|
|
Arbelaez, C., Gonzalez, M., Hirsch, M., Neill, N. A., & Restrepo, D. (2025). Effective field theory and scalar triplet dark matter. J. High Energy Phys., 04(4), 118–22pp.
Abstract: We discuss an extension of the standard model with a real scalar triplet, T, including non-renormalizable operators (NROs) up to d = 6. If T is odd under a Z2 symmetry, the neutral component of T is a good candidate for the dark matter (DM) of the universe. We calculate the relic density and constraints from direct and indirect detection on such a setup, concentrating on the differences with respect to the simple model for a DM T with only renormalizable interactions. Bosonic operators can change the relic density of the triplet drastically, opening up new parameter space for the model. Indirect detection constraints, on the other hand, rule out an interesting part of the allowed parameter space already today and future CTA data will, very likely, provide a decisive test for this setup.
|
|
|
|
Carquin, E., Neill, N. A., Helo, J. C., & Hirsch, M. (2019). Exotic colored fermions and lepton number violation at the LHC. Phys. Rev. D, 99(11), 115028–9pp.
Abstract: Majorana neutrino mass models with a scale of lepton number violation of order tem-electron-volts potentially lead to signals at the LHC. Here, we consider an extension of the standard model with a colored octet fermion and a scalar leptoquark. This model generates neutrino masses at two-loop order. We make a detailed Monte Carlo study of the lepton number violating signal at the LHC in this model, including a simulation of standard model backgrounds. Our forecast predicts that the LHC with 300/fb should be able to probe this model up to color-octet fermion masses in the range of (2.6-2.7) TeV, depending on the lepton flavor of the final state.
|
|
|
|
Donini, A., Gonzalez, M., Hirsch, M., & Neill, N. A. (2026). Leading large Nc contributions to lepton number violating meson decays. Phys. Rev. D, 113(7), 075004–24pp.
Abstract: Lepton number violating meson decays, such as M-1(-) -> M-2(+) l(1)(-)l(2)(-), provide constraints on d = 9 Delta L = 2 operators. Renormalization group equation (RGE)-improved bounds on the Wilson coefficients of these operators have been presented in the literature, taking into account perturbative quantum chromodynamics (QCD) one-loop corrections and the corresponding operator mixing. Here, we present for the first time the contribution of connected diagrams to the hadronic matrix elements < M2 vertical bar Oh vertical bar M-1 >. These diagrams, usually overlooked under the assumption that < M2 vertical bar Oh|M-1 > similar to < M-2 vertical bar J(q3q4)vertical bar 0 > x < 0 vertical bar J(q1q2)vertical bar M-1 > >> < M-2 vertical bar J(q3q2) x J(q1q4 vertical bar)M(1 >), can give indeed a significant contribution to the matrix element. Including these connected diagrams is but the first step toward a full nonperturbative computation of the long-range QCD effects in these operators, that should be performed using lattice field theory techniques. However, connected diagrams represent the leading order in the 1/N-c expansion of the QCD nonperturbative effects and thus our work can be understood as a realistic, first approximation to a complete calculation of the long-range part of the matrix elements.
|
|
