Research interests

Our work focuses on the statistical physics of complex systems, in particular stochastic processes out of equilibrium. I am mainly interested in the development of analytical theory, but naturally most of our work also involves simulations. I have also collaborated with a number of colleagues in other disciplines, most notably in evolutionary and developmental biology, with linguists, economists and social scientists. 

If you are a (prospective) student you may be interested in the methods we use:


Principal research topics (partially overlapping):

Stochastic populations and individual-based models

This is really the main topic of my work. We use methods from statistical physics to study populations consisting of discrete individuals. Our main interest is in the effects of noise. Applications include social and biological populations.

Key papers

Evolutionary dynamics, intrinsic noise, and cycles of cooperation

AJ Bladon, T Galla, AJ McKane

Physical Review E 81 (6), 066122


Mixing times in evolutionary game dynamics

AJ Black, A Traulsen, T Galla

Physical Review Letters 109 (2), 028101


Consensus and diversity in multistate noisy voter models

F Herrerías-Azcué, T Galla

Physical Review E 100 (2), 022304


Stochastic waves in a Brusselator model with nonlocal interaction

T Biancalani, T Galla, AJ McKane

Physical Review E 84 (2), 026201


Competition for resources can explain patterns of social and individual learning in nature

M Smolla, RT Gilman, T Galla, S Shultz

Proceedings of the Royal Society B: Biological Sciences 282 (1815), 20151405


Effects of noise and confidence thresholds in nominal and metric Axelrod dynamics of social influence

L De Sanctis, T Galla






Disordered systems, random matrices and models of complex ecosystems

I did my PhD with David Sherrington, one of the fathers of spin glass physics, so naturally I have an interest in disordered systems. Recent work focuses on the statistical physics of random Lotka-Volterra systems, and how the spectra of random matrices can be used to characterise the stability of `feasible' equilibria. The AI (actual investigator) for most of our recent papers is Joseph W. Baron.



Key papers

Dispersal-induced instability in complex ecosystems

JW Baron, T Galla

Nature communications 11 (1), 6032


Breakdown of random-matrix universality in persistent Lotka-Volterra communities

JW Baron, TJ Jewell, C Ryder, T Galla

Physical Review Letters 130 (13), 137401


Eigenvalues of random matrices with generalized correlations: A path integral approach

JW Baron, TJ Jewell, C Ryder, T Galla

Physical Review Letters 128 (12), 120601


Dynamically evolved community size and stability of random Lotka-Volterra ecosystems 

T Galla

Europhysics Letters 123 (4), 48004





Stochastic systems in switching environments

Many biological systems are subject to changing external environments. In this line of worl we study the statistical physics of individual-based models for which the rules of engagement switch from time to time, often stochastically. We have developed a method to systematically approximate the stationary states of sysems with intrinsic noise in switching environments, and we work on fixation of mutants in changing external conditions. Applications include the evolution of anti-microbial resistance (collaboration with Danna Gifford), and the evolution of mating types (collaboration with George Constable).

Selected papers

Intrinsic noise in systems with switching environments

PG Hufton, YT Lin, T Galla, AJ McKane

Physical Review E 93 (5), 052119


Fixation in finite populations evolving in fluctuating environments

P Ashcroft, PM Altrock, T Galla

Journal of The Royal Society Interface 11 (100), 20140663


Switching environments, synchronous sex, and the evolution of mating types

E Berríos-Caro, T Galla, GWA Constable

Theoretical population biology 138, 28-42


Competition delays multi-drug resistance evolution during combination therapy

E Berríos-Caro, DR Gifford, T Galla

Journal of Theoretical Biology 509, 110524





Systems with delay and applications in biology

I'm interested in non-Markovian stochastic systems (systems with delay), and in particular noise-induced effects in these systems. We have come up with systematic Gaussian approximations for individual-based systems with delay. These methods can be used to study for example gene regulatory circuits. I have collaborated with Nancy Papalopulu and her lab (Jochen Kursawe in particular) on genetic oscillators and cell differentiation in developmental biology.


Selected papers

Intrinsic fluctuations in stochastic delay systems: Theoretical description and application to a simple model of gene regulation

T Galla

Physical Review E 80 (2), 021909


Stochastic processes with distributed delays: chemical Langevin equation and linear-noise approximation

T Brett, T Galla

Physical Review Letters 110 (25), 250601


microRNA input into a neural ultradian oscillator controls emergence and timing of alternative cell states

M Goodfellow, NE Phillips, C Manning, T Galla, N Papalopulu

Nature communications 5 (1), 3399


Stochasticity in the miR-9/Hes1 oscillatory network can account for clonal heterogeneity in the timing of differentiation

NE Phillips, CS Manning, T Pettini, V Biga, E Marinopoulou, P Stanley, ...

Elife 5, e16118


Network Meta-Analysis

A few years ago Annabel Davies (then first year PhD student) and I decided to jump on a ship with unknown destination and to start working on Network Meta-Analysis, a technique in medical statistics. We started collaborating with Gerta Rücker and her group, and we have established some analogies of NMA and random walks on networks. We have also written an introduction to NMA for physicists.


Papers

Network meta-analysis: a statistical physics perspective

AL Davies, T Galla

Journal of Statistical Mechanics: Theory and Experiment 2022 (11), 11R001


Network meta‐analysis and random walks

AL Davies, T Papakonstantinou, A Nikolakopoulou, G Rücker, T Galla

Statistics in Medicine 41 (12), 2091-2114


Degree irregularity and rank probability bias in network meta‐analysis

AL Davies, T Galla

Research Synthesis Methods 12 (3), 316-332




Dynamics of language features

This is a collaboration with Henri Kauhanen, Ricardo Bermúdez-Otero and Deepthi Gopal. We use an individual-based model of the evolution of language features and its statistical physics solution to introduce `linguistic temperature' -- a dimensionless measure of the propensity of language features to undergo change. Using data from the World Atlas of Language Structures, we show that temperature estimates correlate well with conventional measures of instability, obtained for example from phylogenetic analyses.

Paper

Geospatial distributions reflect temperatures of linguistic features

H Kauhanen, D Gopal, T Galla, R Bermúdez-Otero

Science advances 7 (1), eabe6540


Game learning

We are interested in what happens when players learn how to play a game by trial and error. They try out strategies and then use a learning model to decide which strategies work well and which ones don't. This is in contrast to the fully rational players with full information in conventional game theory. With Doyne Farmer I have shown that realistic learning models lead to unpredictable outcome when the number of strategies in the game is large. Thus, the player's actions do not converge to a Nash equilibrium. We have also worked on the influence of noise (imperfect observations) on the outcome of game learning.

Key papers


Complex dynamics in learning complicated games

T Galla, JD Farmer

Proceedings of the National Academy of Sciences 110 (4), 1232-1236


The prevalence of chaotic dynamics in games with many players

JBT Sanders, JD Farmer, T Galla

Scientific reports 8 (1), 4902


Intrinsic noise in game dynamical learning

T Galla

Physical review letters 103 (19), 198702