Low-energy phenomenology of superstring-inspired E6 models

https://bura.brunel.ac.uk/bitstream/2438/7961/2/Preprint.pdf

Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP

In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today’s technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics.

/pdf/fcc-ee-the-lepton-collider-future-circular-collider-61xh2cg09w.pdf

FCC-ee: The Lepton Collider: Future Circular Collider Conceptual Design Report Volume 2

https://escholarship.org/content/qt7653f3f2/qt7653f3f2.pdf?t=paoixg

Physics interplay of the LHC and the ILC

We study cosmic string formation within supersymmetric grand unified theories (GUTs). We consider gauge groups having a rank between 4 and 8. We examine all possible spontaneous symmetry breaking patterns from the GUT down to the standard model gauge group. Assuming standard hybrid inflation, we select all the models which can solve the GUT monopole problem leading to baryogenesis after inflation, and are consistent with proton lifetime measurements. We conclude that, in all acceptable spontaneous symmetry breaking schemes, cosmic string formation is unavoidable. The strings which form at the end of inflation have a mass which is proportional to the inflationary scale. Sometimes a second network of strings form at a lower scale. Models based on gauge groups which have a rank greater than 6 can lead to more than one inflationary era; they all end by cosmic string formation.

How generic is cosmic string formation in supersymmetric grand unified theories

Recent developments in superstring theories have renewed interest in E/sub 6/ as the group for grand unification. E/sub 6/ has rank 6, two more than the standard model, so that an E/sub 6/ grand unified theory can have extra gauge bosons. For example, it can have extra low-energy Z-italic's. If there is just one extra Z-italic at low energy, it can be a mixture of the two extra U(1)'s present in E/sub 6/. We parametrize this mixing by an angle t-italich-italice-italict-italica-italic. We consider the effects of Z-italic(t-italich-italice-italict-italica-italic) in neutral currents, putting limits on its mass. In addition, we consider the branching ratios, Drell-Yan production, and forward-backward asymmetries for Z-italic(t-italich-italice-italict-italica-italic). Another possibility is that, in addition to one extra Z-italic, there is an extra SU(2) present in the low-energy theory. It is SU(2)/sub I-italic/, the SU(2) which commutes with the electromagnetic charge. We consider the effects of the W-italic/sub I-italic/, which are electromagnetically neutral, in production of exotic particles and other rare processes, particularly flavor-changing neutral currents.

Extra Gauge Bosons in E(6)

We perform a comprehensive study of the impact of new-physics opera- tors with different Lorentz structures on decays involving the b → sµ + µ − transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) "' and tensor (T) interactions on the differential branching ratios and forward-backward asymmetries (AFB's) of ¯ B 0 K ∗ µ + µ − , we further explore the polarization fraction fL, the angular asymmetry A (2) , and the longitudinal-transverse asymmetry ALT. We identify the Lorentz structures that would significantly impact these observables, providing analytical arguments in terms of the contributions from the individual operators and their interference terms. In particular, we show that while the new VA operators can significantly enhance most of the asymmetries beyond the Standard Model predictions, the SP and T operators can do this only for AFB in ¯ B 0 → ¯ Kµ + µ − .

New Physics in b ! sµ + µ : CP-Conserving Observables

New tests of lepton number violation at electron-electron colliders

We perform a comprehensive study of the impact of new-physics op- erators with different Lorentz structures on CP-violating observables involving the b → sµ + µ − transition. We examine the effects of new vector-axial vector, scalar- pseudoscalar and tensor interactions on the CP asymmetries in the branching ratios and forward-backward asymmetries of ¯ B 0 s → µ We find that the CP-violating observables in all the cases are sensitive only to new physics which involves vector-axial vector operators. A combined analysis of future measurements of these CP-violating observables could enable the detection of physics beyond the Standard Model, especially of the vector-axial vector kind.

New physics in b ! sµ + µ : CP-violating observables

We consider the effects of ${Z}^{0}\ensuremath{-}{Z}^{\ensuremath{'}}$ mixing, where the ${Z}^{\ensuremath{'}}$ is an ${E}_{6}$ gauge boson, on processes which will be measured at ${e}^{+}{e}^{\ensuremath{-}}$ colliders. Using constraints from current data, we find that significant mixing may be allowed. This mixing leads to measurable changes in the ${Z}^{0}$ partial widths and $\ensuremath{\sigma}({e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$. In one case, we also find that a ${Z}^{\ensuremath{'}}$ lighter than the ${Z}^{0}$ is still allowed. We discuss possibilities for its detection.

David London

Papers

Extra Gauge Bosons in E(6)

New Physics in b ! sµ + µ : CP-Conserving Observables

New tests of lepton number violation at electron-electron colliders

New physics in b ! sµ + µ : CP-violating observables

Effects of Z 0 mixing with an E 6 gauge boson at e + e - colliders