in scattered light [@Wyatt2006]. On the other hand, in this planet migration scenario the distribution of mm-sized dust should match the planetesimal distribution, with prominent clumps that could be seen in millimetre observations.

Finally, secular resonances produced by a single eccentric planet in a massive gaseous disc [@Zheng2017] or by two planets formed interior to the disc could also explain some of the wide gaps [@Yelvertoninprep], but possibly also leaving asymmetric features. Hence debris disc observations at multiple wavelengths can disentangle these different scenarios, and provide insights into the dynamical history of the outer regions of planetary systems, testing the existence and origin of planets at tens of au, which otherwise would remain invisible. Since radiation forces acting on the smallest dust grains have a significant effect on their distribution, the planetary perturbations discussed above can be best studied using ALMA observations which trace the distribution of large ($\sim$0.1-10mm) grains for which radiation forces are negligible, and thus follow the distribution of their parent planetesimals.

In this paper we present new ALMA observations of HD 107146 in both band 6 and 7 (1.1 and 0.86 mm). These observations resolve the broad debris disc around this system at higher sensitivity and 