11,352 research outputs found
Is Cosmological Constant Needed in Higgs Inflation?
The detection of B-mode shows a very powerful constraint to theoretical
inflation models through the measurement of the tensor-to-scalar ratio .
Higgs boson is the most likely candidate of the inflaton field. But usually,
Higgs inflation models predict a small value of , which is not quite
consistent with the recent results from BICEP2. In this paper, we explored
whether a cosmological constant energy component is needed to improve the
situation. And we found the answer is yes. For the so-called Higgs chaotic
inflation model with a quadratic potential, it predicts ,
with e-folds number , which is large enough to
overcome the problems such as the horizon problem in the Big Bang cosmology.
The required energy scale of the cosmological constant is roughly , which means a mechanism is still needed to solve the
fine-tuning problem in the later time evolution of the universe, e.g. by
introducing some dark energy component.Comment: 4 pages, 2 figure
Constraints on the Brans-Dicke gravity theory with the Planck data
Based on the new cosmic CMB temperature data from the Planck satellite, the 9
year polarization data from the WMAP, the BAO distance ratio data from the SDSS
and 6dF surveys, we place a new constraint on the Brans-Dicke theory. We adopt
a parametrization \zeta=\ln(1+1/\omega}), where the general relativity (GR)
limit corresponds to . We find no evidence of deviation from general
relativity. At 95% probability, , correspondingly,
the region is excluded. If we restrict ourselves to
the (i.e. ) case, then the 95% probability interval is
. We can also translate this
result to a constraint on the variation of gravitational constant, and find the
variation rate today as yr ( error bar), the integrated change since the epoch of
recombination is ( error
bar). These limits on the variation of gravitational constant are comparable
with the precision of solar system experiments.Comment: 7 pages, 5 figures, 2 table
Photoproduction of in NRQCD
We present a calculation for the photoproduction of under the
framework of NRQCD factorization formalism. We find a quite unique feature that
the color-singlet contribution to this process vanishes at not only the leading
order but also the next to leading order perturbative QCD calculations and that
the dominant contribution comes from the color-octet
subprocess. The nonperturbative color-octet matrix element of
of is related to that of of by the heavy
quark spin symmetry, and the latter can be determined from the direct
production of at large transverse momentum at the Fermilib Tevatron.
We then conclude that the measurement of this process may clarify the existing
conflict between the color-octet prediction and the experimental result on the
photoprodution.Comment: 11 pages, revtex, 4 ps figure
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