1,018 research outputs found
Improved Estimates of Cosmological Perturbations
We recently derived exact solutions for the scalar, vector and tensor mode
functions of a single, minimally coupled scalar plus gravity in an arbitrary
homogeneous and isotropic background. These solutions are applied to obtain
improved estimates for the primordial scalar and tensor power spectra of
anisotropies in the cosmic microwave background.Comment: 31 pages, 4 figures, LaTeX 2epsilon, this version corrects an
embarrasing mistake (in the published version) for the parameter q_C.
Affected eqns are 105, 109-110, 124, 148-153 and 155-15
Damping of Tensor Modes in Cosmology
An analytic formula is given for the traceless transverse part of the
anisotropic stress tensor due to free streaming neutrinos, and used to derive
an integro-differential equation for the propagation of cosmological
gravitational waves. The solution shows that anisotropic stress reduces the
squared amplitude by 35.6 % for wavelengths that enter the horizon during the
radiation-dominated phase, independent of any cosmological parameters. This
decreases the tensor temperature and polarization correlation functions for
these wavelengths by the same amount. The effect is less for wavelengths that
enter the horizon at later times. At the longest wavelengths the decrease in
the tensor correlation functions due to neutrino free streaming ranges from
10.7% for to 9.0% for . An Appendix gives a
general proof that tensor as well as scalar modes satisfy a conservation law
for perturbations outside the horizon, even when the anisotropic stress tensor
is not negligible.Comment: 14 pages. The original version of this paper has been expanded to
deal with perturbations of any wavelength. While for wavelengths short enough
to enter the horizon during radiation dominance, temperature and polarization
correlations are damped by 35.6%, at the longest wavelengths the damping is
from 9.0% to 11%. An added Appendix gives a general proof that tensor as well
as scalar modes satisfy a conservation law outside the horizon, even during
neutrino decoupling. Some references are also adde
CBR Anisotropy and the Running of the Scalar Spectral Index
Accurate () predictions for the anisotropy of the Cosmic
Background Radiation (CBR) are essential for using future high-resolution
() CBR maps to test cosmological models. In many inflationary
models the variation (``running'') of the spectral index of the spectrum of
density perturbations is a significant effect and leads to changes of around
1\% to 10\% in the CBR power spectrum. We propose a general method for taking
running into account which uses the derivative of the spectral index (). Conversely, high-resolution CBR maps may be able to determine ,
giving important information about the inflationary potential.Comment: Discussion of calculation clarified; error corrected which reduces
estimated effect for chaotic inflatio
Brane cosmology with an anisotropic bulk
In the context of brane cosmology, a scenario where our universe is a
3+1-dimensional surface (the ``brane'') embedded in a five-dimensional
spacetime (the ``bulk''), we study geometries for which the brane is
anisotropic - more specifically Bianchi I - though still homogeneous. We first
obtain explicit vacuum bulk solutions with anisotropic three-dimensional
spatial slices. The bulk is assumed to be empty but endowed with a negative
cosmological constant. We then embed Z_2-symmetric branes in the anisotropic
spacetimes and discuss the constraints on the brane energy-momentum tensor due
to the five-dimensional anisotropic geometry. We show that if the bulk is
static, an anisotropic brane cannot support a perfect fluid. However, we find
that for some of our bulk solutions it is possible to embed a brane with a
perfect fluid though its energy density and pressure are completely determined
by the bulk geometry.Comment: 20 pages, 1 figur
Measurement of Masses and Widths of Excited Charm Mesons and Evidence for Broad States
Using data from the FOCUS experiment we analyze the and
invariant mass distributions. We measure the mass M_{D_2^{*0}} =
(2464.5 \pm 1.1 \pm 1.9) \mev and width \Gamma_{D_2^{*0}} = (38.7 \pm 5.3 \pm
2.9) \mev, and the mass M_{D_2^{*+}} = (2467.6 \pm 1.5 \pm 0.76)
\mev and width \Gamma_{D_2^{*+}} = (34.1 \pm 6.5 \pm 4.2) \mev. We find
evidence for broad structures over background in both the neutral and charged
final state. If each is interpreted as evidence for a single L=1,
excited charm meson resonance, the masses and widths are M_{1/2}^0 =(2407 \pm
21 \pm 35) \mev, \Gamma_{1/2}^0 = (240 \pm 55 \pm 59) \mev, and M_{1/2}^+ =
(2403 \pm 14 \pm 35) \mev \Gamma_{1/2}^+ = (283 \pm 24 \pm 34) \mev,
respectively.Comment: 15 pages, 4 figures. Submitted to Phys. Lett. B. Added preprint
number
Metric Perturbations in Dilaton-Driven Inflation
We compute the spectrum of scalar and tensor metric perturbations generated,
as amplified vacuum fluctuations, during an epoch of dilaton-driven inflation
of the type occurring naturally in string cosmology. In the tensor case the
computation is straightforward while, in the scalar case, it is made delicate
by the appearance of a growing mode in the familiar longitudinal gauge. In
spite of this, a reliable perturbative calculation of perturbations far outside
the horizon can be performed by resorting either to appropriate gauge invariant
variables, or to a new coordinate system in which the growing mode can be
"gauged down". The simple outcome of this complicated analysis is that both
scalar and tensor perturbations exhibit nearly Planckian spectra, whose common
"temperature" is related to some very basic parameters of the string-cosmology
background.Comment: 34 pages, latex, no figure
Detectability of Tensor Perturbations Through CBR Anisotropy (final published version)
Detection of the tensor perturbations predicted in inflationary models is
important for testing inflation as well as for reconstructing the inflationary
potential. We show that because of cosmic variance the tensor contribution to
the square of the CBR quadrupole anisotropy must be greater than about 20\% of
the scalar contribution to ensure a statistically significant detection of
tensor perturbations. This sensitivity could be achieved by full-sky
measurements on angular scales of and .Comment: 10 pages, uu-encoded postscript file, FERMILAB-PUB-94/175-
Search for and Using Genetic Programming Event Selection
We apply a genetic programming technique to search for the double Cabibbo
suppressed decays and .
We normalize these decays to their Cabibbo favored partners and find
\Lambda_c^+ \to p K^+ \pi^-\Lambda_c^+ \to p K^-
\pi^+ and D_s^+ \to K^+ K^+
\pi^-D_s^+ \to K^+ K^- \pi^+ where
the first errors are statistical and the second are systematic. Expressed as
90% confidence levels (CL), we find and respectively.
This is the first successful use of genetic programming in a high energy
physics data analysis.Comment: 10 page
A Non-parametric Approach to the D+ to K*0bar mu+ nu Form Factors
Using a large sample of D+ -> K- pi+ mu+ nu decays collected by the FOCUS
photoproduction experiment at Fermilab, we present the first measurements of
the helicity basis form factors free from the assumption of spectroscopic pole
dominance. We also present the first information on the form factor that
controls the s-wave interference discussed in a previous paper by the FOCUS
collaboration. We find reasonable agreement with the usual assumption of
spectroscopic pole dominance and measured form factor ratios.Comment: 14 pages, 5 figures, and 2 tables. We updated the previous version by
changing some words, removing one plot, and adding two tables. These changes
are mostly stylisti
Dalitz plot analysis of D_s+ and D+ decay to pi+pi-pi+ using the K-matrix formalism
FOCUS results from Dalitz plot analysis of D_s+ and D+ to pi+pi-pi+ are
presented. The K-matrix formalism is applied to charm decays for the first time
to fully exploit the already existing knowledge coming from the light-meson
spectroscopy experiments. In particular all the measured dynamics of the S-wave
pipi scattering, characterized by broad/overlapping resonances and large
non-resonant background, can be properly included. This paper studies the
extent to which the K-matrix approach is able to reproduce the observed Dalitz
plot and thus help us to understand the underlying dynamics. The results are
discussed, along with their possible implications on the controversial nature
of the sigma meson.Comment: To be submitted to Phys.Lett.B A misprint corrected in formula
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