# On the TASEP with Second Class Particles

## TL;DR

This paper derives a determinant formula for the probability that the first class particle remains the leftmost in a finite TASEP with second class particles, under step initial conditions, extending known results.

## Contribution

It provides a new exact determinant expression for conditional probabilities in TASEP with second class particles, linking to known formulas in the standard TASEP.

## Key findings

- Probability expressed as an N×N determinant of contour integrals
- Formula similar to known TASEP step initial condition results
- Extension of asymptotic analysis techniques to second class particles

## Abstract

In this paper we study some conditional probabilities for the totally asymmetric simple exclusion processes (TASEP) with second class particles. To be more specific, we consider a finite system with one first class particle and $N-1$ second class particles, and we assume that the first class particle is initially at the leftmost position. In this case, we find the probability that the first class particle is at $x$ and it is still the leftmost particle at time $t$. In particular, we show that this probability is expressed by the determinant of an $N\times N$ matrix of contour integrals if the initial positions of particles satisfy the step initial condition. The resulting formula is very similar to a known formula in the (usual) TASEP with the step initial condition which was used for asymptotics by Nagao and Sasamoto [Nuclear Phys. B 699 (2004), 487-502].