  Metaverse can obscure the boundary between the physical and virtual worlds.
Specifically, for the Metaverse in vehicular networks, i.e., the vehicular
Metaverse, vehicles are no longer isolated physical spaces but interfaces that
extend the virtual worlds to the physical world. Accessing the Metaverse via
autonomous vehicles (AVs), drivers and passengers can immerse in and interact
with 3D virtual objects overlaying views of streets on head-up displays (HUD)
via augmented reality (AR). The seamless, immersive, and interactive experience
rather relies on real-time multi-dimensional data synchronization between
physical entities, i.e., AVs, and virtual entities, i.e., Metaverse billboard
providers (MBPs). However, mechanisms to allocate and match synchronizing AV
and MBP pairs to roadside units (RSUs) in a synchronization service market,
which consists of the physical and virtual submarkets, are vulnerable to
adverse selection. In this paper, we propose an enhanced second-score
auction-based mechanism, named EPViSA, to allocate physical and virtual
entities in the synchronization service market of the vehicular Metaverse. The
EPViSA mechanism can determine synchronizing AV and MBP pairs simultaneously
while protecting participants from adverse selection and thus achieving high
total social welfare. We propose a synchronization scoring rule to eliminate
the external effects from the virtual submarkets. Then, a price scaling factor
is introduced to enhance the allocation of synchronizing virtual entities in
the virtual submarkets. Finally, rigorous analysis and extensive experimental
results demonstrate that EPViSA can achieve at least 96\% of the social welfare
compared to the omniscient benchmark while ensuring strategy-proof and adverse
selection free through a simulation testbed.
