüller space as a geometric transition between Teichmüller ray structures and Thurston geodesic ray structures

As an application, while there may be many Thurston metric geodesics between a pair of points in Teichmüller space, we find that by imposing an additional energy minimization constraint on the geodesics, thought of as limits of harmonic map rays, we select a unique Thurston geodesic through those points. There are applications to the envelopes of Thurston geodesics between a pair of points.

Anosov representations can be considered a generalization of convex-cocompact representations for groups of higher-rank. In this talk we are considering connected components of Anosov representations from the fundamental group of a closed hyperbolic manifold N, and which contains Fuchsian representations, and their associated domains of discontinuity. We will prove that the quotient of these domains of discontinuity are always smooth fiber bundles over N. Determining the topology of the fiber is hard in general, but we are able to describe it for representations in Sp(4,C), and for the domain of discontinuity in the space of complex Lagrangians in C^4 by using the classification of smooth 4-manifolds. This is joint work with Daniele Alessandrini, Nicolas Tholozan and Anna Wienhard.

We study the growth of log-spectra in subgroups of SL(n,R). Specifically, we study their extremal (rather than statistically predominant) behavior, with connections to the topic of ergodic optimization in dynamics. The main theme is that extremal elements seem to be quite special, similar to how laminations play a special role in the study of Thurston's Lipschitz metric on Teichmüller space.
Joint work with J.Danciger and F.Kassel.

Let O be a compact reflection n-orbifold whose underlying space is homeomorphic to a truncation n-polytope, i.e. a polytope obtained from an n-simplex by successively truncating vertices. In this talk, I will give a complete description of the deformation space of convex real projective structures on the orbifold O of dimension at least 4. Joint work with Suhyoung Choi and Ludovic Marquis.

I will present another Finsler metric on Teichmüller space, which is called the earthquake metric. After giving the definition of this metric, I will show that there is a kind of ‘duality’ between this metric and Thurston’s metric, and that the metric is incomplete, just like the Weil-Petersson metric.