Measurement of heavy-flavour production as a function of multiplicity in pp and p-Pb collisions with ALICE

In these proceedings results are presented from the measurement of open heavy-flavour production as a function of charged-particle multiplicity in pp collisions at $\sqrt {s}$ = 7 TeV and p-Pb collisions at $\sqrt {s_{\rm NN}}$=5.02 TeV recorded with the ALICE detector in 2010 and 2013, respectively. $\rm D^{0}$, $\rm D^{+}$ and $\rm D^{*+}$ mesons are reconstructed from their hadronic decay channels in the central rapidity region, and their production yields are measured in various multiplicity and $p_{\rm T}$ intervals. The per-event yields of $\rm D$ mesons in the various multiplicity intervals, normalized to their multiplicity-integrated value, and their evolution with $p_{\rm T}$ are measured for pp and p-Pb collisions to study the contribution of Multi-Parton Interactions (MPIs) to open charm production in the two systems. The nuclear modification factor of $\rm D$ mesons in p-Pb collisions, defined as the ratio of the $\rm D$-meson yields in p-Pb and pp collisions scaled by the average number of binary collisions $< N_{\rm coll}>$, is discussed in terms of its dependence on the event activity. Several experimental estimators of the event activity are used in order to assess the role of kinematic biases.