Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userVariations of the fine-structure constant $alpha$ in exotic singularity models
182
0
0.0
(
0
)
Added by
Mariusz Dabrowski P.
Publication date
2014
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
Various classes of exotic singularity models have been studied as possible mimic models for the observed recent acceleration of the universe. Here we further study one of these classes and, under the assumption that they are phenomenological toy models for the behavior of an underlying scalar field which also couples to the electromagnetic sector of the theory, obtain the corresponding behavior of the fine-structure constant $alpha$ for particular choices of model parameters that have been previously shown to be in reasonable agreement with cosmological observations. We then compare this predicted behavior with available measurements of $alpha$, thus constraining this putative coupling to electromagnetism. We find that values of the coupling which would provide a good fit to spectroscopic measurements of $alpha$ are in more than three-sigma tension with local atomic clock bounds. Future measurements by ESPRESSO and ELT-HIRES will provide a definitive test of these models.
rate research
Read More
We present evidence for variations in the fine-structure constant from Keck/HIRES spectra of 143 quasar absorption systems over the redshift range 0.2 < z_abs < 4.2. This includes 15 new systems, mostly at high-z (z_abs > 1.8). Our most robust estimate is a weighted mean da/a=(-0.57 +/- 0.11)x10^{-5}. We respond to recent criticisms of the many-multiplet method used to extract these constraints. The most important potential systematic error at low-z is the possibility of very different Mg heavy isotope abundances in the absorption clouds and laboratory: {it higher} abundances of {25,26}Mg in the absorbers may explain the low-z results. Approximately equal mixes of {24}Mg and {25,26}Mg are required. Observations of Galactic stars generally show {it lower} {25,26}Mg isotope fractions at the low metallicities typifying the absorbers. Higher values can be achieved with an enhanced population of intermediate mass stars at high redshift, a possibility at odds with observed absorption system element abundances. At present, all observational evidence is consistent with the varying-alpha results. Another promising method to search for variation of fundamental constants involves comparing different atomic clocks. Here we calculate the dependence of nuclear magnetic moments on quark masses and obtain limits on the variation of alpha and m_q/Lambda_QCD from recent atomic clock experiments with hyperfine transitions in H, Rb, Cs, Hg+ and an optical transition in Hg+.
We propose a new probe of the dependence of the fine structure constant, alpha, on a strong gravitational field using metal lines in the spectra of white dwarf stars. Comparison of laboratory spectra with far-UV astronomical spectra from the white dwarf star G191-B2B recorded by the Hubble Space Telescope Imaging Spectrograph gives limits on the fractional variation of alpha of (Delta alpha/alpha)=(4.2 +- 1.6)x10^(-5) and (-6.1 +- 5.8)x10^(-5) from Fe V and Ni V spectra, respectively, at a dimensionless gravitational potential relative to Earth of (Delta phi) ~ 5x10^(-5). With better determinations of the laboratory wavelengths of the lines employed these results could be improved by up to two orders of magnitude.
The possibility of variation of the fundamental constants of nature has been a long-standing question, with important consequences for fundamental physics and cosmology. In particular, it has been shown that variations in the fine-structure constant, $alpha$, are directly related to violation of the distance duality relation (DDR), which holds true as long as photons travel on unique null geodesics and their number is conserved. In this paper we use the currently available measurements of ${Delta alpha}/{alpha}$ to impose the most stringent constraints on departures of the DDR to date, here quantified by the parameter $eta$. We also perform a forecast analysis to discuss the ability of the new generation of high-resolution spectrograph, like ESPRESSO/VLT and E-ELT-HIRES, to constrain the DDR parameter $eta$. From the current data we obtain constraints on $eta$ of the order of $10^{-7}$ whereas the forecasted constraints are two orders of magnitude lower. Considering the expected level of uncertainties of the upcoming measurements, we also estimate the necessary number of data points to confirm the hypotheses behind the DDR.
We discuss present and future cosmological constraints on variations of the fine structure constant $alpha$ induced by an early dark energy component having the simplest allowed (linear) coupling to electromagnetism. We find that current cosmological data show no variation of the fine structure constant at recombination respect to the present-day value, with $alpha$ / $alpha_0$ = 0.975 pm 0.020 at 95 % c.l., constraining the energy density in early dark energy to $Omega_e$ < 0.060 at 95 % c.l.. Moreover, we consider constraints on the parameter quantifying the strength of the coupling by the scalar field. We find that current cosmological constraints on the coupling are about 20 times weaker than those obtainable locally (which come from Equivalence Principle tests). However forthcoming or future missions, such as Planck Surveyor and CMBPol, can match and possibly even surpass the sensitivity of current local tests.
Bouncing models have been proposed by many authors as a completion, or even as an alternative to inflation for the description of the very early and dense Universe. However, most bouncing models contain a contracting phase from a very large and rarefied state, where dark energy might have had an important role as it has today in accelerating our large Universe. In that case, its presence can modify the initial conditions and evolution of cosmological perturbations, changing the known results already obtained in the literature concerning their amplitude and spectrum. In this paper, we assume the simplest and most appealing candidate for dark energy, the cosmological constant, and evaluate its influence on the evolution of cosmological perturbations during the contracting phase of a bouncing model, which also contains a scalar field with a potential allowing background solutions with pressure and energy density satisfying p = w*rho, w being a constant. An initial adiabatic vacuum state can be set at the end of domination by the cosmological constant, and an almost scale invariant spectrum of perturbations is obtained for w~0, which is the usual result for bouncing models. However, the presence of the cosmological constant induces oscillations and a running towards a tiny red-tilted spectrum for long wavelength perturbations.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
