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.

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Towards experimental confirmations of the type-I seesaw mechanism, we explore a prospect of discovering the heavy Majorana right-handed neutrinos (RHNs) from a resonant production of a new massive gauge boson (Z 0 ) and its subsequent decay into a pair of RHNs (Z 0 → NN) at the future high luminosity runs at the Large Hadron Collider (LHC). Recent simulation studies have shown that the discovery of the RHNs through this process is promising in the future. However, the current LHC data very severely constrains the production cross section of the Z 0 boson into a dilepton final states,. Extrapolating the current bound to the future, we find that a significant enhancement of the branching ratio BRðZ 0 → NNÞ over BRðZ 0 → l þ l − Þ is necessary for the future discovery of RHNs. As a well-motivated simple extension of the standard model (SM) to incorporate the Z 0 boson and the type-I seesaw mechanism, we consider the minimal Uð1Þ X model, which is a generalization of the well-known minimal B − L model without extending the particle content. We point out that this model can yield a significant enhancement up to. This is in sharp contrast with the minimal B − L model, a benchmark scenario commonly used in simulation studies, which predicts BRðZWith such an enhancement and a realistic model-parameter choice to reproduce the neutrino oscillation data, we conclude that the possibility of discovering RHNs with, for example, a 300 fb −1 luminosity implies that the Z 0 boson will be discovered with a luminosity of 170.5 fb −1 (125 fb −1 ) for the normal (inverted) hierarchy of the light neutrino mass pattern. DOI: 10.1103/PhysRevD.97.115023 Although neutrinos are massless particles in the standard model (SM), the experimental evidence of the neutrino oscillation [1] indicate that neutrinos have tiny but nonzero masses and flavor mixings. Hence, we need to extend the SM to incorporate the nonzero neutrino masses and flavor mixings. From a perspective of low energy effective theory, one can do so by introducing a dimension-5 operator [2] involving the Higgs and lepton doublets, which violates the lepton number by ΔL ¼ 2 units. After the electroweak (EW) symmetry breaking, the neutrinos acquire tiny Majorana masses suppressed by the scale of the dimension-5 operator. In the context of a renormalizable theory, the dimension-5 operator is naturally generated by introducing heavy Majorana right-handed neutrinos (RHNs), which are singlet under the SM gauge group, and integrating them out. This is the so-called type-I seesaw mechanism [3][4][5][6][7].If the RHNs have masses around 1 TeV or smaller, they can be produced at the Large Hadron Collider (LHC) with a smoking-gun signature of a same-sign dilepton in the final state, which indicates a violation of the lepton number. Since the RHNs are singlet under the SM gauge group, they can be produced only through their mixings with the SM neutrinos. To reproduce the observed light neutrino mass scale, m ν ¼ Oð0.1Þ eV, through the type-I seesaw mechanism with heavy neutrino masses at...

Inflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field with its value during inflation below the Planck mass (φ I M P l ). In order for a renormalization group (RG) improved effective λφ 4 potential to develop an inflection-point, the running quartic coupling λ(φ) must exhibit a minimum with an almost vanishing value in its RG evolution, namely λ(φ I ) ≃ 0 and β λ (φ I ) ≃ 0, where β λ is the beta-function of the quartic coupling. In this paper, we consider the inflection-point inflation in the context of the minimal U(1) X extended Standard Model (SM), a generalization of the minimal U(1) B−L model, where the U(1) X symmetry is realized as a linear combination of the SM U(1) Y and the U(1) B−L gauge symmetries. We identify the U(1) X Higgs field with the inflaton field. For a successful inflection-point inflation to be consistent with the current cosmological observations, the mass ratios among the U(1) X gauge boson, the right-handed neutrinos and the U(1) X Higgs boson are fixed. Focusing on the case that the U(1) X gauge symmetry is mostly oriented towards the SM U(1) Y direction, we investigate a consistency between the inflationary predictions and the latest LHC Run-2 results on the search for a narrow resonance with the di-lepton final state. In addition, the inflection-point inflation provides a unique prediction for the running of the spectral index α ≃ −2.7 × 10 −3 60 N 2 (N is the e-folding number), which can be tested in the near future.

Inflection-point inflation is an interesting possibility to realize a successful slow-roll inflation when inflation is driven by a single scalar field with its initial value below the Planck mass (φ I M P l ). In order for a renormalization group (RG) improved effective λφ 4 potential to develop an inflection-point, the quartic coupling λ(φ) must exhibit a minimum with an almost vanishing value in its RG evolution, namely λ(φ I ) ≃ 0 and β λ (φ I ) ≃ 0, where β λ is the beta-function of the quartic coupling. As an example, we consider the minimal gauged B − L extended Standard Model at the TeV scale, where we identify the B − L Higgs field as the inflaton field. For a successful inflection-point inflation, which is consistent with the current cosmological observations, the mass ratios among the Z ′ gauge boson, the right-handed neutrinos and the B − L Higgs boson are fixed. Our scenario can be tested in the future collider experiments such as the HighLuminosity LHC and the SHiP experiments. In addition, the inflection-point inflation provides a unique prediction for the running of the spectral index α ≃ −2.7 × 10 −3 60 N 2 (N is the e-folding number), which can be tested in the near future.