# The effect of heterogeneity on financial contagion due to overlapping portfolios

## TL;DR

This paper investigates how heterogeneity in bank and asset networks affects financial stability, revealing that power-law distributions can both weaken and strengthen system resilience depending on the shock type and network structure.

## Contribution

It introduces a detailed analysis of heterogeneity effects in bipartite financial networks, proposing a novel policy of disassortative mixing to enhance systemic resilience.

## Key findings

- Power-law degree distributions in banks reduce robustness to random failures.
- Targeted shocks to specialized or large banks increase default cascades.
- Disassortative mixing improves system resilience against shocks.

## Abstract

We consider a model of financial contagion in a bipartite network of assets and banks recently introduced in the literature, and we study the effect of power law distributions of degree and balance-sheet size on the stability of the system. Relative to the benchmark case of banks with homogeneous degrees and balance-sheet sizes, we find that if banks have a power-law degree distribution the system becomes less robust with respect to the initial failure of a random bank, and that targeted shocks to the most specialised banks (i.e. banks with low degrees) or biggest banks increases the probability of observing a cascade of defaults. In contrast, we find that a power-law degree distribution for assets increases stability with respect to random shocks, but not with respect to targeted shocks. We also study how allocations of capital buffers between banks affects the system's stability, and we find that assigning capital to banks in relation to their level of diversification reduces the probability of observing cascades of defaults relative to size based allocations. Finally, we propose a non-capital based policy that improves the resilience of the system by introducing disassortative mixing between banks and assets.