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Properties of the Dark Energy
P. M. Garnavich
University of Notre Dame
A non-zero cosmological constant is only one of many possible ex-
planations for the observed accelerating expansion of the Universe.
Any smooth, dark energy with a signicant negative pressure can
drive the acceleration and this generic solution has been dubbed
\quintessence". Quintessence often refers to scalar elds rolling
down potentials, but here will include tangled cosmic strings or
domain walls or anything theorists can think up that produces an
acceleration. Quintessence can be parameterized by its equation
of state, w = p=, which in the most general form can vary over
time. Because supernova observations cover a range of redshift,
they can in principle probe the equation of state of the dark en-
ergy. The current SN observations loosely constrain the equation
of state to w < 0:6, ruling out non-intercommuting strings and
textures (w = 1
3 ), but consistent with a cosmological constant
(w = 1) . The constraints achievable from future large SN data
sets and the eects of systematic errors in SN magnitudes are
discussed.
Co-author: Y. Wang/Notre Dame
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