146 research outputs found
A new constraint on cosmological variability of the proton-to-electron mass ratio
Exotic cosmologies predict variability of the fundamental physical constants
over the cosmic time. Using the VLT/UVES high resolution spectra of the quasar
Q0347-3819 and unblended electronic - vibrational - rotational lines of the H2
molecule identified at z = 3.025 we test possible changes in the proton - to -
electron mass ratio mu_0 = m_p/m_e over the period of 11 Gyr. We obtained a new
constraint on the time - averaged variation rate of mu_0 of |d mu /d t /mu_0| <
5 10^{-15} yr^{-1} (1 sigma c.l.). The estimated 1 sigma uncertainty interval
of the |Delta mu/mu_0| ratio of about 0.004% implies that since the time when
the H2 spectrum was formed at z = 3.025, mu_0 has not changed by more than a
few thousands of a percent.Comment: 5 pages, 3 figures, a revised version accepted by MNRA
Possible Constraints on the Time Variation of the Fine Structure Constant from Cosmic Microwave Background Data
The formation of the cosmic microwave background radiation (CMBR) provides a
very powerful probe of the early universe at the epoch of recombination.
Specifically, it is possible to constrain the variation of fundamental physical
constants in the early universe. We have calculated the effect of a varying
electromagnetic coupling constant (\alpha) on the CMBR and find that new
satellite experiments should provide a tight constraint on the value of \alpha
at recombination which is complementary to existing constraints. An estimate of
the obtainable precision is |\dot{\alpha}/\alpha| \leq 7 x 10^{-13} y^{-1} in a
realistic experiment.Comment: 5 pages, 3 postscript figures, matches version to appear in Phys.
Rev.
Quintessence and variation of the fine structure constant in the CMBR
We study dependence of the CMB temperature anisotropy spectrum on the value
of the fine structure constant and the equation of state of the dark
energy component of the total density of the universe. We find that bounds
imposed on the variation of from the analysis of currently available
CMB data sets can be significantly relaxed if one also allows for a change in
the equation of state.Comment: 5 pages, 3 figures. Several references added and a few minor typos
corrected in the revised versio
The SN 1006 Remnant: Optical Proper Motions, Deep Imaging, Distance, and Brightness at Maximum
We report the first measurement of proper motions in the SN1006 remnant
(G327.6+14.6) based entirely on digital images. CCD images from three epochs
spanning a period of 11 years are used: 1987 from Las Campanas, and 1991 and
1998 from CTIO. Measuring the shift of delicate Balmer filaments along the
northwest rim of the remnant, we obtain proper motions of 280 +/- 8 mas/yr
along the entire length where the filaments are well defined, with little
systematic variation along the filaments. We also report very deep Halpha
imaging observations of the entire remnant that clearly show very faint
emission surrounding almost the entire shell, as well as some diffuse emission
regions in the (projected) interior. Combining the proper motion measurement
with a recent measurement of the shock velocity based on spectra of the same
filaments by Ghavamian et al. leads to a distance of 2.17 +/- 0.08 kpc to
SN1006. Several lines of argument suggest that SN1006 was a Type Ia event, so
the improved distance measurement can be combined with the peak luminosity for
SNeIa, as determined for events in galaxies with Cepheid-based distances, to
calculate the apparent brightness of the spectacular event that drew wide
attention in the eleventh century. The result, V_max = -7.5 =/- 0.4, lies
squarely in the middle of the wide range of estimates based on the historical
observations.Comment: 13 pages, 3 tables, 5 figures. Uses AASTeX5.02 and emulateapj
Search for Possible Variation of the Fine Structure Constant
Determination of the fine structure constant alpha and search for its
possible variation are considered. We focus on a role of the fine structure
constant in modern physics and discuss precision tests of quantum
electrodynamics. Different methods of a search for possible variations of
fundamental constants are compared and those related to optical measurements
are considered in detail.Comment: An invited talk at HYPER symposium (Paris, 2002
Searching for spatial variations of alpha^2/mu in the Milky Way
(Abridged) A procedure is suggested to explore the value of F = alpha^2/mu,
where mu = m_e/m_p is the electron-to-proton mass ratio, and alpha is the
fine-structure constant. The fundamental physical constants, which are measured
in different physical environments of high (terrestrial) and low (interstellar)
densities of baryonic matter are supposed to vary in chameleon-like scalar
field models, which predict that both masses and coupling constant may depend
on the local matter density. The parameter Delta F/F = (F_obs - F_lab)/F_lab
can be estimated from the radial velocity offset, Delta V = V_rot-V_fs, between
the low-laying rotational transitions in carbon monoxide 13CO and the
fine-structure transitions in atomic carbon [CI]. A model-dependent constraint
on Delta alpha/alpha can be obtained from Delta F/F using Delta mu/mu
independently measured from the ammonia method. Currently available radio
astronomical datasets provide an upper limit on |Delta V| < 110 m/s (1sigma).
When interpreted in terms of the spatial variation of F, this gives |Delta F/F|
< 3.7*10^-{7}. An order of magnitude improvement of this limit will allow us to
test independently a non-zero value of Delta mu/mu = (2.2 +/- 0.4_stat +/-
0.3_sys)*10^{-8} recently found with the ammonia method. Taking into account
that the ammonia method restricts the spatial variation of mu at the level of
|Delta mu/mu| <= 3*10^{-8} and assuming that Delta F/F is the same in the
entire interstellar medium, one obtains that the spatial variation of alpha
does not exceed the value |Delta alpha/alpha| < 2*10^{-7}. Since extragalactic
gas clouds have densities similar to those in the interstellar medium, the
bound on Delta alpha/alpha is also expected to be less than 2*10^{-7} at high
redshift if no significant temporal dependence of alpha is present.Comment: 7 pages, 1 table. Accepted for publication in Astronomy and
Astrophysic
Constraining fundamental constants of physics with quasar absorption line systems
We summarize the attempts by our group and others to derive constraints on
variations of fundamental constants over cosmic time using quasar absorption
lines. Most upper limits reside in the range 0.5-1.5x10-5 at the 3sigma level
over a redshift range of approximately 0.5-2.5 for the fine-structure constant,
alpha, the proton-to-electron mass ratio, mu, and a combination of the proton
gyromagnetic factor and the two previous constants, gp(alpha^2/mu)^nu, for only
one claimed variation of alpha. It is therefore very important to perform new
measurements to improve the sensitivity of the numerous methods to at least
<0.1x10-5 which should be possible in the next few years. Future
instrumentations on ELTs in the optical and/or ALMA, EVLA and SKA pathfinders
in the radio will undoutedly boost this field by allowing to reach much better
signal-to-noise ratios at higher spectral resolution and to perform
measurements on molecules in the ISM of high redshift galaxies.Comment: 11 pages, 3 figure
Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra
Theories unifying gravity with other interactions suggest spatial and
temporal variation of fundamental "constants" in the Universe. A change in the
fine structure constant, alpha, could be detected via shifts in the frequencies
of atomic transitions in quasar absorption systems. Recent studies using 140
absorption systems from the Keck telescope and 153 from the Very Large
Telescope, suggest that alpha varies spatially. That is, in one direction on
the sky alpha seems to have been smaller at the time of absorption, while in
the opposite direction it seems to have been larger.
To continue this study we need accurate laboratory measurements of atomic
transition frequencies. The aim of this paper is to provide a compilation of
transitions of importance to the search for alpha variation. They are E1
transitions to the ground state in several different atoms and ions, with
wavelengths ranging from around 900 - 6000 A, and require an accuracy of better
than 10^{-4} A. We discuss isotope shift measurements that are needed in order
to resolve systematic effects in the study. The coefficients of sensitivity to
alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis
VLT/UVES constraints on the cosmological variability of the fine-structure constant
We propose a new methodology for probing the cosmological variability of
alpha from pairs of FeII lines (SIDAM, single ion differential alpha
measurement) observed in individual exposures from a high resolution
spectrograph. By this we avoid the influence of the spectral shifts due to (i)
ionization inhomogeneities in the absorbers and (ii) non-zero offsets between
different exposures. Applied to the FeII lines of the metal absorption line
system at zabs = 1.839 in the spectrum of Q1101-264 obtained by means of the
UV-Visual Echelle Spectrograph (UVES) at the ESO Very Large Telescope (VLT),
SIDAM provides da/a = (2.4+/-3.8) 10^{-6}. The zabs = 1.15 FeII system toward
HE0515-4414 has been re-analyzed by this method thus obtaining for the combined
sample da/a = (0.4+/-1.5) 10^{-6}. These values are shifted with respect to the
Keck/HIRES mean da/a = (-5.7+/-1.1) 10^{-6} (Murphy et al. 2004) at very high
confidence level (95%). The fundamental photon noise limitation in the da/a
measurement with the VLT/UVES is discussed to figure the prospects for future
observations. It is suggested that with a spectrograph of 10 times the UVES
dispersion coupled to a 100m class telescope the present Oklo level (da/a >=
4.5 10^{-8}) can be achieved along cosmological distances with differential
measurements of da/a.Comment: 13 pages, 6 figures, corrected version, accepted for publication in
Astron. Astrophy
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