In Ethereum 2.0 (Sharding Blockchain), a new block requires to be signed by all the validators as members of a committee, where blockchain has been sharded in smaller parts for supporting parallel transaction processing to enhance transaction throughput.
This way, a new block created in a time slot by a proposer, needs to be signed by all the committee's members. All the signatures then will be aggregated using BLS Multi-Signatures With Public-Key Aggregation.
The question is:
What if a malicious validator denies to sign a new block in a shard committee in Ethereum 2.0 ?