| Gaia: | <p>Take the linearised FKPP equation ∂th = ∂ 2 xh+h with boundary condition h(m(t), t) = 0. Depending on the behaviour of the initial condition h0(x) = h(x, 0) we obtain the asymptotics — up to a o(1) term r(t) — of the absorbing boundary m(t) such that ω(x) := limt→∞ h(x+ m(t), t) exists and is non-trivial. In particular, as in Bramson’s results for the non-linear FKPP equation, we recover the celebrated −3/2 log t correction for initial conditions decaying faster than x ν e −x for some ν < −2.</p> <p>Furthermore, when we are in this regime, the main result of the present work is the identification (to first order) of the r(t) term which ensures the fastest convergence to ω(x). When h0(x) decays faster than x ν e −x for some ν < −3, we show that r(t) must be chosen to be −3 p π/t which is precisely the term predicted heuristically by Ebert-van Saarloos [EvS00] in the non-linear case (see also [MM14, BD15, Hen14]). When the initial condition decays as x ν e −x for some ν ∈ [−3, −2), we show that even though we are still in the regime where Bramson’s correction is −3/2 log t, the Ebert-van Saarloos correction has to be modified.</p> <p>Similar results were recently obtained by Henderson [Hen14] using an analytical approach and only for compactly supported initial conditions.</p>
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