The experimental rate of neutrinoless double beta decay can be saturated by the exchange of virtual sterile neutrinos, that mix with the ordinary neutrinos and are heavier than 200 MeV. Interestingly, this hypothesis is subject only to marginal experimental constraints, because of the new nuclear matrix elements. This possibility is analyzed in the context of the Type I seesaw model, performing also exploratory investigations of the implications for heavy neutrino mass spectra, rare decays of mesons as well as neutrino-decay search, LHC, and lepton flavor violation. The heavy sterile neutrinos can saturate the rate only when their masses are below some 10 TeV, but in this case, the suppression of the light-neutrino masses has to be more than the ratio of the electroweak scale and the heavy-neutrino scale; i.e., more suppressed than the naive seesaw expectation. We classify the cases when this condition holds true in the minimal version of the seesaw model, showing its compatibility (1) with neutrinoless double beta rate being dominated by heavy neutrinos and (2) with any light neutrino mass spectra. The absence of excessive fine-tunings and the radiative stability of light neutrino mass matrices, together with a saturating sterile neutrino contribution, imply an upper bound on the heavy neutrino masses of about 10 GeV. We extend our analysis to the Extended seesaw scenario, where the light and the heavy sterile neutrino contributions are completely decoupled, allowing the sterile neutrinos to saturate the present experimental bound on neutrinoless double beta decay. In the models analyzed, the rate of this process is not strictly connected with the values of the light neutrino masses, and a fast transition rate is compatible with neutrinos lighter than 100 meV. *

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.

Publisher's copyright statement:Reprinted with permission from the American Physical Society: Mitra, Manimala, Ruiz, Richard, Scott, Darren J. Spannowsky, Michael (2016). Neutrino jets from high-mass WR gauge bosons in TeV-scale left-right symmetric models. Physical review D 94(9): 095016 c 2017 by the American Physical Society. Readers may view, browse, and/or download material for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modied, adapted, performed, displayed, published, or sold in whole or part, without prior written permission from the American Physical Society.Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We reexamine the discovery potential at hadron colliders of high-mass right-handed (RH) gauge bosons W R -an inherent ingredient of left-right symmetric models (LRSM). We focus on the regime where the W R is very heavy compared to the heavy Majorana neutrino N, and we investigate an alternative signature for W R → N decays. The produced neutrinos are highly boosted in this mass regime. Subsequently, their decays via off-shell W R bosons to jets, i.e., N → l AE jj, are highly collimated, forming a single neutrino jet ðj N Þ. The final-state collider signature is then l AE j N , instead of the widely studied l AE l AE jj. Present search strategies are not sensitive to this hierarchical mass regime due to the breakdown of the collider signature definition. We take into account QCD corrections beyond next-to-leading order (NLO) that are important for high-mass Drell-Yan processes at the 13 TeV Large Hadron Collider (LHC). For the first time, we evaluate W R production at NLO with threshold resummation at next-to-next-to-leading logarithm (NNLL) matched to the threshold-improved parton distributions. With these improvements, we find that a W R of mass M W R ¼ 3ð4Þ½5 TeV and mass ratio of ðm N =M W R Þ < 0.1 can be discovered with a 5-6σ statistical significance at 13 TeV after 10ð100Þ½2000 fb −1 of data. Extending the analysis to the hypothetical 100 TeV Very Large Hadron Collider (VLHC), 5σ can be obtained for W R masses up to M W R ¼ 15ð30Þ with approximately 100 fb −1 (10 ab −1 ). Conversely, with 0.9ð10Þ½150 fb −1 of 13 TeV data, M W R < 3ð4Þ½5 TeV and ðm N =M W R Þ < 0.1 can be excluded at 95% C.L.; with 100 fb −1 (2.5 ab −1 ) of 100 TeV data, M W R < 22ð33Þ TeV can be excluded.

We re-analyze the compatibility of the claimed observation of neutrinoless double beta decay (0νββ) in 76 Ge with the new limits on the half-life of 136 Xe from Including recent calculations of the nuclear matrix elements (NMEs), we show that while the claim in 76 Ge is still compatible with the individual limits from 136 Xe for a few NME calculations, it is inconsistent with the KamLAND-Zen+EXO-200 combined limit for all but one NME. After imposing the most stringent upper limit on the sum of light neutrino masses from Planck, we find that the canonical light neutrino contribution cannot satisfy the claimed 0νββ signature or saturate the current limit, irrespective of the NME uncertainties. However, inclusion of the heavy neutrino contributions, arising naturally in TeV-scale Left-Right symmetric models, can saturate the current limit of 0νββ. In a type-II seesaw framework, this imposes a lower limit on the lightest neutrino mass. Depending on the mass hierarchy, we obtain this limit to be in the range of 0.07 -4 meV for a typical choice of the right-handed (RH) gauge boson and RH neutrino masses relevant for their collider searches. Using the 0νββ bounds, we also derive correlated constraints in the RH sector, complimentary to those from the LHC.