Search Talks

Readings:
Kerr Black Holes Are Not Unique to General Relativity, by D. Psaltis https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.100.091101
Gravitational waves from the inspiral of a compact object into a massive, axisymmetric body with arbitrary multipole moments by F. Ryan  https://journals.aps.org/prd/abstract/10.1103/PhysRevD.52.5707
Towards a formalism for mapping the spacetimes of massive compact objects: Bumpy black holes and their orbits, by Collins & Hughes, https://journals.aps.org/prd/abstract/10.1103/PhysRevD.69.124022
Systematic study of event horizons and pathologies of parametrically deformed Kerr spacetimes, by T. Johannsen, https://journals.aps.org/prd/abstract/10.1103/PhysRevD.87.124017
Metric for rapidly spinning black holes suitable for strong-field tests of the no-hair theorem, by Johannsen & Psaltis, https://journals.aps.org/prd/abstract/10.1103/PhysRevD.83.124015
Spacetime and orbits of bumpy black holes, by Vigeland & Hughes, https://journals.aps.org/prd/abstract/10.1103/PhysRevD.81.024030
Regular black hole metric with three constants of motion, by T. Johannsen, https://journals.aps.org/prd/abstract/10.1103/PhysRevD.88.044002

Readings:
Black Holes in Classical General Relativity and Beyond, by D. Psaltis https://www.worldscientific.com/doi/10.1142/9789811282676_0001
The Kerr spacetime: A brief introduction, by M. Visser https://arxiv.org/pdf/0706.0622

The talk will discuss a different modification to the Bala-Goyal framework.  Here agents form beliefs based on their own experience and that of their neighbors, just like in the base model.  But they do not always perform the action they believe is best.  Instead, they weigh their expected payoff from taking a given action against their preference for conforming with their neighbors.  This modification leads to several new effects, including a different way in which polarization may arise, this time due to network structure.  We will conclude by reflecting on what it means that there are multiple, apparently distinct ways in which polarization can arise in simple models. 

Philosophers and economists have used cultural evolutionary models of bargaining to understand issues related to fairness and justice, and especially how fair and unfair conventions and norms might arise in human societies. One line of this research shows how the presence of social categories in such models allows for inequitable equilibria that are not possible in models without social categories. This is taken to help explain why in human groups with social categories inequity is often the rule rather than the exception. But in previous models, it is typically assumed that these categories are rigid, easily observable, and binary. In reality, social categories are not always so tidy. We introduce evolutionary models where the tags connected with social categories can be flexible, variable, or difficult to observe, i.e., where these tags can carry different amounts of information about group membership. We show how alterations to these tags can undermine the stability of unfair conventions. We argue that these results can inform projects intended to ameliorate inequity, especially projects that seek to alter the properties of category markers.

The facultatively multicellular amoeba Dictyostelium discoideum is a model system for studying the transition from unicellular to multicellular organization. It is a remarkable example of microbes with aggregative life cycles, which evolved multiple times independently in distant taxa. A key feature of such cycles is that multicellular aggregates can contain cells that are genetically different, and are therefore subjected to a high degree of conflict.

I will discuss different solutions that have been proposed to account for the evolutionary persistence of such apparently paradoxical life cycles. In particular, in the light of recent experimental results, I will address the link between proximate causes, rooted in single-cell mechanics, and ultimate causation. I will also show how agent-based and eco-evolutionary models can be used to understand the role of heterogeneous motility in the evolution of aggregative life cycles.

 In this era of omnipresent social media, social contagions are becoming a growing matter of interest. Our work integrates insights from systematic survey data, the tool of choice for social opinion exploration, with computational models to demonstrate a novel framework for deriving compartmental models from open-ended questions. By analyzing free-form survey responses and qualitative narratives, we systematically map individual opinions and behaviors into discrete compartments that mirror the stages of influence and adoption observed in various peer influenced dynamics, like public health and marketing campaigns. In the vaccine perception domain, respondents’ descriptions of peer interactions and protective behavior are classified into states analogous to susceptible, influenced, and resistant, capturing the dynamics of opinion formation and behavioral change. Similarly, in the referral marketing scenario, open-ended responses reveal latent engagement stages that inform a compartmental structure reflective of awareness, participation, and advocacy. Our quantitative treatment shows that these data-driven compartments can be effectively incorporated into dynamical systems models, giving rise to interesting opinion diffusion patterns. The proposed framework not only bridges qualitative insights with rigorous mathematical modeling but also highlights the broader applicability of compartmental approaches in deciphering complex social processes from open-ended inquiry.