  The transition to a deeply decarbonized energy system requires coordinated
planning of infrastructure investments and operations serving multiple end-uses
while considering technology and policy-enabled interactions across sectors.
Electricity and natural gas (NG), which are vital vectors of today's energy
system, are likely to be coupled in different ways in the future, resulting
from increasing electrification, adoption of variable renewable energy (VRE)
generation in the power sector and policy factors such as cross-sectoral
emissions trading. This paper develops a least-cost investment and operations
model for joint planning of electricity and NG infrastructures that considers a
wide range of available and emerging technology options across the two vectors,
including carbon capture and storage (CCS) equipped power generation,
low-carbon drop-in fuels (LCDF) as well as long-duration energy storage (LDES).
The model incorporates the main operational constraints of both systems and
allows each system to operate under different temporal resolutions consistent
with their typical scheduling timescales. We apply the modeling framework to
evaluate power-NG system outcomes for the U.S. New England region under
different technology, decarbonization goals, and demand scenarios. Under a
global emissions constraint, ranging between 80-95\% emissions reduction
compared to 1990 levels, the least-cost solution disproportionately relies on
using the available emissions budget to serve non-power NG demand and results
in the power sector using only 15-43\% of the emissions budget.
