•A system of quasi-free electrons is described using Dirac spinor components.•QFT generalizations of the Larmor precession and Zeeman effect are derived.•Magnetic field strength and chirality index ...are essential quantities in the description.•The chirality index is a function of electron spin polarization coefficients.•Experiments with quasi-free electrons in chiral biological systems are discussed.
The effects of a magnetic field on the energy and on the spin of free electrons are computed in the theoretical framework of quantum field theory. In the case of a static moderate field and with relatively slow electrons, the derived formulae are particularly simple. A comparison with the approaches of classical physics and of quantum mechanics shows essential differences and important analogies. The relevance to the magnetic effects of the initial polarization components of the electron states and the possible existence of special values of these quantities are discussed in the final conclusions, which might be useful to explain recent experiments on quasi-free electrons in chiral systems in biology.
We propose a new type of Z polarization asymmetry in bottom-Z production at LHC that should be realistically measurable and would provide the determination of the so-called Ab parameter, whose ...available measured value still appears to be in disagreement with the Standard Model prediction; we discuss the overall expected precision of this measurement and its implications. If Supersymmetry is found, a second polarization, i.e. the top longitudinal polarization in top-charged Higgs production, would neatly identify the tanβ parameter. In this case, the value of Ab should be in agreement with the Standard Model. If Supersymmetry does not exist, a residual disagreement of Ab from the Standard Model prediction would be a clean signal of New Physics of “non-Supersymmetric” origin.
We consider in a quantum field theory framework the effects of a classical magnetic field on the spin and orbital angular momentum (OAM) of a free electron. We derive formulae for the changes in the ...spin and OAM due to the introduction of a general classical background field. We consider then a constant magnetic field, in which case the relevant expressions of the effects become much simpler and conversions between spin and OAM become readily apparent. An estimate of the expectation values for a realistic electron state is also given. Our findings may be of interest to researchers in spintronics and the field of quantum biology, where electron spin has been implicated on macroscopic time and energy scales.
•We present the first field theory treatment of magnetic changes in electron spin.•Changes in spin and orbital angular momentum (OAM) are correlated and calculated.•Expectation values of spin–OAM changes for a realistic electron state are computed.•Earth's magnetic field produces non-negligible changes in spin of a few percent.•Results apply to spin–OAM conversion in electron vortex beams and quantum biology.
We consider the Z polarization asymmetry AZ=(σ(ZR)−σ(ZL))/(σ(ZR)+σ(ZL)) in the process of associated bZ production at the LHC. We show that in the Standard Model (SM) this quantity is essentially ...given by its Born approximation, remaining almost unaffected by QCD scales and parton distribution functions variations as well as by electroweak corrections. The theoretical quantity that appears in AZ is the same that provides the LEP1 Z→bb¯ forward–backward asymmetry, the only measured observable still in some contradiction with the SM prediction. In this sense, AZ would provide the possibility of an independent verification of the possible SM discrepancy, which could reach, if consistency with LEP1 measurements is imposed, values of the relative ten percent size.
Many extensions of the Standard Model involve two Higgs doublet fields to break the electroweak symmetry, leading to the existence of three neutral and two charged Higgs particles. In particular, ...this is the case of the Minimal Supersymmetric extension of the Standard Model, the MSSM. A very important parameter is tanβ defined as the ratio of the vacuum expectation value of the two Higgs doublets. In this Letter we focus on the left–right asymmetry in the production of polarised top quarks in association with charged Higgs bosons at the LHC. This quantity allows for a theoretically clean determination of tanβ. In the MSSM, the asymmetry remains sensitive to the strong and electroweak radiative corrections and, thus, to the superparticle spectrum. Some possible implications of these results are discussed.
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