211 research outputs found
Fine tuning of parameters of the universe
The mechanism of production of a large number of universes is considered. It
is shown that universes with parameters suitable for creation of life are
necessarily produced as a result of quantum fluctuations. Fractal structures
are formed provided fluctuations take place near a maximum of the potential.
Several ways of formation of similar fractal structures within our universe are
discussed. Theoretical predictions are compared with observational data.Comment: 9 pages, 1 figur
Physical Origin, Evolution and Observational Signature of Diffused Antiworld
The existence of macroscopic regions with antibaryon excess in the baryon
asymmetric Universe with general baryon excess is the possible consequence of
practically all models of baryosynthesis. Diffusion of matter and antimatter to
the border of antimatter domains defines the minimal scale of the antimatter
domains surviving to the present time. A model of diffused antiworld is
considered, in which the density within the surviving antimatter domains is too
low to form gravitationally bound objects. The possibility to test this model
by measurements of cosmic gamma ray fluxes is discussed. The expected gamma ray
flux is found to be acceptable for modern cosmic gamma ray detectors and for
those planned for the near future.Comment: 9 page
Quantum Instantons and Quantum Chaos
Based on a closed form expression for the path integral of quantum transition
amplitudes, we suggest rigorous definitions of both, quantum instantons and
quantum chaos. As an example we compute the quantum instanton of the double
well potential.Comment: Extended version with new figures. Text (LaTeX), 5 Figures (epsi
files
The universe formation by a space reduction cascade with random initial parameters
In this paper we discuss the creation of our universe using the idea of extra
dimensions. The initial, multidimensional Lagrangian contains only metric
tensor. We have found many sets of the numerical values of the Lagrangian
parameters corresponding to the observed low-energy physics of our universe.
Different initial parameters can lead to the same values of fundamental
constants by the appropriate choice of a dimensional reduction cascade. This
result diminishes the significance of the search for the 'unique' initial
Lagrangian. We also have obtained a large number of low-energy vacua, which is
known as a 'landscape' in the string theory.Comment: 17 pages, 1 figur
Astrophysical constraints on primordial black holes in Brans-Dicke theory
We consider cosmological evolution in Brans-Dicke theory with a population of
primordial black holes. Hawking radiation from the primordial black holes
impacts various astrophysical processes during the evolution of the Universe.
The accretion of radiation by the black holes in the radiation dominated era
may be effective in imparting them a longer lifetime. We present a detailed
study of how this affects various standard astrophysical constraints coming
from the evaporation of primordial black holes. We analyze constraints from the
present density of the Universe, the present photon spectrum, the distortion of
the cosmic microwave background spectrum and also from processes affecting
light element abundances after nucleosynthesis. We find that the constraints on
the initial primordial black hole mass fractions are tightened with increased
accretion efficiency.Comment: 15 page
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
Primordial Structure of Massive Black Hole Clusters
We describe a mechanism of the primordial black holes formation that can
explain the existence of a population of supermassive black holes in galactic
bulges. The mechanism is based on the formation of black holes from closed
domain walls. The origin of such domain walls could be a result of the
evolution of an effectively massless scalar field during inflation. The initial
non-equilibrium distribution of the scalar field imposed by background
de-Sitter fluctuations gives rise to the spectrum of black holes, which covers
a wide range of masses -- from superheavy ones down to deeply subsolar. The
primordial black holes of smaller masses are concentrated around the most
massive ones within a fractal-like cluster.Comment: 19 pages; 3 figures; The final version accepted for publication in
Astroparticle Physic
A straw drift chamber spectrometer for studies of rare kaon decays
We describe the design, construction, readout, tests, and performance of
planar drift chambers, based on 5 mm diameter copperized Mylar and Kapton
straws, used in an experimental search for rare kaon decays. The experiment
took place in the high-intensity neutral beam at the Alternating Gradient
Synchrotron of Brookhaven National Laboratory, using a neutral beam stop, two
analyzing dipoles, and redundant particle identification to remove backgrounds
Brans-Dicke Theory and primordial black holes in Early Matter-Dominated Era
We show that primordial black holes can be formed in the matter-dominated era
with gravity described by the Brans-Dicke theory. Considering an early
matter-dominated era between inflation and reheating, we found that the
primordial black holes formed during that era evaporate at a quicker than those
of early radiation-dominated era. Thus, in comparison with latter case, less
number of primordial black holes could exist today. Again the constraints on
primordial black hole formation tend towards the larger value than their
radiation-dominated era counterparts indicating a significant enhancement in
the formation of primordial black holes during the matter-dominaed era.Comment: 9 page
Cognitive changes during the menopausal transition: a longitudinal study in women with and without HIV
OBJECTIVE: To assess longitudinal changes in cognitive performance across menopause stages in a sample comprised primarily of low-income women of color, including women with HIV (WWH). METHODS: A total of 443 women (291 WWH; 69% African American; 18% Hispanic; median age = 42 y) from the Women's Interagency HIV Study completed tests of verbal learning and memory, attention/working memory, processing speed, verbal fluency, motor skills, and executive function first at an index premenopausal visit and thereafter once every 2 years for up to six visits (mean follow-up = 5.7 y). General linear-mixed effects regression models were run to estimate associations between menopause stages and cognition, in the overall sample and in WWH. We examined both continuous scores and categorical scores of cognitive impairment (yes/no >1 standard deviation below the mean). RESULTS: Adjusting for age and relevant covariates, the overall sample and WWH showed longitudinal declines in continuous measures of learning, memory, and attention/working memory domains from the premenopause to the early perimenopause and from the premenopause to the postmenopause, Ps < 0.05 to < 0.001. Effects on those same domains were also evident in categorical scores of cognitive impairment, with the increased odds of impairment ranging from 41% to 215%, Ps < 0.05 to < 0.001. The increase in predicted probability of impairment by menopausal stage (% affected) ranged from 4% to 13%. CONCLUSIONS: Menopause stage was a key determinant of cognition in a sample of low-income women of color, including WWH. Many of these changes reached a clinically significant level of cognitive impairment
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