133 research outputs found
Fundamental Constant Observational Bounds on the Variability of the QCD Scale
Many physical theories beyond the Standard Model predict time variations of
basic physics parameters. Direct measurement of the time variations of these
parameters is very difficult or impossible to achieve. By contrast,
measurements of fundamental constants are relatively easy to achieve, both in
the laboratory and by astronomical spectra of atoms and molecules in the early
universe. In this work measurements of the proton to electron mass ratio
and the fine structure constant are combined to place mildly model
dependent limits on the fractional variation of the Quantum Chromodynamic Scale
and the sum of the fractional variations of the Higgs Vacuum Expectation Value
and the Yukawa couplings on time scales of more than half the age of the
universe. The addition of another model parameter allows the fractional
variation of the Higgs VEV and the Yukawa couplings to be computed separately.
Limits on their variation are found at the level of less than over the past seven gigayears. A model dependent relation between the
expected fractional variation of relative to tightens the limits
to over the same time span. Limits on the present day rate of change
of the constants and parameters are then calculated using slow roll
quintessence. A primary result of this work is that studies of the
dimensionless fundamental constants such as and , whose values
depend on the values of the physics parameters, are excellent monitors of the
limits on the time variation of these parameters.Comment: Accepted for publication in the Monthly Notices of the Royal
Astronomical Society, 8 pages, 5 figure
Confronting Cosmology and New Physics with Fundamental Constants
The values of the fundamental constants such as , the proton
to electron mass ratio and , the fine structure constant, are sensitive
to the product where is a coupling constant
between a rolling scalar field responsible for the acceleration of the
expansion of the universe and the electromagnetic field with x standing for
either or . The dark energy equation of state can assume
values different than in cosmologies where the acceleration of the
expansion is due to a scalar field. In this case the value of both and
changes with time. The values of the fundamental constants, therefore,
monitor the equation of state and are a valuable tool for determining as a
function of redshift. In fact the rolling of the fundamental constants is one
of the few definitive discriminators between acceleration due to a cosmological
constant and acceleration due to a quintessence rolling scalar field. is
often given in parameterized form for comparison with observations. In this
manuscript the predicted evolution of , is calculated for a range of
parameterized equation of state models and compared to the observational
constraints on . We find that the current limits on place significant constraints on linear equation of state models and
on thawing models where deviates from at late times. They also
constrain non-dynamical models that have a constant not equal to .
These constraints are an important compliment to geometric tests of in that
geometric tests are sensitive to the evolution of the universe before the epoch
of observation while fundamental constants are sensitive to the evolution of
the universe after the observational epoch. Abstract truncated.Comment: To appear in the conference proceedings of the Sesto Conference on
Fundamental Constants and Coupling
Beta Function Quintessence Cosmological Parameters and Fundamental Constants I: Power and Inverse Power Law Dark Energy Potentials
This investigation explores using the beta function formalism to calculate
analytic solutions for the observable parameters in rolling scalar field
cosmologies. The beta function in this case is the derivative of the scalar
with respect to the natural log of the scale factor ,
. Once the beta function is specified,
modulo a boundary condition, the evolution of the scalar as a function
of the scale factor is completely determined. A rolling scalar field cosmology
is defined by its action which can contain a range of physically motivated dark
energy potentials. The beta function is chosen so that the associated "beta
potential" is an accurate, but not exact, representation of the appropriate
dark energy model potential. The basic concept is that the action with the beta
potential is so similar to the action with the model potential that solutions
using the beta action are accurate representations of solutions using the model
action. The beta function provides an extra equation to calculate analytic
functions of the cosmologies parameters as a function of the scale factor that
are that are not calculable using only the model action. As an example this
investigation uses a quintessence cosmology to demonstrate the method for power
and inverse power law dark energy potentials. An interesting result of the
investigation is that the Hubble parameter H is almost completely insensitive
to the power of the potentials and that CDM is part of the family of
quintessence cosmology power law potentials with a power of zero.Comment: Accepted for publication by the Monthly Notices of the Royal
Astronomical Societ
High Redshift Candidates and the Nature of Small Galaxies in the Hubble Deep Field
We present results on two related topics: 1. A discussion of high redshift
candidates (z>4.5), and 2. A study of very small galaxies at intermediate
redshifts, both sets being detected in the region of the northern Hubble Deep
Field covered by deep NICMOS observations at 1.6 and 1.1 microns. The high
redshift candidates are just those with redshift z>4.5 as given in the recent
catalog of Thompson, Weymann and Storrie-Lombardi, while the ``small galaxy''
sample is defined to be those objects with isophotal area <= 0.2 squ. arcsec
and with photometric redshifts 1<z<4.5. Of the 19 possible high redshift
candidates listed in the Thompson et al. catalog, 11 have (nominal) photometric
redshifts less than 5.0. Of these, however, only 4 are ``robust'' in the sense
of yielding high redshifts when the fluxes are randomly perturbed with errors
comparable to the estimated measuring error in each wave band. For the 8 other
objects with nominal photometric redshifts greater than 5.0, one (WFPC2 4--473)
has a published spectroscopic redshift. Of the remaining 7, 4 are robust in the
sense indicated above. Two of these form a close pair (NIC 586 and NIC 107).
The redshift of the object having formally the highest redshift, at 6.56
(NIC118 = WFPC2 4--601), is problematic, since F606W and F814W flux are clearly
present, and the nature of this object poses a dilemma. (abridged)Comment: 44 pages, 12 figures, to appear in ApJ v591, July 10, 200
NICMOS observations of the HDF
This paper presents initial results and performance levels from the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) observations of the Hubble Deep Field (HDF). These observations represent the deepest view of individual objects yet obtained with photometric colors of some objects indicating redshift values greater than 6. These observations add significant value to the previous optical observations of the HDF with the Wide Field and Planetary Camera II (WFPC II)
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