Current Fluctuations of the One Dimensional Symmetric Simple Exclusion Process with Step Initial Condition

For the symmetric simple exclusion process on an infinite line, we calculate exactly the fluctuations of the integrated current Q _t during time t through the origin when, in the initial condition, the sites are occupied with density ρ _a on the negative axis and with density ρ _b on the positive axis. All the cumulants of Q _t grow like . In the range where , the decay exp −Q _t ³/t] of the distribution of Q _t is non-Gaussian. Our results are obtained using the Bethe ansatz and several identities derived recently by Tracy and Widom for exclusion processes on the infinite line. We acknowledge the support of the French Ministry of Education through the ANR BLAN07-2184264 grant.