Spin 3/2 Particle as a Dark Matter Candidate: an Effective Field Theory Approach

There is no indication so far on the spin of dark matter particles. We consider the possibility in this work that a spin-3/2 particle acts as dark matter. Employing the approach of effective field theory, we list all possible 4-fermion effective interactions between a pair of such fields and a pair of ordinary fermion fields. We investigate the implications of the proposal on the relic density, the antiproton to proton flux ratio in cosmic rays, and the elastic scattering off nuclei in direct detection. While the relic density and flux ratio are sensitive to all interactions albeit at different levels, the direct detection is only sensitive to a few of them. Using the observed data and experimental bounds, we set constraints on the relation of couplings and dark particle mass. In particular, we find that some mass ranges can already be excluded by jointly applying the observed relic density on the one side and the measured antiproton to proton flux ratio or the upper bounds from direct detection on the other.Comment: v1: 18 pages including 6 figs; v2: 19 pages including 6 figs, added more refs, fixed wrong labels (to experiments) in figs. 3 and 4, corrected typos; v3: 19 pages, slight clarifications in response to referee's comments, added more refs, identical to the proofread version for jhep except for the format of ref

LHC Phenomenology of Type II Seesaw: Nondegenerate Case

In this paper, we thoroughly investigate the LHC phenomenology of the type II seesaw mechanism for neutrino masses in the nondegenerate case where the triplet scalars of various charge ($H^{\pm\pm}, H^\pm, H^0, A^0$) have different masses. Compared with the degenerate case, the cascade decays of scalars lead to many new, interesting signal channels. In the positive scenario where $M_{H^{\pm\pm}}<M_{H^\pm}<M_{H^0/A^0}$, the four-lepton signal is still the most promising discovery channel for the doubly-charged scalars $H^{\pm\pm}$. The five-lepton signal is crucial to probe the mass spectrum of the scalars, for which, for example, a $5\sigma$ reach at 14 TeV LHC for $M_{H^{\pm}}=430 GeV$ with $M_{H^{\pm\pm}}=400 GeV$ requires an integrated luminosity of 76/fb. And the six-lepton signal can be used to probe the neutral scalars $H^0/A^0$, which are usually hard to detect in the degenerate case. In the negative scenario where $M_{H^{\pm\pm}}>M_{H^\pm}>M_{H^0/A^0}$, the detection of $H^{\pm\pm}$ is more challenging, when the cascade decay $H^{\pm\pm}\to H^{\pm}W^{\pm*}$ is dominant. The most important channel is the associated $H^{\pm}H^0/A^0$ production in the final state $\ell^\pm\cancel{E}_Tb\bar{b}b\bar{b}$, which requires a luminosity of 109/fb for a $5\sigma$ discovery, while the final state $\ell^\pm\cancel{E}_Tb\bar{b}\tau^+\tau^-$ is less promising. Moreover, the associated $H^0A^0$ production can give same signals as the standard model Higgs pair production. With a much larger cross section, the $H^0A^0$ production in the final state $b\bar{b}\tau^+\tau^-$ could reach $3\sigma$ significance at 14 TeV LHC with a luminosity of 300/fb. In summary, with an integrated luminosity of order 500/fb, the triplet scalars can be fully reconstructed at 14 TeV LHC in the negative scenario.Comment: 41 pages, 20 figures, 7 tables. Version 2 accepted by PRD. 41 pages, 18 figures. Main changes are, (1) rewording in secs III and IV, removing 2 figs and quoting ref [34]; (2) a paragraph added before eq (10) to clarify constraints from electroweak precision data; (3) a paper added to ref [11]. No changes in result

LHC Phenomenology of the Type II Seesaw Mechanism: Observability of Neutral Scalars in the Nondegenerate Case

This is a sequel to our previous work on LHC phenomenology of the type II seesaw model in the nondegenerate case. In this work, we further study the pair and associated production of the neutral scalars H^0/A^0. We restrict ourselves to the so-called negative scenario characterized by the mass order M_{H^{\pm\pm}}>M_{H^\pm}>M_{H^0/A^0}, in which the H^0/A^0 production receives significant enhancement from cascade decays of the charged scalars H^{\pm\pm},~H^\pm. We consider three important signal channels---b\bar{b}\gamma\gamma, b\bar{b}\tau^+\tau^-, $b\bar{b}\ell^+\ell^-\cancel{E}_T$---and perform detailed simulations. We find that at the 14 TeV LHC with an integrated luminosity of 3000/fb, a 5\sigma mass reach of 151, 150, and 180 GeV, respectively, is possible in the three channels from the pure Drell-Yan H^0A^0 production, while the cascade-decay-enhanced H^0/A^0 production can push the mass limit further to 164, 177, and 200 GeV. The neutral scalars in the negative scenario are thus accessible at LHC run II.Comment: v1: 32 pages, 17 figures, 3 tables. v2: added 2 refs (2nd in [61] and [66]), revised Acknowledgments, and corrected grammatical errors according to proofs; no other change