Out-of-field teaching is a global educational challenge. In particular, many teachers whose academic background and main teaching experience is in biology are called to teach middle school physics and have limited opportunities for productive professional development. Based on previous studies, we expect these teachers to hold different epistemic cognitions from the in-field teachers. The present study builds on this epistemic diversity and offers dialogic argumentation as a means to promote mutual learning among physics teachers from different disciplinary backgrounds. We describe guidelines for designing "interdisciplinary dialogic argumentation" activities that aim to encourage teachers to express their disciplinary perspectives in the context of inquiry-based physics and to facilitate a deliberative discourse among them. We demonstrate in a case study the ways in which the discourse of a group of in-field and out-of-field teachers unfolds under the proposed design guidelines. Using the Actor-Network methodology and an analysis of power relations, we uncover a complex interplay between the social and the epistemic in the discourse: when interactions become more dialogic and power relations more equalized, the out-of-field teachers take an active role in the discussion, foregrounding their epistemic practices and enhancing the epistemic practices of the group, including the in-field teacher.