
Abada, A., De Romeri, V., Lucente, M., Teixeira, A. M., & Toma, T. (2018). Effective Majorana mass matrix from tau and pseudoscalar meson lepton number violating decays. J. High Energy Phys., 02(2), 169–57pp.
Abstract: An observation of any lepton number violating process will undoubtedly point towards the existence of new physics and indirectly to the clear Majorana nature of the exchanged fermion. In this work, we explore the potential of a minimal extension of the Standard Model via heavy sterile fermions with masses in the [0.110] GeV range concerning an extensive array of “neutrinoless” meson and tau decay processes. We assume that the Majorana neutrinos are produced onshell, and focus on threebody decays. We conduct an update on the bounds on the activesterile mixing elements, vertical bar Ul alpha 4,Ul beta 4 vertical bar, taking into account the most recent experimental bounds (and constraints) and new theoretical inputs, as well as the effects of a finite detector, imposing that the heavy neutrino decay within the detector. This allows to establish uptodate comprehensive constraints on the sterile fermion parameter space. Our results suggest that the branching fractions of several decays are close to current sensitivities (likely within reach of future facilities), some being already in conflict with current data (as is the case of Kbroken vertical bar > l(alpha)(broken vertical bar)+l(beta)(+)pi(), and tau()>mu(broken vertical bar)pi()pi()). We use these processes to extract constraints on all entries of an enlarged definition of a 3 x 3 “effective” Majorana neutrino mass matrix m(v)(alpha beta).



Abbas, G., Celis, A., Li, X. Q., Lu, J., & Pich, A. (2015). Flavourchanging top decays in the aligned twoHiggsdoublet model. J. High Energy Phys., 06(6), 005–26pp.
Abstract: We perform a complete oneloop computation of the twobody flavourchanging top decays t > ch and t > cV (V = gamma, Z), within the aligned twoHiggsdoublet model. We evaluate the impact of the model parameters on the associated branching ratios, taking into account constraints from flavour data and measurements of the Higgs properties. Assuming that the 125 GeV Higgs corresponds to the lightest CPeven scalar of the CPconserving aligned twoHiggsdoublet model, we find that the rates for such flavourchanging top decays lie below the expected sensitivity of the future highluminosity phase of the LHC. Measurements of the Higgs signal strength in the diphoton channel are found to play an important role in limiting the size of the t > ch decay rate when the charged scalar of the model is light.



Agarwalla, S. K., & Hernandez, P. (2012). Probing the neutrino mass hierarchy with SuperKamiokande. J. High Energy Phys., 10(10), 086–14pp.
Abstract: We show that for recently discovered large values of theta(13), a superbeam with an average neutrino energy of similar to 5 GeV, such as those being proposed at CERN, if pointing to SuperKamiokande (L similar or equal to 8770 km), could reveal the neutrino mass hierarchy at 5 sigma in less than two years irrespective of the true hierarchy and CP phase. The measurement relies on the near resonant matter effect in the nu(mu) > nu(e) oscillation channel, and can be done counting the total number of appearance events with just a neutrino beam.



Agarwalla, S. K., Bagchi, P., Forero, D. V., & Tortola, M. (2015). Probing nonstandard interactions at Daya Bay. J. High Energy Phys., 07(7), 060–33pp.
Abstract: In this article we consider the presence of neutrino nonstandard interactions (NSI) in the production and detection processes of reactor antineutrinos at the Daya Bay experiment. We report for the first time, the new constraints on the flavor nonuniversal and flavor universal chargedcurrent NSI parameters, estimated using the currently released 621 days of Daya Bay data. New limits are placed assuming that the new physics effects are just inverse of each other in the production and detection processes. With this special choice of the NSI parameters, we observe a shift in the oscillation amplitude without distorting the L/E pattern of the oscillation probability. This shift in the depth of the oscillation dip can be caused by the NSI parameters as well as by theta(13), making it quite difficult to disentangle the NSI effects from the standard oscillations. We explore the correlations between the NSI parameters and theta(13) that may lead to significant deviations in the reported value of the reactor mixing angle with the help of isoprobability surface plots. Finally, we present the limits on electron, muon/tau, and flavor universal (FU) NSI couplings with and without considering the uncertainty in the normalization of the total event rates. Assuming a perfect knowledge of the event rates normalization, we find strong upper bounds similar to 0.1% for the electron and FU cases improving the present limits by one order of magnitude. However, for a conservative error of 5% in the total normalization, these constraints are relaxed by almost one order of magnitude.



Agarwalla, S. K., Huber, P., Tang, J. A., & Winter, W. (2011). Optimization of the Neutrino Factory, revisited. J. High Energy Phys., 01(1), 120–45pp.
Abstract: We perform the baseline and energy optimization of the Neutrino Factory including the latest simulation results on the magnetized iron detector (MIND). We also consider the impact of tau decays, generated by v(mu) > v(tau) or v(e) > v(tau) appearance, on the mass hierarchy, CP violation, and theta(13) discovery reaches, which we find to be negligible for the considered detector. For the baselineenergy optimization for small sin(2) 2 theta(13), we qualitatively recover the results with earlier simulations of the MIND detector. We find optimal baselines of about 2 500km to 5 000km for the CP violation measurement, where now values of Emu as low as about 12 GeV may be possible. However, for large sin(2) 2 theta(13), we demonstrate that the lower threshold and the backgrounds reconstructed at lower energies allow in fact for muon energies as low as 5 GeV at considerably shorter baselines, such as FNALHomestake. This implies that with the latest MIND analysis, lowand highenergy versions of the Neutrino Factory are just two different versions of the same experiment optimized for different parts of the parameter space. Apart from a greenfield study of the updated detector performance, we discuss specific implementations for the twobaseline Neutrino Factory, where the considered detector sites are taken to be currently discussed underground laboratories. We find that reasonable setups can be found for the Neutrino Factory source in Asia, Europe, and North America, and that a triangularshaped storage ring is possible in all cases based on geometrical arguments only.



Agarwalla, S. K., Lombardi, F., & Takeuchi, T. (2012). Constraining nonstandard interactions of the neutrino with Borexino. J. High Energy Phys., 12(12), 079–21pp.
Abstract: We use the Borexino 153.6 ton.year data to place constraints on nonstandard neutrinoelectron interactions, taking into account the uncertainties in the Be7 solar neutrino flux and the mixing angle theta(23), and backgrounds due to Kr85 and Bi210 betadecay. We find that the bounds are comparable to existing bounds from all other experiments. Further improvement can be expected in Phase II of Borexino due to the reduction in the Kr85 background.



Agarwalla, S. K., Prakash, S., & Sankar, S. U. (2013). Resolving the octant of theta(23) with T2K and NOvA. J. High Energy Phys., 07(7), 131–24pp.
Abstract: Preliminary results of MINOS experiment indicate that theta(23) is not maximal. Global fits to world neutrino data suggest two nearly degenerate solutions for theta(23): one in the lower octant (LO: theta(23) < 45 degrees) and the other in the higher octant (HO: theta(23) > 45 degrees). v(mu) > v(e) oscillations in superbeam experiments are sensitive to the octant and are capable of resolving this degeneracy. We study the prospects of this resolution by the current T2K and upcoming NOvA experiments. Because of the hierarchydelta(CP) degeneracy and the octant delta(CP) degeneracy, the impact of hierarchy on octant resolution has to be taken into account. As in the case of hierarchy determination, there exist favorable (unfavorable) values of delta(CP) for which octant resolution is easy (challenging). However, for octant resolution the unfavorable delta(CP) values of the neutrino data are favorable for the antineutrino data and viceverse. This is in contrast to the case of hierarchy determination. In this paper, we compute the combined sensitivity of T2K and NOvA to resolve the octant ambiguity. If sin(2)theta(23) – 0.41, then NOvA can rule out all the values of theta(23) in HO at 2 sigma C.L., irrespective of the hierarchy and delta(CP). Addition of T2K data improves the octant sensitivity. If T2K were to have equal neutrino and antineutrino runs of 2.5 years each, a 2 sigma resolution of the octant becomes possible provided sin(2) theta(23) <= 0.43 or >= 0.58 for any value of delta(CP).



Agostini, P. et al, & Mandal, S. (2021). The Large HadronElectron Collider at the HLLHC. J. Phys. G, 48(11), 110501–364pp.
Abstract: The Large HadronElectron Collider (LHeC) is designed to move the field of deep inelastic scattering (DIS) to the energy and intensity frontier of particle physics. Exploiting energyrecovery technology, it collides a novel, intense electron beam with a proton or ion beam from the HighLuminosity Large Hadron Collider (HLLHC). The accelerator and interaction region are designed for concurrent electronproton and protonproton 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 topquark physics. It is shown how the LHeC will open a new chapter of nuclear particle physics by extending the accessible kinematic range of leptonnucleus 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 energyrecovery electron linac (ERL), including a new lattice, magnet and superconducting radiofrequency technology, and further components. Challenges of energy recovery are described, and the lowerenergy, highcurrent, threeturn 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 partondensityfunction physics programmes. This paper also presents novel results for the Future Circular Collider in electronhadron (FCCeh) mode, which utilises the same ERL technology to further extend the reach of DIS to even higher centreofmass energies.



AguilarSaavedra, J. A., Casas, J. A., Quilis, J., & Ruiz de Austri, R. (2020). Multilepton dark matter signals. J. High Energy Phys., 04(4), 069–24pp.
Abstract: The signatures of dark matter at the LHC commonly involve, in simplified scenarios, the production of a single particle plus large missing energy, from the undetected dark matter. However, in Z ' portal scenarios anomaly cancellation requires the presence of extra dark leptons in the dark sector. We investigate the signatures of the minimal scenarios of this kind, which involve cascade decays of the extra Z ' boson into the dark leptons, identifying a fourlepton signal as the most promising one. We estimate the sensitivity to this signal at the LHC, the highluminosity LHC upgrade, a possible highenergy upgrade, as well as a future circular collider. For Z ' couplings compatible with current dijet constraints the multilepton signals can reach the 5 sigma level already at Run 2 of the LHC. At future colliders, couplings two orders of magnitude smaller than the electroweak coupling can be probed with 5 sigma sensitivity.



Alcaide, J., Banerjee, S., Chala, M., & Titov, A. (2019). Probes of the Standard Model effective field theory extended with a righthanded neutrino. J. High Energy Phys., 08(8), 031–18pp.
Abstract: If neutrinos are Dirac particles and, as suggested by the so far null LHC results, any new physics lies at energies well above the electroweak scale, the Standard Model effective field theory has to be extended with operators involving the righthanded neutrinos. In this paper, we study this effective field theory and set constraints on the different dimensionsix interactions. To that aim, we use LHC searches for associated production of light (and tau) leptons with missing energy, monojet searches, as well as pion and tau decays. Our bounds are generally above the TeV for order one couplings. One particular exception is given by operators involving top quarks. These provide new signals in top decays not yet studied at colliders. Thus, we also design an LHC analysis to explore these signatures in the tt production. Our results are also valid if the righthanded neutrinos are Majorana and longlived.

