Final answer:
Those not affected by a Pigouvian tax are third parties not involved in the market transaction who might instead benefit from the reduction of the negative externality thanks to the tax.
Step-by-step explanation:
The individuals not affected by a Pigouvian tax when a negative externality exists are those not involved in the market transaction, also known as third parties. In the context of a Pigouvian tax, this tax is levied to correct the effects of a negative externality in a market. For example, when pollution from a factory affects the health of nearby residents or diminishes their quality of life, the Pigouvian tax would ideally correct this market failure by incorporating social costs into the production cost, thus reducing market quantity to a socially optimal level. Third parties, such as those affected by second-hand smoke from cigarettes or noise from a concert, would not bear the immediate financial burden of the tax but would potentially benefit from the reduced negative externality. Those directly participating in the market transaction, both producers and consumers, are the ones who would be financially impacted by such a tax. The goal of this tax is to bring the market equilibrium closer to the social optimal output and price where actual costs, including externalities, are considered.