systemd definition for pulseaudio in system-mode (example for archlinux).The pulseaudio developers explicitly recommend to NOT run pulseaudo system-mode!

pulseaudio.service

# systemd service spec for pulseaudio running in system mode -- not recommended though!
# on arch, put it under /etc/systemd/system/pulseaudio.service
# start with: systemctl start pulseaudio.service
# enable on boot: systemctl enable pulseaudio.service 
[Unit]
Description=Pulseaudio sound server
After=avahi-daemon.service network.target

[Service]
Type=forking
ExecStart=/usr/bin/pulseaudio --realtime --no-cpu-limit --system --disallow-exit --daemon
ExecReload=/bin/pkill pulseaudio

[Install]
WantedBy=multi-user.target