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Register a new userThe Fundamental Constants in Physics
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H. Fritzsch
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We discuss the fundamental constants of physics in the Standard Model and possible changes of these constants on the cosmological time scale. The Grand Unification of the strong, electromagnetic and weak interactions implies relations between the time variation of the finestructure constant and of the QCD scale. An experiment in quantum optics at the MPQ in Munich, which was designed to look for a time variation of the QCD scale, is discussed.
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We discuss the fundamemtal constants in the Standard Model of particle physics, in particular possible changes of these constants on the cosmological time scale. The Grand Unification of the observed strong, electromagnetic and weak interactions implies relations between time variation of the finestructure constant alpha and the QCD scale $Lambda_c$. The astrophysical observation of a variation implies a time variation of $10^{-15} / year$. Several experiments in Quantum Optics, which were designed to look for a time variation of $Lambda_c$, are discussed.
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.
The values of the fundamental constants such as $mu = m_P/m_e$, the proton to electron mass ratio and $alpha$, the fine structure constant, are sensitive to the product $sqrt{zeta_x^2(w+1)}$ where $zeta_x$ 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 $mu$ or $alpha$. The dark energy equation of state $w$ can assume values different than $-1$ in cosmologies where the acceleration of the expansion is due to a scalar field. In this case the value of both $mu$ and $alpha$ changes with time. The values of the fundamental constants, therefore, monitor the equation of state and are a valuable tool for determining $w$ 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. $w$ is often given in parameterized form for comparison with observations. In this manuscript the predicted evolution of $mu$, is calculated for a range of parameterized equation of state models and compared to the observational constraints on $Delta mu / mu$. We find that the current limits on $Delta mu / mu$ place significant constraints on linear equation of state models and on thawing models where $w$ deviates from $-1$ at late times. They also constrain non-dynamical models that have a constant $w$ not equal to $-1$. These constraints are an important compliment to geometric tests of $w$ 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.
This report summarizes the proceedings of the 2014 Mainz Institute for Theoretical Physics (MITP) scientific program on High precision fundamental constants at the TeV scale. The two outstanding parameters in the Standard Model dealt with during the MITP scientific program are the strong coupling constant $alpha_s$ and the top-quark mass $m_t$. Lacking knowledge on the value of those fundamental constants is often the limiting factor in the accuracy of theoretical predictions. The current status on $alpha_s$ and $m_t$ has been reviewed and directions for future research have been identified.
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.
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