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Register a new userFundamental Constants as Monitors of the Universe
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Added by
Rodger Thompson Prof.
Publication date
2016
fields
Physics
and research's language is
English
Authors
Rodger I. Thompson
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Astronomical observations have a unique ability to determine the laws of physics at distant times in the universe. They, therefore, have particular relevance in answering the basic question as to whether the laws of physics are invariant with time. The dimesionless fundamental constants, such as the proton to electron mass ratio and the fine structure constant are key elements in the investigation. If they vary with time then the answer is clearly that the laws of physics are not invariant with time and significant new physics must be developed to describe the universe. Limits on their variance, on the other hand, constrains the parameter space available to new physics that requires a variation with time of basic physical law. There are now observational constraints on the time variation of the proton to electron mass ratio mu at the 1.E-7 level. Constraints on the variation of the fine structure constant alpha are less rigorous, 1E-5, but are imposed at higher redshift. The implications of these limits on new cosmologies that require rolling scalar fields has already had its first investigations. Here we address the implications on basic particle physics. The proton to electron mass ratio is obviously dependent on the particle physics parameters that set the mass of the proton and the electron. To first order the ratio is dependent on a combination of the Quantum Chromodynamic scale, the Yukawa couplings, and the Higgs Vacuum Expectation Value. Here that relationship is quantitative defined for the first time. When coupled with previous determinations of the relation of the fine structure constant to the same parameters two constraints exist on the fractional variation of these parameters with time. A third independent constraint involving only the three parameters could set the stage for constraints on their individual fractional variation.
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The observation of space-time variations in fundamental constants would provide strong evidence for the existence of new light degrees of freedom in the theory of Nature. Robustly constraining such scenarios requires exploiting observations that span different scales and probe the state of the Universe at different epochs. In the context of cosmology, both the cosmic microwave background and the Lyman-$alpha$ forest have proven to be powerful tools capable of constraining variations in electromagnetism, however at the moment there do not exist cosmological probes capable of bridging the gap between recombination and reionization. In the near future, radio telescopes will attempt to measure the 21cm transition of neutral hydrogen during the epochs of reionization and the cosmic dawn (and potentially the tail end of the dark ages); being inherently sensitive to electromagnetic phenomena, these experiments will offer a unique perspective on space-time variations of the fine-structure constant and the electron mass. We show here that large variations in these fundamental constants would produce features on the 21cm power spectrum that may be distinguishable from astrophysical uncertainties. Furthermore, we forecast the sensitivity for the Square Kilometer Array, and show that the 21cm power spectrum may be able to constrain variations at the level of ${cal O}(10^{-3})$.
Absorption-line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, alpha, and the proton-to-electron mass ratio, mu = m_p/m_e, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in alpha on cosmological scales which may reach a fractional level of 10 ppm . We are conducting a Large Programme of observations with VLT UVES to explore these variations. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. and Rahmani et al. A stringent bound for Delta(alpha)/Alpha is obtained for the absorber at_abs = 1.6919 towards HE 2217-2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in alpha in this system is +1.3+-2.4_{stat}+-1.0_{sys} ppm if Al II lambda 1670AA and three Fe II transitions are used, and +1.1+-2.6_{stat} ppm in a lightly different analysis with only Fe II transitions used. The expectation at this sky position of the recently-reported dipolar variation of alpha is (3.2--5.4)+-1.7 ppm depending on dipole model. This constraint of Delta(alpha)/alpha at face value is not supporting this expectation but is not inconsistent with it at the 3 sigma level. For the proton-to-electron mass ratio the analysis of the H_2 absorption lines of the z_{abs}~2.4018 damped Ly alpha system towards HE 0027- 1836 provides Delta(mu)/mu = (-7.6 +- 8.1_{stat} +- 6.3_{sys}) ppm which is also consistent with a null variation. (abridged)
We investigate the effect of a variation of fundamental constants on primordial element production in Big Bang nucleosynthesis (BBN). We focus on the effect of a possible change in the nucleon-nucleon interaction on nuclear reaction rates involving the A=5 (5Li and 5He) and A=8 (8Be) unstable nuclei. The reaction rates for 3He(d,p)4He and 3H(d,n)4He are dominated by the properties of broad analog resonances in 5Li and 5He compound nuclei respectively. While the triple-alpha process 4He(aa,g)12C is normally not effective in BBN, its rate is very sensitive to the position of the Hoyle state and could in principle be drastically affected if 8Be were stable during BBN. We found that the effect of the variation of constants on the 3He(d,p)4He, 3H(d,n)4He nd 4He(aa,g)12C reaction rates is not sufficient to induce a significant effect on BBN, even with a stable 8Be. The main influences come from the weak rates and the A=2, n(p,g)d, bottleneck reaction.
We use the three-scale framework of Hu et al. to show how the Cosmic Microwave Background anisotropy spectrum depends on the fundamental constants. As expected, the spectrum depends only on emph{dimensionless} combinations of the constants, and we emphasize the points that make this generally true for cosmological observables. Our analysis suggests that the CMB spectrum shape is mostly determined by $alpha^2m_e/m_p$ and the proton-CDM-particle mass ratio, $m_p/mchi$. The distance to the last-scattering surface depends on $Gm_pmchi/hbar c$, so published CMB observational limits on time variations of the constants implicitly assume the time-independence of this quantity, as well as assuming a flat-lcdm~cosmological model. On the other hand, low-redshift BAO, $H_0$ and baryon-mass-fraction measurements can be combined with the emph{shape} of the CMB spectrum to give information that is largely independent of these assumptions. In particular we show that the pre-recombination values of $Gmchi^2/hbar c$, $m_p/mchi$ and $alpha^2m_e/m_p$ are equal to their present values at a precision of $sim15%$.
The observed constraints on the variability of the proton to electron mass ratio $mu$ and the fine structure constant $alpha$ are used to establish constraints on the variability of the Quantum Chromodynamic Scale and a combination of the Higgs Vacuum Expectation Value and the Yukawa couplings. Further model dependent assumptions provide constraints on the Higgs VEV and the Yukawa couplings separately. A primary conclusion is that limits on the variability of dimensionless fundamental constants such as $mu$ and $alpha$ provide important constraints on the parameter space of new physics and cosmologies.
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