Casimir effect for quantum field theory in networks

Abstract This paper studies quantum field theories defined in networks, which are the multi-branch generalizations of interface conformal field theory. We propose a novel junction condition on the node and show that it is consistent with energy conservation in the sense that the total energy flow into the node is zero. As an application, we explore the Casimir effect on networks. Remarkably, the Casimir force on one edge can be changed from attractive to repulsive by adjusting the lengths of the other edges, providing a straightforward way to control the Casimir effect. We begin by discussing the Casimir effect for $$(1+1)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> -dimensional free massless scalars on a simple network. We then extend this discussion to various types of networks and higher dimensions. Finally, we offer brief comments on some open questions.