The disc instability model: original recipe and additional ingredients

TL;DR

This paper reviews the disc instability model for cataclysmic variables, discussing how additional physical ingredients influence light curve predictions and highlighting the challenges of constrained modeling due to many free parameters.

Contribution

It provides an analysis of how various additional ingredients affect the disc instability model and discusses the limitations caused by unconstrained parameters.

Findings

Additional ingredients modify predicted light curves.

Many free parameters reduce predictive power.

Constraints on physics are often weak.

Abstract

The disc instability model successfully reproduces many of the observed properties of cataclysmic variables. However, additional ingredients such as mass-transfer variations, disc irradiation, stream-disc overflow, or inner-disc truncation must be included to explain certain systems. The physics underlying these processes is often poorly constrained, and our lack of knowledge is typically absorbed into extra free parameters, much like the $\alpha$-prescription for viscosity. In this paper, I examine how each of these ingredients affects the predicted light curves and discuss the limitations that arise from the growing number of unconstrained parameters on the model's predictive power.