Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New Hubble Space Telescope Discoveries of Type Ia Supernovae at z > 1:
  Narrowing Constraints on the Early Behavior of Dark Energy   We have discovered 21 new Type Ia supernovae (SNe Ia) with the Hubble Space
Telescope (HST) and have used them to trace the history of cosmic expansion
over the last 10 billion years. These objects, which include 13
spectroscopically confirmed SNe Ia at z > 1, were discovered during 14 epochs
of reimaging of the GOODS fields North and South over two years with the
Advanced Camera for Surveys on HST. Together with a recalibration of our
previous HST-discovered SNe Ia, the full sample of 23 SNe Ia at z > 1 provides
the highest-redshift sample known. Combined with previous SN Ia datasets, we
measured H(z) at discrete, uncorrelated epochs, reducing the uncertainty of
H(z>1) from 50% to under 20%, strengthening the evidence for a cosmic jerk--the
transition from deceleration in the past to acceleration in the present. The
unique leverage of the HST high-redshift SNe Ia provides the first meaningful
constraint on the dark energy equation-of-state parameter at z >1.
  The result remains consistent with a cosmological constant (w(z)=-1), and
rules out rapidly evolving dark energy (dw/dz >>1). The defining property of
dark energy, its negative pressure, appears to be present at z>1, in the epoch
preceding acceleration, with ~98% confidence in our primary fit. Moreover, the
z>1 sample-averaged spectral energy distribution is consistent with that of the
typical SN Ia over the last 10 Gyr, indicating that any spectral evolution of
the properties of SNe Ia with redshift is still below our detection threshold.

37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
11
The categories of this paper are: hep-lat
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
34
The categories of this paper are: chem-ph
23
The categories of this paper are: solv-int
7
The categories of this paper are: hep-th
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol