Nonetheless, says dark matter theorist Katherine Freese of the University
of Michigan in Ann Arbor, “the low-mass
region — that’s the one that everyone is
excited about, up, down and sideways.”
Hooper, who has been in the field for
a decade, says it is hard to explain why
XENON10 is not seeing a signal, but he
still has hope that some of the hints of
low-mass WIMPs will be credible.
“This is the first time in my career
that I’m prepared to make bets with my
colleagues that we’re actually seeing
something,” he says.
New physics, hot debate
There’s a delicate balance in trying to
make sense of the existence of a light
WIMP, explains Weiner. On the one
hand, a low-mass WIMP would have
to interact with ordinary matter in an
unusually weak way — otherwise, atom
smashers would have already revealed
hints of its existence. On the other hand,
WIMPs that interact so weakly would
tend to have too large an abundance in
the universe today to fit with the WIMP
miracle. They would have been less likely
to be destroyed in the dense, early universe, when collisions between particles
were more common.
One solution proposed by Weiner and
other researchers is that nature harbors
not only a low-mass WIMP but also a new
force in the dark sector. The low-mass
WIMP would account for the results
of the experiments, and the dark force
could have depleted enough WIMPs in
the early universe so that there would
not be too many around today.
WIMP wind the DaMa/LiBRa experiment has recorded seasonal variation in particle collisions. since ordinary matter collisions shouldn’t vary as
the earth revolves around the sun, the team suspects that earth is traveling into a WiMP wind in the summer and away from it during the winter.
Seasonal variation in particle collisions
R. BeRnaBei et al/ aRxiv.oRg