 
Summary: Volume 150B, number 6 PHYSICS LETTERS 24 January 1985
A MECHANISM FOR REDUCING THE VALUE OF THE COSMOLOGICAL CONSTANT
L.F. ABBOTT 1
PhysicsDepartment, Brandeis University, Waltham,MA 02254, USA
Received 30 October 1984
A mechanism is presented for relaxing an initiallylarge, positive cosmological constant to a value near zero. This is done
by introducing a scalar field whose vacuum energy compensates for the initial cosmologicalconstant. The compensating sec
tor involves small mass scales but no unnatural finetuning of parameters. It is not clear how to incorporate this mechanism
into a realistic cosmology.
The extremely small observational limits on the val
ue of the cosmological constant indicate that the vacu
um energy density in our universe has magnitude less
than (0.003 eV)4. The vacuum energy density receives
contributions proportional to the fourth power of vir
tually every mass scale in particle physics. Since each
of these terms individually is many orders of magni
tude larger than (0.003 eV)4, mysterious and unnatu
ral cancellations must occur in order for their sum to
produce a sufficiently small total energy density. This
situation is very different from that of a naturally
