1,026 research outputs found
The Long-Term Future of Extragalactic Astronomy
If the current energy density of the universe is indeed dominated by a
cosmological constant, then high-redshift sources will remain visible to us
only until they reach some finite age in their rest-frame. The radiation
emitted beyond that age will never reach us due to the acceleration of the
cosmic expansion rate, and so we will never know what these sources look like
as they become older. As a source image freezes on a particular time frame
along its evolution, its luminosity distance and redshift continue to increase
exponentially with observation time. The higher the current redshift of a
source is, the younger it will appear as it fades out of sight. For the popular
set of cosmological parameters, I show that a source at a redshift z=5-10 will
only be visible up to an age of 4-6 billion years. Arguments relating the
properties of high-redshift sources to present-day counterparts will remain
indirect even if we continue to monitor these sources for an infinite amount of
time. These sources will not be visible to us when they reach the current age
of the universe.Comment: Phys. Rev. D, in press (2001
(Twisted) Toroidal Compactification of pp-Waves
The maximally supersymmetric type IIB pp-wave is compactified on spatial
circles, with and without an auxiliary rotational twist. All spatial circles of
constant radius are identified. Without the twist, an S compactification
can preserve 24, 20 or 16 supercharges. compactifications can preserve
20, 18 or 16 supercharges; compactifications can preserve 18 or 16
supercharges and higher compactifications preserve 16 supercharges. The
worldsheet theory of this background is discussed. The T-dual and
decompactified type IIA and M-theoretic solutions which preserve 24
supercharges are given. Some comments are made regarding the AdS parent and the
CFT description.Comment: 22 pages REVTeX 4 and AMSLaTeX. v3: References and a paragraph on
nine dimensional Killing spinors were added. v4: A few typos corrected and a
footnote was modifie
A Study of the \eta \pi^{0} Spectrum and Search for a J^{PC} = 1^{-+} Exotic Meson
A partial wave analysis (PWA) of the of the system (where ) produced in the charge exchange reaction at an incident momentum of 18 GeV is presented as a function of
invariant mass, , and momentum transfer squared,
, from the incident to the outgoing system. , and waves were included in the PWA. The
and states are clearly observed in the overall
effective mass distribution as well as in the amplitudes associated with
wave and waves respectively after partial wave decomposition. The observed
distributions in moments (averages of spherical harmonics) were compared to the
results from the PWA and the two are consistent. The distribution in
for individual waves associated with natural and
unnatural parity exchange in the -channel are consistent with Regge
phenomenology. Of particular interest in this study is the wave since this
leads to an exotic for the system. A wave is
present in the data, however attempts to describe the mass dependence of the
amplitude and phase motion with respect to the wave as a Breit-Wigner
resonance are problematic. This has implications regarding the existence of a
reported exotic meson decaying into with a mass
near 1.4 GeV.Comment: 19 pages, 29 figures, to appear in Phys. Rev.
Search for Exotic Mesons in pi- P Interactions at 18 GeV/c
The recent search for non mesons in interactions at
Brookhaven National Laboratory is summarized. Many final states such as , , , , , ,
which are favored decay modes of exotics, are under investigation.Comment: 9 pages, PostScript, Presented at the International School of Nuclear
Physics, Erice, Sicily, Italy, September 199
Non-local SFT Tachyon and Cosmology
Cosmological scenarios built upon the generalized non-local String Field
Theory and -adic tachyons are examined. A general kinetic operator involving
an infinite number of derivatives is studied as well as arbitrary parameter
. The late time dynamics of just the tachyon around the non-perturbative
vacuum is shown to leave the cosmology trivial. A late time behavior of the
tachyon and the scale factor of the FRW metric in the presence of the
cosmological constant or a perfect fluid with is constructed explicitly
and a possibility of non-vanishing oscillations of the total effective state
parameter around the phantom divide is proven.Comment: 17 pages, LaTeX; v2: JHEP3 class is used, references adde
Gravitational Coupling and Dynamical Reduction of The Cosmological Constant
We introduce a dynamical model to reduce a large cosmological constant to a
sufficiently small value. The basic ingredient in this model is a distinction
which has been made between the two unit systems used in cosmology and particle
physics. We have used a conformal invariant gravitational model to define a
particular conformal frame in terms of large scale properties of the universe.
It is then argued that the contributions of mass scales in particle physics to
the vacuum energy density should be considered in a different conformal frame.
In this manner, a decaying mechanism is presented in which the conformal factor
appears as a dynamical field and plays a key role to relax a large effective
cosmological constant. Moreover, we argue that this model also provides a
possible explanation for the coincidence problem.Comment: To appear in GR
Observation of a New J(PC)=1(+-) Isoscalar State in the Reaction Pi- Proton -> Omega Eta Neutron at 18 GeV/c
Results are presented on a partial wave analysis of the Omega Eta final state
produced in Pi- Proton interactions at 18 GeVc where Omega -> Pi+ Pi- Pi0, Pi0
-> 2 Gammas, and Eta -> 2 Gammas. We observe the previously unreported decay
mode Omega(1650) -> Omega Eta and a new 1(+-) meson state h1(1595) with a mass
M=1594(15)(+10)(-60) MeV/c^2 and a width Gamma=384(60)(+70)(-100) MeV/c^2. The
h1(1595) state exhibits resonant-like phase motion relative to the Omega(1650).Comment: Submitted to Physics Letters B Eight total pages including 11 figures
and 1 tabl
Partial-wave analysis of the eta pi+ pi- system produced in the reaction pi-p --> eta pi+ pi- n at 18 GeV/c
A partial-wave analysis of 9082 eta pi+ pi- n events produced in the reaction
pi- p --> eta pi+ pi- n at 18.3 GeV/c has been carried out using data from
experiment 852 at Brookhaven National Laboratory. The data are dominated by
J^{PC} = 0^{-+} partial waves consistent with observation of the eta(1295) and
the eta(1440). The mass and width of the eta(1295) were determined to be 1282
+- 5 MeV and 66 +- 13 Mev respectively while the eta(1440) was observed with a
mass of 1404 +- 6 MeV and width of 80 +- 21 MeV. Other partial waves of
importance include the 1++ and the 1+- waves. Results of the partial wave
analysis are combined with results of other experiments to estimate f1(1285)
branching fractions. These values are considerably different from current
values determined without the aid of amplitude analyses.Comment: 22 pages, 8 figure
A partial wave analysis of the system produced in charge exchange collisions
A partial wave analysis of the of the system produced in the
charge exchange reaction: at an incident momentum of
is presented as a function of invariant mass,
, and momentum transfer squared, , from the incident
to the outgoing system.Comment: 24 pages total,8 pages text, 14 figures, 1 table. Submitted to Phys
Rev
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