The Large Hadron–Electron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energy-recovery technology, it collides a novel, intense electron beam with a proton or ion beam from the High-Luminosity Large Hadron Collider (HL-LHC). The accelerator and interaction region are designed for concurrent electron–proton and proton–proton operations. This report represents an update to the LHeC’s conceptual design report (CDR), published in 2012. It comprises new results on the parton structure of the proton and heavier nuclei, QCD dynamics, and electroweak and top-quark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics by extending the accessible kinematic range of lepton–nucleus scattering by several orders of magnitude. Due to its enhanced luminosity and large energy and the cleanliness of the final hadronic states, the LHeC has a strong Higgs physics programme and its own discovery potential for new physics. Building on the 2012 CDR, this report contains a detailed updated design for the energy-recovery electron linac (ERL), including a new lattice, magnet and superconducting radio-frequency technology, and further components. Challenges of energy recovery are described, and the lower-energy, high-current, three-turn ERL facility, PERLE at Orsay, is presented, which uses the LHeC characteristics serving as a development facility for the design and operation of the LHeC. An updated detector design is presented corresponding to the acceptance, resolution, and calibration goals that arise from the Higgs and parton-density-function physics programmes. This paper also presents novel results for the Future Circular Collider in electron–hadron (FCC-eh) mode, which utilises the same ERL technology to further extend the reach of DIS to even higher centre-of-mass energies.

We update the constraints on anomalous dimension four t-b-W and t-t-Z couplings by using CLEO b → sγ and LEP/SLC precision Z-pole data. It is found that the data imposes very stringent bounds on them. Moreover, the 2σ pull from SM predictions of A LR (hadrons), A b and A F B (b) have little chance of being explained by the strongly constrained anomalous couplings.

We study the deep inelastic scattering and photo-production modes of tt pairs at the proposed LHeC and its potential to probe the electromagnetic and weak dipole moments (MDM and EDM for ttγ) of the top quark. A framework of eight independent gauge-invariant dimension-six operators involving the top quark and the electroweak gauge bosons is used. Four of these operators modify the charged tbW coupling which can be probed through the single (anti) top production mode as reported in the literature. One generates ttγ(Z) as well as tbW couplings, while the other two do not generate tbW but only ttγ(Z). Our focus is on the MDM and EDM of the top quark for which the photo-production mode of tt can be an excellent probe. At the proposed electron energies of E e = 60 and 140 GeV the LHeC could set constraints stronger than the indirect limits from b → sγ and the potential limits of the LHC through ttγ production.

We show that a general two-Higgs-doublet model (THDM) with a very light CP-odd scalar (A) can be compatible with ρ parameter, Br(b → sγ), R b , A b , (g − 2)µ of muon, Br(Υ → Aγ), and the direct search via the Yukawa process at LEP. For its mass around 0.2 GeV, the muon (g − 2)µ and Br(Υ → Aγ) data require tan β to be about 1. Consequently, A can behave like a fermiophobic CP-odd scalar and predominantly decay into a γγ pair, which registers in detectors of high energy collider experiments as a single photon signature when the momentum of A is large. We compute the partial decay width of Z → AAA and the production rate of ff → ZAA → Z + "γγ",γγ" at high energy colliders such as LEP, Tevatron, LHC, and future Linear Colliders. Other production mechanisms of a light A, such as gg → h → AA → "γγ", are also discussed.

Recent measurements like the ttγ production by CDF as well as the Br(B → X s γ) and A CP (B → X s γ) are used to constrain the magnetic and electric dipole moments of the top quark. The B → X s γ measurements by themselves define an allowed parameter region that sets up stringent constraints on both dipole moments.Actually, significantly more stringent than previously reported. The measurement by CDF has a ∼ 37% error that is too large to set any competitive bounds, for which a much lower 5% error would be required at least. On the other hand, because of the LHC's higher energy (apart from its higher luminosity) the same measurement performed there could indeed further constrain the allowed parameter region given by the B → X s γ measurement.

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We survey the flavor-changing neutral couplings (FCNC) of the top quark predicted by some extensions of the Standard Model: THDM, SUSY, L-R symmetric, TC2, 331, and models with extra quarks. Since the expected sensitivity of the LHC and ILC for the tcV (V = γ, g, Z) and tcH couplings is of order of a few percent, we emphasize the importance of any new physics effect that gives a prediction for these FCNC couplings within this limit. We also review the constraints imposed on these couplings from lowenergy precision measurements.

We study the one-loop contributions of the effective flavor changing neutral couplings (FCNC) tcZ and tcH on the electroweak precision observables Γ Z , R c , R b , R ℓ , A c and A F B c . Using the known experimental limits on these observables, we may place 95% CL bounds on these FCNC couplings which in turn translate into the following limits for the branching ratios BR(t → cZ) ≤ 6.7 × 10 −2 and BR(t → cH) ≤ (0.09 − 2.9) × 10 −3 for 114 ≤ m H ≤ 170GeV . PACS numbers 14.65.Ha;12.60.C;12.15.M;12.15.L As soon as it was confirmed that the flavor changing neutral couplings (FCNC) of the top quark are highly suppressed in the standard model (SM)[1], it was realized that some of its FCNC decay modes can be enhanced by several orders of magnitude in scenarios beyond the SM, and some of them