252 research outputs found
Running-Mass Inflation Model and Primordial Black Holes
We revisit the question whether the running-mass inflation model allows the
formation of Primordial Black Holes (PBHs) that are sufficiently long-lived to
serve as candidates for Dark Matter. We incorporate recent cosmological data,
including the WMAP 7-year results. Moreover, we include "the running of the
running" of the spectral index of the power spectrum, as well as the
renormalization group "running of the running" of the inflaton mass term. Our
analysis indicates that formation of sufficiently heavy, and hence long-lived,
PBHs still remains possible in this scenario. As a by-product, we show that the
additional term in the inflaton potential still does not allow significant
negative running of the spectral index.Comment: 22 pages, 6 figures, Refs. added, Published in JCA
A High Power Hydrogen Target for Parity Violation Experiments
Parity-violating electron scattering measurements on hydrogen and deuterium,
such as those underway at the Bates and CEBAF laboratories, require
luminosities exceeding cms, resulting in large beam
power deposition into cryogenic liquid. Such targets must be able to absorb 500
watts or more with minimal change in target density. A 40~cm long liquid
hydrogen target, designed to absorb 500~watts of beam power without boiling,
has been developed for the SAMPLE experiment at Bates. In recent tests with
40~A of incident beam, no evidence was seen for density fluctuations in
the target, at a sensitivity level of better than 1\%. A summary of the target
design and operational experience will be presented.Comment: 13 pages, 9 postscript figure
Running Spectral Index and Formation of Primordial Black Hole in Single Field Inflation Models
A broad range of single field models of inflation are analyzed in light of
all relevant recent cosmological data, checking whether they can lead to the
formation of long-lived Primordial Black Holes (PBHs). To that end we calculate
the spectral index of the power spectrum of primordial perturbations as well as
its first and second derivatives. PBH formation is possible only if the
spectral index increases significantly at small scales, i.e. large wave number
. Since current data indicate that the first derivative of the
spectral index is negative at the pivot scale , PBH formation
is only possible in the presence of a sizable and positive second derivative
("running of the running") . Among the three small-field and five
large-field models we analyze, only one small-field model, the "running mass"
model, allows PBH formation, for a narrow range of parameters. We also note
that none of the models we analyze can accord for a large and negative value of
, which is weakly preferred by current data.Comment: 26 pages, 5 figures, Refs. added, Minor textual change; version to
appear in JCA
Stochastic background of gravitational waves
A continuous stochastic background of gravitational waves (GWs) for burst
sources is produced if the mean time interval between the occurrence of bursts
is smaller than the average time duration of a single burst at the emission,
i.e., the so called duty cycle must be greater than one. To evaluate the
background of GWs produced by an ensemble of sources, during their formation,
for example, one needs to know the average energy flux emitted during the
formation of a single object and the formation rate of such objects as well. In
many cases the energy flux emitted during an event of production of GWs is not
known in detail, only characteristic values for the dimensionless amplitude and
frequencies are known. Here we present a shortcut to calculate stochastic
backgrounds of GWs produced from cosmological sources. For this approach it is
not necessary to know in detail the energy flux emitted at each frequency.
Knowing the characteristic values for the ``lumped'' dimensionless amplitude
and frequency we show that it is possible to calculate the stochastic
background of GWs produced by an ensemble of sources.Comment: 6 pages, 4 eps figures, (Revtex) Latex. Physical Review D (in press
Primordial black holes in braneworld cosmologies: astrophysical constraints
In two recent papers we explored the modifications to primordial black hole
physics when one moves to the simplest braneworld model, Randall--Sundrum type
II. Both the evaporation law and the cosmological evolution of the population
can be modified, and additionally accretion of energy from the background can
be dominant over evaporation at high energies. In this paper we present a
detailed study of how this impacts upon various astrophysical constraints,
analyzing constraints from the present density, from the present high-energy
photon background radiation, from distortion of the microwave background
spectrum, and from processes affecting light element abundances both during and
after nucleosynthesis. Typically, the constraints on the formation rate of
primordial black holes weaken as compared to the standard cosmology if black
hole accretion is unimportant at high energies, but can be strengthened in the
case of efficient accretion.Comment: 17 pages RevTeX4 file with three figures incorporated; final paper in
series astro-ph/0205149 and astro-ph/0208299. Minor changes to match version
accepted by Physical Review
The Strange Quark Contribution to the Proton's Magnetic Moment
We report a new determination of the strange quark contribution to the
proton's magnetic form factor at a four-momentum transfer Q2 = 0.1 (GeV/c)^2
from parity-violating e-p elastic scattering. The result uses a revised
analysis of data from the SAMPLE experiment which was carried out at the
MIT-Bates Laboratory. The data are combined with a calculation of the proton's
axial form factor GAe to determine the strange form factor GMs(Q2=0.1)=0.37 +-
0.20 +- 0.26 +- 0.07. The extrapolation of GMs to its Q2=0 limit and comparison
with calculations is also discussed.Comment: 6 pages, 1 figure, submitted to Phys. Lett.
Parity Violation in Elastic Electron-Proton Scattering and the Proton's Strange Magnetic Form Factor
We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A = -4.92±0.61±0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections
Parity-violating Electron Deuteron Scattering and the Proton's Neutral Weak Axial Vector Form Factor
We report on a new measurement of the parity-violating asymmetry in
quasielastic electron scattering from the deuteron at backward angles at Q2=
0.038 (GeV/c)2. This quantity provides a determination of the neutral weak
axial vector form factor of the nucleon, which can potentially receive large
electroweak corrections. The measured asymmetry A=-3.51 +/- 0.57(stat) +/-
0.58(sys)ppm is consistent with theoretical predictions. We also report on
updated results of the previous experiment at Q2=0.091 (GeV/c)2, which are also
consistent with theoretical predictions.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Equation of state for Universe from similarity symmetries
In this paper we proposed to use the group of analysis of symmetries of the
dynamical system to describe the evolution of the Universe. This methods is
used in searching for the unknown equation of state. It is shown that group of
symmetries enforce the form of the equation of state for noninteracting scaling
multifluids. We showed that symmetries give rise the equation of state in the
form and energy density
, which
is commonly used in cosmology. The FRW model filled with scaling fluid (called
homological) is confronted with the observations of distant type Ia supernovae.
We found the class of model parameters admissible by the statistical analysis
of SNIa data. We showed that the model with scaling fluid fits well to
supernovae data. We found that and (), which can correspond to (hyper) phantom fluid, and to a
high density universe. However if we assume prior that
then the favoured model is close to concordance
CDM model. Our results predict that in the considered model with
scaling fluids distant type Ia supernovae should be brighter than in
CDM model, while intermediate distant SNIa should be fainter than in
CDM model. We also investigate whether the model with scaling fluid is
actually preferred by data over CDM model. As a result we find from
the Akaike model selection criterion prefers the model with noninteracting
scaling fluid.Comment: accepted for publication versio
Transverse Beam Spin Asymmetries in Forward-Angle Elastic Electron-Proton Scattering
We have measured the beam-normal single-spin asymmetry in elastic scattering
of transversely-polarized 3 GeV electrons from unpolarized protons at Q^2 =
0.15, 0.25 (GeV/c)^2. The results are inconsistent with calculations solely
using the elastic nucleon intermediate state, and generally agree with
calculations with significant inelastic hadronic intermediate state
contributions. A_n provides a direct probe of the imaginary component of the
2-gamma exchange amplitude, the complete description of which is important in
the interpretation of data from precision electron-scattering experiments.Comment: 5 pages, 3 figures, submitted to Physical Review Letters; shortened
to meet PRL length limit, clarified some text after referee's comment
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